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In Part 1, Hydrogen as Transport Fuel, we looked briefly at some general issues involving hydrogen production and its potential use as a future automotive fuel. That's where the most intense controversy surrounding the hydrogen economy is found. However, hydrogen is likely to have an increasing role to play in the future economy, regardless of how it fares as a transport fuel. In this article, we'll look at some aspects of that.
The Current Hydrogen Economy
Hydrogen is already used heavily in the oil and chemical industries. Firm numbers are hard to come by, but estimates for U.S. hydrogen consumption range from 9 to 15 million tons per year. About half is used to produce ammonia for fertilizer. Most of the other half is used in oil refining. It breaks heavy crude oil fractions into lighter products such as naphtha, kerosene, and diesel fuel in a process known as "hydrocracking". A milder process, known as "hydrotreating" or "hydropurification" is used to remove sulfur and other "hetero-atoms" from crude.
The need for hydrogen in these applications will be increasing rapidly in the coming years, as supplies of "sweet light crude" diminish and refiners are forced to turn to grades that are heavier and/or have higher sulfur content. By some estimates, the need for hydrogen will increase four-fold over the next ten years. Where will it come from? That’s an interesting question.
In North America, nearly all hydrogen used in the oil and chemical industries has been made from natural gas, by steam reforming. But gas production in North America has peaked. Many of the older and larger fields which have supplied the lion's share of North American gas have declined sharply or stopped producing altogether, and many others are nearing that point. While a great deal of gas is thought to remain in the ground, it is now widely dispersed in small pockets that are costly to tap. Newer wells often produce for only a year or two, and barely repay the cost of roads, pipelines, and drilling operations -- to say nothing of their steep environmental costs.
Tightness of gas supplies has driven up the cost of natural gas -- and the hydrogen made from it -- to the point where many fertilizer and some chemical plants in the U.S. have been forced to close. Those that remain in operation are squeezed on their margins. They find it tough to compete with plants in countries where natural gas remains cheap. The infrastructure hurdles associated with increased imports of liquefied natural gas mean that there will be no relief for natural gas prices any time soon.
This in turn means that the present shortage of refinery capacity in the U.S. for heavy crude is likely to persist. North American refiners are reluctant to invest in the new plants and equipment needed to process lower grades of imported crude, when the hydrogen that plays a central role in that processing can be produced more cheaply overseas. It makes more economic sense just to build additional refinery capacity overseas, and import the refined products to the U.S. The result is that, far from reducing our trade deficit and becoming less dependent on oil imports, the natural trend will be for continued job losses, increased imports, and more dependence on foreign supplies.
Reducing Dependency
The reality is that the market, per se, is blind to issues of employment, trade balances, and national energy security. Consideration for those issues can only be imposed on the market by political means. The tools available include taxes and tax incentives, subsidized R&D, low interest loans, and loan guarantees or other programs that reduce risk to investors. All of these tools are "double-edged" and must be used carefully. No program to steer the market can be successful if it simply aims to encourage the use of domestic oil and gas over imports. It would be disastrous, for example, to subsidize the purchase of natural gas by oil refiners and chemical companies so that they could produce hydrogen as cheaply as it can be produced overseas. Since it’s high demand for natural gas relative to North American supply that has caused the high prices in the first place, the last thing one should do is subsidize more consumption.
Any programs aimed at reducing imports and improving energy security must therefore focus on:
reducing consumption of oil;
reducing consumption of natural gas; and
increasing the fraction of energy we derive from sources that don’t have to be imported.
Reducing oil consumption mostly means reducing total miles driven and/or improving average mileage. Options for that were covered in Part 1. So let’s now take a look at options for points b) and c).
Reducing Natural Gas Consumption
High prices have already reduced natural gas consumption (or limited its increase) by making it unprofitable to operate businesses that depend on supplies of cheap natural gas. However, forcing businesses to close or move offshore is hardly the solution we want. Cutting back on gas for electrical power generation could also reduce gas consumption, but again, it’s an unappealing solution. Gas offers the most cost-efficient way to generate power, and is far cleaner than coal. If we had a choice about it, we’d want gas to replace coal for power generation, not the other way around. [1]
There are, however, positive ways to reduce gas consumption. One is by developing alternative means for producing hydrogen at affordable prices; we’ll look at that further below. But first, let’s consider the largest single use for natural gas in the U.S.: low grade heating. According to the U.S. Department of Energy’s EIA, residential water and space heating accounts for 24% of gas consumption. Consumption by the commercial sector, which is also mostly low grade heating, is another 14% of consumption. Can we cut these figures?
