Thermal energy storage may be the cheapest way to absorb intermittent wind power in Ontario, according to a talk I just attended on Monday. Wind is a wonderful free and non-polluting source of energy, but its biggest flaw is that it isn’t constant, controllable, or even regular. In some places like Iowa, Missouri and Illinois, wind is actually anti-correlated to electricity demand. In plain language, that means it generally blows at night during moderate weather, when we have the least need for electricity. If we don’t find a use for that nighttime electricity, it goes to waste, along with all the money and resources that went to building the wind turbines.
This intermittency of wind isn’t the showstopper that the fossil industry would like you to think it is. There are many different ways to absorb it. You can store the energy in batteries, flywheels, compressed gas, thermal energy storage, behind hydroelectric dams, or just throttle down gas plants and save on fossil fuels whenever the wind is blowing. Or you can move it long distances on high voltage DC lines to other places where the wind isn’t blowing. All of those options have different advantages and disadvantages that depend on geography, and they all have high costs. In most of the world, the solution so far has been to throttle gas plants up and down contrary to wind. Another way to say the same thing, depending on your politics, is that gas plants provide back-up power for wind turbines when they’re not moving. That’s the cheapest option, as long as you don’t need to build any new fossil plants. It does not get us to a zero-emission grid, which is absolutely necessary to avert catastrophic climate change.
In Ontario, we’re already at the limit of what you can do by throttling gas plants, because we don’t have that many. Most of our electricity comes from nuclear plants, which have very little flexibility to throttle up and down. Throttling a nuclear plant doesn’t really save any fuel or money, and if you shut down a nuclear plant completely, it takes three days to bring it back up. So what now? Since last September 2013, the new solution has been to pay wind turbines to stop producing electricity when there’s too much wind. That’s the waste I was talking about in my first paragraph. Somebody’s got to pay for the wasted capital investment of building more electricity generation than we can use, and the contracts basically say the province has to pick up that tab.
We need a better solution, and thermal energy storage may well be it. When the wind is blowing, we can use heat pumps to generate hot and cold water, to be used later for heating and cooling while there’s no wind. A tank the size of a hot water heater might use nighttime wind energy to cool your house in the daytime, and a few week’s worth of heat or cold could be stored in geoexchange wells under your property. It turns out that this is much cheaper than building batteries or flywheels or long distance transmission lines. It’s even cheaper than building additional gas plants. And by using that system for heating as well as cooling, we can replace the natural gas used to heat your home with clean wind energy.
In order for thermal energy storage to help, the heat pump would need to know when the wind turbines are turning and when they’re not. Building that level of smarts into the grid is possible, but we’re not there yet. The current generation of smart meters doesn’t do that at all. They just allow different pricing by time of day, regardless of how much wind is blowing or what the demand is. That at least helps smooth out the day/night peaks, and that’s a start. But if consumer prices really followed the real wholesale market, you would see periods of negative prices when the wind suddenly picks up on mild days, and periods where it might triple in price on windless days at the peak of summer. That would provide a good market incentive for thermal energy storage, which would in turn help the whole system run more efficiently and, on average, more cheaply.