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wind friend

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Joined: 01/05/2007
Location: Australia
Posts: 39

Posted: 06:32am 14 Feb 2011

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hi crew,

i have just started mucking around with solar panels. not quite as much fun as hawts (the only moving part is the needle on the ammeter) but amps none the less.

an easy question, if you were to paralell two panels of different wattages how would you do this?

the combined output is still less than the rated max of my solar controller..

thanx in advance

Bryan1

Guru

Joined: 22/02/2006
Location: Australia
Posts: 1344

Posted: 09:49am 14 Feb 2011

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When I installed my FM60 MPPT I found my kaneka panels were too high a voltage for the MTTP. On looking at the panels they were setup as 2 in series x 7 in parallel. I re-wired each panel in parallel and used some 16mm double coated wire as the bussbar. I cut the sheathing off where the joins were required then wrapping the soldered joint first with friction tape then over the top with self amalgamating tape and a final run of electrical tape. Later I put up 2 off 24 volt 175 watts in parallel and as those pv panels were a different wattage and voltage ran them as a parallel circuit direct to the fuse bank.

Rule of thumb if you put 2 panels in series of different wattage the output will only be of the lower wattage panel.

In parallel different wattage panels can be run to a bussbar with no loss.

Cheers Bryan

RossW
Guru

Joined: 25/02/2006
Location: Australia
Posts: 495

Posted: 10:17am 14 Feb 2011

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Bryan1 said
Rule of thumb if you put 2 panels in series of different wattage the output will only be of the lower wattage panel.

In parallel different wattage panels can be run to a bussbar with no loss.

Cheers Bryan

There's a caveat with that - the highest VOLTAGE panels will take the load (first). Depending on how much power you're pulling out, the lowest voltage string may not contribute anything.

If you're pulling lots of power, and you're using a MPPT controller, you'll almost certainly not be on the "sweet spot" of either array.

I know this to be true from the 5 x 600W 120V arrays I have in parallel with an older 480W array that is slightly lower voltage. I get about half that arrays output because I'm not at it's maximum power point, because it's at a different voltage to the other arrays.

Final word: parallelling arrays, you really should consider isolation diodes. You don't want to blow one entire array up like I did due to spikes, and you don't want them badly reverse-biased if one is shaded.

VK4AYQ
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Joined: 02/12/2009
Location: Australia
Posts: 2539

Posted: 01:08pm 14 Feb 2011

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Hi Wind friend

I have tried unmatched panels with poor results in a system, I found it necessary to run a separate regulator on each type for best results. This isolates them as Ross says and allows both to work, but not at maximum efficiency.

If connecting in parallel the panels should be of the same type of cell Mono or polycrystalline, and then match panels using a dummy load (not a politician walking on it), to draw 75% of rated output, then check the voltages of the panels, should be within .2 volts, I used headlight globes for a load, but sometimes they blow from high voltage. Different brand panels of the same type and rating, can vary quite a bit so it pays to check them.

If connecting in series to make 24 or 48 volts, the above test is also a good idea as a lower performing panel will limit its partner/s.

All the best

Bob

Foolin Around

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