Most homes built in the last 25 years meet stricter codes for insulation and infiltration, and most older homes have been upgraded as well. There’s still some room for improvement, but we can’t expect to see major gains from the kinds of conservation measures that were effective in the ‘70s. However, there are two measures not yet widely deployed that could make big differences. The most immediately deployable method is the use of geothermal heat pumps (GHPs) [2].
GHP Basics
When a heat pump draws from a thermal reservoir at moderate temperatures, it can easily deliver four times as much output heat as it consumes in electrical energy. The natural gas that its use replaces, when burned in a modern CCGT plant, can produce at least twice as much electrical energy as the heat pump consumes. So every home that switches from natural gas heating to a GHP system effectively frees up for other uses an amount of gas equal to half of what it was previously using. As a bonus, GHPs are also highly efficient as air conditioners. Their use can reduce electrical demand for summer air conditioning by more than half.
Existing homeowners, unfortunately, are unlikely to invest in GHP systems on their own initiative. For new homes, the added cost of a GHP system over a conventional HVAC system is quickly made up in lower utility bills. But for an existing home that already has an installed HVAC system, the cost to be made up is much greater. Utilities and state governments may need to implement incentive programs, in the form of low interest loans or tax credits, to encourage switching.
Utilities might also want to consider offering a new type of service: district thermal ballast [3]. This would substitute for the local ground loop heat exchanger in individual homes -- the most costly component of a GHP system. Thermal ballast water would circulate to each subscribing home in a district. In winter, it would serve as the heat source to the heat pump in each home; in summer it would serve as the heat sink. The service differs from familiar district heating and cooling systems in that the thermal ballast water is never much warmer or cooler than the ground around the buried pipes that carry it. Heat leakage around the pipes and the cost of insulation to reduce it are therefore non-issues.
Local CHP
The other measure that could reduce heating-related use of natural gas is deployment of systems for Combined Heat and Power (CHP) at the level of individual homes. Gas is used to generate electricity, and waste heat from power generation is used for heating. Locally generated power replaces a portion of centrally generated power, and heating tags along for free.
It’s an efficient system. While still not common, the process is beginning to be used more widely in industry. There, gas combustion turbines generate the power, and their exhaust supplies heat. Combustion turbines are not practical for home use, but it’s expected that in the near future, fuel cells powered by natural gas will become cheap enough to make home CHP an attractive option. Many advocates of the hydrogen economy find this vision of a decentralized power infrastructure appealing. It would be very easy to substitute locally produced hydrogen or synthesis gas for natural gas.
There are some significant technical hurdles that have to be overcome before home scale CHP is practical. However, those issues are beyond the scope of this article. Time permitting, I’ll write about them in a future article.
Alternative Hydrogen
Now let’s look at ways to produce hydrogen that don’t require natural gas.
In Part 1, Hydrogen as Transport Fuel, we briefly covered methods of producing hydrogen. Here we’ll look a little more at the economic issues for different approaches. There are three general alternatives to natural gas for producing hydrogen:
electrolysis of water or steam;
chemical production from fuels other than natural gas; and
thermo-chemical production from high temperature heat sources.
Production of hydrogen by electrolysis of water has a reputation among hydrogen detractors as inefficient and grossly uneconomical [4]. The basis of this is the observation that a given quantity of natural gas can produce twice as much hydrogen by steam reforming as it can by being used to generate electricity for electrolysis. The observation is valid, but doesn’t really say as much as those making it may want to claim. It just means that to be an economically competitive way to produce hydrogen, electrolysis needs electricity at half the price of electricity from natural gas. There are situations where that requirement is met. I’ll say more about that shortly.
Chemical production of hydrogen starting from fuels other than natural gas is possible, and economical as long as the fuels are available. It is likely to be the cheapest way to produce hydrogen through at least the next decade. The chemical bond energies for hydrogen, oxygen, and carbon are such that any carbon or hydrocarbon fuel, mixed with steam at high temperature, will produce a similar equilibrium mixture of gases. CO and H2, along with excess steam, will predominate. Smaller quantities of CO2, methane, and methanol, plus traces of other gases, will also be present. The fuel may be anything from heavy crude to coal to biomass.
