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In parts 1 and 2, we looked at supply management and load management as mechanisms for coping with the variability of renewable energy sources. In this final part, we look at possibilities for energy storage - the ultimate solution for the long term, once the burning of fossil fuels is no longer an option. It's a large subject, and we don't have space or time here to examine all the potential options. Instead, we'll focus on a handful approaches that look promising for large-scale storage suited for load balancing within an RBA.
Setting the Bar
It's often noted that electricity--the flow of charge through a conducting medium--can't be stored. What is stored is always potential energy in some other form that can be more or less easily converted to electricity.
The stored energy needn't necessarily have been put there by the use of surplus electricity. In hydroelectric dams, the energy that we tap for power is stored by the natural flow of water into the reservoir behind the dam. And even when we burn fossil fuels, we are tapping solar energy stored millions of years ago when deposits of organic material were formed.
In fact, the main problem in developing storage solutions for surplus power is that it's so hard to compete with fossil fuels. Coal, oil, and natural gas set a bar that is hard for the competition to clear. At the scale required for electrical load leveling, it's difficult to build any storage system that has a lower capital cost per kilowatt-hour delivered than a dispatched fossil-fueled generator. As long as fossil-fueled plants can use the atmosphere as a free dump for CO2, capital and not fuel will remain the dominant factor in the cost of electricity. That makes building competitive systems for energy storage a challenge.
But perhaps not impossible. Historically, pumped hydro and deep-cavern compressed air storage have been viable, when geographical conditions favor them. However, for general solutions that can be applied anywhere, we need innovation. Advances in key technologies offer some interesting possibilities.
Among the important but less obvious advances, in that context, are those in the technologies for tunneling and excavation. The average costs per cubic meter of rock excavated or dirt moved have been slowly but steadily dropping. That has some interesting consequences for hydroelectric power—the oldest approach to large-scale energy storage.
Within limits, hydroelectric systems can be tapped for power on demand. The limits are set by factors that include installed turbine capacity, tolerance for variations in downstream river flow, and transmission capacity, as well as total annual river flow. In Part 1, hydroelectric power was mentioned as an ideal complement for wind power, because of the discretion it allows for when power is generated. Yet in many cases hydro power is used mainly or exclusively for baseload. Why is that?
Often, the culprit is transmission capacity. Transmission losses on a line are proportional to the square of the power carried. When a hydroelectric dam is located far from the market it serves, there may simply be insufficient transmission capacity to deliver power at anything more than a steady average rate. Attempting to deliver a full day’s energy quota in only a few hours of peak demand could melt transmission lines not built for that level of power flow.
To serve as a dispatchable resource for handling peak loads, a hydroelectric facility needs robust transmission capacity. It must also have turbines capable of meeting peak power loads much greater than the average load. The latter is not usually a problem; hydro plants tend to be built that way as a matter of course, to accommodate large seasonal variations in river flow. However, one further requirement is less commonly met: water from the power plant must discharge into a lake or secondary reservoir that can buffer the plant’s outflow. Although occasional flooding is now recognized as necessary for the health of riparian ecosystems, it’s not good (to put it mildly) for the downstream river flow to cycle daily between a trickle and high flood.
When an adequate secondary reservoir does exist (or can be built), then it becomes possible to extend the load-following and backup capacity of a hydro facility by adding pumped storage. The peak power from a hydroelectric plant augmented by pumped storage can be many times greater than the average power available from stream flow.
But what's the scope?
The conventional wisdom is that hydroelectric potential in the U.S. has been fully tapped, and that we can't expect its contribution to power generation to increase. Certainly, nobody wants to see giant dams built on the few remaining stretches of wild rivers we have left. However, with advanced tunneling technology, it may be practical to expand hydroelectric resources without building any large dams.
As far as power generation is concerned, a dam is nothing more than a way to get water from the reservoir inlet to the power turbine without losing head. A smooth-walled tunnel would serve just as well, as long as it was large enough to allow the water to move relatively slowly. So instead of building a giant dam and flooding hundreds of square miles of river valley, one could have only two small reservoirs, connected by tunnel. A portion of the river's flow would continue in its natural course, but the larger portion would be diverted through the tunnel for power generation.
As a point of reference for how much this type of project might cost, we can consider a recent tunneling project undertaken by the Metropolitan Water District of Southern California (MWD). The Riverside Badlands Tunnel is a 13 km segment of MWD's Inland Feeder Project. It brings 31 cubic meters of water per second from a state facility near San Bernardino to a reservoir near Hemet. The tunnel, with a finished diameter of 12 feet, cost slightly under $10 million per km. to complete. Tunneling conditions varied considerably over the length of the tunnel. Some sections were very difficult, some were easy. Overall, they were probably fairly representative of what might be encountered in a "typical" tunneling project for hydroelectric power.
The Riverside Badlands tunnel takes an approximately level course. But had it been for a hydroelectric project linking two reservoirs at very different elevations, it's instructive to see what its capital cost per kilowatt would have been.
One cubic meter of water dropping 100 meters in elevation releases just under a megajoule. If the average tunnel grade were 10%--100 meters per kilometer--then 31 cubic meters per second flowing through the tunnel would represent about 30 megawatts per kilometer. At a cost of slightly under $10 million / kilometer, the tunnel's contribution to power cost, in round numbers, would be $300 per kilowatt. The turbines and generators and other "balance of system" items would up that figure, but it's still in the ballpark for the cost of dispatchable gas-fired capacity, and well under the $1500 / kilowatt "rule of thumb" for new coal-fired plants.
It's hard to quantify how much potential there may be for reengineering of hydroelectric systems to provide backup for renewable energy. I haven't found any specific studies. If it hasn't already been done, a good preliminary step for a national renewable energy policy would be a detailed engineering survey to identify projects where upgraded transmission, construction of secondary buffer reservoirs, and diversions through tunnels could augment hydroelectric capacity to deal with supply and load variability.
Meanwhile, Back on the Plains
Augmented hydro is all well and good for markets located near mountains, but what about the large areas of the world that are too far from any mountains for hydroelectric power to be of use?
One option for large-scale storage might be to use conventional earth-moving equipment to construct a primary holding reservoir on the surface, then use tunneling machines to excavate a matching secondary reservoir far below the surface. The secondary reservoir would of course have no outlet, so this would be a pure pumped storage system. With large enough reservoirs, however, the amount of energy storage could be sufficient for load leveling.
The idea isn't quite as wild as it sounds. Over the past three decades, towns in the Chicago metropolitan area have been building a series of underground reservoirs to prevent storm run-off from flushing sewage into Lake Michigan. A recently completed segment included 8.1 miles of concrete-lined tunnel bored through bedrock. The cost for the finished project came to roughly $1.00 per gallon of holding capacity, or $265 per cubic meter. If a deep reservoir for pumped hydroelectric storage could be built for the same cost, would it be a feasible solution for energy storage?
The potential energy represented by one cubic meter of reservoir capacity depends on the elevation difference between the source and receiving reservoirs. At the 100 meters of head typical for a large hydroelectric dam, one cubic meter gives only 0.28 kilowatt-hours of energy. At $265 per cubic meter of capacity, that would come to almost $1000 per kilowatt-hour of storage capacity–far too much for economic feasibility. However, with a tunnel-excavated receiving reservoir, head is determined by the depth at which the tunnel has been bored. That could be almost anything.
Up to a few kilometers, the depth should be largely irrelevant to excavation costs. In fact, going deep could theoretically give better tunneling conditions and reduce costs. That's because the cost of tunneling, these days, isn't in the removal of rock. The cutting wheels on a modern tunnel boring machine (TBM) make short work of even hard bedrock. The cost, rather, is in the grouting and sealing operations and special measures that have to be taken to avoid flooding and collapse. At depths of more than a kilometer, in most areas, the rock will be solid and stable, with little or no groundwater penetration.
As long as the project is large enough to amortize the cost of the main access shaft and underground assembly of a TBM, then the finished reservoir cost could come in under $200 / cubic meter. A reservoir two kilometers below the surface would allow each cubic meter of water to flow through the equivalent of twenty large hydroelectric dams in series. Even if the cost of the finished reservoir were $500 per cubic meter rather than $200, that would still be a capacity cost of under $90 / kWh.
Whether $90 / kWh of capacity is a feasible cost for pumped hydroelectric storage depends on the financing model and the capacity turnover time. With minimal maintenance, a pumped hydro facility should have an indefinite lifetime. Capital cost therefore amounts to the cost of interest on construction loans. Assuming a favorable 6%, that would be $5.40 per kilowatt-hour per year. If the average turnover is 33% of capacity per day, then delivered power would be 680 kWh / year per cubic meter of capacity, and interest on capital would add 0.8 cents / kWh of delivered energy.
An added cost of only 0.8 cents / kWh would be very attractive for large-scale energy storage. However, there's a lot of risk in the assumptions on which that figure is based. Underground mining operations have been conducted at depths well beyond 2 km, but as far as I know it's all been traditional "drill and blast" work. I don't know of any experience with very deep TBM operations that might serve to validate cost projections as low as $200 - $500 per cubic meter. And, of course, the cost of the excavated reservoir would only be a portion of the cost of the complete pumped-hydro storage facility–although I think it's safe to assume that it would be the dominant part.
At the end, what we're left with is an interesting possibility. Such a system may well be feasible, but it will require considerably more study to know.
The other established technology that has been used for large-scale energy storage employs compressed air. A large volume of compressed air is stored underground, either in natural or man-made caverns or in deep saline aquifers. When power is needed, the pre-compressed air is used to feed a combustion turbine. In a conventional combustion turbine, about two thirds of the power from the output stage is taken to drive the compressor stage. Avoiding the need to drive the compressor nearly triples the power output of the turbine, relative to the fuel burned. However fuel is burned, so this is actually a hybrid storage and generation system.
To date, there are only two large CAES facilities, worldwide, that are operational. One is in Hundorf, Germany, and has been operational since 1974. The other, built in 1991, is in McIntosh, Alabama. A new and much larger system is being developed near Norton, Ohio, and a group of utility companies is proposing a combined wind farm and CAES facility near Fort Dodge, Iowa. There is also considerable interest in CAES for buffering wind power in west Texas.
A CAES system of the types built at Hundorf and McIntosh has some compelling advantages for providing spinning reserve, regulation, and other ancillary grid services. Startup is quick, and output can be throttled rapidly over a fairly wide range without losing much efficiency. However, as energy storage solutions, these systems are mediocre. The McIntosh facility, with newer technology, is the more efficient of the two. It uses about 0.7 kWh of off-peak electricity and 4500 Btu of gas to generate 1 kWh of output.
If one ignores the 0.7 kWh of off-peak electricity, 4500 Btu per kWh of output looks like an extremely good heat rate. The newest and most efficient combined cycle gas turbine generators have a heat rate around 5680 Btu / kWh, which is a thermal efficiency topping 60%. However, looking at it another way, the 4500 Btu of fuel that the McIntosh CAES plant uses to produce one kWh could have produced 0.79 kWh of electricity in a new combined cycle gas turbine. So the 0.7 kWh of off-peak electricity used for compression is only buying 0.21 kWh of additional output. That's an effective round-trip efficiency for electricity-in to electricity-out of only 30%.
