Testing Solar Panels - Page 1
Forum section: electronics / projects

author: nixfu
author_rank: Unknown
timestamp: June 23, 2014, 04:38:22 pm
content: Anyone ever do some testing of solar panels to verify the output? What sort of setup did you do?I know you can check the voltage obviously of a panel with a multimeter.How did you measure the current? Did you connect it to a power resistor dummy load, or maybe to a charge controller or something?I am wanting as simple a setup as would be useful. Something like a multimeter and resistor possibly?

author: suicidaleggroll
author_rank: Super Contributor
timestamp: June 23, 2014, 04:51:14 pm
content: I did one not too long ago. Basically used ~10 50 ohm power resistors, and made a spreadsheet ahead of time with the total resistance for a bunch of different series/parallel combinations (100 ohm, 50 ohm, 25, 12.5, etc.). Then I took the panel, resistors, breadboard, voltmeter, and the spreadsheet out in the sun and recorded the voltage for each setup. Not amazingly precise, but I was able to build a few nice IV curves for various levels of solar incidence angle and cloud cover in a short amount of time. This was for a 12v 25W panel FWIW, if your panel voltage/power is significantly different you would need to use a different set of resistors, a programmable load, etc.

author: mtdoc
author_rank: Super Contributor
timestamp: June 23, 2014, 05:15:06 pm
content: Quote from: nixfu on June 23, 2014, 04:38:22 pmNo fancy setup, power resistor or dummy load needed. Short the leads (cover the panel first!). Measure current in line or with a clamp meter. Voc and Isc is all you need to test a panel.

author: penfold
author_rank: Frequent Contributor
timestamp: June 23, 2014, 09:00:54 pm
content: The best advice I can come up with is that what ever you're doing to measure the characteristic, if you're doing it under natural sunlight you need to able to do it in as short amount of time as possible to get meaningful results. I've been shocked on many occasions on how rapidly the incident light can fluctuate on an apparently clear day.If all you're doing is verifying the panels are operational then really, all you need is short circuit current and open circuit voltage. If you want a bit more information, perhaps measuring the fill factors and getting indications of efficiencies then you need a bit more information about what's going on between the open circuit and short circuit.To get a descent characteristic you need a large spread of resistances, something similar to what suicidaleggroll suggests. The best 'analytical' method to pre determine the resistances I came up with was to plot the open circuit voltage and short circuit current on a graph as straight lines, so you get a square with a corner at (V_oc, I_sc), then pick 15 or 20 points equally spaced along the sides of the square, calculate the V/I of each one, then go rummaging in the spares bin for enough resistors to satisfy these for the power rating (which you can also calculate as V*I for each point)... then go and use totally difference values because 20 bizarre values at silly power ratings are just too hard to find! If you do it right thought you get a lovely curve with nice evenly spaced points then can tell you a lot about the panel.The big killer is the fact that the panel has both a constant current and constant voltage mode that can play havoc with the stability of electronic loads. But that all depends how much detail you need.RegardsDan

author: olsenn
author_rank: Frequent Contributor
timestamp: June 23, 2014, 09:04:13 pm
content: Don't expect the power output to be anywhere near the rated spec. That number represents the maximum output when placed directly under a special, broad-spectrum lamp turned at max intensity.

author: tautech
author_rank: Super Contributor
timestamp: June 23, 2014, 09:26:59 pm
content: I did a small 6 V 100 mA one some years ago in bright sunlight(midday) with 2 meters and a WW pot.Took about 6 readings and when calc'ed out all where 0.6 W or ever so slightly better specs than advertised.

author: moffy
author_rank: Super Contributor
timestamp: June 24, 2014, 12:05:29 am
content: If you use an MPPT (Maximum Power Point Tracker), it will automatically adjust the output voltage/ current for the solar panel for maximum power. Then you only have to measure 1 voltage and 1 current. Need a suitable load for the output of the MPPT.

author: mtdoc
author_rank: Super Contributor
timestamp: June 24, 2014, 02:52:32 am
content: I guess i read the OP as asking how to verify a panel's power output. Voc and Isc will give you that. Of course if you want to fully characterize a panel, there is lots of other testing one could do.As far as achieving STC rated power output, yes it is difficult to achieve that - mostly due to the effects of temperature. However depending on where a panel is deployed- cold, sunny conditions can give you STC or greater output for brief periods and cloud edge effects can even give very brief outputs well above the STC rating. I've seen the output of my 1800 watt array exceed 2100 watts for a few seconds due to cloud edge effects!