Tuesday, July 13, 2010

Isn't energy from solar/wind better then nuclear power?

I personally think solar and wind have some place in our energy future. The sun is the source of most of the energy available to us, and in some places in the country the wind blows with pretty good regularity. However solar and wind can not be the solution to our energy problems alone, they just don't have the energy density.

The sun outputs roughly 400 watts per square meter to the surface of the earth. With 25% efficiency, that yields 100 watts per square meter. The yearly average number of daylight hours is around 12 hours per day. The peak output of a solar plant is thus 1200 watt hours (1.2 kwh) on average per square meter in the southwest. This is variable over the year, on the summer solstice the number of daylight hours is 14.2 hours per day and 9.8 hours per day for the winter solstice. Even at 50% efficiency, we would only double that to 2400 watt hours (2.4 kwh) per square meter. To reach the same power output of a nuclear power plant with 25% efficiency solar panels, we need to match 24 gigawatt hours per day. This means we need 7.7 square miles of panel area and a technology that can store 12 gigawatt hours of energy without significant losses, so that it can be released over the night. This is a very simplified analysis, and any real installation will be larger. The storage technology that we have now also imposes significant losses and will carry a large penalty in required area.

Wind is much worse, and needs around 270 square miles of area, according to an analysis published by the office of Senator Lamar Alexander, to produce 1 gigawatt of reliable electricity. To replace all our coal fired plants with wind farms would require an area a little bit bigger then the state of Michigan (our 12th largest state at 86,943 square miles).

Solar and Wind just can't compete with nuclear power because of the energy density. With advanced technology and investment they might help generate some more of our electricity in the future. However, they just aren't feasible replacements for baseline loads. To make a significant dent in carbon dioxide emissions and air pollution we need energy that is reliable 24 hours a day, 365 days a year.


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