Old solar tech back in limelight

A handful of solar companies are focusing on a venerable technique to harvest more sunlight.

The high price of silicon--the most common material used in solar panels--is prompting engineers to design solar concentrators, devices that squeeze more electricity out of a slice of silicon or other photovoltaic cells.

Concentrators are one of many solar technologies being tested with the hope of bringing down the cost of solar power, which is seeing a surge in demand. Relatively young companies are coming to market with concentrator products of various forms. The products, aimed mainly at the commercial space, are expected to hit the market this year and next, according to company executives.

The idea of tracking the movement of the sun and intensifying sunlight with mirrors has been around for many years. But the rising cost of electricity, coupled with technical advances in making more efficient solar cells, are fueling new approaches to the concept, say experts.

"That area (of concentrators) is enjoying a resurgence, which went into disfavor in favor of flat panels," said Emmanuel M. Sachs, professor of mechanical engineering at the Massachusetts Institute of Technology. "Because there are 35-percent-efficient cells, as opposed to 20-percent-efficient cells, it makes sense to look at concentrators again."

Much of the use of solar concentrators has been with high-efficiency germanium solar cells in space or at large-scale installations, where arrays of panels are lined up in desert areas, for example, said Sachs, who developed technology at MIT now being commercialized by Evergreen Solar.

But now several companies are developing scaled-down concentrators, which can be placed on roofs and serve one building as a supplement to a grid-tied electricity source.

Although technical hurdles remain--notably excessive heat--and new machines are not yet fully proven in the marketplace, analysts said that growing demand for alternative electricity supplies is prompting entrepreneurs to experiment with new twists on the technique.

Price performance
One company, called Practical Instruments, has designed a prototype concentrator solar panel that borrows an idea out of the PC market: standard components.

The Pasadena, Calif.-based firm intends to build concentrators that fit into standard-size, flat solar panels. Its first-generation product, which the company intends to make in volume next year, will use silicon-based solar cells with concentrators placed in tubes that rotate during the day to follow the sun.

Company CEO Brad Hines said the design is meant to fit into the existing solar panel industry's delivery network for commercial buildings and potentially for residential homes.

"Since we install as the same solar panel, we can sell to the existing channel of installers; we don't have to build our own network," Hines said.

The first product from the company will deliver about the same amount of power for a "lot less money," Hines said, declining to offer specific pricing plans. Practical Instruments is seeking to raise a round of venture capital, Hines said.

Prism Solar Technologies, a small company based in Stone Ridge, N.Y., is also designing solar concentrators for on-roof solar panels, but is using completely different techniques.

The company's panels have special optics that use holograms, what CEO Rick Lewandowski calls a "high-tech Jell-O" sandwiched between pieces of glass. The holograms direct light onto a line of silicon cells, keeping the rays from reflecting off the panel's outer glass, to generate more electricity from a single panel.

The hologram approach can cut down on the amount of silicon in a panel by between 25 percent and 85 percent, thereby lowering the overall cost to about $1.5 per watt, Lewandowski said.

The company intends to raise $5.3 million this year to set up a manufacturing facility, with any eye toward delivering its first product within six months. It is also working on a newly designed panel that generates more power.

Lewandowski said that Prism Solar's design, which amplifies the light only slightly, eliminates the heat problems that can stem from highly concentrated sunlight.

"The issue (with concentrators, in general) is thermal issues, which means you need active systems to manage them. We just take the portion of the wavelength we want," he said.

Cranking it up
Still, the lure of more cost-effective electricity is driving many other solar companies to pursue high-magnitude concentrators.

Energy Innovations, for example, has developed a heliostat (a device that follows the sun during the day) for use on flat roofs of commercial buildings. It uses 25 mirrors which reflect light onto a silicon solar cell, a level of light concentration that requires a fan to keep the solar cell from overheating.

Meanwhile, solar start-up SolFocus is developing a concentrator in conjunction with Xerox's Palo Alto Research Center (PARC). Those machines, now in testing, will be placed on a pole that rotates during the course of the day.

Ultimately, engineers at SolFocus and PARC envision using high-efficiency solar cells and magnifying the light 500 times to generate a higher throughput of electricity.

Practical Instruments, too, is pursuing higher magnification after its first product, said CEO Hines. Its second-generation panel, targeted for release in 2008, will be designed to magnify light 1,000 times and concentrate it onto triple-junction Germanium cells, he said.

These cells are far more costly than silicon cells, but the combination of high efficiency and concentrated light can produce the equivalent of three times the electricity output of a traditional solar panel, or about 400 to 450 watts, he said.

"Suddenly, even at a higher cost, 1,000-times (concentration) makes sense when you make that much power," said Hines. "By doing that, we save money and we can put much more power on your roof."