If it takes one thousand gallons of gasoline to produce 10 thousand gallons of ethanol, then it could be a net win by requiring less gasoline production later or something.

But I have no clue how the numbers actually work out.

The laws of thermodynamics alone lead me to suspect that that's probably not the case.

The energy input to crops that later become ethanol is the sun, not the gasoline burnt in the production process, so there is no necessary relationship inferrable by thermodynamics between fuel burnt and the energy content of crops or the resulting ethanol.

If there were, then human-powered farming would have been pointless as a food production method.

I assume you're speaking in theoretical terms, but it bears mentioning that in practice, fossil fuels are a critical input to the production of crops, to the extent that EROEI for corn ethanol remains stuck at around 1.

I stand corrected.

Ethanol makes perfect electoral sense: Democrats get to pass "green" legislation which their base likes while Republicans get to give subsides to farmers, one of their main constituents.

It depends on whether the ethanol is generating net positive energy. If I burn one joule of petroleum to get two joules of ethanol, it's a net success. If I burn two joules of petroleum to get one joule of ethanol, it's a net failure.

I very much doubt it would have survived as long as it has as a technology if it were a net energy loss.

> I very much doubt it would have survived as long as it has as a technology if it were a net energy loss.

Most of the assessments I have seen generally always show that bio-ethanol is a net loss. Only subsidies keep it afloat.

None of the bio-* will make any sense until we have a lot more renewable electricity on the grid. At that point, producing bio-* will basically become an energy storage solution and a way to soak up excess energy production that you couldn't store any other way.

As an aside, I suspect once transport and commuting are handled by EV vehicles, ethanol will stick around as a small scale fuel for motorsport enthusiasts.

Frankly, I love my combustion engines for fun and sport, and while I fully support the switch to EV, I have long been wondering how the switch will effect my ability to use them for fun Sunday drives. Eventually they will be banned from the roads and the production and distribution of petroleum will slow right down.

With many motorsport vehicles using Ethanol based fuels for its lower temperature burn and higher power output, I suspect that is the fuel that will stick around as a special use product. Appropriately priced, no doubt.

economically a net loss or ecologically?

I sort of assume both, but I'd like to hope for one of them.

Both. Here's some data from the late Prof. MacKay: http://www.withouthotair.com/Errata.html#284 :

" 1 acre produces 122 bushels of corn per year, which makes 122 x 2.6 US gallons of ethanol, which at 84000 BTU per gallon would mean a power per unit area of {0.2 W/m^2}; however, the energy inputs required to process the corn into ethanol amount to 83,000 BTU per gallon; so 99% of the energy produced is used up by the processing, and the net power per unit area is about {0.002 W/m^2}. The only way to get significant net power from the corn-to-ethanol process is to ensure that all co-products are exploited; including the energy in the co-products, the net power per unit area is about 0.05 W/m^2."

Ethanol production has never been a net positive for energy production. It has always survived to maximize the use of the subsidies the american corn farmer.

Don't underestimate the power of farming subsidies and lobbying.

Very much so. We should not have any of these laws; if bio-whatever makes economic sense, you won't need laws mandating its use.

It you wanted to kickstart a technology I think it could make sense for shorter periods of time. For example Electric Vehicle tax credits make it much easier for car companies to develop their electric car lines, but the credits expire after so many cars.

I don’t understand this argument. It assumes thay petroleum will always be needed to run tractors and other infrastructure around it, which seems unreasonable considering the vast number of alternative fuels out there?

According to Wikipedia, the energy balance of ethanol in my country is 8 or more, so it would be more like getting a crisp new $100 bill and turning it into eight $100 bills.

I'm guessing this is someplace that sugar cane can grow? The EROI from corn ethanol is much, much worse. Ethanol does make a lot of sense for, say, Brazil, but not much sense for the US.

modern tractors run on diesel (although I have two that run on gas) for the low end torque curve and slight increase in fuel-to-energy conversion efficiency. Although my person preference is gas tractors, commercial farmers all use diesel for these reasons. For me, gas tractors so much easier to rebuild a carburetor then a diesel injection pump. My diesel tractor has been down for almost a half year due to an injection pump rebuild (Case 530CK Roosamaster pump)