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Solar Hot Water System Advise - Evacuated Tubes

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  • Solar Hot Water System Advise - Evacuated Tubes

    I have established a fund for my house with the long term goal being either off grid or grid tied with minimal dependance. So I figured the first place to start is to get my household as energy efficient as possible. And the best place to begin is replacing our electric hot water system. Our house is 3 bedrooms, 2 adults and 1 child.

    I have a plumber mate who reckons my 315L tank can be retrofit for solar hot water. So I should only need to purchase an appropriate solar hot water system to connect to the tank.

    I am in the early stages of research but thus far my research suggests "evacuated tubes" are the best option.

    I would really love to hear any feedback or recommendations from anyone who has implemented (or is planning to implement) a similiar setup or has anything useful to add about this setup.

    I will post my progress here as I go so it helps others that might embark on the same solution.


    Last edited by jelloir; 03-22-2014, 10:04 PM.

  • #2
    Hey James,

    I had a solar hot water system with evacuated tubes installed when we built our house a few years back. We ended up selling the house after about a year, so I can't give you a long term view of the system.

    I can say that I was pretty impressed with the system and how efficient it was. I'm going off memory with the exact details, but here's something close to what we had.

    Our system was not only used to provide hot water, it was also used for our hydronic heating system (which I must say is the most efficient and hygienic form of heating in my opinion). I think we had 30 tubes and a 250 litre stainless steel storage tank.

    Basically the system worked like this:
    1. Cold water enters the tank.
    2. Solar "pre-heats" the water in the storage tank, which is being pumped between the tubes and the tank.
    3. The tank then supplies heated water into the gas booster.
    4. If the water is not hot enough, the gas booster tops it off to the desired temperature.

    On warm to hot days the gas booster never kicked in and even during winter when the sun was out and the hydronic on it was rare for the gas booster to come on either.

    On the down side, it's a pretty expensive system compared to the mainstream methods out there, but if you plan on being there for at least 5 years it's a good option. I estimate over the course of a year we probably halved our hot water and heating bills with the system so the ROI would probably be around 10 years.

    If you do decide to go down this road, make sure your plumber mate or whoever you decide to install it has had experience with installing these systems. Our plumber didn't have that and we had to get him back a couple of times to fix it. (We had >100 degree celsius water running into our gutter at one point). The hot water between the head unit and the tank can get way over boiling temperature as it's under pressure. So this means also having good fittings and good insulation around the pipes between these units to minimize losses.
    This also means you need have the units installed outside for ventilation as things get too hot to have the units locked in cupboards indoors.

    Hope this helps...

    John K.


    • #3

      Not sure where you live, but the average American home wastes roughly 50% of the energy it uses. About 50% of the average US home energy bill is for heating and cooling. The average home has a 1 square foot hole in the wall if you add up the leaks.

      Energy wise, the biggest bang for the buck is to actually reduce heating and cooling costs. Hot water is between 10-15% of the average home's energy use, which really isn't that much compared to heating/cooling.

      But if you want to start with water heating, either heat pump water heaters if you want to use electricity can produce the same hot water for about 1/3 the cost. Stiebel Eltron Accelera 300 is the best one available.

      I'm interested in evacuated solar tube collectors to pre-heat hot water heater water (even if I had a heat pump water heater) and boiler water for the gas fired furnace. They seem to be more efficient than the panel collectors and the prices are gradually coming down. I have a good setup to put the collectors below the level of my tank so through thermal siphoning, I won't need a pump to send the hot water to the water tank, hot water rises for free.
      Aaron Murakami

      You never change things by fighting the existing reality. To change something, build a new model that makes the existing model obsolete.” ― Richard Buckminster Fuller


      • #4
        Thanks for the information John and Aaron.

        Aaron, I live about 1 hour south of Melbourne on the Mornington Peninsula in Aus.

        My tank is ground level outside, so although I love the idea of thermosiphon it looks like I will need a pump to get the water up to the tubes as the geography of my land means the roof is the only place for the tubes. This bothers me as the goal is to be efficient not introduce more consumption of power.... unless the pressure from the town supply is enough to push it up there, maybe... Additionally It looks like I will need to get myself a rain water tank as if the panel is too efficient it can superheat the water. The HWC/panel is designed to dump water if it gets too hot, so would be wasting water which is not cool... get it . If I have a watertank and pump then this could just run back into the tank and not be wasted. I have been meaning to get a rainwater tank anyway as over here we can have drought conditions and water restrictions.

        Then there is the plumbing... I know it has leaks and some of my taps are long overdue for replacement, I am thinking of replacing all of the failing ones with ball valve type taps so I don't have to deal with the rubber gaskets failing on globe valve type tap.

        Insulating the copper piping properly also needs to be done as heat is being lost to the environment here also. It takes 40 seconds for piping hot water to reach the kitchen tap! Besides being annoying it wastes a lot of water as this the most used tap in the house. My plumber mate suggested that I could install a smaller 25 litre tank under the sink but it kind of defeats the purpose if I have to electrically heat that water. Have to think about that one...

        My house also has a ton of gaps where the roof has been joined to the exterior walls. In some spots I can see through tiny gaps to the outside, so that gets added to the list of things to fix.

        John, I'm curious about the hydronic heating system. Was this underfloor or via elements on the wall?


        • #5
          James, the hydronic was an under floor system. All of the hydronic elements are connected in series and the elements fitted with taps so you could switch off the rooms that didn't need heating. There was a thermostat with timer fitted in the main living area to control the temperature and timing.
          The heating elements in the bathrooms were hydronic towel warmers. Nothing like getting out of the shower on a cold winter morning to a warm towel

          John K.


          • #6
            So a quote to install a 30 tube, 315L Gas boosted system is AU$5200. With labour and parts the quote is AU$8200 based on the work I need done, I would get almost $2000 back from rebates. So $6200 installed, which is still expensive.

            So I have begun looking at heat pumps as they are cheaper to buy and much easier to install and maintain and I can get rebates. I am thinking this might be a better way to go and electricity it does use can be supplied by my planned TST5 Solar setup.

   is apparently a decent (Australian based) brand and they have an interesting product, the Siddons BOLT-ON, so I am now thinking if the price is ok I can mega insulate my existing 8 year old tank, disable it's electric and attach one of these. I am finding out how much one of these costs, so we will see how it pans out.



            • #7
              Solar Hot Water System Advise Evacuated Tubes

              Advice please Coach #439 1997 Newell
              Electric aqua hot works fine but diesel side will not start. When switch is turned on the light comes on for a few seconds and*then goes off. Could this just be a blown fuse?



              • #8
                what a good idea about keeping the electric bill safe. I mean it. and it is very good to use solar for the water heater.