Lighting a town
Published on Nov 22, 2005 at 7:59 pm.
1 Comment.
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In the newspaper, I was reading about this small Austrian town and its winter lighting problems. You see, the town of Rattenberg is built in the Austrian mountains. From November to February the Sun does not shine directly on the town. Hmm. How can that be, you ask?
As the Earth orbits the Sun, its rotational axis is inclined with respect to axis of its orbit. In layman’s terms, it is tilted over 23.5 degrees. This means that during part of the year, the northern hemisphere is tilted towards the Sun, and it is summer (winter in the southern hemisphere that is tilted away from the Sun then). Half a year later, the reverse happens, and the southern hemisphere is tilted towards the Sun, making it summer in the south and winter in the north. So, how does that affect the sunlight in Rattenberg? Well, about June 21, when the northern hemisphere is tilted mostly towards the Sun, the Sun appears directly overhead for a person at 23.5 degrees north latitude (the Tropic of Cancer). The closer you are to the Tropic of Cancer, the closer the Sun will be to appearing overhead. Where I live in Texas, we are about 10 degrees north of the Tropic of Cancer, so on the Summer Solstice, the Sun appears 10 degrees south of the zenith. Rattenberg, at 47 degrees north latitude, sees the Sun at about 24 degrees south of the zenith. At the Vernal or Autumnal Equinoxes, the Earth is tilted in a line perpendicular to the line between the Earth and the Sun, so neither the northern nor southern hemispheres are tilted towards the Sun. The Sun appears directly overhead from the Earth’s equator. In Rottenberg, the Sun appears 47 degrees from the zenith at noon. In other words, even at noon, the Sun is no higher than 43 degrees above the southern horizon — not even half way to directly overhead! At about December 21, the Winter Solstice, the southern hemisphere is tilted towards the Sun, making it summer in the south and winter in the northern hemisphere. The Sun appears directly overhead for someone living at 23.5 degrees south latitude (the Tropic of Capricorn). For Rattenberg, the Sun will rise well to the southeast, and go up only to an altitude of only a measly 20 degrees above the southern horizon, before setting in the southwest. This is why the days are shorter in the winter.
This is true of anywhere with a latitude farther north than the Tropic of Cancer or farther south then the Tropic of Capricorn. The numbers that I gave before are for any city at latitude 47 degrees north. The problem for Rattenberg, though, is that an alitude of only 20 or 30 degrees is not high enough for the Sun to clear a mountain south of the town. So, from November to February, Rattenberg is in shadow. The people there claim that is is gloomy. Of course, they built the town there. After all, the mountain was there first!
So, now, they have decided that after 700 years of this situation they are tired of the gloominess. So, they want to put giant mirrors up to direct sunlight into the town during these months. This involves putting rotating mirrors, called heliostats, on a nearby mountain that will track the Sun. These mirrors will shine sunlight onto another bank of static mirrors that will in turn direct sunlight into the town. This will produce a dozen or so sunlit patches in the town.
OK, leaving aside any environmental concerns about what suddenly putting sunlight someplace that has not had it during that time of year for the last few million years, the mountain was there before Rattenberg. Also, this will cost an estimated $2.4 million according the newspaper. The EU is putting up half the money. This is all for a town of ONLY 440 people!!!!! That means nearly $5500 per person just to have direct sunlight for about three months (a luxury, since they have lived without that direct sunlight for 700 years). This is the initial cost. These mirrors and heliostats will need routine maintainance, at the cost of possibly well over $10k per year. Is this money well spent?
-Astroprof
Astroprof’s Page » More on Space Based Solar Power … on October 15, 2007 at 2:25 pm: 1
[…] SBSP has been kicked around for decades now. As I said before, it is only now just becoming feasible. One of the earliest proposals was to use giant mirrors in space to focus light onto the Earth below. In fact space mirrors were proposed by Hermann Oberth in the 1920s. The idea would be that ordinary ground based solar energy stations would benefit from having extra bright sunlight with which to work. There were proposals to also use these mirrors to light cities at night, eliminating the need for streetlights and many other artificial light sources, thus saving electricity. In 1999, Russia even attempted to build and test a mirror in space, though the mirror did not unfurl. Had it done so, a five mile wide swath of light would have swept from Germany, through the states of the former Soviet Union, across Seattle, in the northwestern portion of the continental United States, and across part of southern Canada. Interestingly, a similar solution has been proposed for the Austrian town of Rattenberg. In the case of Rattenberg, though, the mirrors would be located on adjacent mountains directing light into the town that is in the shadow of other mountains all the winter. Proponents of the space mirror idea pointed out that such mirrors could be used to provide temporary broad lighting for disasters, for military operations, and for special outdoor nighttime sporting events. The space mirrors have also been suggested for crop management purposes. […]