Sell ep5 for ep12? Or stick another ep5 in?

[carrot1401]

Hello! I need some feedback on whether it's worth replacing my EP5 with an EP12. We got the system installed in April 2025 and it's been brilliant. The ep5 is non heating version that has done 572 cycles, with a SOH of 92%. In hindsight I should have went for the ep11 but I didn't know at the time that you cannot mix and match different sized batteries. With recent weather we've drained the battery overnight with fans, and regularly drain it quickly in the winter months as I usually game on my PC in the evening. So I have 2 options:

• Grab another ep5 with a junction box, and have no heating element. I think I read somewhere about mixing different SOH not being a good idea, but someone please correct me.

• Grab an ep12 with heating element and try and sell my ep5 (no idea what it would go for....or even if I could sell it?!?!)

What do you lot think? I have a H1 Gen 2 inverter and 5kw/h export, with 12 panels (but I doubt that changes anything here)

[MaterialBarracuda48]

What energy tariff are you on? Is it same rate 24/7 or do you have cheaper night time prices (EV / heat pump / E7 etc?)

Do you have plans in the future to have a heat pump for example in next few years?

[carrot1401]

What energy tariff are you on? Is it same rate 24/7 or do you have cheaper night time prices (EV / heat pump / E7 etc?)

Do you have plans in the future to have a heat pump for example in next few years?

Octopus agile, so we try our best to shift load. Am aware the last few weeks have been not as good as previous months but our bill for July showed us importing just 36.7kWh at an average price of 4.36p/kWh costing £20.97, while we exported 602.9kwH and made £72.35 (we were on holiday last week of July). So far in august it's 21.1kWh import and 247.38kWh export.

No plans on heat pump or electric car in short term; very well believe in "if it ain't broken, don't fix it" and boiler is fine. Car may change in 2028 but would look at getting vehicle to load charger and have a 50kw+ battery on wheels

[MaterialBarracuda48]

I am on Agile too, have an EP11 to mop up the cheaper electric times.

From your figures, it doesn't seem like you use much electric, which makes me think it might not be worth it?
Do you have 'To load & battery' & 'From PV & Battery for July (aware the holiday will skew it) Ideally, can you take 3 weeks and add those figures up, and then divide by 21 days to get your average daily?

So let's say you are using 8kWh each day, then you might only be buying a little amount in, so you don't need EP12 levels of storage. I am aware Winter will change the amount of import of course.

[CDubbs]

Just to add my views

On IOG, had the install a year this week, I fully believed I needed 2 EP11s at install, the installer said it would not be a viable return and 1 will suffice, over the first 11 months bills, I’ve used £55 of peak rate electric, and exported £495
My installer has a 25% of offer on additional batteries for September, and quotes 2k installed for an EP12 + connector box.
They were right, at round £60 a year for peak rate, I’ll will be 6’ under before I break even.
Thumbs up for my installer.

[MaterialBarracuda48]

On IOG, had the install a year this week, ....

Happy anniversary, and you cannot put a price on a year's worth of data to look back upon.

[CDubbs]

On IOG, had the install a year this week, ....

Happy anniversary, and you cannot put a price on a year's worth of data to look back upon.

Thanks

The only price is the ROI of 6 years is looking a pretty good forecast as was their calculation of PV generation of 6050kw which actually been 5850, so spot on, and I feel would have been surpassed by some margin had the panels not derated day after day with the excessive heat

[carrot1401]

I am on Agile too, have an EP11 to mop up the cheaper electric times.

From your figures, it doesn't seem like you use much electric, which makes me think it might not be worth it?
Do you have 'To load & battery' & 'From PV & Battery for July (aware the holiday will skew it) Ideally, can you take 3 weeks and add those figures up, and then divide by 21 days to get your average daily?

So let's say you are using 8kWh each day, then you might only be buying a little amount in, so you don't need EP12 levels of storage. I am aware Winter will change the amount of import of course.

I think my problem is my hobby; my gaming PC pulls 800w an hour so couple of hours of that in the evening is already 1.6kwH. Plus 200w "standby" overnight is another 2kwH so already 3.6kwH down. With a couple of kids, in the winter we are eaten into that 5kw for tea and bath time, so easily down to 10% battery come like 7pm!!

[CDubbs]

I think that’s why you need to look at your overall peak spend and how many days you are dropping onto the grid until the next cheap rate top up.
Then you can make some rough calculations if the spend of the EP12 makes sense.
Over the last year, or winter namely, I only run out of battery in the evening a handful of times, and that’s largely due to the wife using a thing called a steam generator iron, which draws about as much power as a small town.

[MaterialBarracuda48]

I think my problem is my hobby; my gaming PC pulls 800w an hour so couple of hours of that in the evening is already 1.6kwH. Plus 200w "standby" overnight is another 2kwH so already 3.6kwH down. With a couple of kids, in the winter we are eaten into that 5kw for tea and bath time, so easily down to 10% battery come like 7pm!!

Even if your battery runs out, it's all about bringing down your average price per unit of power (see below)

Octopus agile [...SNIP...] our bill for July showed us importing just 36.7kWh at an average price of 4.36p/kWh costing £20.97

Do you have a more long term look at your Agile import costs? (average rate ideally)
Reason is, that it's your overall import price over a month is going to show the cost to your pocket.

July was 2.15p/kWh, August was 5.86p/kWh for me on Agile.

[carrot1401]

The more I look at this, the more I think you're right in sticking what I have, import so far this year:

January: 328.3kWh @ 17.81p/kWh
Feb: 290.8kWh @15.43p/kWh
March: 170.2kWh @ 14.2p/kWh
April: 153.8kWh @ 0.34p/kWh
May: 6.5kWh @ 15.15p/kWh
June: 57.9kWh @ 5.85p/kWh
July: 36.7kWh @ 4.36p/kWh
August: 60kwH @ 18.65p/kWh

Total so far this year: 1104.2kWh @ 13.15p/kWh

[MaterialBarracuda48]

Total so far this year: 1104.2kWh @ 13.15p/kWh

So ~£145.20
I think what @CDubbs was saying will be true, probably not going to save you a great deal, or a very long ROI for new battery.

[CDubbs]

This thread has got me reaching for my calculator and looking at the cost in a different way guys, so thanks

I’ve stuck with IOG all year, just too lazy to switch in and out and I have no automation setup.

I’ve used imported electric 3682 kw in 10 months, of which 5% has been at peak rate, it equates to 6.22p per kw.
For me, well happy with that, plus I’ve exported 3900kw at first at 15p, now 12p.

For that I’m charging the wife’s PHEV at night, never from solar, the EP11 is topped up to 100% each night, dishwasher, washing machine, tumble are run at various times of day and night, not my dept. so don’t get involved.
I don’t mess about force discharging, then recharging on off peak, so just let the system do its own thing, which probably makes me the bang average user.
Total convert to solar and battery use.

I’ve realised although I made the statement about ROI, I’m driving the battery to full each night with 7p kw grid feed, so I’m getting the best of both worlds, and not everyone has those tariffs, but clearly everyone’s use is different and they have to make their own calls on their setup.