If the hydrogen is selectively removed, the concentration of the other gases shifts to compensate. The result is to produce more hydrogen. Ultimately, the end effect is that the hydrocarbon fuel is completely "burned" in high temperature steam, producing hydrogen and CO2. But the reaction is strongly endothermic, so heat must be supplied to drive it. That’s normally done by mixing oxygen with the steam, burning a portion of the fuel in a conventional manner. This reduces the amount of hydrogen that can be produced from a given amount of fuel, but it’s the easiest way to do the job. The amount of hydrogen that can be produced is still double or more what it would be if the same amount of fuel were burned to provide power for electrolysis of water.
The possibility does exist to use other means to supply the thermal energy needed to drive the reforming reactions. Doing so might increase the hydrogen yield from a given amount of fuel by 25 – 50%, depending on fuel type and reaction efficiencies. On the other hand, if a high temperature heat source is available, there are a number of closed loop reaction schemes that will produce hydrogen and oxygen from water and heat alone, not consuming any fuel. These are thermo-chemical production methods. One of the most favorable is the sulfur iodide cycle, studied by General Atomics and others for producing hydrogen from nuclear reactors [5].
Economics of Electrolysis
I wrote earlier that there were circumstances where the cost of electricity could be low enough to make hydrogen production by electrolysis of water economical. Currently, that cost is about 3¢ per kilowatt-hour. The average retail cost of electricity in the U.S. is 7.5¢ per kilowatt-hour. How can we get large quantities of electricity at only 40% of the average retail price?
Given an appropriate regulatory environment and IT infrastructure, short term variations in power demand over the course of a day would make it attractive for utilities to run a "spot market" for electricity. When there is supply whose costs have been "sunk" and which would otherwise be wasted, it makes sense for utilities to sell it cheaply for applications that can match their use to available supply. Electrolysis is perfect for that. The capital cost of water electrolysis equipment is not so great that the equipment must be run full time to recoup its cost. Because its power level can be changed instantaneously, online electrolysis capacity can be used for load leveling. It would permit fuller utilization of cheaper baseload electric capacity, and minimize the need for peaking units.
Dispatchable electrolysis capacity also facilitates the integration of wind and solar power into the grid. There will be times, for instance, when wind farm output is high while regular demand is low. Being able to increase power to the electrolysis units at such times allows the temporarily excess supply to be used productively. So long as the amount of hydrogen and oxygen produced this way have a ready market in the oil refining and chemical industries, it isn’t necessary to worry about the comparatively poor round-trip efficiency of hydrogen as a solution for power buffering [6].
Both electrolytic and thermo-chemical hydrogen production have the advantage that they do not consume hydrocarbon fuel and they emit no CO2 -- assuming that the source of electricity or heat is wind, solar, or nuclear energy. When used for oil refining, hydrogen and oxygen produced from water will increase the yield of gasoline, diesel, or jet fuel obtained from each barrel of crude oil. Depending on the grade of crude, the difference can be significant. In the extreme case of processing bitumen from Athabascan tar sands in Alberta, 100 barrels of bitumen will yield 76 barrels of "syncrude" when processed without hydrogen, or 106 barrels when processed with hydrogen [7]. For conventional grades of crude, the difference is less, but it’s still large enough to justify the cost of hydrogen production.
Conclusion
Regardless of how hydrogen fares as a future transportation fuel, the demand for hydrogen is already substantial and is growing rapidly. It will continue to grow in the years ahead, as lower grades of crude must be refined and production of synthetic fuels ramped up.
Natural gas has been the preferred source of hydrogen, but there is currently insufficient supply within North America. A well-formulated incentive program could slash the considerable amount of natural gas now used for low-grade heating, and free up some supply for more economically productive power and hydrogen generation.
In addition, electrolytic production of hydrogen is viable, and has several advantages:
With discounted off-peak electricity, it is economically competitive.
On-line electrolysis capacity, under real-time control by utilities, can be used to stabilize the grid, minimize the need for inefficient peaking units, and enable higher penetration by wind and solar.
Electrolytic or thermo-chemical hydrogen production powered by wind, solar, or nuclear reduces CO2 emissions, and increases the refinery yield from each barrel of crude.
Oil and gas depletion are long term problems that will not go away, and cannot be permanently "solved" by efficiency measures alone. However, the above measures for more intelligent use of natural gas and for alternative production of hydrogen take us in the right direction. They help to get us moving along a path that we will have to take in any case, if we hope to survive the end of cheap oil.
