Megawatt

It’s a lot. But it gets complicated, because energy exists in two dimensions:

1. As a rate at any particular instant in time (“megawatt”)
2. As a sustained, aggregated amount delivered over a period of time (“megawatt hour”)

So, “a megawatt” is an amount of power being delivered at a singular moment. If you deliver that same amount of power for an hour, you have delivered “a megawatt hour.”

It’s like driving. Going “60 mph” doesn’t move you any distance at any particular instant. But if you keep that up for an hour, you’ll have moved 60 miles.

The average American home consumes about 10,800 kilowatt hours per year. The numbers vary based on location (homes in the south run more air conditioning) and the type of home (mobile homes are often electrically heated).

(According to this analysis your air conditioning uses about as much power as everything else in your house combined, with your clothes dryer coming in a distant second.)

Converting to megawatts (1,000 kilowatts in a megawatt), this means the average American home consumes 11 megawatt hours per year. Or, at any single moment in time, the average American home is consuming .001 megawatts.

There are 8,766 hours in a year. This means that a power source consistently generating 1 megawatt will generate 8,766 megawatt hours per year, which could theoretically power about 800 homes over the course of a year.

Here are the potential outputs of various sources:

• One acre of solar panels: 1 Mw
• A normal sized wind turbine: 2-4 Mw
• A very large wind turbine: 13-16 Mw
• A basic nuclear power plant: 1,000 Mw

Now, it’s important to note that these are potential outputs, which is how much these sources can theoretically output in any given instant. If we switch to megawatt hours, which is what they actually produce over time, the numbers change dramatically

The key point: you can’t really store electricity on a large scale. You can store it for small localized output (a car battery, for instance), but there are no “grid scale” batteries that can store enough electricity to power a entire electrical grid. At our current state of technology, you can’t “bank” electricity – you either output it and put it to use at the exact same time, or it’s lost.

The percentage of power a source can realize over time is its “efficiency rating.”

Obviously, solar panels depend on the sun. They will generate basically nothing at night, and less when the sun is weaker, like during the winter months. Windmills require the wind to blow. On calm days, they don’t turn or turn slowly. Wind turbines normally have efficiency ratings of 25-33%.

This means the sustained power production of solar and wind over time is much lower than their potential output, because they’re only outputting that for a fraction of the time.

Nuclear power plants are the steadiest option. They mostly run 24/7, except when they have to be taken down for maintenance. I saw a statistic that an average nuclear power plant has efficiency rating 93.5%. Coal power plants are about the same. They run wide-open, all the time.

Doing the math on a nuclear plant: producing 1,000 megawatts for 8,766 hours times 93.5% is 81,962,210 megawatt hours every year, which would power 745,000 homes, or a mid-size American city.

(Also of note – the output capacity of nuclear varies greatly. The smallest nuclear plant in the United States can output 582 Mw; the largest, 2,340 Mw.)

As a final piece of trivia, the average bicyclist generates .11 kilowatts. This means they would generate .96 megawatt hours per year if they cycled 24 hours a day, 365 days a year. So, 11 of those could power your house.