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2 Battery or Not 2 Battery

edited 30 November -1 at 1:00AM in Green & Ethical MoneySaving
20 replies 3K views
hvaghelahvaghela Forumite
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edited 30 November -1 at 1:00AM in Green & Ethical MoneySaving
Hi everyone


For some years I've been considering solar PVs, but now I've decided to take the plunge before the FIT is abolished and now I have electric cars.
I've done hours of reading on the forums about Solar PVs and I've been reading Mart's thread on Solar PV FAQs and On-grid domestic battery storage.
I'm currently in the process of getting quotes (I've already excludes Project solar UK). I have a couple already. I'll open a new thread once I get some more quotes to get your opinions on them.
However my key question to you guys is should we get a battery?
In our family we like our electric cars - we have a plug in hybrid (14kw battery), a fully electric car (40kw), and next year the new tesla model 3 (80kw) will be arriving. Thus we will have 3 EVs in the house which will need charging.
The plug in hybrid is used daily - thus charged every day, the Leaf will need charging probably twice a week, and the tesla with its long range will be charged fortnightly.


Both the quotes I have so far are with Pylontech US2000B Plus for about £2,000. I don't know if they are worth it for us. I would greatly value some opinions.
Cheers
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Replies

  • edited 19 September 2018 at 7:29AM
    Martyn1981Martyn1981 Forumite
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    edited 19 September 2018 at 7:29AM
    My thoughts on batts, as you'll be aware, are that we aren't there yet. However, if you can make use of a big battery, like the Powerwall II (13.5kWh) then the numbers improve, though still probably not good enough. The Pylontech kit looks a similar price to the PWII if you go to about 6 or 7 2.4kWh units, but I think (?) it's DIY?

    There's no point IMO of adding a small battery if you intend to use it for an EV as you can deliberately charge the EV from E7. So you want to make sure that the batt can displace daytime leccy import that you can't avoid, first.

    So to have say 8-10kWh of spare battery to charge an EV each day, you'll need a bigger batt to cover daytime high demand, and late afternoon/evening demand when PV gen has dropped down.

    Does that make sense - so perhaps you need to think of the domestic battery keeping the hybrid topped up each day, and the other EV's charging off cheaper nighttime rates, and all three charging at night during the winter months ...... I think?

    Should add, that on this subject I'm simply thinking out loud - I really don't know what is right, nor what will work, but it's really interesting chatting about it, and to see how this will develop as those that are taking early adopter steps report back and educate us all.
    Mart. Cardiff. 5.58 kWp PV systems (3.58 ESE & 2.0 WNW)

    For general PV advice please see the PV FAQ thread on the Green & Ethical Board.
  • NigeWickNigeWick Forumite
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    hvaghela wrote: »
    I don't know if they are worth it for us.
    Depends on your financial situation.

    I could afford to be an early adopter and so have solar panels, BEV and Tesla PW2 battery. I could not claim financial benefit for the battery or the car (public transport & taxis would cost a bit less), but, the solar system will eventually pay for itself even without the FiT I get. I've had about 2,000 miles of driving the BEV from the solar array.

    I'd say if you can easily afford it, go for it. If finances are a consideration, do the sums to see if you can gain financially in the long run.
    The mind of the bigot is like the pupil of the eye; the more light you pour upon it, the more it will contract.
    Oliver Wendell Holmes
  • hvaghelahvaghela Forumite
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    Thanks for the replies- sorry for the delay.
    I've got a handful of quotes in now for panels and battery.
    I wouldn't say I could 'easily afford' it, but number crunching over the weekend and sums could work out for us.


    I'll keep you guys posted.
    Cheers
  • Exiled_TykeExiled_Tyke Forumite
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    The consideration for batteries should not be a simple matter of being able to afford them. It's whether they are financially viable. I've had a few conversations with installers recently. Each time I've asked whether batteries are worth going for they have enthusiastically encouraged me to take the plunge. However when I've explained the calculation to ascertain whether it's viable they've gone very quiet. As Martyn says, we are not there yet.

    The calculation is a relatively simple one (and taught to me by Martyn - with grateful thanks Mart) . Divide the total cost of the battery installation by the amount of electricity it will discharge over it's life. This needs to take into account, % efficiency, depth of discharge and most importantly the number of cycles the battery is good for. This calculation will give a cost per unit of electricity discharged. In all the cases I've looked at this cost is not yet significantly lower than the price of buying electricity from the grid.

    There is if you want it, a further enhancement to this calculation - that would be to estimate the likely increase in cost of electricity over the life of the battery AND also to take into account the cost of borrowing (or the lost interest savings) of the money spent. I like to assume that these could roughly cancel each other out.

    As far as I can see, any other calculation to justify this spend would be a mistake.

    Hope this helps!

    E. Tyke (F.C.A. - just in case anyone needs the assurance)
    Install 28th Nov 15, 3.3kW, (11x300LG), SolarEdge, SW. W Yorks.
    Install 2: Sept 19, 600W SSE
    Solax 6.3kW battery
  • edited 24 September 2018 at 7:41PM
    Martyn1981Martyn1981 Forumite
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    edited 24 September 2018 at 7:41PM
    As far as I can see, any other calculation to justify this spend would be a mistake.

    Thank you for the kind comments.

    One possible area that could change things (but is still within your calculation) is if the companies widen their warranty as they gain confidence in the product.

    I'm basing cycles only on the warranty period, which isn't really fair, but as these products are new(ish) I'd be worried to go further. So if they say doubled the warranty from 5yrs to 10, or 10 to 20, and the number of cycles, perhaps from 5,000 to 10,000, then the economics improve massively, even though the price doesn't change.

