Why control the ISL solar system on light levels rather than water temperatures?
We prefer the ISL control system to a differential temperature controller because it’s simplicity. Also with a differential controller (comparing temperatures between panel and cylinder) it is quite difficult to find positions in either the solar panel or the stratified hot water cylinder which are truly representative for use in a differential controller. Therefore we measure the amount of solar radiation and start the pump running when the sun is providing 150-180 watts per square metre, which is enough to exceed the heat losses in the pipe work.
