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Table of
Contents The Solar CDs are eight small solar cells soldered together and then glued to a CD. Each solar cell produces about .55 volts of electricity for a total of about 4.4 volts. Under typical conditions, the output of a solar cell will vary according to light conditions, dust, angle to the sun etc. This is why the output of solar panels under *optimum* conditions exceeds the what is required for the circuit: to compensate for typical "less than optimum" conditions. This CD has had its reflective medium removed: that is why it is clear. Speaker wire leads extend from the CD for connecting to the circuit. |
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The solar cells were bartered from SnowFlake Village in 2001. The Solar CDs were originally made as part of the AEZ Solar Tree Project in 2001. 2002 sees them return to the AEZ as Solar Pathlights. It was wonderful to have access to these beautiful solar panels for the pathlight project...and for more than one reason! They are just about perfect for the pathlight concept: small, sturdy, appropriate voltage and very cool. And, it is pretty expensive to buy small solar panels: there were very few 4 volt panels available: cost was around $10...more expensive than a complete "cheapie" solar pathlight from the store! Doh! So the Solar CDs truly made this project possible! After acquiring the Solar CDs, the outputs of them were measured and prototype circuits were tested. You can learn about measuring outputs on the Multimetering page. How do solar cells work? It is magic!
Read all about it here: |
The first prototype circuit design - One
LED schematic - had one LED and 2 AA 1.2 volt 550mA batteries.
Although the voltage output of the Solar CD was appropriate for this One LED circuit design, after testing the mA output of the Solar CD, Mike Tarrant writes: "I measured the output of the solar-CDs. They output 220mA on a sunny Seattle day. I bet they will peak at 250mA on the playa. So the good news is that they will be easier to adapt. The bad news is that they will still fry your batteries if we don't redesign the circuit." Of course, anybody has to test this idea: "Fry batteries?" The One LED circuit was tested with the Solar CD out in bright sunshine. After the first day, the batteries were obviously *very* well-charged: the LED lit up like some alien UFO on acid. After a second day in full sun, the LED wouldn't light up at all. Testing revealed that one of the two batteries was dead. Ah, the joy of learning! One of Mike's solutions was to add a second pair of AA batteries and a second LED: Two LEDs Schematic. The circuit and other components remain the same. Mike also proposed an alternate solution: " There is actually a simpler solution. Get some of the art board that looks like corrugated cardboard, but is made out of plastic. They sell a type that is translucent. Cut out a CD sized circle and place it over the solar CD. I found it reduced the power output by 20%. Two layers would probably reduce it by 50% -- which would be good -- just where we want it to be." |