Should I get more battery capacity? - Is it worth the cost?
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- Опубликовано: 27 май 2024
- I've been collecting data and running some calculations to see if it would be worth adding an extra home storage battery to our existing GivEnergy system. Let's see what conclusions I've drawn from that exercise.
Addendum here: • Post
Our home system summary:
6.8 kWp solar array split E/W
5 kW Gen 2 GivEnergy hybrid inverter
14.7 kWh GivEnergy batteries
A2A heat pump heating/cooling system
Myenergi eddi hot water diverter
Fiat 500e EV
Solar and battery tour:
• Solar PV and battery t...
A2A heating tour:
• A tour of our air-to-a...
00:00 Introduction
00:43 Reasons for adding more battery capacity
04:04 Cost calculation
12:32 Current battery prices
16:41 Conclusion
17:50 Closing remarks
Please note that Tim is not a professional consultant, just an enthusiastic amateur, so cannot reply to requests for advice or opinions on specific systems or green investment opportunities. Thank you for your understanding.
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Before adding a comment I'd recommend reading this community post where I've added a bit of extra detail to better illustrate how I view the payback of the extra battery: ruclips.net/user/postUgkx3IwGg11F0Q8f0WOVl_RVqag2jGQS2UI3
Did I miss the calculations for conversion losses?
What about leaving an extra buffer? You won't want to force discharge all of the battery every day.
A higher power inverter such as a Sunsynk could discharge at a much quicker rate than the GivEnergy does.
This video reinforces my view that home storage batteries are not a no brainer.
Calculations are always needed.
The idea of this video was to get a ballpark figure, not a precise one, given there are many variables involved. Conversion losses are a minor factor in a sea of many other assumptions so wouldn't change the conclusion at all.
Agree but 20% is not minor. Just makes the figures look even worse
@geoffreycoan 12% at most. And very minor considering all the other assumptions such as this Winter's data being representative. Or being able to actually force discharges all the extra capacity. Both of those have larger margins of error.
@@TimAndKatsGreenWalk Yep, agreed.
Apologies if my comment seemed abrupt and argumentative, that wasn't how I intended it.
I don't do well late at night!
The main point you've made is a good one and I agree with the conclusion.
You put forward the best, most optimistic case for an extra battery and it's not worthwhile for your personal situation.
It also shows that many don't need as much battery capacity as they think.
@@UpsideDownFork no worries. You're right, I essentially assumed the best possible case for potential savings, to give the extra battery a fighting chance, and it still came down on the side of not being worth it, so any reduction in the savings caused by relaxing any one of my assumptions just enhances that conclusion, as you say. If the result had been slightly in favour of the extra battery it's at that point that it's worth starting to see where those assumptions need refinement, including accounting for conversion losses. My feeling is that the basic calculation would have to result in savings a factor of two more than the cost of the battery before it's worth considering adding it.
Just had a second Powerwall fitted and have been surprised by how much more flexibility it gives us which means we run the dishwasher and washing machine when we want, its much easier to use all the electricity we generate and the ability to charge the car directly from the battery is very useful (charge and discharge is now 10kWh), when we get a second Air-Air heat pump we can run it on cheep electricity. As I don't sell back to the grid (I'm on the last of the FIT) I don't have to worry about excessive cycling. I have found focusing just on the financials can blind you to other benefits.
Well, indeed, and I did mention there were other benefits, so it comes down to customer choice at that point, and if you'd rather get more battery because of those other benefits I'm not saying you're wrong to do so. The sub-title of the video was "is it worth the cost?" so in that respect I answered that for our particular situation (everyone's situation is different of course).
@@TimAndKatsGreenWalk The Fogstar stuff is remarkably cheap but also at £6K, do I really need an extra 30 kWh? Maybe not
I don't believe that the economics are quite there yet but as battery prices tumble, perhaps one day we will do exactly that
Thank you! The conclusion has not changed, feels like battery costs need to come down to make this viable……
Yup, for sure. In the mean time I'm thinking I'll investigate extra generation instead, but that's a future video...
@@TimAndKatsGreenWalk I’m at max generation, managed to get 18 panels on my roof… ..I just need to take the plunge on a heat pump now! I’m waiting to see what the new Cozy is like
@@David-yr8yt nice.
Great video (as usual) I have 2x reasons to increase the battery capacity. 1) I have a Solax system and can force discharge at 5kWh 2) and the biggest for me…. I would like to retire in 8 years or so. I currently earn a nice income and whilst I could invest the surplus cash, I have chosen to improve my solar and battery capability and eventually retire without a huge gas/ electric bill each month. My monthly bill was £278 and it’s now £80. I don’t think that £14,000 sat in the bank would have made me £198 per month. So when people ask when my ROI will start, I feel that my answer should be “instantly” or “last year”
Oh, I agree, a solar and battery system is a lot better than money in the bank. I'm planning on doing a video on that very subject at some point (which I'm sure will annoy a lot of the people who keep asking me about ROI!). But for us I think we've hit the point where any more battery capacity would be a waste and that we'd be better off putting that money towards getting more generation instead. That's another video I plan on doing soon!
I found that with with solar and batteries because my out goings are less i have more to spend from my pension, i dont consider ROI
Great analysis Tim, thanks.
Nice video Tim - thanks. The interesting bit that I picked up in all this was your understandable reluctance to manually insert into your lifestyle any daily force discharging to the grid. We installed 2 x Powerwall2 late last year and one of the beauties of that system is that if you put it in “reduce cost” mode, it does all of those calcs itself and effectively ensures that by the start of the cheap/recharge period, you have dumped any extraneous power to the grid to pickup the arbitrage. Even better, even though we are on Outgoing Octopus Fixed, so exporting is always 15p, I’ve configured the Tesla gateway to think that we make more money by exporting between 5pm and 7pm, so it keeps the battery as full as it can up until 5pm, and then throws everything it’s got at the grid just at the peak usage period. And all of this with no manual input by me. It occasionally misjudges and we run out of the battery before the cheap period starts, but not often and not by much. So there are some advantages to the Powerwall setup.
