Prospects for Grid-Scale Seasonal Energy Storage

Harry Valentine | Jul 06, 2010


In many countries, the market demand for electrical energy is cyclical on a daily as well as on a seasonal basis. Numerous technologies already exist that can divert large amounts of overnight off-peak electrical power into short-term storage systems. Weather patterns alter demand for electric on seasonal basis in countries that experience major changes in ambient temperature, when the demand for energy to operate air conditioning systems during the summer months escalates.

Nations and regions that undergo major seasonal climatic changes usually have ample generation capacity during the cooler months. That capacity could manifest in as additional winter rainfall to operate power dams, higher velocity winds to drive wind turbines and even more favorable ocean waves and ocean tidal currents that may serve as sources of renewable energy. Having access to grid-scale seasonal storage capacity would make more productive use of such available generation capacity.

While there is potential for seasonal energy storage between Lake Ontario and Lake Erie as well as between the Qattara Land Depression in northern Egypt and the Mediterranean, there are numerous political and economic challenges to be address and managed in the course of developing such large-scale pumped hydraulic storage. The option to adapt compressed air energy storage (CAES) or some variation of it to grid-scale seasonal storage could offer a less complicated route by which to introduce and develop such energy storage. Research and exploration undertaken by the natural gas industry already provides one possible CAES option.

Seasonal CAES:

The largest salt domes in the world measure up to a mile in diameter by up to 30,000-feet in vertical height. When flushed of rock salt, the emptied salt domes can hold natural gas at some 100-times atmospheric pressure. There is scope to adapt a large emptied salt dome to compressed air energy storage. A dome of 4000-feet in diameter by some 20,000-feet in vertical height can provide some 2.345 x 1011 ft3 of storage volume for air at 1500-psia at 5.4713-lb/ft3 of density with the dome top located some 3000-ft below ground surface. Earth has a density of 110-lb/ft3 and at 3000-feet depth will exert a downward pressure on the dome roof of 2290-psia. Air pressure may be allowed to drop to 1200-psia or 4.377-lb/ft3 of density during operation.

Air may be released from the emptied salt dome over 4-months duration (154-days) at a rate of 17,629-ft3/sec and involve a change of density of 1.094-lb/ft3. The air may pass through a 2-stage power turbine with a pressure ratio of 9:1 per stage and involve computer controlled 2-stage (reheat) combustion. Maximum combustion temperature using natural gas may be set at 1540 F with temperature drop of 870 F across each stage of the power turbine. The peak continuous power level would be 17,629 x 1.094 (lb/sec) x 0.24 (Cp) x 870 x 3600/2545 x .745/1000 (conversion to MW) x .81 (efficiency) = 6000MW.

There is the potential to raise seasonal power output by pumping the same cavern to 1500-psia allowing pressure to drop to 1000-psia. Air density would decrease from 5.4713-lb/ft3 to 3.64-lb/ft3 over a season and releasing 1.82374-lb/ft3 through the 2-stage power turbines operating at 8:1 pressure ratio at a rate of 17,629-ft3/sec. The denser air would undergo a temperature drop of 820 F across each turbine. Continuous power level would be 17,629 x 1.82374 (lb/sec) x 0.24 (Cp) x 820 x 3600/2545 x .745/1000 (conversion to MW) x .81 (efficiency) = 11,000MW over 154-days duration.

The power system would include a regenerative heat exchanger to preheat air flowing toward the high-pressure turbine. Exhaust heat may be used to preheat water used in a downstream steam power system, desalinate seawater or generate steam for a water-based steam-vacuum district cooling system. The turbo-compressor system may involve a 3-stage system with a 5:1 pressure ratio per stage plus after-coolers. The heat of compression may be put to productive use as seawater desalination, district heating or to preheat water being used in a steam-based power system. Seawater may be used to condense the combustion exhaust and yield potable quality water.

