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Mixing Panel Sizes


MincePie
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Hi there need some information please

So i have a client who added JA Solar 250W Panels yonks ago.
He wants to now add a new set of strings to push more to the inverter but i cant find those 250W panels anymore.

He has 3 strings at the top of 5 each making about 1.25kW x 3= 3.75kW
He wants to install a 5kW inverter and remove the 3kW

Now heres the question can i add another string of 5 x JA Solar 345W Panels to make up 1.72kW?

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Using different panels with different electrical charcteristics on the same MPPT is not really recommended as the overall wil only perform as well as the weakest.

You can get around this by using multiple MPPTs (just make sure that the inverter is capable of handling multiple MPPTs)

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When connecting string in parallel to the same MPPT the one thing they all have in common is the voltage. That means that you need each string to have (close to) the same optimum voltage.

Looking at the specs of these panels, the 250W has a Vmp (optimum operating voltage) of 31V, the 345W is 35V.

Perhaps you could reconfigure this way: take the existing 15 panels and make 2 strings of 7 each.  Put in parallel the 6 x 345W panels.  That way you will still have a small mismatch (217V vs 210V) but it is not too bad.

Better would be to find 6 panels with Vmp of 36V (total 216V) - that would be an almost perfect match.

You would obviously need to check that the inverter can handle the max open circuit voltage of the new configuration.

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