Well that's all good and well but I'm not going to replace my system with Powerwalls 😉. I'm glad it works well for you though.
Top video Tim. Thanks. Best regards Martin
Thanks Martin.
Thanks Tim, I did find it useful to watch you work through these numbers. Wow, you use a lot of power. If we ever meet up we must do some U-Value calculations something seems wrong somewhere!? I agree with your conclusions, when you think we don't get 100% sunshine and installation costs. Expensive for benefit as there are other items you didn't take into account as I am sure you will know. Shame really, I was hoping I could buy that 5.2 Kwh battery from you AS I am doing similar calculations for my system..🙂
All my stats are available to view in my stats videos, and I can assure you our heating is pretty typical (less than some more than others). Also check out my heat loss calculation video in relation to our windows. Maybe also check out some other videos from folks who run heat pumps to see how their demand compares (e.g. Tom Bray). 30+ kWh per day during a cold snap is not unusual, and as you can see that was only for a few days over the Winter.
Another consideration would be to look into the practicality of whether additional battery can actually be charged during the cheap tariff period based on inverter and battery max charging rates
Yes, I mentioned the issue of not being able to fully discharge the extra battery but neglected the charging aspect. Assuming a 6 hr off-peak period for IOG we'd be able to charge up 20+ kWh, so adding an extra 5.2 kWh battery to our existing 14.7 kWh would be fine in our case. In the Summer the extra battery could easily be charged using excess solar, so no problem there either.
It's worth mentioning if you have a 3 phase connection you can discharge 3.6KW per phase so 10.8KW in total
Yup, although sadly we're not in that category, with only a single phase available to us. I'd have thought three phase would be the standard in new builds by now but oh well.
Great analysis. 14kwh is ample - my analysis of my heat pump house’s usage was that 9.5kwh battery would give me 80% of the financial value of a 44kwh battery (which would cover all import). Still deciding whether to get an AIO though.
The AIO is a great battery. The extra power output and gateway backup are nice perks too. That's what I would have got if it had been available when I had my system installed.
Hi Tim,
So many variables to consider. Presumably the changes in the overall cost of electricity over time is less important than the difference between import and export?
Not only a second hand battery market to consider but improvements in battery technology to keep an eye on.
Also vehicle to grid technology can be an option in the future.
Yes, indeed, lots of things to consider that might pop up in the future, so I'm keeping my eye on the situation and not rushing into anything just yet.
This is great, thank you. I've been going through the same process recently; we have 9.5kwh and over winter it pretty much always runs out at some point between lunchtime on the coldest days or mid evening most days. I concluded that even though an evening of peak rate electricity is often several times more than the rest of the day's offpeak, it's still cheaper than investing in a new battery.
Buuuuuut... I'm still leaning towards getting another 9.5kwh (or maybe just a 5.2) before next winter anyway, because it's not just the financial value, there is value in the satisfaction of being able to make better use of our soar generation all year round, and avoiding using peak time grid electricity when it's at its dirtiest. This time of year annoys me because we export lots during the day when the battery is full, but it still runs out before the sun comes up the day after if we leave the heating on.
Plus maybe sharing the load between two batteries will make them last a bit longer...?
Yes, it's not only about the cost, I agree, but in our particular situation I think we're already at that sweet spot, more or less. Until batteries become cheaper at which point I might well go for a bit extra.
@@TimAndKatsGreenWalk I think you're right. Our setup is similar to yours but a smaller battery; I think I worked out that about what you've got now would be ideal but (at least when I looked then) the cost per kwh falls quite a lot as the battery size gets larger, so if I was going to upgrade at all it might as well be the larger one...
Thanks for this! It saves me working it out.
Well, the exact result will depend on your own usage profile but you can probably get some good rules of thumb from this at least.
@@TimAndKatsGreenWalk Yep. The devil's in the details. Having said that, when I did project management for a living, I'd guesstimate a plan and then spend a long time working a "real" plan. The "real" plan was within 10% of the guesstimate.
I've already looked into this myself using my own calculations. From those calculations some battery is good but a lot (until batteries become a lot cheaper) seems like a waste of money.
@@jchidley a waste of money is what most people spend on interest rates with financing stuff. Often overlooked as seems to be the normal thing to do.
@@jsouto77 Yes, you have to account for financing costs otherwise it is meaningless. (I don't understand why normal people buy brand new, expensive, cars but that's just me). Also, I see inflation costs used to flatter the business case for PV. Having said all of that, PV and batteries can pay for themselves. For heat pumps, it much more difficult to make the financial case but heat pumps do save massive amounts of CO2.
We have 4kw solar array running a 10kw system with 31.5kWh of storage cost us about £10k 2 years ago. I plan to run the batteries at 80% of thier capacity durring good solar production, and 100% durring the winter months to help prolong the life of the batteries.
Yeah, that should last you a good long while.
Interesting analysis and video. I’ve done exactly the same thing as you’ve described but with Tesla powerwalls and solar panels. However we have a heat pump and 2 x EVs to charge. In my case my calculations worked out in favour of getting the additional storage , but it is very much a case by case on your personal usage and circumstances. The one thing you didn’t touch on though that’s probably worth thinking about is the potential future rise in grid import costs per kWh in the future. You might find in years 8 onwards for example the cost is much higher which means your payback is quicker than originally estimated.
It's funny you should mention increasing electricity prices being an upside to installing this sort of kit. I agree with you. But most people say I'm too optimistic because I didn't account for the fact that you could invest the money instead and earn interest on it! As it happens I deliberately chose to ignore both of those things because I believe they essentially cancel each other out. Both are correct (to arguably different degrees but that's another matter), and so my assumption was that the interest you could have earned by investing that money instead is equal to the extra savings you'd make over time due to increasing electricity prices. Regardless, I do agree that everyone should do their own calculation taking into account their own situation and what they think is most important. I'm glad you did this for yourself and came to a conclusion that suits you.
