7 ms·

The primary reason why most panels don't do this is longevity. A panel is designed to be put onto the roof and stay there for 25 years, it is entirely solid sta

The primary reason why most panels don't do this is longevity. A panel is designed to be put onto the roof and stay there for 25 years, it is entirely solid state and its weather hardened to survive hail, wind and lots of sunshine. The moment you introduce water to just the panel you make the panel more efficient but you also drastically increase its failure rate, water corrodes and over 25 years its much more likely to cause a failure. On top of that the pump is a moving part and its going to require replacements over the lifetime of the panel. In many countries around the world Solar heaters for water are quite common. Using tubes to heat water you can get near 99% efficient capture of the suns energy to heat which compares very favourably to the 20% of a solar panel to electricity. But their rated lifetime is quite a bit shorter and their pay off period looks quite different as a result. So while there are benefits to combining them it increases the cost considerably and decreases the longevity and it just doesn't make much economic sense most of the time. Besides on a hot sunny day your panels are going to do great anyway, its clouds that really reduce the collection. As an example my system will give me 34KWh on a cool 100% sunny day but on a hot day its more like 31KWh. But on a cloudy rainy day it can get down to 7KWh. The heat isn't as big as an issue as its made out to be.

hef19898 3y ago
As long as the utilits scale projects in the UAE don't use active cooling or systems tracking the sun, I don't see a reason why I would do it.
- idiotsecant 3y ago
  Utility scale projects in the uae don't want hot water. Your house does, though.
MichaelZuo 3y ago
As long as it's properly designed, built, and assembled, keyword properly, then a 25 year service life is absolutely achievable for the median customer even with an integrated water cooling system.
- dymk 3y ago
  Well that sounds like you'd have a higher failure rate in the margins then, because current solar panels can practically be thrown on the roof with nails and they'll work for 25 years. There's value in simplicity, and something that's going to be ignored on a roof for multiple decades needs to have an idiot proof installation process.
  - MichaelZuo 3y ago
    I imagine many customers will opt for simplicity, some will opt to pay more for properly built installations with integrated cooling and enjoy the advertised benefits, and some will opt for cut-rate installations that will prematurely fail, thinking they got a deal. That seems to be the general pattern whenever a new, non-trivial, innovation is introduced.
    - dymk 3y ago
      People will pay for the system with the best ROI, which is a simple system with simple installation and simple failure modes.
      - deleted 3y ago
        [deleted]
      - bluGill 3y ago
        If this is really a win (see other posts - I question that), then solar panels can be made with integrated pipes for the cooling, and pumps that will last. We can even make a wire/water pipe all in one unit so you just have one connector to install. The pump likewise can be combined with other parts you have to have. All of this will reduce costs for this. Again, I question if the ROI can be good enough to be worth it, but if it really is a win there are lots of options to reduce costs.
tjoff 3y ago
I feel the failure mode should be pretty good though, degrade to a normal solar setup - probably with less airflow and higher temps but not worse than that. Heat degrades panel longevity too so I'd actually assume a water-cooled system to outlive a normal one, in the long run I would be surprised if it wouldn't end up being cheaper. I do agree with the simplicity of a solid state setup though. Whether it makes sense probably depends on where you live. Thinking about it, temporarily running "warm" water might help with keeping snow away, though I am aware that many setups won't generate much in the winter anyway.
- bluGill 3y ago
  Longevity doesn't really matter as most roofs are only good for 25-30 years. As such you are removing the panels anyway to repair the roof, there is not much additional cost to just replace them. Odds are newer solar technology will exist by then and so you will want to upgrade.
  - londons_explore 3y ago
    My tile roof is 120 years old, on a house that is 220 years old. Yo my knowledge it has had basically no maintenance in that time.
    - JenrHywy 3y ago
      Yeah our (concrete tile) roof is about 80 years old. The only maintenance has been replacing broken tiles after a particularly bad hail storm.
      - spiderice 3y ago
        Wait really? Why are we using regular (asphalt?) shingles?
        MetallicCloud 3y ago
        As an Australian who has moved to the USA, I don't know why it's done. I don't know a single person in Australia who has ever replaced their roof. My dad lives in the same house I was born in 40 years ago, same roof. I've been in Colorado for 4 years. We had a new roof put on 2 years ago, then another 6 weeks ago due to a bad hail storm.
dv_dt 3y ago
People often mixup performance of some component of the system, with total system performance, and system cost performance. Even this breakdown is probably oversimplifying. I would suspect you're right on simpler being better here. That doesn't mean this isn't worth exploring. But one practical tradeoff calculation to make to see how viable this is right now is take the component cost of the cooling system and put that into more "simple" solar panels and see what trade of power generated is. If that benefit isn't a win of the cooling system, then a lifetime reliability of the cooling system being less than a lifetime reliability of the solar electric components can only make that tradeoff even worse. But making that calculation might still give someone a target for cost, performance specs to become a viable market option.
