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The steadily increasing demand for electrical energy would likely result in greater use of energy storage technology in the future. Advanced developments in several renewable technologies promise lower cost per kilowatt. Several renewable technologies that generate power during periods of low market demand would warrant the use of some form of energy storage. Advanced high-temperature nuclear technology could benefit from access to energy storage to allow it to operate at constant temperature and constant pressure, meaning constant output.
A group of researchers recently published a plan in a popular journal on the potential of mass solar electric power generation in the southwestern United States. The cost per kilowatt of various concentrated solar technologies is expected to decline over the next 10 to 20-years to levels that are comparable to traditional power technologies. Proponents of other promising renewable energy technologies have touted future benefits that include generating large amounts of power at competitive costs per kilowatt.
Research being undertaken into high-altitude wind energy by groups such as Makani Wind Power and also by Sky Wind Power that promise to greatly increase renewable power generation at competitive costs per kilowatt-hour. The expected time frame would be over the next decade. Ocean power proponents are making similar claims of eventually reducing their generation costs per kilowatt-hour. There are however geographic regions where large amounts of renewable energy are available seasonally, mainly during winter. The demand for electric power is also seasonal with peak demand occurring during summer when much of the power is used to drive air conditioners during hot humid weather.
The availability of electric power that is out of sync with the market demand for the power creates a potential need for the seasonal storage of electric power. Such storage of energy may be possible and would be based on existing storage and generation practices from within the energy industry. The natural gas industry devised various methods of storing natural gas close to markets on a seasonal basis so as to ensure customers of an adequate supply during times of high demand. The preferred method of storing gas under pressure is to use salt domes that have been flushed of salt.
The storage volume can measure up to a mile in diameter by up to 6-miles in vertical height. Any number of compressed gases that include natural gas, hydrogen, carbon dioxide or even air can be stored under very high pressure in the subterranean cavity. There are at least 2-examples around the world where compressed air is being stored in such caverns as a means of energy storage. The practice of pneumatic storage is not without its critics, however, the storage efficiency can be greatly enhanced if the heat generated by compressing the air can be put to some productive use.
Proponents of the slowly emerging hydrogen economy have touted the benefit of storing compressed hydrogen in flushed salt caverns. Energy from powerful winter winds and from winter ocean energy at certain locations would provide the electric power needed to split the hydrogen from the oxygen on a massive scale. Some of the hydrogen would be used for various purposes during the winter months while the major portion would be pumped into seasonal storage and used during the peak summer. A few locales across the United States and Canada have the appropriate winter weather wind and ocean conditions to allow for such operation.
A seasonal change in demand for electric power could warrant the thermal power industry to operate a portion of their generation technology seasonally. One alternative would be to use the technology more efficiently and store some of the heat chemically during the off-peak season. Researchers at several Japanese universities and institutes undertook such research over the past decade. They explored the heat of decomposition of various metallic carbonates that released carbon dioxide when heated to a certain temperature and leaving a metallic oxide.
The carbon dioxide was later reacted under pressure with the metallic oxide to produce a metallic carbonate and heat at temperature of over 1000? C or over 1800? F. Such temperate can energize an externally heated gas (air) turbine engine or it can generate ultra-critical steam at over 4000-psia that can drive steam turbines. During winter, heat from either a nuclear facility or other thermal power plant can be used to decompose certain metallic carbonates under very carefully controlled conditions. The carbon dioxide that is released from such a process would then be pumped into underground seasonal storage.
The metallic oxides and metallic carbonates would be stored in giant warehouses that would be connected to other related thermo-chemical facilities by transportation systems based on auger and conveyor belt mechanisms. Computers would monitor and control the heat of decomposition process so as to avoid glazing the metal oxides. Some glazed metallic oxides can be reacted with steam to produce heat and a hydroxide that can then be reacted with carbon dioxide to produce a carbonate, as is the case with calcium.
