Toward The Sunset: California Solar Industry Eyes West-Facing Roofs

There's a whole lot of west-facing roof space that could be covered in solar panels here. | Photo: Duncan Rawlinson/Flickr/Creative Commons License

Rooftop solar has changed the way we use electrical power in California -- and that's changing the way regulators are thinking about rooftop solar.

Ever-more widespread installation of solar panels on roofs has put a serious dent in what the state's traditional mid-afternoon peak in energy demand, as mid-day is when solar panels in their customary south-facing orientation put out the most power.

But every day the sun heads west and the output from those south-facing panels drops, and that's caused a new dinnertime energy demand peak, running from about 6-9:00 p.m. And that's why the California Energy Commission is suggesting a literal shift in perspective -- 90 degrees to the right.

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Facing rooftop solar panels southward makes sense for the individual homeowner: sunlight is stronger in mid-day and the raw amount of power panels can produce is higher if they're facing that southerly mid-day sun.

That's discouraged many property owners from putting solar panels on roofs with a westward slope. But the output from all those south-facing panels starts dropping in mid-afternoon. Take a look at this graph, taken from the California Independent System Operator's website on Thursday:

Power supply and demand for January 15, 2015 | Image: California Independent System Operator

Those lower, blue and purple lines show a pronounced dip in energy demand in mid-day, which is at least partly due to output from the state's many megawatts of rooftop solar panels. Once those solar panels' output started to flag, around 4:00 pm ("hour 16" at the bottom of the graph), net demand starts to spike.

That's a steep late-afternoon and evening peak to deal with, and it's an obstacle to greater reliance on rooftop solar as a way of filling our demand for electrical power. In August, the California Energy Commission announced new additional incentives for installing solar panels on west-facing rooftops. The incentives can mean as much as $500 more in a property owner's pocket than would be the case if that same property owner installed solar panels aimed south. That probably won't make up for the fact that west facing panels wouldn't generate as much total power as those facing south, but it might just make the difference for properties with no suitable south-facing roofs.

And while west-facing panels wouldn't do much good after about 4:00 p.m. this time of year, they could continue producing power as late as 9:00 p.m. on a summer night, at a time when many Californians are finally turning their air conditioning off for the day.

California Energy Commissioner David Hochschild told the trade publication Solar Industry this week that despite opposition to west-facing panels found among regulators in other states, Californians seem keen on the idea.

"The peak has shifted over the last few years from the middle of the day to late afternoon," said Hochschild. "[M]ost people know that is the shape of the load in California.... We have no stated opposition."

For ongoing environmental coverage in March 2017 and afterward, please visit our show Earth Focus, or browse Redefine for historic material.
KCET's award-winning environment news project Redefine ran from July 2012 through February 2017.

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