Solar Panel Specs for MPPT-- Issues
I had some "issues" come up this year with panel specs that may be of interest.
Ideally, you can check the panel specs to see if their voltages will be a match for use with MPPT so as not to confuse the tracking. However, here is what happened in real life. No idea how common this kind of thing is.
First I got a Poly Coleman (Sunforce) 100w panel, which says on the box you see in the store "100w with 5.8 amps current in ideal conditions." So Isc was 5.8 it seemed. 5.8 seemed a bit low to me since I would expect a 100w panel to have an Isc of about 6.2 amps like my old Sun 100w panels did (sold those three years ago)
Then at home, got the panel out of the box and on the back its says
Voc-21.5, Vmp- 17.1, Imp 5.8. No mention of Isc. I called Sunforce and they agreed Isc would be 6.2ish
Next (unplanned) got two Poly 100w panels at a garage sale. These twin panels made in India in 2015, say Model 100Wp:
Specs: Voc- 22.7, Isc 5.8, Vmp- 18.8, Imp 5.3.
So I figured no way these two would work with the other one so I planned to keep those two and sell the other. I even bought a new MPPT Tracer 20a controller sized to run just the two It would be over panelled with three 100s. (My older model Eco-W 20a can't even do two 12s in series--It does great with a single 255w-- but the Tracer can with its higher Voc input limit of 100v)
Later on in the year, at last I got good solar conditions to try them out. Put the Coleman next to an India one same sun angle etc, and Ta Da!
Both read 6.1a Isc and 20.3 Voc with my meter. Identical. (Voc is reduced a bit in the sun by panel heating) Both Indias confirmed identical too.
So this summer I had all three side by each in my twirler contraption using MPPT. Tried both series and parallel. No issues with MPP tracking at all. Worked great. (The 20a Tracer was over-panelled with 300w but that didn't matter-- it has a self-limiter to its rating)
In series, the controller readout in Bulk for Vmp was steady at 52v indicating each panel was near 17 Vmp (like the Coleman's rating, but way off the Indias' rating.) And in parallel, Vmp shown was steady at 17v
So the lesson is, if you are shopping for panels to "match", you should use same brand, same specs, and Hope they are indeed identical.
BUT if you already have the panels and see the specs don't match, don't give up just yet! Take them out in the sun and see what they really do--you might be ok after all.
Another lesson is the usual one that you can't always believe what you read on those spec labels. Trust but Verify :)
Ideally, you can check the panel specs to see if their voltages will be a match for use with MPPT so as not to confuse the tracking. However, here is what happened in real life. No idea how common this kind of thing is.
First I got a Poly Coleman (Sunforce) 100w panel, which says on the box you see in the store "100w with 5.8 amps current in ideal conditions." So Isc was 5.8 it seemed. 5.8 seemed a bit low to me since I would expect a 100w panel to have an Isc of about 6.2 amps like my old Sun 100w panels did (sold those three years ago)
Then at home, got the panel out of the box and on the back its says
Voc-21.5, Vmp- 17.1, Imp 5.8. No mention of Isc. I called Sunforce and they agreed Isc would be 6.2ish
Next (unplanned) got two Poly 100w panels at a garage sale. These twin panels made in India in 2015, say Model 100Wp:
Specs: Voc- 22.7, Isc 5.8, Vmp- 18.8, Imp 5.3.
So I figured no way these two would work with the other one so I planned to keep those two and sell the other. I even bought a new MPPT Tracer 20a controller sized to run just the two It would be over panelled with three 100s. (My older model Eco-W 20a can't even do two 12s in series--It does great with a single 255w-- but the Tracer can with its higher Voc input limit of 100v)
Later on in the year, at last I got good solar conditions to try them out. Put the Coleman next to an India one same sun angle etc, and Ta Da!
Both read 6.1a Isc and 20.3 Voc with my meter. Identical. (Voc is reduced a bit in the sun by panel heating) Both Indias confirmed identical too.
So this summer I had all three side by each in my twirler contraption using MPPT. Tried both series and parallel. No issues with MPP tracking at all. Worked great. (The 20a Tracer was over-panelled with 300w but that didn't matter-- it has a self-limiter to its rating)
In series, the controller readout in Bulk for Vmp was steady at 52v indicating each panel was near 17 Vmp (like the Coleman's rating, but way off the Indias' rating.) And in parallel, Vmp shown was steady at 17v
So the lesson is, if you are shopping for panels to "match", you should use same brand, same specs, and Hope they are indeed identical.
BUT if you already have the panels and see the specs don't match, don't give up just yet! Take them out in the sun and see what they really do--you might be ok after all.
Another lesson is the usual one that you can't always believe what you read on those spec labels. Trust but Verify :)
