While reading the article, I was wondering why combined PV/water heating conventional panels aren't taking off on rooftop installations. Looks like something that would make a lot of sense.
People spend a lot money in heating water. My folks did a hot solar hot water system in the 90s, and I think that the payback period was something like 3 years.
The system exchanges a fluid (I think glycol, but don't quote me) into a coil in front of the water heater water supply. So instead of dumping cold water in the tank, you're feeding it warm water. With a tankless system, it's even better.
My guess is they're not as popular because the overall installation complexity is much higher: you have to run the piping, and I'm not even sure exactly what you do with the hot water that comes out. There won't be room for it in your existing hot water heater, so you'll need a second tank, and where do you put it? How big does it need to be? And what happens when it fills up? Are the panels cooled only with fresh cold water, or do you reuse the water in the second tank once it's full? And if the latter, what happens when that water gets too hot to use? I guess you'd start letting some of it evaporate -- that'll be the fastest way to get rid of the excess heat, but may be undesirable in a water-poor area; and once you start evaporating water, you have to worry about scale formation.
Probably somebody knows the answers to all these questions, but they're not obvious to me. For new construction, they're probably not that hard to solve, but for a retrofit on an existing house -- which is the vast majority of where the panels are going -- the complexity seems prohibitive.
Somebody please correct me if I'm mistaken!
You only see either solar cells or heat collectors though.
Why there are no/not many combined setups, no clue. Maybe the efficiency goes down to much and limits the range of regions where it is viable? Maybe there are regulatory issues with water + power systems so close together (driving up installation and maintenance prices).
Actually, efficiency for PV would go up (the colder the cell, the higher the efficiency).
> Maybe there are regulatory issues with water + power systems so close together (driving up installation and maintenance prices).
Maybe, that would be interesting to learn :)
You recirculate water from your hot water tank through a heat exchanger that receives heat from the solar panels via a closed fluid loop. If the heat exchange would cool rather than heat your water, a thermostat turns the pump off.