SolFocus will manufacture solar systems at $2 per watt when it opens its first concentrator plant next year; and he says gigawatt-scale production will cut the cost per watt to just 50 cents. The second generation should cut costs further, says Conley, to as low as 32 cents per watt.
Solfocus uses quarter-sized mirrors that focus sunlight on photovoltaic "dots" just one millimeter square.
SolFocus' design, for example, uses one-thousandth as much semiconductor material per watt produced as a conventional silicon photovoltaic cell. The technology uses compound photovoltaics such as germanium and gallium arsenide, originally designed for use in satellites, which can capture up to 40 percent of the solar energy hitting them -- more than double the efficiency of high-end silicon cells.
But the bulk of the materials reduction comes from the concentrator, which Conley says resembles the headlight in most modern cars. "Put the cell where the light bulb is and you have our design," says Conley. Mirrors are the key: a primary mirror that focuses sunlight onto a smaller mirror perched above, which, in turn, focuses the light on the solar cell.
SolFocus' current, first-generation design molds an array of 635 one-square-centimeter primary mirrors into a glass plate. Secondary mirrors attached above them reflect light through holes in the plate onto one-centimeter-square high-efficiency cells below.
A second-generation design squeezes the process into a single glass block: light beaming through the top of the block reflects off primary mirrors shaped into the bottom face, up to secondary mirrors shaped into the top face, and back to one-millimeter-square photovoltaic cells popped into the center of the primary mirrors.