Compressed Air-over-water Energy Storage:

There may be a limited number of sufficiently large salt domes that can offer seasonal CAES capacity. It may be feasible to combine compressed air with pumped hydraulic storage to provide seasonal storage capacity using emptied salt domes of sufficient diameter and limited vertical height. The hybrid concept involves using the change of pressure with water depth and will involve using smaller salt domes, available caverns or specially excavated caverns at suitable locations.

The top of a salt dome may be located some 4000-feet below ground level and some 3000-ft below maritime sea level (land elevation 1000-ft above sea level). The ground above the dome of 110-lb/ft3 will exert a downward pressure of 4000 x 110/144 = 3055-psia. The dome may measure 2000-ft diameter and use 3000-ft of its vertical height of 6000-ft to 10,000-ft for energy storage. Modern drilling technology would be able to drill a borehole into the salt dome and the ocean at a depth of 6000-feet below sea level, with pressure of 6000 x 64/144 = 2670-psia.

A 3-stage air turbo-compressor with 6:1 pressure ratio per stage would be able to generate pressure of over 2700-psia, sufficient to pneumatically pump water from the salt dome. The air density in the dome would rise to 10.9-lb/ft3 in a storage volume of 1.047197 x 1010 ft3. The air would be released over a period of 154-days at a rate of 787-ft3/sec or 8578.68-lb/sec and pass through a 2-stage power turbine with 9.5:1 pressure ratio per stage.

Heating and reheating would be achieved by either natural gas combustion (night) or concentrated solar thermal energy (day). Temperature drop per stage would be 870 F. A regenerative heat exchanger would transfer exhaust heat into the incoming air. Power level would be 8578.68-lb/sec x 3600/2545 x 0.24 x 870 x (2-stages) x 81% efficiency x 0.745/1000 = 3000MW for a period of up to 4-months. A dome of 3000-ft in diameter (1500-ft radius) and 3000-ft in height (2.474 x 1010 ft3 volume) allocated to air-over-seawater pumped storage could generate 6500MW over the same duration.

On an even larger scale, it would be possible to generate some 11,000MW over a season using the top 3000-ft in height of a dome of 4000-feet in diameter. Such an option may be considered if a dome of such diameter and vertical height of under 10,000-ft were located near an oceanic coast or next to a lake. While such dimensions would limit the scope and magnitude of using the dome for seasonal CAES operation, the location and the dimensions would enhance the attractiveness of adapting such a dome for seasonal air-over-water energy storage operation.

Air-water Separation:

The development of a grid-scale compressed-air-over-seawater energy storage system would require the development of special separator technology that would prevent or minimize the diffusion of air into seawater. A layer of oil floating on the water has long been shown to separate water and air and could prevent the compressed air from diffusing into water. It may also be possible to install giant inflatable plastic or polymer bags into the cavern to separate air and water. There has been research into submerging air-inflatable bags pumped with compressed air into seawater as a form of small-scale energy storage.

While there is potential to keep a small-scale air-inflatable bag submerged under seawater, keeping larger air bags submerged at greater depths becomes more challenging. Placing multiple large air-inflatable bags inside a cavern located in impermeable rock offers the option of large-scale and seasonal energy storage. While much of the technology needed to operate an air-pumped hydraulic energy storage system is already long proven, there is a need to develop additional technology to make a mega air-over-water seasonal energy storage concept more workable.

Compound Pumped Hydraulic CAES:

There are salt domes and earth caverns that have roofs located at over 5000-ft below sea level where hydraulic pressure would exceed 2250-psia. A modified air-over-hydraulic energy storage system may be applied to empty salt domes of limited vertical height, sufficient diameter and roofs at extreme depths. For a seasonal height fluctuation in seawater in the cavern, hydraulic pressure would rise to 3600-psia at 8000-ft of depth.

