These days, when most people think of solar panels, they are thinking of photovoltaic (PV) panels which generate electricity from sunlight. PV panels are becoming popular as they gradually come down in cost and it is becoming common to see arrays of PV panels mounted on residential and business rooftops and sometimes in open fields.

But, there is another type of solar panel that is not so well known, even though it should be. That is the solar thermal panel, which is also mounted on rooftops or in yards or other open spaces. Unlike the PV panel, which generates electricity, the thermal panel collects heat directly from sunlight, which is then used for purposes like heating hot water or space heating for residential and commercial buildings.

Thermal solar systems are a little more expensive to operate than PV systems, but their initial installation cost is much lower, so the overall economics of solar thermal systems are much more attractive than solar electric systems in today’s economy. Solar thermal systems also qualify for the same energy tax credits that apply to photovoltaic systems under current federal and state clean energy programs.

It is a little known fact that rooftop solar thermal systems provided a large percentage of residential hot water in the Miami area during the early decades of the last century. The collectors disappeared only when cheap natural gas became available for water heating. So, thermal solar is an old idea whose time may be coming back around.