Friday, July 23, 2010

Will ‘solar trees’ sprout in parking lots?

July 14, 2010, 7:27 am

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. … 

Will ‘Solar Trees’ Sprout in Parking Lots?

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