Can You Really Heat Your Home With Mirrors?

Array of four heliostats. (image: practicalsolar.com)

It’s a simple but effective idea: using mirrors to reflect sunlight to heat and light your home. Practical Solar , a Boston-based manufacturing company, has created the first PC-controlled, do-it-yourself system that enables homeowners to collect and maximize heat onto a fixed target. The heliostat, a metal pole that tracks the sun, has mirrors attached to it, and can be used for anything that requires light or thermal energy, according to an article on greentechmedia.com.

Through a window or skylight, the mirrors on the heliostat can light and heat a north-facing room, or any other area that is perpetually shaded. How much heat?  On a clear day, a single heliostat generates as much visible light as forty 100-watt light bulbs, as well as 600 watts of thermal energy, which equals a space heater on a high setting. The cost of running each heliostat is minimal (running100 heliostats all day uses less power than running one nightlight all night, says the company brochure). Each heliostat, which stands less than five feet tall, delivers 3000 times more power than it consumes as it tracks the sun.

The hardware requirements for the system, however, are considerable. In New England (where the majority of the systems are being sold), a 2,500-square-foot house would need about 25 heliostats, although the company stresses that each house is different, depending on its primary heating systems, the energy efficiency, etc.  Each heliostat is 3 feet square, comprised of a pole, a frame, and eight mirrored tiles, and can be installed in a home’s yard or on its roof.  The software and driver box can control up to 200 heliostats, which can be programmed individually and/or automatically with a built-in timer– or you can manually switch between targets with a click.

Why, you may ask, with such a simple and logical concept, aren’t heliostats more popular? Well, as usual with any energy-saving initiative, it’s not as easy as it seems. Although it is easy for us to go outside and hold a mirror to reflect sunlight, it’s extremely hard for a machine to do the same thing. Over the years, this difficulty had prevented the development of a small, home-installed system like the new one from Practical Solar.

In an article in Northeast Sun, the magazine of the Northeast Sustainable Energy Association, Practical Solar’s founder, Bruce Rohr, talks about how he had envisioned this system over twenty years ago – but was not able to realistically build it until computers had become more ubiquitous, the technology manageable, and the materials more affordable. The heliostats must be rugged enough to withstand weather changes (especially high winds) yet be simple and lightweight enough so that a homeowner can install them. Rohr expects that, like most new technology, the price will go down over time.

Practical Solar’s heliostat package includes the control system (software, driver box, and accessories) for $345, with each heliostat (the housing for the mirrors and mirror frame) costing $995. Purchasers are expected to buy their own standard one-foot-square mirrored tiles which retail for about $1.25 each.

Because of their high expense and space requirements, heliostats are not yet viable as complete home lighting and/or heating systems.  However, they do provide an enticing option to bring natural heat and light into homes and help lower heating and electricity bills.