I did some searching to find out the energy efficiencies involved in producing biofuels. As I suspected, I found some good news and some bad news:

From mauigreenenergy.org/biodieselfaqs.htm

"Biodiesel also has a positive energy balance, generating three or more units of energy for every unit required to make it. And because it is biodegradable and nontoxic, biodiesel poses little to no environmental threat while in transit.

Can biodiesel help mitigate global warming?

A 1998 biodiesel lifecycle study, jointly sponsored by the U.S. Department of Energy and the U.S. Department of Agriculture, concluded biodiesel reduces net CO2 emission by 78 percent compared to petroleum diesel. This is due to biodiesel’s closed carbon cycle. The CO2 released into the atmosphere when biodiesel is burned is recycled by growing plants, which are later processed into fuel."


Translation: Biodiesel, like solar, generates 3 times the energy required to create it. The 78 percent figure cited by the DOE is probably assuming that fossil fuels were used to produce the biodiesel, which is totally unnecessary.

Ethanol is a bit more controversial. One estimate places the energy produced by making Ethanol at 1.67 times as much energy as required to produce it: www.usda.gov/agency/oce/oepnu/net%20energy%20balance.doc

while another source estimates that 71% more energy is required to produce a gallon of Ethanol than is contained within it: hubbert.mines.edu/news/Pimentel_98-2.pdf

Yet another report estimates a positive energy ratio of 1.37 for Ethanol and 3.2 for Biodiesel:
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Note that the 1.37 figure for Ethanol in this report is highly dependent upon the increased crop yields for the corn crops studied in recent years and likely would not be obtainable without the use of pesticides.

In both the cases of producing biodiesel and Ethanol one should consider the costs of other inputs such as water. Some of these studies also include the energy content of pesticides, though why a pest free crop would be needed when it is not going to be eaten is not clear, unless the yield is a critical issue as it is with Ethanol.

Solar power requires a considerable investment in energy content as it takes 10 years of sun shining on a solar panel before the solar panel produces as much energy in the form of electricity as was required to create it. I was not able to find a reference to back up that information. But it seems obvious that solar electric panels produced from fossil fuel would not be an option if we suddenly run out of fossil fuel.