Further Reading
The hydrogen economy is a large and controversial topic. Even in a two-part article such as this, it’s impossible to cover more than a fraction of the relevant issues and options. For a balanced understanding, there are four articles available on the Internet that I especially recommend. One is Twenty Hydrogen Myths by Amory Lovins, a favorite of hydrogen’s boosters. Another is a favorite of hydrogen’s detractors: The Future of the Hydrogen Economy: Bright or Bleak, by Bossel, Eliasson, and Taylor . The last two are critiques of the first two. The articles can be found at the following URLs:
For the hard core, there’s a page at my own web site that has some 40 links, along with short descriptions of each one. These are links to the web sites I drew on for this article. Go to http://www.silverthornengineering.com and click on the "links" navigation button.
End Notes and References
[1] Which, of course, was precisely the plan, until we found that gas wasn’t as abundant and easy to obtain as we’d been led to believe.
[2] A good fact sheet explaining geothermal heat pumps and their operation can be found at http://www.eere.energy.gov/consumerinfo/factsheets/geo_heatpumps.html
[3] http://www.silverthornengineering.com/Tech Papers/ThermalBallast.html
[4] A good technical article that makes this point is by Don Lancaster in his July 2001 Tech Musings newsletter: http://www.tinaja.com/glib/muse151.pdf
[5] http://gcep.stanford.edu/pdfs/hydrogen_workshop/Schultz.pdf
[6] The round-trip efficiency of electricity to hydrogen and back to electricity is currently about 50%. Several other methods, including pumped hydro-electric storage, compressed air energy storage (CAES), and so-called "flow" batteries, manage around 80%.
[7] http://www.eia.doe.gov/oiaf/aeo/issues_4.html
For information on purchasing reprints of this article, contact sales. Copyright 2013 CyberTech, Inc.
Good to see you injecting some cool common sense into the debates. Kudos. Especially important is your statement "the market, per se, is blind to issues of employment, trade balances, and national energy security. Consideration for those issues can only be imposed on the market by political means." It seems unfortunate that most of the tools normally used for the purpose have recently been given away through international trade agreements eg. WTO etc. I'd guess its time to relegate domestic refining to the list of "rustbelt" industries and start trying to figure out how to organize afterward. Apart from servicing each other's consumption it's hard to see a role for the large majority of population. Looks like the elites have figured this out a long time ago.
BTW, love the concept of "district heat sinking". Should be readily doable as a low-cost retrofit if heat-pumps are desireable. I think instead we shouldn't be waiting for residential fuel cells. The easiest is, starting now with northern climates, adding small CHP engine/generators and some thermal storage to each padmount transformer. Pick up nearby nat. gas supply at high enough pressure to supply the burners without costly compressors. Stays under utility ownership / management, no liklihood of injuring linemen. Move meters for electricity and thermal into the padmount where they can be cheaply read remotely with the same simple phone line used to shut them down etc. on grid failures. Easy, no?
Roger Arnold 12.10.04
In line with your comment, Len, not too long after I finished and submitted this article, there was a pertinent news article. It announced that Saudi Arabia was building facilties that will use hydrogen to upgrade the heavy, sour crudes that apparently comprise much of their remaining reserves.
It makes sense for them to do so, since they also have a lot of stranded gas for making hydrogen. The investment should pay off nicely for them, because the spread between sweet, light crude and heavy, sour crude is currently close to $10 a barrel. The Saudi plans could be seen as vindication for US refiners, who have been very cautious about investing in facilities for handling heavy, sour crude in this country. But it's yet another hit to our trade balance.
We really, really need to be developing industries that will produce viable exports. We can't continue on the basis of arms sales--which are becoming an increasing fraction of what we do manage to export. I vote for energy conservation and alternative energy technologies. They're bound to be growth markets.
