New solar cell efficiency

In a recent article in IEEE Spectrum, there is an announcement of a new record efficiency for single-junction solar cells: Solar Cell Breaks Efficiency Record.

The new design uses a thin layer of single-crystal gallium arsenide and a more reflective metal backing to increase the efficiency to 28.2% (the old record was 26.1%).  More interestingly, they claim that they’ll be able to produce modules at the same price per watt as much lower efficiency CdTe cells.  If true, that is a good thing, since the same wattage module would be about half the size, so total installed cost would be much less.

The high cost of GaAs comes from the cost of materials and the need for very high purity. They use a very thin film of GaAs (1 micron thick) which reduces their material costs considerably. Of course, they aren’t in production yet, and lab scientists’ beliefs about manufacturing and sales prices are often total fantasies, so I wouldn’t hold my breath waiting for low-cost, high-efficiency solar panels.

The installed price per watt of solar panels has not gone down as dramatically as the solar industry has claimed it would for the past 20 years, nor has the cost of electricity soared. One believable claim (at http://www.txchnologist.com/2011/declining-cost-per-watt-solar, with the original source being http://openpv.nrel.gov/) is that the installed cost per watt has dropped from $10.87 in 1998 to $7.16 in 2010 ($8.26/watt in California).  With morning fog, overcast days, and fixed-orientation panels, the local multiplier is about 5 hours per day average, so one watt at the panel is about 1.8kwH per year.  At 12¢ per kwH, payback periods are over 37 years, even if no time value is given to money.  If I’m interested in increasing my energy efficiency, I’m still better off investing in insulation, timers for fans, and high-efficiency lighting than in putting solar cells on my house.  I’m beginning to run out of such investments to make though.

Of course, that $7.16/watt or $8.26/watt figure is misleading, since it averages both small home solar systems and huge industrial ones.  The huge installations cost much less per watt than the small ones, so the price for home solar is more like $11 a watt (according to the OpenPV project), and payback periods are longer than the life of the installation (probably about 40 years).  Of course, if our government took the trillions of dollars they spend on wars for oil and invested it instead in solar panels and other non-fossil-fuel energy sources, I’d be able to afford solar panels.

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