Why it is not recommended to connect different solar panels?
- Apart from rated power, each panel has a power degrade percentage.This means solar panels’ output degrade in a different way over time.Moreover the stated degradation not always coincides with what is written on a panel’s nameplate. Therefore it’s not easy to find an exact panel match of different solar vendors. ‘Exact match’ means both almost similar ratings and ratings degradation.For panels connected in series, voltage is additive while current is the same, provided however that all the panels have equal current rating.If among the panels connected in series there is a panel with rated current lower than the others, it will drag down the current passing through all the remaining panels.Therefore each of the remaining panels (with higher current rating) will underperform which means that will produce lower current (and power) than stated on its nameplate.In other words if two dissimilar modules are wired in series, the voltage is still additive, but the current will be equal to the current produced by the panel with the lowest current output in the series string.
- For panels connected in parallel, current is additive while voltage is the same. If among the panels connected in parallel there is a panel with rated voltage lower than the others, it will drag down the voltage on all the remaining panels.Therefore each of the remaining panels (with higher current rating) will underperform which means that will produce lower voltage (and power) than stated on its nameplate.
- Mixing solar panels with different electrical characteristics is not recommended if you use an MPPT charge controller. Different wattages make impossible for the controller to find the optimal operating voltage and current, since they are different for each panel type.
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