Worth pointing out that force discharging your GE battery at the end of the day is straightforward. I've got it set up in the app to export anything left in the battery at the start of the off peak period. So I make a little bit of money with whatever I didn't use. All automated so no hassle or manual input required
I have mine set to discharge just before the cheap period (well, I let it overrun by 10-15 minutes)
That is fair, although you run the risk of a little extra peak import before the off-peak period starts if you discharge a bit too much and drain your battery before the off-peak. Probably not enough to worry about though.
I changed from 10kWh to 15kWh hours battery last summer as a number of times through the previous winter on a standard tariff I was running out. But then I got OI Go and in the last winter I very really dropped below 50% and that was only when I took part in a saving session, so now I'm wishing I had held fire and stuck with the 10kWh as its not working very hard at all. The only thing it gives me is that I don't have worry too much about pushing dishwasher and tumble dryer usage into the off peak time slots as there is always enough battery power. I guess the 15kWh would be useful if I add a heat pump but at the moment I can't see how I can make that pay for itself.
Yes, that extra capacity really comes into its own when combined with a heat pump, for sure. If we didn't have a heat pump I think we'd have been absolutely fine with 9.5 kWh.
That automation is really not difficult.
Happy to help you, show you my automations which work with IO
No, thank you, I'm good.
@@TimAndKatsGreenWalk Fair enough - the offer is always open if you want another "viewers setup" video though.
@@JohnR31415 thank you, I do keep meaning to get back to those videos at some point. There always seems to be something else to be doing though. One day.
My current thinking is that what would make most difference to me is going to an AIO, mostly for the additional power capability.
Don’t think they’re yet usable alongside the “normal” AC coupled inverters though.
Speak to the Geek has a combined AIO plus 3kW AC inverter setup and runs them with some success. Although it does require some external balancing using Home Assistant, so it's not a plug and play setup just yet. Still, he's got lots of tutorials to that effect on his channel if you're interested in looking into it further.
I did consider however, the route I now think is using my cars massive 65 kWh battery to backfeed back in to the house, it can already feed a 13 Amp socket from the charge socket so a suitable EV charger and car and we are looking at 7Kw to the consumers unit
Yup, I do believe that V2X will play a significant part in the future.
I jumped in a few months ago and added a 2nd 9kw battery. It’s increased the payback but I think the return on investment for me was the most important factor - 40yrs in financial services!! Love your monthly updates as I have 12 south facing panels and hence with your EW array we are very similar. Sadly I’m having a battle with Give as 2 days ago the system mysteriously showed minus 850kwh generation to home. This has completely mucked up cumulative data and makes a nonsense of the break even report. They don’t seem to be interested at all - I hope it never happens to you !😢
Oh no! That is very odd. Keep pressuring them, I'm sure it must be something they can fix. Otherwise can you make a manual correction yourself (assuming you download the data and make your own reports)?
Actually, thinking about it, you should have a separate generation meter for your solar, which would give you an independent measurement you might be able to use instead?
@@TimAndKatsGreenWalk Update, I insisted that this be escalated - their reply was "there is a data packet in the data that is throwing off the data on the 15th" - too many datas in one sentence? The solution to the problem is to delete everything from the rogue info day (I hesitate in using data again!). It's not a solution but I've seen on social media forums that this is not an isolated event and occurs more than once. You will forever have one version of the truth! Your monthly updates will never be the same again!!
@@bearders22 interesting. Well, a partial solution at least, better than nothing. I'll keep an eye open for similar issues with my system, thanks for making me aware of it.
Glad to have this analysis Tim but the cat is only deductible if installed by an installer and not reclaimable by individuals- I tried to buy an extra battery and I couldn’t find anyone that would sell one vat free.
Yes, I assumed it'd be installed by an installer.
@@TimAndKatsGreenWalkyes, the cost makes it even harder to justify- I tried and failed. At current prices, extra battery storage increase has to be coupled with inverter capacity which makes it even harder to justify. My rule of thumb has been that if the difference between import and export price is less than 7p, it’s not worth exporting due to battery wear
@@Magic-Smoke yup, that's fair enough. I suspect battery prices will fall a lot over the next few years so perhaps it'll become more viable in due course.
If you are adding an additional inverter, there is also another consideration/cost, which is you would need to go back to the DNO for approval for the additional generation. So not only is it an additional cost, but you may be restricted (G100) and wouldn't benefit from the whole capacity.
True, although I'd already discounted going down that route so didn't bother worrying about that.
Would have been good to give us a link to your initial calculations before you got a battery at all for comparison as you probably made a video of that as well?
Well, you could always scroll back through the video list, but to save you the trouble: ruclips.net/video/g0KbYqfCq1w/видео.htmlsi=0Kis-NZM9AYCsOTr
It's not super relevant to this particular question though.
@@TimAndKatsGreenWalk To be fair yes I could and pretty sure I had seen it before. Just thought better you did for a bit of context. Thank you :)
Hi Tim. You've done a good example of the current costings however you've not taken into account that over 10 years the cost for electricity would have increased and therefore even at today's cost of the battery and/or the price of batteries going down that in the 10 years there would be a saving that would increase year on year
Yup, that's fair, although it's hard to predict the trajectory electricity prices will take, so this is a reasonable approximation in the first instance. I'm expecting battery prices to come down a fair bit over the next few years so I'll be keeping an eye on it and reassessing regularly.
Tim
Great video on battery capacity but you have not considered buying an All in One 13.5 KWH battery rather than a 9.5 KWH battery as this would allow you to export more and also ensure you also don’t import so much power when your system is at capacity, although appreciate this final factor may not add much saving.
