Over at The Oil Drum Robert Rapier argues biomass energy has a very limited role to play as compared to solar photovoltaics.
The fundamental problem here is that photosynthesis is not very efficient. Consider the rapeseed oil yield above. Gilgamesh made a table that is basically the solar capture/conversion to oil from various crops. The gist is that only a few hundredths of a percent of the incoming solar energy gets converted into liquid fuels. Of course some did get converted into other biomass, which could be otherwise used for energy, but generally we get a very low capture of the sun's energy for use as liquid fuels. (This exercise can still be proven by assuming the theoretical limit for photosynthesis. One must just make more assumptions and it is not as easy to follow for a general audience).
Consider instead direct solar capture. Let's not even consider the record 40+% efficiency that Spectrolab announced last year. Let's not consider any of the more exotic technologies that are pushing the envelope on direct solar capture efficiency. BP's run of the mill silicon solar cells operate with an efficiency of 15%. That's about 250 times better than the solar to rapeseed oil route. Or, to put it a different way, you can produce the same amount of energy with direct solar capture in a 13 ft. by 13 ft. area that you can by photosynthesis in 1 acre of rapeseed. And odds are that you have a roof with an area that size, which could be used to capture energy without the need to use arable land.
Rapier has reached the same conclusion I've preached for years: We need to develop the technology we need to shift to electric power for transportation.
Of course the disadvantages are 1). The costs for solar are still relatively high; and 2). We have a liquid fuel infrastructure. But in the long run, I don't see that we have any chance of maintaining that infrastructure. If we are to embark on a Manhattan Project to get off of our petroleum dependence, we should direct our efforts toward an eventual electric transportation infrastructure.
Biomass energy will eat up too much land and agriculture will generate too much pollution with a poor ratio of Energy Return On Energy Invested (EROEI). Synthetically created photovoltaic materials will convert sunlight to energy far more efficiently than plants can manage. This fact might one day enable nanobots to outcompete DNA-based life. But for the foreseeable future the use of photovoltaics instead of biomass energy will protect nature.
Airplanes probably aren't going escape their use of liquid fuels when cars shift to electric power. So the relative cost of air transportation will rise vis a vis ground transportation. But overall the cost of transportation will fall once we can power vehicles off of electricity.
|Share |||Randall Parker, 2007 July 26 10:50 PM Energy Electric Generators|