Solar Industry Gets Aid to Fight Shade

By DON CLARKJune 30, 2008; Page B6
Shade is a perennial problem for the solar-power industry, but a Silicon Valley chip maker thinks it can help.
National Semiconductor Corp. on Monday plans to announce technology that is designed to sharply reduce the impact of partial shading on solar panels, which generate electricity from sunlight.
National Semiconductor
National Semiconductor says these devices recoup power lost when solar panels are partially shaded.
The technology, dubbed SolarMagic, is being tested by REgrid Power Inc., a company in Campbell, Calif., that installs solar panels. Tom McCalmont, REgrid's chief executive officer, estimates SolarMagic can recoup as much as 40% of the power that otherwise would be lost to partial shading. "We've seen a really dramatic difference," he said.
Partial shading -- often caused by trees, nearby buildings or other obstacles -- has a pronounced impact because of the way solar panels are arrayed. A string of panels is typically attached to a device called an inverter that converts the direct current the panels generate into the alternating current used by appliances in the home and required to return power to the utility grid, said Mark Culpepper, vice president of enterprise solutions at SunEdison LLC, a solar-energy-services provider based in Beltsville, Md.
Inverters typically require a minimum threshold of voltage to operate. Partial shade on just one panel of a string of them can bring their combined output below that minimum threshold. "It can effectively knock out an entire string of panels," Mr. Culpepper said.
National -- a Santa Clara, Calif., company that makes chips that manage power in cellphones and other products -- is developing small modules that attach to each solar panel and compensate for variations in voltage caused when shade or dirt block light from hitting parts of panels. The company isn't disclosing many details about how the technology works.
Brian Halla, National's chief executive, said he expects the modules to cost about 10% of the price of a solar panel. He expects to begin selling the modules in early 2009, assuming they pass tests to certify they are safe to use with other electrical products.
National isn't the only one trying to attack the partial-shading problem. Some companies are developing "microinverters," which perform electrical conversions for each solar panel and thereby avoid the problem of one shaded panel disrupting the output of others.
But REgrid's Mr. McCalmont said microinverters contain circuitry that may be impacted by the harsh environment of a sunny rooftop. He said he believes National's technology will be more reliable.
National is one of many longtime chip makers that are diversifying into solar-power initiatives. Mr. Halla estimated that the SolarMagic product line could eventually grow to account for 25% of his company's sales. "It is the single most important and highest-prioritized initiative in the company today," he said.
Write to Don Clark at don.clark@wsj.com