Well, if I was speccing my system today rather than 18 months ago I definitely would have got an AIO rather than the 9.5 + 5.2 that I got installed (essentially the same usable capacity as the AIO). However, the AIO wasn't available then, unfortunately, I was about a year too early! Adding an AIO now to the existing system would be massive overkill (we certainly don't need double our current capacity right now), but if it was possible to simply switch the existing system out for an AIO for little extra expense I'd definitely do it. As it stands I don't think it would be cost effective to do that, however.
I have 3x 3.6k kWh batteries. I am thinking about getting more if our heat pump passes planning permission. I believe my batteries will be flat before the Agile peak time if I don’t have some more.
With a heat pump to run a little bit extra capacity is probably a good idea.
Very interesting - I have 2 9.5 batteries with a 5kw inverter. The issue is the batteries will only output a max of 2.6 kw. I would like to have 2 inverters put a battery on each so that when I need higher output I have it. That solution is not currently available. So in conclusion I have the battery source but can’t use it to its potential. That needs taking into account when adding batteries.
Ah, that's a shame. We have the Gen 2 inverter which can do 3.6 kW from the batteries, so slightly better, but as you say it limits how useful extra batteries would be when added to that existing inverter.
Are you sure it’s worth worrying about it, those brief moments when you’re over 5.2kw probably are a few minutes a day, let the grid pick up the difference imo, not worth another grand on another inverter.
This is a massive issue with the Givenergy equipment, the 5.2kWh battery will discharge at max 2.6kW and the 9.5kW will discharge at a maximum of 3.6kW, it’s just not good enough.
Related problem. I have the GivEnergy 5kw inverter plus 3 5.2 batteries. Using Octopus Go you can only charge for 4 hours on cheap rate, at an effective rate of 2.4kw, so can only get 9.6kwh - not enough to fill the battery in winter. Looking for ways to resolve this.
You can’t charge/discharge any higher than 2.6kW with a 5.2kWh battery, I’d suggest trying to get on octopus intelligent go with a smart charger. Try and swap your 3 x 5.2kWh for a 9.5kWh battery as it’d be more useful with a 3.6kW charge/discharge.
Do you find you pull energy from the grid at tea time?
Yes, it seems as if you have a reasonable amount of storage. There are not too many days where your winter electricity uses peak energy, and your new heat pump running style certainly looks effective. Time to enjoy the garden, or else improve the insulation of your dot-and-dab walls? 🙂
Not much I can do about the walls but I did add extra loft insulation part way through the Winter, which might also have helped slightly. Definitely going to enjoy the garden this Summer though.
Of course battery prices and technology are likely to change over the coming years. Your price model has possibly one issue, cost of electricity import/export this will change but by how much and will the ratios between import and export; peak and off peak change?
Indeed, there is always a better technology on the horizon. And you can only make decisions based on what you know now.
Tim it might be worth actually getting some quotes, I copied your calculation and got some quotes,
For supply and fit:
8.2kWh Battery for £2550+VAT@0%
9.5kWh Battery for £2890+VAT@0%
Crikey, those are good prices. You're right, of course, I will be contacting my installer about another matter (to be discussed in a future video), so I will be asking for a quote out of interest at the same time. I suspect it'll still be not viable for us but you never know.
Are you accounting for the losses from charging the battery and then converting DC to AC?
No, this is an optimistic estimate of the savings that could be achieved, with every opportunity given to the battery to prove that it's worthwhile. Even under those conditions it doesn't pay for itself so any other factor that reduces those savings further enhances the conclusion that it's not worth it. Had it been the other way around that's the point where I'd have started to question the assumptions to see if it would still make sense, including accounting for losses (and imperfect force discharging etc. etc.). Since that was not the case I didn't see the point adding more complexity to the calculation.
If you have a tame electrician who is able to open a trade account with Midsummer, the can benefit from a fairly substantial trade discount. That might make a difference to your cost / benefit equation.
Yup, I'll be asking for a quote from my original installer just to see, but from my linked community post I suspect it'd have to be substantially cheaper to be worthwhile. Still, it is worth checking, as you say.
Calculating round-trip inefficiencies through the inverter and battery is a bit tricky. Personally I think that the battery industry has reached a stage where the government should be asking battery and inverter manufacturers and suppliers to state expected losses, with a formal test.
I'd bet there is a range of efficiencies in the market, and it would surely encourage manufacturers to strive for higher efficiency, and enable consumers to make a more informed choice.
Most batteries have the expected conversion efficiencies on the data sheets nowadays, and most are pretty similar. They're all pretty good tbh.
31kwh here has only just been enough for us over Winter without a Heat Pump. At least twice daily usage I'd recommend.
Just bought a 3rd 15.5kwh battery to give us 46kwh battery for £1950 and they are truly awesome. 180amps charge/ discharge per pack.
April until September last yr - 100kwh from Grid. £25 for 6 months.
5kw output with battery only, 6kw output with some Solar available.
Solis 6kw Inverter - £1150
3x 15.5kwh batteries - £5850.
Now enough to store 70% of a full car charge.
At 0.18C rate, they'll last 26+ years and since first installed 24th April last year, saved over £1600 on our electricity and gas bills.
Blimey, that's a lot of capacity!
@@TimAndKatsGreenWalk below 15kwh, it's living hand to mouth each day.
I recently worked with a guy also with 31kwh storage. He fully recharges car and batteries at night regardless of Solar. During the day all his Solar is exported for 15p, while batteries run the house. By exporting 30kwh, he effectively gets 60kwh back for free at night. Selling 1kwh for 15p, buy back 2kwh at night for 15p, it's not worth him self-consuming Solar. He puts to Grid to multiply it.
We can bounce over days of cloudy weather after one good sunny day if needed. Store enough to 3/4 charge the car overnight - cut usage in a power cut to last running boiler, lights, fridges and TV for nearly a week. Longer with enough Solar.
