Wednesday, April 1, 2009

Concentrating Solar Getting Hotter, Worth Watching

Higher efficiencies, lower cost per watt

It's a good time to be watching concentrating solar technologies. CPV is the natural next step to reducing installed cost per watt for mostly large-scale systems although some makers have residential possibilities.

The most common of the CPV technologies is the parabolic trough system which concentrate solar rays onto a receiver pipe located along the focal line of a trough shaped reflector. Nine such systems are successfully producing power in California's Mohave Desert achieving a daily solar-to-electricity conversion efficiency of 18%. Power towers are another method in which sun-tracking mirrors (heliostats) reflect sun rays to a receiver atop a tall tower. Both systems heat fluid which passes through a heat exchanger to boil water for a steam engine that generates electricity. A third system uses a parabolic dish to focus solar radiation on a receiver mounted at the focal point of the dish. Instead of producing steam, dish systems heat fluid for a Stirling heat engine which produces the electricity.

Three companies use silicon cells with variations of optics, mirrors and trackers to concentrate sunpower.

Solfocus of Mountain View, Ca combines high-efficiency solar cells with advanced optics providing high yields using just 1/1000 of the PV material used in standard PV cells. The Solfocus reflective optic system includes a primary mirror to capture sunlight and a secondary mirror and non-imaging optic to concentrate it at 500 suns onto high efficiency solar cells. The company contends 38%+ efficiency with their cells compared to the 13-19% standard range.

Whitfield Solar of Reading, England says its CPV product competes with flat-plate PV in four ways: lower cost; lower weight; lower embodied energy; and requires lower-tech manufacturing processes. Using Fresnel lenses Whitfield uses just 2.5% of the silicon cells required of conventional panels. The Whitfield CPV unit includes built-in tracking which combines tilt-and-roll of the panel and troughs to find and follow the sun wherever it is installed. The unit can also withstand hail and wind and does not have to "park" flat in high winds. (

Opel International of Shelton, Connecticut makes high and low concentration panels. The Mk-I High Concentration PV Panel uses a dual element refractive concentrator and triple-junction Boeing-Spectrolab solar cells to produce 36.7% efficiency with the same 25-year power output warranty of most flat-plate panels. The Mk-III Concentraing PV Panel is a low-cost panel designed for grid-tied systems in low to medium solar radiance. No cell efficiency is listed on the Mk-III's tech sheet. (


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