Solar panel efficiency shines

Solar photovoltaic panels are not only getting cheaper, they're getting better.

The big blue panels that power remote homes, civil defense sirens, some street lights and all kinds of consumer electronics, are moving more and more into the mainstream.

Part of that is economics. Solar panels a couple of decades ago cost as much as $10 per peak watt (meaning a 100-watt panel cost $1,000). Today you can pick them up for $3 to $5 a watt. And the price continues to drop.

The site SolarBuzz has some stats on pricing.

The holy grail of solar panels is getting prices down to $1 a watt. A number of systems have promised such pricing soon, but nobody's there yet.

With any panel system, the panels are just part of the bill. There are additional costs for permitting, roof mounting systems, inverters, wiring and contractor expenses. But a whole system can now often be installed for prices in the range of $7 a watt.

And with state and federal tax credits, that number can be cut by 65 percent.

But there's still the issue of how much space it takes to put up significant quantities of solar power.

That's where efficiency comes in.

The most efficient commonly available panels are monocrystalline silicon units, which can convert somewhere between 15 and 24 percent of the energy sunlight into electrical power. Polycrystalline silicon does a little less well, at 14-18 percent. And amorphous silicon gets 6 to 13 percent.

The higher numbers tend to be what they can get under perfect conditions in a laboratory, while the lower numbers are closer to actual field experience.

Understandably, the more efficient units cost more, and for many solar aficionados, a cheaper inefficient array simply takes up too much space for the power it produces.

But in laboratories around the world, scientists are using new compounds and new geometries to develop panels that can turn dramatically more of the solar resource into electricity.

A pair of German researchers, Andreas Bett and Frank Dimroth of the Fraunhofer Institute for Solar Energy Systems ISE, report they have achieved 41.1 percent efficiency with what they call a metamorphic triple-junction solar cell, using gallium indium phosphide, gallium indium arsenide and germanium.

“This special structure makes it possible to optimize the use of almost the entire solar spectrum for energy production,” they say in a press release.

One key to their success is working in three dimensions. They have stacked solar cells 20 layers thick. Another key is concentrating the sun's power using a fresnel lens, so they get more sunlight onto each expensive photovoltaic surface.

The researchers concede that the 40-percent efficiency is a laboratory number. In the field, they're looking at 25 percent or so. They hope to have panels built this way on the market as early as next year (2011).

Theirs is not the first photovoltaic system that has been able to surpass 40 percent in the lab, but many of the others are fairly complex systems that don't lend themselves to being converted for casual rooftop use.

© Jan TenBruggencate 2010