Solar Reflector - Old CDs

[Joe Blake]

http://i82.photobucket.com/albums/j245/saxeharp/general/Picture59.jpg

http://i82.photobucket.com/albums/j245/saxeharp/general/Picture32.jpg

http://i82.photobucket.com/albums/j245/saxeharp/general/Picture21.jpg


Some rather tacky piccies of a sunlight reflector I built from a few old CDs.

The hardest part I found was creating the hexagonal template. I did it about 5 times trying to construct it with ruler and compass, using a formula I found on the net, but I could never get it EXACTLY hexagonal, hence the rather large gaps between individual reflectors. (Next time I may cheat and use a CAD program.)

To cut them into the hexagonal shape was quite easy, the middle piccy is supposed to show the paper guillotine I used. Cost me about $30 and cuts the CD plastic cleanly. However, a couple of tips. Mark the cutting lines on the coated side of the CD and cut on that side (ie shiny side facing down). When lifting the cutting arm, move it out sideways so it doesn't drag against the cut edge. This minimises peeling of the aluminium coating from the CD.

I used silicon sealer to fix the discs to the backing board, and tried to smear it on the cut edges of the CDs, again to try to stop the coating peeling off.

I tried it out on one my smaller solar arrays, and also on my solar AAA battery chargers. It certainly gave the battery chargers a real boost, and kicked the needle off the end of the meter, even on an overcast (indeed raining) afternoon. I think the simplest way to use it is if your panel array is on or near ground level, just lay the reflector on the ground in front of it and adjust the angle until the light shines maximally on the cells. It does generate a bit of extra heat though.

Could probably be more useful in making hot water, or running a Stirling Engine. Or building something like the Sun Flower.

http://www.energyinnovations.com/sunflower.html


I only completed it during the week, so I can't give you any details on its longevity or weatherproofing (haven't done that yet). But it does the job and recycles the CDs into something quite useful.

I've got plenty of old CDs (but not many backing boards) so I'll experiment.

I built something similar last year, but just wrapped aluminium foil around a piece of chipboard, then swaddled the whole thing in clear food wrap. It lasted a surprisingly long time, just lying on the ground unattended, in front of one panel.

Joe

[Ralph Day]

Joe

I'd thought about the same thing back in thewinter. Then realized i'd have to clean snow off my arrays, solar hot water collector AND a reflector. Winter here has it's drawbacks. It's the time of year when i get the most efficiency from my PV, but only for the shortest time of day/number of hours.

Do let us know how much more energy you collect and also what kind of temp increases you get on panels. Do you have on of those neat IR thermometers you point and click?

Thanks.

ralph

[Joe Blake]

Yes, Ralph, I do have such a thermometer.

I'm just waiting for the rain to stop (but not WISHING it to stop - it's been really drought-busting) so I can do a little bit of "figurising". Snow is one problem I DON'T have to worry about, luckily.

I suppose if it was a problem I'd approach it by making some kind of "fulcrum" set up with counterbalances, set up high(ish) off the ground so when a certain amount of weight gets on the reflector it tips down and dumps the snow off, then swings back in place.

A pretty (although theoretical) problem.

;)

Joe

[Joe Blake]

Well, a nice sunny day (for winter) so I got out my infra-red thermometer and ammeter and did said figuring.

I set the reflector against my shed door, and aimed the beam in through my back door so it shone on the internal walls and ceiling. Certainly made a marked difference in the internal light level (white ceiling, unpainted brick). Because the sun was moving of course I wasn't able to measure directly the amount of heat, but with the reflected light shining on the side of my computer desk (wood veneer), after about 2 minutes, there appeared to be a surface temperature increase of between 1 and 2 degrees C, but this was not able to be maintained because of solar movement. The light was shining through a glass pane and I measured the temperature of the glass inside with the thermometer pointed directly at the reflector, and there was a difference of 6 degrees C (15 to 21) between the "lit" glass and the unlit glass. I then opened the window and pointed the thermometer at the reflector and obtained a reading of over 60 degrees C. Closed the window and measured again, pretty much the same figures.

I've got two separate PV arrays, one consisting of 16 small (size of A4 paper) Uni-Solar panels mounted on a frame concocted from PVC water pipe. This array has is own ammeter. I laid the reflector on the ground in front of the array and adjusted the angle to get the maximum reflection. Very interesting. On a bright day the array generates 1.8 amps of current. Just by using the reflector the current went up to 2 amps.

A couple of points. The reflector is "circular" (or more correctly hexagonal) about 60 cm in diameter. The PV array is 1.3 metres wide and .95 metres high, so not all panels can receive reflected light. I suspect if I build a more appropriately shaped reflector there'll be an even better power increase.

Measuring the temperature of the panels shows that the "unlit" panels are between 33-36 degrees C on the surface, whereas those panels getting the extra reflected light measure 44-49 degrees C.

I wonder whether placing a sheet of glass between the reflector and the panels will drop the temperature?

The reflector has been outside now for a week (dry but cool weather) and already about 3-4 of the CDs are losing their alumunium coating (wrinkling). I haven't as yet put the clear plastic around the reflector to "weatherproof" it. I'll wait until I can build a more "rectilinear" panel before putting too much effort in.

Joe

[Mike Gibson]

I made my reflectors out of dish tv sattilite dish. I wraped one in allumium foil, The other i had a broke mirror so i just finished braking it into smaller pieces then hot glued the peices on to the dish. being on the dish really concentrates the light and heat . Would really be good for a stirling. Will have to work on that. Haven't done any test but i know it really heats up whatever it is aimed at.