Newspaper article International New York Times

Getting Direction Right on Home Solar Panels ; Southward Direction Maximizes Total Output but Misses Peak Period

Newspaper article International New York Times

Getting Direction Right on Home Solar Panels ; Southward Direction Maximizes Total Output but Misses Peak Period

Article excerpt

The conventional southward direction maximizes total output but is not so helpful when demand reaches a peak.Then, westward is better.

For years, homeowners who bought solar panels were advised to mount them on the roof facing south. That captures the most solar energy over the course of the day, which benefits the homeowner, but does so at hours that are not so helpful for the utility and the grid as a whole.

Mount them to catch the sunlight from the west in the afternoon, and the panels' production over all would fall, but it would come at hours when the electricity is more valuable.

But that idea has been slow to take hold. A new study of 110,000 California houses with rooftop solar systems confirmed that most of the panels were pointed south because most of the panel owners were paid by the number of kilowatt-hours the panels produced. Pointing them southward maximizes production over all, but peak production comes at midday, not in late afternoon, when it would be more helpful.

In late afternoon, homeowners are more likely to watch TV, turn on the lights or run the dishwasher. Electricity prices are higher at that period of peak demand. "The predominance of south-facing panels may reflect a severe misalignment in energy supply and demand," said the authors of the study, Barry Fischer and Ben Harack. They work for Opower, a company that provides software that electric companies can use to manage customer relationships.

Houses with solar systems consume less than half as much utility- delivered electricity as ordinary houses, the study found. But from about 4 p.m. through the night, they consume more, and they add to the system's peak demand, which comes around 5 p.m.

Pointing panels to the west means that in the hour beginning at 5 p.m., they produce 55 percent of their peak output. So a 10- kilowatt system would make 5. …

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