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Discuss Immersion Heater - PV electricity in the Central Heating Systems area at ElectrciansForums.co.uk.

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  1. pauldreed
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    pauldreed Guest

    I have solar panels fitted which generate up to 3.3kw, but most days it's 1 to 2KW.

    I want to heat my water with that power, and have sourced a 1kw immmersion heater element (it was designed for boats!) with a suitable 2 1/4" BSP thread, but it is only 11" long.

    If I mount this at the top of my water cylinder, would it eventually heat all of the water in the tank - or just the top 12" or so? (hot water rises).

    I anticipate that the element would be solar powered for 5-6 hours, and if necessary the water temp could be topped up later via the gas boiler.
     
  2. antimatter
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    antimatter Guest

    Last edited by a moderator: Oct 26, 2010
  3. pauldreed
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    pauldreed Guest

    Thanks, but the supply is 240VAC and I would need a 1kw element to heat the water in the time allowed (whilst the sun is shining!)
     
  4. spud1
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    spud1 Regular EF Member

    Location:
    Somerset
    A 1kw 12" element would struggle, I imagine, to heat a full sized cylinder of water when mounted into the top. Your best bet is to change the cylinder for the type that has 2 immersion heaters in the side (dual cylinder) and power the the lower of the two from you PV panels. this I think would heat the vast maj of the volume of a well insulated cylinder over the period you mentioned. You can get retrofit immersion heater kits that you can drill into the side of an existing cylinder to add for example an off peak immersion heater. But by the sounds of it you have an indirect cylinder that has a boiler heated coil within, and this would hinder the fitting of one of these. Hope that helps.
     
  5. pauldreed
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    pauldreed Guest

    Thanks, I have found a company today that would be prepared to manafacture an element to whatever specification I need, for about £60 so I may go with that idea.
     
  6. spud1
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    spud1 Regular EF Member

    Location:
    Somerset
    Good good.
     
  7. robsparky1975
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    robsparky1975 Trusted Advisor

    Location:
    isle of wight
    dont forget to drain the water out before you drill it lol
     
    • Like Like x 1
  8. daniel hill
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    daniel hill Electrician's Arms

    will your inverter allow you to do this i no that the sunny boys that i have fitted in the past dont as they need a constant supply to them as yet i havent come across one that does as it is a major safety feature on them as if the supply fails or working on the grid they would still be a supply from your inverter on a line they think is dead
     
  9. pauldreed
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    pauldreed Guest

    I do not intend to interfere with the invertor or interupt the grid supply to it. The immersion element would be powered from the ring main (which on a bright day is supplied by the panels).
     
  10. Millerman
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    Millerman Guest

    Hi folks, just a quick update on this subject. I have designed a unit that will monitor the power produced by the solar system (FIT) and compare it with the household usage and will switch certain appliances on an off as required.

    For example the solar panel is producing 2000w and the household is not using all of the power, so the surplus feeds back into the grid. This unit will switch the immersion heater on,(1Kw Heater).
    If the householder switches the kettle on for example the immersion will switch it's self off. when the kettle has boiled the immersion will switch its' self back on, providing there is still enough power produced from the solar panels.

    andyb09 at btinternet dot com
     
  11. pauldreed
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    pauldreed Guest

    Me too!
    And it's installed and working now, but it's only heated a total of about 4kwh over the past 3 weeks due to cloudy weather & snow on PV panels.
    I am hopeful that it will pay-off as the sun gets stronger.
     
  12. moush
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    moush Guest

    Hello,

    I would be very interested in knowing which company supplied the immersion heater with lower rating, and also about your design to automatically switch power at the most efficient time.

    I have a similar set up and have been wanting to do something similar.

    Thanks and regards,
    Stephen.
     
  13. pauldreed
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    pauldreed Guest

    The firm which supplied the immersion heater was Howden-Electroheating who made the unit to my specification - costs about £65.
    I designed the unit at component level to ensure that it only activates the immersion heater when the solar panels are generating enough power to support the load.
    It was a steep learning curve!
    But can now (even in January) start to reap the benefits.
     
