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Revitalising Defunct Solar Hot Water System

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  1. #1
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    Default Revitalising Defunct Solar Hot Water System

    My 2 storey house has solar water panels on the roof. There is no roof tank. I think the system is supposed to be connected to a pump which circulates water to a ground floor storage tank when the panels heat the water to some set point temperature.

    The electric hot water tank in the ground floor garage burst just before the house sale settled and the previous owner replaced the tank with a small tank that is not connected to the solar panels.

    This small tank has stopped working so I am looking at replacing it with a bigger tank and ideally connected up to the solar panels again.

    Do I need a special hot water tank for it to be capable of being connected to solar or can I get a normal hot water tank?

    I was going to go for 80l as that is more than I need even though it is small for the house. Do solar systems need big tanks or would 80l be OK?

    I followed the piping in the loft to the roof holes out to the panels. There does not seem to be a pump anywhere on the system. Is there supposed to be a pump or do some solar HW system s not use a pump?

    One of the panels pictured here

    img_20201029_191116-copy.jpg
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  2. #2
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    Some quick answers. If the tank is not close coupled, and/or not above the height of the heat source, you'll need a circulation pump and controller. The old pump was probably on or near the old tank, so that might explain why it's missing. You don't necessarily need a special tank, but that depends on what you are trying to achieve. 80 litres is very small for a solar hot water system. On a sunny day size tank will heat very fast so most of the day's potential solar energy won't be put to use. You'll have no ability to carry hot water over for a cloudy day. Small tanks lose heat fast, it will cool down a lot overnight, so you'll effectively have a solar tepid water service, which boils on sunny days.

    I am off grid and have solar hot water with no backup. I reused a relatively new 250 litre electric storage tank that was already installed when we purchased the house. We never run out of hot water, but this is not the normal experience - it's taken quite a lot of effort and challenging conventional wisdom to achieve this.

    We have evacuated tube collectors which are a lot more effective on cloudy and/or cold days than plate collectors, giving between 50 - 100% more heat when you need it most. The tank has been super insulated so it stays hot over several days. (I would guess that a typical hot water tank in Australia bleeds half or more of the energy put into it into the surrounds.) The plumbing is optimised so that minimum cold water is drawn off before hot water arrives, wasting as little heat as possible. Our tank is within a metre of the washing machine and shower, taps further away like the vanity basin and bidet are fed with small bore pipes. We have a seperate tank for the kitchen within a metre of the sink and dishwasher.

    Evacuated tubes do not have water inside them, but feed heat into a water jacket header or manifold which can be pressurised. If the manifold corrodes it can be replaced and the tubes reused. Also individual tubes can be replaced if one were to be damaged, and a damaged tube does not cause a leak or the failure of the HWS.

    Setting up an effective solar hot water system to work properly is not cheap. If you already have a backup instant gas booster then replacing the booster with one selected for energy efficiency would be cheaper that reusing the solar collectors, and likely cheaper for future energy costs as well. The flat plate collectors have a finite life, so you may be needing to replace then sooner than you realise. Also plate collectors can't usually take high pressure, so either work in a gravity feed system, or need a heat exchanger in the pressurised storage tank.
    Before you speak, ask yourself: Is it necessary, it is true, does it improve on the silence? - Baba

  3. #3
    4K Club Member Marc's Avatar
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    Quote Originally Posted by mojorising View Post
    My 2 storey house has solar water panels on the roof. There is no roof tank. I think the system is supposed to be connected to a pump which circulates water to a ground floor storage tank when the panels heat the water to some set point temperature.

    The electric hot water tank in the ground floor garage burst just before the house sale settled and the previous owner replaced the tank with a small tank that is not connected to the solar panels.

    This small tank has stopped working so I am looking at replacing it with a bigger tank and ideally connected up to the solar panels again.

    Do I need a special hot water tank for it to be capable of being connected to solar or can I get a normal hot water tank?

    I was going to go for 80l as that is more than I need even though it is small for the house. Do solar systems need big tanks or would 80l be OK?

    I followed the piping in the loft to the roof holes out to the panels. There does not seem to be a pump anywhere on the system. Is there supposed to be a pump or do some solar HW system s not use a pump?
    A standard solar hot water tank with electric backup is usually 400L. An 80L tank is there only because it was the cheapest option for the seller. You should demand the same size tank and solar circulation pump be replaced,and not accept an inadequate tank since you purchased a house with a solar hot water system, and you now have ... hum ... nothing really.
    A HW fit for a caravan may be.

