The Oil Drum

The efficiency of the Photosynthesis process for plants is indeed typically 1% or 2%. But only a very small part of the energy is converted into usable oil. According to the article I referred to, rapeseed converts only 0,15% of the solar energy into oil!

Roughly speaking, a tracking PV panel produces about one third more electricity as an optimally positioned fixed PV panel (not flat on the ground). A panel lying flat on the ground produces about 85% of an optimally positioned fixed PV panel (at least in Germany, on the equator the optimal position is flat on the ground). But than you could use the whole field, instead of only about one third, because then you don't have the problem of one panel shadowing another. In total you would even have more yield pro hectare, but at a much larger cost because you need a lot more panels!

And that brings us to costs. In Germany, they have a feed-in tariff of 35.49 cents/kWh for freestanding PV-plants. So, a car consuming 16kWh/100km has a 'fuel cost' of about 5.68€/100km... The fuel cost of a typical 7.4 l/100km (32mpg) gasoline car is considerably higher! (at least in Europe) And feed-in tariffs are falling (up till now 6,5% a year, from next year on probably 8,5%), whereas oil prices are rising. For a PV powered hybrid car, not as much the price of the "PV fuel" is the problem, it's the battery cost!