4 ms·
> Currently I suspect most people are better off with a dedicated solar heater and solar panels separately Right now most people are better off (from a total
by danans 3y ago
> Currently I suspect most people are better off with a dedicated solar heater and solar panels separately
Right now most people are better off (from a total cost of ownership perspective) with PV panels + heat pump water heater. The latter can achieve a COP of 3.0 (300% "efficiency"), and also can just use grid electricity on a cloudy day. Unless you are off-grid, the additional cost/complexity of running plumbing to the roof for a solar water heater doesn't pencil out.
- zbrozek 3y agoWhere are you finding COP for water heaters? The best I found was a field study by the Canadian government where it seemed like most units operating in ambient temperatures relevant for me (in central California) get about 2.5.
- danans 3y agoThe COP is roughly equivalent (but more forgiving) than the UEF rating. Many new heat pump water heaters have a UEF of 4 [1], but this accounts for things like standby losses, so the COP of the heat pump itself is higher than that. Some premium hot water heaters like the SanCO2 can achieve COP of up to 5.0 [2], so high that they don't need backup resistance elements, even in northern climates. 1. https://www.energystar.gov/productfinder/product/certified-water-heaters/results https://www.energystar.gov/productfinder/product/certified-w... 2. https://www.smallplanetsupply.com/small-planet-blog/2021/1/7/the-fundamentals-of-game-changing-hot-water https://www.smallplanetsupply.com/small-planet-blog/2021/1/7...
- zbrozek 3y agoHere's the definition of UEF: https://www.govinfo.gov/content/pkg/CFR-2016-title10-vol3/pdf/CFR-2016-title10-vol3-part430-subpartB-appE.pdf https://www.govinfo.gov/content/pkg/CFR-2016-title10-vol3/pd... It would be really nice if manufacturers published delta-T vs COP curves.