On-grid domestic battery storage

1961Nick

Solarchaser wrote: »

Yeah, I take that as 25a not what it can do for 15 seconds, not the recommended max tbh.

I'm just slightly concerned you might be disappointed with the performance of the lux using two batteries, as everything I've read says you want to use 3.

As a comparison for the sofar. With 2 batteries. You set the internal software for a max charge and discharge of 50a. So taking a nominal 50v, that's only 2500w output.

I'm sure they could run the 50a each, but I'm not sure for how long, nor how it would do for battery health long term.

I say this as someone who has been trying to wrangle a way to get the lux parallel system and going to 4 batteries between the 2, and it just would seem very limiting.

Though this is all my opinion only... happy to be wrong, not least as it will save me £1500

The recommended power for 2 pylons & a Sofar ME3000 is 2400w charge & discharge. I can't imagine there's much point in exceeding that because with a maximum of 4.08kWh available, they'll soon be depleted & you'd be back to importing anyway.

Solarchaser

Ahh, see I took nominal 50v, you have taken it as 48v.
In reality what you limit is current at 50a.
So you can argue that when the battery is at 52v its outputing more kw than at 48v, and you would be right, but generally you state the middle that's why I said 50v nominal.

However I would say you want as much output as possible to cover things like washing machines, the heat up cycle might be 30 mins, so take a quarter of your battery.... then the clouds clear and it gets replenished again.

EVandPV

I'll see how it goes with the 2 batts, can always add a 3rd if need be.
My wife is taking early retirement in 18 months and will no doubt burn more leccy through the day so we may need a bit more capacity at that point anyway.

orrery

EVandPV wrote: »

I'll see how it goes with the 2 batts, can always add a 3rd if need be.
My wife is taking early retirement in 18 months and will no doubt burn more leccy through the day so we may need a bit more capacity at that point anyway.

But that may lead to you being better positioned to make use of solar anyway. e.g. sticking the washer or wishdasher on because you have the power.

gzoom

EVandPV wrote: »

I'll see how it goes with the 2 batts, can always add a 3rd if need be.
My wife is taking early retirement in 18 months and will no doubt burn more leccy through the day so we may need a bit more capacity at that point anyway.

You need as big battery as you can afford.

Well I learnt yesterday even a Tesla PowerWall 2 is no match for in-laws + no sun!!

Started at 8am with full PowerWall charged off E7, by 8pm it was dead.





Today even with more sun than yesterday I suspect the PowerWall will be emptied by 5pm at the rate electrons are been gobbled!!

EVandPV

orrery wrote: »

But that may lead to you being better positioned to make use of solar anyway. e.g. sticking the washer or wishdasher on because you have the power.

Very true, certainly in the summer. Not so much in the winter.
And of course, I'd have to train my other half to align her useage with the surplus.

EVandPV

gzoom wrote: »

You need as big battery as you can afford.

Budget's pretty much blown at 4.8kwh having already bought an EV and Zappi this year.
Sounds pretty easy to upgrade though once more funds become available.

joefizz

EVandPV wrote: »

Budget's pretty much blown at 4.8kwh having already bought an EV and Zappi this year.
Sounds pretty easy to upgrade though once more funds become available.

I agree with both. I thought 4.8kw would have been enough for me but after using it for 6 months thought what extra I could do with double that!
Took longer to build the frame for the 4 batteries than it did to add them in physically.


The addition of other batteries also helps when you arent at max input/output, the larger number of batteries, the lower the rate of charge/discharge of each, so less heating, less effect on longevity.
Saying that though from what Ive noticed with the sofar it does a pretty good job managing that sort of thing, been quite impressed with it really.



Im probably there or thereabouts now.


One thing I dont know if Ive expanded on is my reason for placing the batteries in the spare room. All to do with battery temperature/performance curves.

I can limit the SOC in the software but one of the other main influencers of longevity is the temperature range exposure, so if you can place it somewhere with not much temperature fluctuation and within the published preferred temperature range then youve done all you can with that one.
Main reason I didnt put it in the loft.
The pylontechs are at the safer/more longevity end of the battery chemistry spectrum and whilst their cells are bespoke it wont be difficult to find replacements for depleted cells.
The tesla uses more power with less longevity type cells but they are cheaper per unit and again should be easy to find replacement cells/modules.


Went away for 4 days at the start of the week and expected to come home to a fully charged battery, 32%!
Getting some charge in it today but in reality they will be mostly dormant now until mid Feb.
I bought the upgrade batteries this Jan but it took almost 2 months for the management system to get up to speed fully with them so bear that in mind with any winter install.

Zarch

Using the excellent Agile app from OpenEnergyMonitor, using the data collected from my emonPi.

https://guide.openenergymonitor.org/applications/octopusagile/

It shows over the past month that my average import price on Agile is around 10p-11p per unit.



So as much as I'd love the geekyness of owning batteries, i'm struggling with the maths/justification again for them.

My budget would be around £2.5k, so maybe get 4.8kWh of Plyontech with inverter and installation for that?
https://thinkrenewables.co.uk/lux-ac-48kw-battery-storage-system

Say 4kWh usable on the Plyontech?
4kw x 10p = 40p saved per day x 365 days = £146

£2500 / £146 = 17 years.

This seems to confirm.
https://great-home.co.uk/solar-battery-calculator-likely-bill-savings/

But feel free to correct me if those figures are wrong.

Maybe I just need to sit tight and wait of the prices to fall some more? But they'd have to almost half to get under ten years ROI?

Seems like time of use tariffs, with cheaper pricing outside of Solar generation periods is making the battery justification even more difficult than if on a fixed tariff say around 14p per unit?

I'm wondering if the 'battery money' would be better invested in an EV or some other consumption device to make use of the cheaper pricing?

joefizz

Zarch wrote: »

Seems like time of use tariffs, with cheaper pricing outside of Solar generation periods is making the battery justification even more difficult than if on a fixed tariff say around 14p per unit?

Your figures are a reasonable ballpark to go off. At 11p a unit its really not feasible in monetary terms. Im optimistic about the lifetime of mine but with family history 17 years might outlast me!



Thats cheap for electric, Im paying 18.34p a unit import and getting about 4p export although thats gone up over 20% since I got the batteries bringing the ROI in a bit.


The calculator shows a loss for me of about 160 quid over the warranty period but the battery allowed me to install an ashp and use the immersion to cut down on oil usage so have probably saved that over the time already. Add in compound interest if youd just saved the money and thats back up again.
Then again electricity/oil prices fluctuate so back to square one.
The calculator also doesnt take account of the drop off over the warranty period (down to 60% over 10 years for the pylontechs), so likelihood is that its a fair bit longer.

Ive changed usage patterns to use more of the normally exported electricity during the summer, using the battery so might go through 2 or more cycles during summer, but again thats pretty marginal at those prices.

You could flog it half way through warranty and so on...
Or treat it as a share you are never going to sell but gives you a good dividend every year ;-)



Its definitely not going to make you money, thats for sure...