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.
(www.solfocus.com)

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. (www.whitfieldsolar.com)

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. (www.opelinc.com)

Solar Pro Sees Good Year for Buyers

Anyone who has made a living in solar power over 30 years has had to have another kind of power of his own: stay power. After all, it's only been since 1996 that solar photovoltaics (PV) have been a true growth industry averaging 25% growth annually. Before that Wall Street and Main Street lumped solar professionals together with treehuggers and hemp growers by mainstream America.

Since 1978 Larry Slominski, of the San Diego suburb of Ramona, has been one of those solar pioneers with equal parts passion, know-how and vision. His success stems from an engineering background; a stint with the Peace Corps in Micronesia working on "off-grid" village solar systems; National Energy Planner for the Federated States of Micronesia; public utility regulator in Massachusetts; and over 20 years working for solar module manufacturers and system integrators. Today he is an independent solar energy consultant specializing in utility-scale projects and large airport solar applications.

Slominski sees a good year for solar power in 2009.

"The field looks really bright if you're a buyer. It's a complete 180 degree shift from a year or year and a half ago when you couldn't get modules," he said referring to the dearth of silicon cell manufacturing that could not keep up with the demand for solar panels. Now there appears to be an oversupply of silicon and panel prices are dropping, if only for awhile.

Slominski also admits dropping oil prices, although not directly related to PV, have had a softening effect on the urgency to invest in alternative energy. However, the cost of energy worldwide, the polluting effects of conventional energy production, and the related global warming issue still makes solar a solid, long-term solution.

What can we look for within the PV industry?

"Crystalline (panels) has been the heavyweight in the industry for a long time. But the big charge is coming from thin-film on one side and concentrated solar on the other in trying to reduce the cost of solar power. You could see this beginning to happen three to five years ago and these two competing technologies will reduce the use of crystalline panels significantly.

"Concentrated solar (CPV), in its several forms, is just now proving to be on par in cost with conventionally-produced electricity. I think concentrated solar is set to make a good run as witnessed by the recent 70 megawatt installation in Nevada. We're going to see CPV becoming a major producer of power on a utility scale," Slominski foresees.

Leading up to the elections last year, Slominski said all of the candidates spoke to renewable energy so that's a good sign that that issue has gone mainstream. He sees a public and private partnerships for renewable energy advancement.

"As for coal, it's going to be hard not to see that it's an old and outdated way to produce electricity. Coal will continue to be a major component of energy production for the next fifty years but it will continue to get pressure related to the greenhouse gas emissions and gross pollution of the air where plants are located. Clean energy technologies being developed now and over the next generation will simply replace coal, Slominski concluded.