Solar geyser efficiency





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  1. #1
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    Default Solar geyser efficiency

    My solar geyser performance were BAD.
    Plenty hot water when the sun is out, cold water in the morning.
    The geyser 200L was a retrofit mounted outside on the wall with solar panel 20 tubes
    mounted on the roof + solar panel and pump to circulate the water.
    I did the following to gain huge gains.
    1: Fit geyser blanket - small improvement, water in the morning luke warm.improvement.
    2: Moved geyser into the laundry and re-route and insulate pipes through the roof , huge
    improvement.
    3:Still losing a lot of heat when the sun is not shining. I fitted 4 temp sensors hooked up to a arduino to monitor the temperature , Hot water out of geyser, water inlet to solar panel, water out from solar panel and cold water inlet.
    By observing the temps I found that the hot water from the geyser were circulating to the solar panel and returning cold water to the geyser. So i fitted a anti syfering loop after the non return valve in the pipe from the solar panel to geyser, improvement once more.
    4:Next observation, the hot water temperature drops a lot when the sun starts to go down or it get cloudy. On investigation I found that the solar powered pump still circulate hot water to the colder solar panel . Next step: Going to install a relay in the supply from solar panel to the pump , to switch the pump off when the input temperature of the solar panel goes higher than the output from solar panel.

    Comments and suggestions is welcome.
    Hope this can help others.

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  3. #2
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    Default Re: Solar geyser efficiency

    short answer - another BAD installation.


    These installation engineers are supposed to provide "flow back" prevention to stop syphoning at night and thus cooling the water.

    There are a couple of ways to achieve this :
    - one way valve
    - a "kink" in the pipe (upside down U-trap)
    Last edited by Elders; 2017/03/17 at 08:56 AM.

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  5. #3
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    Default Re: Solar geyser efficiency

    Interesting observation on the solar pump. I considered it that but now I'm glad I didn't go that route.

    The GeyserWise Max controller works great to run the pump when the panel is hot and switch on the geyser element when the water is not warm enough for a shower. You can consider that.

    We also had big problems with thermal syphoning, loosing up to 20'C a night. A spring-type NRV sorted that out. I found the swing/ flap-type only works if mounted vertically (with the normal flow going up) otherwise the flap doesn't close properly.

    Insulating the geyser made no difference but insulating the pipes is definitely worth it. When the water is hot, feel which pipes are hot and insulate all of those.
    Niel
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  7. #4
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    Default Re: Solar geyser efficiency

    Now I remember why I chose a heat pump powered by PV Panels.
    Cheers

    ZS5KAD
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    The frogs are starting to notice that the water is getting warm but it is already too hot to do anything about it.....

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  9. #5
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    Default Re: Solar geyser efficiency

    Quote Originally Posted by Musashi View Post
    Interesting observation on the solar pump. I considered it that but now I'm glad I didn't go that route.<br>
    <br>
    The GeyserWise Max controller works great to run the pump when the panel is hot and switch on the geyser element when the water is not warm enough for a shower. You can consider that.<br>
    <br>
    We also had big problems with thermal syphoning, loosing up to 20'C a night. A spring-type NRV sorted that out. I found the swing/ flap-type only works if mounted vertically (with the normal flow going up) otherwise the flap doesn't close properly.<br>
    <br>
    Insulating the geyser made no difference but insulating the pipes is definitely worth it. When the water is hot, feel which pipes are hot and insulate all of those.
    <br>
    <br>For the last 4 weeks I only had to use the geyser element once otherwise it remain switched off (manual)<br>
    I am considering to leave the arduino with the temp sensors connected permanently.<br>Adding the function to switch solar pump off, a switch to boost geyser temperature if below say 45 if switch were pressed with led (ready to shower)&nbsp;<br><br>One question is it necessary to take precaution in winter prevent solar panel from freeing&nbsp;

  10. #6
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    Default Re: Solar geyser efficiency

    Quote Originally Posted by Banjo View Post
    <br>
    <br>For the last 4 weeks I only had to use the geyser element once otherwise it remain switched off (manual)<br>
    I am considering to leave the arduino with the temp sensors connected permanently.<br>Adding the function to switch solar pump off, a switch to boost geyser temperature if below say 45 if switch were pressed with led (ready to shower)&nbsp;<br><br>One question is it necessary to take precaution in winter prevent solar panel from freeing&nbsp;
    Frost is not a problem we have in the Cape but it can be an issue where it gets cold. As far as I know, the Geyserwise Max circulates warm water into the panel at night when it gets below freezing. It might be easier than trying to design the set-up yourself.

    Our element usually remains switched off from about October to April. One benefit of sunny summers.
    Niel
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  11. #7
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    Default Re: Solar geyser efficiency

    These problems is so common it is actually very sad to hear.

