Boston (MA) - Computer simulations and real lab testing conducted by a team of physicists and engineers at MIT have revealed new ways to extract greater efficiency from existing solar cells. The findings show 50% increases are possible. Today's most efficient solar cells yield about 45% efficiency and are extremely costly to produce, though typical applications are around 30% efficient. Cells made with this new technology could be over 60% efficient, while costing much less to mass produce because they'd use only 1% of the most expensive component today: refined silicon.





Simple effective approach



MIT researchers analyzed one of the limiting factors in solar cell efficiency today. Namely that the light striking a solar cell is only in a position to be converted to energy for an incredibly small amount of time. By using computer simulations which add reflective coatings to the front and back of the solar cells, the light bounces around inside for far longer. This results in the greater efficiency seen because were the reflective coatings not there, the light would just bounce off away from the cell.





Many computer simulations



The MIT team took a very straight-forward approach in conducing this research. They looked at the amount of time sunlight was in a position to be converted into energy. The team ran thousands of simulations with each one designed to try a slightly different approach toward keeping photons within the cell for longer.



In the end, the team found the best result in a multi-layered reflective coating coupled to a tightly spaced array of lines. These are deposited on the back of the ultra-thin silicon films, with another coating on the front. It basically acts like a laser around the cell, allowing light to bounce back and forth before finally exiting.



This approach increases the energy output of the cells by as much as 50%. This would make today's highest-end solar cells, which achieve roughly 45%, achieve nearly 68% efficiency. They would be capable of extracting approximately 675 watts per square meter from the Earth's surface.


Laboratory testing


Once the computer simulations were completed, the results were verified by "lab scale tests" conducted by "the relentless dedication of graduate student Lirong Zeng, in the Department of Materials Science and Engineering, to refining the structure and making it." According to Lionel Kimerling, who directed the project, "The experiments confirmed the predictions, and the results have drawn considerable industry interest.".





MIT's goals



The team will report their findings on December 2, 2008 at the Materials Research Society's annual meeting in Boston. A paper on their findings has already been submitted and accepted for future publication in Applied Physics Letters.



The MIT Deshpande Center specifically selected this project for what's called an "i-team" study. This evaluates its business potential. The team found significant benefits in both manufacturing and electrical power delivery. These applied to both on-the-grid and off-the-grid clean power generation.





Interesting cost benefits



One of the biggest cost savings from this design was the extremely thin-film layers of silicon used, approximately 1% of the silicon used today.



Said Peter Bermel, a postdoctoral researcher in MIT's Research Laboratory of Electronics who has been working on the project, this project, along with other research work going on now in solar cells, has the potential to get costs down "so that it becomes competitive with grid electricity." While no single project is likely to achieve that goal, this work is "the kind of science that needs to be explored in order to achieve that [goal]."





Research team



The team was led by Lionel Kimerling, along with Peter Bermel and Lirong Zeng. Additional work was done by John Joannopoulos, Bernard A. Alamariu, Kurt A. Broderick, Jifeng Liu; Ching-yin Hong, Yasha Yi and Xiaoman Duan. Funding was provided by the Thomas Lord Chair in Materials Science and Engineering, the MIT-MIST Initiative, the Materials Research Science and Engineering Center Program of the NSF and the Army Research Office through the Institute for Soldier Nanotechnologies.

Read more on MIT's press release.



Read on next page... Author's opinion...

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Author's Opinion



This new research comes on the heels of additional research from Ohio State University last month. It was reported that Ohio State also sought to increase the amount of time sunlight can be converted into electricity. Though their approach was different, the result was the same: far greater efficiency than has previously been possible. Ohio State showed through initial lab testing an almost 100% efficiency.



It seems very clear that solar cell technology is advancing at a phenomenal rate. I would suggest something - rather than spending a fortune on alternative combustible fuel sources (Richard Branson, billionaire Virgin airline mogul, has said that he's investing about $3 billion in ethanol plants in the United States), why not give these scientists a dozen years or so (and a billion dollars or so) to work out the kinks and find ways of turning our energy needs completely around by going 100% solar and 100% green?





Real power



The average 1,200 square foot home's roof area is about 120 square meters. Using technology like this at only 50% efficiency (instead of 68% - so it's cheaper to mass produce), each home would be capable of generating a maximum output of 60 kwH of continuous output during daylight hours using no backyard space. And whereas modern homes require approximately 5 kwH continuous on average to power things like refrigerators, air conditioners, etc., most homes would be able to make due with far less using batteries.



About 1,000 watts per square meter of energy strikes the earth's surface from sunlight. All modern homes have roofs which are more than sufficient area-wise to power our own homes plus a couple battery powered vehicles. It would be of extreme benefit to the environment to develop ways of powering our homes independently and off-the-grid.



No longer would we need dangerous wires running from a central power source to all of our homes. No more power outages in bad weather. Just inexpensive, readily produced solar panels built out of silicon (sand), which is one of the most plentiful elements on the Earth, coupled to some of the silicon-based battery technologies which TG Daily also recently reported on.



This solution built around silicon sounds most desirable, both for our environment and for our real needs.