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Discuss Solar Panel immersion heater automatic switch. in the Solar PV Forum area at ElectrciansForums.co.uk.

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  1. Gary K
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    Gary K Regular EF Member

    Location:
    norwich
    Last edited: Feb 17, 2012
  2. Earthstore
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    Earthstore Guest

    This question has popped up before on here.
    The problem that I have with this is; do you know what the true cost of heating your hot water is anyway?
    You would need to make sure your hot water tank needed warming on a day that you had enough spare PV to do so.
    Think about it, modern hot water cylinder, low heat loss, washing machine cold fill, dishwasher cold fill, if you have an electric shower cold fill.
    So really it is down to washing your hands and the odd bath, how much do you think that costs?
    I accept that every little helps, but if you were to change you heating system and then have this in a heatstore it would be beneficial, would you not agree?
     
  3. Gary K
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    Gary K Regular EF Member

    Location:
    norwich
    Earthstore.
    Like you, I don't use loads of the stuff- thats her job when washing up(no dishwasher), the boy has an occasional bath and mostly we have showers, but regardless of this fact, I and probably everyone else on here keeps an tank of hot water topped up and on standby.
    My water is heated by gas so there is no cheap rate as such but I sure could save a few pennies by heating with PV. If this was sucessful I could quite easily change the plumbing to give the option of hot filling the washing machine to save a bit more.

    Have not seen any posts before regarding this particular item but simply wondered if anyone else had got it and how effective it was as it seem alot of money
     
  4. Earthstore
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    Earthstore Guest

    Gary, if you type in the word "heater" in the advanced search at the top right of this page, then scroll down, there is a thread about immersion heaters in the photovoltaic threads, sorry, not sure how to do a direct link.

    Hope this helps
     
  5. SRE
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    SRE Trusted Advisor

    Location:
    North West
    Please she knows her place ;-)
     
  6. Gary K
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    Gary K Regular EF Member

    Location:
    norwich
    Way of the world! - no?
    I work and earn, she tidies and spends!!!
     
  7. madmurg
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    madmurg Guest

    sounds quite expensive to me, I have just built the same item which uses the exhisting 3kw immersion heater and it cost me about £35 to build. I now get free hot water on sunny days and it also saves me on my gas bills.
     
  8. babba
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    babba Regular EF Member

    For the money its good, in all a handy device a 1KW immersion in peak pv season will give free hot water no problem.
    A one KW immersion on pv is the best option and will save you £4000 on a solar hot water and the FITS return far outways
    the HITS return.
    There is another one called EMMA but its a lot more money.
     
  9. Gary K
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    Gary K Regular EF Member

    Location:
    norwich
    I agree it is quite expensive but as I have no electical knowledge or background making my own is not an option.
     
  10. madmurg
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    madmurg Guest

    I has no electronics knowledge either but reading online it only took me a couple of weeks to learn how to do it. Trust me it really is very easy to do.
     
  11. JosephABird
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    JosephABird Guest

    How did you do for such a low price ? Do you measure the imported/exported/generated power and to you automatically vary the power to heater inline with the surplus power available?
     
  12. madmurg
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    madmurg Guest

    I have a ct on the mains and a ct on the cable from the pv. I them measure the difference between the two, this is the spare power availiable. The power is then controlled with a phase angle control relay which is controlled with 0-5v. So 1v would be 20% power to the immersion and 3v would be 60% power etc. But if someone turns a kettle or oven on the unit automatically switches off.
    The electronic parts only cost £2 the microcontroller cost £11 and the phase angle controller cost £11 second hand on ebay. Plus a box lcd screen etc cost about £30. Lots of sun today heated my cylinder right up to the limit on the stat.
     
  13. JosephABird
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    JosephABird Guest

    Are you measuring power or simply current, the mains current may reverse if the output of the PV exceeds the total connected load. ?
    Is the mains sensor current also including the current/power taken by the heater or is it excluding the heater current ?
    I would appreciate some details on the micro controller.




     
  14. sharpener
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    sharpener Regular EF Member

    This looks like a copy of the Parsons Switch. The main drawbacks of this concept are
    (i) it does not measure the energy balance, it just assumes the other loads in the house are <500W
    (ii) if the solar output is <1.5kW you do not get any solar hot water at all
    (iii) you have to fit a 1kW immersion heater, which will be unduly slow to heat the water if you have >1.5 kW solar output, or if your gas boiler is unusable for any reason and you want to revert to mains electricity. At least with the Parsons Switch you get a 1kW/2kW dual element included in the price.

    For all these reasons I - like madmurg - have built my own proportional controller (though it works on a slightly different principle).

    The main discussion thread on this topic is to be found here http://www.electriciansforums.co.uk...ms/23969-immersion-heater-pv-electricity.html

    HTH
     
  15. madmurg
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    madmurg Guest

    I am measuring true power and if the mains current exceeds the pv load the heater will not switch on. It will only switch on if there is surplus unused power. The micro controller is an arduino which are really easy to use.
     
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