Solar water heater

Is anyone familiar with solar water heater systems? The water temp varies from 90 to 140 degrees at different times. Also, the solar panel has a lot of condensation in it and discoloration. Apparently a plumber looked at it and walked away, telling them to call a solar company.
Also, the differential thermostat is plugged in to an outlet that is not grounded… not sure if that may affect it …

I disclaim them and recommend that they have the system evaluated by a specialist. I will report if I see any leaks though.