Metallic carbonates are not the only means by which to store heat over extended periods. In a similar way some metallic hydrides decompose at certain temperatures and release hydrogen. That hydrogen may be pumped into seasonal underground storage. The heat of formation released by the reaction of magnesium and hydrogen is sufficient to operate any of several types of externally heated engines that include steam engines and several of the evolving solid-state engines such as the thermo-acoustic engine.
There are a few locations around the world where pumped hydraulic seasonal storage would be possible. One location is in the southwestern United States and would depend on whether some communities would be willing to relocate and a railway company willing to relocate a main railway line. There are proponents who are promoting the use of the Salton Sea as an appropriate site for pumped hydraulic storage. One advantage is the fact that it is located several hundred feet below sea level in a land depression and evaporation would actually raise the efficiency of pumped hydraulic storage to well over 80%. The United States and Mexico would need to co-operate to bring such a storage system to fruition. The pumped storage system will need to be connected to the Sea of Cortez, a.k.a. Gulf of California.
The major land depression located in Egypt south of the Mediterranean Sea would be a possible candidate for seasonal pumped hydraulic storage. An international long-distance power grid is being built across North Africa and the Middle East. Undersea power cables will eventually connect Southern Europe and North Africa, perhaps within the next decade.
Several Southern European, Middle Eastern and North African nations are planning to introduce nuclear power stations over the next 2-decades. Initiatives are underway to increase the use of renewable energy technologies across much of that region where the demand for electric power during summer increases by over 60% above the demand during winter. Egypt may finally get to build the long planned Qattara hydroelectric and pumped storage project and likely use it quite feasibly as a seasonal pumped hydraulic storage installation that can serve many nations.
Conclusions
While the concept of storing energy on a massive scale has its critics, storing energy over the short term as well as seasonally may necessary. The cost per kilowatt (and per megawatt) of several evolving renewable technologies is likely to drop to competitive levels over the next decade. Thermo-chemical seasonal storage using compressed gas like hydrogen or carbon dioxide is one possible technology. Seasonal pumped hydraulic storage would be possible in locations such as Southern California, Egypt and even Israel and Jordan if UHV-DC undersea power cables were to be connected to Cyprus and into Southern Europe.
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Wind Energy does NOT require enery storage today -- this article makes the common mistake of assuming that due to the variable output nature of renewable energy, wind and solar in particular, that this somehow indicates that energy storage must be needed to "firm up" renewable energy. Wind energy is being integrated in large quantiites around the globe today and without the need for energy storage anywhere.
The recently-completed U.S. DOE study on "20% Wind Energy by 2030" painted a very clear scenario where fast-response natural gas plants are added to provide additional capacity in the 20% wind scenario while 305 GWs of wind projects provide 20% of the energy needs of the U.S. While more fast-response natural gas plants are added in this scenario, the plants themselves are run 50% LESS and thus save 50% of the emissions from these plants at the same time. Electricity from coal-burning plants is reduced 18% and the resulting new enery mix results in significant reductions in CO2 emissions from the electricity sector with overall net positive SAVINGS to U.S. consumers. See the report at: www.20percentwind.org
Learn how wind power can be and is already being integrated into the grid in large quantities WITHOUT the need for expensive energy storage technologies. Energy Storage will have great value as a system resource, on its own, providing system operators with another tool in the toolbox, but it is NOT needed for wind energy today or antime in the near future.
Jeffrey E. Anthony American Wind Energy Association
Roger Arnold 9.28.08
@Jeffrey
You're rather touchy about the subject of storage, aren't you?
I don't think Harry was intending to address near-term requirements to achieve a wind penetration of 20%, with dispatchable fossil-fueled generation supplying most all of the rest. I think he was addressing a longer term, in which depletion of fossil sources and / or CO2 emission limits reduce dispatchable fossil-fueled generation to a fraction of its current level.
Just out of curiosity, however, what is your position as to what a fair price to wind farms would be for the energy they deliver to the grid? Since they do nothing to reduce the amount of dispatchable generation that a utility must maintain, would you say that they should be paid at only the cost of the fuel that they displace? Say 2 - 3 cents per kWh? The dispatchable generators that are idled by wind farm operation still incur all their fixed costs, after all.
