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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
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Heating and cooling: ASHP + Solar PV

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    • CommentAuthorDiarmid
    • CommentTimeAug 4th 2023 edited
     
    Rather than installing an expensive battery I was mulling over the idea of installing an ASHP and a solar panel array. Currently we heat via UFH powered by lpg (expensive) The house is south facing, 55ºN and well insulated. I would have the solar PV feed directed to heat water by default IYKWIM. I'm retired so at home during the day. I realise that between October and April power generation would be limited. Currently consumption about 2000 kWh per year. Thoughts?
    •  
      CommentAuthordjh
    • CommentTimeAug 4th 2023
     
    How much LPG do you use? Ideally in kWh per year. That will tell you roughly how much a heat pump will cost to run, and may help with deciding how big it needs to be. How many months do you run the boiler?

    When you say "I would have the solar PV feed directed to heat water by default" do you mean using a diverter? That's reasonable but it may make sense to use the heat pump to heat water in the winter (and maybe in spring and autumn too)
    • CommentAuthorDiarmid
    • CommentTimeAug 4th 2023 edited
     
    Usage currently about 1200l a year, apparently 1 Litre of propane = 7.08 kWh therefore about 8400kWh. A diverter yes and have doubts that a solar PV system (on the small scale I'm talking about) would make any impact on supplying sufficient power for our needs outside the summer. We don't use the UFH between May and September but still use the lpg for DHW during this time.
    • CommentAuthorGreenPaddy
    • CommentTimeAug 7th 2023 edited
     
    Very roughly (keeping numbers round to get the general point across):

    - a regular nominal 4kWp array might give you 3000kWh of energy per year

    - the PV array would likely give about (prob less) 1000kWh over the Oct-Apr (incl) heating period

    - you prob use about 7000kWh of energy for heating

    - so you'll need say 2000kWh of elect to get that from your ASHP

    - you may well use more than that (PV generated) 1000kWh of elect in that heating period for non-heating elect usage (fridge/frzr, lighting, TV, computers, etc).

    Basically, there's no correlation between solar PV arrays and heating sources (in normal domestic sizes). That's not to say having PV and an ASHP is not a good idea.
    • CommentAuthorGreenPaddy
    • CommentTimeAug 7th 2023 edited
     
    deleted/ duplicated
    •  
      CommentAuthordjh
    • CommentTimeAug 7th 2023
     
    Posted By: GreenPaddythere's no correlation between solar PV arrays and heating sources
    Indeed, that's why I bought a share of a Ripple turbine.
    • CommentAuthorDiarmid
    • CommentTimeAug 10th 2023
     
    Thanks for your useful comments...I think this is the way to go.
    • CommentAuthorjms452
    • CommentTimeAug 12th 2023
     
    Late to the party here but can work great in the shoulder months when the demand's not that high and it can be sunny. In mid winter it will be pretty Limited.

    The smaller the heat pump the better - part of why it works nicely for us is that we have 4kW PV and a circa 800W (input) Air to Air (A2A) heat pump. i.e. we're normally exporting a few hundred watts even when it's horrible.

    As our A2A doesn't do hot water we've recently added a Eddie immersion diverter that heats the hot water in any gaps when the A2A isn't running or is throttled right back.
    • CommentAuthorrevor
    • CommentTimeAug 12th 2023 edited
     
    Just a thought if your boiler still has life in it why nor wait until HP are cheaper and dust has settled a bit. If you go for PV and a battery (which should be cheaper I guess) you have an extra energy source which gives far more degrees of flexibility and freedom on how to reduce your energy bill. We have a propane boiler fed from bottles but only use about 4 to 5 bottles a year. We have a thermal store with thermal panels and since March the boiler not been on. The solar pv 6kW and 10kW battery means we rarely use any from the grid during summer and overall we are about 65% efficient over the year. We do not divert PV to the store via an immersion I think the energy in the battery gives me more degrees of freedom in how I use that energy. From about November to March we have the log burner on for a couple of hours an evening which also helps Even the weak sun during winter provides some heat to the thermal store so uses less gas for the UFH. We are very well insulated and make good use of solar gain allowing it into the house and trapping it in. You are south facing so any mileage in making use of that and any scope for more insulation. Our gas bill is about £300 pa so a heat pump for us is not justifiable but we do our eco bit in other ways.

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