November 2008

Solar tubes have advantage over panels

This solar solution is tubular, man!

A California company's sun-based electricity producing technology uses a novel thin film coating and does not use silicon. The company, Solyndra, is a startup with a pile of money in Fremont that has developed a novel type of solar panel that is cheaper to install and produces more power than conventional panels.

MIT's Technology Review reported unlike conventional solar panels, which are made of flat solar cells, the new panels comprise rows of cylindrical solar cells made of a thin film of semiconductor material. The material is made of copper, indium, gallium, and selenium. To make the cells, the company deposits the semiconductor material on a glass tube. That is then encapsulated within another glass tube with electrical connections that resemble those on fluorescent light bulbs.

The new shape allows the system to absorb more light over the course of a day than conventional solar panels do, and therefore generate more power. What is more, arrays of these tubes offer less wind resistance than con- ventional flat solar panels, which makes them easier and cheaper to mount on roofs.

The cylindrical solar-cell design has a number of advantages for generating solar power on the flat rooftops of big-box stores, warehouses, and other commercial buildings.

Ordinary flat solar panels can catch the wind, so one must bolt or weigh them down with ballast. Solyndra's panels consist of rows of cylindrical tubes with spaces between them that allow the wind to pass through, decreasing wind loads and making it unnecessary to bolt or weigh down the panels, even with winds up to 130 miles per hour.

The cylindrical design also allows the solar panels to absorb more light. Solar panels work best when light hits them directly, such as when the sun is directly overhead.

To get more power from solar panels, we mount them on tracking systems that keep each panel pointed at the sun all day. However, these tracking systems do not work in high winds, add cost, and take up space that other solar panels could occupy.

The cylindrical solar cells provide another way to increase the power from a solar panel. At any point in the day, some part of the curved surface is facing the sun more or less directly, and therefore absorbing a large share of that light.

The company said within a few years, it plans to produce solar systems that generate electricity competitive with the average cost of electricity in the U.S., which is 10 cents per kilowatt-hour.