  14. moush
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    moush Guest

    Thanks for the prompt reply.
    Will post again to describe what I install.
     
  15. inie meanie
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    inie meanie Regular EF Member

    Location:
    South Wales
    I have been looking at a unit to just that but it is SO expensive. I have 3.8 kw pv and would like to spill the excess to the immersion heater. Any chance of some info on how you are doing it?
    Thanks
     
  16. pauldreed
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    pauldreed Guest

    I measure:
    A) The power generated by the solar panels
    B) The power used by the ring main
    * deduct B from A (plus a further 1KW - to accomodate the power used by the immersion heater)
    * and if the result is positive, then a relay switches on the immersion heater - if it is less, then it is switched off.

    This is achieved by a circuit built from components sourced from Maplins and Ebay, a bit of fiddly soldering, and a lot of patience!
     
  17. inie meanie
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    inie meanie Regular EF Member

    Location:
    South Wales

    That sounds great, exactly what I want to acheive. Any chance of a bit more information or pictures? Many thanks.
     
  18. pauldreed
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    pauldreed Guest

    I don't think pictures would help, because the unit is contained within a '2 gang mains surface box/blanking plate', so the photo would just be a small white box. It's the circuitry inside the box which makes the decisions.
    I am contemplating marketing the device, so I'm a little reluctant to release the full circuit diagram at this time, but the operating principle I posted above is basically how it works.
    I can't wait for some decent sunshine now, but even today, the unit switched 2kwh to the immersion heater, not enough to fully heat the store of water, but hey, it all helps!
     
  19. inie meanie
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    inie meanie Regular EF Member

    Location:
    South Wales
    HI
    I understand that. You may have a problem as there is a device on the market which might be copyright protected, it is called EMMA. It costs about £1500. I was just wanting to make some thing for my self with no interest in selling on. Hey but well done on making it work.
     
  20. mac1
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    mac1 Guest

    Hi can you tell me more about your device
     
  21. pauldreed
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    pauldreed Guest

    What do you want to know? I have covered the basic principles in post #16 of how it works.
     
  22. mac1
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    mac1 Guest

    Hi yes you described how it worked but can you let me know what you have used to monitor the system to enable it to switch the immersion on and off at the appropriate time. Thanks.
     
  23. pauldreed
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    pauldreed Guest

    I use current transformers, one on the power feed from the invertor (which measures the power being generated) and a second on the ring main power feed (to measure the power being used in the home).
    My circuit then compares both measurements, and if the generated power exceed the power being used by 1kw, then the circuit activates a relay which in turn powers the immmersion heater.
    As both measurements are being constantly monitored, if the generated power diminishes (passing cloud!) then the relay is de-activated.

    This link is a similar current transformer to what I use.
     
    Last edited by a moderator: Mar 3, 2011
  24. inie meanie
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    inie meanie Regular EF Member

    Location:
    South Wales
    Hi Pauldreed
    Are you using an op amp to do the comparison to then drive a relay or do you have an all in one module?
    Thanks
     
  25. pauldreed
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    pauldreed Guest

    Op amp, as I couldn't find an all inclusive module.
     
  26. flyman
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    flyman EF Member

    This is interesting as I've been thinking of doing something similar and stumbled across this post. It may be worth considering using a simple programmable micro-controller rather than op-amps particularly if you want multiple comparitors. It is possible to get a cheap 8 pin PIC with 3 ADCs to monitor 3 current monitor inputs and still drive up to 3 outputs. It is also easier to build in timer delays and hysterisis to prevent rapid switching as outputs rise and fall.

    Now if I can find an immersion heater timer with a wireless remote input.... a minimal wiring modifications solution is possible.
     
  27. pauldreed
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    pauldreed Guest

    Yes, hysterisis has been a problem, and I had to modify my circuit after a few weeks as the relay couldn't cope with the rapid switching.
    I have never used, or know anything about micro-controllers, so I can't comment on your suggestion, but good luck.
     
