If just one solar panel in a rooftop array falls under shade, the performance of all of the panels typically drops. That's because an array's electrical voltage and current are usually set at just one point: the inverter that changes direct current to alternating current. The settings the inverter can choose are determined by the worst-performing solar panel. National Semiconductor of Santa Clara, CA, has developed power management circuitry that adjusts the voltage on each panel to match its power output. Field tests show that the gadget can reduce losses from unshaded panels by 57 percent.

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