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The Cost Of Energy Storage

The Cost Of Energy Storage

I taught my students that intermittent renewable electricity (wind and solar) was third class compared with dispatchable fossil fuels (first class) and baseload nuclear power (second class). But that renewables may be turned into a first class electricity source with the development of affordable grid-scale storage. There are two important qualifiers to this statement and those are 1) affordable and 2) grid-scale. By grid scale I mean electricity storage that could power a medium sized town for a day or longer, or every night when the sun is down.

In this short post I want to begin chronicling new storage projects as they are announced for future reference and begin with three very different approaches.

Three Reasons Oncor’s Energy Storage Proposal Is a Game Changer

The first case is Oncor Energy’s plan to install vast amounts of battery storage distributed through the Texas grid.

Early last week, Texas transmission and distribution company Oncor announced a proposal to install 5,000 megawatts of battery energy storage on the Texas grid. The words “game-changing” get thrown around a lot about energy storage projects—usually prematurely. But in this case I think there are some clear reasons why Oncor’s proposed deal could be a game-changing development for grid battery energy storage:


Oncor’s proposal calls for installing thousands of battery systems ranging from the size of a fridge to a dumpster around the state with a combined power capacity of 5,000 megawatts and a combined energy storage capacity of 15,000 megawatt-hours. These numbers sound big, but what do they mean, really?

The vital statistics:

Deliverable load: 5,000 MW
Storage capacity: 15,000 MWh
Cost: $5.2 billion
Normalised costs: $346,667 / MWh or $1,040,000 / MW

Related: More Battery Storage Would Improve Texas Grid

The article also says that the Texas grid has a capacity to deliver around 69,000 MW. Assuming average load of 70% translates to daily consumption of 1,159,200 MWh. So $5.2 billion buys 18.6 minutes of storage. Of course that storage can be used every day if the batteries can be-recharged. Reading the article it is evident that this project is more about grid stabilisation than storing electricity from renewables. Perhaps it might have been better to not destabilise the grid in the first place?

Renewable energy plan hinges on huge Utah caverns

The second is for a truly gigantic compressed air energy storage (CAES) facility in a salt dome in Utah to be built by Magnum Energy.

A proposal to export twice as much Wyoming wind power to Los Angeles, as much as the amount of electricity generated by the Hoover Dam, includes an engineering feat even more massive than that famous structure: Four chambers, each approaching the size of the Empire State Building, would be carved from an underground salt deposit to hold huge volumes of compressed air.

The caverns in central Utah would serve as a kind of massive battery on a scale never before seen, helping to overcome the fact that — even in Wyoming — wind doesn’t blow all the time.

Air would be pumped into the caverns when power demand is low and wind is high, typically at night. During times of increased demand, the compressed air would be released to drive turbines and feed power to markets in far-away Southern California.


The air would be pumped into four caverns, each 1,300-feet high and 290-feet wide and capable of holding enough air to generate 60,000 megawatt-hours of electricity through turbines at the surface.

The vital statistics:

Deliverable load: ? MW
Storage capacity: 60,000 MWh
Cost: $1.5 billion
Normalised costs: $25,000 / MWh

CAES is only a small part of this project that begins with a large wind farm in Wyoming, power lines to the CAES site in Utah and more power lines from Utah to Southern California. Total price tag of $8 billion.

The Coire Glas Pumped Storage Scheme – A Massive But Puny Beast

The third is Scottish and Southern Energy’s plan to build a huge pumped hydro storage scheme at Coire Glas that I reported on last year.

First new large scale pumped storage scheme to be developed in UK for over 30 years

Consent for the Coire Glas scheme was granted in December 2013 however, despite the obvious benefits that pumped storage offers, making a Final Investment Decision to progress the Coire Glas scheme will require overcoming a number of commercial and regulatory challenges. These include changes in the existing transmission charging regime for pumped storage and a satisfactory and supportive long-term public policy and regulatory framework. Therefore any final investment decision is unlikely before 2015 at the earliest.

