Making the jump to batteries (only)

[Gomev]

I'm looking to add batteries to the home. No solar, that's decided.

We are low users, average less than 5kWh per day excluding car charging. The purpose of the batteries is for my own satisfaction, it will not pay back (even/especially with solar), so that is not the dilemma.

The purpose will be to move all use to overnight cheap rates. So should I go with my preferred set up of
A).
Battery
3 × Alpha ESS SMILE-G3-BAT-4.8S · 4.8kWh
610 × 435 × 212 mm · 4.56kWh usable · LFP · Datasheet · Warranty
Battery size (14.4 kWh 13.68 kWh usable)
Inverter
1 × Alpha ESS SMILE-G3-S5 · 5000W
Single phase · 97.3% max. efficiency · Datasheet · Warranty

Installed cost £6010 including £500 to add a second CU for the EVSE which is currently on the main CU.

or
B)
Fox ESS EVO10 Battery 10.24kWh of Battery Storage
1 x EVO 10-5-H (Fox ESS) 3.68kW Inverter.

Installed cost £4600 (no additional CU)

I think the common sense answer is staring me in the face, but I need help convincing myself or otherwise.
We rarely if ever use more than 3.6kW power and whichever I'm not really going to make anything out of export, or am I, to contribute towards the cost.

This is the basic info.

 

[MickeySw]

The purpose will be to move all use to overnight cheap rates. So should I go with my preferred set up of
A).

Absolutely, bigger inverter, larger battery is the way to go (I also use a 5KW inverter with an ex Zoe battery), never looked back..

3 days backup without much limitations, plus the MGs V2L capacity to recharge the batteries if (localised) outages last longer…

 

[Everest]

We rarely if ever use more than 3.6kW power

Really? What is your peak power usage? It only takes two appliances out of any of the following to exceed 3.6kW. Kettle, Washing Machine, Oven, Non-gas hob, Microwave, Immersion heater, Granny charger.

 

[Bam Bam]

I think energy trading potential is probably the key determinant.

Does the Alpha system fare any better on this front?

If not I would go for the Fox as it is much cheaper.

While you might very occasionally exceed 3.6kw when having two or three items on at once it will probably be rare in the grant scheme of things. Plus the battery will still cover over 50% of your usage even when you are drawing 6kw.

It is probably only going to happen when you are cooking as you might have hob, oven and microwave on at the same time. Possibly kettle depending on the meal. Washing matchine and car charging can be done at other times of the day.

Ovens switch off and on periodically once they get up to temperature so it isn't continuous once pre-heated.

It might mean you limit your behaviour, though, and try not to have the oven running at the same time as the other items @Everest lists. Would that be a pain for you?

 

[GaryMG4]

I was considering adding an a/c coupled battery to our house, we have solar on FiT so I didn't want to disrupt the payments. We are a low user of peak rate electricity, currently on IOG flexible so 5.2p and 27.8p, over the last 12 months we averaged 4.1 kWh per day of peak rate power.
My calculations were based on ignoring the solar as in the summer we may only use 2-3 kWh peak and in the winter we don't produce much solar.
So, 10kWh (usable) battery would cost 10x5.2p =52p overnight. Using @Everest measured efficiency that would give 8.5kWh of a/c power to use. If I managed to only use the batter during the day it would save me 4.1x27.8p=£1.14, plus I would have 4.4kWh to sell to Octopus 52.8p so a 'profit' of £1.15 a day. But adding even a 3.6kW inverter will likely need G99 authorisation as we already have a G98 in place, we cook with electric so its not uncommon to peak loads approaching 5kW so it is unlikely that we would be able to use zero peak rate. The 85% efficiency is likely to be based on a hybrid inverter, I suspect an a/c coupled system may be lower.
From the solar aspects, some FiT payers want to switch the deemed export part the payment to SEG if you have a battery, probably not a bad thing looking at EDF rates currently, although FiT rates can only go up (with inflation) whereas SEG rates are market driven.
Ultimately the £5k to but the system is sitting in a cash ISA earning £225 a year so that a profit of a little under £200 a year from the system so I decided against it.

If there's a flaw in my reasoning please point it out as I do like the idea just the CBA doesn't seem to hold up.

