Biodiesel is gaining popularity due to environmental benefits and ease of integration. (Rudolf Diesel invented his engine to run on unrefined vegetable oils.) Understanding that the fuel produced from biomass is solar energy collected and stored in energy-dense chemicals provides interesting perspectives regarding efficiency.
Comparing Maximum Efficiencies of Solar and Bio Conversion
Increasingly, there is interest in using algae as a biomass source is gaining over interest in using oil seeds. Algae show promise for greater solar to diesel conversion efficiency.
Characterizing that efficiency is tricky, and the results indicate that biofuels must benefit society in ways other than replacing petroleum. Results published by Vasudevan and Briggs in their 2008 article "Biodiesel production – current state of the art and challenges” from volume 35 number 421 of the Journal of Industrial Microbiology and Biotechnology, provide an estimate of maximum quantum efficiency of solar to chemical energy conversion of roughly 11.6%.
One use for this figure is to compare energy production efficiencies of solar to biodiesel and solar to electricity. Today's solar panels have typical conversion efficiencies of 15-20%. Even though they are more efficient at converting solar energy, electricity is not currently a viable solution for transportation. This is one reason researchers continue to pursue biodiesel.
Actual Conversion to Biodiesel Fuel
The range of incident solar energy is known for most of the world. Vasudevan and Briggs use this information to estimate that 28,000 gal/acre-year of biodiesel is theoretically possible in the sunniest parts of the United States. This is calculated strictly on an energy basis. As engineering and science suggest, actual yields are nearly always less than theory.
In volume 141 of Biological Conservation, Koh and Ghazoul's 2008 article "Biofuels, biodiversity, and people: understanding the conflicts and finding opportunities," point out that soybean crops actually produce between 45-60 gal/acre-year of biodiesel. Vasudevan and Briggs estimate the lower yield.
Algae can Produce Biodiesel Oil
Haag estimates that an algae crop could yield over 9510 gal/acre-year in his 2007 article "Algae bloom again," found in Nature, volume 447. Estimates for biodiesel yield from algae vary wildly. The quantum (energy conversion) maximum of 28,000 gal/acre-year should be kept in mind when evaluating these estimates.
Vasudevan and Briggs report one of the higher yields of biodiesel from algae at Huntley and Redalje's Hawaii site. Their algae crop yielded over 1200 gal/acre-year (a solar conversion efficiency of only 0.6%), which is far better than conventional oil seed stock.
Unfortunately, affordable and practical algae technology is years off although efficiencies indicate algae are the best choice for biodiesel production. Algae pose little threat to global food security and cause the least amount of land use change.
Algae are also able to use water supplies that are not suitable for agriculture or industry. This alleviates concerns of water crisis developing from increasing demand for biofuel feedstock.
Continuing Biodiesel Research is Important
The transportation industry currently relies mostly on diesel fuels, so it is important to develop environmentally neutral fuel supplies. Biodiesel can help reduce dependency on foreign oil and provide the world's poor farmers with new streams of income. However, regulation will be required to avoid unintended consequences such as famine and water crises associated with land use change driven by increased feedstock demand.
Also, decision-making must take into account actual conversion efficiency as governments recognize the need to reduce dependency on petroleum for growing energy needs. Ultimately, scientists and researchers agree that biodiesel has a place along with hydro, wind and solar power in the world energy portfolio.
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