Although the stored energy is shifted from off-peak to premium on-peak power (regulation capacity), that level of loss makes it hard to justify the investment in wind farms feeding the system. More to the point, with 79% of its output deriving from combustion of fuel, this system will never allow wind and solar to become our predominant energy sources. For that, we will need something better.
To be fair, when the McIntosh facility was designed and built, natural gas was still cheap and expected to remain so. The primary aim of the facility would have been responsive power generation, not high round-trip energy storage efficiency. No doubt with some tweaking of control parameters and flow rates, it could be operated with a larger input of off-peak electricity and a smaller input of fuel. The effective round-trip storage efficiency might then be raised to 50%; the tradeoff is that it would run through its compressed air storage more quickly, and be able to supply peak power for a smaller number of hours each day.
In Europe, a group of researchers are studying a different approach. It eliminates fuel consumption altogether, so that the system functions as a pure storage facility. They call it Advanced Adiabatic CAES.
The idea for AACAES is that, in the charge cycle, hot compressed air is passed through a counter-flow heat exchanger before being sent to its storage cavern. The compressed air transfers its heat to a thermal storage fluid, which then enters a well-insulated storage tank of its own. In the discharge cycle, both flows are reversed, and the cool compressed air from the storage cavern recovers most of the heat it gave up before being stored. The now-hot compressed air exiting the heat exchanger drives an expander turbine to generate power.
If the heat exchanger and thermal storage work well, then efficiencies approaching those achieved with pumped hydroelectric storage should be possible. However the requirements are challenging. The counter-flow heat exchange system must span a temperature range from ambient to 650º C, and store a large volume of 650º fluid for the better part of a day or more without significant temperature loss.
Another approach to improved storage efficiency is isothermal CAES. In an isothermal process, temperature remains constant. Isothermal compression minimizes the work required to compress a gas, while isothermal expansion maximizes the work extracted when expanding it. The problem is that the usual means to achieve near-isothermal compression and expansion are inherently slow. That means high cost in capital equipment, relative to throughput.
There is a potential way to achieve near-isothermal compression and expansion with high throughput, but as far as I know, it's unproven. The gas is injected into a stream of water or other carrier liquid, and then the gas-liquid foam is compressed or expanded. The liquid constitutes at least 90% of the mass of the foam. During compression, it absorbs heat from the tiny gas bubbles entrained throughout its volume; during expansion, it supplies heat to the expanding bubbles. The result is that the temperature of the gas remains nearly constant.
A possible configuration for an isothermal CAES system works as follows:
There are two columns of fluid, one ascending from and one descending to a deep underground pressure chamber;
To pump gas into the deep chamber, gas bubbles are injected into the descending column. As the entrained bubbles are carried downward, they are compressed by the increasing weight of fluid in the column above them;
At the bottom of the columns, within the storage chamber, the bubbles separate from the fluid.
The fluid, now free of entrained bubbles, exits the chamber via the ascending fluid column.
To discharge gas from the chamber, the flows are reversed. Bubbles of compressed gas from the chamber are injected at the base of the fluid column, and expand isothermally as they are carried upward in the fluid column.
The column with the entrained bubbles is less dense than the column of bubble-free fluid. When the low-density column is descending (carrying compressed air into the chamber), energy must be supplied by pumps to maintain its flow against the pressure of the heavier column of ascending fluid. Conversely, when the low-density column is ascending (carrying compressed air to the surface), the lower pressure at its base, relative to chamber pressure, provides a head for generating energy.
An isothermal CAES system of this type closely resembles a pumped hydroelectric storage system. There's an important difference, however: the energy capacity per cubic meter of storage reservoir is approximately six times larger than it would be for a pumped hydroelectric system. That makes the system much less sensitive to the cost of excavation of the underground storage chamber. If deep tunneling costs are under $500 per cubic meter, then the cost of storage capacity is under $15 per kWh. At that cost, high turnover is not really needed, and it becomes realistic to talk about banking an entire week's worth of energy production.
The Solar Thermal Connection
It's possible to use the entrained bubble system in "one-way" mode, as an efficient means to deliver compressed air to the deep storage chamber. The compressed air would then be delivered straight to some type of heater before driving an expansion turbine. The heating allows the expander turbine to deliver more power than was used to compress the gas.
If the heating is supplied by combustion of natural gas, then the system is a more or less conventional CAES system. It gains a bit from the more efficient compression and from the constant pressure of its air supply as water replaces compressed air during discharge. It still burns fuel, however.
As an alternative to burning fuel, heating for the compressed air could be supplied by concentrated solar thermal energy--either direct or stored. It would serve as an alternative to steam or Sterling engines for solar-thermal power generation, with the advantage of much higher power capacity when operating from pre-compressed air. Net thermal efficiencies should be similar.
This series has looked at supply management, load management, and energy storage as means for coping with the inherent variability of renewable energy sources. It appears that:
1) Existing mechanisms of supply management for coping with daily load variations are also sufficient to cope with any levels of RE that are likely to be reached within at least the next five years;
2) Power pricing policies that support and encourage the development of responsive loads are desirable irrespective of RE accommodation. They will help to level load curves and enable better utilization of capital assets. At the same time, they will enable substantially higher levels of RE penetration than what could be economically accommodated through supply management alone.
3) Feasible technologies do exist for long-term energy storage at levels that would ultimately allow for the elimination of most fossil-fueled power generation. Further research and actual pilot projects are needed to establish the best designs and economic feasibility of these systems.
What I find most interesting, in terms of a national energy policy, is how much commonality there is in research needs and regulatory policy, independent of what our energy sources are to be. There is no looming fork in the road, that I can see, where we must decide between RE vs. nuclear energy, for example. Nuclear, the ultimate in reliable baseload generation, has as much to gain from responsive loads and energy storage solutions as a system that relies heavily on wind and solar energy.
The real divide is rather in how seriously we take the threat of CO2-related global warming. Do we have the will to impose a serious carbon tax and cut our dependence on fossil fuels, or will we hang on to the current model and "business as usual" to the bitter end? Time will tell.
Notes and References
 It's actually worse than that, since wire resistance increases at higher temperatures.
 For example, the two great reservoirs on the Colorado River–lake Mead and lake Powell–each cover more than 1000 square miles of former canyon land.
Article detailing experience and issues encountered in building a 13 km water tunnel through varied geology.
 As a side note, if a pumped hydro reservoir were to be dug at a depth of 2 km or more, it would be a great source of hot water for geothermal district heating. The geothermal gradient averages about 20º C per kilometer, so at a depth of two kilometers, the temperature of rocks around the reservoir tunnel would likely be about 60º C (140º F).
Paper from NREL on CAES with gasified biomass for "baseload wind" capacity. Cites an article in Energy Conversion Management for statistics on McIntosh CAES facility.
Technical paper on AACAES from researchers at University of Koeln in Germany.
For information on purchasing reprints of this article, contact sales. Copyright 2013 CyberTech, Inc.
Great article. Literally boldly going where no one is even thinking.
I found the reference to the storm drain developments quite interesting. There are many such projects in the works, due to (ironically) the energy costs of processing so much water unnecessarily through waste treatment plants. But you they don't want to send it untreated to streams and lakes either, hence the dilemma. Given this construction, perhaps some energy generation might also be possible? Some kind of underground low head hydro? Intriguing.
I am somewhat confused by the costs. You don't seem to mention the cost of the original input electricity itself? Is this inconsequential? I'm not sure of the efficiency of a pump, but assuming 30%, then you'd need 1/.3 or 3.33 units of energy to get 1 "RAW" unit of energy stored as water (at a higher level). Then if the turbine is also 30%, you'd get .3 units out as usable electricity. So, you'd need a total of 11.1 units of electricity to store 1 unit of electricity that can be recovered at a later time. I call this "roundtrip efficiency". Perhaps my calculations are not accurate.
My view on energy storage is that the best media depends on the expected time of storage (seconds, hours, days, weeks, months). Short durations can have more expensive storage media that work at high efficiency -- longer durations are best served with less efficient storage media that are low cost. The water storage seems to fall more in the later category.
Roger Arnold 1.10.07
Thanks for the link, Len. I should have included it in my "notes and references" as the first note, since it covers a lot of the storage landscape that I wasn't able to include.
Jim: thanks, I think. ("Boldly going where no one is even thinking"? I think I'll just take that as a complement and not ask any questions. ;-)
The costs mentioned in the article are always added costs, on top of whatever is paid for the off-peak or "as-available" power. An added cost of as much as 7 cents might be tolerable, in situations where the off-peak source provider has a sunk investment and no recourse. But it's probably too high, in the long term, if renewables are to attract new investment money and energy storage is to compete with responsive loads for off-peak power.
The pumps for a pumped hydro system are remarkably efficient. Well over 90%, for the pump itself. End-to-end efficiencies of 78% are reported for newer pumped hydro installations, and that includes motor and pump losses on one end, plus turbine and generator losses on the other.
Edward Reid, Jr. 1.11.07
"...once the burning of fossil fuels is no longer an option."
Someone has finally acknowledged the end point of the AGW hysteria. Thank you.
Now, perhaps, we can stop talking about "7% below 1990 levels by 2012"; and, we can have an open discussion of the time frame within which we must achieve zero fossil fuel consumption. The most common time frame I've seen is 2050, to stabilize CO2 concentrations at ~500 ppm.
We can also, perhaps, have an open discussion of how "life-as-we-know-it" must change in a world of hydro, geothermal, solar and wind plus massive storage with dramatically reduced demand and sufficient storage (or legislation and regulation) to match intermittant supply to that reduced demand.
I realize that politicians and AGW "affirmers" would rather have the general population step off the edge onto the slippery slope "with eyes wide shut". However, I believe the general population has a right to know what it will be like living in caves again - without fire this time.
Let the fun begin!
Todd McKissick 1.11.07
I know a few families in Nebraska that could answer that question, Edward. However you won't find most of them at home right now. Now and for the next week, as projected by the local power company, you'll have to look to the local gymnasium. I don't have a number for them, but I might be able to track down a number for three families which are staying at one house that still has power. It seems that his renewables missed the "lights out" cue from the ice storm that hit the area .... let's see.... 11 days ago.
A point that never seems to come up in these discussions is that in just such an emergency, distributed generation not only distributes the load and aleviates the transmission, but it distributes the risk of an outage as well.
Regarding 2050 being "the time frame", that is most likely by people making a guess at when the majority of the fossil fuels use will be behind us. Net zero (total) energy houses are popping up all over. As price comes down and technology increases, that pace will accelerate. When net producing houses and businesses become economic, it won't take long for large scale renewables to cover the remaining load. Since storage cost is easier to distribute than centralize, that excess could be called up at any time. You just have to think outside the box.
If that's the kind of fun you were referring to, then by all means... Let the fun begin!
Jim Beyer 1.11.07
I think Edward makes a point (sort of) and actually supports Roger's article.
Will ending fossil fuel use as end "life-as-we-know-it" or will continuing to use them do the same thing? I've literally heard both sides declare that by taking the other path, we will end up living in caves, but without the fire.