Except that a compound pumped hydraulic CAES could reduce pressure levels inside the cavern. Such an installation would place Kaplan pumping turbines at a depth of 2000-ft below sea level. The pumping action of the pumping turbines would reduce hydraulic and air pressure levels of between 2250-psia and 3600-psia within the empty salt dome to between 1335-psia and 2670-psia, pressure levels usually found at depths between 3000-ft and 6000-ft.

The 5000-ft of depth of earth above the dome would exert a downward pressure of some 3800-psia. For 1000-ft elevation above sea level, some 6000-ft of earth located above the salt dome would exert a downward pressure of over 4500-psia on the dome roof. The pressure from above on the dome roof would balance pressure inside the empty salt dome and offer a measure of safety at the surface while assuring the viable long-term operation of the emptied salt dome for seasonal storage.

The CAES component of a compound pumped hydraulic CAES installation would generate near equal output over the same duration as the equivalent size of empty salt dome adapted to the same operation at higher elevation. Except that the Kaplan pumping turbines would generate additional output over the same time duration. The compound system would use salt domes that may be deemed too small for pure CAES operation and where natural gas may be stored in nearby empty salt domes.

Raising Seasonal CAES Productivity:

Intercoolers placed downstream of each turbo-compressor may extract heat that may be used productively in such areas as district heating, preheating water for a steam-based thermal power station or desalinating seawater. The exhaust heat from the power turbines may be put to similar productive use during the hot summer months and also be able to energize a steam-vacuum cooling system for district cooling.

The cool incoming seawater may be cooler that the summer air and may serve as a heat sink for a district cooling system. During winter, the warm water being pumped out may serve as a heat source for a heat-pumped district heating system. There is potential at some locations to use dry cooling or available seawater to condense potable water from the power turbine's combustion exhaust gas.


Much of the technology needed to develop grid-scale, seasonal energy storage systems is well proven. While seasonal pumped hydraulic storage is technically possible in Lake Erie and Niagara Falls, there are political factors that would likely delay the development of such a project. However, a few giant salt domes that may be available at some locations that may be adapted for seasonal CAES operation. Smaller salt domes with limited vertical height may be adapted for air-over-hydraulic energy storage.

Groups of salt domes usually occur in close proximity to each other allowing an adjacent emptied salt dome to store compressed natural gas to sustain the summer operation of the seasonal CAES installation. By operating air turbo-compressors on other energy sources during the winter months, the CAES and air-over-water energy storage systems would save 40% to 50% of the natural gas that gas turbine engines would otherwise consume. Both variations of the seasonal energy storage concept would also benefit from economy of scale.

Pneumatic-over-hydraulic energy storage systems in the form of hydraulic accumulators are well proven in many applications. Researchers have more recently expanded on the concept and demonstrated the operation and potential viability of compressed-air-over-seawater energy storage systems involving airbags submerged in deep seawater and pumped with air. There is market application for large, grid-scale versions of such technology adapted to seasonal energy storage operation at coastal locations in many countries. Seasonal CAES and air-over-water CAES technology promises to be viable and productive.

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This is just one of four ways to store electricity for night time use.

Salt domes and below ground caverns are rather few and far between in the U.S. Thus, for most large scale utility solar power plants the choice is not there. Solar PV power conversion to hydrogen is still the most immediate and widespread use for storing electricity for night time use. The efficiency is:

0.86 x 0.92 = 0.78 (78%)

efficient in turn around back to electricity. There are already plans to build the world's largest solar-hydrogen power facility, 500 MWe in So. California.

By the way, the Hidenburg blimp explosion WAS NOT caused by hydrogen. That is just a myth. NASA engineers have proven otherwise. The fire was started in the silk and aluminized cellulose (rocket fuel) outer "skin" due to lightning strike.


Harry, What is the efficiency of compressing air, pushing it into a salt dome and then decompressing it and generating electricity. Seems not a very efficient process to me. It is done for natural gas to level out supply and demand from natural gas supplies so efficiency is not the prime consideration there. Not sure that's the same argument with electricity generation. Would you not lose a significant amount of energy compressing the air because of Charles Law and Thermodynamics.

