Lots of things of course. You could use it to provide light and warmth to a room in winter like this guy does. You could provide additional light on an existing installation of solar panels (with a sensor to remove it if those panels reached high temps as redrok suggests). You could heat pool water (OK, parabolic, very different, but it’s too great a blog not to link).
But, like many others, I’m interested in solar as an alternative to extracted fuels like coal and oil. So I think mainly about three applications (in order of interest):
1) A residential use of concentrated solar on PV cell.
2) A quasi-residential use of concentrated solar thermal paired with storage (and converted to electricity by stirling engine or micro steam turbine).
3) Commercial power tower applications
I focus (ha ha) on the first of these because it seems the most plausible. No one sells cheap (consumer, single junction) solar panels that can handle the high temps of multiple suns. But I think (hope) that is more because there is no market for them than because there are technical constraints to creating them. A cheap heliostat might create a market for a consumer level solar panel that could handle higher temps. So there may (or may not) be a market for a solar panel that could sustain 10-50 sun concentrations. Further, it would be easy to make the target high in the air (like on a roof), which minimizes the physical danger of that level of solar concentration.
1000 watts per square meter is the canonical number of solar insolation for calculations. 50 times concentration (think of 50 heliostats shining on 1 square meter solar cell – it needs a lot of space) is 50,000 watts per square meter. 50,000 / 10,000 (number of centimeters per sq meter) = 5 watts per square centimeter. 100 square centimeters (a 4” square) would be 500 watts per 4” square. It’s hot, but not that hot. It seems possible that in an outdoor application, passive heat removal (or, a small fan) could work. It’s useful that you are immediately adjacent to an infinite heat sink (the great outdoors). You want to avoid water cooling because it carries complications and cost. Incidentally, that configuration (50 stats), with a 10% efficiency of conversion to power, in the US Southwest (300 days of sun/year, 5 usable hours/day) generates 7,500kW-hr per year (50 x 1kW x .1 x 300 x 5). People in the US use around 11,000kW-hr each year. Your mileage may vary, as they say on the inter-googles.
Residential applications are appealing because they’re cheap – many individuals would happily self-finance if it returned 10% and they had the space. And, the money is spent largely on installation and maintenance. That means you are paying people, in your community, instead of firms with large capital requirements.
One could make a good case that residential applications won’t have much impact on climate change. But, it proves out the technology and is interestingly disruptive in the same way wi-fi was. If it works at a household level, it could be expanded to “community size” or larger.
Speaking of community sized applications, I think option 2 – CST with thermal storage – is the more sensible approach in a larger picture. If you have a cheap way to collect heat, cheap thermal storage has a large multiplier effect. That super expensive 20% efficient 25kW Stirling engine can now run for 24 hours a day instead of just 5-6 hours, so it amortizes way better. And, of course, it addresses the fact that we sometimes use power at night.
Look, I hope for magic technology bullets as much as the next guy. But at this stage, everything is possibility, a clean energy reality doesn’t exist. And, I believe that the more competitive the clean energy options are, the faster they will move the most viable options into place. My project isn’t going to slow anything down. If I am very fortunate, it will speed someone else up (or cheapen them).
So that’s some of what you might do with a cheap heliostat. Perhaps someday it will be worth writing up more thoughts on option 2. But, far more valuable is to just develop a cheap ‘stat and see how people use it.
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