is a well-funded solar startup that has been tight-lipped about its technology and progress. The firm is releasing a few technological tidbits in a paper to be presented at the PVSC37 conference this week in Seattle
Chris Norris, the CEO of Alta, a gallium arsenide (GaAs) thin film solar firm, has said that their goal is to "compete with fossil fuels without government subsidies" and get to a levelized cost of energy of $0.06 to $0.07 per kilowatt-hour. Norris said that the firm has received $120 million and he thinks they're "halfway there" in terms of the amount of funding raised. Investors include August Capital, Kleiner Perkins Caufield and Byers, Crosslink Capital, DAG Ventures, NEA, Presidio Ventures, Technology Partners, Dow Chemical, AIMCo, Good Energies, Energy Technology Ventures, and Constellation Energy.
Norris said that the single crystalline, direct bandgap structure of GaAs, "a perfect crystal," distinguishes its technology from the CIGS players.
When the scientists at Alta Devices began seeing their solar devices achieve efficiency results beyond what was previously thought possible, they realized that something scientifically important was going on. Their conclusion: a good solar cell also emits light, and collecting that light increases cell performance.
Previously, the efficiency of a solar device was understood to be based in part on the amount of external light that could be captured and retained, but this understanding didn’t account for the necessity to maximize the number of photons being generated within the device itself in order to achieve even higher efficiencies.
Alta will disclose details of how it achieved record cell efficiencies of 27.6 percent late last year, as well as its best result to date of 28.2 percent; both results have been verified by NREL. The theoretical maximum solar cell efficiency limit for a single junction device has been shown to be 33.5 percent (called the “Shockley-Queisser Limit”), but efforts to attain this efficiency have been slow in coming.
“Up until now it was understood that to increase the current from our best solar materials, we had to find ways to get the material to absorb more light,” said Alta co-founder Eli Yablonovitch of UCB. “But, the voltage is a different story. It was not recognized that to maximize the voltage, we needed the material to generate more photons inside the solar cell. Counter-intuitively, efficient light emission is the key for these high efficiencies.”
The Alta paper being presented at the PVSC37 conference is entitled “27.6 percent Conversion Efficiency, A New Record For Single-Junction Solar Cells Under 1 Sun Illumination." The abstract is here. Prof. Yablonovitch’s paper is “The Physics Required to Approach the Shockley-Queisser Limit." The abstract is here. Harry Atwater of Cal Tech, Alta co-founder and Director of the Energy Frontier Research Center on Light-Matter Interactions, will give a plenary talk in this conference entitled “Paths to High Efficiency Low Cost Photovoltaics." The abstract is here.
As GTM Research Senior Analyst Shyam Mehta suggested in his recent piece of solar analysis:
After manufacturing cost, efficiency is perhaps the most closely examined and easy available competitive metric. Module conversion efficiency is inversely proportional to area-related balance-of-system costs, such as land, substructure, racks, labor, and cables.
SunPower has been the heavyweight champion of the world when it comes to commercialized cell and module efficiencies for the last half-decade -- and by a significant measure. The company's back-contact cell design, in commercial production since 2005, moves the metal contacts to the back of the wafer, maximizes the working cell area, and eliminates redundant wires. SunPower has been able to achieve consistent improvements in efficiency with each successive generation of commercialized cells, and this has translated to gains in the module arena as well. The firm's Gen 3 cells have efficiencies in excess of 23 percent.
(NASDAQ: SPWRA, SPWRB) just announced their newest solar panels with total area efficiencies of more than 20 percent. The 96-cell solar panels use SunPower's 22.4 percent efficient cells and boast a positive power tolerance rating.
SunPower is likely to be the efficiency leader when it comes to high-volume PV cells and modules for the foreseeable future. The problem, as this article by Michael Kanellos points out, is that 24 percent is awfully close to the realistic ceiling, meaning there may not be much further to go from there.
Note that Alta's results so far are for hero cells. Can Alta produce commercial product at their efficiency and cost goals?
Alta's CEO emphasized that their first product is still two years from commercial shipment and that they remain "agnostic" about whether the end-product is a cell, a flexible module, or a rigid glass module. The target cost remains $0.50 per watt and the the CEO sees that as achievable because "the lever that we have on our side is energy density."
The epitaxial lift-off technique pioneered by Eli Yablonovitch allows Alta to produce layers of GaAs that are flexible and only one micron in thickness. Norris cited Mylar films, used in kids' balloons, as an industry that regularly handles films that thin. Additionally, the process doesn't consume a lot of materials.
But there remain a lot of questions to be answered about Alta. Are they building cells or modules? Are they trying to license the technology a la Innovalight? Can the technology and material requirements scale to hundreds of megawatts and gigawatts?
Like many renewable energy firms, Alta aims to be competitive with fossil fuels in a non-subsidized environment. That's a noble goal, but one that's exceedingly difficult to realize -- no solar company, not even First Solar, has yet hit that milestone.