The Energy Return Over Investment (EROI) Method for evaluation of alternate fuels

Alternate Fuels here refers to any other fuel than Gasoline/Petrol or Diesel, as derived from petroleum. The term is used for general-use IC engines, and does not concern aviation fuels. That makes CNG, LPG, LNG, Biodiesel, Alcohols, DME, Gasified Coal et cetera all alternate fuels.

Why is there so much focus on alternate fuels? I'll let you figure that out.

A few months ago, while interviewing a Mr Andy Walker of the NREL (US DOE) about solar cells, I asked him if the solar cells would give out (in an average lifetime) energy more than what was used to create them. (I remember he said they would. I'll refer to the original transcript and edit my post later.)

I later discovered from an ASME Mechanical Engineering issue that this is what is called the Energy Return Over Investment, or EROI, of any fuel/energy source. I've read the term only very recently, but I think it makes total sense. So, what does EROI entail?

Say your factory turns corn into ethanol, which is later burned in engines. Your factory would need engineering equipment for that. It takes energy in using various forming techniques to manufacture all that equipment. It also takes energy to run all this equipment. The corn itself needs energy to grow; various fertilizers you'll use take energy to manufacture, the tractors to plow the fields use energy, the harvesters harvesting the corn need energy, the trucks trucking the produce into your factory need energy. The people running the plant and the farm and the farm machinery need energy to live.

The sum of all these energies is the Energy Investment.

I could say that in the end, you get ethanol, whose calorific value is the Energy Return. But it won't be so. You'll need to burn the ethanol in order to get energy from it, meaning the useful energy it will be delivering will be drastically reduced by Second Law of Thermodynamics.... get my drift? And, this useful energy the Ethanol will deliver will be slashed by the friction etc of the engine you'll be burning it in. Can we say the brake horse power will be the Energy Return? Not quite. We need to take into account the energy conversion into electricity that your factory will eventually run upon.

I can safely say that the Energy Return would be rather smaller than the calorific value of the Ethanol.

The way I see it, your factory is successful only if the ethanol you are producing can run your plant, your farm and all its related equipment and people, as well us give us an equivalent amount of energy (after deducing the 2nd law Tax) it took to manufacture your factory and your machinery. And after that, you still should have some ethanol to spare, which we can now burn in a car.

If it's any comfort, the energy input it took to build your factory and its equipment etc need to be repaid one-time only.

Your views?