You can't insulate the collector.
You only need to power off the circulation pump that circulates the fluid from the collector to the water heater.
you probably have a temperature sensor inside your collector that powers on your circulation pump after the temperature has reached a certain temperature and one inside the water heater that powers the circulation pump off after the water in the water heater has reached a certain temperature.
but it might be best if you dont mess with such technical stuff , you would need to power off all the sensors so that
they dont just sit there trying to turn the pump on or off all day if you have the pump power disconnected.
but still if the insulation on your water heater is not thick
enough it will lose heat faster than a thicker insulation would.
and when your water heater looses heat a sensor in the water heater allows the sensor in your collector to power on the circulation pump to heat the water back up again if the temperature in the collector has reached a high enough temperature.
it may all be controlled by a circut board.
