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01/17/2013

Photovoltaics vs. Biofuel

 
In the photovoltaic vs biofuel battle, one alternative energy option may be a definitive choice.

As facility managers and building owners prepare for another year of green pushes and renewable energy options, has research determined a winner in the photovoltaic vs. biofuel energy battle?

As electric vehicles (EVs) increasingly enter the market and charging stations are built to serve them, EVs are competing with alternative-fuel vehicles.

Using electricity generated by coal-fired plants to power the cars defeats the purpose to some extent, but what if the energy comes from the ultimate clean and renewable source – the sun itself? How would that compete with ethanol in terms of land use, life-cycle emissions, and even cost?

The question, says UCSB Bren School of Environmental Science & Management Professor and LCA expert Roland Geyer, is which makes more sense, growing fuel crops to supply alternative-fuel vehicles with ethanol and other biofuels or using photovoltaics (PV) to directly power battery electric vehicles (BEV)?

"The energy source for biofuels is the sun, through photosynthesis," says Geyer. "The energy source for solar power is also the sun. Which is better?"

To find out, Geyer joined former BrenSchool researcher David Stoms and James Kallaos, of the Norwegian University of Science and Technology, to model the relative efficiencies of the technologies at converting a given amount of sunlight to miles driven.

The results, which appear in a paper titled "Spatially Explicit Life Cycle Assessment of Sun-to-Wheels Transportation Pathways in the U.S." and published in the Dec. 26 issue of the journal Environmental Science & Technology, showed photovoltaics (PV) to be much more efficient than biomass at turning sunlight into energy to fuel a car.

"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."

The researchers examined three ways of using sunlight to power cars: a) the traditional method of converting corn or other plants to ethanol; b) converting energy crops into electricity for BEVs rather than producing ethanol; and C) using PVs to convert sunlight directly into electricity for BEVs.

Because land-use decisions are local, Geyer explains, he and his colleagues examined five prominent "sun-to-wheels" energy conversion pathways – ethanol from corn or switchgrass for internal combustion vehicles, electricity from corn or switchgrass for BEVs, and PV electricity for BEVs – for every county in the contiguous United States.

Focusing the LCA on three key impacts – direct land use, life cycle greenhouse gas (GHG) emissions, and fossil fuel requirements – the researchers identified PV electricity for battery electric vehicles as the superior sun-to-wheels conversion method.

"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."

PV conversion also has lower GHG emissions throughout the life cycle than do cellulosic biofuels, even in the most optimistic scenario for the latter. "The bottleneck for biofuels is photosynthesis," Geyer says. "It's at best 1-percent efficient at converting sunlight to crop, while today's thin-film PV is at least 10-percent efficient at converting sunlight to electricity.

Finally, while cost was not a key component of the study, Geyer says, "The cost of solar power is dropping, and our quick calculations suggests that with the federal tax credit, electric vehicles are already competitive."

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."

 

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04/16/2014

The U.S. Army plans to start development of a solar array that will provide about 25% of the annual installation electricity requirement of Fort Huachuca, Arizona.

04/15/2014

The EPA's annual greenhouse gas emissions report is now available.

04/14/2014

Are you what some would call a “climate-change denier”? If so, you'll want to read this.

04/10/2014
Los Angeles has remained the top city for ENERGY STAR certified building since 2008, while Washington, D.C. continues to hold onto second place for the fifth consecutive year, according to a new list released by the EPA.
04/09/2014
Green construction has grown massively over a short period of time.
04/07/2014
Field demonstrations of newly proven energy-efficient technologies are yielding valuable results for the U.S. Navy, helping it meet energy goals.
04/03/2014
Building owners in Chicago now have more options when it comes to getting their building energy data verified.
04/01/2014
According to a new report from Eaton, such outages are up 15% in 2013 over 2012 and over half of those surveyed believe that downtime could have been prevented.
03/31/2014
The newly revised ANSI/ASHRAE Standard 105-2014, Standard Methods of Determining, Expressing, and Comparing Building Energy Performance and Greenhouse Gas Emissions, aims to provide a consistent method of measuring, expressing, and comparing the energy performance of buildings.
03/27/2014
Facility managers face an every expanding array of sustainability choices and challenges, but for the next generation of FMs, green practices could be second nature as sustainability literacy enters the K-12 school system.
03/25/2014
While the economic recession explains the decline in sales in 2008 and 2009, it is much less clear why sales have continued to fall.
03/24/2014
University of Washington (UW) scientists have built the thinnest known LED that can be used as a source of light energy in electronics.
03/21/2014
Mississippi Governor Phil Bryant signed Senate Bill 2378 into law, effectively enacting the state’s first building code.
03/19/2014
In an attempt to improve building energy performance, the DOE’s National Renewable Energy Laboratory has released a web-based tool called the Technology Performance Exchange, or TPEx.
03/18/2014
Could green building practices pose unanticipated life-safety hazards?
03/13/2014
Worried about workplace violence in your facility? Researchers have discovered that “mindfully observing” high-risk employees can avert danger and workplace violence.
03/11/2014
Through the DOE’s Building Energy Codes Program, every dollar the DOE has spent on building energy codes over the past two decades has resulted in $400 in energy cost savings.
03/07/2014
It is possible to harvest energy from Earth's thermal infrared emission into outer space, according to new research from the Harvard School of Engineering and Applied Sciences.
03/05/2014
Is your building prepared to handle an emergency?
03/04/2014
NASCAR revealed five newly installed charging stations for employee use.
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