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Cool Projects

 


Solar Skylight
 

How to fabricate a low-cost solar skylight with a minimum of parts!


This is a really cool project. A while ago I wanted to put a skylight tube in my kitchen. You know, the type with the tube of reflective metal and a plastic dome on the roof. Thing is, it was going to be $450 for the hardware alone, It required an 18 inch hole through the roof and really, I could have used the light more in the hallway and basement (where I couldn't put a light tube). I was also concerned about leaks on the roof hole and just didn't want to lay out the $450. Well, I just designed a solar skylight you can easily build - that fixes all three problems.

Background: Just recently, warm-white high-power LED's have become available directly from Hong Kong. They have the same quality light as a tungsten bulb and kick out as much light as a 60W bulb. They are about $7.50 each- delivered. They run 8 hours a day for 45 years. They are incredibly bright.

My thought was this: Could I run these directly off of a solar panel? No battery, no charge controller.. a direct connection with no other parts? The answer is YES. A typical 40 watt $100 solar panel produces about 20Volts. These LED's will run between 9-12Volts. Two of them wired in series run perfectly off one 40W panel. Could you run 4 of them? Yup, but they light up much earlier in the morning and go off later if you just run two.

I found an old light fixture I had bought at a garage sale and mounted two of the LED's inside it. The LED's  are mounted on "heat sinks" that conduct away excess heat from them. These metal pieces have screw holes in them, so I just screwed them onto the metal of the lighting fixture (inside).  To test it, I laid the small solar panel on the roof.
It's about 2 ft X 2 ft.  I drilled a tiny hole in the side of one of my attic vents and routed the two wires down through the attic. I drilled a 1/4 inch hole in the ceiling and mounted the lighting fixture in the kitchen. The wires from the panel came through the little hole in the ceiling under the fixture. It literally took 15 minutes total.

When the sun comes up, the lights light up (and visa versa)! I'm installing two more in my dark hallway. Even on cloudy days, they light up about half way. This setup is fantastic.
 

Here is a picture of two types of warm-white LEDs that are available from Hong Kong on EBay. I mounted this one on a metal heat-sink from a computer chip. These are available as junk parts from computer repair shops. I drilled in a few holes and screwed it on. You might consider adding a little heat-sink compound (silicone paste) under the LED. The computer repair  shop has this too.

Here is the other common type. It came with it's own heat-sink. Cost was $7.60 delivered. I like this type.
These make incredibly bright and warm white light. I'd say they are the same as a 75W incandescent bulb. Search for "10 watt warm-white LED heat sink". These are $50 in a fixture at the home improvement stores. Make your own!


Wiring them up is easy. One lead is marked + and the other -. The little markings are small, so I usually put a piece of red tape on the positive lead or a black marker mark on the negative lead to keep things straight. For one 40 Watt panel, you'd wire two of these in series. This is like batteries in a flashlight.. positive to negative - one to the other.
   
Here is the wiring setup for the basic system. You can clone this for multiple locations in the house...or get a 60 watt panel and try running 2 sets of two in parallel.
   
It's a good idea to buy a in-line fuse holder and fuse from Radio Shack and put it in the place shown in the diagram. There is no on-off switch. This works just like a real skylight. Wire for this can be 14 gauge "zip" lamp cord.
 
This is a terrific way to light up a dark hallway or bathroom. Calculating the life of the panel and LED's, it should run for 45 years at 8 hours a day! Total cost is about $125.


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