Can you connect 100W and 200W solar panels together?

You can connect 100W and 200W panels together, and the rule for doing it well is one sentence: parallel wants matching voltage, series wants matching current.

In series, the string's current drops to the weaker panel's current, so a 200W panel behind a 100W panel surrenders output. In parallel, mismatched voltages drag both to the lower operating point.

Practical fixes: group like panels into their own strings, or give the odd panel its own charge controller; small MPPT units are cheap enough that this often beats clever wiring.

Check the spec sheets for Vmp and Imp before deciding. Two panels within a few percent mix fine; a big mismatch means the expensive panel works part-time.

Size the combined wiring with the solar cable conduit calculator once the layout is settled.