What Is the Cheapest Energy Storage Idea of Them All?

Long time reader, first time commenter.  I really love the coverage you guys provide, and I personally have high hopes for CAES.  But as an engineer working in renewable energy, I humbly ask that you PLEASE keep a closer eye on your units, specifically: kilowatts = power; kWh = energy.  Your assertion that, via cheap solution mining, “the cost of adding another kilowatt comes to around $1 to $2” is misleading and/or false.  Perhaps I’m being overly critical, but it seems that such mistakes would tend to undermine your credibility as an info source in energy world.

Like the previous commenter, I agree that GreenTechMedia is usually better than this -sloppy confusion of units, no new information, and other problems in this piece.  Let me try to help.  As of now the only truly competitive energy storage is pumped hydrostorage in mountainous terrain.  Reality may be setting in on the proposed CAES Iowa Stored Energy Park (ISEP).  It was originally proposed to be completed in 2003.  Drilling of test wells finally started in 2008.  Their current target for completion is 2013.  The facility – as it is currently proposed – will only be able to accommodate the additional load of 280 MW peak, and there’s no real info available yet on how much energy it might store, or what it will really cost, or what the projected peak and mean efficiencies might be…  A recent estimate is $220/kWhr of storage capacity.  Best case storage-cycle efficiency for stand-alone CAES is probably about 54%.  CAES is now usually advocated as being able to help peak efficiency of gas power plants – but do we really need more gas-fueled power plants?  (Read Matt Simmons latest discussion on peak gas.) 

Energy storage by CAES or batteries probably ranges from $100 to $1500/kWhr. 

Fortunately, there’s a much better option: store the energy in stable liquid fuels like ethanol and jet fuel synthesized from CO2 and off-peak wind energy.  The tank-component cost of storing energy in stable liquid fuels is only $0.02/kWhr.  There is no better option for storing and distributing large amounts of energy.  The world currently requires 6 PWhr of energy storage (60 days worth) in liquid fuels for our transportation infrastructure to operate smoothly.  That’s about one trillion times the energy storage in a Prius battery, or several million times the amount of energy that might be stored in the ISEP CAES project – a single, 15-year project.

Enormous progress is being made in efficiently synthesizing WindFuels (hydrocarbons and alcohols) from CO2, H2O, and off-peak wind energy.  With off-peak wind energy at $15/MWhr, these synthesized fuels could compete when oil is as low as $50/bbl.

Of course, WindFuels still won’t be the best answer for peak grid supply.  For that, the best option will be a novel thermodynamic cycle (called the DORC) that allows a geothermal-CSP hybrid to achieve much higher efficiency during daytime hours than current CSP.  A paper (ES2009-90220) will be presented on this new engine at the ASME Sustainability conference in San Francisco in July.  The abstract is available at the conference website.

Back to energy storage, there are currently several Gt of dead pines (killed by the pine beetle) covering about 500,000 km2 in North America.  These dead trees will be largely consumed by forest fires over the next 6 to 8 years.  The energy stored in these dead trees is about 3 times more than in the petroleum North America uses in one year.  Harvesting all these dead trees and co-firing them in power plants would result in about 100 times more net GHG and net energy savings than from biofuels (globally) this year. If we really are concerned about climate and energy, we should be insisting that tens of billions of dollars be immediately made available to cut our use of coal in half by burning these trees – as long as this extraordinary (but steadily oxidizing) resource is available. - David Doty