Published on January 18th, 2013 | by Joshua S Hill22
Are Photovoltaics Or Biofuels Better At Energy Conversion?
January 18th, 2013 by Joshua S Hill
Editor’s Update: I’ve added an extensive reader comment to bottom of this post.
“The energy source for biofuels is the sun, through photosynthesis. The energy source for solar power is also the sun. Which is better?”
This is the question posed by University of California – Santa Barbara Bren School of Environmental Science & Management Professor and life cycle assessments (LCA) expert Roland Geyer.
The premise is simple: in 2005 the US saw corn ethanol as the new wave of powering vehicles while doing the environment and the local economy a wealth of good. Subsequently, 4 billion gallons of renewable fuel were added to the gasoline supply in 2006, which rose to 4.7 billion gallons in 2007 and 7.5 billion in 2012.
Life cycle assessments have shown that corn ethanol has little to no effect on reducing carbon dioxide emissions and may in fact increase them. On top of that, the farmland needed to grow all that corn is encroaching on natural habitats. Considering that in 2010 fuel ethanol consumed 40% of the US corn stocks, and the US is also responsible for 40% of the world’s corn supplies, corn prices have skyrocketed.
Since 2005, we’ve seen the battery electric vehicle (BEV) increase in popularity and efficiency, but charging an electric vehicle from fossil fuels doesn’t make a lot of sense (even though doing so is still much better for the environment than using petrol/gasoline). It would be ideal if we could charge our electric cars using renewable sources, like solar.
Here is where Geyer — and former BrenSchool researcher David Stoms and James Kallaos, of the Norwegian University of Science and Technology — re-enter the picture. They wanted to find out what would be better; corn grown from the sun turned into fuel or electric vehicles charged by the sun.
Even the laxest of CleanTechnica readers would be able to make an educated guess at the result.
According to the research, published in the journal Environmental Science & Technology, photovoltaics is a much more efficient option than biomass.
“PV is orders of magnitude more efficient than biofuels pathways in terms of land use – 30, 50, even 200 times more efficient – depending on the specific crop and local conditions,” says Geyer. “You get the same amount of energy using much less land, and PV doesn’t require farm land.”
And when you include recent WWF research that shows that land used for solar panels is being significantly underused, the biomass option seems absurdly outdated.
Geyer and his colleagues set about examining three ways in which sunlight is able to power cars:
- convert corn or other plants to ethanol
- convert energy crops into electricity for BEVs rather than producing ethanol
- using photovoltaics to convert sunlight directly into electricity for BEVs
They then examined five prominent “sun-to-wheels” energy conversion pathways for every county in the contiguous US. These included:
- ethanol from corn
- ethanol from switchgrass
- electricity from corn
- electricity from switchgrass
- photovoltaic electricity
By focusing the life cycle assessment on three key impacts of electricity generation — direct land use, life cycle greenhouse gas emissions, and fossil fuel requirements — they found that photovoltaic electricity for battery electric vehicles was easily the best option.
“Even the most efficient biomass-based pathway… requires 29 times more land than the PV-based alternative in the same locations,” the authors write. “PV BEV systems also have the lowest life-cycle GHG emissions throughout the U.S. and the lowest fossil fuel inputs, except in locations that have very high hypothetical switchgrass yields of 16 or more tons per hectare.”
What does this mean for the future? “What it says to me is that by continuing to throw money into biofuels, we’re barking up the wrong tree,” Geyer explains.
“That’s because of a fundamental constraint, which is the relative inefficiency of photosynthesis. And we can’t say that right now, biofuels aren’t so great but they’ll be better in five years. That fundamental problem for biofuels will not go away, while solar EVs will just continue to get more efficient and cheaper. If they’re already looking better than biofuels, in five years the gap will be even greater. A search for a silver bullet is under way through ‘synthetic photosynthesis,’ but using genetic engineering to improve the efficiency of photosynthesis is a pipe dream. If there is a silver bullet in energy, I think it’s solar power.”
Taking into account the previously mentioned WWF report — which detailed the fact that if 100% of the planet’s electricity was generated by solar farms the total land use would only amount to less than 1% — Geyer’s faith in photovoltaics is well held.
Putting aside for a moment the tremendous cost currently invested in developing and growing ethanol fuel crops, the other uses to which those funds (and crops) could be put to use, and the unsure science of “clean ethanol,” the reality is that photovoltaic power is turning out to be a more financially and economically efficient option.
Featured Reader Comment:
Hello Zach: I’ve been a faithful reader of your great newsletter for several years. I must admit you have provided me with a great education in the science and technology of renewable energy. Now, I have to challenge your article published in today’s newsletter. There are some basic inaccuracies in that article which are in need of clarification.
1. 40% of the U.S corn crop may be used to produce corn ethanol but that does not CONSUME the corn. Fermentation of the corn and production of ethanol yields distillers dried grains [DDG's] as a byproduct of the process. DDGs are used to feed livestock and produce food for the American public. This foodstuff for livestock (DDGs) replaces the equivalent amount of raw corn which would have been used for the same purpose. So, the production of corn ethanol does NOT consume the corn–only the starch in the corn kernel–and the remaining protein is harvested and utilized as a high protein animal feed. This is not to say that production of corn by current farming practices does not have adverse environmental impacts (i.e.: Runoff of Nitrate contaminated water from corn fields, and contamination of groundwater from over fertilization of cornfields). That’s another issue for another forum of discussion.
2. Harvesting of algae for the production of biofuels may very well tip the scales in favor of biological efficiency. Currently billions of gallons of treated wastewater are discharged into U.S. waterways laden with excessive Nitrogen and Phosphorus
These nutrients could be utilized to grow algal biofuels instead of polluting our streams and lakes and causing noxious algae blooms and resultant fish kills. Production of algal biofuels is a technology in it’s infancy. Give it a few years and see how it competes with P-V production of electricity to chage our electric vehicle batteries.
So in summary I’m saying lets compare apples to apples. Or better yet, let’s compare Jonathan apples to Jonathan apples (and not Red Delicious apples).
Your loyal reader
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