I guess one could ask who is being more alarmist, the folks that say we HAVE to get off of fossil fuels, or the folks that say leaving them will have us living in caves again.
Given this apparent uncertainty, one should see how progress can be made in areas that have common ground. After all, one could agree there is much work to do, if only to achieve the more modest goal of less dependence on imported oil and NG. (Can we at least agree on that?)
As a practical matter, people will keep using fossil fuels (esp. coal) as long as it is cheaper than alternatives. Roger has described some interesting ideas that bring the practicality and cost of renewable energy somewhat closer to the lowest cost alternative -- coal. And again, from a practical viewpoint, fossil fuel (i.e. coal) use will only stop when a less costly alternative IS found. I see no problem in striving for that, whatever one's viewpoint would be.
Todd's point is also germane, we always talk about efficiency and cost, but what about robustness? Look how delicate our infrastructrue has become -- after 3 days of no power or water in New Orleans, society basically dissolved. I think a little more insurance in this regard makes some sense too.
Edward Reid, Jr. 1.11.07
Three days to "progress" from dissolute to dissolved? Wow! Is that a record?
Huddling in a gym may indeed be our future, especially if we start down the "slippery slope" before we know how far down the bottom really is. Signing on to CO2 reductions under Kyoto is like agreeing to be a little bit pregnant, except that we all know where being a little bit pregnant leads.
Todd McKissick 1.11.07
Edward, I see no reason to inhibit the progress of renewables, either large or small scale with repeated insinuation that they lead to anything worse than we have now. Nearly every recent year, we have to bail out large populations that relied on centralized power, whether it's due to hurricanes, floods, tornados, snow or ice storms. With this in mind, consider the possibilities of terrorist actions. You may be able to secure a given plant, but how many other ways are there to cut people's power on a large scale. One only needs to cut the resources needed to said plant or the lines leaving it and the people still lose power. The more centralized we have our power, the greater that threat. Critical businesses already don't trust this situation and choose to install their own backup generators. How do you account for that capacity that's being underutilized? I'm guessing it doesn't figure in since it was an individual choice.
Your stand seems to come from knowing that it is more expensive to clean up our power than to continue with the status quo. Where do you get this information? Is it based on today's technology or predicted? If you include unproven technology, which only makes sense, then you must give renewables the same courtesy. I think some diligent research into those advancements might allow you to quote facts rather than catchy phrases like 'living in a cave' and 'slippery slope' which have no place in the discussion.
Jim, You hit the nail on the head when mentioning the economics of the alternatives as compared to the least cost existing. Renewables of either scale will not be adopted en masse until they do become cheaper. Sure subsidies will facilitate early (and uneconomic) switches, but that will only go so far. When federal, state, local and individual budgets can't afford it, it will most definitely slow before 'economic disaster' strikes. This is why almost every alternative has that 'price to beat' forefront in their offering price. I don't see people jumping ship until that price becomes attractive.
One downside to this 'delay' is that renewables don't actually get credit for most of their benefits. When someone goes RE, he not only saves peak generation demand and transmission needs, he also saves health related expenses, his and his neighbor's outage risk, foreign dependancy, war excuses, AGW issues (the thousands of unknown ones as well), lots of environmental problems related to mining and poluted water, aesthetics, governmental oversight at every level, energy gaming and corruption, etc., etc. None of these externalties get priced in, while some aren't even mentioned in the externals discussions. However, they do benefit all of society and if considered in the energy prices, it would already be much cheaper to switch to renewables today on every scale.
Ferdinand E. Banks 1.12.07
Great article and comments. Hopefully some means will be being found so that they will reach more than members of the EnergyPulse 'club'-
Len Gould 1.12.07
Todd: I'd like to re-emphasise your last paragraph above as very important, but point out in addition to your list of benefits, that any massive adoption of CHP / DG / RE stands to gore the oxen of a lot of powerful corporations and their supporting groups and shareholders who no doubt view the change as less benign, particularly to their personal interests. Bottom line, don't hold your breath for those clearly valuable anciliary contributions to be recognized in any meaningful way any time soon.
Edward Reid, Jr. 1.12.07
I have no problem with renewables, with the exception of those which rely on the conversion of food crops to fuel. I am a big fan of DG; however, to Len's point just above, if you want to "gore my oxen", don't expect me to be there for you when the wind doesn't blow, or the sun doesn't shine, or your DG system fails.
I do have a problem with those who suggest that various renewables are competitive now, when they are really "comparing apples and opals". Comparing the cost of "source of opportunity" power with the cost of reliable power is just plain silly.
I have a problem with those who suggest that CO2 reductions will be cheap and easy, which may be true for the initial few percent but will certainly not be true as the reductions get deeper. I also have a problem with the "holier than thou" Kyoto signers/advocates who have committed to reductions they will not achieve.
I have a problem with those who encourage starting down the path of CO2 reductions without being honest about where that path leads. It doesn't lead to a "7% reduction from 1990 levels by 2012"; it leads to more like 95% reductions (US) from 1990 levels by 2050, as part of a worldwide 75% reduction from 1990 levels, if the goal is stabilization at ~500 ppm.
I spent a lot of time on the "externalities" issue several years ago. Most everyone agrees that externalities exist. Many agree on one or the other of the approachs to quantifying externalities. Fewer still agree on the actual numbers. Go down that path if you like, but prepare to be very frustrated. (California had 3 different environmental externalities cost numbers for powerplant emissions in the 1990's, depending on whether they were emitted in the LA basin, in the balance of the state, or out of state; and, yes, the cost for out of state emissions was the lowest, by far. Sound cynical to you? It did to me.)
Todd McKissick 1.12.07
While looking for a shortcut or acronym applicable to the above list of comparable traits among energy solutions, I listed them out and with only a couple changes, came up with the following. Amazing is that most of the letters innocently happened in the right order as if to make sure I didn't try to make a different word. Had to share. For comment / clarification / critique:
C Cost of Energy
H Human / Health Impact
T Transmission Lines
I Infrastructure Impact
T Trade Employment
I Import / Export Impact
C Consumer Equity
Edward Reid, Jr. 1.12.07
Both thorough and clever.
Jim Beyer 1.12.07
An acronym for the energy debate
W WHY can't things just stay the same?
E ENERGY should be an unlimited resource
A The ATMOSPHERE should be an unlimited resource
R Heck, all RESOURCES should be unlimited!
E EVERYONE should be able to reproduce as much as they want.
D DON'T tell me what to do! Ever!
O The limits to growth and resources use should be OTHER peoples' problems.
O Unprecedented social and political ORGANIZATION? Thank you, I will stick to my tribe....
M ME ME ME ME!
E We are stuck here. Until rockets get a lot cheaper, we are EARTHBOUND.
D DENY, deny, deny.
Todd McKissick 1.12.07
Edward, I think we're more in agreement than not. I do have a few comments that basically amount to looking at it from the other side of the fence.
I don't think using food crops is automatically a bad thing, but I strongly believe it should be a producer choice and not mandated from above. For instance, the beef industry is taking a hit from shortage of feed corn due to overuse for ethanol. Also, when drought conditions occur most farmers bail hay and grass from ditches to keep their livestock alive. No legislation considers these type of ramifications.
Goring the oxen is a result of people wanting to get away from the mandated energy choices that have been made for them in the past. People have that right and for you to have contempt for that seems like you're protecting your profits at the cost of the masses. I'm sure if your power went out for weeks in the dead of winter, you'd accept the boarding your renewable-supplied neighbor offered if it meant keeping your little ones warm. On a personal level, I don't desire to put big energy out of business - just inject enough fair competition back into the mix to kill the monopoly (or oligopoly). Either Roger or Jim stated nearly 2 years ago that the ROI for lobbying was 100:1 so there's definitely rules-gaming going on.
The "opals" are equally frustrating to me. Opportunity energy should be priced as such, period. Any storage needed or geographical balancing should either be included in the project to affect that price or should be reduced from the market price and paid to the storer. With that in mind, there are numerous small scale and a few large scale options that include storage and/or backup in the project right now and more continue to pop up. The costs are currently too high but consistantly dropping. I was really looking forward to Roger listing some of them in this series of articles, but I think his scope was only utility scale options.
I agree that CO2 reductions will be expensive and are basically a finger in the dyke of Kyoto's wishes. New methods may be available or coming, but on some time frame, they're useful lifetime is limited. That still doesn't justify not doing what we can in the interrum. I'm more scared of the enemy I can't see which is the unknown positive feedbacks resulting from each step of GW that we pass. I don't like guesses. They usually come back to bite ya.
The part I do like about Kyoto is simply the awareness it brings to the average Joe. Those average guys really are in the dark about what's going on. I also think Kyoto is basically benign busywork to keep the world's leaders busy while the storm passes. Of course, I'm optimistic that we'll have sufficient technical solutions prior to needing them, so I can say this.
Regarding the exteralties, sure most people are aware of them but when do the energy companies use them as decision support? The only time is when they're touting how much renewables progress they plan. "Due to environmental and health concerns, we're planning 11 new coal plants in Texas." Ha! I don't think so. It's all about shareholder value. Big red flag here. I will grant you, however, that do-gooder environmentalists that exaggerate their pros or others' cons, do more harm to the whole situation. I also see the big effort to quantify each as a huge waste of time. Unless you're going to link it to price, why isn't it just good enough to just say, "smog is bad" or "we don't want to increase oil imports"? There are simply too many grants and other societal costs wasted on superfluous reports.
Edward Reid, Jr. 1.12.07
My point with regard to "oxen being gored" is as follows. You want to self-generate, that's fine. You want to connect to the grid, that's fine too. You want to sell me your excess power at the realtime cost of power, that's fine too. You want to sell me your surplus power at your real cost, rather than the realtime market cost, I've got a problem. You want to stay on the grid, but don't want to pay the fixed costs of that connection, I've got a problem. You expect me to provide you "no-notice" service at my average costs, to the detriment of the remainder of my customers, because I've got to buy "last kW" power to meet your needs, I've got a problem.
I am not willing to accept that Kyoto is benign. It is fundamentally dishonest. My big concern is that "lower CO2" technologies, such as CCTs and IGCCs, more efficient gasoline vehicles, condensing gas furnaces, etc. are not on the technological path to the levels of reductions envisioned by its proponents. CCT and IGCC plants have expected useful lives beyond the timeframe for "...once the burning of fossil fuels is no longer an option." The residual value of such facilities is an economic dead loss.
Todd McKissick 1.12.07
Edward, good conversation, 'eh? Lots of progress.
It seems we've reached the point where a difference exists between the large and small scale types. Taking small DG first, he should be able to sell power to you at the market price (as opposed to cost). His 'cost' shouldn't figure in at all. This little guy is a small fish in a large pond of DGs and his capacity changes are mixed by the minute with his neighbor's demand changes. For example, there's little difference between me adding a kw or my neighbor subtracting one. Being so distributed, these guys add to capacity so it would be hard to justify a "no notice" cost to me without TOU metering on my neighbor. Plus, I'm pretty sure the trend in DG systems will be to export to the grid with a bias toward peak times once their storage can be justified, so you're actually gaining on the whole.
Looking at large scale renewables like farms, etc. I do agree that their variability justifies a cost or mandatory storage fee unless they can guarantee capacity.
