Thursday, Jun 22, 2006 at 15:21
There is no way you will get 1.66A from a 20W pannel. The peak power OP of a pannel is not calculated at the 12V point on the current Vs voltage curve. For starters if you wanted to calculte power OP for batery charging then you would have to use a figure of around 14.5V – that is the voltage needed to charge a battery.
The peak output of a 36 cell pannel occurres at around 17-18V. This is useable in water pumping applications as some pumps are disigned to accept this. If your pannel peaks at 17.5V then the current at peak power is around 1.15A. If you load its OP to 14V you will get a little more and you will get more again if you short circuit the pannel.
An example is a Model NE-80E1U pannel listed on the 12V
Shop web site. It has an open circuit voltage of 21.3V, a peak power voltage of 17.1V & current of 4.67A and a short circuit current of 5.31A.
To add to that we generally mount our pannels flat on the roof of our van- don't we? I do but I have compensated for the losses with a bigger pannel. If you can get more than half the short circuit current out of your pannel into your battery for a few hours a day in the far north of Australia in Summer then you are doing
well. You can improve this a little if you are prepared to sit around
camp all day and adjust the angle of the pannel every now and again to face it squarely at the sun.
PeterD
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