Featured Research

from universities, journals, and other organizations

Photovoltaics beat biofuels at converting sun's energy to miles driven

Date:
January 17, 2013
Source:
University of California - Santa Barbara
Summary:
In 2005, President George W. Bush and American corn farmers saw corn ethanol as a promising fossil fuel substitute that would reduce both American dependence on foreign oil and greenhouse gas emissions. Accordingly, the 2005 energy bill mandated that 4 billion gallons of renewable fuel be added to the gasoline supply in 2006. That rose to 4.7 billion gallons in 2007 and 7.5 billion in 2012. Now a new study shows solar power is not only better in terms of energy efficiency, land use, and greenhouse gas emissions -- but it is cost competitive, too.

Credit: © itestro / Fotolia

In 2005, President George W. Bush and American corn farmers saw corn ethanol as a promising fossil fuel substitute that would reduce both American dependence on foreign oil and greenhouse gas emissions. Accordingly, the 2005 energy bill mandated that 4 billion gallons of renewable fuel be added to the gasoline supply in 2006. That rose to 4.7 billion gallons in 2007 and 7.5 billion in 2012.

Since then, life cycle assessments (LCAs) have shown that corn ethanol has modest if any effect on reducing CO2 emissions and may actually increase them, while posing a threat to natural habitats and food supplies, as food stocks are turned to fuel and marginal lands are put under the plough to keep up with demand. In 2010, fuel ethanol consumed 40 percent of U.S. corn production, and 2012 prices are at record highs. Since the U.S. also accounts for 40 percent of the world's corn, U.S. ethanol production has affected corn prices around the planet.

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," he says. "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."


Story Source:

The above story is based on materials provided by University of California - Santa Barbara. Note: Materials may be edited for content and length.


Journal Reference:

  1. Roland Geyer, David Stoms, James Kallaos. Spatially-Explicit Life Cycle Assessment of Sun-to-Wheels Transportation Pathways in the U.S.. Environmental Science & Technology, 2013; 47 (2): 1170 DOI: 10.1021/es302959h

Cite This Page:

University of California - Santa Barbara. "Photovoltaics beat biofuels at converting sun's energy to miles driven." ScienceDaily. ScienceDaily, 17 January 2013. <www.sciencedaily.com/releases/2013/01/130117105901.htm>.
University of California - Santa Barbara. (2013, January 17). Photovoltaics beat biofuels at converting sun's energy to miles driven. ScienceDaily. Retrieved April 23, 2014 from www.sciencedaily.com/releases/2013/01/130117105901.htm
University of California - Santa Barbara. "Photovoltaics beat biofuels at converting sun's energy to miles driven." ScienceDaily. www.sciencedaily.com/releases/2013/01/130117105901.htm (accessed April 23, 2014).

Share This



More Earth & Climate News

Wednesday, April 23, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

California Drought Is Good News for Gold Prospectors

California Drought Is Good News for Gold Prospectors

AFP (Apr. 22, 2014) — For months California has suffered from a historic drought. The lack of water is worrying for farmers and ranchers, but for gold diggers it’s a stroke of good fortune. With water levels low, normally inaccessible areas are exposed. Duration: 01:57 Video provided by AFP
Powered by NewsLook.com
Raw: MN Lakes Still Frozen Before Fishing Opener

Raw: MN Lakes Still Frozen Before Fishing Opener

AP (Apr. 22, 2014) — With only three weeks until Minnesota's fishing opener, many are wondering if the ice will be gone. Some of the Northland lakes are still covered by up to three feet of ice, causing concern that just like last year, the lakes won't be ready. (April 22) Video provided by AP
Powered by NewsLook.com
Is North Korea Planning Nuclear Test #4?

Is North Korea Planning Nuclear Test #4?

Newsy (Apr. 22, 2014) — South Korean officials say North Korea is preparing to conduct another nuclear test, but is Pyongyang just bluffing this time? Video provided by Newsy
Powered by NewsLook.com
Nasa Gives You An Excuse to Post a Selfie on Earth Day

Nasa Gives You An Excuse to Post a Selfie on Earth Day

TheStreet (Apr. 22, 2014) — NASA is inviting all social media users to take a selfie of themselves alongside nature and to post it to Twitter, Facebook, Flickr, Instagram, or Google Plus with the hashtag #globalselfie. NASA's goal is to crowd-source a collection of snapshots of the earth, ground-up, that will be used to create one "unique mosaic of the Blue Marble." This image will be available to all in May. Since this is probably one of the few times posting a selfie to Twitter won't be embarrassing, we suggest you give it a go for a good cause. Video provided by TheStreet
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
 
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:  

Breaking News:
from the past week

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:  

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile iPhone Android Web
Follow Facebook Twitter Google+
Subscribe RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins