[andrewksu]

Agree, there would only a handful of days where the combo of temps and solar gain would provide the right boost.

PCM's (phase change materials) might work better in this application. However, air tightness and a consistent insulation layer is best.

[newman314]

Interesting. I read up more on PCMs.

The challenge I've had is keeping the house warm in the winter where internal temps will drop down to the 50s without the heater on. During the summer, I rarely have to turn on the AC even when it's a 100+ day so there's plenty of insulation. I suspect much of the heat loss is due to the giant windows that I have even though they are double pane.

[dangravell]

PCMs are being used in the domestic market for DHW (domestic hot water) now. Interesting developments - the batteries tend to leak much less energy than standard water based hot water cylinders.