- PaulKeeble 3y ago
  Based on the numbers I have provided for the best days a day (of which I might get 50 a year) we can get 9% more output, but over a year that is maybe a few percent. If the pump needs replacing on typical pump periods of 5-10 years that will cost more than I would gain as each is going to be £200 (100 replacement and 100 for the pump) and that alone is more than a few percent of the system. If it drops the life of the panels to 20 years or requires one maintenance on the roof all the savings disappear instantly. Also if the panels cost more than 3% more than the electrical gains aren't worth it alone. The problem is the gains are just too small and the risks and extra costs far too high. Its not really fair because what you would do is flow this hot water into a water cylinder and get ~6KWh of water heating out of it a day. It will produce a lot more heat than that, you get nearly 4x as much heating as you do electricity but i can't use it, I don't need 120Kwh of heated water for showers and in the winter its not going to be enough to heat the house. That is fairly substantial amounts of extra power but I don't need that amount of panels of water heating I likely only need 1 solar heater, the rest is going to be wasted and not help in cooling the panels. Who ever its for its not for people like me.
  - dv_dt 3y ago
    I wonder if it would be interesting for a hybrid pool heating & filtration system where you are already in for a cost of a pump. The differential cost would be for an additional panel array loop and some isolation valves etc.
stephen_g 3y ago
I ended up just getting a bigger PV system and a heat pump hot water system. The clincher is - how much hot water do you actually need? Just running for about two hours at 1kW draw, the heat pump generates all the hot water I need for the next 24 hours. So since I have limited roof space, it’s better for me to use that for PV and just use a few kWh of that per day for water heating, instead of dedicating space to a solar hot water collector.
- Xylakant 3y ago
  The idea behind the combined panels addresses the limited space concern - these are full-size PV panels with a back plane that harvests the heat and cools the panel up front.
- WithinReason 3y ago
  There is that idea where you use water to pump heat under your house over the summer and use it for heating over the winter, and vice versa for cooling.
RandallBrown 3y ago
I'm not sure you'd actually need a pump to get water to most rooftops. Your municipal water pressure should be enough to push it through. I'm not sure corrosion is that big of an issue either. Plumbing in people's houses often lasts far longer than 25 years. Simply running some pipes behind the solar panel and having that fill your hot water tank or flush your toilet wouldn't be terribly difficult, although maybe hard to retrofit.
- benhurmarcel 3y ago
  > I'm not sure you'd actually need a pump to get water to most rooftops. Your municipal water pressure should be enough to push it through. You'd use a closed loop, not fresh water continuously. What a waste of water otherwise...
  - RandallBrown 3y ago
    Isn't the context of this article using the heat from the solar panels to heat water for your home? You wouldn't use a closed loop for that.
- PaulKeeble 3y ago
  Typically the way this works is its a closed loop with antifreeze in it for cold weather and it coils through a water cylinder to do the heating. So the water that flows through the roof panels never goes anywhere. There are a few reasons for this, mainly the extremes of weather both hot and cold you don't want 90C water in your shower nor to freeze water in the system and break it. All of which adds to the cost any complexity but if you dont do it they don't work.
perlgeek 3y ago
Ever since I've learned that cold solar panels are more efficient, I've dreamed about water-cooled PV that uses the heat for warm water supply. One thing I'm worried about in such an integrated solution is water leakage. It looks like you'll need quite a few of these elements to form your roof, and there's got to be a joint between each pair of elements, and each joint has the potential for leaks, for example due to thermal expansion and contraction. With traditional roof shingles (at least as they are done in central Europe), the tiles overlap, so that you don't need a perfect fit, and when the tiles expand at higher temperatures, the overlap still keeps water out. Doesn't seem like that simple mechanism could work if water flows through the solar tiles.
sparrowInHand 3y ago
So? drag the heat out via Peltier and have a safe layer of material between solarlayer and heat transport?
psadri 3y ago
34kwh!? That’s a pretty beefy setup.
rjmunro 3y ago
I read that the primary issue for similar combined water and PV systems is that it's great for making a large amount of slightly warm water, but it can't make water hot enough for general domestic use while keeping it cold enough to improve the solar panels efficiency significantly. Also when the sun is shining, there isn't much demand for heating, so you can't use the hot water in radiators. I've heard it works well with swimming pools, as the temperature of the water required in the pool is cold enough to help the panels keep cool, and you generally want a pool to be warm on hot days in summer when you will use it most.
ZeroGravitas 3y ago
More generally, the trade off is: buying/deploying more panels. So adding water cooling adds materials and work and potential repairs etc. Translate that into money, and use that to buy and install more panels, which one wins? Same applies to more efficient panels, trackers that follow the sun and most other solar innovations. As panel prices drop the calculus shifts more and more towards more panels. There are some constrained environments that drive innovation in size/weight or whatever but the mass market is driven by electricity output/dollars.

