[Giorgos]

Wikipedia says that biofuel is a renewable source. In the case of ethanol it explains the case. http://en.wikipedia.org/wiki/Ethanol_fuel#Chemistry

But how about biodiesel from animal fat? Where is the light's role?

Also, in the case of photovoltaic panels it is said that we are using sunling to make electricity. Can the same be said when using ethanol fuel to power electric generators?

Thank you.

[Arkcon]

Fuel from ethanol and biodiesel from plant or animal fats are pretty much the same thing in this sense.  We grow the raw material, process it, then burn it for energy.  Eventually, the released CO2 gets fixed again as biomass by plant or animal or microbe life.

[Arkcon]

While browsing a bit, I found this old reference on an EDU domain.  A through breakdown of the costs.  http://www.uidaho.edu/bioenergy/NewsReleases/Biodiesel%20Energy%20Balance_v2a.pdf

[vmelkon]

Also, in the case of photovoltaic panels it is said that we are using sunlight to make electricity. Can the same be said when using ethanol fuel to power electric generators?

Nope. The energy of sunlight is converted multiple times.
1. Photosynthesis produces sugar. (chemical potential energy)
2. The sugar is converted to ethanol by yeast. (chemical potential energy)
3. Then you burn the ethanol to boil water. (chemical potential energy converted to kinetic energy)
4. The kinetic energy of the steam pushes on turbines. (kinetic energy converted to rotational energy)
5. Turbine spins the electric generator. (rotational energy converted to electric potential)

One has to ask, which method wastes the least amount of energy.