Sounds a lot but it soon gets used and we are still using Gas for heating. I will not remove the Gas boiler as currently Global events could take us again to expensive electricity and possibly rationing. It's easier to heat a house in a Blackout with boiler.
The biggest benefit being storing enough overnight off-peak energy to still have capacity for Solar if tomorrow is sunny. We always have a days worth of free or cheap held in reserve. If forecast is sunny for a few days, batteries get dumped into car overnight to free up room to catch Solar.
9.45am and currently charging at 3.2kw, soon be 5kw (max) but C Rating is teeny so should last years.
I know one thing, they should outlast me by a lot of years.
Our typical usage (excluding heat pump) is about 8 kWh per day, so it sounds like you're about three times higher than that. So three times our battery capacity sounds roughly inline with ours too.
@@TimAndKatsGreenWalk today is interesting- car is full, house is 90% so will be warm and toasty tonight with what looks like 10kwh spare.
What batteries are you using? Using the examples in this video it seems impossible to make a reasonable case for a battery-only system, but using the example cost you mention (£1950 for 15.5kWh) it sounds like it might be a different story?
Pretty similar to my guess that it is just not worth it to oversize the battery.
Not to mention can you actually get enough electricity out of the Inverter ?
Indeed. As soon as you need to start adding extra inverters to the mix you know you've already lost.
Hi Tim
Have Octopus switched your tariff to IOF?
I've switched to regular Flux for the time being as I had trouble switching to IOF. I'll try again in May.
Is that chart showing an average import cost of 26.3p (£157.96/599) We have a similar setup with A2A, Solar, 13.5kWh Batteries but no EV and our import price averages at 21p on Octopus Cosy.
That chart shows only the peak rate import, not the total import. The vast majority of our import was at the off-peak rate of 9 p/kWh (we were on Go), so our average over the Winter was significantly less than 21 p/kWh (Dec averaged 14.9 p/kWh for example, Jan was 13.6, and Feb/Mar 9.3!).
interesting and useful, as always
as others have said, your 10 year projections did not have any inflation
acknowledging there are quite a few variables and assumptions at play; energy provider tariffs, peak/off peak, arbitrage amounts, etc. Any of these can change at any time, altering the cost benefit analysis.
having said that, I think relatively long term inflation (3% / year?) would be worth incorporating
if your fans are considering their first solar + storage installation, they might buy larger battery + inverter up front if it means their insulated against rising prices for 12 years.
the perception of energy security that solar + storage offers is also hard to beat; it isn't cheap, but it's reassuring in these turbulent times
re second hand batteries; could you buy an old EV and use V2G? The car remains on your drive, now relegated to a stationary battery? In the early days of EVs, Nissan and Mercedes planned for this; they knew EV batteries would degrade; they might not be suitable for EVs, but would continue to have sufficient power and capacity to be repurposed as home batteries. Alas, that plan never materialised. If it had, things might have been very different...
would you consider another thought experiment...?
could you go *entirely* off grid?
one of the highest efficiency and affordable panels are AIKO's n type all back contact (ABC) panels, coming in at nearly 24% efficiency. Another is aeg-solar.com/solar-modules/abc-back-contact-n-type/
if you've watched ruclips.net/video/zPs2pY5sLk0/видео.html you'll see that peak rating is more-or-less irrelevant in the UK.
at the time of writing, these two panels will probably generate the most in the UK's less sunny and overcast conditions
the glass-glass editions are warranted for 30 years
if your *entire* roof was covered with these panels - "front" and "back", edge-to-edge, and you had something like Tesla Powerwall 3 [LFP battery (= long life); hybrid inverter (=eliminate solar DC - inverter AC - inverter DC - battery DC conversion losses, so more power), how much of the year could you go off grid? You might even have two Tesla Powerwall 3 batteries; that would give you 27KWh capacity but also redundancy [now that you're off grid]
LFP batteries probably offer 20 year operational life [though warranted for less]
GivEnergy now warrant their inverters for 12 years. Tesla have probably learnt a thing or two installing and monitoring 500,000 Powerwalls; should we be optimistic and say Tesla Powerwall 3 - including inverters - should operate for 20 years?
National Grid need to invest many, many billions on restructuring the grid, and they're raising the standing charge - SUBSTANTIALLY - to fund it. It could rise quite a bit over 20 years, if the last 2-3 years is an indicator
so, the cost benefit analysis might consider the investment against remaining connected over a 20 year lifespan
The rising standing charge, increasing efficiency and effectiveness of solar and the projected fall in LFP battery prices (cleantechnica.com/2024/02/26/catl-byd-to-slash-battery-prices-by-50-in-2024-boom-evs-win/) mean going entirely off grid sounds more achievable.
you might not be able to go off grid for the entire year; you might go off grid March-October, then reconnect for the four months with short, overcast days. Who knows, if, in 10 years, affordable, practical solar panels hit 30%-35% efficiency, you might be able to replace the panels you already have, and go off grid for the entire year
In 2024, perhaps just a thought experiment; but as
- technology becomes more efficient
- technology lasts longer
- technology capital costs fall
- but labour costs rise
- grid standing charge just keeps rising,
...going entirely off grid becomes worthy of consideration
I don't want to go off-grid, I get too much income from exporting.
The mathematical formula for ideal capacity is n+5kWh….where n= what you have now 👍
Haha! Fair.
17:44 Did you consider getting a 9.5kWh and selling the 5.2 (effectively you create the second hand market) to offset the cost and then switching to IO and giving you an extra two hours to charge and discharge?
It's an option but I still doubt it'd be financially worthwhile just yet. I'll see where battery prices go in the next few years and reassess.