Warren - how much land does a 500 MWe solar PV plant use. That is big.

Agree that the Hindenberg fire was not caused by the hydrogen but once started it was the hydrogen that burned. Hydrogen, because it is so much lighter than air is a very safe fuel...much safer than the gasoline we use daily in our cars. Nevertheless must be handles with care.


Warren, I don't think your efficiency for storing hydrogen is realistic.

To go from high voltage ac to low voltage dc then through the electrolysis of water process then to a compressor alone gets us less than your 78% turnaround figure.. Once in a pressure vessel how are you going to use your hydrogen? If you burn it as fuel to displace coal you get about 34% of its heating value back as electricity for an e of maybe .98 x.85 x .95 x .34 = .27 or 27 % even if the electricity to be stored were free. But if it was generated at 34% e then we would get back about at about 9.2% e from the original fuel, and much capital investment would go unused much of the time.

Unless I have made a huge mistake , it doesn't look viable to me.

Don, Looks like data manipulation worthy of an AGW enthusiast to me. In my many years of operating and working with compressed air equipment I am very certain that the process of compressing air from atmospheric to several hundred psi generates significant heat (the reason for coolers and intercoolers on such machines). So where does that heat come from....the electrical energy driving the air compressor. Therefore the process is not very efficient. I would be very surprised if such a compressed air storage system would get much more than 50% efficiency and likely far less than that given the large water cooling systems typical of large air compressor stations.

Also the reason for using salt domes to store natural gas is that gas wells cannot supply enough during winter months. I suppose it is a kind of peak lopping but done for a very different reason.

Seems like daft idea to me.

The other method proposed by Warren looks equally dubious and I think a 9% efficiency is about right. I am not sure why people do not understand that changing any form of energy into anything else is inefficient and the more changes you make the less efficient it is. Even if each transfer was 80% efficient after 4 such transfers you have lost 60% of the energy you started with. (0.8 to the power 4).

Also sounds like a daft idea.


Did not get a reply from Warren on how much land a 500MWe solar plant would take up. I think it is alot - even in sunny California. But since it is not sunny half the time does not one need a 1000MWe plant to produce the average of 500MWe? 500 MWe is required for the day demand and and additional 500 Mwe is used to prodiuce power to store. So to get 500MWe continuous one needs 1000MW. I think that is one very large piece of property.

To supply California would likely require covering the place in solar panels...Arnie might not like that.


Broad brush CAES summery: process is basically compressing air (with intercoolers to reduce compressor power) and then running the air thru a combustion turbine, with an dwell time for the compressed air in a cavern. Presumably, the gas turbine exhaust would be used to also create steam for a steam turbine generator.

More conventional processes (classic combined-cycle power plant) do not use compressor intercoolers, with the air heated by the compressor further heated by fuel gas to the firing temperature of the gas turbine. Efficiency is around 50% (Higher heating value).

While the inter-cooling does reduce the energy required by the compressor, you have to use fuel to get the stored air back up to the hot air temperature discharged by the non-intercooled compressor, with fuel then used to get to the firing temperature of the gas turbine.

Bottom line is that I would not characterize the CAES process as necessarily inefficient, but it is not as efficient as a combined-cycle plant configuration. However, the reason for CAES is tied to economics and the ability to use low cost energy associated with off-peak electrical generation.

While the elements discussed in the article are available, I suspect that that from a practicality standpoint, the competitive economics are not.

Building this plant to then only use it to charge/discharge once a year seems a very expensive proposition.

"Dividing the global yearly demand by 400 kW•h per square meter (198,721,800,000,000 / 400) and we arrive at 496,804,500,000 square meters or 496,805 square kilometers (191,817 square miles) as the area required to power the world with solar panels. This is roughly equal to the area of Spain. At first that sounds like a lot and it is. But we should put this in perspective.

