Something for nothing

[Jehanne]

Please correct me if I am wrong, but, I have read that if the United States would harvest every photon of light from the Sun that such energy (in Joules) would only meet 50% of that which we consume.

It's wrong. Energy usage of the US is about 93 quadrillion BTUs a year, which amounts to just less than 10^20 Joules per year. The solar constant is 1.361*10^3 Joules per square meter per second. That gives about 4*10^10 Joules per square meter per year. Dividing the two, we see that (capturing *every* photon) would take about 2.5*10^9 square meters, which is a square that is 50 kilometers on a side.

Now, efficiency and hours of daylight increase this, but it is still a long way from the total area of the US.

We use a trillion watts on average, right?

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We use 93 quadrillion BTUs annually; one BTU is 1055.06 joules; a quadrillion is 10^15, and so, the US uses approximately 10^20 joules per annum:

EIA -- US energy

The Sun gives us 1360 watts per square meter.

NASA Earth Observatory

The US has 3.797 million square miles, and so,

3,797,000 square miles * (2,590,000 square meters / 1 square mile) = 9,834,230,000,000 square meters in the US, or 9.8 * 10^12 square meters.

Taking 10^20 joules / (365*24*3600 seconds) = 3.17 * 10^12 watts

Taking 3.17 * 10^12 watts / 1360 watts per square meter = 2.33 * 10^9 square meters of solar panels.

And, so, we need a few hundred million square meters of solar panels, a 100,000 km by 10,000 km array.  Not enough land, or so it appears.

Nope. that is in square *meters*, not square kilometers. So, a 50km by 50km area would do it.

Yep, I messed up.

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And, so, a 50 km by 50 km array is completely doable!