@Harry
I'd like to hear more about energy storage in decomposable carbonates. Sounds interesting, but I'm unfamiliar with the chemistry involved.
I'd suggest you forget the nonsense about pumped hydro between the Salton Sea and the Sea of Cortez. It's 100 miles between the two, with a mean elevation difference of only 227 feet. (Sea of Cortez being subject to tidal variation of ~20 feet.) A water tunnel connecting them would have an average slope of only 0.04% -- not a whole lot more than the course of the Mississippi river. And it would take a tunnel with a cross section approaching that of the Mississippi to move useful amounts of water without excessive loss of head.
Well, OK, slight exageration -- but only slight. It would need a diameter of at least 100 feet, to move enough water over that much distance to generate ten gigawatts. And that's the minimum size that would be needed to begin to justify such an enormous megaproject.
Joseph Somsel 9.30.08
Contra to Mr. Anthony's assertions that everything is hunkydory with large amounts of wind, our European friends have had many issues with too much wind capacity. Even here in California, wind has failed us when we needed it most:
"The cost per kilowatt of various concentrated solar technologies is expected to decline over the next 10 to 20-years to levels that are comparable to traditional power technologies."
Count me out of that expectation as I serious doubt that solar power systems will ever decline to current traditional generation capacity costs. There is just too much material required for so liitle energy output. Even if they did, the lower capacity factor of solar would still make that source much more expensive.
I have to second Roger's concern - just how much are we paying for wind? There are so many hidden subsidies and pushed-off costs that it is almost impossible to tell. I'm pretty good at noodling out power costs but wind is a blackbox, perhaps intentionally.
As for storing hydrogen, remember that producing hydrogen from electrolysis requires one to throw away (as oxygen) half the electricity before system inefficiencies. Maybe store BOTH then use them to make a more efficient flame?
I also support Roger's point that wind should only earn fuel elimination credit for what the peakers and intermediate load generation DON'T burn. We still have to buy and maintain the fossil fuel generation equipment. Capacity credits of 8 to 10% on PJM and ERCOT reflect that to some degree.
Sorry, but wind has been grossly oversold to our political class and we ratepayers are picking up the tab.
Graham Cowan 9.30.08
I'd like to hear more about energy storage in decomposable carbonates. Sounds interesting, but I'm unfamiliar with the chemistry involved.
If you calcine limestone at the usual temperature, IIRC 1,200 Celsius, and don't let the CO2 go, you can get a fairly hot reaction when you bring them back together. Just in air, quicklime of course recarbonates itself quickly but without raising its temperature much, so the quicklime would also need to be stored carefully.
In pursuit of boron I found a similar scheme with magnetite and wustite:
To be sun-driven it requires a really sharp solar focus, but has the advantage that the released oxygen does not have to be stored. Plus you can do things with FeO in addition to just recombining it with the oxygen that was driven off; link below.
AWEA has long been against electricity storage, so Jeffrey Antony's position is not surprising. We want to keep the cost of wind low, unless you own a wind farm perhaps. Here in Minnesota, I have heard of wind farms being shut down due to lack of transmission capacity. While our CAPX 2020 may eventually alleviate that situation in this area, it is unclear that wind will have a priority for that capacity. If you can store power at the farm, then move it when there is room on the wires or when you can get a better price (a wind merchant plant), then there are real advantages for a wind farmer. Power could also be stored at the load centers for peak demand and backup. Will the NIMBYs and BANANAs stall or even stop expanded transmission?
Roger Arnold talks about the utilities still needing "dispatchable power". Cost effective storage would eventually eliminate the need for peaking plants, saving the cost of the gas they burn and of the course the capital and operational cost as well.
I think storage is an important subject, and I encourage further comment from those more closely connected to these issues.