If divided into 5,000 super-site installations around the world (average of 25 per country), it would measure less than 10km a side for each." -- Total Surface Area Required to Fuel the World With Solar Note: Basis = 1 kw / sq meter insolation 8 hrs / day for 250 days / year, 20% solar conversion efficiency. All quite rationally rounded, though present-day solar thermal only runs about 15% efficient for large tough systems the large tracking stirling engine systems run above 25%.

So the entire US could collect its entire power needs from 1000 plots of land 10 km x 10 km. California 100 sites 10 km x 10 km, or a strip of land 20 km wide and 500 km long, more in the range of the area California has paved and built buildings on. If the US started now at the pace with which it built Interstate Highways from 1960 to 1990, it would be done in three years.

Today there are far more people without electricity than a hundred years ago, or fifty years ago. Today there are far more people than ever before who don't have access to a sanitary toilet. Are these billions of people stupid or do they (their children, the aged, the infirm) prefer using a slit trench in sweltering heat and freezing cold?

They don't have electric service because there has never been nearly enough money to build the least costly generating plants.

Out of 7 billion people perhaps 1.5 of us have good electric service. Yet only an infinitesimal portion of it is solar - is very costly and has an inherently very poor capacity factor. But take notice you other 5.5 billion, can't say we haven't furnished you with a green solution.

If wishes were horses beggars would ride. (Mother Goose)

Great concept Len, but a few minor items to consider. These stations would need to be in Sunny climates. The owners of the countries in the sunny climates would need to agree to sell their solar electricity to us poor souls in the North where it snows a lot and tends to bury our solar panels in reflective white stuff. Mother nature also inflicts on us some other unfortunate weather such as ice storms and minus 40 temperatures none of which seem conducive to making our own solar electricity. Mother nature also cause the Sun to be on the other side of the earth 50% of the time - it is called night time and therefore the amount of solar area needs to be doubled to account for the required storage.

A better idea would be to put a gigantic satellite with huge solar panels and beam the energy down via microwave.

Geothermal energy works too and does not take up anywhere near as much land area. All we need to do is drill a few thousand 10 mile deep holes in the earth and voila - all the energy your heart desires. The minor issues of setting off earthquakes (as was recently reported from Switzerland where an immediate moratorium on such practices was ordered) should not deter the intrepid energy hunter.

Everything sounds so simple on the internet.


Don, I agree, if it were so simple you wonder why those dumb 5.5 billion people dont just put up a few thousand panels in the Sahara (very sunny there) and make their life much easier. They can't even afford a simple pump to move water around let alone solar PV panels.

Doing the math is one thing -doing the work is something very different.

Slight other problem overlooked is that to avoid circuit losses PV cell contacts are coated with highly conductive materials (usually gold and/or silver). That number of solar panels will likely consume the entire worldwide supply of those metals. But not a problem in the theoretical world where all materials are infinitely available.


Malcolm: "A better idea would be to put a gigantic satellite with huge solar panels and beam the energy down via microwave. " -- I think you'll find the cost of that, and thus the liklihood, to be exhorbitantly higher than any other option, unless some genius figures out how to construct a fiber strong enough to manufacture a space elevator.

And your method of argument, eg. the straw-man illogic of declaring "solar can't work for the US because it can't work for Nunavut in the artic" is becoming very tiresome indeed.

Alternate energy really need not work well for the 1.5 billion of us who have affordable, reliable electric service from existing generating facilities. You, the 5.5 billion who don't, already suffering, are the problem. We 1.5 billion are in good faith, but regrettably rather fatuously, trying to reduce our CO2 emissions while the 5.5 billion are building new coal burners as fast as they can. Didn't I see just yesterday that the UN wants to give developing nations umpteen billion dollars to build, you guessed it, coal burning generating plants. Those trying to reduce CO2 emissions are absolutely swamped by those bent on increasing emissions. But what do we hear from the media? A new solar plant in Spain, a new wind farm in China, a new nuclear plant in India. Nobody in the media does any arithmetic.