I would expect to pay for my portion of the connection costs, but don't go charging me $25 every month. That's 40% of the average local power bill WITH electricity.
We seem to differ on how likely it is that new technologies will reduce CO2 enough and in time for Kyoto, but does it really matter? Whatever we accomplish is progress, right? I don't see anyone pulling the plug when we hit the limit. There will just be more political posturing. I really don't even see much price increase happening from the reduction being forced since the options are becoming available. The good side to this is that by taking the largest hit early on, we will most likely be the ones owning the technology to be exported around the world and we'll miss out on more of the last oil bidding.
I do have a problem with your last thought. I see no reason for me to foot the bill to pay off plants built on the knowledge that they will outlive their usefulness. The option has been on the table for 30+ years for new generations of plants to be built. It kind of equates to the risk involved in starting a renewables company. Rest asured tho, fossil fuels won't die off overnight and your losses will still be transferrable to the consumer somehow.
Jim Beyer 1.12.07
I don't think a rational person would have any issue with your concerns.
Todd is more aware of the need for renewables to be competitive conventional sources than most.
I don't think anyone thinks Kyoto is benign. The argument is whether it is necessary or perhaps whether it is sufficient. Some Swedes came out with a study that even if ALL existing known reserves of oil and gas were burned up, it would only raise the CO2 level some 10's of ppm. Kyoto is particularly not benign to coal. But global warming is all about coal, and always was.
And I agree absolutely that one cannot rationally plan on building needed coal-fired plants with 50+ year lifetimes, with the threat of a carbon tax overhead. Those constructions need to be made with everyone's eyes wide open.
With various subjective interpretations, these are the cards we have been dealt. Perhaps dealt to ourselves. Everyone's ox is really being gored by this. Welcome to the 21st century.
What concerns me a bit is how concerned you seem to be about the subsidization (for lack of a better term) of renewables at the expense of conventional sources. With RE such a tiny fraction of our energy use, why the concern? If you are concerned about the camel's nose syndrome, the natural uneconomic nature of renewables will stop them in their tracks if the subsidies must be continued over the long haul.
And please ignore California -- with respect to energy: "how economical they are, arrogance and ignorance in the same package".
And with respect to crops for fuel, why not? I don't think the economics really support them long-term, but won't the free market decide that? If you ask of someone to limit how they use crops, then one should ask of all others to limit how they reproduce. Rwanda, Darfur, Gaza, these are horrible human tragedies exacerbated by overpopulation (Gaza intentionally so). While in theory there is enough food and energy to go around, in practice our imperfect social and political systems keep this from occurring. What's the point of developing a begnign, sustainable energy technology if our numbers will grow to overwhelm that as well? Coal is a great fuel for a planet with 1-2B people. Hopefully we can get RE to work for a world of 6+B, but probably nothing will work for 10B.
I think all that Todd is asking is that some of these technologies get a fair shake. Maybe we are so far off from reality that it is even ludicrous to ask that. If so, please articulate why. And perhaps what alternative suggestion you might have for the situation we find ourselves in.
Edward Reid, Jr. 1.12.07
"I would expect to pay for my portion of the connection costs, but don't go charging me $25 every month. That's 40% of the average local power bill WITH electricity."
The typical electric utility customer service charge recovers ~25% of the fixed cost of serving that customer. The balance of the fixed costs are recovered through the variable portion of the rate. That is why utility earnings go up in periods of high energy consumption and economic activity; and, go down in mild weather and during periods of economic softness. Twenty five dollars per month is pretty close to the utility's fixed costs of service.
Subsidization by government of new technology during the market entry/development period is not my problem. Forced subsidization by private companies of the products and services of other private companies is part of my problem. I am a retired utility guy. I try hard not to place utilities on a pedestal; I also do not automatically consign them to the stocks or the rack. Requirements of free or discounted standby service impose costs on the utility; and, ultimately, on its other customers. RPS requirements imposed by government, with no real appreciation of the technical issues imposed as a result, impose costs which may be difficult for the utility to recover through rate proceedings. At very low market penetrations, these impacts are minimal; however, as penetration increases, the costs and risks multiply. For example, as wind penetration approaches conventional capacity reserve margin in a given market, the intermittancy of wind power threatens to destabilize the grid in that market.
I would argue (I have argued) that it is well past time to rationalize energy utility and energy industry regulation. However, this cannot start with individual initiatives at the 52 public utility commissions. That is how we got where we are today, to a large extent.
A carbon tax is not as much of an issue for a new coal generator as CO2 emissions limits, especially if those limits require reductions far greater than those envisioned by Kyoto. Kyoto is merely phase 1 of an ill-defined multi-step process to reduce abiogenic CO2 emissions to ~0. Under reasonable regulation, a carbon tax could be recovered in rates. It is not very likely that "stranded assets" would be allowed to be recovered again - been there, done that, lost our shirts.
Len Gould 1.12.07
Question to Ed: If a hypothetical neighbourhood were made up only of 10 residential customers who paid the electric utility a fair price for their share of capital cost of the local distribution system as a regulated flat rate / month, and each customer had their own CHP generation sized at eg. double their average consumption and capable of being automatically dispatched, and the neighbourhood had no external connections, THEN is the utility STILL warranted to collect 1) connection fees 2) standby fees ?
Now scale that to a city of 1 million.
Edward Reid, Jr. 1.12.07
Standby fees only if required to stand by and provide service if required; otherwise, no.
Connection fees only if the utility owns or is responsible for the operation and maintenance of the connection; otherwise, no.
In the simplest case, a new community established off the grid could install its own distribution system with no utility involvement at all. Backing a utility out of an existing market is a more complicated case, but the general principle applies: if you use, or have a call upon, utility facilities or utility services, the utility deserves compensation for the use of its facilities or the demands on its staff.
If the city builds or buys the distribution system and has no interconnection to the utility, the utility has no investment and no responsibility and thus should receive no revenue. If the city leases the distribution network from the incumbent utility, the utility receives the negotiated lease revenue and provides the negotiated services.
Some US cities have "municipalized" existing utility properties, usually after an acrimonious negotiation regarding price. Some municipal utilities have their own generation, for all or part of their load. Some buy power from co-ops.
BTW, the neighborhood example you provide is probably not economic, because of the overly large capacity reserve margin.
Todd McKissick 1.12.07
How would an individual or group of them that decreasingly use the utility's service, receive their portion paid back? And how would an individual that only supplies his excess to the utility get compensated without his connection fees overriding that payment? After all, in the latter case, the utility is using their own distribution system to purchase power.
What are you basing your statement, "...probably not economic..." on?
Edward Reid, Jr. 1.12.07
It is not possible for a regulated utility in the US to conduct a negotiation with an individual customer regarding an issue like this. Therefore, how it happens must involve the regulator. However, the utility should be willling to pay the market price for power, with the regulators' approval.
The connection fee is what it is. Presumably, the customer would not be willing to give up standby service and become strictly a supplier of the utility. However, even in that case, someone would have to own and maintain the connection and meter and bill the net transaction. I can't wave my magic wand and make the cost of the facilities and the cost of maintaining them and billing disappear.
If you wish to continue this discussion, we probably should take it offline. I am certainly willing to do so. Len has my e-mail address.
Edward Reid, Jr. 1.13.07
"...probably not economic..."
Len's case sets average load factor at ~50%, as presented. Low load factor, typical of residential customers, makes on-site generation less economical than the same system operating closer to capacity.
Len's case is based on 10 residences. Assuming on-site systems of about 15 kW, the small scale of the systems would typically make them more expensive than larger systems on a per kW basis.
CHP systems typically require high percentage thermal energy recovery and use to optimize economics. In the northern plains, the combination of space and water heating loads may be sufficient. However, in much of the rest of the US, space cooling is also a large load, frequently larger than space heating. Residential capacity, low temperature absorption cooling systems are available in Japan and Korea, but are not inexpensive. Even high efficiency electric air conditioning systems would likely drive the capacity of the CHP system, therefore reducing load factor and adversely affecting economics. Reduced cooling capacity electric systems combined with cool storage would reduce the electric load on the CHP system, but add to system complexity and cost.
Finally, the cost of controls for small capacity systems is a larger percentage of system cost, since they must offer the same capabilities as in larger systems, but that cost is spread over many fewer BTUs and kWh.
These assumptions are all generalities; they are obviously not specific to any system.
Roger Arnold 1.13.07
About RPS, I agree with Edward that RPS requirements that don't take account of the costs of variability are a large and unfair subsidy to RE providers at the expense of the regulated utilities. I'm not against subsidies when they promote beneficial behavior, but the cost should be borne by those who will ultimately benefit. It's wrong for legislators to hide the cost of subsidies by foisting them onto the regulated utilities "because they can".
Developers of wind and solar resources should either be responsible for the cost of the storage facilities required to make them "good citizens" on the grid, or they should expect the irregular power that they provide to be discounted enough to cover the costs incurred by the utilities. The same applies for DG with grid backup. I like Edward's statement that what we need is to "rationalize" utility and energy industry regulation. Not abolish it through de-regulation, but "rationalize" it--make it more intentionally rational, in light of technical, economic, and environmental realities.
Concerning rational regulation, I think one of the more shortsighted policies for utilities to adopt is unconditional opposition to DG and net metering. Rather, they need to push for rules that allow for integration of DG in a way that provides reasonable control and is non-disruptive to other operations. There really is very little functional difference, to grid operation, between irregular loads and irregular sources. If the loads over many customer sites in a small area rise and fall together as a result of passing clouds, it will cause pretty much the same headaches for the utility as if DG sites supplying the grid were rising and falling to the same degree. By accepting power supplied from distributed sites, the utilities gain leverage to either insist that the DG supplier include a control interface and enough storage to make their supply predictable, or that the purchase rates are discounted to allow the utility itself to provide the needed remedies.
Warren Reynolds 1.14.07
A great article with some creative solutions. However, you left out hydrogen as an energy carrier and storage method. Of course, hydrogen storage is pretty obvious. Although, if the Danes had their electrolysis/hydrogen storage system in place to store their excess wind generated electricity, they would not have had to "dump" all that power into the European grid and create power management problems for other countries. Come on Denmark, get with it !
In addition, you did not mention natural gas liquefaction as a storage media. There are several large liquefaction storage facilities under construction and others planned on the East Coast at port facilities. These will be used to transfer and store the liquified NG from the ocean tankers. This approach will shortly parallel the "oil-geopolitical" problems we are now having. All the previous discussion about DG, RPS, CHP, ad. naseum, does not store 1 microwatt of power. Let us get the Solar-Hydrogen Economy moving forward and the storage projects done.
Roger Arnold 1.14.07
I left out hydrogen as an energy storage method because it's not currently competitive with pumped hydro and CAES. I don't think it's likely to ever be.
For energy storage, hydrogen's round-trip efficiency is too low. 50% seems to be about tops, and that's without AC to DC and DC to AC converters included. A good bit of the loss is inherent, due to irreversible reactions at the gas-liquid interfaces at both cathode and anode. Somebody might conceivably come up with a clever way to get around those losses, but I don't expect it.
