Could Solar Water Heaters Become Popular Again? - Slashdot

Posted by EditorDavid

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  They are pretty popular in my country, and have been so for the last 15 years, give or take.
  And they are not really expensive either.

  • 1 hidden comment

  • Re:

    In fact in some countries they are mandatory on new construction, at least they were 20 years ago.

    The problem with them in the northern part of North America is that you have to use some kind of non-water fluid and heat exchanger to heat the water. In climates where it never freezes the water can be heated directly.

    I've long been interested heating air instead of water, using a box with drain-pipe air channels painted black, covered in glass. Could easily heat a garage even in a cold climate. Even with j

    • Re:

      I have always found that solar water heaters was the smartest, simplest and most efficient use of solar energy.

      • Re:

        Indeed. I live in the Philippines and see them on almost every rooftop.

        Whoever wrote TFA needs to get a passport and go see the world.

        Even in America, thermal solar is common for heating swimming pools.

    • Re:

      I should have added that in Canada, I have seen some where you simply drain the system and put it to rest when freezing temperatures arrive. The heat exchange thing kind of make it more complex and break the simplicity principle. I'd sure incorporate one in a new house if I ever build one from scratch. It seems like a no-brainer to me.

      • Re:

        Perhaps a dual purpose system could be constructed for northern latitudes. During the winter fill the system with antifreeze and redirect the fluid through a radiator that helps the furnace maintain a home's temperature on sunny days (which even in northern Ohio is one in four days in the winter, but at least its something).

        • Re:

          So like a heat pump, but less efficient?

          • Re:

            Yeah, I suppose that would describe it. So hard to come up with energy efficient and green solutions.

            • Re:

              I'm unclear on the heat pump / solar NET efficiency..23 *.75 (assuming OAT > 0C) is STILL only 17.25% (of insolation) and that's nearly impossible to reach.

          • Re:

            Like a heat pump, but does not require power.

            • Re:

              Except it wouldn't be a heat pump. A heat pump uses a unit of energy to move a certain number of units of heat energy from one medium to another. This would just be a heat exchanger, which passively moves a certain fraction of the energy in one fluid to another. So way less efficient than a heat pump. Except of course that efficiency doesn't really matter here, provided the system was cheap, robust, and consumed little or no electrical power.

    • Water-only system for deep-freeze climates

      > you have to use some kind of non-water fluid

      Not necessarily. You can also have the panels drain into a reservoir overnight, with the circulating pump only turning on again in the morning once the panels have gotten warmer than the reservoir. Why have fluid in the panels when there's no heat to be collected?

      A DIY system I've occasionally considered building: https://www.builditsolar.com/P... [builditsolar.com]

      • Re:

        My parents had one of these on our house when I was growing up in the 80s/90s. I didn't use any kind of recirculated loop. The actual tap water you consumed ran though it. Basically when it was installed they diverted the cold water going into the electric water heater up to the solar heater on the roof, then the water returning from the solar heater went into the "cold" input on the electric heater. If the sun was out and it was bright enough the electric water heater wouldn't have to kick on or run for as

    • Re:

      Here people are using anti-freeze and we get very cold winters. For systems that use concentrators water isn't a good fit so they use oil and a heat-exchanger to heat the water.

      And in regards to heating air, there was a company that sold such equipment here - intended for small unheated buildings, like garages or cabins. It was just a box you mounted on a south-facing wall, it had a small PV that delivered power to a fan that drew the air through the box and pushed it into the building. Extremely simple des

  • Re:

    They could really use these in Canada. Just think of how much energy is wasted on refrigerator ice makers each year.

  • Re:

    Solar water heater system is about $3500 to install in the US, and $5K when I priced one for my place (where everything is more expensive than the national average). A 50-gal electric water heater is about $700 to replace. Since nearly every home in the US is already plumbed for a central water heater, the cost to swap in a new unit is cheaper than installing a whole new system.

    I am still thinking about getting one, because I have a good climate for it. Clear sunny days even a few days a week in the winter.

• During the past month we've had about four days of sunshine. Not because I live near the Arctic Circle, but because we've had cloud cover for that long. Today started out cloudy and snowy, followed by about a total of two hours of sunlight. Now the clouds have returned and we won't see clear skies until sometime next week.

  And this is every winter. While I'm a big fan of letting the Sun warm my place by having its light come through my windows, when you don't see it for two months at a shot it's a big difficult to heat your water using this system.

  • "four days of sunshine" is not the same thing as "only four days of solar energy". The Sun is always there, it's just more or less occluded by varying atmospheric conditions. A solar thermal system is much more efficient at gathering insolation than PV cells because (among other factors) it has a broader range of incoming wavelengths that it can convert to useful energy. Basically any wavelength that can reach the pipe network and get absorbed, will be converted into heat. In particular, PV cells are insensitive to short-wavelength light, which is _exactly_ the wavelengths that pass more or less freely through cloud cover.