You criticize me but do not offer arguments to refute me. Answer these questions please since the response is critical to the debate.

1. You calculation here shows how much land area is required to supply the current electrical demand with solar energy and you conclude that there is sufficient land area to do this.
Question. What does the calculation look like when you include the current 5.5 billion that you excluded from your calculation.

2. As tiresome as it may seem to you it IS a fact that there is no Sun approximately 50% of the time.
Question: In order to supply the electricity required at night when the solar panels are NOT producing electricity what storage system do you propose to overcome that problem. What is the cost? How would you envisage the deployment and maintenance of such storage?

3. In order to meet demand solar panels must have sufficient installed capacity to do 2 things. One is to supply the actual demands placed upon it. Two i it must have sufficient additional capacity to provide electricity to the system you have determined to store it.
Question: Was the additional capacity required to charge the storage system during the day added to your calculations or is this the amount of land area required just to meet to demand during the day. Is that factored into the land area calculations.

You never answer my questions about this hence the reason for my "tiresomeness" It is a fundamental question to be answered by those who propose solar PV as a solution to meeting the worlds growing demand for electricity production. You have not answered it so I will keep on posing the question. How Len?

Bottom line Len a the worthy attempt at a realistic calculation but it severely underestimates the amount of land area required for solar PV production.

Other factors also not discussed (or avoided) are decrease in PV performance due to weather conditions and cleanliness of the PV collector. As noted this would present major problems in Canada and most of the Northern USA as well as other countries not due only to snow and other factors such as ice sheet formation on flat panels (a tiresome reality in Northern Climates). I do cordially invite you to come and see a winter in Canada when some days one cannot see across the road due to blizzards. I suspect PV output on those days will be about zero.

So all I ask you to do Len is provide the answers to some obvious (if tiresome questions). I will keep on asking until I get an answer that makes even 10% sense.

The solar satellite idea - which has received considerable support by some learned researchers, makes as much sense as covering major land areas of the planet in PV panels.



I could not agree with you more. I thinkl I said somewhere else that China was building a 1000MW coal fire power plant once every two weeks (being tiresome again I guess). But it is important to restate that in the context of your post because it underscores that any attempt by the west to reduce CO2 emissions will be overshadowed by events in Nations such s India and China and the only way I can see to prevent it is to deny those populations our standard of living - which is electricity and fossil fuel dependent.

Those countries may find that quite unacceptable.

I don't think the lack of arithmetic is confined to the media Don. Some of the posts here dismiss such obviously important items as population growth - an example of which is noted above which even discounts as non-existent five and a half billion souls.

I have been doing some thinking and research on your position regarding population as being the major problem and I am beginning to see your point. In fact I looked back into my old notes on neutron doubling time in nuclear reactors which has exactly the same mathematics as population doubling time. At a population of 6 billion I am realizing that we are in fact at the point of no return mathematically. With currently available technology we cannot do it. Within 36 years that population will be 12 billion. Within 72 years 24 billion. It is not winnable is it?

So even if we built enough power plants to supply the existing population on earth with a basic electricity supply even at a modest net growth of 2% we would need to do it all over again in 36 years. (Rule of 72, 72/2=36)

I think that is all but impossible Don....even for nuclear. I don't even think we have enough raw materials to build that number of nuclear plants - or solar panels - or anything else on the scale required for that matter.

Don - I concede you are right. Population is not a problem. It is THE problem. Nothing else matters.

And congratulations - you are the first person here who has caused me to change my views.



1. If you'd followed the link I provided above, you'd see that it refers to "Total Surface Area Required to Fuel the World With Solar" I simply presumed that the US consumes 1/5th of world total energy and divided their figures by 5. For world, multiply mine by 5.