@@TimAndKatsGreenWalk I’m in similar position, I could do with 5.2 more to fully take advantage of IO cheap rate electricity running the house 365 of the year. But the payback time at present prices (+ install costs to commission) just don’t make it worthwhile. I don’t have solar so my payback on my 9.5 is relatively long (approx 7.5 years) combined with Ripple, this is due to the suitability of solar on our Victorian property and the fact we are likely to move in the next 8-10 years, so like the flexibility to take the system with us (well with some strong movers to shift the 110kg battery)
I've got a 5KWh battery and have wondered about getting a second especially now VAT is removed. But my spreadsheet says I'd only have saved about 42p per day so far on average. So it's nowhere near worth it given I can't force export and don't have power cut backup.
But things will probably change soon. We might be getting a heat pump, if we get an EV the arbitrage (good word that) between charge cost and peak saving will grow.
I did find a seller of Huawei batteries in Germany on eBay. But post Brexit would mean importing would be a huge hassle. Shame as they're about £500 cheaper than I found in the UK.
Yeah, adding an EV or heat pump does dramatically change the potential for savings with extra battery capacity. Definitely worth reassessing if you get either of those.
@@TimAndKatsGreenWalk I watched a video by CarWow a few days ago about how old EVs still perform. He bought the cheapest one in the country for £1,500 (2013 Nissan Leaf) and tested it, still had about 65 miles range. Definite food for thought about replacing our second car (2004 Astra estate I use for dump runs, big shops and for the roof rack) just to get on the cheaper tariff. We'd save a lot by electrifying 90% of our transport use as well as all electricity use would be cheaper. It'd depend on finding a cheap second hand car that can do smart charging though.
But the trusty old Astra has just passed its MOT so bought itself another year of going to the dump and back filled with garden waste and DIY waste that I try to sneak through for free.....
@@FlatToRentUK haha! Yeah, interesting point about getting a cheap second hand EV for the better tariffs available. Honestly, I think these tariffs should be available to anyone, since they're still beneficial to the grid generally, but I suppose they're trying to encourage EV take-up, which is fair enough.
@@FlatToRentUK You can get smart tariffs by using a charger that supports them - which is in many ways better anyway.
@@JohnR31415 Do you mean by just installing a smart charger like the Ohme one which Octopus recommend? I have wondered about that in the comments on another of Tim's videos and he mentioned that you need to actually charge a car once a month to get it. I suppose I could install one and then offer to charge my mates' E-Up for free every few weeks!
Maybe I’ve missed something when watching, but in the summer wouldn’t a lot of your battery charge be “free” from your solar? So the payback would be higher?
The battery can either be charged off-peak at 14 p/kWh or charged from solar for "free" but then you'd miss out on exporting that solar to the grid at the day rate of 14 p/kWh, so actually it makes no difference how you charge your battery in the case of the current Flux tariff rates, the arbitrage work out the same regardless.
Yes except for conversion losses you better off charging from solar than overnight electricity.
But by charging the battery you miss the potential export opportunity which is only beneficial if you can actually manage to discharge at the flux peak rate in the time period as you said
Hi Tim,
Some great calculations there but I believe there is a fundamental flaw in your assumptions if I may be so bold depending which way you look at it - but don't worry it's good news.
It comes down to the assumed "payback period" and annual saving.
You may have already made a calculation about the whole system cost of PV plus battery and heat pump and how much that saves. I don't know what your figures are but here's mine as an example.
The whole system cost around £20k and saves around £3.5k per year compared to my previous combined gas and electricity consumption. I know that because that's what it did cost and I'm still positive in the Octopus account after banking the summer surplus on Flux and using cheap electricity Intelligent Go imported over winter i.e. I'm breaking even over the whole year so zero bills overall. Therefore the whole old system cost, is now a new system saving every year. 20k/3.5k = 5.7 years payback time.
Now, if I do the same calculation as you've just done on the potential of adding some extra battery capacity (say double) to avoid peak tariff import in December/January etc then I might save say £300 per year and divided into the extra battery cost gives a payback period of about 25 years so just not worth it.
❕BUT hold on ✋❕
That assumption completely ignores the fact that my system is paying me £3,500 per year which would pay for said battery in two years not 25.
Put another way if I removed my existing battery and then considered adding it back in should that same battery have a payback of 2, 5.7 or 25 years? 5.7 years of course because I know that already from the calculations of the whole system. You should base the calculation on the whole system not one element in isolation.
It might be more obvious if you think of adding or subtracting just 1kWh of battery capacity. The total payback time is still going to be close to the system 5.7 years for that 1kWh either way. I hope that's encouraging😉👍
If you already have a system in place the payback period of that original system is irrelevant when it comes to adding more batteries. You only need to consider the extra being added in the way I did, to assess whether that extra is worthwhile or not. It's called a marginal cost calculation and I stand by it.
@@TimAndKatsGreenWalk
I'm surprised at your comment Tim. How then do you explain a +/-1kWh variation on the battery capacity in the existing system only making a marginal difference to the calculated saving and payback time? According to what you are saying it would always be a 25 year or whatever result as it should be considered in isolation - but how can it when it's already in the system?
This just comes down to a matter of perspective in the choice of a baseline and I suggest that your choice of perspective results in a pessimistic result - but it doesn't HAVE to be like this. One could choose to add extra battery capacity when specifying the original system or afterwards - why does the passage of time determine whether to treat extra capacity in isolation? If that time delay tends to zero then it's part of the system obviously so why does a finite time delay determine its non inclusion in the system? That seems an arbitrary rule to me.
Let's not just respectfully disagree. Let's put the question to peer review. I'll ask my engineering and scientific research colleagues how they would tackle this interesting conundrum and get back to you and you ask Gary and other colleagues of yours and let's compare results so we gain consensus.
Honestly I think this is a fascinating puzzle of perspective and its solution could have far reaching effects.
