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Thread: Solar Water Heating

  1. #11
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    Name: Nabs (Neil)
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    Quote Originally Posted by wildebus View Post
    He is using either a programmable load output or similar from his Controller. To quote his post:
    "I have wired to my solar charge controller that can be set to come on and off at desired voltages so I never have a flat battery and it just uses the excess solar energy that my batteries dont need"
    Ah okay, missed what that bit meant, thought it was just pulling from the battery bank and solar topping the bank up again. Would that be an option if you dont have the load output?

    Currently the heat exchange from the Eber doesn't seem to do much but we have not had heating on for any length of time to test, running engine has a full tank of hot water fairly quickly, half an hour gives hot showers as if we were at home. A way of hating water from solar/12v would finish things off nicely otherwise it showers in evening rather than morning if you want them hot

  2. #12

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    Quote Originally Posted by Nabsim View Post
    Ah okay, missed what that bit meant, thought it was just pulling from the battery bank and solar topping the bank up again. Would that be an option if you dont have the load output?

    Currently the heat exchange from the Eber doesn't seem to do much but we have not had heating on for any length of time to test, running engine has a full tank of hot water fairly quickly, half an hour gives hot showers as if we were at home. A way of hating water from solar/12v would finish things off nicely otherwise it showers in evening rather than morning if you want them hot
    What I would do is manually turn the heater on at peak sun - the effect would be the solar controller would go from float to charge mode and provide the power, so it would certainly be an decent option - but my problem is forgetting to turn it off again! It is only a small handiwash unit I have - so good for hands and face but not a shower type setup.

    On the subject of "solar hot water", I plan to have a water container, black or painted black, filled with water and left in the sun during the day. That will be good for nice warm water as well in the evening when combined with an electric shower pump system I bought. Can have nice indoor/outdoor showers that way (outside, but in Safari room)
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  3. #13
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    I have seen the solar showers with black PVC/Vinyl?canvas whatever they are made from so it gets maximum heat transfer. Great for what you are talking about but not so useful for heating a 22ltr steel tank full. Then again didn't you used to be able to get a solar panel that had water tubes in them, just heated water or is my dementia slipping in again?

    Would be adding weight and complexity not wanted on motorhome though so I will end that thought train here haha

  4. #14
    Byronic Guest
    Quote Originally Posted by Nabsim View Post
    I have seen the solar showers with black PVC/Vinyl?canvas whatever they are made from so it gets maximum heat transfer. Great for what you are talking about but not so useful for heating a 22ltr steel tank full. Then again didn't you used to be able to get a solar panel that had water tubes in them, just heated water or is my dementia slipping in again?

    Would be adding weight and complexity not wanted on motorhome though so I will end that thought train here haha
    I installed a passive water heating (black pipe) system on my house roof in NZ over 30 years
    ago. Was more efficient when I upgraded it to active, (essentially pumped). The significant thing with
    reliance on solar for hot water supply is that more often than not the hot water is required hours
    after el sol input becomes negligible. In other words you need well insulated storage. But so long
    as the water temp. is above that of the c.w. supply then it's a win of varying levels.
    Those vinyl shower bags seem to have a short lifespan cheap enough. You have to time your
    usage, because again, once the sun is off them, doesn't take much time for them to cool off.

  5. #15

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    Quote Originally Posted by Nabsim View Post
    I have seen the solar showers with black PVC/Vinyl?canvas whatever they are made from so it gets maximum heat transfer. Great for what you are talking about but not so useful for heating a 22ltr steel tank full. Then again didn't you used to be able to get a solar panel that had water tubes in them, just heated water or is my dementia slipping in again?