2. what storage system do you propose to overcome that problem. What is the cost? -- As I've stated often before, thermal storage connected to solar-thermal generation. 3x collector area vs. generation capacity gets you 83% reliability, which is plenty to carry a grid through the nights eg. off-peak hours.

3. You have, throughout these discussions, CONSTANTLY re-interpreted my statements as if I am talking about solar PV generation. PLEASE understand i AM NOT, I propose SOLAR THERMAL (tower or trough, whichever develops most economically) baseload with PERHAPS SOME concentrating PV peaking, installed in ideal locations, and with HVDC transmission to load areas.

I'm also PRIMARILY promoting that for the large preponderance of the worlds population living near enough to dry areas near the equator to most effectively use it, eg. between 50 degrees N and S latitude, within the reasonable reach of HVDC transmission to areas like the Sahara and Arizona etc. Resolve those and the few remaining of us can make do with Nuclear, Hydro, Wind etc.

Solar satellites are DIW (dead in water) until you can come up with a system of superconductors cheap enough and reliable enough to withstand space conditions because you cannot concentrate sufficient electricity in one place in space to make the microwave transmission viable without it. (Low voltage DC solar cellls, conversion to A/C and step-up-down transformers are too heavy and inefficient. That's NASA's conclusion also. Far more rational to take the hit for 25% exposure time and 30% attenuation, and keep the equipment on the ground where it can be reasonablly maintained.

And fer gosh sakes get off associating my comments on solar with PV!!!! (at least until the Optical Rectenna arrives, which will change the whole game.) I talk Solar Thermal at this time

Assessment of Parabolic Trough and Power Tower Solar Technology - Cost and Performance Forecasts - Sargent & Lundy LLC Engineering Group Chicago, Illinois

[QUOTE]For the more technically aggressive low-cost case, S&L found the National Laboratories’ “SunLab” methodology and analysis to be credible. The projections by SunLab, developed in conjunction with industry, are considered by S&L to represent a “best-case analysis” in which the technology is optimized and a high deployment rate is achieved. The two sets of estimates, by SunLab and S&L, provide a band within which the costs can be expected to fall. The figure and table below highlight these results, with initial electricity costs in the range of 10 to 12.6 ¢/kWh and eventually achieving costs in the range of 3.5 to 6.2 ¢/kWh. The specific values will depend on total capacity of various technologies deployed and the extent of R&D program success. In the technically aggressive cases for troughs / towers, the S&L analysis found that cost reductions were due to volume production (26%/28%), plant scale-up (20%/48%), and technological advance (54%/24%).[/QUOTE]

Given Sargent & Lundy Engineering's worst case scenario provides peak time solar electricity at $0.062/kwh by only building 2.8 GW and doing a few minor and definitely achievable R&D improvements, plus transmission, and a clear path is provided to offering 83% capacity factor using cheap sand and gravel tanks for thermal storage with 3x collector area and no additional central plant, which should make the installation no more expensive PER KWH if only the industry can get to 2.8 GW installed, I don;t see what we are waiting for.

It also appears to me that the more agressive forecasts of NREL / SunLab of $0.035 / kwh if we can get to 8.2 GW insalled quite quickly is entirely within reach.

Just about all the comments I see here, and other places, dwell on the wonderful things being done and will be done to save the planet. It's great that people have ideas but few seem to realize it's all about numbers and the annoying requirement of starting from the present situation - is almost universally ignored.

Would anyone here suggest that the answer to world health is really quite simple - merely have excellent hospitals and kitchens dispensing ideal meals available in every neighborhood. Is this any harder than affordable electricity for everyone from non-polluting sources?

Unless it could be rated as poetry or as kabuki the Kyoto Protocol was a fraud. The world was told in 1997 that we were at the tipping point as to atmospheric CO2. It would be too late to have any delay in reducing CO2. emissions. (I don't know, maybe so.)

