It’s not up on Discover’s website yet, but the folks at Idealab (and it’s not on theirs, either) are said (according to the August 2003 issue of Discover magazine) to be planning on rolling out a solar power system that generates electricity for $1/watt. It uses a parabolic mirror to focus sunlight on a Stirling engine which drives a generator. The unit’s enclosed in a clear plastic dome and is designed to track the sun.
The focused sunlight heats the Stirling engine up to 1,200 + F and will cause a piece of wood placed at the focal point to burst into flames almost immediately. The average American home would need something like 4 to 8 of the units to supply its needs (no idea if that means the house only uses solar power during daylight hours, or if some of the units are charging a bank of batteries for nighttime/cloudy days).
If they actually start showing up in the market place for that price, I might have to look at getting one.
Stirling engines require a large temperature difference in order to function.
Getting the heat is not necessarily the problem, keeping the “cold” side of the cylinder cool enough to get any maningful work of the unit is something else entirely. They start up fine but once the whole assembly heats up, power is reduced and eventually lost.
Dean “It’s not a scooter, dammit!” Kamen is supposedly working on a self-contained Stirling-based generator/water-purification system, but it’s widely suspected that he’ll run into the same heat-pump difficulties.
I’m a pretty big supporter of alternative energy, but this leaves me underwhelmed. My budget took a serious hit, this summer, when the “green” aggregate that talked its way into my township jumped their summer rates from 0.033 kw/h to .052 kw/h and I’m supposed to jump at the chance to invest in something that will only cost 20,000 times the higher cost?
OR are they claiming that the cost of the unit will be $1 per output watt as a one time charge for purchase? The OP is not quite clear.
One time charge. A unit will generate 250 watts and cost $250 once they get the production runs up (projected to be a few years from now, according to the article).
It sounds like it would have to run for 20,000 hours to be as cheap as 5¢ per kW·hr. That’s just over two years of continuous operation. Of course, if it only generates power during daylight hours, it could be more like six years. But I guess it’s conceivable that this could be cheaper than what some people are paying, in the long run.
I remember hearing about this.
Seems like an ideal power source for use in space where the temperature difference between sun and shade can be hundereds of degrees.
One way to solve the cooling problem is to line it with ceramics and bury the cold end underground.
It’s not that easy to cool something in space. Even though deep space is “cold”, the only way to transfer heat to deep space is by radiative cooling. You need a radiator with a big surface area. The ISS has big radiator panels just to get rid of waste heat. Still, a reflector can be much lighter than a solar panel so it might still be useful in space.
Anyway, does the system mentioned in the OP require a pointing mechanism of some kind? Sounds like a high-maintenance system to me.
Six steppers? Why does it need so many? I’d think with a polar mount it would only need one motor.
Incidentally, my first thought when I saw mention of the Stirling engine was, “how are they going to keep the cool side cool?” Apparently I was not alone. Still, sounds like an interesting idea.
It has multiple mirrors, so presumably the steppers are used to align individual mirrors.
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The article’s not too detailed on that point, though from the way it reads they might simply be heating a fluid at the focal point of the mirrors then pumping it to the stirling which is located somewhere else.
Putting the cool end underground might do it for earth-based engines.
As for heat disposal in space, as long as the cool side is totally shaded from the sun it shouldn’t be too hard.
The engine itself is quite simple and has very few moving parts compared to a conventional engine.