Solar PV with ground scource - Using excess electricity

Hi all, just got a 4KW solaredge PV setup to complement our ground scource heat pump (GSHP) in the hope it will reduce the running costs of the house.

The GSHP that we have has an internal water tank and a 2 stage immersion at 3 & 6 kw. We have been in the house about 6 months and during that time the immersions have never needed to operate as the GSHP is heating both the house and the water adequately.

I have been reading about these new immersion devices that only operate when excess solar is being produced with great interest and wondered if these could run with our GSHP - could the imersion be wired to one of these devices or even to a cheap timer to operate it when there is an excess.

GSHP is a Thermia TWS6


  • [Deleted User][Deleted User] Forumite
    0 Posts
    Part of the Furniture 1,000 Posts Photogenic
    MoneySaving Newbie
    It really depends on your GSHP running times. If the heating generally runs early morning/late evening as our ASHP does or running the bulk of the time during the night on cheap rate then PV will not make much if any difference.

    With regard to hot water our first cycle is 5:30am so again no PV benefit. The second DHW cycle is 3pm. As I was at home yesterday I watched the electricity meter when the ASHP water heating kicked in and the meter stayed static :) So this is why the Immersun is going to get installed as we are not using much of the PV generated electricity.

    With our setup the immersun will replace the ASHPs immersion controller. All the ecodans immersion controller does is boost the hotwater from 50c to 65c every 15 cycles for bugs. This will be turned off on the ecodan and the immersun boost will be used instead. Pretty straight forward.

    Even in Oct the PV was ticking over at 3kw ish which leaves about 2.5kw to get dumped into the tank. I doubt we will even use all the excess PV but is big step forward.

  • Kernel_SandersKernel_Sanders Forumite
    3.6K Posts
    jeepjunkie wrote: »
    every 15 cycles for bugs.
    Excuse me??
  • Excuse me??

    Legionella bacteria I presume.
  • Just a word of warning, the ImmerSUN can only proportionally control a resistive load (eg an immersion, storage heater, electric bar heater) not an inductive load (eg fan heater, air conditioning unit, electric pump).

    In the case above, it looks like janz70's setup works fine with this as the proposed load is one (or two) immersion elements.
    Cider Country Solar PV generator: 3.7kWp Enfinity system on unshaded SE (-36deg azimuth) & 45deg roof
  • janz70janz70 Forumite
    59 Posts
    I was hoping it would be ok - I would have to get somebody to install as I know nothing about electrics or electronics.

    I have since discovered that our ground source actually has a 3 stage element of 3/6/9kw. I wasnt thinking of using it for the underfloor heating, just purely to heat the hot water but if it can be used for heating as well then why not.

    jeepjunkie - I would say our GSHP runs at similar times to your ASHP, mainly early morning and later in the evening and when ever the hot water is used as this seems to take prority over the heating (still trying to get to grips with how it operates and when).

    sly_dog good to hear it will drive the immersion, indirectly my solar actually drives my GSHP - during the day at least

    Anybody fitted this or similar with a GSHP I would be keen to hear how well it operates and how easily it is fitted ????

    I never thought about using it for staorage heaters, what about oil filled radiators
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