Poor electrical round-trip efficiency could be OK, if the capital cost of equipment and hydrogen storage were very low. But they're not, and again, I don't see that as likely to change.
One thing that hydrogen does have going for it is that it scales down well. It works with pretty much the same efficiency and the same capital cost per kilowatt on the scale of an individual home as it would for a large central facility. But even at the home scale, it's not really competitive for energy storage alone. It could be better than current lead-acid battery systems, but that's not saying much. There are a number of better candidates in the pipe
One of those candidates is a unit from VRB systems. VRB has been building a factory for mass-production of 5kW vanadium-redox flow battery systems. The modules are designed as replacements for the lead-acid battery systems at telecom sites. However, they're just about the right size for buffering solar and wind power for an off-grd home. Their initial cost will be somewhat higher than lead-acid batteries, but lifetime and maintanance needs should be much better. Unlike lead-acid batteries, whose lifetime is shortened drastically by deep cycling, VRB batteries can be deeply cycled with no loss of efficiency or lifetime.
Prototypes of the units are in testing at a number of locations. I don't think they can be purchased yet as "off the shelf" items, but anyone interested can contact the company or a sales rep. The company's web site is www.vrbpower.com. There is a downloadable brochure on their 5kW modules that's informative. Their sales rep, for western North America I believe, is
Charles R. Toca firstname.lastname@example.org (949) 474-0511 x203
Jim Beyer 1.15.07
I think these posts are pointing out some of the limitations of energy storage of RE. To obtain reasonable efficiency at low cost (per kWh) , a very large construction effort is needed. Smaller storage is both less efficient and more costly. Even the VRB system is not exactly small (350 lbs to store 1 kWh) and not inexpensive either.
Edward has pointed out the very real (if somewhat premature) concerns of utilities footing the bill for RPS. And Edward is also correct in pointing out the metering of 1000's of microsources is not free, and someone has to pay for them and pay to maintain them.
I think it should be noted that other countries have jumped into this without thinking these points through. Denmark has been cited. I also believe Germany has allowed all RE generated by customers to be sold back to the grid at retail rates. Is this true? If so, this decision may prove problematic as RE penetration increases, perhaps even to the point of causing severe losses by their utilities.
I think a truce from the large utilities and small RE suppliers is needed. Some points of discussion include:
1. Roger points out that small levels of RE penetration will have little affect on the grid. Low level participation should not be stifled with excessive bureaucratic foot dragging. It is not enough in total dollars or kWh to worry about. However, we can learn a lot about how systems can be structured to work together. So to the big utilities: take a chill pill about small levels of RE penetration on the grid.
2. We need to educate the public (read: politicians) about the practical reality of RE in a world used to on-demand power. We'd all like RE to play a bigger role in the grid, but we must understand the costs of this. Smart loading may allow better use of this resource without excessive energy storage needed. So to the RE proponents: The big utilities do a lot to insure your on-demand power. Don't take that for granted.
3. The hidden message in all of this is that (sustainable, clean ) energy is going to get more expensive. Why? Twofold. First, the fuel of choice, cheap coal, is too dirty. If a carbon tax was apportioned to it, along the lines of working toward Kyoto or better, then its cost would sky rocket. Second, fuel-based energy supplies are inherently less expensive w.r.t. energy storage. They are basically on-demand power systems.
4. Higher energy costs leads to the traditional energy values of more conservation, more efficiency, and more insulation. Some motivation is needed for utilities to actually get their customers to use less energy, but that does not seem to be immediately forthcoming.
Roger Arnold 1.16.07
Jim, excellent synthesis. I agree with all four points.
Regarding prospects for affordable energy storage at the scale of individual households, I wouldn't rule it out. You're right that the VRB system is damn heavy, in terms of weight per kilowatt-hour. When I said their 5kW, 20kWh units were about the right size" or an off-grid home, I should have said "capacity" rather than "size". At 7000 lbs, you definitelly wouldn't want to put one of on an upper floor. It needs to go in the basement. But 95% of its weight is electrolyte solution and the tanks to hold it. And something like 95% of the electroyte is just water. The vanadium content is rather low, and vanadium itself is not actually rare. So the potential for low cost is there, ultimately.
The problem of low energy density in VRB flow batteries favors rather large implementations, like that being built for the Sorne Hill wind farm in Ireland, over the 20 kWh units on which VRB is focusing. Underground storage tanks for millions of liters of cheap electrolyte solution are no big deal for a wind farm or utility company. But presumably the 5kW power cells at the heart of the 20kWh units can be stacked for big installations, without changing the basic design or the production line. Just different plumbing.
There are also competitors to VRB systems that might end up being more suited for the small DG market. Firefly Energy ( www.fireflyenergy.com) promises a dramatically better type of lead-acid battery. It will have something like one fourth the lead content and twice the energy density of conventional lead-acid batteries. They have a large customer signed, and are scheduled to begin full-scale commercial production this year. The batteries are supposed to be highly resistant to sulfation, and aren't bothered by deep discharging. We'll have to see what comes of that.
Len Gould 1.16.07
I disagree with much of the direction of these comments, specifically that all are thinking too short-term. It's time some thought is put into encouraging the development of the grid we want, not just the grid we are given. For example:
a) the whole discussion of renewables energy storage simply "goes away" for free IF auto manufacturers are nudged, perhaps a little more harshly than last time, to produce and market plug-hybrid autos such as the one Chevrolet is displaying at Detroit show this week. I see no real technology hurdles to using this to "level out the load curve" except that it will perhaps make a bunch of gas peakers obsolete.
b) in a perfect world, these autos would also be capable of generating peaking power back into the grid, on command. For this to work, they need a 15A/120 or 30A/240 plug at their parking spot at work.
c) for b} to work, each parking spot needs a smart parking meter, see prior comments.
d) why put a big costly VRB battery in the home when there is likely at least one auto parked there with equivalent capability? Much smarter to invest the battery money into lion batteries in autos than big fixed battery units.
Several other issues with "current thinking" re. grid as well.
Jim Beyer 1.16.07
Wow. I'm glad I caught Len's comment.
Yes, I agree with him. A plug-in (PHEV-20) would have about 5 kWh of storage in it. It's expensive storage, but cars are expensive, and we are all used to that. (A gallon of gasoline at $2.00/gallon provides about 10 kWh of utility, or $0.20 per kWh. We don't care about this, but if this was the wholesale cost of our electricity, we'd be screaming. Odd creatures, us humans, eh?)
So, I think Len is saying we can leverage our existing comfort with high energy costs of transportation to smooth out the grid, especially with respect to RE.
Another way to put it is: PHEVs at least have a reasonable chance of success, heck even GM is working on them (so is Ford, and others) so the utilities really should take (another) chill pill.
Taking the side of the utilities, one could argue all these cars are not close to the power plants (so the power lines may be overloaded) and there is still the metering issue. Again, the metering can be folded into the price of the car, I'd expect. You also can't source more than 50-100 amps into the PHEV battery, so more of them are needed than you might otherwise think. Vehicles spend something like 90% of their lifetimes idle, so there is a lot of wasted resource here that could potentially be exploited. The Amory Lovins notion of banks of hydrogen fuel-cell cars powering the grid is faulty, but it can be ressurected as banks of PHEVs sinking and sourcing the grid as needed. If widely applied, then a huge distributed variable load is potentially accessible by the grid operators. (This does mean PHEV adoption needs to match RE penetration increases to some extent.)
I don't think one should pooh-pooh the cost of the battery packs, however, and should they be exposed to additional charge/discharge cycles, the utile lifespan of the packs will be shortened further. PHEV advocates (of which I am one) need to keep their eyes open to the real costs of the battery packs. The automakers aren't completely stupid, and the main reason electric vehicles have not been introduced has always been battery cost. An auto engineer once told me that no technical hurdles can't be solved if battery pack cost problem can be solved, and if the battery pack cost problem can't be solved, then electric vehicles are not economically viable.
So, I think Len reminds us of a key point:
We are willing to pay 10X more for our transportation energy compared with our grid energy. There should be a pony here that can benefit grid stability, even with more substantial RE penetration (perhaps 20%).
Anyway, sorry for blathering on, and thanks to Len for clearing our heads a bit.
Len Gould 1.16.07
Jim: Re battery costs, currently lion battery manufacture is essentially an entirely manual process, eg. workers in clean-suits hand-feed sheets of lithium through small roller mills, then manually fold them up with sheets of insulation to produce these little "2/3 D" size units etc. etc.
If the demand were large enough to justify hiring a company like ATS Automation to design a large autoamted factory to produce decent sized units, you may be surprised at how cheaply per kwh those things could be produced.
Also for high cycle-counts at high (dis)charge rates for eg. the first 5 kwh in an auto, supercapacitor technology is advancing very rapidly, and is likely already in a position to economically handle that part, or could be with automated volume manufacturing. A smart power unit manager exploiting 5 kwh of supercaps to optomize the life of 45 kwh of lithium batteries could almost certainly compete with gasoline as a fuel source. Haven't I heard that there's a couple of auto manufacturers who might appreciate some public support for some development work with public benefit?
Randy Park 1.16.07
Everyone, The debate around costs for renewable versus fossil fuel generation, and storage, is relevant at today's prices for NG, coal and oil. However, last winter we saw a huge spike in NG prices. This year we have had an unseasonable winter, and low NG consumption, resulting in relatively low prices.
NG production in North America is in decline; conventional oil has been in decline for decades; in fact the majority of oil producing countries worldwide are in production decline. If we compare costs for equipment designed to last at least two decades on the basis of today's fossil fuel prices, it seems to me we are making a big mistake. In fact, just look at cost comparisons which would result using prices from 5 years ago.
Yes Kyoto and carbon capture have monetary costs. But a glance to possible future scenarios suggests that by the time the politicians get around to figuring out how to price CO2, the price of fuel will make the decision between RE and, say, NG easy. One of the biggest benefits of the threatened costs of Kyoto and carbon capture may be to prevent the construction of numerous fossil fuel plants which will have expensive and/or scarce fuel supplies a few years from now.
Todd McKissick 1.16.07
One would think that any RE system that is almost cost competitive in comparison to grid power would immediately become cost competitive when offsetting vehicle fuel use.
Regarding these systems becoming too costly and complex, I think it should be noted that when you look at the equipment needed in today's home, we only need to move some functions around. For example, lots of homes already have 2-3 compressors (some configured as heat pumps), a dozen or more DC power supplies, heat exchangers, heat & cold storage tanks, fuel burners, temperature control systems, computer networks, alarm systems, sprinkler systems, attic ventilation systems, water filtration systems, exhaust systems, etc. This doesn't even take into account the expensive passive systems that add to the complexity of the modern cave. All we need to do is reconfigure all this equipment towards the end goal we'll probably see we're mostly there already. (wow, how did houses get so complex?)
Suddenly a RE system using CHP in conjunction with PHEVs doesn't sound so complex or costly. With the number of options available this way, it should be possible to balance energies around to become a grid connected a) net user b) net zero c) net supplier in any fashion desired (random or reliable). It just boils down to the price of energy bought vs. sold.