  28. flyman
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    flyman EF Member

    Thanks Paul. Microcontroller are really very simple once you get the hang of them and so flexible for this sort if thing and limited only by imagination and a couple of pounds gets something capable of automating and running most thing in a house. They are probably simpler than other ICs and changes are a simple reprogram rather than changing components. I use them a lot for sports based control systems.

    Once I have the pv system installed I'll potter around with something to sort out the immersion heater etc.

    If you think you might want to know a bit more by all means drop me a note - it might be a simple relaiable solution for optomising pv.
     
  29. pauldreed
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    pauldreed Guest

    I was educated in electronics 30 years ago, so microcontrollers have not figured until now!
    Presumably, you need a programmer - to interface to a PC, which in turn writes the instructions to a chip.
    The chip with minimum support components would then retain the instructions and operate independently to the programmer?
     
    Last edited by a moderator: Mar 13, 2011
  30. flyman
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    flyman EF Member

    Yes, thats pretty much it really. In essence the curcuit for most things consists of a regulated 5v supply from a 7805 a couple of capaitors to decouple the supply, outputs dependant on whats needed - LED, mosfet, piezo etc. Timer crystals arent needed as most have internal ones. The programming removes the need for logic gates and timers and a PIC can drive 20mA on each pin so I use a mosfet to drive a relay. programmers are fairly cheap at £30-50 and software free. PIC has plenty of memory so its easy to play about with. Inputs can be 5v logic or 0-5v dc on analog inputs making it easy to interface with most things.

    I guess the biggest cost is time learning the programming but as its only 35 words and there are lots of tutorials online. And if that doesnt suit there are people who'll do a chip for you.
     
  31. inie meanie
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    inie meanie Regular EF Member

    Location:
    South Wales
    Hi Flyman
    Your idea sounds fascinating. I will be very interested in how your project progresses. I too learnt my electronics 30 yrs ago and now am a bit rusty. I can catch on with some guidance. :) Do you have a specific programable device in mind and do you have a link to it so I can read up a bit? Many thanks
     
  32. flyman
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    flyman EF Member

    There are several micros but I tend to stick to Microchip PIC based ones. 12F675, 16F628 or 16F818. For simplicity there are modified versions aimed at the education market with drag and drop flow diagram type programming but there are restrictions on use for commercial applications. Do a search under Google for picaxe. The newer kid on the block is Arduino but its open source but a bit more involved.
    For a DIY one off I'd suggest exploring PICAXE... you can even buy pre made circuit boards for lots of applications and you can program and test on screen with the software simulator but you'll have to accept the non commercial aspect of it. For a more comprehensive and slightly more challenging option, Microchips PIC 12f675, 12F683 or 16F818 a chunk of veroboard a soldering iron and a few other bits.
    By all mean contact me if you need any help.
     
  33. benzama123
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    benzama123 Guest

    It is possible to get a cheap 8 pin PIC with 3 ADCs to monitor 3 current monitor inputs and still drive up to 3 outputs.
     
  34. flyman
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    flyman EF Member

    As with anything it helps to start with a wish list and select a suitable circuit to provide it. The pin allocations on the 12F683 allows for a total of 6 inputs or output pins. The datasheet will give a better explanation of their allocation and is worth a read but basically of the 6 pins, upto 4 can be ADCs. One pin (GPIO3) can only be configured as a digital input but not an ADC. Whilst it is possible using logic gates to do 3 outputs from 2 pins you'd be better off with a 16F series PIC if you want more ADCs and outputs. A check on prices for suitable PICs and pinouts will show the extra cost is a couple of pounds or so.... and you could drive lots of outputs. :)
     
  35. Andrew Shaw
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    Andrew Shaw Guest


    please tell me more about this company

    Thanks
     
  36. pauldreed
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    pauldreed Guest

    Post 13 of this thread gives you a link
     
  37. Millerman
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    Millerman Guest

    Hi again folks, finally had my solar panels fitted (6th May) and just about to "road test" my device. i am using a plc unit (crouzet) with current transformers measuring the load and solar production.

    This unit can easily cope with the constant flucuations in demand /supply the unit is fairly easy to programme.

