SolarCity says it can make commercial rooftops into better power plants

The country's largest residential rooftop solar installer, SolarCity Corp., announced yesterday that it has a new approach for installing on flat rooftops that could help some commercial buildings boost their solar power by 20 to 50 percent.

The news reflects how dropping prices for solar modules are stimulating a race to alter and improve other parts of the solar system, with ripple effects that could change the economics of the solar business.

It used to be that the module -- the solar cells and the box they come in -- was by far the most expensive part of a solar system. But with those modules having dropped from $3 a watt to 70 cents a watt within two years, solar firms are beginning to try approaches that never before would have penciled out, said MJ Shiao, director of solar research for GTM Research.

SolarCity's subsidiary, Zep Solar, will offer dense arrays of solar panels that will face each other like opened butterfly wings. And those panels will be oriented east-west, instead of south.

Most arrays in the U.S. point south because that orientation allows each panel to turn every last sun ray into electrons. This is an important consideration when solar modules are expensive, Shiao explained.

Now that modules are cheaper, SolarCity will use more of them, said Zep Solar founder Jack West. Each panel may create up to 5 percent less electricity, but there will be 20 to 50 percent more panels on the roof, depending on what weight the roof can handle. Overall power capacity could rise by 20 to 50 percent, West said.

Facing east and west, instead of south, also has a subtle but profound effect on how the panels interact with the power grid.

South-facing panels produce little power in the morning and evening but reach a pinnacle of power production in the middle of the day. Put enough of them together, and they create an oversupply of electricity in the early afternoon that could make it hard for more steady sources of power, like coal or natural gas plants, to justify running. This phenomenon is sometimes called the duck curve.

The east-west duo, by contrast, provides less power at midday and more power in the morning and evening. This coincides with when the grid experiences a bump in need, as people prepare for and wind down from their workday.

In some states, SolarCity and its customers may be paid better rates for the solar power they feed back onto the grid, because utilities need that "shoulder" power more. The first installation will be in Quincy, Mass., in January, West said.

Not every flat-topped edifice will necessarily benefit from the new design.

"This does appear to be real innovation for the commercial sector, but it will not be a one-size-fits-all solution. It will be another 'tool in the shed' for SolarCity to use depending on the individual energy characteristics of a particular site," said Dexter Gauntlett, a solar analyst for Navigant Research.

More consistent output from the solar panels, and without a peak, means that the inverter can be smaller, which further reduces costs and makes the inverter work more efficiently, Shiao said.


Along with its new orientation, SolarCity claims to have made strides in lowering the weight of its components, which makes the installation of more panels feasible.

The commercial market, Shiao said, is "a space where a good idea can catch a lot of steam."

Twitter: @DavidFerris | Email:

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