Solar electric vs Solar Thermal for HVAC.
Initially we planned to use solar thermal for heating water for our radiant floors, but ultimately chose – after extensive modeling – electric heating through a heat pump, the electricity coming from photovoltaic (PV) solar electric panels. This is highly counter-intuitive as solar hot water panels have efficiencies of 60-70% while PV has efficiencies of 15-20%. However, the heat pump helps equalize the differences because the compressor cycle offers a ~2.5X gain in effective efficiency. Additionally – when traveling and the home is vacant, the solar thermal system heat cannot be used. By contrast the PV energy can spin the meters backwards and the electricity can be “banked” with the utility. We definitely needed a PV system at least for the home electric needs – choosing PV for water heating also eliminated a second system. The solar hot water systems have plumbing complexities and offer more limited architectural choices than the PV systems.
Solar (Photovoltaic) Panel Choice
For PV, we chose SunPower. SunPower manufacturers the industry’s highest efficiency PV cells and it’s material has a more uniform, darker cell, than other PV due to unique technology. SunPower manufacturers standard configuration PV modules, which have outstanding power density, and a roof-integrated product called SunTile. SunTile was invented by Tom Dinwoodie, while we were both working at PowerLight. SunTile offers lower power density than the SunPower’s standard PV panels, but looks fantastic as a louvered roof tile.