    If you really want to have stress free hot water, get a 2nd 200L geyser, then you should never run out of hot water


    2007 Nissan Navara 4L Auto - Worshond


  12. #8
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    Default Re: Solar geyser efficiency

    Quote Originally Posted by Musashi View Post
    Frost is not a problem we have in the Cape but it can be an issue where it gets cold. As far as I know, the Geyserwise Max circulates warm water into the panel at night when it gets below freezing. It might be easier than trying to design the set-up yourself.

    Our element usually remains switched off from about October to April. One benefit of sunny summers.
    With my setup with the arduino it is just a line or two of code to circlate water at freezing conditions, 1 temp probe measure the outside temp already
    Last edited by Banjo; 2017/03/17 at 12:44 PM.

  13. #9
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    Default Re: Solar geyser efficiency

    Quote Originally Posted by Wetkit View Post
    These problems is so common it is actually very sad to hear.

    If you really want to have stress free hot water, get a 2nd 200L geyser, then you should never run out of hot water


    I was thinking of adding a 50l geyser to heat water when needed if main geyser water is to cold,but only on demand

  14. #10
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    Default Re: Solar geyser efficiency

    Quote Originally Posted by Fluffy View Post
    Now I remember why I chose a heat pump powered by PV Panels.
    as part of a larger PV installation ... yes then that makes sense.


    For the guy just wanting to safe a bit on the geyser operating costs - the dual element with PV panels WORKS !! VERY VERY happy with our system !!!!!!

  15. #11
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    Default Re: Solar geyser efficiency

    Quote Originally Posted by Banjo View Post
    I was thinking of adding a 50l geyser to heat water when needed if main geyser water is to cold,but only on demand
    Something to think about .....

    Geyserwise offers a nice concept on their dual element setup. They use a probe that allows you set different geyser temperatures for different time zones.

    So in the morning I have 52 degrees water - if needed the electrical element will be used.

    Then at 11:15 the electrical element will heat the water to 40 degrees, only if the sun was completely hidden by severe weather.

    16:00 the water will be heated to 52 degrees, again only if the sun have not done so already.


    Summer month the sun provides about 98% of our heating - the rest typically a result of us needing water outside of our schedule and reducing the water temp just before one of the re-heat cycles.

    Winter months the bulk of the heating is still by the sun. I was VERY surprised to see just how much heating is still achieved on overcast days with LIGHT (white) clouds.



    I am sure you could do similar with the arduno ....

  16. #12
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    Default Re: Solar geyser efficiency

    Quote Originally Posted by ChrisF View Post
    Something to think about .....

    Geyserwise offers a nice concept on their dual element setup. They use a probe that allows you set different geyser temperatures for different time zones.

    So in the morning I have 52 degrees water - if needed the electrical element will be used.

    Then at 11:15 the electrical element will heat the water to 40 degrees, only if the sun was completely hidden by severe weather.

    16:00 the water will be heated to 52 degrees, again only if the sun have not done so already.


    Summer month the sun provides about 98% of our heating - the rest typically a result of us needing water outside of our schedule and reducing the water temp just before one of the re-heat cycles.

    Winter months the bulk of the heating is still by the sun. I was VERY surprised to see just how much heating is still achieved on overcast days with LIGHT (white) clouds.



    I am sure you could do similar with the arduno ....
    Slightly overcast can in fact give more energy than 100% clear sky. Instead of the panel only getting direct sunlight from one direction it also gets reflected light.

    So if a panel is receiving both direct and incident light the difference can sometimes be significant, especially if the incident is at a favorable angle to the panel.

    Better Solar Calculators will actually factor this into their yield predictions.
    Cheers

    ZS5KAD
    3 V8's
    NA TwinTurbo SuperCharger
    A V6 and an inline 4

    The frogs are starting to notice that the water is getting warm but it is already too hot to do anything about it.....

  17. #13
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    Default Re: Solar geyser efficiency

    Not to hijack this thread, I'm looking at going with a 300L Solar Geyser, suggestions welcome.

    Doesn't have to be a retrofit, but simply give some kind of working solution with minimal fuss. I've seen specs indicating 70% efficiency on some makes.

    So far I've come up a high pressure 300l Solar geyser coupled to a gas geyser. The idea being that the gas heater adds anything the solar didn't, more solar heated water, less gas used. So user experience is always the same, the difference being in the savings on gas between the summer and winter months.