Len Gould 1.16.07
(ok sorry, the 5 kwh supercaps will need to wait for nanotube cap technology, meanwhile Maxwell can provide 0.5 kwh in 220 lb pkgs)
Stephen Bagstad 1.16.07
Just a little comment RE: CAES "A new and much larger system is being developed near Norton, Ohio..." This once-proposed system is near my Akron, Ohio location - and as far as I can tell is pretty much dead. The last activity on their website http://www.caes.net/ seems to be from 2001, and there has basically been little/no positive news about it since that I can find.
Roger's note "However, as energy storage solutions, these systems are mediocre." has I think basically been confirmed in the Norton "project" - So I suggest we no longer say it's being developed - better if we want to note it at all to say something like "was once planned near Norton, Ohio..."?
Roger Arnold 1.16.07
There's a well-known tendency among prognosticators to overestimate change in the short term while underestimating it in the long term. The possibilities that we can foresee often take much longer to develop than it seems to us they should--if they don't get sidetracked completely. But meanwhile, possibilities we didn't foresee mount up, and before we know it, we find ourselves in a game we didn't anticipate, with new rules that we struggle to figure out.
In the long term, I'm as bullish as anyone on the future of PHEVs and straight battery EVs. Electrons are destined to become "the new oil". But it's going to be longer than their boosters expect before PHEVs and EVs achieve the level of market penetration needed to impact the utility business. For business reasons, it's unrealistic to expect the cost of lithium-ion batteries to decline by more than about 20% per year--even if it would be technically possible. It will take five years of 20% declines for prices to drop to one third of current levels. That's about the minimum it will take before battery-powered vehicles begin to look good for the mass auto market.
Unless appropriate programs are established ahead of time, the transition to battery-powered transportation is likely to be very stressful for utilities. They will find themselves facing a rapidly growing secondary load peak in the early evenings when commuters arrive home and plug in their cars. Without mechanisms to regulate the charging loads and spread them out, the early evening peak could easily grow beyond the utilities' ability to handle. Smart metering is probably a necessary part of the solution, but I doubt that it's sufficient.
Roger Arnold 1.16.07
Len, the current market for li-ion batteries is not exactly small. About 200 million batteries per year, I believe, for laptops and cell phones. But manufacturing for the current generation of batteries requires clean room conditions--a major impediment to more automated production.
Some of the newer "inherently safe" lithium battery chemistries are not subject to the thermal runaway problem that plagues current lithium batteries. That should allow a more "automation friendly" manufacturing environment, and could prove a decisive advantage for these batteries--despite some loss in energy density.
But don't expect to see a quick drop in battery prices. Even if new facilities with low manufacturing costs come on line, the market is too large for them to supply more than a small piece of it, initially. The companies with the new facilities will just enjoy fat margins for a time, and plow their profits into expansion.
Jeff Presley 1.16.07
The acronym wars inspired me to kick in my own two cents:
W - When? H - How? O - Ontime?
M - Money? E - Energy solution?
We all should greatly appreciate that Roger is taking the time to both think about, and write about these things. Kudos to you sir.
Others need to actually DO things to make the transition happen. I have all the respect in the world for those folks toiling away in basements and garage shops attempting to SOLVE these problems. Innovators gave us energy in the first place, and the appetite we now have for it is caused by all those useful innovations that have come along since the first current was flowing over those first wires. Over consumption has caused this situation and now innovation needs to balance it. Edison would be astonished if he could see what progress has wraught, but would quickly be rolling up his shirtsleeves to tackle the problems/opportunities we now face.
Jim Beyer 1.16.07
Ugh. (well, tiny ugh....)
A bit of chastizement toward Roger and Len. (Well all gotta keep each other on the straight and narrow, ya know?)
I really think you are being a bit premature on battey cost/life. While there is reason to be hopeful, it is not a slam-dunk by any means, and the margins are tight enough that the first PHEVs may not even be economically viable if they a grid connected and have extra charge cycles imposed on them. A reasonable goal might be $500 per kWh for a battery pack capable of 1000 cycles. That's sound pretty good, except that means you are paying $0.50 per kWh of electrical storage for JUST the battery. No cost of electricity is added. So it is still tough going. But I think they are going to get there.
And your comments on ultracaps are also overly optimistic. True, ultracaps have millions of charge/discharge cycles within them, and they could play a role with PHEVs, but they are not viable for bulk electric storage, and probably will never be so. (I wouldn't hold my breath.) Maxwell has cited a large purchase price of a penny per Farad (2.5 volts) which is much cheaper than they sell now, but still quite expensive to store any reasonable amount of energy. The likely role of UCAPSs for PHEVs would be to source/sink enough energy to bring a vehicle up to crusing speed and back to rest. That would handle the lion's share of high current draws for a vehicle. Finally, any reference to carbon nanotubes solving anything (they were also going to store lots of hydrogen gas....) always sets off alarm bells in my head.
Roger, while your comments about the cost of batteries is correct, I really think it unlikely that PHEV use could grow fast enough to cause a discernable secondary load peak in our grid. It's taken over 5 years for ordinary hybrids to capture what? 1% of our automobile market? The grid will have plenty of time to adapt to PHEVs. Your comments about PHEVs disturbing the grid are a bit extreme.
I think a problem (and opportunity) here is that PHEV and RE developers and the grid may need each other to make each other economically viable. RE needs cheap energy storage to be viable. The grid needs cheap energy storage to accept non-trivial RE penetration. PHEVs need greater utility to be economically viable.
So, RE folks need to understand the storage problem is a non-starter from the viewpoint of the grid folks.
PHEV makers need to understand the value of the vehicles for energy storage. They should design them with this in mind, and incorporate the economics of this into their vehicle pricing. They need to understand that the grid connect may be the difference between viable and non-viable vehicles.
The grid needs to understand that RE can be offset with greating PHEV penetration, providing adequate metering can be developed. And once again, they should take a chill pill, cuz neither of these are going to grow very fast anytime soon.
Roger Arnold 1.16.07
Steven, thanks for the note about the Norton CAES project. I've wondered about the lack of recent news myself.
I still think CAES can be a viable energy storage technology, but it needs some work. That's why I raised the possibility of new approaches.
If anyone else has information about what's really happening at Norton, I'm sure we'd all welcome it.
Todd McKissick 1.16.07
Jim, while it is a good idea to have your PHEV actively help level the grid, this would require an inverter with a full compliment of grid sync and anti-islanding installed somewhere in the loop to send any power back to the grid. (assuming you want to offset more than just the homeowner's personal load). This is most likely the biggest roadblock to that scenerio. Timing charge and discharge cycles really doesn't amount to much more than adding a clock to the charge circuitry. Your point still stands though.
All, with regard to RE storage, don't forget there are more ways to store energy than in batteries. When working with residential scale energy loads, lots of other methods become cost effective. For example, solar heat (for CHP generation) can be very cheaply stored at nearly 100% efficiency. These upcoming storage methods make the RE systems of today look very attractive.
Jeff, just a little historical clarification. Nikola Tesla made our electrification possible and even gave up the royalties to ensure it survived. Edison was a charliton (sp) who didn't 'invent' anything including the light bulb. However, I'm sure the innovators in the crowd apprectiate your sentiments. If you really wanted to make a difference yourself, you could find your favorite solution and support it in some tangable way.
Jeff Presley 1.16.07
Tesla helped us all by going with AC rather than DC. However, if he hadn't we might have a whole different situation, with micro powerplants every few blocks. If you look at some of the comment stream here, you'll see that we are potentially going toward that eventuality anyway. I'm not altogether convinced that Edison was a charlatan, although it is certainly possible he was a better promoter than inventor, personally. That doesn't really matter, Bill Gates gets a lot of credit for what Microsoft does, and for good reason. He was an innnovator with a vision, and he's kept that vision alive and made multiple billionaires (including himself) in the process. Tesla conversely, had a power delivery scheme that guaranteed "free" power. Needless to say, spending money to produce a product and then giving it away for free didn't ingratiate him with his investors.
In point of fact, I have done precisely what you are saying. I have come out of an early retirement, and have inveigled two other scientists to likewise 'un-retire' so we can do precisely that. We've already submitted multiple patents, including one that directly relates to wind power and energy storage (of a sort, more like energy conversion). There will be an article about it in the IEEE later this year. We've even already given a presentation about some of our work at the DOE last year. So yes, I didn't just make those statements to be blowing smoke, I did it with the intention to motor-vate a few of the lurkers on this list, who likewise might feel they can and should make a contribution to the solution, rather than just bemoan the eternal "them" not solving the problem.
I'm sorry the acronym didn't cut and paste properly here, it was supposed to look like the others did above, with a letter per line. Who me? How about Who, us? ;_)
Todd McKissick 1.17.07
Hi Jeff. Congratulations on your un-retirement and any progress you've made. I wish you steady progress through the point of your end goal. It's good to hear of others making headway. There are at least 4-5 others in this group (myself included) that I know of with similar projects in the works.
It sounds like your project is topic related so I'm sure everyone would be interested in any comments you would have available for us. I understand if you didn't want to release specific details, but I (we) would even be interested in the financial/political/logistical roadblocks that you have run up against. They all affect the outcome.
Regarding Edison, I have nothing less than total disgust for the man. His DC system would not have made our current skyscraper laiden cities even possible. (some would argue that WAS a benefit, lol) He knew this but continued to push for it solely due to his personal desire for a monopoly on the entire national system. He publicly executed thousands of animals (including criminals) in his efforts to scare off any use of AC. Whether it was AC vs. DC or any other invention, he stole the idea from the true inventor for greed. Unlike Tesla, Gates and a few others, he never put society's benefits ahead of his own.
Regarding Tesla giving away free energy as a bad plan, his goal was to sell the transmitter and receiver equipment and let the volume go uncharged. This is essentially the exact business plan for my system. I believe this provides more benefits for society as a whole. Picture renting your car by the mile as opposed to simply purchasing it.
Jim Beyer 1.17.07
I was trying to stay on-topic with this article, namely storage of intermittent RE energy loads nominally placed on the grid (i.e., electric). But your point stands also. Perhaps grid balancing is best done with a garage of PHEVs. That might make more sense.
Thinking again about Len's point, I again see a problem. If we assume even $250 per kWh for PHEV batteries (this is low -- much lower than can be achieved today) and 1000 cycles, then we are left with 25 cents per kWh for storage -- still much too high to be of interest to the utilities.
Ultracaps very expensive and bulky. Even at a penny per Farad, enough ucaps to store a kWh would cost about $12,000. Yikes! But they last for many, many cycles. If we assume 1 million cycles, then we have a usage cost of only 1.2 cents per KWh -- this is more in line with what utilities could accept. Assuming, say 250 Wh per vehicle, then 4,000 parked cars could provide 1 MWhr of storage.
Todd McKissick 1.17.07
Jim, I was indeed referring to storing intermittant RE collection in the form of electricity for the use of leveling the grid. The difference is that instead of collecting the sun and immediately making the electricity which needs storing, my approach is to store the sun first and use it to make electricity on demand. This storage (a heated tank) is by far the cheapest, most reliable and most efficient form of storage discussed. If it is used in a CHP application, it can even periodically hit 100%.
