During the late 1980s and early 1990s, EPRI commissioned a series of studies to assess the economic feasibility of storage technologies. Colleagues of mine at the time were on the project team. Their findings suggested that because it is so capital intensive, storage would only make sense when on-peak prices were consistently about twice as high as off-peak electricity prices. I suspect they would reach the same conclusions today.

I would be very interested in seeing an article that sets out the economic analysis in support of the ISEP, Norton and TVA projects.

I have been involved in analysing CAES economics since 1983. In the 80's and early 90's the popular source for benchmark economics was the EPRI TAG book. This book listed the cost of a 110 MW CAES plant at around $800/kw.

In the mid 90's, Destec Energy worked with a major OEM and developed a CAES configuration in the 350mw range which had an EPC cost of less than $300/kw.

As a principal in ES&GS Ltd. since 1997, myself and my collegues (former Destec Energy executives) have developed multiple CAES unit configurations with various OEM's for much less than the cost of today's CCGT's.

Getting a CAES plant built today is not a problem of economics, but more of a problem of financing due to the lack of a committment for the offtake. In Texas for example, many power companies are concerned about over capacity, but Texas is an ideal market for a CAES facility. There is i) a very volatile real time market for compression power, ii) additional revenue opportunities in the open ancillary services market (including black start), and iii) any additional capacity is offset by a 75% increase in demand (compression).

The work that Jason Makansi and Richard Baxter at ESC has done in the area of energy storage has proven to be invaluable. The value propositions energy storage brings to today's markets (i.e. full requirements, system optimization, wind dispatchability, transmission benefits, etc.) are unique and energy storage will be leading the next generation of energy supply.

Not to detract from the comments Paul Ahenrs made--power plant costs are very site specific and must address such issues as Fuel --Water and Emissions. CAES must therefore be evaluted against the best CC plant with low fuel consumption and low emisions with post combustion SCR to achieve 4.5 vppm Nox. The bottom line is CAES uses less premium fuel, has much lower emissions per MW/hr generated and provides fast start up and ramp capabilities and therefore dispatches economically before the CC plant and can deliver full rated capacity from 8 to 16 hours a day--that is up to 4000 hours a year and deliver lower Cost Of Electrcity(COE) .CAES plants have another important feature--the compressors , motor driven are decoupled and act as load absorbtion devices when there are load swings or excess capcacity and further more allow Clean coal and efficient plants to operate at optimal ratings on a continuos basis--this is a win win situation.

CAES plants can be built at the same or lower cost than a CC plant . When comparisons are made all costs must be included--fuel -cost of power--debt-O&M etc.With fuel prices at $3.80 MBTu and higher off-peak or excesspower @ $13 MW/hr or lower will show the CAES plant delivering lower COE That is only one part of the answer--there are the Ancillary services as well--Spinning Reserve --Voltage regulation --Frequency control --Load management etc.

The delta between off-peak and on-peak does not matter much--if you can affird to build and run a CC plant you can certainly do better with CAES and have more added value in the electricty supply chain. CC power plants today range from $450 to $600kw/ installed--and many were idle with the surge in NG prices.CAES plants would have operated and helping other fossil ot Nuclear plants providing lower cost baseload.

CAES Power Generation and Management facilities have an achilles heel--they cannot be located randomly--storage facilites -such as salt domes -strata -depleted gas wells aquifers are required--even hard rock caverns--fortunately 75% of the US Geology can sustain such facilites.The staregic approach is to match current known suitable storage with key load or Transmision lines to strengtern and bolster the grid.This is of great economic value--reducing wear and tear on cycling plants absorbing Wind Energy that flows only when the wind blows--creating another value to fossil plants that need to meet the short fall or abundace thereof, mainly at the wrong time.

Capital cost is important and so is fuel effciecny coupled with emissions--the BOTTOM LINE is COE delivered as well as sustaining a reliaible and sturdy grid. ------Brulin Associates LLC-----

I spent a good deal of time studying this project. I estimated that the overall efficiency of the 2700MW installation would be about 27% (HHV). The maximum air pressure was to have been about 2000 psi, minimum about 800 psi. To maintain such pressures every day of the week an enormous amount of heat would have been rejected from the air compressors, even with three stages of compression and intercooling. The generation phase would not have been as efficient as might be expected either, judging from the information available to the public.

