The research is the first of its kind to evaluate the energy production of solar panels oriented in different directions. Pecan Street analyzed 50 homes in the Austin, Texas area. Some had only south-facing panels, others had west-facing panels, and some had both.
South-facing panels produced a 54 percent peak reduction overall, while west-facing solar PV panels produced a 65 percent peak reduction.
“There’s no other residential demand response tool generating 60 percent reductions,” said Brewster McCracken, CEO of Pecan Street. “Those are pretty extraordinary peak reductions.”
When the data was normalized for a 5.5-kilowatt system, the panels turned to the west generated nearly 50 percent more electricity during peak demand hours than did their southern-facing counterparts.
Homes with west-facing systems also produced slightly more electricity, with those panels producing 37 percent of total daily electricity use, compared to 35 percent for the south-facing panels.
During times of peak demand, which is defined as 3 p.m. to 7 p.m. in Texas's ERCOT territory, 84 percent of electricity in west-facing systems was used in the home.
The information could help inform utility rebate programs for rooftop solar panels and demand response programs. Most homes currently have south-facing panels. For the research, Pecan Street paid a premium to participants to induce them to turn their panels westward. If more utilities were to move to dynamic pricing models, where power cost more during days of high peak demand, west-facing panels could potentially be more attractive to certain households with high peak loads.
The next round of research will also include information about the pitch of the roof. Panels on flat roofs tend to have higher rates of electricity generation, but most homes in the U.S. have pitched roofs, as did all of the participants in the first study. Pecan Street will also look beyond Austin in the next stage of the study. McCracken said there are plans to include homes in Colorado, Dallas and potentially California.
You’d think it would be easy: the sun is “up,” and, like leaves and basking reptiles, solar panels should face in that general direction. But most installers of solar panels, especially the ones for homes, follow conventional wisdom handed down from architects, which holds that in the northern hemisphere, windows and solar panels should face south.
This makes intuitive sense since it would seem to maximize the amount of sunlight a panel will get as the sun tracks from one horizon to the other. But it isn’t true, at least according to a single study of homes in Austin, Texas. The Pecan Street Research Institute found that homeowners who aimed their panels toward the west, instead of the south, generated 2% more electricity over the course of a day.
More importantly, those west-facing panels reduced household electricity usage during the times when electricity is most expensive—and power grids are most likely to become overloaded—by 65%, while south-facing panels only reduced usage during those times by 54%. In Texas, as in most places, those “peak times” are from 3pm to 7pm, and correspond with the heat of the day.