A Meditation on Power

Image Credit Fred Bruenjes (moonglow.net)

Image Credit Fred Bruenjes (moonglow.net)

Electrical power, that is. The “clean coal” companies want a few billion dollars of the Obama stimulus money to “invest” in more coal power plants for our country, which they claim will be “cleaner” than current coal plants and thus provide cheap power without hurting the environment. Nirmal had a great post a few weeks ago highlighting some of the deception behind the “clean” part of “clean coal”, which I recalled today when I read there was just another such ash spill in Alabama. Also, coal power is by far the biggest contributor to global warming – even more than those fearsome SUVs!

We shouldn’t build any more coal power plants at all. What should we do instead? Personally, I’m a big fan of solar power. Photovoltaic solar panels don’t emit any carbon or other pollution once they’re built (more on that some other time). Solar power is completely sustainable for as long as the sun keeps burning (about 5 billion more years). And, with current technology, it can easily provide all of the power America needs. I find that last statement surprises a lot of people, so I’ll walk through a simple calculation to back it up. This is one of my favorite arguments for solar power, and some of you may have heard it before, but for those who haven’t, it’s really worth following it through one time. And I guess I should warn that it contains some numbers and very basic math. Feel free to challenge assumptions in comments if you’d like.

The solar luminosity is 3.8×1026 watts, and the average distance from the Earth to the Sun is 150 million kilometers, so the average flux from the sun (F = L/4πd2) should be about 1340 watts per square meter. The measured value is known as the solar constant, and it’s actually 1367 watts per square meter. This is the average amount of energy contained in sunlight that hits the Earth. Taking into account the fact that half the planet is facing away from the sun at any given moment, we get 1367/2 = 684 watts per square meter of sunlight available on average at any moment at any location on Earth. So we get enough energy from sunlight to run twenty-two 30-watt lightbulbs continuously in every square meter of the planet.

To convert this power directly into electricity, we use photovoltaic solar panels like these at rightemu_panels. (Incidentally, the science behind these solar panels was discovered by Einstein, and this discovery was what won him his Nobel Prize, not Relativity.) The technology behind solar panels is continuously improving, but you can conservatively estimate about 15% efficiency for cheap mass-market solar panels, which means that covering a square meter with them would yield 15%*684 = 103 watts on average. However, the true power generated depends on the angle of the solar panel as well: At a latitude of 38 degrees (the average for America), a rough estimate is cos2(38 degrees)*103 = 63 watts per square meter if you align the panel correctly.

Now, the United States uses about 42 quadrillion BTUs of electricity per year, which works out to an average of 1.3 terawatts (1.3 trillion watts). This means that we would need to cover an area of 1.3 trillion watts / 63 watts per square meter = 22300 square kilometers with solar panels to provide enough electrical power for this nation. That sounds like a lot of area (it’s about the size of New Jersey), but it’s actually an attainable figure. For example, imagine every house in the country had its roof covered with solar panels. There are about 127 million homes in the US, and the median square footage is 1769 square feet (or 164 square meters). Assume this is roughly equal to the useable roof space (a garage is usually not included in square footage, but then not all of the roof is always useable), and there is 127 million * 164 square meters = 20800 square kilometers of space on the roofs of our houses. If you want to do even better, add the 1999 figure of 67 billion square feet from commercial buildings and that’s 27000 square kilometers of space on America’s rooftops.

So there you go. Pass a law that every building must have solar panels installed on its roof, and suddenly we become a solar-powered nation, with no dependence on nuclear power, no need for natural gas and coal imports or mining, no pollution, and no danger of price shocks if the supply gets cut off. A bright future indeed!

Of course it’s not quite as simple as this – there are factors to consider like transmission lines, clouds, storing electricity at night and in winter, and producing enough solar panels to cover every roof. But these are the sorts of proposals I want to see from the Obama Administration, and the sorts of things I want in my infrastructure stimulus plan.

And, as always, Atrios sums it up better than I ever could.


One Response

  1. […] cont’d (and robots) Good timing! I got the clean coal post up right before this nice Time magazine takedown of clean coal came out. It’s quite a good […]

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