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Registered Member #96
Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4059
Hi all, thought you'd like this. I recently acquired a bag of "dead" solar lights from a friend as part of his garden clearout. As none of them worked, it was a simple matter to gut them and save all the "good" bits such as the expensive solar cells and LEDs which had intact leads.
So, it became necessary to test the extracted cells. Hooked up one of my broken security lights to 12V, which is a panel of infrared LEDs. Lo and behold, it makes a really nice daylight simulator 8.3mA Isc at 1.86V Voc from a little 4 cell, and confirms that most of the solar cells are fine.
Even though the panel clearly has dead spots of low/patchy light, it works fine as a solar cell tester and is pretty close to the 940nm peak of Si cells.
Has anyone else stumbled across this effect? I'd think it would be very handy indeed for the folks DIYing solar panels from odd cells on Ebay, as in this instance one bad cell ruins the whole panel's max Isc.
I've also just acquired two 3W 940nm IR LEDs, which would be an interesting comparison to my IR panel as this is supposed to be a 10W according to the original documentation. It gets hot in use so a fan would be essential for long term testing.
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
I've done some testing of PV panels in a solar simulator. The original version was just a small room with the ceiling covered in a matrix of 150W PAR floodlamps. (Sunlight is approximately 1kW/sq.m. at midday in summer.)
These were great for testing solar thermal setups, but for PV they gave poor results, because the infrared content was greater than real sunlight, so the panels got extremely hot, giving an abnormally low output voltage.
So, for PV work, we covered a wall in mercury discharge lamps and got some really good sunglasses. This didn't work either, as the light output had a big ripple component at 100Hz, that seriously confused the grid-intertied inverters we were trying to test.
Commercial solar simulators have a xenon arc lamp powered by smooth DC.
Registered Member #96
Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4059
As promised, here are pictures of the array.
It did occur to me that replacing the "bad" diodes might give me a bit more power, as I've got a few spares here purchased for another project. Not too sure about matching though, any suggestions?
The design really sucks, lots of power wasted in bigass 3w resistors on the back which probably worsened the overheating problem.
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Solar cell hacking
