I was disappointed to learn that solar collectors would only convert about 14% of the sunlight to electricity. When this is coupled with 80% efficiency for a battery and around 90% for an inverter, a 100% efficient light bulb is still only giving off around 10% of the sunlight powering it.
Overall efficiency and high cost gave me the push I needed to look for better ways to light my house, one of the big energy users in my household. I considered just using the light pipes coupled with skylights, but they did not work out for storage mediums. Stretched out straight they did OK, but had limited volume. If I curled them around, the wrinkles seemed to trap light. It was pretty astonishing, but as always, there is a simple explanation. As the light bounces back and forth in the chamber, some photons are bound to be canceled out by resonance, just like two sound waves interfering with each other. Big wrinkles would trap and cancel some of the longer wavelengths, and the smaller ones would bounce shorter wavelengths back and forth until all of that particular wavelength was canceled out. One chamber, if left undisturbed for about an hour, would give back a pure emerald green. Unfortunately, even the canceled photons turned to heat, and I burned it up trying to save light for St Patrick's Day last year.
The answer, of course, was to build a chamber with no wrinkles, and it turned out easier than you might expect. A sphere was out of the question, because no matter how big you make it, there will be a harmonic of some wavelengths with resultant resonant cancellation. I ended up with the most common of storage chambers, a 55 gallon drum. The inside is lined with the best shiny mylar I could find, but I think the cost will be justified within a few months. The grooves separating the upper and lower thirds from the center even have their purpose, sending light that was just going back and forth scurrying to another part of the drum and keeping wavelength cancellation to a minimum.
If I let the light set in storage too long, I not only lose significant fractions, but it develops an unhealthy-looking pink cast. Probably that is selective absorption by the mylar, or, it could be my eyes after a long night.... It's been a long row, but I think I now have a usable system.
Some of the traps I got caught in:
Don't try to store too much light. Those photons do have pressure. To capture a full day's light, your collector mouth should be no more than 10% of the wall area of your storage chamber.
The fancy LCD shutter thingys did not work. They are dark when turned off and burn up from the absorbed light. A simple sliding first-surface mirror worked much better as a gate valve, although it is a bear to adjust. I finally set up a servo arrangement with a photocell and wheatstone bridge to keep the light delivery constant as the level in the storage chamber dropped. Of course some people are going to use computers and such, but my way does work.
IR filters should be used first thing to keep the hot light out of the chamber. I know it is a big expense, but it needs to be done.
I used two one-way mirrors to trap the light, one at the mouth of the collector funnel and one at the throat to the storage chamber. One allowed too much leakage, and three absorbed too much of my incoming light.
Tracking is not critical for the collector, as you might imagine. I just built a rough tracker using the differential pressure of two black propane bottles and it works fine. Remember if you do this the ram has to have the same area on each side to balance out. The easiest way to do this is to find a hydraulic or pneumatic cylinder that has a ram coming from each end, not just one. Don't be stingy, here. Replace the seals and lap the ram and lubricate it well. I know the propane is cheap, but you could lose pressure in one side of the tracker, not notice it, and have no light to make supper with.
If you decide to go for more efficiency and sputter a gold coating in your chamber, do not try to use a steel drum for the vacuum chamber. You can waste $20 worth of gold that way real easy.
A small mirror hung from a thread can direct the incoming light tangentially around the drum so it does not get in a rut. That thread has to be shiny so it does not heat up.
I only have rough estimates to work with, but have guesstimated the whole system is about 60% efficient with another 1% or so per hour of storage. Without some calculus it would be hard to evaluate, and I have no way of knowing how much light I fail to collect due to increasing photometric pressure in the evenings.
As always, have fun with it and let us know how your projects are turning out.
