There's a sort of "gee-whiz" article about generating electricity
with solar-powered stirling engines in the August issue of
Discover magazine. The bad news is that the device they're
describing is not a real product (yet), just a research project
funded by a private investor.
The interesting part is that the technology they're describing is
not new at all-- the only question is whether they can get the
cost down to where they can find a market for it. Their target is
250 watts for $250.
Part of the project was designing a stirling engine that could be
manufactured cheaply, and since the "fuel" doesn't cost anything,
they were willing to sacrifice some thermal efficiency to get
more "watts per dollar". The article says its about half as
efficient as the best stirling engines, but *much* cheaper to
build. They don't describe it in any detail, though.
For the solar part they're planning to use a 6'x9' array of small
mirrors, automatically aimed by stepper motors (and somehow
ganged together so they can use fewer steppers). By focusing the
light on a small area, they can produce temperatures up to 1200
degrees farenheit. And because the array is relatively flat, they
can cover it with glass or plastic to protect it from the weather.
My thought was that even if they miss their cost target, as long
as the total price is low some people might buy one just to thumb
their noses at the power company. They say a typical house would
need between 4 and 8 of these, which would be a $1,000-2,000
investment. You might need demand-priced electricity to make it
worthwhile economically (peak sunlight coincides with peak A/C
Their website at describes an
earlier version of the product and says it will be on the market
next year, but the Discover article sounded like they're now
working on a completely different design (with more reflectors,
and a rectangular array rather than round). Their web designer
really likes the word "revolutionary"...
The basic concept is similar to some government-sponsored
research described at , but on a smaller
scale. The Discover article quotes a guy from Sandia saying
"In principle, this could work.... I'm going to stay skeptical
until I see their data, but if they do pull it off, it could be huge."
BTW the magazine also has a brief article about people who
collect sliderules, with photos of some unusual ones.
For some history on solar-powered steam engines, check out a book
called "A Golden Thread: 2500 years of solar architecture and
technology" by Ken Butti and John Perlin (1980). The first solar
engine was demonstrated in 1866, and the first "practical" one
was built in Egypt in 1913 (it was abandoned during WWI).
18 years ago