Here comes the sun

Talk to anyone involved in photovoltaics (PV) research and you will hear predictions that solar-electric technology is about to turn the corner. Photovoltaics, the direct conversion of sunlight to electricity, is gaining ground as a viable alternate energy source because it's clean, quiet, reliable, and unlimited. First used in the '60s to power satellites, PV's potential became more apparent during the oil embargoes of the '70s when consumers began looking for more control over their energy source. Currently, solar electricity is used to power loads such as lighting and small appliances, and in remote areas where high reliability and low maintenance are prerequisites.

In Dish/PVCC, all sunlight focuses on the entrance of a sphere. The interior cavity wall is lined with sets of solar cells tuned to particular frequency bands in the solar spectrum. Each cell has a specially designed filter on top that lets in only the portion of the solar spectrum that matches the spectral response of the cell beneath.

PV's power comes from solar cells which use semiconductor material to directly convert sunlight into electricity. About 95% of today's solar cells are made from crystalline silicon, the other 5% use newer thin-film technology. A typical crystalline silicon cell is about 4 in. around and 0.010 in. thick and generates 2 A of direct current at 0.5 V in direct sunlight. Of late, silicon cells are about 12 to 14% efficient, while thin-film falls between 7 and 10%. But researchers from the Dept. of Energy's National Renewable Energy

Laboratory believe thin film is the way of the future. It uses significantly less semiconductor material than crystalline silicon and is easier and less expensive to make. While the PV market is growing at about 25 to 30%/year worldwide, solar technology still isn't cheap enough to compete with conventional energy sources. For that, manufacturing costs must go down and efficiency must rise, which is why the PV industry has developed a plan to catch up.

Mapping the Future
The DOE and the U.S. photovoltaic industry, through the National Center for Photovoltaics, have created a plan for domestic PV as far out as 2030. Their PV Roadmap calls out short, medium, and long-range goals as well as barriers to the technology's success.

The goal is to make PV a more significant source of electricity within the next 20 to 30 years. By 2030, the industry hopes PV will provide 10% of U.S. peak generation capacity. To make this projection reality, the Roadmap implores government to level the playing field with other powerproducing technologies via tax credits, manufacturing incentives, and by establishing standards, codes, and certification.

The plan hinges on overcoming a host of technical barriers. Chief among them is the high cost of manufacturing solar-electricpower components. Low-cost, highthroughput manufacturing technologies for high-efficiency thinfilm and crystalline-silicon cells are a must. The industry has established an 18 to 20% conversion efficiency goal with a cost of less than $0.50/W for each module technology. To produce crystalline silicon at these efficiency and cost models, solar-grade silicon must be available at less than $20/kg.