    [email protected]

    andy
     
  38. pauldreed
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    pauldreed Guest

    The Crouzet PLC's look ideal as you will be able to introduce hysteresis to prevent relay chatter, and programme other functions in too.
    Has your unit got the LCD display? presumably once calibrated, it could display/accumulate useful information.

    My unit is working fine, and during the recent sunny weather I have not used the central heating boiler at all to heat the domestic water. I had doubts that a 1kw immersion heater would be powerful enough to heat the water during the sunny periods, but no problem at all.

    Let us know how you get on.
     
  39. echase
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    echase Regular EF Member

    Location:
    UK
    I designed a PIC based solar controller for solar water heating. The design was published in Everyday Practical Electronics in June 2009. Everyday Practical Electronics They sell back copies and the bare PCB. I sell the programmed PIC. All in it costs about £50 in components.

    Now that I have PV panels I was thinking of extending the software to add functionality to provide this immersion heater switching. No change to the hardware would be needed apart from an external relay to switch the immersion.

    As someone here says with software it is extremely simple to add hysterisis, delay, etc.
     
  40. pauldreed
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    pauldreed Guest

    What did the original solar controller do?
    I'm interested in the PIC, but can you tell us more about circuit that supports it. I don't want to spend $12 to buy back issues (June & July) if the design is too difficult to build, will not work as expected, or succesfully integrate with my PC system.
    If you designed it, are you able to share the circuit diagram with us?
     
  41. echase
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    echase Regular EF Member

    Location:
    UK
    It is a solar water controller which uses a small PV panel to provide all the power to run the controller and pump so there is no mains needed. But it can be mains powered if you want. It’s mainly designed to switch the water pump on and off in response to the solar power and temperatures in the system. It also has 2 relay outputs to power the gas boiler/immersion heating top up function. These would do 1kW with an external relay needed for more than that.

    It would not connect as is to a PV electric system, but with simple modifications:

    1) You could add CT inputs. To mimic your unit paukdreed it would need a couple of input circuits to convert the CT output to a 0-2.5V aprox DC value.
    2) It could log the power in the PV system too which is useful in system where the inverter is in the loft and so its power meter is not visible.


    As you designed and soldered your own unit mine is not difficult. There are no surface mount components. But it’s outside the capability of a complete novice in electronic assembly.

    June 09 covered the design and software with July for how to build, test and connect it.
     
  42. Gazzdid
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    Gazzdid Active EF Member

    Location:
    Midlands
    a simple thought...... dont forget to introduce a cylinder stat to your circuit so it wont continue to heat the cylinder to a dangerous temperature! :)
     
  43. pauldreed
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    pauldreed Guest

    The input circuitry would add significantly to the overall circuit design. A simple passive diode bridge would not suffice, as I am sure you will be aware. This part of the circuit design was the steepest learning curve for me, and took the longest time to sort out.
    You say that there are no surface mount components, but surely there must be components to provide the right environment for the PIC to operate? (sorry never seen a PIC or had anything to do with them).
    Can you change variables in the PIC once it has been programmed (such as histeresys, switching thresholds ect) without actually re-programming it?

    Edit - Yes I've got an immersion heater with an integral thermostat set about 5 degrees higher than my gas boiler water thermostat. So the central heating boiler does not heat the water (unless its been a dull day!)
     
    Last edited by a moderator: May 15, 2011
  44. echase
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    echase Regular EF Member

    Location:
    UK
    There are extra components on the analogue inputs but they are little more than resistor dividers and overvoltage protection resistors. But you would need to convert the CT ouput to DC with something like an op amp.


    My standard device has >20 variables that can be altered by menu. If I changed the software to provide this function I’d add extra variables to alter the extent of input power averaging, switching hysteresis, etc.
     
  45. pauldreed
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    pauldreed Guest

    I use op amps to monitor the CT's which give me 3 volts at 5kw power flow (which can be changed via a shunt resistance).
    If I can help, especially with the 'front end' circuit - let me know.
    I'll PM you my email address..
     
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