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While reading the article, I was wondering why combined PV/water heating conventional panels aren't taking off on rooftop installations. Looks like something th

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.

ScottBurson 11y ago
It's a good question. The panels are available, for example these: http://www.solimpeks.com/pv-t-hybrid-solar-collectors/ http://www.solimpeks.com/pv-t-hybrid-solar-collectors/ 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!
- danmaz74 11y ago
  Yes I'm sure there is some good reason, but considering that solar for water heating - without PV - has been sold for ages already, there should be a market. Let's hope somebody with a real-world understanding of the problem will answer, I'm really curious :)
- michaelbuckbee 11y ago
  Swimming pools - in areas like the NC Outer Banks - the systems give you an extra month or so of swimming on each end of the season.
- detaro 11y ago
  The heating water part is really common here in Germany and not that big of a deal, and not just for new constructions. Basic heat storage/exchange parts often easily fit in existing rooms or even in the space the old heating system took. 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).
  - danmaz74 11y ago
    > Maybe the efficiency goes down to much and limits the range of regions where it is viable? 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 :)
    - detaro 11y ago
      I don't know if cells would be colder, since the heat collection parts works at liquid temperatures of 80°C or if they don't use water directly even over 100°C. The heat collecting system wants to be as hot as possible, the solar cells as cold as possible. Also, the cells decrease efficiency of the heat collection part.
      - danmaz74 11y ago
        If you get the heat from the cells, they need to become colder for sure.
- nitrogen 11y ago
  ...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? 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.
Spooky23 11y ago
Most of the new installations are linked to energy leasing vehicles. Water doesn't work there. Also, most folks use gas or propane to heat water, and gas prices are very low. 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.
hacker234 11y ago
I don't have a link, but combined Solar Electric / Hot Water panels are relatively common Australia. My neighbor has them on his new house. I'll go ask him for details.
- danmaz74 11y ago
  Thanks, that's interesting to know. Never saw any promotion about them here in Italy.

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.

ScottBurson 11y ago

It's a good question. The panels are available, for example these: http://www.solimpeks.com/pv-t-hybrid-solar-collectors/ http://www.solimpeks.com/pv-t-hybrid-solar-collectors/ 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!

danmaz74 11y ago
Yes I'm sure there is some good reason, but considering that solar for water heating - without PV - has been sold for ages already, there should be a market. Let's hope somebody with a real-world understanding of the problem will answer, I'm really curious :)
michaelbuckbee 11y ago
Swimming pools - in areas like the NC Outer Banks - the systems give you an extra month or so of swimming on each end of the season.
detaro 11y ago
The heating water part is really common here in Germany and not that big of a deal, and not just for new constructions. Basic heat storage/exchange parts often easily fit in existing rooms or even in the space the old heating system took. 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).
- danmaz74 11y ago
  > Maybe the efficiency goes down to much and limits the range of regions where it is viable? 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 :)
  - detaro 11y ago
    I don't know if cells would be colder, since the heat collection parts works at liquid temperatures of 80°C or if they don't use water directly even over 100°C. The heat collecting system wants to be as hot as possible, the solar cells as cold as possible. Also, the cells decrease efficiency of the heat collection part.
    - danmaz74 11y ago
      If you get the heat from the cells, they need to become colder for sure.
nitrogen 11y ago
...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? 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.

Spooky23 11y ago

Most of the new installations are linked to energy leasing vehicles. Water doesn't work there. Also, most folks use gas or propane to heat water, and gas prices are very low. 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.

hacker234 11y ago

I don't have a link, but combined Solar Electric / Hot Water panels are relatively common Australia. My neighbor has them on his new house. I'll go ask him for details.

danmaz74 11y ago
Thanks, that's interesting to know. Never saw any promotion about them here in Italy.