  • Re:

    Temperature inversion is a bitch. Same here in Northern Ohio.

  • Re:

    The systems I have seen simply preheat the water going into the water tank, no pumps no nothing. An home made series of pipes painted in black on your roof do the trick. Near Arctic circle, drain the pipes in winter and bypass the system, standard water pipe valves do the trick. In summer, a lot of sunshine near the Arctic circle, use your home made pipe system and save on water tank heating cost.

  • Re:

    So you're saying that if you had a solar hot water system you'd have saved energy 4 days in the past month. What's the downside again? I assume you realise that these systems do not rely 100% exclusively on sunshine right?

• If the cost is more than recovered over the expected lifetime of the option, by a higher margin than other options, go for it.

  If the upfront cost is too high, but still results in a net savings for everyone... it's time to consider a subsidy.

  • Re:

    Okay, but what about personal and societal benefits that cannot necessarily be assigned a dollar value?

    =Smidge=

    • Re:

      When you're talking about providing subsidies funded by taxation... you get experts to guess at it and use their analysis to make your determination.

      I mean, if you're doing it correctly. Realistically I suppose you do whatever the biggest lobby bribes/convinces you to do.

• by test321 ( 8891681 ) on Saturday February 17, 2024 @01:51PM (#64247788)

  I understand it's not popular in the US, but there is no need to quote anecdotes from the 1980s. This technology has been very popular in the Mediterranean area. According to Wikipedia:
  * 90% of Israeli homes are equipped https://en.wikipedia.org/wiki/... [wikipedia.org]
  * 30-40% in Greece https://en.wikipedia.org/wiki/... [wikipedia.org]
  * installation now compulsory in new buildings in Spain (by the building code) https://en.wikipedia.org/wiki/... [wikipedia.org] .

  • Re:

    Can confirm. The rooftops in Athens are covered with solar water heaters.

  • Re:

    Not just. You can barely drive down a street in Australia without seeing solar hot water. They are also insanely popular in China, and even places like Austria, which has miserable weather for a large part of the year.

• ... is that solar water heaters don't use any exotic materials from questionable and/or polluting sources or expensive dedicated factories; you could fab one yourself easily. It's basically just a grid of pipes on your roof, and you run your water through it before it hits the water heater. The ones I used to see a couple decades ago weren't actually "pipes in a glass box" as the article describes; they were a zigzag of pipes covered with a black tarp-like material to reduce albedo. I can see how the greenhouse effect of a glass box would make it even more useful, however. Even in situations where you don't get enough insolation to make it shower-hot, you still get a very useful preheat that reduces the amount of energy your water heater has to inject to get the water to temperature. And the systems are very durable. Additionally, you don't have any of those pointless and annoying battles with local electric company regulations that make rooftop solar electricity an exercise in frustration in many areas. Solar water heating is a 100% win.

• New U.S. subsidies , that is poor people paying for rich people's toys. See also EVs.

  • Re:

    It's not a toy. Would you rather have a hot roof or hot water for your bathtub, given that you can get either of them for free?
    • 1 hidden comment

    • • Re:

        Roof penetrations are easily weather proofed, just use a vent cover with a 90 so that the hoses from the system pass through the gooseneck and into the attic. PEX lasts a looooong time, as do sun-resistant hoses. Plug those into the hot water system and you have a bulletproof solution.

• Solar hot water heat is required by law in all new housing in Hawaii. This is not "forgotten technology", just because some journalist can't do basic research...

  • Re:

    I think you can get away with PV and a heat pump now legally, but yes they are widely used (and required) for low-rise residential. Still bothers me that highrises don't require solar hot water tempering, but such is life.

    • Re:

      Except that PV is more expensive and less efficient, a heat pump water heater is more complex, lasts less time, etc...

      Or you just go simple - pipes on the roof that collect the solar energy as heat directly.

      • Re:

        I only really have statistics for Hawaii, but solar hot water is very expensive. A replacement system for me is about $30k in plumbing cost, plus I will need carpentry and drywall work to replace the big tanks if I go like-for-like. It also isn't foolproof; if it malfunctions it dumps a lot of water quickly. It is hard on check valves and you absolutely need to make sure the plumber isn't lazy with roofing details... oh yeah, you need a roofer too for the replacement, but it still doesn't guarantee no le

• Not great for the environment because it uses disposable plastic. But I often bring large thick black plastic trash bags camping for hot showers. Just fill it with water from a stream or lake. Tie it up somewhere in direct sunlight above head level for a few hours. Poke a few small holes in it when you are ready to bathe. Pack out everything when you leave. I’m sure one could devise a reusable one. But single use bags are pretty darn inexpensive.

  • Re:

    I'm sure these are illegal in California. Or they cause cancer. Or both.