    The circulation pump comes with the solar water tank and is screwed to the side of it. You will also need to check if the thermostat in the solar panel and the safety valve work.
    You can not use an ordinary electric hot water tank if you want to have booster for rainy days. The solar tank has the heating element near the top of the tank so that it only heats 1/4 of it in emergency and not the whole tank. Using a normal tank would defeat the purpose of the system.
    I am surprised you have more than one panel for one tank.
    I suggest to visit your local supplier and explain what you have. You will need a plumber to fix everything up anyway.
    “It is not necessary to accept everything as true, one must only accept it as necessary”
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  4. #4
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    I've a 250l tank with the circulation pump on the side of the tank. On sunny days, the pressure relief value operates as its essentially boiling.
    My set up is similar to yours with 3 flat plate solar on the roof and HW tank on the ground with circulation pump at mains pressure (pressure pump at the water tank) and operates fine.
    The temp sensor is a wire from the top of the panels back down the the tank that is connected to the circulation pump with another sensor on the HW tank.

    If I were to do it again, I do like the idea of having a booster element at the top rather than the single element at the bottom so like Marc said, if needed your only heating up the top 1/4.....unless you have a largish solar electric set up in which case, the bottom works perfect to maximise the solar electricity usage

    Now that I only heat water during the day (Solar Water & new 12.7kW Solar electricity with a timer switch to turn the element off at sun down), what John says makes perfect sense with a lot of heat loss during the night. If the 250L water was just warm when I went to bed, then its stone cold in the morning....and 80L would be a lot worse. So no cloths washing late in the arvos to ensure we have a full tank of HW before the sun goes down and therefore plenty in the morning.

    An 80L tank wouldn't be a good solution for all the reasons John stated below and being up in southern QLD, you would get even more sunny days than here in Melb.

  5. #5
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    Thanks for the detailed answers John and Marc and Bart

    An 80L tank is there only because it was the cheapest option for the seller. You should demand the same size tank and solar circulation pump be replaced
    It is only 50l. I was planning on going big at 80l..!

    The deal went down a couple of years ago so I think that boat has sailed and I am stuck with my caravan tank.

    Here is the old 315l tank with what might be a pump on the side.

    The strange thing is that the small tank has started working again spontaneously sometime since I last checked it 2 weeks ago. I was just checking some details on the spec panel when I noticed it was hot again.

    I might defer my solar resurrection plan until I have done the cost benefit payback calculation. Those big solar tanks seem quite expensive and my leccy bills are small.

    img_20211121_175955.jpg


    img_20211121_180221.jpg
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  6. #6
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    The strange thing is that the small tank has started working again spontaneously sometime since I last checked it 2 weeks ago. I was just checking some details on the spec panel when I noticed it was hot again.[Q


    For the existing 50 litre to go cold you possibly have one or more of the following
    Faulty thermostat
    Faulty element
    Faulty off peak switch
    Faulty wiring

  7. #7
    4K Club Member Marc's Avatar
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    Quote Originally Posted by mojorising View Post

    It is only 50l. I was planning on going big at 80l..!

    The deal went down a couple of years ago so I think that boat has sailed and I am stuck with my caravan tank.

    Here is the old 315l tank with what might be a pump on the side.

    The strange thing is that the small tank has started working again spontaneously sometime since I last checked it 2 weeks ago. I was just checking some details on the spec panel when I noticed it was hot again.

    I might defer my solar resurrection plan until I have done the cost benefit payback calculation. Those big solar tanks seem quite expensive and my leccy bills are small.
    I failed to mention that if you have a decent off peak rate, the solar hot water is a waste of time and money. When we installed it some 10 years ago or more... it was only because the old tank was on the way out, and the whole shebang cost me the same I would have paid to replace the tank, thanks to Kevin Rudd's generosity with other people's money.

    When all was installed and running I compared a bill with solar and without. Without solar I was paying then $30 towards HW with off peak. With solar I went down to $6. Big whoop. Sure those are ancient prices, today the difference is likely to be bigger, but clearly not worth spending much money.

    Get a decent size tank and hook it to off peak electricity, for as long as the morons concede you gracefully to use off peak. When the punishing green cavalry comes charging, maybe you can install a wood fired hot water system, or a diesel one.

    As far as the small tank playing up, what Cyclic said, plus ... the replacement from the solar system to the caravan tank, was most likely not done by a plumber, so who knows what the solar panels and pipes are doing to the poor little project of a hot water tank. Better get it checked.

    Ps ... I would call the solicitor that did your conveyancy and check if you have a recourse.
    “It is not necessary to accept everything as true, one must only accept it as necessary”
    Franz Kafka

  8. #8
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    https://www.yourhome.gov.au/energy/hot-water-service

    some good general info with a diagram on your potential setup (at least how it was likely configured in the past)...thanks to the post from Bloss

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