The vital statistics:

Deliverable load: 600 MW
Storage capacity: 30,000 MWh
Cost: $1.26 billion / £800 million
Normalised costs: $42,000 / MWh or $2,100,000 / MW

Related: California Public Utilities Vote No On Energy Storage

In my earlier post I summarised Coire Glas thus:

The idea is to pump water into the reservoir when it is windy. The UK wind carpet recently produced 6GW peak output and so let’s assume that 3 of those 6GW were used to pump water into Coire Glas and other such schemes, and 3GW got fed directly onto the grid. If we are to have a renewables based system that can run independently of fossil fuel back up then it needs the stamina to survive a 7 day lull in the wind. So what we need to know is the amount of storage for 3GW of supply to run continuously for 7 days. This also assumes that we had 7 days producing 6GW of wind beforehand to fill the reservoirs – and we are still light years away from achieving that!

3GW * 24 hours * 7 days = 504 GWh of storage

That is 17 times greater than Coire Glas and 3 GW is only about 5% of UK peak demand. Coire Glas, therefore, is simply window dressing in efforts to “Green” UK power supply with pylons, turbines and dams.


The Utah CAES and Coire Glas pumped hydro schemes have in common vast scale and huge capacity but in the case of the latter, impotent to address the problem it is designed to address. The UK certainly does not have sites to build 17 let alone hundreds of facilities like this. I imagine the same will be true for the Utah CAES scheme. I do not know how many caverns can be safely excavated into this salt dome.

The Texas battery scheme is very different. Utah and Coire Glas are designed for “stamina” and moderate energy output with time. The Texas battery has a huge amount of muscle but zero stamina. Here’s how the costs compare:

Texas battery: $346,667 / MWh
Utah CAES: $25,000 / MWh
Coire Glas pumped hydro: $42,000 / MWh

I wonder if any will ever be built?

By Euan Mearns

Source – www.euanmearns.com  

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  • OmahaJoe on November 30 2014 said:
    There is yet one more "scheme" to store electricity created from wind and solar. Demand Side Management. For example, some of the aluminum refining could be throttled according to the availability of excess power (aluminum needs 14 MWh per ton), or ammonia (corn fertilizer) factories could variably obtain hydrogen from the electrolysis of water instead of the reforming methane (ammonia needs 12 MWh per ton and we use millions of tons per year). Ice storage could be used in large buildings that have hydronic cooling (1 ton of ice needs approximately 90 KWh of cooling) but of course this only helps in the summer. If every home and office were equipped with special controls, things like electric water heater temperature could be manipulated. One home wouldn't "store" much, but thousands of homes would do so.

    The holy grail of demand management would center around electric vehicle charging. If 5% of all autos were pure electric, and the on board chargers could learn from the utility companies when electricity was cheap or expensive, then EVs could soak up much of the excess without the installation of much base load generation.
  • John Scior on December 01 2014 said:
    It seems to me that a less expensive alternative would be to stop the traditional generation of electricity during times when wind and solar were available and then restart them at night or when winds are not sufficient. I think the problem though comes from the electric utility ownership of those generating facilities and the reluctance to cede generation to another source even if it were a more carbon free source.
  • Bill Stewart on December 01 2014 said:
    Solarcity is targeting $200 per KWH for home storage, or $200,000 per MWH with the Gigafactory. They are assuming large demand by individual homeowners based on strong ROI. There is also maturing software for peer-to-peer power sharing and load balancing.
    Perhaps the top down models you review of grid scale solutions may become less necessary. To the huge detriment of utilities

  • Kie on December 01 2014 said:
    What is the potential price of generating hydrogen when there is over-production of renewables (cheapest electricity), storing vast quantities and using it to generate electricity when there are renewables shortfalls?
  • Michael Hogan on December 04 2014 said:
    Further to the comment by Omahajoe, it is disappointing, though not surprising, to see yet another lame swipe at the feasibility of integrating intermittent renewables based on a selective review of energy storage options. These sorts of inadequate analyses ALWAYS overlook the enormous potential emerging of responses by non-time-critical and lower value loads in response to more variable supply. The costs cited here for "grid-scale" electricity storage (and I would include the hugely uneconomic idea of "power-to-gas" storage by converting electricity to hydrogen in that category) are certainly valid, but the cost of end-use energy storage, in thermal and other end use applications, is feasible using current technology for about $15/MWh. Yes, that's a vanishingly small fraction of even the most optimistic projections for battery, CAES and other fanciful grid-scale options. Ignoring the immanent potential for end-use energy storage signals either that you don't actually know what you're talking about, or that you're real agenda is to misinform people about the low-cost, feasible options for integrating large shares of intermittent renewables.

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