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Is it a financial no brainer to get a battery system if you are getting a heat pump?

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  • michaels
    michaels Posts: 29,094 Forumite
    Part of the Furniture 10,000 Posts Photogenic Name Dropper
    NedS said:
    I think it's going to be different for everyone.
    I have a heat pump, solar and am on Octopus Cosy.
    At this time of year, I'm using 30-40kWh per day with minimal solar contribution. My average import price is 20p per kWh. I'd love to decrease this, but the numbers don't really stack up (although I may just go ahead and do it anyway)
    If I buy a 10-13kWh battery, I can probably shift all my usage to the Cosy cheap slots at 12.86p, saving around 7p per kWh at most. I estimate that may save me £4-500 per year. A Tesla PW3 costs around £8k installed, so may take 16-20 years to break even, before allowing for conversion losses etc, so not really economical for me (cheaper batteries are available). I don't see installing 30kWh of capacity and charging once overnight any more appealing (would need a minimum of 6 hours of cheap rate and a 5kWh inverter to charge 30kWh of batteries) plus I have no use for 30kWh of battery storage capacity for 8-9 months of the year when I import very little and have a negative bill due to solar export.
    The numbers can change though. What if SEG rates plummet or electricity prices rise significantly.

    Obviously you could use that 30kwh in the summer to import at say 7p on eon next drive and export on their 15p SEG.
    I think....
  • Reed_Richards
    Reed_Richards Posts: 5,281 Forumite
    Part of the Furniture 1,000 Posts Photogenic Name Dropper
    The Eon Next SEG rate is 16.5p per kWh provided you are a supply customer.
    Reed
  • john-306
    john-306 Posts: 745 Forumite
    Part of the Furniture 500 Posts Photogenic Name Dropper
    edited 15 February at 10:52AM
    michaels said:
    john-306 said:
    I had a 6.5kwh battery installed with my solar that worked well with my usage.
    Since heat pump added the battery runs out in this cold weather about an hour before the next Cosy 12.52p cheap rate top up.
    Adding another 1k battery cost to keep everything inside cheap Cosy rate would only save less than £50 a year, so not worth it.


    What if it let you  run 24/7 on Tomato 5p or first utility 7p per unit though?
    To run on tomato 5p 24/7 over colder months I'd need another 25kwh battery, a quick check for the same battery's to match would cost £6500

    A quick calculation, I'd save £300 over November to February inclusive. 
    Again, not worth it.


  • QrizB
    QrizB Posts: 18,129 Forumite
    10,000 Posts Fourth Anniversary Photogenic Name Dropper
    michaels said:
    I think first utility do an E7 of about 7p per kwh no EV required?
    Are you sure? Can you provide a link?
    IIRC, First Utility became Shell Energy, which Shell then sold to Octopus a couple of years ago. Has someone launched a new supplier using the old name?

    N. Hampshire, he/him. Octopus Intelligent Go elec & Tracker gas / Vodafone BB / iD mobile. Ripple Kirk Hill member.
    2.72kWp PV facing SSW installed Jan 2012. 11 x 247w panels, 3.6kw inverter. 34 MWh generated, long-term average 2.6 Os.
    Not exactly back from my break, but dipping in and out of the forum.
    Ofgem cap table, Ofgem cap explainer. Economy 7 cap explainer. Gas vs E7 vs peak elec heating costs, Best kettle!
  • The Eon Next SEG rate is 16.5p per kWh provided you are a supply customer.
    I believe the OP is reducing that rate to make up for discharge losses for charging the battery at a cheaper rate then discharged to the grid later at the export rate.
  • It's clear batteries by themself range from 10-20 years payback with none that I am aware of offering the bigger of those payback years as warranted. Inverters also fail and not sure you can get a 15-20 year warranty so payback could be pushed out further.

    So back to the original OP's question Is it a financial no brianer then the answer is NO.

    What it does give you is more control and more options of tariffs and if configured with the right equipment to survive power cuts.
  • michaels
    michaels Posts: 29,094 Forumite
    Part of the Furniture 10,000 Posts Photogenic Name Dropper
    QrizB said:
    michaels said:
    I think first utility do an E7 of about 7p per kwh no EV required?
    Are you sure? Can you provide a link?
    IIRC, First Utility became Shell Energy, which Shell then sold to Octopus a couple of years ago. Has someone launched a new supplier using the old name?

    Old brain cells - utility warehouse
    I think....
  • QrizB
    QrizB Posts: 18,129 Forumite
    10,000 Posts Fourth Anniversary Photogenic Name Dropper
    michaels said:
    QrizB said:
    michaels said:
    I think first utility do an E7 of about 7p per kwh no EV required?
    Are you sure? Can you provide a link?
    IIRC, First Utility became Shell Energy, which Shell then sold to Octopus a couple of years ago. Has someone launched a new supplier using the old name?

    Old brain cells - utility warehouse
    That makes more sense :)
    Looking at Cheap Energy club, UW are offering me "UW Fixed Saver 40":
    Unit rate 36.661p per kWh
    Economy7 unit rate 5.793p per kWh
    Standing charge 57.683p per day
    Tariff ends on Fixed until 31 January 2026
    Which would be quite tempting, if you could guarantee to only use electricity during the off-peak period.
    N. Hampshire, he/him. Octopus Intelligent Go elec & Tracker gas / Vodafone BB / iD mobile. Ripple Kirk Hill member.
    2.72kWp PV facing SSW installed Jan 2012. 11 x 247w panels, 3.6kw inverter. 34 MWh generated, long-term average 2.6 Os.
    Not exactly back from my break, but dipping in and out of the forum.
    Ofgem cap table, Ofgem cap explainer. Economy 7 cap explainer. Gas vs E7 vs peak elec heating costs, Best kettle!
  • Reed_Richards
    Reed_Richards Posts: 5,281 Forumite
    Part of the Furniture 1,000 Posts Photogenic Name Dropper
    But the Utility Warehouse best rate for export is 8p per kWh, as far as I can see.  The economics of a battery must include charging it cheaply overnight then discharging it for more money paid for export.
    Reed
  • QrizB
    QrizB Posts: 18,129 Forumite
    10,000 Posts Fourth Anniversary Photogenic Name Dropper
    But the Utility Warehouse best rate for export is 8p per kWh, as far as I can see.  The economics of a battery must include charging it cheaply overnight then discharging it for more money paid for export.
    The calculation by @michaels doesn't rely on export, or on eg. solar PV generation. It's just about time-shifting your consumption.
    You might be able to increase your savings by exporting at peak times, but that's not essential to the calculation.
    I'n currently saving ~£1 a day vs. the SVT even allowing for losses, by charging my system overnight at 7p/kWh then running on that stored power for the rest of the day, when Id otherwise be paying 25p/kWh. And that's in a dual-fuel household where we're only using 6-7kWh/day outside of cheap rate hours.
    N. Hampshire, he/him. Octopus Intelligent Go elec & Tracker gas / Vodafone BB / iD mobile. Ripple Kirk Hill member.
    2.72kWp PV facing SSW installed Jan 2012. 11 x 247w panels, 3.6kw inverter. 34 MWh generated, long-term average 2.6 Os.
    Not exactly back from my break, but dipping in and out of the forum.
    Ofgem cap table, Ofgem cap explainer. Economy 7 cap explainer. Gas vs E7 vs peak elec heating costs, Best kettle!
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