Western Energy News reports that the small utility that serves Aspen, Colorado is already running entirely on clean energy. This is very misleading, and as Paul Harvey used to say, “now, for the rest of the story.”
When someone says they have achieved 100% renewable energy, they mean capacity, not energy. For example, let’s say a city has 10 megawatts of demand, and they have a 10 megawatt wind farm to provide electricity. That wind farm has the capacity to produce 10 megawatts of energy when the wind is blowing at the appropriate speed. However, and this is important, the wind is not always blowing. When the wind is not blowing (or not blowing optimally), that wind farm is producing much less than the 10 megawatts necessary to provide adequate electricity to the city.
Electricity generating units, no matter the fuel source, do not always perform at their peak capacity. A unit’s capacity factor is the average power generated, divided by the rated peak power. Let’s take a wind turbine rated at five megawatts. If it produces power at an average of two megawatts, then its capacity factor is 40% (2÷5 = 0.40, i.e. 40%). In 2017, the U.S. Energy Information Administration reported that the average capacity factor for wind generation is the U.S. was 36.7%. By comparison, the average capacity factor for coal was 53.5%.
But wait, Terry, you say. Can’t you just build enough extra capacity over what you need to get to the 100%? Well yes, you can, but that still does not change the fact that the wind does not always blow. Some days, very little wind energy is generated, especially when it is very hot (and power is most needed). Anyone who regularly drives by wind farms can tell you that many times, the wind turbines are not turning at all. You have to have another source of power on which to rely.
Where does the city get its needed electricity when the wind isn’t blowing (or isn’t blowing optimally)? Most likely from more traditional forms of power generation, like coal, nuclear, or natural gas. So, the city is not running 100% on clean energy. Not even close.
This is not a knock on wind energy. I have always been in favor of an all-of-the-above energy strategy. We need all forms of power generation for reliable and affordable electricity. Making decisions on the mix of fuel sources to provide reliable and affordable electricity is hard enough without misleading information. Wind can be a good source of generating electricity, but it can’t supply 100% of our energy needs.