Will ‘Solar Trees’ Sprout in Parking Lots?

Part of the fine print in solar power systems is that whatever wattage number is quoted, it is usually “peak watts,’’ or the amount of electricity that the panel would deliver when the sun is directly overhead. For the rest of the daylight hours, the output is lower; a graph showing minute-by-minute production resembles a sharp mountain peak.

One way to do better is to mount the panel on a metal backbone and let it tilt over the course of the day, keeping itself pointed towards the sun from sunrise to sunset. This is called a single-axis tracker. Better yet is a two-axis tracker, which also adjusts the angle to compensate for how high the sun is in the sky. Then the graph showing output would resemble a plateau. But all of this adds cost.

Envision Solar, a San Diego company, has found a niche in the solar world by building shaded parking areas with solar panels fixed to the roofs. The panels do not track the sun, but they are angled to take advantage of it: they are usually tilted to the south.

But parking lot designers seldom take solar orientation into account when painting the stripes for the parking spaces; the company has sometimes had to realign the parking stalls so that the roofs will have good solar orientation, with the rows of cars running east-west. In the ideal configuration, said Robert Noble, an architect who founded the firm and is its chief executive, the sun rises in the windshield and sets in the back window, or vice versa.

Now Envision is trying out another idea. On Wednesday, it will announce that with financing from the state of Pennsylvania, it is trying out a “solar tree” mounted on a gimbal, a mechanical device with rings mounted on axes at right angles to each other.

It can track both east to west and north to south and is intended for parking lots. It does not provide shade as reliably, but it does produce about 20 percent more electricity than a fixed panel, turning the peak into more of a plateau. In the video animation above, the patterns on the panels look a bit like sunflowers.

Mr. Noble calls it “solar forestation.”

The company is pairing the solar tree with batteries built by Axion of New Castle, Pa., so that the installation can deliver current after sunset. The two technologies, solar tracking and battery storage, are independent of each other, however.

Much depends on how much maintenance the tracking system will require, but it could make many of today’s rooftop solar arrays obsolete by delivering more electricity from each panel, Mr. Noble said.

But covered parking has other benefits, some of which would be preserved by the solar trees. They require electric cables laid in trenches, affording an opportunity to set up charging stations for electric vehicles or plug-in hybrids, he pointed out. And if a driver can charge up at work as well as at home, the daily range of a car may be doubled, he said.

Energy from the panels will flow back into the power grid, and if charging stations are installed, they will draw energy from the grid. That way electric cars can charge when it is cloudy or dark.

What is more, Mr. Noble said, “you can charge more for shaded parking.”'

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