Most people would recognize these statements as nonsense. After all, it seems obvious that weight isn’t measured in horsepower, and a quantity of liquid isn’t measured in volts. In both cases, the speaker got the units of measure wrong.

While these mistakes may be absurd, in the field of energy generation and storage, similar errors are made all the time, and hardly anybody seems to notice. The core problem is confusion of two related, but different, physical quantities: energy and power. They’re not the same thing! If you read and understand this article, you’ll know more about the difference than a lot of reporters, and when you hear that a new wind farm will generate “250 megawatts per year,” you’ll know that something is wrong!