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# Solar Tubes

Fold a flat panel collector into a tube
 (+1, -2) [vote for, against]

A square flat panel that is 12" per side will cover 1 square foot of surface with 1 square foot of collector panels. If you take that square solar panel and roll it into a tube, you can fit multiple tubes onto the 1 square foot of space. Instead of shining the sun on a 1-sqft flat panel, the sun will now shine down into multiple tubes with far more than 1 square foot of solar panel exposed to sunlight.

The problem is that the quality of the sunlight will be poor because it is not as direct as it would be on a flat solar panel. But what is the tradeoff? If the sunlight is 50% less direct, but if you have 200% more panel surface, do you nevertheless generate more power per square foot of footprint?

One way to maximize the amount of light inside the solar tube would be to install a mirror at the bottom so the panel can catch light coming and going.

 — Hurricane1008, Oct 28 2009

Solar tracker http://en.wikipedia.../wiki/Solar_tracker
Useful [8th of 7, Oct 28 2009]

 Wow, talk about patience. [Hurricane 1008] joined us in April of 2007, has annoed twice, and this is the first idea submission.

I suspect that maths will not bear this out, but it's not my specialty.
 — normzone, Oct 28 2009

 The ground gets (very roughly) 150W of solar energy per square meter that you can collect. That's it, however you arrange the panels. I'm not very well versed in this stuff, but I don't think this is going to help.

Keep posting though, we're all hoping our next idea will be world changing.
 — wagster, Oct 28 2009

 1 kW per m^2 peak. The 150 number is average over a day (and possibly worldwide). You're much better off using a rough surfaced (near fractal) flat panel than these tubes, since you'll get a much higher temperature (for thermal). The technology for this allready exists. We have paints and surfaces that push 99.999% absorption already.

For PV, higher concentration is much better than quantity, since the cost of the cell itself is your major driver.
 — MechE, Oct 28 2009

Now that there's a couple of peeps here that actually know something about this - could we get some links? This is interesting stuff, and I'll have to retract that bone if [daseva] is correct.
 — wagster, Oct 28 2009

I'm not at liberty to publicly discuss ongoing research within my organization. Suffice it to say that radiation absorption is dependent on contact angle and surface area, and the optimization (more area, less angle) can lead to new geometries for enhanced performance as long as the price of materials is sufficiently low.
 — daseva, Oct 28 2009

 What [bigsleep] said.

 For optimal PV performance, the incoming radiation should be normal to the face of the array.

Mirrors are a cheap and efficient way of increasing the amount of incident energy but then alignment of the optics becomes more important. And the peak power density has to be kept below limits, particularly in the IR band - which tends to be absorbed rather than converted (because its energy is below the PV bandgap energy) and can cause the array to overheat.
 — 8th of 7, Oct 28 2009

A reflecting telescope would burn out photo-voltaic cell.
 — wjt, Oct 30 2009

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