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Specifications for switch?

whjohnson

I don't generally touch anything to do with solar kit but have been asked to come up with a method whereby an immersion heater can be switched from mains to solar or solar to mains.

A straight forword solution is simply a change over switch with 2 supplies in and one supply out to the heater, but because one of the input supplies is coming from solar - post-inverter so mains voltage - I would like to know if I can use a conventional change over switch or are there some special requiements for switching the mains output derived from a solar supply?

Comments welcome

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  • I'm a bit confused so far. If it's a conventional grid-tied PV system there won't be separate solar and mains electricity system to switch between - they're both connected together already. It might therefore be just a matter of turning on the immersion at an appropriate time - by the normal laws of physics it'll then draw what it needs, the solar system will provide what it can and if insufficient the rest will come from the grid (or the excess exported to the grid if the PV is generating more than the whole installation including the immersion needs). Otherwise you're into all sort of problems matching demand with variable PV output. Battery PV systems tend to operate on similar principle just that some of the PV output can be time delayed to try and better match the installation's demand.

    If there's no choice about when the HP need backup from the immersion, I might be as simple as letting the HP turn it on as it wishes - if there's spare solar capacity that'll be used otherwise the grid will make up the difference as normal. 

      - Andy.

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  • I'm a bit confused so far. If it's a conventional grid-tied PV system there won't be separate solar and mains electricity system to switch between - they're both connected together already. It might therefore be just a matter of turning on the immersion at an appropriate time - by the normal laws of physics it'll then draw what it needs, the solar system will provide what it can and if insufficient the rest will come from the grid (or the excess exported to the grid if the PV is generating more than the whole installation including the immersion needs). Otherwise you're into all sort of problems matching demand with variable PV output. Battery PV systems tend to operate on similar principle just that some of the PV output can be time delayed to try and better match the installation's demand.

    If there's no choice about when the HP need backup from the immersion, I might be as simple as letting the HP turn it on as it wishes - if there's spare solar capacity that'll be used otherwise the grid will make up the difference as normal. 

      - Andy.

Children
  • in reply to AJJewsbury
    AJJewsbury said:
    If it's a conventional grid-tied PV system there won't be separate solar and mains electricity system to switch between

    Precisely. So, whjohnson, which is it please?

  • in reply to Chris Pearson

    This is one of the questions I have to find the answer to. At first when the heat pump went in,  and there were no panels, a cable was run to a FCU next to the tank from the aux consumer unit which also feeds some sockets and lights in the plant room. This was connected just to a 16A mcb and left switched off

    The solar guys came along, pulled out the immersion heater cable from the cu and ran it into an adaptbale box. Into this box they ran another twin and earth from upstairs and I think it comers from the solar switchgear next to the house CU which is on a different phase.

    It may well be that.the solar feeds into the house cu to the grid.

    The heat pump has its own independent consumer unit. Both this and the aux CU are fed from a different phase to that of the house. Another questions which phase is the solar feeding back to?

    Hopefully find the answers this afternoon.

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