  18. #14
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    Default Re: Solar geyser efficiency

    My system is a 300 solar geyser with a heat pump. Heat pump is on a timer & only
    kicks in when needed in the mornings (4am to 9am).
    In the summer months very seldom needed, & only heats the water to 53deg.
    Have seen that solar has heated the water to 88deg.
    Was caught out only once right in the beginning when we had a few days of rain and
    wanted to shower in the evening, was fine for me but the wife was a bit put off by the tepid water.
    Now just put the bypass on if needed in the evenings.

    Cheers
    Graeme
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  19. #15
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    Default Re: Solar geyser efficiency

    I am looking at going PV with DC/AC element and geyser wise controller.

    What other components do I require apart from the following?


    1. 4 x 255watt PV panels R 1300 exc ex vat - current automation
    2. 1 x 900watt DC/AC geyser-wise element R 2166 - Sustainable.co.za
    3. 1 x geyser wise controller R 1400.00 - Sustainable.co.za
    4. Solar panel brackets for the roof - not sure on cost or where to get them
    5. Some cable and installation, also not sure what i need here or how much


    can the panels be connected directly to the element or is there some type of controller required?

    any input or advise would be appreciated

  20. #16
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    Default Re: Solar geyser efficiency

    Quote Originally Posted by Musashi View Post
    Interesting observation on the solar pump. I considered it that but now I'm glad I didn't go that route.

    The GeyserWise Max controller works great to run the pump when the panel is hot and switch on the geyser element when the water is not warm enough for a shower. You can consider that.

    We also had big problems with thermal syphoning, loosing up to 20'C a night. A spring-type NRV sorted that out. I found the swing/ flap-type only works if mounted vertically (with the normal flow going up) otherwise the flap doesn't close properly.

    Insulating the geyser made no difference but insulating the pipes is definitely worth it. When the water is hot, feel which pipes are hot and insulate all of those.
    A NRV (Non Return Valve) can stop the flow of water in an undesired direction 100% efficiently. It can however not prevent hot water from escaping in an upward direction.

    The hot water will heat the NRV, the NRV will heat the water above it.

    This is how hot water leaks past the NRV.

    Your comment on insulation of the pipes is very important and to many people give no attention to it. Even the cold water side should be properly insulated.

    The key word is insulation.

    I have been fiddling with solar heating for a very long time. I made a lot of errors. One was to think all insulation are equal.

    A proper solar panel can melt most insulation on the hot side.

    Melted insulation do not offer any protection.

  21. #17
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    Default Re: Solar geyser efficiency

    Quote Originally Posted by FreeLander2 View Post
    I am looking at going PV with DC/AC element and geyser wise controller.

    What other components do I require apart from the following?


    1. 4 x 255watt PV panels R 1300 exc ex vat - current automation
    2. 1 x 900watt DC/AC geyser-wise element R 2166 - Sustainable.co.za
    3. 1 x geyser wise controller R 1400.00 - Sustainable.co.za
    4. Solar panel brackets for the roof - not sure on cost or where to get them
    5. Some cable and installation, also not sure what i need here or how much


    can the panels be connected directly to the element or is there some type of controller required?

    any input or advise would be appreciated
    Step ONE - contact Meinhard at Geyserwise in Goodwood. He will gladly provide you with the correct information. He is pasionate about his systems !


    Panels - DO make sure you get the CORRECT panels !!! It is NOT just the wattage. The voltage MUST match the rest of your system - and there are different systems and options, so no single answer.

    Then the correct size cables to the geyser (well to the rest of the system at the geyser). the "correct size" is a function of the Voltage, Ammps and distance .... Mine was a long run, so we opted for 10mm2 wire. Think my neighbours is 6 or 8mm2, but a much shorter run, AND a different voltage configuration to mine.

    MPPT unit

    Geyserwise dual controller

    back up battery - for the control system in the event of a power failure

    dual element

  22. #18
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    Default Re: Solar geyser efficiency

    Hi guys, i found a study on how to improve the efficiency of evacuated tubes. The study is on science direct. They fill the tubes with heat transfer oil. Anyone tried something like that? I will try to post the link.

  23. #19
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    Default Re: Solar geyser efficiency

    Quote Originally Posted by Fluffy View Post
    Now I remember why I chose a heat pump powered by PV Panels.
    I have that plus the solar geyser panels. I switch off any power to the system from October to April. Free hot water enough for 8 people a day.
    2001 Isuzu Frontier 4X4 DT280 LX 2.8 Turbo Diesel (Tourer)
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  25. #20
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    Default Re: Solar geyser efficiency

    Hi guys,
    To answer your question about improving your evacuated tube performance would ether slip a sheet of stainless steel under your collector
    if it is mounted to tile or slate roof or if mounted to a flat concrete slab paint the underneath area of the frame with silver paint regularly,this will definitely improve your systems efficiency. (Hilton allwest solar)

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