The power output of solar panels can be boosted by 10 percent just by applying a big transparent sticker to the front. Developed by a small startup called Genie Lens Technologies, the sticker is a polymer film embossed with microstructures that bend incoming sunlight. The result: the active materials in the panels absorb more light, and convert more of it into electricity.

The technology is cheap and could lower the cost per watt of solar power. Also, unlike other technologies developed to improve solar panel performance, this one can be added to panels that have already been installed.

The polymer film does three main things, says Seth Weiss, CEO and cofounder of Genie Lens, based in Englewood, CO. It prevents light from reflecting off the surface of solar panels. It traps light inside the semiconductor materials that absorb light and convert it to electricity. And it redirects incoming light so that rather than passing through the thin semiconductor material, it travels along its surface, increasing the chances it will be absorbed.

Researchers designed the microstructures that accomplish this by using algorithms that model how rays of light behave as they enter the film and encounter various surfaces within the solar panel--the protective glass cover, the semiconductor material, and the back surface of the panel--throughout the day. The key was bending the light the optimal amount, enough that it enters the solar panel at an angle, but not so much of an angle that the light reflects off and is lost. If light does reflect off either the glass or semiconductor surfaces, the film redirects much of it back into the solar panel.

Tests at the National Renewable Energy Laboratory showed that the film increases power output on average between 10 percent and 12.5 percent, with the best improvement under cloudy conditions, when incoming light is diffuse. [Note: The original version of the article cited a range from 4 to 12.5 percent, but this referred to an earlier version of the technology.] Adding the film--either in the factory, which is optimal, or on solar panels already in use--increases the overall cost of solar panels by between 1 percent and 10 percent. But the panels would then produce enough additional electricity to justify the price. What's more, increasing the power output of a solar panel decreases other costs--such as shipping and installation--because fewer solar panels are required at each installation, says Travis Bradford, a solar industry analyst and president of the Prometheus Institute.

Yet the overall benefit depends on how long the polymer film lasts. The cost per kilowatt hour of solar power is figured by estimating the total power output of the solar panel over its 20- to 25-year warranty. If the film is scratched, attracts dust, or becomes discolored after years or decades in the sun, it could actually lower power output over time. "Durability is a big issue," Bradford says. The materials used in solar panels today have been tested over decades, and although Weiss says his company's films will last for 20 years, their durability hasn't been verified.

Meanwhile, many solar panel companies are developing related approaches for increasing the amount of light a solar panel will absorb. For example, Innovalight, based in Sunnyvale, CA, has developed a method for printing silicon nanoparticles that can improve the amount of light conventional crystalline silicon solar panels absorb. It's working with two major solar manufacturers, JA Solar and Yingl, to commercialize the technology. Unlike many of these other approaches, which are developed for particular kinds of solar panel materials, the Genie Lens films can be applied to any type of solar panel--including crystalline silicon and newer thin-film solar panel technology.