How a Solar Thermal (Hot Water) System Works

Graphic showing how a solar hot water system works
System Description

The second active renewable energy system in the home is a solar water heating system. Unlike photovoltaics, which convert sunlight into electricity without involving heat, the solar hot water system converts the suns rays directly into thermal energy to heat water. The energy is used to heat water in an 80 gallon tank, stored for use when needed. A collector on the roof, which holds sixteen evacuated tubes, will produce about 80% of the hot water used by 2-3 people. Evacuated tube collectors have a few advantages over the more common flat plate collector. They are able to perform a bit better in very cold weather, are easier to handle and install, and individual tubes can be replaced if ever needed without draining the system or removing the collector from the roof. A heat transfer fluid, consisting of water and antifreeze, moves the collected energy from the collector down to a double walled heat exchanger suspended in the bottom of the water storage tank. An electronic controller turns on a small pump when the collector temperature rises above the tank temperature by a few degrees and shuts it off when it cools down after the sun sets.

Web Content created by Wagner Zaun Architecture and Conservation Technologies under a grant from the Minnesota Pollution Control Agency 2007