Curiosity got the better of me. I had to do the math. Solar Energy input to the field is not included the graph. I was sure it would be huge. I greatly underestimated how much.
You may disagree with some of the input numbers, but I think you will see the result at the end is so large it cannot be included in the numbers.
An acre of U.S. corn yields about 7110 pounds of corn for processing into 328 gallons of ethanol.
77,000 BTUs per gallon of ethanol
http://healthandenergy.com/ethanol.htm
I used 5 kWH/m2/day for the solar energy input.
http://www.nrel.gov/gis/images/us_csp_annual_may2004.jpg
90 day season (just a guess, please correct me)
450 kWH/m2/season
4,070 m2/acre
http://www.onlineconversion.com/area.htm
1,821,085 kWH/acre/season
3,412 BTU/kWH
http://www.onlineconversion.com/energy.htm
6,213,799,475 BTU/acre/season
18,944,511 BTU/gallon of ethanol
246 BTU Solar input per 1 BTU ethanol.
Not a fair comparison in my mind, but they definitely did not include the field's solar input in the numbers.
When you look at it from purely energy input, we should cover the field with solar cells and build lots of batteries. Of course that wouldn't produce distillers grains or winter wheat.
OK, thanks - that’s really quick work on your part.
Growing season - it varies widely. A “90 day corn” is on the shorter end of some corn varieties, 110 day is on the longer end, but 90 is a workable starting point. The longer we make the growing season, the greater your numbers, of course.
The by-product of DDG’s needs to be taken into account here in two ways - there’s a whole lot of energy used in drying those distillers’ grains (which, if we could assume a feedlot very close to the ethanol plant, we would not need), and the feed value of the DDG’s is giving us a huge win as feed. We’d either be using cracked corn for feed, or DDG’s. Either way, we’re going to grow corn - so IMO, getting ethanol *and* feed from the same acres, same crop and same growing season means we’re getting a win here.
Unless America is going to become a nation of tofu-nibblers, the feedlots are going to be cramming *some* sort of feed into those cattle to finish them. We can either use cracked corn and get no ethanol, or distillers’ grains and get the ethanol. The big point I have to keep driving home to people is that the majority of both corn and beans (soybeans to non-farmers) grown in the US go into cattle feed, so when we have a viable after-product from biofuels that still feeds cattle, we really need to take that use into account, because we’d be using the diesel/etc to produce feed that has no fuel component removed anyway.
