A heliostat — an axis-mounted mirror moved by clockwork or computer to reflect a sunbeam steadily in one direction (see the 18-second time-lapse video below) — installed on your roof or an outside common area can redirect sunlight onto a target of your choice, providing both hea ( to, say, melt an icy sidewalk) or light (like through atrium windows or a skylight).

The company says each heliostat reflects about as much visible light as forty 100-watt bulbs, as well as 600 watts of thermal energy (heat). Its heliostats, which cost $995 each (quantity discounts available), are individually programmed and controlled by a single, $345 piece of software that runs as a background program on your computer. Multiple heliostats can redirect sunlight to different targets simultaneously, or to a common target for concentrated solar power. A timer even lets you do this automatically.

After the initial costs, operating expense is minimal — the company calculates that each heliostat delivers 3,000 times more power than it consumes. Practical Solar also admits straightaway that heliostats only work when the sun is shining, and don't provide heat/light at night or when it's stormy or cloudy. Yet while it's designed an an auxiliary to help reduce some of the use and cost of conventional grid electricity, you could always get a standard thermal reservoir from a company that specializes in that if you want to store energy — making hay while the sun shines, so to speak.

Aside from everything else, you might even be eligible for federal / state tax credits and sales tax exemptions - check it out at the Database of State Incentives for Renewables & Efficiency. So, mirror, mirror on the co-op / may be the cheapest way to light up!

Practical Solar, Inc. • 516 E. 2nd Street, Unit 18, Boston, Mass. 02127 • (617) 464-1770 • info@practicalsolar.com

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