What’s the difference between solar thermal and solar electric systems?

First, let’s look at how they are similar – their differences will then be easier to understand. Both systems tap into the energy of the sun. In the Southeast, we are blessed with fairly good sunshine. Averaged across the year, the sun bathes North Carolina with between 370 and 460 watt-hours of energy per square foot each day. Solar electric and solar thermal systems are each capable of capturing some of that energy. Both systems are sensitive to shade or other obstacles that may block or impair their ‘view’ of the sun. And each works best when they are facing the sun directly; as their angle to the sun changes, so does the amount of energy they can intercept and capture for your use. Solar electric, as the name implies, converts solar energy directly into electricity. It uses a technology— photovoltaics–which is clean, silent, and has no moving parts. Photovoltaic panels are mounted on your roof or on a rack on your property and are positioned during installation to capture as much sunlight as possible. The more panels you have in your system, the more energy you can capture. Whenever the sun shines, they produce electricity. After the electricity is converted and conditioned by other equipment in the system, it is indistinguishable from the electricity supplied by your local utility company. Solar thermal, as the name implies, involves heat. Different kinds of panels, called solar or thermal collectors, are mounted on your roof or on a rack located on your property. Siting and orienting thermal collectors is similar in practice to siting photovoltaic panels. Thermal collectors are fairly simple devices – they contain heat absorbing materials and a network of tubes. The heat absorbing materials draw as much heat as possible from sunlight and transfer the heat to the tubes. A liquid, usually water (or an antifreeze-based liquid) draws the heat out of the tubes, and under the influence of a small pump, circulates into a hot water tank. The pump is controlled by one or more sensors that determine when the sun has heated the liquid enough to raise the temperature of the water in the tank. On cooler days, your existing hot water heating system will be needed to ‘top off’ the water temperature – taking it the last few degrees to its final desired temperature. The water pre-heated by the sun is then available for cooking, drinking, washing and bathing, and heating your home. Both system types can dramatically reduce your consumption of fossil-fuel generated power and many of our clients elect to install both solar electric and a solar thermal for their comprehensive renewable energy system.