CAES might be effective in some cases, but I can find no justification for the Norton Energy Storage project. It would waste too much energy. If air is to be compressed for storage, it probably should be done at the power plant that is supplying the off-peak power for compression. There would be no power line losses to the compressors. The power plant would most likely be coal-fired, so it coulf use some of the waste heat generated by the air compressors. As Septimus van der Linden notes, there is roughly a 75% chance that such a power plant would be located over a geological formation (aquifer) that could be used for storage of the compressed air without significant underground work. (But Septimus, I am dubious about your statement that CAES uses lower quality fuel and has lower emissions. CAES would probably use coal-fired power for the compression phase. This is low quality fuel but high emissions for that part of the cycle. The generation phase would use high quality fuel - natural gas - but have low emissions. Overall emissions is the question here.)

I proposed to Norton Energy Storage that they use the Norton mine for a hydraulic air compressor. This is an isothermal compressor, the most efficient possible. The compressed air would be used as soon as it is produced, to supply recuperated gas turbines. This is a well-studied technique. It is as efficient as a CCGT but much simpler, and far more efficient than CAES. Even though it is not an energy storage method, the gas turbine/hydraulic compressor can provide superior energy savings. Perhaps it could also provide the load management services mentioned above, if some air storage capacity were included in the plant.

Many capital power projects have "faded' or have been cancelled since 9/11 and the Enron debacle. Norton got caught in that web as well. Norton is just one site, a very advantageous one at that--there are other suitable sites in many locations.

2000psi is not an optimum pressure for that site --that will be a waste of energy. 1250/1500psi is optimal when the daily operating regime and available night time pumping hours are considered. This would be applicable to other sites as well--and depending on the storage volume available could be at lower storage pressures. Yes heat would be rejected (that is for 6/8 hours per night)--most thermal plants reject heat--cooling water or directly into the atmoshere.

Efficiency is not the real issue--only the COE --CAES will dispatch economically before other NG fired plants and fill the role of Mid merit generation --8/16 hours a day.

CAES uses both preimium fuel NG and fossil or Nuclear off-peak night time power--such plants need to operate in any case--so absorb the energy vs turndown. As I had noted before, operating a coal fired plant at optimal rating is a win situation.

Emissions are credited to the power generation site and that is what is measured for the MW/hrs delivered. The supplier plants for compression power emissions are accounted for at their respective sites--and in the case of Wind Energy--there is a big bonus--zero !.

Energy Storage is required regardless--even with many new concepts of generation being planned or contemplated.

Energy Storage is the the buffer--the shock absorber for load swings and resulting load management--the Associated Press today reported "Blackout study looking at power borrowing"--when such "borrowing" is suddenly terminated Energy Storage comes into play and can save the day!

Future devlopments in Thermal Energy Storage from compression could spur development for Adiabatic Compression and Expansion, requiring no premium fuel.

Lets get the current concepts into action first--grid stability is important.

As a result of obtaining access to the Offsite Consequence Analysis for the proposed Regenesys facility for the Oak Ridge, TN area, per 40CFR1400.3 in late 2002, I learned the following.

According to TVA's own Offsite Consequence Analysis, for TVA's worst case scenario, TVA estimated that approximately 690,000 pounds of bromine gas could be released to the atmosphere in about 14 minutes, if the 500,000 gallon, double-walled tank were to somehow catastrophically fail. As a result, the facility has a worst case distance to toxic endpoint of greater than 25 miles! Less severe assumptions led to alternative scenario distances of 3.5 miles and 5.5 miles. The toxic endpoint concentration is the maximum airborne concentration below which it is believed individuals could be exposed for one hour without irreversible or serious health effects that could impair the individual's ability to take productive action. TVA was nearly able to conceal these estimates from the public.

This is for a system that may store all of 120 MWh.

Unless we compare the real risks and benefits, we are not able to make rational choices.