Murray Duffin 12.11.04
Great article Roger! I would question one point, the extent to which home efficiency opportunities have been realized. I lived on Long Island in the 1980s and taking advantage of a LILCO DSM offer I upgraded my attic insulation from about R9 to about R27. In the winter of '85/'86, when it snowed, every house in a many block area had bare roofs when I still had snow on my roof. I was the only house in perhaps 200 that had done the upgrade. Now my daughter lives in Wilkes-Barre Pa. Last March when I was visiting it snowed. After a couple of days almost every house roof was bare, but unheated porch roofs, facing the same way still had near 6" of snow. This observation applied to by far the majority of houses in WB and Scranton. My conclusion is that, at least in the NE, the opportunity hasn't yet been scratched. Murray
Roger Arnold 12.11.04
I think you're right, Murray. I had second thoughts about that paragraph myself, when I was doing further research on how many BTUs of heat were needed to heat homes in different areas. It's not nearly as related to average winter temperatures as one might expect. There's a strong "leveling effect", indicating that homes in colder climates are much better insulated than those in milder climates. If heating bill are below a certain level that they consider "affordable", homeowners don't bother with measures to reduce heat loss. Quite rational, in one sense, but it practically guarantees crises.
Jim Beyer 12.14.04
Roger, good article. I was wondering what were the possibilities of making use of the waste heat from electrolysis. (This heat might be greater in a cheaper, less efficient system). The point is that homeowners who have some on-site electric generation (wind/solar) may occasionally have some extra amps to spare. I think the cost of getting this small amount of electricity back on the grid can be large enough so that it is effectively a "use it or lose it" situation for the homeowner. So, if an electrolyzer could share it's waste heat, it might compete with a grid connect. Just wondering.
Also, I'd like to point out that though hydrogen is indeed cheaper when produced from natural gas, this cost does not account for the resource depletion, at least adequately. I understand our economics do not currently recognize this, but it is true nonetheless. Our economic and foreign policies that we pursue today, for example, would likely be different if our Texas oil reserves were completely intact. It is unlikely that we adequately covered this cost (in terms of more limited policy options) with the price that was paid for this oil by its consumers.
Tom Catino 12.14.04
U.S. Wind Farming, Inc. (Trading Symbol: USWF:PK)
15712 Orlan Brook Dr. Suite #151 Chicago, IL 60462
Toll Free 800.853.6768 Telephone 708.460.1936 Fax 800.853.6768 Wind Energy Cooperatives to Produce Electricity and Hydrogen for the Residential, Commercial and Transportation Industry Nationwide
CHICAGO--(BUSINESS WIRE)--Nov. 17, 2004--U.S. Wind Farming, Inc. (Pink Sheets:USWF - News): U.S. Wind Farming, Inc. will install the "Next Generation" of Integrated Renewable Energy Systems utilizing Decentralized Hydrogen Technology. This will become an important application for the Nation's Agricultural Community providing a considerable economic base while going far in removing this nation from dependence on foreign oil.
U.S. Wind Farming, Inc. (Pink Sheets:USWF - News), "America's Only Publicly Traded Wind Energy Company," (www.uswindfarming.com) announced their plans today to commission the Advanced Technology of GE Wind Turbines and Stuart Energy's Proprietary Integrated Hydrogen Generation Water Electrolysis Technologies. This is to provide U.S. Wind Farming's Wind Energy Cooperatives the ability to produce Commercially Viable Renewable and Clean Energy Commodities (Electricity & Hydrogen) thus "Unlocking" Substantial New Renewable Energy Reserves Nationwide.
U.S Wind Farming announces the next generation of Wind Farming Technologies creating not only electricity for sale during Peak Load Requirement times, but then producing Hydrogen for sale during off-peak times. This provides U.S. Wind Farming with the ability to "Harvest the Power of the Wind" to create valuable commodities garnering prime prices during all times of wind generation. This also allows U.S. Wind Farming to establish Wind Energy Electricity/Hydrogen Cooperatives nationwide in areas previously thought to not be viable candidates for wind energy development because of reduced wind velocities.
U.S. Wind Farming expects to commission GE Wind Energy (www.gewindenergy.com) to install and maintain all Wind Turbines for their Wind Energy Electricity/Hydrogen Cooperatives nationwide.
U.S. Wind Farming expects to commission Stuart Energy (www.stuartenergy.com) to install and maintain all Hydrogen Production/Pressurization/Storage and Dispensing equipment for their Wind Energy Electricity/Hydrogen Cooperatives nationwide.
Existing wind farms and new wind energy capable sites for these revolutionary new Wind Energy Electricity/Hydrogen Cooperatives have approached U.S. Wind Farming. Initial sites under consideration for development are located in California, Hawaii, Nebraska, North Carolina, New York, Tennessee, Oregon, Colorado, Wisconsin, South Dakota, North Dakota and Iowa.