    Would be adding weight and complexity not wanted on motorhome though so I will end that thought train here haha
    You are quite right about solar tube for DHW (Domestic Hot Water) Systems. That was my first foray into solar around 12 years ago. I did a system that Combined Solar DHW with a Combi-Boiler that could accept Pre-heater water (most UK ones wouldn't at the time) and a Thermal Store. Had a data logger on it which I could analyze the numbers (you might have noticed I like doing that. ) and worked out it would have paid for itself in around 6 years which is a great ROI.
    Also had a second coil in the store that was fed by the Rayburn so instead of excess heat being dumped into a radiator or opening the window (the usual solution in the summer) it would heat my water

    But no, not a solution for a motorhome!
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  6. #16

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    Quote Originally Posted by Nabsim View Post
    The way Dean has done it doesn't need a load output I dont think, just drawing from the batteries then solar tops up the battery
    This is correct, my solar charge controller switches on and off at set volts eg off at 12.6v and then back on at 14.4v so I just using the excess power the panels are producing.
    Thanks
    D
    Also the charge controller only controls the relay that is connected to the batteries, I have a switch inline so it doesn't have to be on all the time, also a thermostate that will turn it off when the water gets to temperature.
    Last edited by gypo; 19-05-2018 at 14:30.
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  7. #17

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    My solar water heater is based on a 22 ltr container with a small pump 12V DC 3M CPU Cooling CAR Brushless Water Oil Pump Waterproof Submersible | eBay that feeds water up to a serpentine solar collector. This is made of solvent weld waste pipe housed in a twin-wall polycarbonate "greenhouse". The feed to the collector goes up the bathroom wall and is teed off to a trigger bum-gun. This is used as a shower, bidet and toilet flush. The solvent-weld collector pipe has a temperature sensor inside it connected to a controller STC100 which starts the circulation when the water in the solar collector gets to the desired temperature. In hot weather 45-50 degrees, when cooler maybe 35. The controller switches off when the collector temp. drops maybe 7 degrees or so.

    When filling water is fed into the 22 ltr container from the main tank. There is also a tube with a funnel for manual filling from a kettle when needed. Milton type fluid is added via the manual feed to prevent bugs.

    Last year I was having to dump hot water on a regular basis as it was over 40-50 degrees and there is no mixer, Just add cold water to the container which also has a temp. sensor. Today the water was at 38 degrees from 20 degrees fresh fill in 6 hours.

    The supply/return pipes are a mix of 15mm barrier pipe and garden hose. Total cost of the system about £50, the most expensive part was the twin-wall.

    Mr B.
    Last edited by mrbigglesworth; 19-05-2018 at 16:14.
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  8. #18
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    Here you go Dave, set voltage to start feeding element then lower setting to turn off, that will do it won’t it?

    12V 24V Digital Voltage Sensing Relay 10A - battery protection / dump load / auto switch battery banks
    Don't Worry, Be Happy

  9. #19

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    Quote Originally Posted by Nabsim View Post
    Here you go Dave, set voltage to start feeding element then lower setting to turn off, that will do it won’t it?

    12V 24V Digital Voltage Sensing Relay 10A - battery protection / dump load / auto switch battery banks
    Hi Neil,
    Interesting looking device.
    This approach might work. I am looking at the Relay feature of the Victron BMV-712 and I believe I can actually do the above direct from the Battery Monitor (although it is purely a relay-control level of power at just 1A).
    You can also set the relay to work on the State of Charge - so very similar in essence to the Load Output of a Solar Controller - except you can only set it to come ON at a lower SOC and off at a higher one, not the other way round (It is designed to start a generator when the battery level is low)
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  10. #20

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    Quote Originally Posted by wildebus View Post
    Hi Neil,
    Interesting looking device.
    This approach might work. I am looking at the Relay feature of the Victron BMV-712 and I believe I can actually do the above direct from the Battery Monitor (although it is purely a relay-control level of power at just 1A).
    You can also set the relay to work on the State of Charge - so very similar in essence to the Load Output of a Solar Controller - except you can only set it to come ON at a lower SOC and off at a higher one, not the other way round (It is designed to start a generator when the battery level is low)
    If it is the same as my controller (Tracer) you can alter the low voltage on and low voltage off within the setting. So mine is set that the load comes on at 14.4v(low voltage on) and the load goes off at 12.4v(low voltage off) this then controls a relay that switches the power to your water heater element.
    D

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