For Powering Cars, Solar-Electric Is ‘Orders Of Magnitude’ More Efficient Than Biofuels

Climate Progress recently reported on a study that found both economic and environmental benefits if homes in the northeastern United States upgraded older heating systems by moving from heating oil to switchgrass. However, one point to emphasize was the findings were specific to those circumstances — the region, the homes, and that particular use.

Switchgrass was not nearly as good an idea for electricity generation or transportation fuel. Further confirming the need for a diversity of renewable solutions to our energy needs, a recent study determined that electricity generated by solar beats out biofuels for powering cars under myriad scenarios.

The report, put together by a team from the University of California, Santa Barbara and the Norwegian University of Science and Technology, and published in Enviornmental Science and Technology, compared five different approaches to see what was the most efficient way to power a compact passenger vehicle for every 100 kilometers driven:

Battery-electric vehicles (BEVs) run on electricity from solar power.Battery-electric vehicles run on electricity from switchgrass.Internal combustion vehicles (ICVs) run on switchgrass biofuel.Battery-electric vehicles run on electricity from corn.Internal combustion vehicles run on corn-based biofuel.

The analysis considered land-use, greenhouse gas emissions, fossil fuel use, and took into account the production and use life cycles of both the fuels themselves and the vehicles they power.

In terms of land-use, solar significantly out-performed all other options. It performed modestly better than switchgrass in terms of greenhouse gas emissions, and significantly better than corn-based biofuel. Solar was actually equal or slightly worse than switchgrass when it came to fossil fuel requirements over the totality of the life cycle, but it still out-performed corn-based internal combustion. (And, of course, gasoline.)

So all things considered, a pretty clear win for solar-powered electric battery vehicles:

A write up over at Green Car Congress has more details on the assumptions and variables in the study’s modeling.

“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,” Roland Geyer, a UCSB Bren School of Environmental Science & Management Professor, told Science Daily. “You get the same amount of energy using much less land, and PV doesn’t require farm land.” The central bottleneck, as the report notes, is the low efficiency of photosynthesis:

Biofuels for ICVs and bioelectricity for BEVs use photosynthesis to convert solar radiation into transportation services, that is, they are sun-to-wheels transportation pathways. While photosynthesis has a theoretical maximum energy conversion efficiency of 33 percent, the overall conversion efficiency of sunlight into terrestrial biomass is typically below 1 percent, regardless of crop type and growing conditions.

“Today’s thin-film PV is at least 10-percent efficient at converting sunlight to electricity,” Geyer explained — hence solar’s superior performance. In fact, the WWF’s Solar PV Atlas found that as far as land-use goes, solar is so efficient that less than 1 percent of global land areas would be needed to supply all the world’s electricity needs in 2050.

Traditional corn-based biofuels are problematic on all sorts of levels: Carbon emissions from agricultural production over their full life cycle largely wipe out any carbon benefits at the point of actual vehicle use. They compete with human food supplies and food cropland, driving up global prices and contributing to global poverty and instability. And new cropland sequesters less carbon from the atmosphere than the grassland or forest it typically displaces.

Switchgrass and other cellulosic biofuels, while they avoid disrupting food supplies, are not immune to these other flaws either. On top of that, their commercial viability at any time in the near future is far from certain.

For the clean car fleet of the future, electrical and hybrid vehicles relying on a grid powered by solar — and presumably wind, hydroelectric, and such — still appears to be the way to go.

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Biofuels cuts harmful to energy security

Gas prices these days are far higher than they should be for this time of year, costing Pennsylvanians at the pump and creating a headache for politicians. The good news is that we already have a fuel technology that is cheaper than gasoline, cleaner than oil, and most importantly for me, comes from right here in the USA. It’s renewable fuel.

As a former Lieutenant Commander in the United States Navy, I know firsthand that how we fuel our vehicles affects more than our pocketbooks – it affects how well we protect our country. Luckily, the military is leading the way to develop the next generation of clean, renewable fuels. The Navy is using advanced biofuels, derived from sources like recycled waste oil and algae, to power its ships and aircraft. These fuels promise to cut us loose from a dependence on oil that reduces our military’s readiness and costs billions more than we ought to be paying.

The bad news is that not everyone sees the importance of the military’s investment in biofuels. The high price of gas has prompted a few politicians to turn against these fuels, and unfortunately Sen. Pat Toomey (R-Pa.) is among them. Senator Toomey has been a strong supporter of our armed forces and veterans in the past, but this time he’s got it wrong, and if he succeeds he’ll be dealing our troops a significant setback. As a Pennsylvania resident I am disappointed, and as a veteran, I am outraged.

Right now the Department of Defense invests a small portion – about four percent – of its energy initiatives budget in alternative fuels. Senator Toomey would like to cut that investment to zero. That small investment, however, has big benefits. It is already making it possible for our ships, planes and ground vehicles to run on a wide range of fuels. That kind of flexibility makes it easier for our troops to adapt and fight effectively.

I have seen firsthand the importance of energy security and flexibility. I led the medical team for the first ground troops who entered Iraq in 2003, overseeing the care of over 1,500 Marines and sailors and treating over 300 trauma injuries as the first physician on the scene. When troops and equipment are more mobile and more adaptable, they are more capable of avoiding situations with a high potential for casualties. As long as we are stuck with a single fuel source – oil – we will remain less flexible and agile than we could be, and that will cost lives.

There’s also a simple dollars-and-cents reason to protect military biofuels. According to DoD, every 25-cent increase in the price of a gallon of oil costs the military $1 billion in additional fuel costs. Oil prices rise and fall constantly, as anyone who’s gassed up lately knows, and that price volatility means an unpredictable military budgeting process that can hamstring basic military functions from medical care to essential training and readiness. It is naïve to think that the price of oil will go down and our problems will vanish. According to the International Energy Agency, even if we expand domestic oil drilling in the near term, oil will still cost over $215 per barrel in 2035.

The military is poised to lead the shift away from oil, toward domestic, stable and safe fuel alternatives. Our history of technological breakthroughs supports this claim; the military played a critical role in the development of what are now everyday technologies, like GPS and microchips. As with these technologies, military biofuels innovation will translate into cheap biofuels in Pennsylvania and across the nation.

Cutting funding for biofuels now would erase the progress our military has made and imperil technologies that are being used by the warfighter today. Weakening national security and stifling innovation in any circumstance is a bad idea, and Senator Toomey should know that. I hope that he sees the light and recognizes the importance of operational flexibility for our Navy and all service branches. And I hope our troops continue to benefit from this clean, homegrown fuel.

Dr. Trivedi is an Iraq war veteran, board-certified internal medicine physician and a spokesman for the clean energy campaign, Operation Free.

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