U.S. Wind Farming, Inc. states that with the advent of this new paradigm of energy production, their Wind Energy Electricity/Hydrogen Cooperatives will not only provide extreme gains for our environment which is attractive to all the inhabitants of this Planet, but they have developed a way for Wind Energy to compete with all aspects of the fossil fuel industry, while providing considerable financial gain to the company and local farming communities. The company states that their Wind Energy Electricity/Hydrogen Cooperatives will go far in removing this nation's reliance on foreign oil.
ADDITIONAL NEWS: U.S. Wind Farming, Inc. has entered into a development contract for a 100-Megawatt Wind Energy Electricity/Hydrogen Cooperative in the Baltic Sea region of Poland.
U.S. Wind Farming has entered into a development contract with two new Wind Energy Electricity/Hydrogen Cooperative sites in China.
U.S. Wind Farming has entered into a development contract to provide and operate a Hydrogen Cooperative attached to a 350-Megawatt Gas-Fired facility in upstate New York.
U.S. Wind Farming has approached Aruba, St. Croix and several other Caribbean Islands to install Wind Energy Electricity/Hydrogen Cooperatives. Final negotiations and contracts are forthcoming.
The Company relies upon the Safe Harbor Laws of 1933, 1934 and 1995 for all public news releases. Statements, which are not historical facts, are forward-looking statements. The company, through its management, makes forward-looking public statements concerning its expected future operations, performance and other developments. Such forward-looking statements are necessarily estimates reflecting the company's best judgment based upon current information and involve a number of risks and uncertainties, and there can be no assurance that other factors will not affect the accuracy of such forward-looking statements. It is impossible to identify all such factors. Factors which could cause actual results to differ materially from those estimated by the company include, but are not limited to, government regulation; managing and maintaining growth; the effect of adverse publicity; litigation; competition; and other factors which may be identified from time to time in the
Len Gould 12.15.04
In looking for some financial details of the co-ops, I found the details of their old electrical-only co-ops, and man, ever sweet. see http://www.uswindfarming.com/about4.html On a 10 unit 15 MW install, the farmer makes $100,000/yr, the co-op gets 7% interest, and USWF makes $806,846 for financing whatever part the co-op isn't, while the utility pays $0.05/kwhr, 30 yr fixed contracts. Course their site requirements are very stringent, but man, anyone who could qualify should be hammering on their doors.
USWF expects its "Next Generation" Wind Energy Electricity/Hydrogen Cooperatives will produce at least 25% more revenue than current generation Wind Energy Projects. This will provide the Company with the ability to be even more competitive within the existing wind energy industry, and allow it to compete with the fossil fuel industry in delivering cost-effective electricity and fuels without government subsidies and tax incentives.
They must be counting on a fairly high price for hydrogen, but if atainable, good.
Roger Arnold 12.15.04
Jim, the idea of using waste heat from electrolysis to provide heat in a home system is interesting. I hadn't considered it. There are some obvious issues centered on cost, but it might be possible to work out something practical.
The most obvious issues are with capacity and availability. Home wind systems don't have the advantage that the big commercial systems have of being mounted atop an 80 meter tower, so their capacity factors are not as good. They do make good complements to home solar, however, since wind and solar outputs tend to be anti-correlelated. Even with a combined system, however, there will often be times when heat is wanted, but neither the wind turbine nor the solar panels are putting out power. Also, the amount of heat produced as waste heat from a small-scale electrolysis system is pretty small to begin with. So we have a couple of challenges there.
Next there's the question of how we use the hydrogen and oxygen. They probably have the highest intrinsic value when used to produce synthetic fuel from coal or biomass. That's a bit much to ask from a home system, however. The obvious alternative is to store them in pressure tanks, and use them to generate power when the wind turbine and solar panels are not producing. That's an inefficient way to store and recover power, if power buffering is the only objective: 50% round trip efficiency vs. 80% or more from deep discharge lead-acid batteries. But if part of the purpose is heating, the lower efficiency wouldn't usually matter. The waste heat from the fuel cell would simply add to the waste heat from electrolysis as part of the net heat production.
I think what we're looking at is a super insulated enclosure containing tubes of eutectic salts mixed for perhaps 85 C melting point for heat storage, a hot water tank, a reversable PEM electrolyzer / fuel cell, plumbing connections for water and for medium high pressure hydrogen and oxygen tank connections, and a blower for controlled air flow in and out of the enclosure. Plus electrical power in and out, of course.