But what has happened since 1997? The base point for the Protocol was 1990. In 1990 3489 million metric tons of coal were burned. A good estimate of current usage is about 6200, or 178% of the rate from which there could be no recovery. And it is getting worse. The rate of coal usage is increasing more than ever before.

The Kyoto Protocol was under the auspices of the UN. Only a few days ago I saw the UN was touting a program to furnish many billions of dollars to build coal generating plants. Alas, you only build a generating plant on the premise that it will operate for 40, 50 years or more.

Don: For an alternate take on world population, try reading The Next Hundred Years by George Friedman, founder of STRATFOR and from my reading a vert smart analyst. His position is that world population is not the problem many make it out to be.

To claim that something more than the Kyoto Protocol should have been implemented is ridiculous, since the largest economy and energy consumer in the world wouldn't even sign on to attempt that piddling little starting step.

The 500 MWe solar-hydrogen power plant will only take around 1200 acres. This and more has been acquired already.

You need to upgrade yourself in all the different aspects of energy conversion.
We will NOT burn the hydrogen in a turbine. The efficiency is poor. The hydrogen is generated directly by the DC solar cells (no AC conversion necessary). This is generated and stored at 10,000 psi (no compression needed) in carbon fiber tanks. During nighttime, the hdyrogen is the converted to DC electricity in an innovative 3 MWe units (x 40 units) utilizing high efficiency NON-platinum electrodes at elevated pressures. We expect the 78% efficiency turnaround. There will be about a 3% loss in going from DC to AC. The design of this system is on-going and we expect to be operating in 2012.

Holy smokes Warren....I don't think I want to be around a 10,000 psi hydrogen storage tank. Tell me where this plant is so I will remember to go nowhere near it. And people think Nuclear Plants are dangerous. Has any one actually stored hydrogen commercially at those pressures.

How does one get hydrogen pressures of 10,000 psi with no compression and without using energy. Seems kinda suspect to me. But I'll believe you - for now.


Sorry Len - I did make the assumption that you were talking about photovoltaic solar energy. I agree that solar thermal has much to offer - especially developing nations since it is easily deployed and generally low tech.

But nevertheless the issues I mention still remain since in many parts of the world - especially the Northern Hemisphere weather and solar conditions are not very conducive to these systems. They would work in the short months of summer but will not produce much in winter. Some years ago my brother in the UK installed a solar water heating never paid for itself and had to be scrapped in less than 12 years of operation. In Japan there are many many of these systems. If you go to Tokyo you will see them on just about every house. I presume that even with this level of deployment they do not contribute all that much to Japans energy picture - which is likely why they also have one of the worlds largest nuclear programs.

I am not sure where you live Len but in Canada for almost all of us here solar thermal is not viable since we would need to install a solar thermal system as well as some sort of back up - likely natural gas - when it is not available.

Maybe good for California. No good for Canada waaay to cold and snowy.


I went to the link to book sales at that Len provided and read the reviews. Looks like some far fetched crystal ball gazing to me. I suppose to do it justice I'd have to buy it and read the thing but I doubt it is worth my time. Not too many people have been able to predict the future with any accuracy and I don't think Mr Friedman is going to be any better at it than his numerous and almost always wrong predecessors.

Population growth is a matter of simple mathematics and with advances in medicine moving at supersonic speed the death rate is going to be lower even to the point where people don't actually die of any disease any more. Imagine world population growth with a zero death rate. Ironically almost everything we do to preserve life makes the population problem worse.


Malcolm: a) 10,000 psi hydrogen storage tanks have been in development for quite a while. I wouldn't be at all aurprised if they're now available and no more dangerous than the 5,000 psi ones. b) 10,000 psi with no compression is easily done. Proton Energy has been offering it at 5,000 psi for a long time. All they do is pressurise the electrolyser to eg. 10,000 psi with a water pump pumping the input water prior to H2 and O2 separation, very little pumping energy required.