February 15, 2009 – Vol.13 No.48
REFLECTING LIGHT FOR ENERGY.
by Bruce Mulliken, Green Energy News
It’s really not that hard to build a house that needs little, if any, source of heat other than the Sun, operating appliances (like the heat from a refrigerator), and the warmth radiating from our bodies. Thick, heavily insulated walls, airtight doors, and tightly sealed windows aimed mostly at Old Sol should hold that heat in on all but the most frigid days. That simple formula, plus a few other ingredients (like the inclusion of an air-to-air heat exchanger to bring in fresh outside air without the loss of heat) is pretty much what the spreading Passivehaus effort from Europe is about to build self-heating homes.
But people seem to be very conservative when it comes to homes. Even when they buy or build new homes they prefer homes that look old or fit into a traditional style sprinkled with modern features.
Houses built for passive solar efficiency, with big windows facing the Sun and little ones on non-sunny sides look anything but conventional. It is, after all, the look of our windows and doors that help us define the style of our homes inside and out. (Window manufacturers, correctly, remind us of this over and over again.)
Yet if the goal is to have a home that is heated by the Sun through windows, then sunlight will have to be brought to windows that have no direct exposure.
The world’s largest solar power purchase to date has been announced by Southern California Edison and BrightSource Energy. Within the next few years BrightSource will be building solar power plants that employ mirrors to reflect and concentrate sunlight on a single receiver. Temperatures at the receiver end will get rather high, as you can imagine, enough so that water will be boiled to make steam that will drive turbines to generate electricity.
The power plants that BrightSource plans to build in the California desert, will rely on hundreds of heliostats to keep light focused on the receiver throughout the day as the sun arcs across the sky. With the wonders of tracking devices made of computer controls and electric gear motors, the mirrored heliostats can be kept in perfect alignment with the receiver from dawn to dusk.
While it wouldn’t be a good idea to build a solar thermal power station in your backyard, it is now possible to buy one or a few heliostats that are technically similar to those to be used in California. The heliostats now offered by Practical Solar of Boston, Massachusetts, can be used to reflect and direct sunlight to the dark side of a house to those windows, and the rooms within, that will never have direct sunlight. The reflected sunlight can add daylight to a room where there was none before or to heat it. The company says that on a clear day (even in winter) each heliostat can reflect 600 watts of heat and the light output equivalent to forty 100-watt incandescent bulbs. Each heliostat delivers 3000 times more power than it consumes in its tracking operation.
The company’s software that keeps the heliostat tracking the Sun can drive up to 200 units individually for separate targets. The software includes timer settings so the heliostat can be switched on and off during the day. Aside from heat and natural lighting, the heliostats may eventually be teamed up with photovoltaic cells for concentrated solar generated electricity.
Practical Solar’s heliostats can be installed by handy homeowners and are of course not limited to homes. Any building that needs more daylight and would benefit from clean solar heat could employ one or multiple heliostats.
The price? Right now under $1000 per unit. The control system with software, driver box, cables and sighting tool under $500.
Passive House Institiute US
Passihaus Institiut - Germany
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