EPRI on Renewable Energy: Compressed Air Energy Storage

There is a new energy storage that is just now becoming public knowlwdge with the ability to store hours worth of energy storage but they take the electricy from wind solar off peak electrical nad store it in the form of heat with near 100% efficiency. I have seen their test sites and business plans for load leveling thre technology works but is also very economical at this time. check them out at elcalresearch.com

What does “KW” of storage mean? You store kWh of energy; KW describes nothing more than the capacity of the generator, the question is for how long can a generator of a given size be driven? And what does it cost to install that capacity X time, i.e kWh?

You’re talking about mega-joules when talking about energy.  Which highlights the issue of watts vs watt-hours.  The metric used to compare alternative energy sources to traditional energy sources is cost per kilowatt over the life of the installation: $.04 per kilowatt for natural gas fired plants; $.07 per kilowatt for windpower; $.20 per kilowatt for solar.  But storage is usually expressed as cost per watt or kilowatt without the lifetime maintenance costs included.  To be accurate, the storage energy should reflect the cost of components which wear out during the course of 20 or 30 years of operation, such as battery replacement. I’ve seen figures from $1.35 to $5.00 per watt for batteries, but if they have to be replaced every 6 to 8 years then the real cost over the life of the installation is about four times that figure.

Well Alan obviously doesn’t believe we need to cut our carbon so we can rule out his opinion.

EPRI should have been clearer in their statements since they know (or used to know) that Thermal storage (cool storage at the building, not Grid side which EPRI seem to be focused on in their statements) has dramatically better storage efficiencies than CASE or pumped hydro, costs much less, and stores what most of the electrons are needed for on a peak day, namely cooling something.  All sorts of Energy storage are going to be needed but ignoring the proven basic type is a mistake.  An back to Alan’s comments, the Grid needs to be dramatically over-sized in order to react to the the demand fluctuations precisely because it has basically no short or longer term storage.  True that it is a different and initailly more expensive way but the system streamlining should make up for that.

I agree with Lee.  Many energy articles leave a lot to be desired in terms of how they are written.  Are they talking Watts, Watt / sec or Watt -sec?  Then are they talking instantaneous or continuous?  In terms of costs, are costs just for a machine, are the costs all in, capital or OM&A or both? and lifecycle?  Often times the way to sell something is not to give you all of the information, but just enough to get you interested, and often by the time you have explored all the facts in detail, you find you may have wasted a lot of precious time and you’re not much wiser in the end. In this case, air on a warm summer night is pumped into a cavern where the ground is at about 5 deg c or maybe a bit higher due to the temperature of the compressed air.  Energy is not only lost through the compressor stages but to the earth itself.  To recoup the energy of the compressed air, how much energy is coming from the compressed air and how much is coming from the natural gas?  And what is the efficiency of the turbine and the pump?  And how exaclty are they proposing to convert the entire process from diabatic to adiabatic?  What is the storage medium? and system equipment?  Are all those moving parts really worth it compared to alternatives?  Eric

The centralized storage discussed here by EPRI does not help with grid size, but rather with storing centralized wind and solar power output making it dispatchable and reducing the need for inefficient reserve capacity. Distributed storage,like smart metering, would lead to less flucuation in demand. Both storage systems have their role, one on the supply side and the other on demand side.

The units of power define capital outlays for a particular system.  They are one aspect necessary to calculate the cost of energy from a particular system.  For example, windpower may cost about 2,000$ per KW to install, but produce varying amounts of energy depending on the resource (wind speed). Both the installed cost and energy production as well as O&M costs, longevity of the system as well as type of finaincing will allow for calculation of energy cost per kWhr.  With fossil fuel power plants besides the construction cost in $/kW one would add fuel costs to calculate the cost of enerergy produced.  Storage systems are built to some maximum capacity, and this price in $/kW together with accounting for energy conversion efficiencies and fequency of use would have to be factored into the cost of energy available from such a system.  Still such cost could be better than maintaining fossil powered reserves that backup intermittent centralized renewable energy systems.

There is a company that is working on closed loop pumped storage and have filed preliminary permits on 10 sites in the western US. Such projects who stabilize the hue influx of wind coming soon or now on the grid. Only thru storage can the renewables be maximized; at 85% efficiency closed loop pumped storage is the answer to peak demand, grid congestion and off peak storage of renewable energy at a low installed cost, long life and efficient use of resources.

Closed loop pumped storage, the best solution, low water use, low environmental effects, 85% efficient, and long life. Google Symbiotics LLC

Burning the natural gas is a high carbon footprint.  A better alternative than burning natural gas with heated compressed air (yielding an estimate of less than 50% efficiency - wasting fuel and producing carbon by-products), is to drive the combustion for a more perfect reaction producing 12% CO2, with virtually 0% CO, etc.  It is out there folks.

Hey Eric, how about GTM to produce a really authoritative piece on the KW vs. kWh mix up.  It looks like your consumer base could use further clarification.

Here’s I site which I have found very useful for understanding the basics of almost everything “renewable energy”.  It’s very well written, easy to understand, and well organized.  Kind of an on-line reference book.