hef19898 3y ago

As long as the utilits scale projects in the UAE don't use active cooling or systems tracking the sun, I don't see a reason why I would do it.

idiotsecant 3y ago
Utility scale projects in the uae don't want hot water. Your house does, though.

MichaelZuo 3y ago

As long as it's properly designed, built, and assembled, keyword properly, then a 25 year service life is absolutely achievable for the median customer even with an integrated water cooling system.

dymk 3y ago
Well that sounds like you'd have a higher failure rate in the margins then, because current solar panels can practically be thrown on the roof with nails and they'll work for 25 years. There's value in simplicity, and something that's going to be ignored on a roof for multiple decades needs to have an idiot proof installation process.
- MichaelZuo 3y ago
  I imagine many customers will opt for simplicity, some will opt to pay more for properly built installations with integrated cooling and enjoy the advertised benefits, and some will opt for cut-rate installations that will prematurely fail, thinking they got a deal. That seems to be the general pattern whenever a new, non-trivial, innovation is introduced.
  - dymk 3y ago
    People will pay for the system with the best ROI, which is a simple system with simple installation and simple failure modes.
    - deleted 3y ago
      [deleted]
    - bluGill 3y ago
      If this is really a win (see other posts - I question that), then solar panels can be made with integrated pipes for the cooling, and pumps that will last. We can even make a wire/water pipe all in one unit so you just have one connector to install. The pump likewise can be combined with other parts you have to have. All of this will reduce costs for this. Again, I question if the ROI can be good enough to be worth it, but if it really is a win there are lots of options to reduce costs.

tjoff 3y ago

I feel the failure mode should be pretty good though, degrade to a normal solar setup - probably with less airflow and higher temps but not worse than that. Heat degrades panel longevity too so I'd actually assume a water-cooled system to outlive a normal one, in the long run I would be surprised if it wouldn't end up being cheaper. I do agree with the simplicity of a solid state setup though. Whether it makes sense probably depends on where you live. Thinking about it, temporarily running "warm" water might help with keeping snow away, though I am aware that many setups won't generate much in the winter anyway.

bluGill 3y ago
Longevity doesn't really matter as most roofs are only good for 25-30 years. As such you are removing the panels anyway to repair the roof, there is not much additional cost to just replace them. Odds are newer solar technology will exist by then and so you will want to upgrade.
- londons_explore 3y ago
  My tile roof is 120 years old, on a house that is 220 years old. Yo my knowledge it has had basically no maintenance in that time.
  - JenrHywy 3y ago
    Yeah our (concrete tile) roof is about 80 years old. The only maintenance has been replacing broken tiles after a particularly bad hail storm.
    - spiderice 3y ago
      Wait really? Why are we using regular (asphalt?) shingles?
      - MetallicCloud 3y ago
        As an Australian who has moved to the USA, I don't know why it's done. I don't know a single person in Australia who has ever replaced their roof. My dad lives in the same house I was born in 40 years ago, same roof. I've been in Colorado for 4 years. We had a new roof put on 2 years ago, then another 6 weeks ago due to a bad hail storm.

dv_dt 3y ago

People often mixup performance of some component of the system, with total system performance, and system cost performance. Even this breakdown is probably oversimplifying. I would suspect you're right on simpler being better here. That doesn't mean this isn't worth exploring. But one practical tradeoff calculation to make to see how viable this is right now is take the component cost of the cooling system and put that into more "simple" solar panels and see what trade of power generated is. If that benefit isn't a win of the cooling system, then a lifetime reliability of the cooling system being less than a lifetime reliability of the solar electric components can only make that tradeoff even worse. But making that calculation might still give someone a target for cost, performance specs to become a viable market option.

