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Is there any way to test how much a solar panel on a given position can generate for let say a day or few days. Like a multimeter that can automatically test the wattage days example? Or create a circuit to do that? Anyone recommend anything?

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  • \$\begingroup\$ Short circuit current is a reasonably close match to insolation (light level). IF you have a logger that can integrate current measurements it will give you what you want "near enough". A very simple program running on eg an Arduino program could easily do this. pass panel current through a resistor to get voltage proportional to current (at well below panel rated voltage. Sum the voltage reading every N seconds. The sum is proportional to the average current. | A motor driven counter whose speed is proportional to voltage would do similarly. | \$\endgroup\$ – Russell McMahon Jun 6 '19 at 8:17
  • \$\begingroup\$ A water pump with volume proportional to voltage similarly. \$\endgroup\$ – Russell McMahon Jun 6 '19 at 8:18
  • \$\begingroup\$ Unless you are wanting to test a specific panel then doing the above woth a small test panel would be about as good. \$\endgroup\$ – Russell McMahon Jun 6 '19 at 8:18
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Basic measurements are Voc, Isc and compute R=Voc/Isc as your ideal MPT load from 82% Voc at max solarity.

Since PV’s are a current source, your loading resistance at some voltage must track this variable equivalent resistance source with a matched impedance load. As this current reduces, the optimum Vmpt also reduces to 72% Voc at half power and continues down from here.

Depending how you convert to store this variable power, will determine the useable energy per day.

The efficiency drops away from these MPT operating points.

Voc = open circuit voltage.
Isc= short circuit current.
MPT = maximum power Transfer (operating point)

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