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See Inside April 2006

Lifting the Winter Dark

Mirrors to reflect light into a town that gets no sun
HERE COMES THE SUN



BARTENBACH LICHTLABOR GMBH
Springtime light may lift the spirits, but in Rattenberg, residents have a long memory for shadows. From late fall to midwinter, this tiny Austrian town, famous for its glassblowing, gets no sun at all. And it has been that way for centuries. Next time, though, the villagers may finally see the light--thanks to giant rotating mirrors known as heliostats.

Bartenbach Light Laboratory in the Austrian Tyrol plans to begin construction of the heliostats this August. "The idea is not just to light the village," says Silvia Pezzana, an engineer at the firm. "The idea is to give them the impression they have sun."

Some 600 years ago Rattenberg's founders settled between the river Inn and the 3,000-foot-tall Stadtberg and Rat mountains, sheltering the village in the shadow of the rock as a measure of security against bandits and wartime fighting. (A civil war broke out at the time between supporters of the Austrian duke Frederick the Handsome and the Bavarian duke Louis of Wittelsbach.) Raids and plundering ended; the shade remains. To this day, when the cold months come the daylight stays below the horizon, blocked by the mountains. "The sun left us at the beginning of December," says Gundi Schmidt, a social worker born and raised in Rattenberg. She's lucky: shadows creep over other parts of town starting in November.

Bartenbach's answer will be a set of 15 mirrors about a quarter of a mile away, across the Inn River in a sunny field. Pezzana says they will be set on poles, and each will measure about six feet across, tracking the sun using custom software running remotely from Rattenberg. On days when the sun is out, light will be reflected to a mirror-covered tower standing next to the ancient stone fort that once protected the village. "Those secondary mirrors point the light to small mirrors on buildings in the village, which takes the light down into the street," Pezzana says. The small mirrors will also diffuse the light, minimizing fire hazards and preventing glare. On the street, the effect will seem to be more of a dappling than full sun.

All the necessary measurement and calibration have added up in the past to price tags that have kept heliostats from being an everyday proposition. But the Bartenbach project will cost an affordable $2 million or so to develop and install. What is making the heliostats cheaper these days are big improvements in measuring and manufacturing glass mirrors, resulting in a less flawed and more reflective plane surface. The development of dust- and weather-resistant materials has also helped, as has increased software processing power, which allows the mirrors to be more precisely positioned.

Schmidt is a little skeptical about the project--her solution, only half in jest, is to take down the mountains--but there is no joking when she says the town has been losing population. Old-timers are dying off, and young people, given the choice of building a cheaper new house in the sun, are leaving. The town burghers are also hoping a more pleasant winter environment will boost overnight stays and improve daily commerce during the winter months, when tourism dips and Rattenberg's crystal flowers sit unsold on the shelves.

Whether light can make such a difference is not known, but about 60 other Alpine towns face similar gloom, so heliostats may become more common. Cheaper heliostats might also cut office lighting costs--Bartenbach uses one to reflect natural light into basement offices and to power special solar lamps. More such applications may overcome long-disappointed expectations for everyday use of solar power. For the town of Rattenberg it may be enough to chase six centuries of winter blues into the past.

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