  • Re:

    https://www.amazon.com/Portabl... [amazon.com]

    No reason it has to be disposable.

  • Re:

    IIRC, evacuated tube collectors are mostly made from glass and have a very long service life.

• The more people talk of crazy stuff like solar water heaters the more people will look to getting more nuclear power plants built. People want warm water for cleaning themselves and their dishes and such. These things tend to happen while people are at home, in the morning before the sun comes up, or the evening after the sun has set.

  I know people will suggest using timers for washing clothes,dishes, and such for when the sun shines. For those willing to put solar water heaters on their roof that might b

  • 2 hidden comments

  • Re:

    In México at least, most of the solar water heaters have a water deposit attached to them. And that tank keeps the water hot, *very hot*, for a very long time. At least from the moment when you want to use it (as you say in your example, the morning or the evening) to the next moment where the water will be able to be heated by the sun.

    I actually don't think you can really use them as "instant" heaters, at least not this kind of models I know. They took their time to heat the water, but then you have

  • Re:

    Good old MacMann, back spouting bullshit every time he can to support his nuclear nonsense.

    It's not "crazy stuff" - it's proven, existing technology in a number of countries outside the USA. But then having fact based arguments refute your points has never changed you in the past, has it?

    A society heating water from sunlight is a society that doesn't need nuclear. And that's what you're afraid of - that people will see your industry for the uneconomical, unsustainable, unwanted crap that it is.

  • Re:

    The great thing about heat is that water is actually a *really* cheap and easy way to store a LOT of it.

    Most solar water heated systems I've seen store at least 5-10 days worth of heat - after all it only costs you the price of an insulated water tank. Unlike electric batteries, it's easy to budget for the a worst-case scenario.

    Heck, I know one guy that has a huge enough tank that he stores heat in the summer to heat his house through the winter.

  • Re:

    In countries where this is used, in the morning water is still pretty warm from the previous evening.

• by stikves ( 127823 ) on Saturday February 17, 2024 @02:48PM (#64247888) Homepage

  The reason we don't have those are the subsidies in the first place.

  New U.S. subsidies can cut the price in half depending on location, the article points out.

  Good luck with that!

  Back in Arizona, I was visiting a friend who was getting a price quote for exactly this to be installed. A dummy water tank that will be integrated with his hot water plumbing at home. And the prices, somehow started just over the subsidy levels. And given the subsidy was large all option prices were amplified as well.

  (So, you could get a similar system in any other country say for $500 to $2,500. Here can't remember the exact number but say the subsidy is $3,000, then the prices were something like $3,500 to $10,000. I might not be exact, it has been a while, but should be in the ballpark).

  That is why "we can't have nice things". Anytime there is a subsidy, the pricing immediately includes that (remember the $40 HDTV/ATSC conversion boxes)? And not only that, but can make the overall product totally unaffordable (looks at college with guaranteed loans).

  • Re:

    Down here in Belgium, it is by many considered as a waste of money for a simple economical reason. The costs of sun based waterheaters are close to that of a decent array of solar panels. When your water is at temperature, your water heating installation is useless. Solar panels keep delivering power that you can sell or store. In other words, you need to shower a lot to get an advantage out of it.

    • Re:

      Sell, yes. Store, not so much. Storage requires a larger battery bank and messes up the ROI economics of your system.

      Storage in a solar collector system requires more hot water tanks. A relatively low tech (read: cheap) solution.

      Not everyone can sell power back onto the grid at an economically useful price. Privately owned utilities hate the competition. Public utilities hate the loss of revenue that they can shuffle through their Three Card Monte revenue distribution system.

    • and amount used

      >Down here in Belgium, it is by many considered as a waste of money
      >for a simple economical reason.

      there's also the question of the amount used and needed.

      When my gas water heater failed a few years ago, I considered one of these systems.

      Living in the desert, my most recent summer gas bill had been $17. $10 of that was for the connection charge, and only $7 for the gas used--with three long haired females showering daily!

      Of that $7, most would be for the water heater, with some for the stove, and may

  • Re:

    This is a paranoid and broken conception of economics. Subsidies do not drive up prices in a market like this unless there is some sort of artificial barrier to entry that generates a monopoly for the installer which I highly doubt is the case for solar water heating. If subsidies are generous enough they do drive pro-active sales efforts -- which is part of the point of subsidies in the first place, after all they are put in place to motivate the marketplace. Any good salesman is going to try to up-sell,

    • Re:

      There has always been overhead in terms of permitting and inspection. Doesn't explain increases in US rooftop PV pricing despite dramatic decreases in underlying material cost.

      Subsidies obviously drive costs - the only question is by how much.

      • Re:

        What possible mechanism do subsidies have to drive costs?