PaulKeeble 3y ago
Based on the numbers I have provided for the best days a day (of which I might get 50 a year) we can get 9% more output, but over a year that is maybe a few percent. If the pump needs replacing on typical pump periods of 5-10 years that will cost more than I would gain as each is going to be £200 (100 replacement and 100 for the pump) and that alone is more than a few percent of the system. If it drops the life of the panels to 20 years or requires one maintenance on the roof all the savings disappear instantly. Also if the panels cost more than 3% more than the electrical gains aren't worth it alone. The problem is the gains are just too small and the risks and extra costs far too high. Its not really fair because what you would do is flow this hot water into a water cylinder and get ~6KWh of water heating out of it a day. It will produce a lot more heat than that, you get nearly 4x as much heating as you do electricity but i can't use it, I don't need 120Kwh of heated water for showers and in the winter its not going to be enough to heat the house. That is fairly substantial amounts of extra power but I don't need that amount of panels of water heating I likely only need 1 solar heater, the rest is going to be wasted and not help in cooling the panels. Who ever its for its not for people like me.
- dv_dt 3y ago
  I wonder if it would be interesting for a hybrid pool heating & filtration system where you are already in for a cost of a pump. The differential cost would be for an additional panel array loop and some isolation valves etc.

stephen_g 3y ago

I ended up just getting a bigger PV system and a heat pump hot water system. The clincher is - how much hot water do you actually need? Just running for about two hours at 1kW draw, the heat pump generates all the hot water I need for the next 24 hours. So since I have limited roof space, it’s better for me to use that for PV and just use a few kWh of that per day for water heating, instead of dedicating space to a solar hot water collector.

Xylakant 3y ago
The idea behind the combined panels addresses the limited space concern - these are full-size PV panels with a back plane that harvests the heat and cools the panel up front.
WithinReason 3y ago
There is that idea where you use water to pump heat under your house over the summer and use it for heating over the winter, and vice versa for cooling.

RandallBrown 3y ago

I'm not sure you'd actually need a pump to get water to most rooftops. Your municipal water pressure should be enough to push it through. I'm not sure corrosion is that big of an issue either. Plumbing in people's houses often lasts far longer than 25 years. Simply running some pipes behind the solar panel and having that fill your hot water tank or flush your toilet wouldn't be terribly difficult, although maybe hard to retrofit.

benhurmarcel 3y ago
> I'm not sure you'd actually need a pump to get water to most rooftops. Your municipal water pressure should be enough to push it through. You'd use a closed loop, not fresh water continuously. What a waste of water otherwise...
- RandallBrown 3y ago
  Isn't the context of this article using the heat from the solar panels to heat water for your home? You wouldn't use a closed loop for that.
PaulKeeble 3y ago
Typically the way this works is its a closed loop with antifreeze in it for cold weather and it coils through a water cylinder to do the heating. So the water that flows through the roof panels never goes anywhere. There are a few reasons for this, mainly the extremes of weather both hot and cold you don't want 90C water in your shower nor to freeze water in the system and break it. All of which adds to the cost any complexity but if you dont do it they don't work.

perlgeek 3y ago

Ever since I've learned that cold solar panels are more efficient, I've dreamed about water-cooled PV that uses the heat for warm water supply. One thing I'm worried about in such an integrated solution is water leakage. It looks like you'll need quite a few of these elements to form your roof, and there's got to be a joint between each pair of elements, and each joint has the potential for leaks, for example due to thermal expansion and contraction. With traditional roof shingles (at least as they are done in central Europe), the tiles overlap, so that you don't need a perfect fit, and when the tiles expand at higher temperatures, the overlap still keeps water out. Doesn't seem like that simple mechanism could work if water flows through the solar tiles.

sparrowInHand 3y ago

So? drag the heat out via Peltier and have a safe layer of material between solarlayer and heat transport?

psadri 3y ago

34kwh!? That’s a pretty beefy setup.

rjmunro 3y ago

I read that the primary issue for similar combined water and PV systems is that it's great for making a large amount of slightly warm water, but it can't make water hot enough for general domestic use while keeping it cold enough to improve the solar panels efficiency significantly. Also when the sun is shining, there isn't much demand for heating, so you can't use the hot water in radiators. I've heard it works well with swimming pools, as the temperature of the water required in the pool is cold enough to help the panels keep cool, and you generally want a pool to be warm on hot days in summer when you will use it most.

ZeroGravitas 3y ago

More generally, the trade off is: buying/deploying more panels. So adding water cooling adds materials and work and potential repairs etc. Translate that into money, and use that to buy and install more panels, which one wins? Same applies to more efficient panels, trackers that follow the sun and most other solar innovations. As panel prices drop the calculus shifts more and more towards more panels. There are some constrained environments that drive innovation in size/weight or whatever but the mass market is driven by electricity output/dollars.