Hard to see how solar panels can impact the wifi performance of your router. They don't emit electromagnetic radiation as far as I know. They can physically block/impede TV reception from outside the home but obviously your router is inside the house.
The wiring connection from the panels down to the inverter is DC and shouldn't be generating any EMR to speak of.
Since the power to the house was probably switched off in the installation, it may be the router needs to be powered down and restarted and/or reset.
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