Depending on climate and building characteristics, a system sized for the electicity needs of the home might produce more heat or less heat than needed. In the case of more heat, there's really not much that can be done. By timing electricity use more closely with availability from the solar panels and wind turbine, the amount of buffered power used and hence the amount of heat produced by the system can be reduced. Water pumping and refrigeration allow that, to some extent. But the ratio of buffered energy to thermal waste energy from the electrolyzer/fuel cell can't be arbitrarily increased. In summer, it might be necessary to spill some of the waste heat. But I'd imagine that the more common case would be less heat production than needed. In that case, the thermal output would need to be augmented in some manner. A wood stove would be a natural possibility.
Whether a system like that can be produced cheaply enough to find a market sufficient to recover the manufacturing setup cost is the $64 question. I think it could, but it would take some focused "due diligence" to come up with a convincing answer.
Graham Cowan 12.16.04
Ballard says its air-breathing Nexa fuel cell, 13 kg 1.2 kW, converts to DC electricity 41 percent of the free energy of the hydrogen it consumes, i.e. loses 59 percent as heat. Sea level, beginning of life. Surely this makes it difficult for a round-trip to and from electricity to lose, as Arnold says above, only 50 percent? Or has he some specific, updated fuel cell model in mind?
Graham, fair question. The Nexa fuel cell is optimized for automotive application, is it not? It gets its oxygen from the air, which must be compressed to the operating pressure of the cell at substantial energy cost. That cost is subtracted from the net output of the cell. It's also optimized for high power to weight ratio, which means high current densities and high internal resistance losses.
A system designed for power buffering would store both hydrogen and oxygen in pressurized tanks. It would not use compressors to store the gas, but would simply operate the electrolyzer and fuel cell at whatever pressure was currently stored in the tanks. It would probably also be larger and more expensive, relative to power capacity, than a fuel cell intended for automotive use. Current densities would be lower, for higher efficiency.
A good data point would be the system implemented for the Helios solar research aircraft that crashed after a structural failure earlier this year. I'll try to find out from someone at the company that built it what the round trip efficiency for Helios' hydrogen-based energy storage system actually was. However, I don't think 50% is a difficult target, in a system designed specifically for stationary power buffering.
Mind you, I'm still not very enthusiastic about using hydrogen for power buffering. Even if a round trip efficiency of 50% is realistically achievable--as I think it is--it reduces the energy delivery capacity of an RE system by 50% when it is operating from buffered energy. Capturing the waste energy to provide hot water and limited space heating is only a "bandaid" on the efficiency losses. It's makes use of energy that would otherwise be wasted, but it still requires the RE system to be substatnially larger--and more expensive--than it would be if a more efficient storage system were available. The heating use to which the waste energy is put could be more economically met by a solar water heater. The solar hot water system would cost less than the added capacity required in the wind / PV system to account for the losses. However, if large storage capacity and long lifetime do drive one to the use of hydrogen for power buffering, then it makes sense to capture and use the waste energy.
Graham Cowan 12.18.04
"Optimized for automotive application" -- no, I don't think so. 1.2 kW from 13 kg would make for a 400-kg fuel cell to support the ~35-driveshaft-horsepower peak power demands that even motorists who don't think of themselves as performance nuts would, perhaps, find barely adequate.
The cell that they do optimize for car-propulsion levels of specific power is, if I'm not out of date, the Mk902, 85 kW, 96 kg. As far as I know they don't publish its hydrogen consumption so I cannot derive an efficiency.
I did turn up a NASA press release from 2001 that gave numbers on the amount of energy needed to charge the tanks of a prototype for the system used on Helios, and the amount of energy then delivered by the stored hydrogen and oxygen. It was much worse than I thought: 16kWh to charge the tanks, in return for 4.6 kWh delivered. That's a round trip efficiency of slightly less than 30%.
If that hasn't been dramatically improved, then generating hydrogen for power buffering isn't just inefficient, it's grossly inefficient. Short of a major breathrough in PEM electrolyzer / fuel cell technology, better options for off-grid home RE systems are more likely to come from flywheels, small scale CAES, or better battery technology. It's an area that needs R&D support, but there is no constituency for it that could attract government funding.
