I sometimes confuse people and refer to active thermal systems as just thermal solar. Passive solar is also thermal, but for some reason I prefer to put it in a catagory by itself. Maybe because I see photovltaics and active thermal solar as systems added to a structure or as an appliance. Whereas, passive solar is predominantly about architectural design.

In any case, active refers to movement of fluids, typically with a pump or fan. Thermal, of course refers to heat, and system refers..well, to a collection of parts that work together to take the sun’s energy, heat a fluid, move the fluid where heat is needed and….aaaaah a nice hot shower awaits. Or a room is heated. Or a pool.

Speaking of pools…The picture below was captured one morning after a particularly blustery night. THAT active thermal solar system USED to heat my pool water. I guess we’re back to the solar blanket only….a very Passive Solar system.