When called for by the control system, the stored energy is sent to a Stirling generator to make only the electricity desired. As per the consumer's desires, the actual generation profile can be optimized for a) longest term storage, b) largest grid or net metering gain, c) offsetting other variable RE generators or loads, or d) max PHEV utilization. This eliminates energy conversion losses for the storage system altogether, leaving only the initial RE efficiency to deal with.
Len Gould 1.17.07
Agree all. A good site for batttery technology is http://www.batteryuniversity.com/partone-5A.htm
Roger Arnold 1.17.07
Jim, new lithium-ion batteries can do considerably better than 1000 cycles--provided that they're cycled several times a day, keep within a range of 20% minimum charge to 90% maximum charge, and aren't overheated.
There's some pretty good information on battery lifetimes in the blog entries on the web site for Tesla Motors. It turns out that li-ion batteries are subject to both calendar life and cycling life considerations. They lose capacity over time, even if not cycled at all. There's not a precise figure that I know of; it depends on the temperature environment and how much capacity you're willing to lose before deciding that it's time to buy new batteries. I think four or five years in EV use is expected, but it may be longer. Cycle aging is similar--a gradual loss of capacity until, after perhaps 3000 to 5000 cycles, they're down to 50% of original capacity--if they haven't been abused in the meantime.
Even with more optimistic lifetime assumptions, battery cost for lithium-ion batteries will still make them uneconomical for use in load-leveling. Or would, under utility costing models. But when you have lots of storage capacity sitting around that was acquired for other reasons, who knows?
Battery lifetime and cycling considerations are why I think there's a future for VRB flow batteries. A flow battery has some similarities to an ultracapacitor. The electrodes don't undergo any chemical reactions and don't degrade over time. The reactions responsible for energy storage involve only ions desolved in the electrolyte solutions, which can't degrade. So there's no cycle aging whatsoever. There's some physical aging in the proton exchange membrane, and mechanical wear in the pumps, but the lifetime is good and refurbishment costs (should be) pretty low. It's similar to the profile for renewables: a steep capital investment up front, but then use costs next to nothing.
Todd, someday we'll have to discuss your thermal storage system. AFAIK, there is no good solution for seriously high temperature thermal transport and storage. Not on the small scale required for a home system. There are thermal oils good for about 350 C, but with a reservoir temperature that low, I don't believe that even a Stirling engine can squeeze out a thermal efficiency of more than 15 - 20%. If collection and transport to the thermal storage reservoir is as high as 80%, you'd be in the same range of efficiency for electricity as solar PV (with the obvious bonus of heat). But it would be a solar tracking system, and I find it hard to believe that the cost wouldn't be significantly higher than fixed panels.
I could be wrong, of course. There's nothing fundamental that says you can't do it. It just looks hard to me.
Jim Beyer 1.18.07
I agree the grid energy storage via Lithium Ion batteries is a non-starter when realistic economics are applied. The same may not be true of ultracapacitors.
I am looking at the VRB flow batteries with an open mind. It sounds like you like them, but gee, are you their spokesmodel?? :)
Anyway, they are a bit vague on price. Doing some figuring, a 300 kwhr system would cost $200K? It doesn't sound like a 25 kwh system (home use) could be had for much less than $50K. Like you have said, the electrolyte is basically free, but I don't think it scales down too well. Maybe they need to redesign it for smaller units (less efficient, less costly parts, etc.).
They are also vague on power output. 120 watts/kg is not particularly illuminating. Given that it is membrane based, that means it is limited to the membrane surface for a given current rate at high efficiency. As the current gets higher, it may still be able to source/sink it, but at the cost of efficiency, probably a pretty high cost. (The is a big problem with PEM fuel cells as well, do you make them big/expensive or inefficient?) Again, I might be full of beans here, so correct me if I'm wrong.
I like the infinite cycling, not particularly thrilled about the membrane. Maybe it will last a long time. I wish it would scale down a bit more.
Roger Arnold 1.18.07
I'm definitely not a spokesman for VRB. I've always liked the concept of flow batteries, ever since I first read about it years ago. And I have spent some time in discussions with VRB people, after I was contacted by the sales rep whose contact info I posted above. They have a good story, but if the case for VRB batteries were a clear "slam dunk", they would not still be the small company that they are. The technology has been around for at least a decade, and has a track record of successful demonstration projects. But the cost projections have deterred a lot of potential customers.
The most basic problem that VRB batteries have is their low energy density. That's not something that anyone can do much about. It's inherent to the battery chemistry, due to the limited solubility of the vanadium salts employed. So the only path forward they have is to reduce costs and improve the power density of the battery cells. That's dependent on PEM technology, and there's some potential there. Various companies seem to be making progress on proton exchange membranes that will be some combination of cheaper, more durable, and more highly conductive than the current standard.
The fundamental question for VRB is not whether they can bring costs down and meet market growth, it's whether they can do it fast enough to stay ahead of the competition. Also, for large wind and solar energy farms, that competition is not confined to other battery technologies. It has to include the kind of pumped hydro and CAES systems that I wrote about--not to mention responsive loads.
Jeff Presley 1.19.07
Real time metering. Coincidentally from the sister site to this one: http://www.energycentral.com/centers/news/daily/article.cfm?aid=7677717
I'm not positive, but I'd guess they are using the AMR from Itron, where I worked in a previous life. Now that you see it in practice, perhaps some of the ideas concerning micro generation have a little more traction now?
Glenn Andersen 1.22.07
The example of the "Riverside Badlands Tunnel" would seem to indicate that there is very signifigant room for tweaking the total efficiency of the use of hydro power in this and many other countries. Even if improvements in the usage of hydro power were only possible near mountainous areas, as stated, would not the total increase in generated power be signifigant? I would like to know the percentages this technology potentially represents nationwide and worldwide, in terms of total electricity generated, and the costs relative to generating other types of energy. Thank you for a very informative article.
Roger Arnold 1.22.07
Looks like viewings and comments have tapered off on this article, so I don't know how many will see this. But I wanted to add a link for anyone seriously interested in CAES, and also pass on some comments I received from one of the engineers responsible for the McIntosh CAES facility.
Oops, my bad! Didn't close the anchor properly. Let's try again:
<..> The link is here (too long to display; if clicking "here" doesn't work, google "CAES Future Scenarios"). It's the recent master's thesis (January 2006) for a student in energy planning at the University of Aalborg in Denmark. He defines three CAES technology "scenarios", and then applies a model for future Danish energy demand and pricing variability to analyze their economic feasibility. The three technology scenarios are "Current Day Practice" (as represented by the McIntosh plant); "State of the Art Technology" (moderate upgrade of the McIntosh design for higher turbine firing temperatures, as employed in the GE "H" system of very high efficiency turbines); and "Advanced Technology" (more agressive upgrade, to capture and store compression heat for air going into storage, and recycle some of it to preheat compressed air coming out of storage.)
The interesting result is that the "Current Day Technology" never becomes profitable (under the model used). The "State of the Art Technology" does, but only a few years down the road, after demand and price variability have risen. The "Advanced Technology" option shows up as profitable from the start, with present demand and price distributions.
The comments I received offline were from Dr. Rodney Gay of Energy Storage and Power Corp. He took issue with my characterization of current CAES technology as "mediocre" as an energy storage solution. The heat rate that I used to calculate the effective round trip energy storage efficiency for the McIntosh plant was that of the best combined cycle plants available for baseload operation today. He pointed out that had I used the much higher rate characteristic of the large majority of units in actual use for the types of regulated load-following services that the McIntosh plant provides, then the effective electricity-in to electricity-out for the CAES portion looks very good. That's true, of course. Nonetheless, the plant is still reliant on burning natural gas for the greater part of its output. As the Danish master's thesis suggests, it's possible to do significantly better.
Now let's see if this works. (Dang, I wish EP would provide a "preview" button.)
Len Gould 1.23.07
Not arguing the details, but CAES suffers from the unavoidable difficulty of continuous energy loss in storage as heat-of-compression leaks away thru the walls of the storage chamber, constantly reducing the charge pressure and thus the stored energy. There would seem to be no way to avoid this significant inefficiency, which increases (to a fixed max.) the longer the storage cycles are. It seems apparent that if water reservoirs at eg. 100 meter or more difference in height can be found, (should be quite common almost everywhere) then setting up water pumped storage makes a lot more sense.
Len Gould 1.23.07
except by storing the heat of compression in a second thermal storage medium, which may work but begins to get complex
(and I'd add an Edit button to the wish list. eg www.physorg.com)
Chuck Scroggins 1.23.07
Great series. How about part 4, the effect that superconductor power line technology will have on DG, RE and energy storage.
Jeff Presley 1.24.07
superconducting power lines and other exotica
Here's a link to an good article about warm superconductors. The applications are more than just transmission, the windings of a generator made out of superconducting wire improves the efficiency enormously.
Hokay, that sort of worked. Not sure why it error'd on my text starting "Eperimental link posting..." and underlined it as if it were a link. Of course I didn't do anything fancy like
Graham Cowan 1.26.07
Sounds as if Jeff was about to make a slighting reference to our benevolent extraterrestrial masters. You don't want to do that.
Drafted for http://www.energypulse.net/centers/article/article_display.cfm?a_id=1404 but the low-frictional-loss part has not been made precise.
The water flywheel comes back to mind. Start with a circular canal whose outer bank is a circular gravity dam, spin the water up with motors when you have excess power, turn them into generators when you have not enough.
But how fast will you make that water go? Try 25 m/s. Suspect it's not, for the radii that are likely if we want to store a gigawatt-day, going to lie up on the outer bank all that much. 35 m/s fully charged, fully discharged at 10 m/s, so per kilogram of water 562.5 J, per gigawatt-day 153.6 billion kg. The cross section of a short piece of the canal, let's assume, is a semicircle of radius 15 m, area 353 m^2, and that makes its length if it were straight 435 km, circular diameter 138 km. That seems inconveniently large, so let's dig the canal deeper than 15 m, but there too there are limits ...
But with a 69-km radius and 35 m/s maximum flow speed, the water surface is hardly going to tilt at all, maximum tilt angle arc-tangent of (35^2/69000/'g'), 0.10°. This means the cross section of the water doesn't have to be semicircular, can be a regular canal shape. Let us try rectangular, 20 m deep by 200 m wide. Now our 153.6 million m^3 of water can fit in a length of 38.4 km, radius 6.1 km. This will increase the maximum tilt to 1.2°; the water level at the inner bank of the canal will be 4.1 m lower than the level at the outer bank.
If you want to scale down to a megawatt-day, you keep the 20-m canal depth, because having all that water that, hydrodynamically speaking, is unaware of any wall and doesn't know it's moving -- "still waters run deep", or more to our point, deep waters run still -- is where the very low frictional power loss comes from. That implies canal width and radius both diminish 31.6-fold, to 6.3 m and 193 m. That doesn't work. OK, depth diminishes to 10 m, width ...
The 4-m water surface height difference from inner to outer bank, at full kinetic energy charge, is constant, and limits how narrow the channel can be. Let's guess that it limits it to no less than 80 m. Depth can be reduced to 10 m, and of the thousandfold down-scaling, a factor of 200 must now come from radius; from 6.1 km down to 31 m, so the inner banks of the 80-m-wide canal are at radius -9 m. Thousand-fold scale-down doesn't seem to work.
