For Rooftop Solar, Is Facing West Best?

It was a small sample – just 50 homes in all – in one city during one summer, so how far it can be extrapolated is hard to say. But new research out of Austin, Texas, suggests that west-facing rooftop solar can do better than south-facing systems at cutting peak summer demand.

Overall, the study by PSR Analytics for Pecan Street Research Institute found that residential solar, which has been under attack by utilities in the past year, can benefit those very utilities by taking a substantial bite out of the peak power demand they need to provide.

rooftop solar net metering

image via U.S. Department of Energy

“Counting only the electricity generated by a rooftop solar system that is actually used in the home (and therefore not counting electricity that was sent to the grid because it could not be used in the home),” Pecan Street said, “homes averaged a 58 percent peak demand reduction for electricity from the grid.” That’s a benefit that solar advocates have long cited.

But the upside to orienting the panels to face west – that’s an interesting development.

“South-facing solar systems cut peak demand from the grid by 54%,” Pecan Street said, “while west-facing systems reduced their homes’ peak demand from the grid by 65%.”

The general approach (in the northern hemisphere) has always been to try to orient panels facing south, in order to be able generate energy throughout the day. But peak summer demand comes in the afternoon and into the early evening (the Austin study used 3 p.m. to 7 p.m.) – so when you think about it, it could make sense to give up some morning generation in order to maximize peak-period generation.

That’s exactly what the Austin study found. “During summer peak demand hours (3-7 pm) … west-facing systems produced 49 percent more electricity during those hours than did south-facing systems.”

Given, that, Pecan Street said, “utilities that offer residential rooftop solar rebates may want to extend rebate eligibility to west-facing systems and even offer higher rebate levels than is provided to south-facing systems.”

According to Pecan Street, 50 single-family homes were analyzed in the report, randomly selected from 175 homes with rooftop solar PV participating in a research trial. Roughly half (24) the homes studied had south-facing solar arrays, 14 were west-facing arrays, and 14 were a combination of west- and south-facing arrays.

Pete Danko is a writer and editor based in Portland, Oregon. His work has appeared in Breaking Energy, National Geographic's Energy Blog, The New York Times, San Francisco Chronicle and elsewhere.

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