I linked to the hydro up-rate page, but you can use the Index in the upper right to find your way around the site.

http://neuralenergy.blogspot.com/2009/06/hydroelectric-uprating.html

Let’s go back to CAES for a moment.  Remember, the goal is to cut our CO2 emissions ASAP and as affordable as possible.

If we had a choice of only coal or natural gas we would choose NG as it releases about half as much CO2 as does coal per unit energy produced.

But if we add non-CO2 releasing wind and solar energy to the mix and use some of it to compress air then we can afford to use some NG to further heat the compressed air and end up with a small fraction of the amount of CO2 we would have released by burning coal.

“CAES systems use gas turbines almost identical to normal natural gas peaking turbines.  However, they only use about 1/3 the natural gas, because 2/3 of the natural gas energy in a regular turbine is used to compress air before it enters the turbines, and this compressed air would now be supplied by the stored air.  Natural gas would still be needed to heat the air before it enters the turbines.”

CAES isn’t a perfect CO2 solution, but it’s a big help.  And it can be installed in almost all parts of the US.  The exception is the Southeast.  Other parts have limestone caverns, salt domes, and aquifers which serve the purpose well.

Half the CO2 as coal.  One third the CO2 as pure gas turbines.  Now we’re down to 1/6th as much CO2 released by stored wind/solar as from burning coal.

Great article on utility scale energy storage and contains a good map on what sorts of storage are available in different parts of the US.

Craig calculates that baseload electricity created by a wind/CAES system would cost between $0.105 and $0.13 per kWh.  Expect the price of wind to decrease.
http://energyeconomyonline.com/Utility_Scale_Storage.html

A critical value from renewables is largely driven from what it does for our domestic infrastructure as it relates to national security, trade imbalances, and moving toward a supply chain not so heavily shadowed by the existing landscape of the Big Oil oligarchy .  Environmental pollution is the critical factor in many arenas, but economics will still rule the day.  Speaking of which, Eric/Bob who owns the subterranean real estate where CAES lives?

Glenn - interesting question.  Sometimes the person who owns the surface of the land does not own what lies under it.  When buying land I’ve always been careful to insure that the deed includes timber and mineral rights.  If you don’t own the mineral rights you could find someone undermining your land.  I would suppose the same issue would hold for using an underground cavern. 

Or perhaps not.  One can sink a water well or oil well and extract what does presently lies under your neighbor’s land.  As you extract the oil/water/gas under your land more flows in from under your neighbor’s land.  (“I drink your milkshake.”)

I’d guess the lawyers will make some money sorting out this new issue….

As for economics driving the solutions, I think you’re right.  But until we put an accurate price to fossil fuels the transition will be slower.  If we were to charge fossil fuels for security/military costs, health costs, and environmental damage we would be installing renewables much faster than we are today.  Just think what you would pay at the pump if the cost included paying for our military presence in the Middle East.  And what you’d pay for coal-produced electricity if the price included health and environmental costs.

There’s one above ground CAES in the Southeast that has been in operation for almost 20 years.  I don’t know if it makes economic sense to choose that route as opposed to pump-up hydro.  (TVA’s Racoon Mountain pump-up facility has been operating for a number of years..)

“McIntosh Power Plant

McIntosh Power PlantPowerSouth’s generating units at McIntosh, Ala., include the compressed air energy storage (CAES) unit and twin gas-fired combustion turbines, for a combined winter capacity of 348 megawatts and a summer capacity of 338 megawatts.

Designated McIntosh unit 1, the CAES unit was declared commercial May 31, 1991, and officially dedicated Sept. 27, 1991. It is the only plant of its kind in the United States; the only other CAES plant in the world is in Germany.

The CAES unit uses air, compressed and stored in a 19-million-cubic-foot underground cavern, in the generation process. During peak load periods, the stored air is released and mixed with natural gas in a combustion process to generate electricity. The plant uses off-peak electricity to pump air into the cavern and then uses the air in the generation process during peak periods.

In June 1998, two single-cycle combustion turbines were constructed at the McIntosh site and designated McIntosh units 2 and 3.”

http://www.powersouth.com/about_power.aspx

Ir you check the CAES map on http://energyeconomyonline.com/Utility_Scale_Storage.html you’ll see that only southern Georgia, southern Alabama, and Florida are lacking CAES underground potential.  They also don’t have a lot of elevation change for pump-up potential.  (Although going down for pump-up is a possibility.  Florida, for example has limestone caverns, IIRC.)

It might be that the extreme SE might have to look for another storage solution or run HVDC lines to some place such as Louisiana.  Some people are saying that utility scale batteries are not far off so that might be their best option.

Overall, I don’t think there is any ‘one size fits all’ solution, just as there now isn’t.  The Midwest and coastal areas have lots of wind.  The SW desert has lots of sun.  The Pacific NW hand upper Atlantic NE have lots of hydro.  And I expect we’ll run a lot of HVDC (possibly superconducting underground lines) to tie everything together to make for a smoother supply to the grid.  Get enough ability to move large amounts of power with little transmission loss and the game completely changes.

