Will water be heated on a cloudy day?

Yes. Although the output of the collector will be reduced on cloudy days, they are still able to provide a significant amount of heating. It is all based and engineered with your location and SOLAR INSOLATION. Basically, the amount of available sunlight at your piece of the earth over a 10 year period. This is what we use to design and engineer your Solar Thermal System. See our design web site.

The cloudier the day, the more your backup gas, oil, or electric heater will be used to maintain the proper temperature in your hot water. This ensures that you never run out of hot water, regardless of your weather conditions. Snow does not stop the use of your panels, as it still gets solar radiation through the snow.

During a recent visit in April to one of our 6 year old Colorado  solar systems, we covered the Evacuated Tube Solar Panels with blue tarps while we turned off the circulator pump to do some work on the DHW in the house. It was 45 degrees outside but sunny. At the end of the day, the Heat Transfer Fluid in the panels had heated up to 110 degrees F... while covered up with a blue tarp.