PV-Thermal hybrids have recently become popular because these systems make more effective use of valuable solar roof space. The Hybrid collector effectively more than doubles the per square foot power output of PV alone. This is done by producing heat for hot water or space heating as a byproduct, in effect, a solar co-generation process. On its own, Solar Thermal usually produces over 4 times the energy of PV in thermal terms. A thermal collector covered with PV is going to work at lower efficiency because most of the direct sunlight is blocked by the cells. If the thermal portion of the Hybrid collector was working at only 25% efficiency, the gross energy output would be doubled. Now add to that increased PV panel efficiency and decreased cooling load and you have a real winning combination. Read more about this idea.