California Moves Toward Power Storage Future, But How Much?

California's three largest utilities must obtain a significant amount of electrical power storage capacity by 2020, and that capacity must be online by 2024. That's according to the state agency that regulates utilities.

The California Public Utilities Commission ruled Thursday that Southern California Edison, Pacific Gas & Electric, and San Diego Gas & Electric most procure 1,325 megawatts of electrical power storage capacity within the next decade.

The ability to store electrical power is a longtime goal of both grid operators and renewable energy advocates, as storage capacity would make the grid both more resistant to outages and more capable of taking advantage of intermittent renewable energy sources.

We've put together an explainer on the different kinds of electrical power storage in the box to the left. But the tl;dr version is that there are a few different ways to store electrical power including batteries, flywheels, pumping water uphill, and some experimental technologies.

There are two big problems. One is that pesky Second Law of Thermodynamics, which implies that in every transaction of energy and matter, some of that energy will be lost. In other words, you can never get as much energy out of a storage system as you put into it. The other problem is that storage media as they currently exist are pretty expensive.

But with the state's rather large storage target, the CPUC and others hope that investment in the technologies will drive improvements in both cost and efficiency.

One other issue with the CPUC's announcement: unless ReWire is missing something, there's an important measurement missing from that 1,325-megawatt target. Watts are a measure of instantaneous power, but we and the grid use power over periods of time. Turn on your 1,000-watt air conditioner for an hour, and don't use 1,000 watts of power: you use 1,000 watt-hours.

It's worth noting that at least in small applications like batteries, storage capacity is more usually expressed in "amp-hours" or some variation thereof. Amp-hours and watt-hours are related, that relationship depending on the system's voltage. Watt-hours divided by voltage equals amp-hours. Check out the explainer above for more on that if you're interested. The important part is that without that "hours" factor, "1,325 megawatts" is an impressive but not very helpful measure of the state's storage target. How long will that storage capacity be able to deliver 1,325 megawatts for? 20 minutes? Six hours? It makes a difference.

Unless the actual target storage capacity in megawatt-hours is buried somewhere in the technical jargon in the CPUC's decision, that information would seem to be lacking. (The text string "hour" appears nowhere that we could see.) We placed a call to the CPUC's press office seeking clarification but haven't yet heard back. We'll let you know when they get back to us.