Soulust pointed me to this link, where system is being tested is described: http://www.youtube.com/watch?v=C-EvV90MeDY Basically a large area is covered with UV damage resistant clear plastic sheeting suspended on polls a few meters above the ground (air under it gets warm). At the center of this collection field is a tall chimney on concrete posts so the warm air can enter at the bottom and rise. Not far from the bottom is a fan turned by the rising air whose shaft drives a generator, conveniently sitting on the ground. The test prototype is operating with a 200 meter chimney and producing economically competitive power, so they claim. Tall chimneys are not expensive or high technology and certainly plastic sheeting is very cheap compared to solar cells or mirrors used in other solar power system. As the ground is heated, there is only a small decrease in power produced during the dark hours. Instead of locating it where they have (a desert) I would suggest it be on the top of a mountain, preferably a conical peak. The mountain slope is free vertical rise so Chimney need not be so tall as if the collector were covering a flat surface for the same efficiency. The efficiency will be low. Less than (T -t)/T where T is the absolute temperature of the air entering the chimney base and t is the colder ambient air temperature at the top of the chimney. (Although not immediately obvious, this is a Carnot limited heat engine.) Imagine that the circular plastic sheet cone covering the side of the mountain extends all the way to the bottom of the mountain, then T would not be much lower than it the system were on flat land as the air is taken at the lower elevation periphery of the conical sheet. However, the ambient air temperature, t, at the top of the mountain would be lower and still decreasing with the chimney height. Thus the chimney should be a tall as is practical. Compared to installed on flat land system, the air entering the base of the chimney will already have accelerated up the mountain slope, so the chimney can have a smaller diameter for the same mass flow up it. As the air will continue to accelerate within the chimney as it rises, this diameter could slightly be smaller with altitude. This save on its cost and reduces the weight on the supporting concrete post at it bottom. I am inclined to this this system is the most cost effective of all solar power systems. What do you think? PS the "conical sheet" of plastic would probably be only half of the cone, or less, as in Norther Hemisphere, little sun would fall on the mountain's north side and slopes should not be too steep.
Yes I agree it deficiently is, The only reason I made a reference to the flat desert is that with the mini Eco stems, It may be possible to turn desert land into fertile land, as well as generate power. But your idea if done right Probally would deliver extremely higher efficiency, in the raw amps it produces. per cost,
Yes I have always like this idea. The mountain thing may not be so good because it is quite difficult to build things on mountains, and there is all that foliage etc in the way, but who knows. Besides I guess it is generally sunnier in the desert. I have heard plans to build monolithic versions of these things out in the desert, which would be pretty cool I think, apparently could generate a decent amount of power too. I think the plans I saw included turning the space under the plastic into a giant greenhouse, filling it with plants and things, which I think increased the airflow somehow, perhaps from the plant's respiration, or maybe it just helps trap heat.
