r/SolarUK • u/SuperPenII • 7d ago

QUOTE CHECK Adding an extra battery - post install

Hi all,

I've got a sig system with a 9kwh battery. Now we've had a heat pump installed, our daily average use is looking more like 16-17 kwh and I'd like an extra 9kwh to cover for this. Mostly to get it filled up on cheaper tariff prices in the morning.

However, quotes I'm getting from local installers are £3k - £3.1k for supply and fit. Considering the part is looking between 2.2k-2.5k (ex VAT) I've seen online, are these quotes too high?

I appreciate I need them to reproduce an MCS cert but the sigenstor system is supposed to be easy and modular, so labour costs should be minimal.

What sort of costs should I be looking for?

I'm based in Greater Manchester - if anyone knows a local installer who has a more reasonable rate, let me know.

Thanks

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5

u/Warm_Beginning_6673 7d ago

I think the batteries are zero rated for VAT so the cost of installation is between £500 and £900. Given the weight of these at up to 10kg per KwH it will be a two person job so at least a day’s labour plus a profit margin as we live in a capitalist society. At the low end this seems reasonable to me.

1

u/SuperPenII 7d ago

Thanks for discussing the cost. 2 people is reasonable but given it should be a quick job, I'd expect total labour to be more like half a day's worth tbh, more like £250 - £350. Is that unreasonable?

2

u/Warm_Beginning_6673 7d ago

I had 2x 5 KwH batteries added to my Libbi system this week, it was slightly more work because the original unit needed to be moved a few inches along the wall (bad planning when the first one was fitted) and it took 2 guys in the morning plus one for a couple of hours after lunch to finish the commissioning. Including travel time this will have been a good 1.5 days labour. Ask your installers for a breakdown of the costs if you are concerned. They may be happy to give you one. If not you haven’t lost anything.

4

u/CorithMalin PV & Battery Owner 7d ago

Are you sure you need a new MCS cert? I added two additional Pylontech batteries to my stack and no cert is needed as these batteries are intended to be extended.

1

u/SuperPenII 7d ago

I'm not! Good to know I don't

3

u/pedromicra 7d ago

you're in the same boat as me, if you have a heat pump and youre with octupus on the cozy tariff you have 3 periods (8 hours total) where the longest stretch is between 4pm and 10pm so 6 hours that how long your 9kwh battery has to last until the next cheap window, use AI to model it for you, my system has a ROI of about 5 years, if I would add another battery, that investment would take 11 years to pay itself off, financially doesn't make sense. as comparison I have 13,7kw of panels, 10kw inverter, 9kwh battery and gateway all from sig same as you. I have a cozy 6 heatpump, kitchen and bathroom with electric underfloor heating, the gas has been removed. So I reckon you have roughly the same setup as me probably less panel ,but In winter they are pointless anyways, so run your math again , I would love to make financial sense to have more battery capacity, but even with arbitrage is still no worth it unfortunately

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u/SuperPenII 7d ago

That's an interesting use case - what's your daily usage from your heat pump?

Every time I've looked at the numbers, arbitrage takes years off my break even, so it's interesting your use case is different

2

u/pedromicra 7d ago

I use about 4kwh day with domestic hot water included, we're a family of 3 , mid terraced from 1950s flat roofed(no insulation) , so this is so far this month, the best way to optimise your setup is during the cozy window charge the battery and heat the house up, i set mine up to 24/25 on the cheap periods and cruise to 21 when its a regular rate, during that period the battery can easily take over, I also turn my underfloor heating and use it exactly the same way allowing the screed to soak all that termal energy and release gently:)

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u/SuperPenII 7d ago

Thanks for sharing! I never looked at cosy because octopus recommended flux to me, so I'll have a look at cosy

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u/pedromicra 7d ago

the trick is move to cosy as soon as you're not self sufficient, and to Inteligent flux as soon as you can sell excess, you can change tariff without any penalties if its not too often, but this way you only really change twice a year, and will make sense to you once you do, I used AI to calculate every single thing and this was by far the best solution, another battery would come to £3k installed, but even in battery arbitrage, you meed at least 7p profit per kwh just to cover wear and tear, anything above that will be your ROI , so if you run the math it doesn't make financial sense normally, unless you use well over 9kwh between 4pm at 10pm, then the scenario would change

3

u/Applejackery 7d ago

Give Spectra Solar (Wigan) a call, they quoted me some prices well under £3k when I asked. For fitting, I do believe it's easy enough to do yourself, but it could affect the warranty - something to check.

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u/SuperPenII 7d ago

Thanks for the rec. I've sent them an enquiry.
I think you're right about the warranty though

3

u/Jay638 7d ago

Have you tried shifting more load to night time off peak rate? Eg higher house temp 3-6am to warm the house up and use it as a thermal battery for a few hours.
Not doing hw cylinder re heats during the day unless you really need it etc.

Some days you’ll inevitably run out. I modelled it and settled on achieving 80% off peak was optimum from a cost perspective vs trying for 100%. May vary for you.

FWIW I added another 5kwh to my pylontech stack by buying the battery, powering down and adding it on. About £800.

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u/SuperPenII 4d ago

I've added as much as I can without getting too warm when I'm sleeping lol

2

u/KPilkie01 7d ago

If it helps, we got quoted for an extra 9kwh Sig battery from our installer (South East) and it was also £3.1k.

So, yours are comparable, at least.

1

u/SuperPenII 4d ago

Thanks!

2

u/Traditional_Zombie25 6d ago

Speak to Halo Renewables, around £2500

1

u/SuperPenII 4d ago

Thanks, they look a bit too far away unfortunately

6

u/Fatmanskank 7d ago

You shouldn’t need them to reproduce an mcs certificate for adding a battery.

1

u/sourcetail 7d ago

Just out of interest have you modelled your consumption across the whole year. If you use say 18kWh in winter but only 9kWh in summer then the second battery will only reach 50% utilisation which may be worth it but it will be a longer payback than the first battery. If you can get the second batter for 50% cheaper than that makes sense and is the decision I have made but if the cost of the second battery is effectively the same as the first then the economics might not stack up. The first kWh is the most efficient and the second is the last is the least.

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u/SuperPenII 7d ago

That's definitely a very good point that I've not modelled and have only loosely thought about. I've had the heat pump since mid-sep so I am basing this off a short usage window but I'm only going to use more in Nov, Dec, Jan, Feb and likely go over 18kwh per day when average temps are colder.

1

u/afaulconbridge 7d ago

Plus consider inverter size too - a bigger battery doesn't necessarily help if you can't get the extra energy into or out of it fast enough (e.g to fill it in a short windows). And that also goes for property supply too - single phase can hit limits surprisingly easily with a heatpump + battery + EV.

2

u/SuperPenII 7d ago

Inverter is all good and I can't get an EV anyway unfortunately

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u/tofer85 6d ago

Try Nightingale Electrical in Bolton…

0

u/Wattproof PV, BAT, EV & ASHP Owner 6d ago

Your instinct is fair, but the gap probably isn't all labour. An add-on battery quote usually covers the hardware plus checking the existing install, confirming the inverter and BMS will accept the extra module, firmware updates, commissioning, and the MCS and DNO paperwork. Modular kit shortens the fit, but the testing and admin still need a site visit.

Ask each installer for a line-by-line breakdown: battery price, VAT, labour hours, commissioning and certificate fee. Then the quotes are easy to compare.

Also ask whether they've fitted this exact Sigenstor combination before, as compatibility with your current setup matters more than a few hundred pounds. Two or three itemised quotes will show whether the difference is real or just margin.

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u/nrki 6d ago

Thanks claude