Solar Power News: Sooner or Later, Solar Breaks Out

Solar energy is too good, too vast, not to become an important energy player eventually. Orbital solar is best, but terrestrial solar will be important once the storage and cost problems are solved. A hybrid solar roofing "shingle" that collects both light and heat energy from the sun, might make a difference.

The broad concept of building a solar panel that is tough enough to act as a roof panel yet sensitive enough to capture as much of the sun's energy as possible is likely feasible, says David Ginger, an associate professor of chemistry at the University of Washington in Seattle. "Of course, putting all these ideas into the same package in a cost-effective manner is often more challenging than pitching the idea on paper, which is why you want clever engineers trying out new designs and then testing them in real-world environments," he adds.


And although this idea of "building-integrated photovoltaics" (BIPV) is not new, the Columbia-Weidlinger multilayered hybrid design is different from anything currently available to builders. SolarWorld AG in Germany, for example, sells a technology it calls Energyroof, which consists of panels covered with solar laminates that generate electricity but does not include a layer of thermoelectric material.


In October, The Dow Chemical Company announced its Powerhouse Solar Shingle, which the company says can be integrated into rooftops with standard asphalt shingle materials. These solar shingles, which feature thin-film copper indium gallium selenide (CIGS) photovoltaic cells, are expected to be available in limited quantities by mid-2010 and projected to be more widely available in 2011. In 2007, the DOE had given Dow $20 million in funding to develop building-integrated solar arrays for the residential and commercial markets. _SciAm

Solar thermal power holds more promise for large scale utility power generation, because heat can be more easily and cheaply stored than electricity. One interesting form of solar thermal uses the Stirling heat engine, which can run on relatively low levels of heat differential.

Stirling engines are significantly more efficient at converting sunlight into energy than most photovoltaic panels or concentrating solar power plants, whether parabolic trough or tower designs. The test units have reached 31 percent efficiency, compared to 16 percent for parabolic troughs and about 14-18 percent for PV panels in use today (though newer designs not yet on the market range from 24 to as high as 41 percent). _SciAm

It is easy to imagine a hybrid solar thermal plant which uses a tower to generate steam hot enough for combined cycle (gas turbine plus steam turbine) operation. The exhaust water from the steam turbine could drive a Stirling engine. So you have three cascading heat engines operating simultaneously. Then, after dark, stored heat can drive the Stirling engine well into the night to cover maximum peak times. The idea is to extract as much energy -- at the right times -- as possible.

The issue of heat storage is a different topic, but it is likely that heat storage will be more efficient than electrical storage for at least another 1 or 2 decades.