Scaling up from a gigawatt-day to half a gigawatt-year, as one might wish to do if one had 3 GW(e) of northern hemisphere summer solar power capacity and wanted to turn it into a year-round 1 GW(e), could be done by increasing the 38.4-km-circumference, 200-m-wide, 20-m-deep canal's dimensions to 367 km circumference, 1.9-km width, 40 m depth.
Much though the required earth-moving and concreting would be, it's all up where the sun shines; and therefore, I think, much less trouble than creating even five percent as much water reservoir capacity deep underground.
It is, however, all motivated by an apparent assumption that end-users are always best served by getting their energy supply as electricity. Consuming boron at a 1-GW(B) rate, accumulating a half-gigawatt-year heap of B2O3 by the end of winter and turning it into a heap of B by the end of summer, you find that the biggest heap is the end-of-winter B2O3 one, and it's 930 kilotonnes, covering a circle 255 m in diameter, 5.1 hectares, piled in a 20° cone 46.4 m high at the centre.
At recent years' prices that's a US$2B boria heap. That's a lot, but compare the cost of a very wide, very deep 367-km canal whose bottom is never torn up by a very fast current.
(When charged up, it would provide a lot of inexpensive transportation, provided there were ship on-ramps and off-ramps, so to speak. This make the idea of a further large increase in diameter, to as large the largest flat parts of North America will accommodate, interesting.)
What is the round trip efficiency for the Boron cycle? If it is much less than 80%, then it is unlikely to be attractive to a major utility.
Graham Cowan 1.27.07
Electricity to electricity through boron would indeed be much lower in efficiency than 80 percent. Its use to support nonelectrical loads, and perhaps its production by nonelectrical means, are interesting, to me anyway.
Graham Cowan 1.27.07
I probably should have written something like, "a very wide very deep canal whose bottom is never torn up by a very fast current, even though such a current is present".
Am I right to think that Arnold worked out how wide the tunnel has to be, and how fast the water, for a man-made high and low pair of reservoirs for pumped storage, but did not worry about how big the big bits at the ends have to be? They have to be big; similar in volume to the ring canal.
Graham Cowan 1.27.07
Well, that's where the $265 per m^3, $1,000 per kWh comes in, I now see. $50 per kWh if the low reservoir were as deep as the Sudbury Neutrino Observatory. They've hoisted the heavy water out of there, or are in the process of doing so, so that's already a megawatt-hour or so of pumped storage. Or hoisted storage, anyway.
Len Gould 1.27.07
Graham. That's a brilliant idea, and that broad canal with surface travelling at 75 mph. would make a superb heavy transport means (when it's fully charged). Question: Have you figured out whether summer evaporation from the charged storage ring would amount to a significant energy loss?
Len Gould 1.27.07
Could we build the ring at the level of Lake Ontario (eg. bottom of Niarga Falls) and charge it up by diverting part of Niagra Falls in off hours?
Len Gould 1.27.07
And reference your last, re "storage volume at the bottom of the system", how about making the bottom of the system far enough down that geothermal heat from the earth's core would evaporate the water, letting it rise again to the surface "under it's own steam" as it were. Should work at least near Mauna Loa.
Graham Cowan 1.28.07
Mightn't that blow up the planet, leaving a new asteroid belt?
Someone should do the high-Reynolds-number stuff for whether the ring canal's frictional power dissipation really is small. Might not be all that small, integrated over six months.
Len Gould 1.28.07
Of course one would provide a conveninet escape shaft to the suface for the steam. Interesting also is that it is more economical to provide your own thermal energy source underground (a simple reactor) to evaporate the spent water from the turbine and send it back to the surface than to excavate storage space for it underground. With eg 1000 MWt reactor underground evaporating water 24 x 7, one could provide a large peaking turbine which refills the small underground reservoir as demand required, amounting to a simple short-term energy storage system.
Jim Beyer 1.29.07
Gee, I leave you guys alone for a few days and look at all the trouble you cause.
It sounds like you are talking about storing energy in the kinetic motion of water? That's completely impractical. The resistance in the water, even under laminar flow (your only hope) would quickly dissipate any energy stored. Roger's system was based on the potential of a source due to its height, not the movement of the water. True, the water does have to eventually move when it gets to the turbine, but the stored energy is due to the height of the water head, not the motion.
Go to any water park that has a wave machine, and you will see how quickly any water motion will dissipate. Or how many pumping stations are needed on the Alaskan pipeline, just to keep the oil flowing.
Graham Cowan 1.29.07
Well there's Beyers best attempt at doing the high-Reynolds-number calculation. Anyone else?
Energetically speaking, those kinetics have a lot of potential. Let's not get to dissipative about it. Graham and Len are thoroughly enjoyable!
Don Giegler 1.29.07
Make that "...too dissipative..."
Roger Arnold 1.29.07
Actually, Graham's notion of a "water flywheel" has some elements in common with an energy storage system I invented 45 years ago (in high school). I called it an "externally contained flywheel". Flowing water would never work (there's Arnold's attempt at the high-Reynolds-number calculation) but magnetic levitation could! Picture a maglev train many kilometers long chasing its tail through an evacuated tunnel in a ring an equal number of kilometers in circumference.
The interesting thing about the system is that the larger the radius of the ring, the faster the train can go before centrifugal force exceeds what the maglev system can support. So while cost scales with the circumference of the ring, storage capacity scales with the square of the radius. Regardless how high the linear cost of the tunnel + maglev suspension system, there's always a scale at which the cost per kWhr of energy storage drops below any set figure.
The only questions are (1) what is the linear cost (and thus the radius needed for cheap storage capacity; and (2) is there a market for storage on the scale resulting?
What I concluded 45 years ago was that the system would have to wait for the development of a renewable energy economy and much cheaper superconductors before the storage market was large enough and the costs low enough to make the system economically attractive.
Are we there yet?
Graham Cowan 1.30.07
Arnold and Beyer are right. Keeping the 38.4-km-circumference ring at a full 35-m/s charge turns out to take most of a petawatt.
I found some references to the energy cost of moving oil in a pipeline. Let me see if I can find them again:
550 BTU/ton-mile for crude oil in a 6 inch pipe. This drops to 180 BTU/ton-mile if you use a 40 inch pipe.
This says nothing about the velocity, just moving it probably at very low (comparative) speeds. Oil is much more viscous than water, so it's resistance to flow will be higher.
Jeff Presley 1.30.07
Gentlemen: Keep discussing laminar flow energy producing rings, and evenually, you'll rediscover magnetohydrodynamic dynamos. Add in the new advances in Tokamak's and I don't think you'll have to go for the full 38 km ring. Now if only Mr Cowan can figure out a way to substitue boron hexaflouride for sodium???
So, from hydroelectric storage to flywheel storage in 5 steps. Isn't there a show like this called connections??
Graham Cowan 1.30.07
"Substitue boron hexaflouride for sodium"? Sounds like a technology beyond my ken.
First you take up the canal bed and zip its banks together, making it into a pipe of circular cross section. 200 m width times 20 m depth becomes circular cross section diameter sqrt(4*20*200/pi), that's ~71.365 m.
The following follows ""FRICTION LOSSES FOR FULLY-DEVELOPED FLOW IN STRAIGHT PIPES", which is still on the web but apparently no longer free.
We can use the pressure drop in 38.4 km of straight pipe of this diameter and then join the ends together, turn the pascals into J/m^3, and take that off the kinetic energy density, which is 0.5*(35 m/s)^2 *1000 kg/m^3, 612500 J/m^3. Pressure drop,
delta P = 4 f (L/D_e) * 0.5*rho*V^2
where 'D_e' is equivalent diameter, 71.365 m as above said, and 'L' is the 38.4 km length-cum-circumference, and the 612500 J/m^3 can be seen as the right half of the right half.
delta P = ~1318293934 f
All we need is 'f'. But as I recall it has things like the ratio of roughness height to channel diameter in it, and the Reynolds number. The latter is easy: water's dynamic viscosity 'mu', 1 mPa·s, on the bottom, channel flow speed and diameter -- equivalent diameter -- on top, and I think density on top also.
Re = 35 m/s * 1000 kg/m^3 * 71.365 m / (0.001 Pa·s)
But is water's 'mu' really that low? Normal fluids are thousands of times more viscous at three or four times the absolute 'T'. Yes, 0.0100 poise at 20°C, it's really 1 mPa·s. Or more conveniently for the above arithmetic, 0.001 kg/(m s).
Re = 35 m/s * 1000 kg/m^3 * 71.365 m / (0.001 kg/(m s))
= 35 * 1000 * 71.365 / (0.001 )
This is a lot more than 2,000 so there is no chance of laminar flow. However, low drag does not require laminar flow. Dolphin and golf ball skins are dimpled so as to break up those laminae.
How high are the bumps on a concrete canal bed? Not rare ones but the ones that define the texture. I guess they're 2.5 cm high. This roughness height is called 'eps' in the following iterative rule,
which is the Colebrook and White rule for the intermediate zone between hydraulically smooth and hydraulically rough. Are we in fact in that zone? Our bump height is 0.00035 of our channel equivalent diameter, and from Figure 1 it looks as if we're definitely in the hydraulically rough regime. Figure 1 only goes to Reynolds number 10 million, but the trace for (eps/D_e) 0.0004 is straight and level from three million to that limit so I assume it stays level out to 2.5 billion.
So the iterative rule gets simplified a little:
1/sqrt(f) = 4 log_10 ((3.7*D_e)/eps)
= 4 log_10 (10562)
In fact it's not even iterative any more. 'f' is 0.0038603. Delta 'p' is 5088982 Pa, so to flow water at 35 m/s through a 71.365-m-diameter pipe 38.4 km long you must replace its kinetic energy 8.3 times on the way. The transit time is 1,097 s so per m^3 kinetic energy is dissipated at a rate of 4638 watts. Times 153.6 million m^3 that makes 0.712 TW.
Here's some data on the mississippi river. Flow rate at New Orleans - 600,000 cu ft / sec Elevation change in lower half approx. 600 ft. in 1200 miles Flow speed at New Orleans - 3 mph Average time from point at lower half to ocean - 45 days (?) Calc. flow speed from above 1200/(45 * 24) = 1.11 mph
so is it failr to assume that an energy input equivalent to a 600 ft drop in 1200 miles is needed to keep a flow of water moving at avg 1.11 mph?
Graham Cowan 1.30.07
Alligator shoals. Without them, it would drain out in a day.
Paul Dietz 3.28.07
One idea from the 1970s for energy storage I've akways liked is the magnetically confined kinetic energy storage ring. Basically, it's a very large ring-shaped flywheel in which magnetic levitation provides the centripetal acceleration, not the strength of the flysheel material itself. This was explored at Argonne under the awkward acronym MCKESR.
The nice thing about this concept is its scaling. Assuming the cost is proportional to ring radius (for constant centripetal acceleration and ring mass/length), then the cost per unit energy stored is inversely proportional to radius. Eventually power-related costs will dominate, but until that happens the system can be made arbitrarily cheap per unit energy stored just by scaling it up.