Photos: Clean-tech start-ups swing for the fences

A heliostat is a device that reflects natural light into buildings. Practical Solar plans in a few months to start manufacturing this heliostat, which uses 8-inch square mirrors and a controller (the box in the center). It has designed software to make the mirrors turn to follow the sun during the daylight to maximize light indoors.

Initially, the company intends to sell to businesses and consumers for daylighting. But ultimately, the Boston-based company expects to use the heliostat for heating applications, said David Howell, the company's chief operating officer. Several of the arrays could heat water for a building's hot-water needs or heating. The unit will initially cost $990, but as manufacturing volumes go up, Howell expects the price to go down.