Some folks had questions about this a while back, so looking to share our experience. *Not* affiliated with the companies mentioned in any manner.
We had a set of seven of the open-coil solar thermal collectors on our roof, tied to our in-ground pool, as part of the house we purchased a couple years, ago, here in DC. Those surely helped to add a few degrees of heat during the Spring and Fall, but, we wanted to use this great, Southern exposure to its fullest potential. We envisioned using that space for solar panels, using a pool-only heat pump, to extend the season, and to provide a bit of electricity for the rest of the year.
After a bit of research and networking, we were pleased to find a guy with a *lot* of experience and good references who, after some engineering and math wizardry, has shown the power of an integrated, full-hybrid PV(T) system (Photovoltaic and Solar Thermal).
We are in the final design process of adding:
- A few racks of 21% efficient, 'SunPower' photovoltaic panels to the roof.
- A matching set of 'SunDrum', solar thermal collectors, that attach to the normally-toasty backside of the PV panels.
- A 'Water Furnace', heat pump with three heat exchangers. (Often part of a ground-sourced heat pump system.)
The SunDrums use a glycol loop to send heat to/from the Water Furnace. There, the system connects out to heat and cool the house, pre-heat potable hot water, and it uses the pool as a heat sink, in the summer, and as a heat store, during the winter. Rather than just 'heat the pool', this will take on a lot of tasks, but it is not overly complex. (Our pump and filter are in conditioned space, already. With some insulation under the cover, heat being monitored, and cycling, freezing should not be an issue. /Knock on wood.)
There will be added electric use, due to using the heat pump and variable-speed pool pump, more often. That is offset by the power from the PV panels, time-of-use electricity savings, and significantly reduced natural gas usage- only used to top off the potable hot water and as a back-up HVAC heat source, when necessary.
Finalizing the details, now, so hope to add, more, once the final design comes along.
Wish us luck!