Energy Storage Discussion Thread

Debate over large-scale energy storage is a regular theme in the comments on this blog. The post is intended to be a place to centralise this discussion. Some questions that might be considered in the comment thread:

1. What is the cost (per Watt hour, kWh, MWh, GWh — how does this cost scale up, and how does this scale as higher levels of reliability are required, e.g. energy delivered on demand 90% vs 99% vs 99.9% of the time)?

2. What is the energy density of the proposed storage technology currently, and what are its physical limits? (i.e., how good can it get, with perfect engineering, and how long can the energy store be held?)

3. If the storage technology becomes cheap, what is to stop baseload plants like coal and nuclear from undercutting renewables, given that they can charge large batteries in low-demand times and then sell the power during peak (high-price) periods?

4. What are the material inputs for the storage system, and how does this effect the energy returned on energy invested of the paired energy technology (e.g., what is the EROEI and life-cycle CO2 emissions of, say, a 2kW solar PV system with no storage vs the same system with 10 hours battery storage to cover nights [ignoring winter and long cloudy periods])?

5. Lifetime: how many cycles can the storage technology handle (100, 10,000, near-indefinite [e.g. conversion to hydrogen])?

6. Does the storage technology need its own power-generation system, or can it be paired to the original generating technology (e.g., a molten salt heat storage can create steam for use in the same turbine set as the solar thermal plant itself, whereas compressed air energy storage for wind requires a different generation system to the wind itself)?

(If people can propose some other general questions, I’ll add them to this list)

Anyway, to kick the discussion off, here is something sent to me by George Stanford, in response to the following missive:

Seems to me the answer to intermittency is more wind and solar power and larger grids so they have over capacity and can share across larger areas. Conversely consider energy storage devices, flywheel systems, pressure accumulators, batteries, etc. If you consider all the economic benefits of the positive environmental savings of wind and solar (when getting away from coal) then the overcapacity costs would balance out in the end.

The end benefits of ending destructive mining practices, decreased oxides of nitrogen and mercury emissions and disposal issues with fly ash probably make it worth it alone. Has anyone found a study that shows the costs of that.

George replies:

Large-scale energy storage faces hurdles like cost, scale, material availability, and environmental disruption. For example, regarding battery storage, I have found this on the Internet:

Conway, E. (2 September 2008) “World’s biggest battery switched on in Alaska” Telegraph.co.uk, 12:01AM BST 28 Aug 2003

Excerpt: The world’s biggest battery was plugged in yesterday to provide emergency power to one of the United States’ most isolated cities.

The rechargeable battery, which at 2,000 square metres is bigger than a football pitch and weighs 1,300 tonnes, was manufactured by power components specialist ABB to provide electricity to Fairbanks, Alaska’s second-largest city, in the event of a blackout.

Stored in a warehouse near the city, where temperatures plunge to -51 degrees Centigrade in winter, the battery will provide 40 megawatts of power – enough for around 12,000 people – for up to seven minutes.

This is enough time, according to ABB, to start up diesel generators to restore power, an important safeguard since at such low temperatures, water pipes can freeze entirely in two hours. . . .

The earthquake-proof contraption contains 13,760 NiCad cells – bigger versions of those used in many portable electronic appliances including laptop computers and radios. Each cell measures 16in by 21in and weighs more than 12 stone [168 lb].

Notice that this system will store 40 MW x 7 minutes = 280 MW-min of energy. So let’s do a little ball-park arithmetic. The US uses roughly 500 GW-hr of electrical energy per hour. Suppose we want enough storage to supply 1% of that energy for 10 hours (feel free to plug in your own guesses). That’s 50 GW-hr, and 3,000,000 MW-min / 280 MW-min = 10,714.

So for our postulated backup system, multiply the Fairbanks numbers by 10,700. This gives us:

Area: 21.4 million sq. meters = 21.4 sq. km.

Weight of whole system: 1,300 tonnes x 10,700 = ~ 13.9 million tonnes

Weight of NiCad cells= 13,760 x 168 lb x 10,700 = ~ 12.4 million tons = ~12 million tonnes.

Weight of Cd: ~ 3 million tonnes (this is a guess).

World reserves of cadmium: 0.6 – 1.8 million tonnes (inadequate for just US need).

In other words, current battery technology would be unable to support battery storage for any significant part of the electric supply. Equivalent considerations apply to the other storage techniques.

Without storage or hydro backup, wind power looks hopelessly impractical as a major supplier of electrical energy. Larger grid? Apart form the elaborate new transmission network needed, remember that it’s not sufficient merely to always have power being produced somewhere — you constantly have to have enough power to supply the whole grid. Think of the over-capacity needed to accomplish that! Much of the time, most of the windmills would have to be feathered to prevent over-production.

Here-s a year’s worth of daily wind energy from all the wind farms in Germany:

(The Web site I got the above chart from seems now to be inactive.)

You can see almost-real-time info about the wind contribution to the Bonneville Power Authority here:

As for ending the destructive mining practices, etc., that can’t be done more than partially (if that) by wind and solar power — but it certainly can be done, in spades, by fast reactors such as the IFR.

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Then there is this comment by Tom Blees, putting recent solar costs into context (see also my recent comparison in TCASE 15):

This is being cheered on the internet by the windies and sunnies:

The Energy Department on Wednesday approved two loan guarantees worth more than $1 billion for solar energy projects in Nevada and Arizona, two days before the expiration date of a program that has become a rallying cry for Republican critics of the Obama administration’s green energy program.

Energy Secretary Steven Chu said the department has completed a $737 million loan guarantee to Tonopah Solar Energy for a 110 megawatt solar tower on federal land near Tonopah, Nev., and a $337 million guarantee for Mesquite Solar 1 to develop a 150 megawatt solar plant near Phoenix.

The loans were approved under the same program that paid for a $528 million loan to Solyndra Inc., a California solar panel maker that went bankrupt after receiving the money and laid off 1,100 workers.

These people can’t do math. A solar power plant rated at 110MW will have a capacity factor of about 18% tops (because of when the sun shines). Less in winter, of course. So that’s effectively about 20MW for $737 million. The price per gigawatt, then, is about $36 billion! And people complain about the high cost of nuclear power?! Even at the ridiculous prices for new nuclear in the states of about $6-8 billion/GW (and mind you, that’s for 24/7 availability, unlike solar), this solar investment is patently ridiculous.

Edit: It was pointed out in the comments that with Tonopah’s projected capacity factor of 55 % (with energy storage), the capital cost comes to a bit over $13 billion per GWe average power.