Paul Stevens 10.1.08
If large scale storage becomes economical, why not just build enogh nuclear plants (lowest cost producer) so that enough off-peak energy is stored to meet peaking requirements? And not mess with the variabilities of wind/solar.
Joseph Somsel 10.1.08
Mr. Higdon,
We just concluded a very spirited and informative discussion based on my article on the economic laws of electricity storage:
The efficient storage of electricity on a large or a small scale is certainly a goal worth pursuing. Pumped storage schemes do work but require the right geological formations and they are very expensive to construct but are relatively efficient. I have heard of many proposals that seem to defy the laws or thermodynamics (compressed air storage to name one) so I am rather sceptical. Battery technology is making good progress and for smaller scale applications I can see some of those technologies filling a useful gap. But on a large scale I don't see much out there that shows any promise of being economic.
I agree with Mr Anthony of the USWEA - wind energy does not require storage - provided the grid is available. When the wind is not moving with sufficient velocity the turbines don't generate anything much so the grid - largely based on fossil and nuclear power plants comes to the rescue. If fossil fuelled plants and nuclear were not routinely available then of course wind energy plants would require storage capacity as would any uncontrollable energy source. If not then I think the lights would go out.
That is the reason wind and solar energy sources cannot be anything other than a marginal source of electricity production for industrialised nations.
But I feel there is no need of large scale electrical energy storage if proper use is made of storage capacity already available for other energy supplies notably natural gas. Production of hydrogen on a large scale could readily be converted into methane by combining with coal or any other carbon rich material. Once methane is produced then it can be piped into the existing natural gas infrastructure and stored along with natural gas from other sources. No need to redesign the existing pipework to carry hydrogen.
The City of Vancouver is piloting a project to pipe methane produced from their Municipal sewage system into the natural gas pipelines....now there is some common sense at work. Similarly if hydrogen is produced from excess electricity production at night (from wind or nuclear) it can be converted into methane and piped into the existing system which already has massive storage capacity.
There is no need to develop another expensive storage infrastructure...we just need to be a little smarter about utilising what we already have in place. Perhaps the gas and electricity industries need to talk more.
Malcolm
Malcolm Rawlingson 10.1.08
As a footnote to my post above, should large scale electricity storage become available it will overcome one of the major difficulties with most current nuclear installations - which is that they cannot load follow easily. Wind and solar cannot load follow at all since the fuel supply is not within human control. New nuclear plants are better suited to load follow but really a nuclear plant needs to be run at full capacity all the time to take advantage of its low fuel costs and high reliability.
The availability of cheap storage will basically put an end to wind and solar since the amount of installed nuclear plant will no longer be limited by the availability of sufficient base load demand. The storage becomes part of base load and is discharged at peak periods without the need for nuclear plants to load follow.
As Paul Stevens says it would make the best use of a predicatble supply with low fuel costs and no carbon dioxide emissions.
Malcolm
Len Gould 10.3.08
Malcolm: No need to wait for cheap storage to facilitate nuclear, wind and solar. Simply add a small amount of intelligence to the consumer part of the grid, one which rewards consumers for desired actions (shifting consumption off-peak). I'm convinced the rewards, for utilities, will be enormous.
Paul Stevens 10.3.08
Len: You know, timers for freezers and refrigerators might be able to make a significant difference. If freezers had timers built into them, I'm talking commercial and consumer, I bet runnig them at night only would provide sufficient cooling to protect food all day long. Are they doing this for other appliances, like dishwashers, laundry appliances etc.? They should be.
Len Gould 10.6.08
Agreed Paul. That's exactly the sort of action I think will resolve a lot of future problems for utilities and their customers.
Darel Preble 10.17.08
Clearly the smart grid must happen to enable Large scale adoption of plug-in hybrid cars, which appears to be coming down the pike in a few years. Tghis will enable smart water heaters, A/C, etc., Internet over Power lines is also in the pipeline - that also means we need to do a better job of worrying about the cyber security of our infrastructure. It is really disappointing to hear of power plants knocked off line because of net "noise", Wi-Fi and cell phones in the control room.
