Originally Posted by simonpickard
Never heard of this mis match of panels before? So it's not a good idea to mix say 100watt panels with 50's going into the same controller? I would have thought a good MPPT controller would handle this?
MPPT controllers work
by selecting the the voltage from the panels that gives the maximium output. Ideally when connected in parallel each panel would always put out the same voltage. In practice this does not happen because of shading differences etc, but panels need to have fundamentally similar voltage characteristics.
The general rule
is the Vmp has to be within 0.5v and closer is better.
Panels can be of different wattages, but have a similar Vmp so it is possible to connect 100w and 50w panels reasonably successfully, but you need to at least check the Vmp's are close and if mixing different types of panels (from different manufacturers, or with different cells for example) there will be some slight losses due to the panels having different voltages under different conditions even if the Vmp's are identical.
Series connection is different (matching of current
output becomes important).
The OP does not state the models of the panels he is planning to use. Most 280w panels are high voltage and not many 150w panels will match well. Perhaps the OP has found an appropriate model, but it sensible to warn him that not any 150w panel is suitable to use with one controller when 280w panels are also connected.