Len Gould 12.19.04
Roger: A good study i've used for energy of compression H2 is 2003 Praxair at http://www.eere.energy.gov/hydrogenandfuelcells/pdfs/liquefaction_comp_pres_praxair.pdf. There they state (slide 14) the energy req'd to compress 1 kg from 100 psi to 7000 psi is 2.6 to 3.6 kwhr. Given H2 LHV energy content at 33.33 kwhr / kg the energy of compression looks, to me, like only about 10% of content. It would seem reasonable in this application to use electricity directly for compression and not charge this portion of the energy with storage first. (For liquifaction, slide 8, they quote 12.5 to 15 kwhr/kg, closer to 45% of content. That is bad.)
Then Stuart energy's electrolysis systems at http://www.stuartenergy.com/main_our_products.html state an all-in energy input of 4.8 kwhr/N cuM, or 57.3 kwhr / kg, (approx. 58% LHV).
A good recent overview of fuel cell is at http://planetforlife.com/h2/h2fuelcell.html. "The efficiency (of the Ballard bus engine) is given as 35% to 45% on an LHV basis. The efficiency decreases as power output increases." Actually that figure includes the efficiency hit of the motor as well, but let's say the fuel cell could convert 1 kg of H2 into 33.3 * .45 = 15 kwhr at the fuel cell.
Summary: 15 kwhr out 57.3 kwhr in electrolyser 3.2 kwhr in compression
So 15 / (57.3 + 3.2) = 24.8% effic. full circle.
Given not much chance to improve on the 45% in the fuel cell, only opportunities are in the compression (cheaper to pump the water up to full pressure before splitting it. Reduces compression input, see Protonenergy) or electrolyser (High temp with waste heat from ??? Not very likely).
The real trick is to sell the H2 at a (very) high price once it's made, not convert it back into cheap electricity. Or, sell the electricity at peak rates >> 4x base rate by enough to pay off equipment.
Graham Cowan 12.20.04
I doubt the "35% to 45% on an LHV basis" ... "includes the efficiency hit of the motor as well". If the page Gould quotes were a Ballard page, and it didn't directly state that motor losses were included, I would gather that they weren't. But it's from a page whose name includes "planetforlife.com". What that sort of name indicates to me is that their only expertise is turning implied falsehoods that benefit government's fossil fuel interest into direct lies that benefit government's fossil fuel interest.
("We know fuel cells are efficient, so obviously 55 to 65 percent losses can't be for anything less comprehensive than the whole powertrain. The whole powertrain must be 45 percent efficient. Hey! If anyone doubts fuel cells are efficient, look here -- this Ballard-powered bus scores 45 percent tank-to-wheel !")
We are indebted to the late Isaac Asimov for the observation that circular reasoning "is the chief delight of the intellectually feeble".
But here's an interesting Honda press release saying they, like, got rid of that Ballard crap, thus "elevating the new vehicle's torque energy efficiency, a measure of the extent to which energy is converted to torque, to 55% ..."
I like converting idiosyncrasy to compressed hegemony. Aside from that, what's misleading about their claims?
Well, I have to acknowledge that even though planetforlife.com/h2/h2fuelcell.html does seem to assume, unwisely I think, that 35 to 45 percent efficiency must be the whole bus propulsion unit, not just the fuel cell, it is otherwise a pretty straight web page. That'll teach me not to judge a web page by its URL. A new concept! Perhaps it can be generalized!
Reference "Honda's fuel cell developments", a long time ago I think it was G. Ballard who got in a fight with the new CEO hired by the investors over whether or not to lease evaluation units to the Japanese (G. didn't want to, figured they'd just tear 'em apart and duplicate them) Needless to say, cash flow won and G. Ballard is no longer with the company. I may be missing a bit but i clearly recall the "not to the Japanese" part. Can't find an academic quality reference though. 8<]
Roger Arnold 12.22.04
FWIW, I got an e-mail through an acquaintance at Aerovironment, saying that the round trip efficiency for the type of energy storage system that Helios used is, indeed, around 50%. That's, AFAIK, an unofficial number and should not be quoted. However, they had to know pretty well what it was, because it's a critical factor in sizing the PV array on the wings and setting the payload capacity. Since it matches exactly my own guesstimate of what it should be, I'll assume it's correct.
Graham Cowan 12.22.04
In the maxim, "extraordinary claims need extraordinary evidence", the second "extraordinary" generally has been understood to mean extraordinarily good.
