Land Use: Ethanol vs Solar

This article was originally published on my blog at www.sustainablewestseattle.org in 2013

On a recent trip to Minneapolis, I looked out the window of the plane and saw a vast expanse of land growing corn. It had me thinking about ethanol, since much of that corn is being grown to feed not man nor beast, but cars and trucks. I wondered if we wouldn’t be better off covering that land with solar panels. On my return, I looked up some numbers and my suspicions were confirmed: we could produce about 4 times the electricity consumed in the US by covering the land now used to grow corn for ethanol with solar panels.

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Here’s the math:

Acres of corn under cultivation 100000000
Fraction of corn used for ethanol production 0.28
Square meters per acre 4047
Solar irradiance [kW/m2) 1
Efficiency of solar panel 0.12
Duty cycle (e.g. factor in weather & night) 0.2
Transmission/storage efficiency 0.7
Average Solar Power capacity on land now growing corn for ethanol [GW] 2000
Total US electricity consumption in 2011 [GW.hr] 4 million
Average Power [GW] 430
What % of US electricity consumption could be powered by solar panels on land now growing corn for ethanol? 433%

I’m not suggesting we take some of the best agricultural land in the world and cover it with solar panels. I’m suggesting we grow food on that land, and cover 10% of that much land in the desert or on roof tops with solar photovoltaic panels to generate some of the energy we need. My point is the idea that solar power takes up too much land is absurd.

So let’s do a little bit more math. Suppose we have a goal to produce 30% of our electricity with solar power. How much land is that? That is less space than parking lots consume. Much of that could be on rooftops of homes and business, or covering parking lots.

Average Power [kw] 4.28E+08
Average power generated on one 1m2 [kw] 0.0168
Area needed to generate 30% of our electricity [m2] 7.64E+09
Area needed to generate 30% of our electricity [square miles] 2,951
Area of parking spaces in the US [sq miles] 3,590
Fraction of the area of parking lots 82.2%
Area of the US 3.80E+06
Fraction of the US needed to generate 30% of our electricity from solar power 0.08%

With the cost of solar dropping quickly, it seems likely the solar will soon be playing an important part of meeting our energy needs. One things that won’t be stopping this growth is running out of room.

 

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