@johnh9449 marginal cost calculations are pretty common, and totally valid. I'll adjust my original reply, the payback of the existing system isn't irrelevant. Imagine adding 1 kWh of battery in increments to a new system that doesn't already have batteries. Each time you add 1 kWh the payback for the whole system will change slightly. To start with the total payback time will decrease as you gain extra benefit from adding that battery capacity. At some point the payback time will start increasing rather then decreasing at which point there's no point adding more capacity as you've reached the optimal. You can do that marginal calculation at any time because you're assessing how much each increment would save relative to the existing system. That's all I'm doing here. The payback of my original system is about 7 years, and this extra battery would have a pay back of more than 10 years (when added to the existing system in the way I described in the video), so in combination the system pay back would then be longer than it was before (somewhere between 7 and 10 years). In other words it would push it beyond the point of optimum battery capacity (which I believe I'm pretty much at right now). If the payback of the new battery was less than 7 years it would result in the whole system pay back decreasing slightly from where it was before, and so therefore it would be worth getting that extra capacity as it demonstrates that the system isn't yet at the optimal amount of battery capacity. And if battery prices drop a lot then the payback of that new battery may well become less than 7 years, at which point it'd be worth adding more. Hopefully that makes my reasoning a bit clearer.
@@TimAndKatsGreenWalk
I agree with what you've just said - but that's because you are including the whole system and re-calculating the payback time of the whole system with the extra battery capacity. Yes you will marginally increase the payback time every time you add 1kWh and at some point you reach an optimum beyond which the payback time becomes too long to justify.
In my case doubling the battery capacity results in the payback time increasing from 5.7 years to 7.1 years approximately so arguably still justified when considering the lifetime of the battery.
What you seemed to be doing in your video (forgive me if I misunderstood) was to calculate the saving from the extra capacity and dividing that into the capital cost of just the extra battery capacity and thereby ending up with a very long payback time. 25 years in my example.
So perhaps we are singing off the same hymn sheet after all. 😊
@@johnh9449 I edited my earlier reply for clarity. I was incorrect to say that the original system payback time was irrelevant. In my example, however, the payback time of the extra battery was a bit longer than 10 years, and nowhere near 25. Adding it would still increase the payback time of the whole system and therefore not worth it in my opinion. I think we're pretty well optimised already with what we've got. You can absolutely work out the payback of that extra battery on its own terms though, you don't need to include the full cost of the existing system. As long as the payback of the new battery is less than the payback of the existing system you're good to go, otherwise you know (without having to include the original system cost) that you will increase the payback time when combined together.
Your figured and conclusions came out more or less the same as mine, there isn't the economic payback right now, but maybe in 5 years lithium batteries will be cheaper or sodium will be around, or they'll have cracked residential flow batteries. It's also hard to predict the price of residential electric in 10 years
Yes, indeed, all very good points. The situation is always changing so I'll certainly come back to this question again at some point in the future.
One big omission is taking future energy cost into account. They never go down only up. in five years time they could be doubled up. If it kinda make sense now the rewards will come later.
See my reply to another recent comment. I agree you're partially right but I get even more comments saying I've not accounted for the interest you could have earned if you invested the money instead! In reality they somewhat offset each other, although I'll be covering that in a future video so keep your eye out for that one.
I would actually disagree there. If Tony Seba is correct, prices may well crash by the end of the decade
This is especially true if global demand for fossil fuels also goes down and they have to compete even more with renewables, which results in event more competitive prices
@@waqasahmed939It would be great if oil consumption was reduced, but I can't see that happening, renewable needs another 20 year before they become a major player.
@@brandX15Look at how quickly countries are moving away from oil, especially in the global south.
Your calculations don't take into account that the 4 hr cheap period will only let you charge 4hr x 3.6kW = 14.4 kWh. You currently have 14.4kWh of battery storage so you cannot charge any more batteries up. If you moved to Eon next drive you would get 7 hrs of charge time @ £0.095/kWh and could charge up 25.2kWh of batteries
My assumption was I could get Intelligent Go, which would allow for 20+ kWh charging over six hours.
@@TimAndKatsGreenWalk Thanks for your response. That would work. I have 2 x 5kW Givenergy Hybrid inverters, 1 with 2 x 8.4 kWh batteries and the other with 1 x 8.4kWh battery and I looked at the cost benefit of adding a 2nd battery to the 2nd inverter but it was not cost effective. I am looking at adding solar either this year or next depending on finances.
Mid-Summer will charge you VAT - you will only be VAT free if you buy through a company and they WILL need to make a profit - in essence your figures do not that that into consideration ~ just saying
I'm assuming you'd get it via an installer, and I did say it would cost more including installation. That only makes my conclusion stronger, btw.
Typical of our lousy establishment to come up with vat free when it isn’t.
I know people on Octopus that during the saving sessions saved over £20 a session with force export
Yup, I received £32 on one session (although that was with the GivBack scheme run by Axel energy).
You can get 'server rack' batteries significantly cheaper from brands like Pylontech or Dyness, but then you might not be able to access Intelligent Flux.
I'm not interested in adding a different type of battery to my system, that's far too complicated.
You have to sweat a battery system to get value out of it, that means cycling it fairly deeply every day, trying to cover winter loads is not economical and current prices.
That's what I showed.
ITS Technologies 9.5 kwh gen2 £2,634 without the VAT
Wow, that's a great price.
Good content thanks.
I suppose it doesn’t work if you look at it with just money and payback in mind.
Bear in mind the trend for electricity cost is always going up not to mention the carbon cost.
There will be a carbon tax soon no doubt.
Great video though thanks.
That is true, it's certainly worth coming back to this periodically to see how things have changed. I'm willing to bet it'll only be a few years before getting extra capacity will be a much more beneficial thing to do.
Urm. Not withstanding we've gone from nearly 38p kwh to now 23p in around 18 months.
@@stuartburns8657 the general trend is upwards though, over long periods of time. We're still way up on where we were three years ago, for example.