Denmark has maxed out at 20% wind power in their mix without the need to import fossil (coal) based power from Germany.  What is Denmark doing for storaga to make wind more dispatchable?

With the rising importance of demand response (DR) and peak load reduction, adoption of Thermal energy storage technologies is expected to accelerate in the next few years according to EPRI:  http://portfolio.epri.com/ProgramTab.aspx?sId=PDU&rId=146&pId=4842&pjId=4850

Denmark has not “maxed out” at 20% wind power.  They’re currently getting more than 20% of their power from wind, getting close to 25%.  Denmark has not built adequate storage to supply shift wind and rely on Norwegian hydro and pump-up storage to help power their grid.  They also purchase some power from other countries as needed.

We’re in the early part of the transition away from fossil fuels.  Europe is making bold moves to rid itself of burning sequestered carbon.  The already initiated European SuperGrid will create one big grid that stretches from hydro and geothermal rich Iceland, to windy and high tidal areas of northwest Europe, to areas of northern Europe with good hydro and excellent pump-up locations, to the sunny parts of southern Europe and even very sunny North Africa.

Denmark will contribute a lot of wind power to Europe’s SuperGrid.  Look for Denmark to sell Germany wind power so that Germany can quit burning coal down the road.

Would that we here in the US get that smart….

I applaud Denmark for showing that an electrical grid can handle high share of wind power and that temporary oversupply from heavy winds can drive a lucrative electricity export business. I am a bit skeptical of these high-profile transmission infrastructure projects. They tend to give the impression that renewable electricity can only be made sufficiently cheap and plentiful by building large, centralized plants and transporting their output over large distances. That is not necessarily accurate and (worse) seems to distract countries from using the resources in their own back yard. There may be stronger winds 1 or 2 states away but that doesn’t mean delivered power will be cheaper after factoring in the cost of building the necessary transmission lines and the attendant transmission losses (these are 7% in Germany, potentially higher in the USA due to older infrastructure). We will need those transmission lines eventually *anyway* but in the meantime, it might make more sense both economically and from an energy security perspective, to build wind farms (and solar, and biogass/biomass, etc. etc.) closer to the load centers even when those have ostensibly lower renewable energy potential. That makes them not only faster to deploy but also cheaper (per kWh delivered power) than might seem likely at first glance. And the best part: deploying those systems now drives up manufacturing volume, thereby driving the cost/price of future windmills (and solar panels, etc. etc.) down, thus strengthening the economics of those transmission lines once they come online.

BTW, Germany is already displacing coal- and gas-fired power generation with it’s own solar- and wind-power. It could replace even more if it hadn’t done a deal with domestic brown-coal producers to accept their entire production but at least imports of black-coal and natural gas are kept in check. This isn’t stopping Germany from planning new coal-fired plants (there are at least 12 now in the planning stage, I think) but the penetration of renewables in Germany keeps accelerating. That makes coal-fired plants increasingly risky (because they can no longer assume they will be able to deliver 100% of their output and stay within their optimal utilisation rate), so their cost of capital is increasing…which further tips the scales in favor of renewables even without carbon taxes or caps. That wouldn’t be happening if Germany had waited for big transmission lines to import wind power from Denmark.

I would urge the USA to pursue CAES and other energy storage methods, certainly. But I would not wait for them. Rather I would urge the US (as a country and as individual states) to diversify into various renewables using local resources. This lowers (but does not eliminate) the immediate need for energy storage and can slow down or halt plans for new coal-fired generation. Once those plants are built, we’re stuck with them for decades.

Bob,

CAES is only about 50% efficient on a t btu in/btu out basis.  Life-cycle cost has to include cost of natural gas,  VRB flow battery can be sited almost anywhere.  Also can be sited near the load, saving on line losses.  Efficiency is about 70% and no carbon footprint.  Hours of storage can be sized separately from capacity, so you can size 2 hours per MW, 4 hours, etc., Initial system lasts 10 years or more with minimal O&M and can be extended another 10+ years by replacing the PEM.  Why use clean and renewable wind energy to power a fossil fueled turbine when other alternatives are available?  http://www.Utility-Savings.com

I agree with Brian in terms of Distributed Generation vs central plants. What about small scale local storage coupled with new micro and community wind turbines or solar panels? Is anyone aware of advances in localized small scale (flywheels, batteries, etc) storage that could then optimize dispatch of local resources assuming its tied into a smart grid.

DR needs DR tariffs, and if you can dynamically call up local peak resources and dispatch them and get compensated on the basis of a well thought through DR tariff which is a win win for all. That is the better map to follow then centralized plants and high costs of transmission as has been pointed out. How many rooftops, open fields, large parking lots does this country have. The challenge is micro sizing efficiency and then having an intelligent dispatch and payment system to allow 3rd parties to build new business models around it.

Hi, new to this site, I was wondering after reading all the comments: What if there were a totally new approach to electrical energy storage? I’m wondering if the people here are truly open to radical that works very efficiently? Serious replies are welcome.

Thanks!