Storage.

Electrical utilities must maintain a constant load to work. They monitor use of the resource on one end, push new electricity into the system at the other.

They're used to thinking big. And they want their big inputs to be flexible. Coal and natural gas are very flexible. You can turn them down, turn them off, turn them back on pretty quickly. Solar and wind power aren't flexible. If the wind doesn't blow or the Sun doesn't shine it doesn't matter how much demand you have for what they make -- you won't get supply.

So while most states, including Georgia, have laws requiring  utilities to buy alternative energy -- it's called net metering -- most limit the amount of power a utility is obligated to buy. In Georgia it's .2% of the system's peak load. If it's unreliable the power company won't treat it seriously.

The key to making alternative power reliable is storage. When I first approached this subject, I assumed the best way was to turn electricity into hydrogen, then store-and-forward the hydrogen in some way, either as a gas or as liquid ammonia, NH3.

Turns out that's not the only way to go about it, and right now the power loss from the round-trip hydrogen conversion makes it uneconomic anyway.

Most current mass energy storage methods -- raising water, compressing nitrogen, underground heat storage, wind bags -- are still on the drawing board. Two are not:

  • Beacon Power is building a 20 MW plant in upstate New York (above) that uses a flywheel, spinning on magnets, to store power until it's needed. The company says it can scale this to the GW range.
  • General Compression uses excess power to compress air, which is stored underground, and then released to create power when needed. It's planning a commercial launch next fall and is backed by, among others, Duke Energy, so it should have customers.

Both these plants are relatively small. Even a 1 GW plant will only handle the energy needs of a single office building for a year. That's why the New York Power Authority is still looking to fuel cells, which run on hydrogen, as the long-term solution.

The problem with current fuel cells, of course, is where the hydrogen comes from. It comes from natural gas. Having hydrogen produced directly, at a solar, wind, or geothermal plant, then piping it using the same infrastructure natural gas now uses, is what I consider a long term solution. But it's still a long way away. Those natural gas pipelines we have now are all in use. It would cost serious money to build an overlay system, based on hydrogen.

Encourage the construction of new lines and the natural gas industry might eventually have excess capacity hydrogen can take over, unused lines worth buying, but any such system would have to be isolated from what currently exists, and that will also take money.

All this is early days. It's good people are thinking about these things, and good that solutions are in the works. But it's cold comfort to people who want to generate alternative power right now that the grid is not yet ready for them.