@@TimAndKatsGreenWalk Oh absolutely. Will we see such significant price increases in the next couple of years, my feeling is no.
Beyond that, yes, even with all the green energy. Green doesn't come cheap, at least in terms of upgrading lines, grids, substations, large scale battery storage etc.
BEV's and heatpumps can mean a household which typically used to consume 8-10kwh per day, can suddenly be consuming 60-80 kwh or more depending on the EV battery size.
@@stuartburns8657good point but it’s the first time in my life it’s gone down and we are still up on where we were a few years ago.
Good explanation. I have looked at increasing our battery capacity. Currently have two SolarEdge 10Kw batteries and a 6Kw inverter. Was thinking of adding another 10Kw battery but our 6Kw inverter would not be able to charge 30Kw of batteries on Octopus Go (4 hours over night).
I have the money for an EV and like the look and price of the new Renault 5 EV which has V2L the larger of the two battery options is 52Kw.
Will wait to see if Octopus will have a tariff that integrates with V2L and if Renault as a brand becomes accepted for Intelligent Go. Also having three of our largest windows changed from 20+ year old double glazed to triple glazed on 29th April 2024.
I'm really hoping V2X becomes much more common over the next few years. That'd be a total game changer, for sure
for that there are calculators you know what you are using and the cost from it.
Are you suggesting online tools do this? I'm sure there are. Those won't give you daily peak use though, which is an important factor. I'd rather do the calculation myself.
@@TimAndKatsGreenWalk that is the best way so you can not blame other for you misstake
Also you are saving, by potentially reducing the effect of inflation.
Yes, possibly. Hard to account for properly so this was very much just an indicative calculation.
You also have to calculate that if you save £10,000 compounded at 5% interest for 10 years you would have nearly £16,500. So my view is definitely not worth it. You also have to add on how much it would cost to fit the extra battery.
£5000 over 10 years would leave you at just over£8200 that’s around £320 a year in interest which is twice projectors savings per year. That’s presuming 5% interest is available for the next 10 years.
I did mention that it would cost extra for installation. Btw, saving £160 per year on an installed cost of say £2k is 8% ROI (these are the values for the extra 5.2 kWh battery), so that beats your 5% interest rate.
Sorry it wasn’t meant to be a slight on your video or calculations, I think they’re brilliant by the way. As this video was just about the money saving aspect of solar and batteries I was just saying that if you invested the initial cost how much interest you would accrue over 10 years using an imagined compounded 5% you may even be able to get more if you locked it up for 10 years. I’m not 100% sure what you mean by £2000 installed cost. Maybe I missed something .apologies if I did. I did miss the bit where you talked about the install cost. My bad. Keep up the good work.
No worries, no apology needed. The cost of the extra 5.2 kWh battery was about £1800 and installing it would probably cost a couple of hundred quid, so £2k installed cost, give or take. That battery would save £160 per year according to my calculations, hence the 8% ROI. Although of course you might then need to replace that battery after 10 years, so that 8% ROI probably isn't reasonable, actually. It's all pretty approximate, to be fair, it was more about seeing how close it was to being worthwhile or not, and since it's not a clear winner I'm holding off for now. Although I appreciate some people like comparing home improvements like this to investing money instead, I don't personally consider it a useful comparison as presumably that money is being invested so that it could be spent later anyway. If I've got a use for it I may as well spend that money now on something I want (and so much the better if it also then saves me money over the next few years, which isn't the case for a kitchen renovation, say).
Sorry Ignore me I’m sorry I thought it was £5000 for the extra battery. It’s not £1700 as you say 2000 installed as you say.
I just bought a 5 kw lifepo4 battery for 870,- euro's
Nice
Damn, where from? And what inverters does it work with?
It didn’t look like you took account of the 10-20% energy conversion losses unfortunately incurred in charging and discharging the battery.
I did my own similar calculations and came up with 5-22 years depending on which assumptions I made. Clearly not viable!
Does make me wonder about original battery purchase, but there we are. Batteries are not good value. Extra solar panels are
Conversion losses are only worth worrying about if the conclusion was on the side of getting the battery. And only then if it's marginal. You need a clear signal to start with using a basic estimate before worrying about the details.
how about the cost of installation £300-£400
I did mention installation would cost a bit more, but that just further enhances the conclusion anyway, it doesn't change it.
Interesting ideas. However you have not included the opportunity cost of the batteries. If you had invested the cost of the batteries at, say 5% pa, the your numbers look very unattractive. If you do the sums on compound interest even worse. If it was an ISA then the tax free benefit erodes the benefit even more.
I concluded it wasn't worth getting, so anything else that enthances that conclusion is irrelevant at the point.
@@TimAndKatsGreenWalk A fair point but perhaps it might have done if you had started there. When considering how to configure a solar and battery installation I constructed a spreadsheet including all the offset costs I could fit in which showed that bigger the battery capacity the less attractive the investment became. Of course this was based on the cost I was quoted last September and they might have fallen quite a bit now. I decided to defer installing anything until I reviewed the situation in October this year when the fixed term bond (6.2%) which would have paid for the installation matures. I can send you the spreadsheet if you would like to look at it but I suspect you have something similar yourself.
cant you just sell the 5 and get another 9, may be cheaper and neater
I had a quote for panels and one 9.5kwh battery and asked them how much for a second installed at the same time and it was an extra £2000 so that would make it worthwhile
That's an option but would probably still be on the threshold. If battery prices come down it's something I'll consider.
Quick note: When comparing the battery prices, you assumed 4.2 working capacity on the 5.2 battery; but the full 9.5 on the 9.5 battery.
According to the GivEnergy datasheets the 9.5kWh battery has a 100% depth of discharge, whereas the 5.2 has an 80% depth of discharge.
Yeah, they’re not 100% though - you can’t have less than a 4% “reserve”.
Those are indeed the usable capacities, 80% DoD for the 5.2 and 100% DoD for the 9.5.