        You start overcharging because of the subsidy - all one of your competitors has to do is keep charging a fair price and they'll drive you out of business. Widespread collusion between small businesses is actually fairly uncommon - that's more megacorp territory, where the precautions and lawyers to avoid getting caught are a tiny marginal cost of doing business, and it's incredibly rare that anyone "who matters" ever goes to jail.

        What they may do is

• Some manufacturers (eg DualSun) make it possible to have both in one panel. Electricity is made at the front and hot water is made behind the photovoltaic cell. This also ensures that the solar cell does not get too hot.
• PV cells are now at about 24% of efficiency. Use the electricity to power up a heath pump and you draw circles around thermal panels. For example, my pump has a gain of about 4.2 to heath water at 60 degrees, when ambient temperature is close to zero. I pulled the plug from my solar heaters since a year, I will never come back.

  • Re:

    What plug?

    • Re:

      The advantage of the electric solar / heat pump hot water setup is that you can use the electricity for other stuff when your hot water is hot enough, and if you have to boost the temperature it's a lot cheaper than the resistive heaters that most thermal solar boosters use.

      Thermal solar panels are ridiculously expensive here in Australia - I can buy 6kw of electrical solar panels and an inverter for the same price as a 300L close coupled thermal solar, which range from about $4000 - $8000.

  • Re:

    Of course the cost of heat pumps plus 3x the area of PV panels is dramatically higher than solar thermal, so if your limiting factor is money rather than available area with good solar exposure that's not such a great trade.

• It seems like nowadays you would be better off just using a heatpump. Before heatpumps became popular, I often wondered why we don't have more thermal solar. But now that heatpumps are widely available it probably makes more sense to use PV on the roof and a heatpump for hot water.

  Of course it does depend somewhat on the climate where you live. There are some sunny cold places. Maybe direct solar heating would be better in those places since the heatpump COP is degraded when it is cold. I mean, the therma

• For people near the equator, sure a couple cheap black plastic connectors make sense if they can't afford to fill up their roof with PV. Those will work for them for most of the year.

  If you live anywhere which requires evacuated tube collectors, you're better off with more PV and an electric/heatpump boiler.

  • Re:

    My dad did this at the guest house he ran the 70's - lots of coils of black poly pipe on the roof, connected to the inlet of the gas hot water system, so the water was at least partly pre-heated, reducing the amount of gas needed.

• My situation might be unique, but my 15-year old system has another 3-5 years of life in it and after that it is gone. A heat pump water heater plus extra PV and battery makes significantly better use of space for us. Solar hot water doesn't work well (at least in my climate) to temper inlet hot water for a heat pump system, so any supplemental heating needs end up with resistive load. Solar hot water needs a lot of storage, but storing heat in a water tank is only good for a ~2-3 day buffer, and most of

• Classic US centric journalism : if it doesn't exist in the USA so it doesn't exist at all.

• Here in Australia we have a Solahart solar hot water heater on our roof. We'd never buy another house with one and we're praying for a severe enough hail storm to destroy the one we have so that we can replace with with an electric hot water system on insurance.

  The technology itself is ok in theory, the problems are to do with maintenance and reliability. The system has an electric controller that operates electric pumps to drive cooler water from the bottom of the storage tank, up to the panels on the roof

  • Re:

    A friend that worked at the SERI out in Golden Co told me that the ongoing maintenance costs to clean the pipes and collectors, replace the pump(s) and valve(s) etc push solar hot water over the edge of economically viable.
• The USA discovers an energy source that is already popular around the world & has been for at least a century. It is & always has been a complete no-brainer. It's so cheap & efficient that some countries & regions require it by law on all new buildings.
  
  Well, I guess better late than never.
• For the most part hot water heat pumps have superseded solar hot water systems. Roof are better suited to photovoltaic panels and electricians to be. Frank are a lot lighter than plumbers. Iâ(TM)d much rather have electricians running around on my roof than Plumbers hot water heat pumps work better in cloudy winter conditions which are often the design conditions for a future, renewable energy grid as there is less solar and wind resource in winter than in summer as a general rule Sanden, for example,

• Compare 70% efficient direct solar with 20% efficient solar PV driving a hot water heat pump. Those pumps can easily exceed 350% efficiency, making PV the winner. I have a system that uses CO2 as the refrigerant and it works down to 10C (and has no booster). It's probably not suitable in colder climates but then direct solar hot water can struggle there too. A big advantage is that you can program the heat pump to come on during the middle of the day, when the air is hottest (making it most efficient) a

  • Re:

    Slashdot ate my −. I meant -10C.

• We bought a house ~5 years ago.
  It had solar hot water panels on the roof, installed in the 80s or 90s.
  They worked; they gave a boost to the heat and H/W.
  But...the panels were at end-of-life, and were starting to leak, and nobody, nobody, services these things any more.
  We ended up scrapping them and installing solar electric panels in their place.