Imagine if the world had a renewable source of energy with a zero carbon footprint that is predicted to last for about four billion years? Sounds good? We’ve got it. It rises in the east and sets in the west, inspires lovers and the writers of the last scene of cowboy movies, and in one second puts out far more energy than the planet will ever need for its entire existence.
Solar power generates a lot of talk. Many people view it as the savior of the planet, many see it as an expensive, inefficient waste of time. Most people fall somewhere in between. In any case, solar power technology continues to march forward in the form of photovoltaics (PV), the technology that changes solar radiation into electricity using certain semiconductors that exhibit something called “the photovoltaic effect.” By arraying a number of solar panels covered with cells of photovoltaic material (which includes monocrystalline silicon, polycrystalline silicon, amorphous silicon, cadmium telluride and copper indium selenide/sulfide, if you’re keeping track) in a sunny spot, you can generate electricity. If you have a lot of solar panels, you can generate a lot of electricity. The problem with solar panels, however, is that they’re very inefficient. Solar panel efficiency is measured by an “energy conversion ratio” – how much energy comes out in relation to how much goes in. A “acceptable” energy conversion ratio for most solar panels on the market today is 12 to 18 percent, depending on the properties of the materials used for the solar cells. Using the very common amorphous silicon-based cells, efficiency can be as low as six percent.
Yeah. You read that right. Which is why you need so many solar panels to generate even a moderate amount of electricity.
As a result, the big research and development work being done in the solar industry right now is focused on improving the efficiency of solar panel materials (and, more importantly, making those efficiencies feasible and affordable for commercial markets). The current commercial marketplace leader in solar panel energy conversion rates is a company called SunPower, based in San Jose, California. SunPower has consistently demonstrated efficiency rates above 24 percent, a near- record for the commercial solar panel industry. Sharp owns the actual record for the highest efficiencies with traditional solar panel cells manufactured with a technology called “triple junction manufacturing.” In the lab, Sharp managed to attain a whopping (relatively speaking) 35.8 percent efficiency ratio.
Labs, of course, are where the exciting work is taking place. Scientists are determining ways to boost efficiency by concentrating the light – doubling and tripling the layers of solar cells. Efficiencies of 42 percent were reported by scientists at the University of Delaware working in conjunction with DuPont. The effect was achieved with so-called “concentrator systems” that require fewer cells to produce the same energy as conventional solar cells. As a result, more of them can be fit onto a panel, thus increasing the energy output without requiring more desert real estate.
The problem with the work being done in labs, of course, is that it’s generally not feasible or affordable for commercial use, though that may change soon if the work of a company called Spectrolab, an R&D subsidiary of Boeing, is as far along as their press releases claim they are. Spectrolab is poised to make mass production of high-performance solar cells feasible with the announcement of its C3MJ+ solar cells: the company is claiming an average conversion efficiency of 39.2 percent, and that the cells are ready for their commercial market close-up. In fact, the company has shown that its high-efficiency, multi-junction concentrator solar cells are capable of achieving energy conversion ratios of up to 41.6 percent in the lab, a current global record for solar cell efficiency. (Previous to that, the record was held by researchers at the Fraunhofer Institute for Solar Energy Systems in Germany, where researchers reached 41.1 percent efficiency.)
To achieve these kinds of efficiencies, multiple-junction solar cells made of materials with sexy names like “gallium indium phosphide” or “gallium indium arsenide on a germanium substrate” actually concentrate the sunlight by a factor of over 450. Exciting, to be sure, but it’s the commercial implications that are most interesting. Previous to the work of Spectrolab and others, energy conversion ratios above 30 percent achieved with high-efficiency cells were not very economically feasible. According to GizMag, 30 percent efficient multijunction cell based on newer, more experimental materials such as gallium arsenide or indium selenide and produced in labs in very low volumes cost about a hundred times more than mass-produced solar cell material that achieves eight percent efficiency. Despite costing a hundred times more, the newer materials are only four times more efficient.
Not exactly numbers to excite venture capitalists to trip over themselves to give you money.
These newer multijunction solar cells built by Spectrolab and others are different, however. They are far more efficient because they capture energy from more colors of the spectrum than “old-fashioned” silicon cells. Silicon cells typically convert about 15 percent of sunlight to energy. The concentrator cells Spectrolab actually sells (not just messes about with in the lab) have an average conversion efficiency of 35 percent, and the company maintains that its target is 45 percent in the near future, bolstered by its recent world record of 41.6 percent efficiency (a record that was confirmed by the U.S. Department of Energy’s National Renewable Energy Laboratory).
“Given the new cells’ close similarity to our existing production cells, we believe that our current C3MJ customers will be able to easily upgrade for more efficiency,” said Russ Jones, Spectrolab director of CPV Business Development.
Spectrolab, whose products thus far are primarily used in space (it produces the solar cells for about 60 percent of the satellites currently orbiting the earth, and all the solar cells used to generate power on the International Space Station), hopes that with the introduction of its new high-efficiency solar cells to the marketplace, it will be poised to claim the same mastery of the earth-bound solar cell industry as it does with the space-based one. The company’s plans are ambitious: it expects to achieve an average 40 percent efficiency in its production of terrestrial solar cells by the end of this year.
Spectrolab, of course, warns customers in advance that their system costs more. But, says the company, replacing a traditional silicon-based solar panel with their concentrator system can provide more than twice the electricity over the course of the panels’ useful lives. Said Spectrolab, with worldwide energy demand expected to double over the next 20 years, their new system is “an elegant way to get the cost of electricity down in widespread application — and help utility companies grow or supplement their production with affordable green energy.”
The high-efficiency solar cells could certainly solve some dirty-energy problems. “If you populated a chunk of California desert just 150 kilometers square (93 miles by 93 miles) with 35-kilowatt solar dishes using…high-efficiency concentrator solar cells,” said Jeff Peacock¸ a VP at Spectrolab Photovoltaic Products, “you’d generate about four million gigawatt hours annually.”
That’s about as much energy as the entire United States used last year.
To make the newer cells affordable, of course, companies needs to streamline their manufacturing processes and increase automation. (Right now, these multi-junction cells are the Gucci handbags of the solar cell business.) “Automation is part of our work under the Solar America Initiative, and it’s part of our capitalization plan,” said Jim Hanley, director of solar panel operations for Spectrolab. “We’re borrowing and adapting ideas from our space-cell production for terrestrial-cell manufacturing; and by expanding our robotics into welding, testing, piece handling and packaging, we expect…to be making 200,000 of these pieces every week. In several years more, it could be two million. And we’ll be reapplying everything we learn about cost reduction to space–solar cell manufacturing.”
Essentially, the company believes that by modifying its existing space-based solar cell production process just a little, it can mass-produce the new multi-junction cells, bringing the costs way down and making them feasible for the commercial solar panel marketplace.
In the meantime, companies and organizations trying to push solar cell efficiency ratios out even further are confident that the percentages will just keep creeping upwards. “Over the past decade, Spectrolab’s efforts developing terrestrial solar cell efficiency have achieved an average improvement of approximately one percentage point per year, and we expect to continue that pace,” said Spectrolab president David Lillington.
If that happens, fairly soon, vocal critics of solar power won’t have much to talk about anymore.