    In reality, the warranty tends to suggest a point where the capacity might be 80%, so overspecing from the start by 20-25%, means that the product is still sound and suitable even after it's 'degraded' out of warranty. [Edit - actually, overspecing then setting the battery to avoid the top 10-20%, and the bottom 10-20% might greatly improve the batts life, since that is where the damage seems to occur. M]

    But, just to repeat, I'm not happy personally throwing post warranty use into the financial calcs yet, too young and expensive a product I think. But when the numbers do look good, then there's a great chance that the batts will do much better by simply ticking along for an extra decade .... maybe, possibly, I don't know?
    Mart. Cardiff. 5.58 kWp PV systems (3.58 ESE & 2.0 WNW)

    For general PV advice please see the PV FAQ thread on the Green & Ethical Board.
  • JKenHJKenH Forumite
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    The consideration for batteries should not be a simple matter of being able to afford them. It's whether they are financially viable. I've had a few conversations with installers recently. Each time I've asked whether batteries are worth going for they have enthusiastically encouraged me to take the plunge. However when I've explained the calculation to ascertain whether it's viable they've gone very quiet.

    Whilst I cannot argue with the financial logic one could make the same argument about most expenditure. Not everything we spend our money on makes financial logic: a meal out when we could eat at home, buying a GLX spec car when an LX would do the job, changing the bathroom suite that is perfectly functional. Not everything is a pure financial decision; we have to take into account Utility which varies from individual to individual.

    I was unsure about batteries before I got one. Financially I am perhaps less convinced about their merits now than I was when I put my money down. What I do, though, get from a battery is that sense that I am not wasting as much of the solar PV that my panels have produced. ( I recognise others get satisfaction from exporting to the grid but for me, personally, exporting energy is like watching £5 notes blowing out the window.)

    As I say, it is a personal thing, but having a battery might give you something more than the pure financial benefit.
    Northern Lincolnshire. 7.8 kWp system, (4.2 kw west facing panels , 3.6 kw east facing), Solis inverters, Solar IBoost water heater, Mitsubishi SRK35ZS-S and SRK20ZS-S Wall Mounted Inverter Heat Pumps, Nissan Leaf (plus some ICEs:) )
  • jimjamesjimjames Forumite
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    If you have a plug in car, could you not use the battery on that to take the excess during the day?
    Remember the saying: if it looks too good to be true it almost certainly is.
  • Exiled_TykeExiled_Tyke Forumite
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    jimjames wrote: »
    If you have a plug in car, could you not use the battery on that to take the excess during the day?

    Yes you could. I think in most cases car owners tend to be out at work during the day which creates the lost opportunity. I've seen this as another argument for buying batteries, charge them by day and discharge into the car on an evening. But again, financially this just doesn't add up as it's still cheaper to buy from the grid.
    Install 28th Nov 15, 3.3kW, (11x300LG), SolarEdge, SW. W Yorks.
    Install 2: Sept 19, 600W SSE
    Solax 6.3kW battery
  • hvaghelahvaghela Forumite
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    So I've got a sensible quote - thoughts pls:


    15xJA Solar Black Mono 280w panels, SolaX X1Boost inverter, Solar iBoost, Pylontech 2.4w battery (x2) +SoFar Me3000.
    Includes mounting kit & fixings, electrical materials, isolators, cables, structural survey, EPC, scaffoldings, MCS cert, installation.


    All for £6,700.
  • edited 26 September 2018 at 9:30AM
    pensionpawnpensionpawn Forumite
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    edited 26 September 2018 at 9:30AM
    There are a number of tests that can be applied from basic to more complex. In order:
    1. Look at your annual import and assume (incorrectly, however this is only to maximise the simplicity of the analysis) that your chosen battery will completely eliminate this import. Multiply this value by your electricity rate and for the number of years that your chosen battery is warranted. Compare this number to the installed cost of the battery. If your number is less then try again in 6 months! For simplicity I assume that the saving against increasing electricity costs is cancelled out by gradual battery degradation. For example, my annual electrical import is 5200 on a tariff of 12.76p = £664. Multiply by 10 for a Powerwall 2 and I get £6640. So until Powerwall 2's are less than this basic test I'm not interested.
    2. If your chosen battery meets test 1 above then test 2, which is a little more involved, is against actual predicted savings, which will be much less than the theoretical maximum. Just common sense tell you that you need more electric than you produce in the winter and produce more than you need in the summer. The optimal time of year for a battery is about this time of year and correspondingly in the Spring. I would say the three month period which have the equinoxes slap bang in the middle. What the champions (sales reps) of batteries seldom tell you is that during the summer you are probably pushing around 70% of your house's electrical needs directly from the roof i.e. the battery will only be good for 30% of your daily summer requirements. Whereas in the winter your battery will probably only prevent import during daylight hours (i.e. when clouds appear). I bit the bullet and plotted almost a whole years worth of generation and demand and estimated (I do need to run the numbers again for a more up to date / accurate figure) that one Powerwall 2 would take only 33% off my annual import. That's ~ £220 a year, £2200 over ten years. Even if I'm out by 50% battery tech, for me, is not going to be an economically viable solution for a number of years.
    3. So what is going to give you the best return on all that excess solar energy. For me it's moving to an EV. I export around 2.9Mwhrs a year and dumping some (most?) of that in a car to replace fossil fuel is a no brainer in running cost (no car tax either, yet!) Even charging it with day rate is around 5 times cheaper. However the extra capital premium cost for an EV needs to be carefully weighed up. Also, government grant may expire (reduce probably) in October as will subsidy on home charging point. Battery will have it's day, though not for a few year I reckon.
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