A new study from Austin’s Pecan Street Research Institute finds that residential solar PV panels oriented to the west may have more benefits for homeowners — at least in the summer and in Austin, Texas. That research flies in the face of conventional wisdom that PV panels should face south where the amount of sunlight that can hit them is maximized.
The main reason why is that solar panels facing west in Austin can reduce peak electric generation demand on the grid during the summer. By facing the solar panels to west, they can harvest more afternoon and evening light, when people are using the most electricity in their homes. Pecan Street defined summertime peak demand in Austin between the hours of 3 p.m. and 7 p.m. when the afternoon sun is most likely to heat houses and people have returned from work and school.
The study looked at 50 solar homes — with the data normalized for 5.5. kilowatt arrays — in Austin between the period of June 1, 2013 and Aug. 31, 2013 — out of 175 participating homes. Of that, the study examined 24 homes with south-facing arrays, 14 with west-facing arrays and another 14 with a combination of south and west-facing solar panels (52 homes in all). It found that homes with west-facing solar arrays reduced their homes’ peak demand by 65 percent, whereas homes with south-facing solar power arrays reduced their peak demand use by 54 percent.
The report also found that west-facing solar systems produced more solar electricity than south-facing systems on both an actual and a normalized basis, according to the report. “During summer peak demand hours (3 to 7 p.m.), the gap was even more pronounced: west-facing systems produced 49 percent more electricity during those hours than did south-facing systems,” the report stated.
“Residential solar systems have understandably raised concerns about their impact on electric reliability,” said the report’s lead author, Pecan Street CEO Brewster McCracken. “These findings suggest that rooftop solar systems can produce large summer peak reductions that benefit utilities and customers alike without requiring customers to change their behavior or sacrifice comfort.”
In all, during peak hours homes in the sample used, 80 percent of the solar power their PV arrays generated, and sent the excess generation — about 20 percent of their systems’ capacities back to the grid. The numbers of personal use were higher for homes with west facing systems, with 84 percent of energy used in the home and 16 percent going on the grid. In south-facing homes, according to the report, 78 percent of the power generated was used with 22 percent going on the grid.
Overall homes in the study produced 32 percent of their energy during peak demand. They used 64 percent of the electricity their arrays produced during daylight hours. The remainder — 36 percent — went back to the grid. Despite that, the arrays produced 36 percent of the electricity that the homes used over the course of a full 24-hour day.
What the study suggests is that in places where utilities have time-of-use energy pricing systems, west-facing systems could produce more value for homeowners. And utilities may want to consider creating solar incentives or rebates that encourage west-facing solar arrays. However, the study is limited in scope and region and what works in Austin may not be as appropriate in other parts of the country or world. The study also only looked at the summer months so it’s impossible to tell from the study whether or not it holds true for an entire year or the lifespan of an array.
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