 

[Gomev]

Absolutely, bigger inverter, larger battery is the way to go (I also use a 5KW inverter with an ex Zoe battery), never looked back..

3 days backup without much limitations, plus the MGs V2L capacity to recharge the batteries if (localised) outages last longer…

That was my original thought but then I asked myself Why ? We rarely go above 3.6kW load, and even 10kWh is 2 days worth of usage. So what real gain is there for £1500 ?

Really? What is your peak power usage? It only takes two appliances out of any of the following to exceed 3.6kW. Kettle, Washing Machine, Oven, Non-gas hob, Microwave, Immersion heater, Granny charger.

Rarely above 3.6kW.
Heating/water is gas. Only 2 of us in the house and most cooking is accomplished with 1 or 2 hobs.
Hob is induction and any 2 zones, small, medium or large only total max 3.5kW (Small Zone: 1.2 kW, Medium Zone: 1.5 kW, Large Zone: 2.0 kW) and an air fryer. The air fryer with both drawers at full pelt is 2.4kW for short period. Most hot drinks are made with a pod machine rather than a kettle. Microwave is rated at 800W so less than 1kW actual.
55 inch OLED TV, with sky Q box, a router and a soundbar as the most constant 'on' things are under 100W combined. All lights are LED and are usually dimmed to some extent.
Haven't used a granny charger since 2020, and I did mention not including car charging, but if needed for any reason it would be overnight and timed for off-peak.

I was considering adding an a/c coupled battery to our house, we have solar on FiT so I didn't want to disrupt the payments. We are a low user of peak rate electricity, currently on IOG flexible so 5.2p and 27.8p, over the last 12 months we averaged 4.1 kWh per day of peak rate power.
My calculations were based on ignoring the solar as in the summer we may only use 2-3 kWh peak and in the winter we don't produce much solar.
So, 10kWh (usable) battery would cost 10x5.2p =52p overnight. Using @Everest measured efficiency that would give 8.5kWh of a/c power to use. If I managed to only use the batter during the day it would save me 4.1x27.8p=£1.14, plus I would have 4.4kWh to sell to Octopus 52.8p so a 'profit' of £1.15 a day. But adding even a 3.6kW inverter will likely need G99 authorisation as we already have a G98 in place, we cook with electric so its not uncommon to peak loads approaching 5kW so it is unlikely that we would be able to use zero peak rate. The 85% efficiency is likely to be based on a hybrid inverter, I suspect an a/c coupled system may be lower.
From the solar aspects, some FiT payers want to switch the deemed export part the payment to SEG if you have a battery, probably not a bad thing looking at EDF rates currently, although FiT rates can only go up (with inflation) whereas SEG rates are market driven.
Ultimately the £5k to but the system is sitting in a cash ISA earning £225 a year so that a profit of a little under £200 a year from the system so I decided against it.

If there's a flaw in my reasoning please point it out as I do like the idea just the CBA doesn't seem to hold up.

Similar to my thoughts, I would like to get batteries but they wouldn't be a sound financial decision, it requires a heart over head to buy them.

 

[Everest]

All good points and, like @GaryMG4, with low usage the sums don't always add up as one would intuitively think.

With your low usage, my 2p's worth would be to go for a half-way compromise... Specifically the Alpha 5kW inverter, but with 2, rather than 3 batteries to give you around 10kW of storage.

Street price for the hardware (excl VAT, obviously) for that is under £2900. So hopefully that might work out about £1000 less than the price you were quoted for the fully installed price - i.e. a comparable price to the FOX installation but with some more oomph on the inverter's output.

Alpha 5.0kW ESS Hybrid Inverter + IP65 10.1 kWh Battery Bundle

Achieve true energy independence with AlphaESS, a leading global specialist in intelligent battery energy storage systems (BESS). Since 2012, AlphaESS has engineered innovative solutions designed to maximize your solar PV system's potential. AlphaESS systems allow you to efficiently store your...

www.cityplumbing.co.uk

 

[GaryMG4]

All good points and, like @GaryMG4, with low usage the sums don't always add up as one would intuitively think.

With your low usage, my 2p's worth would be to go for a half-way compromise... Specifically the Alpha 5kW inverter, but with 2, rather than 3 batteries to give you around 10kW of storage.

Street price for the hardware (excl VAT, obviously) for that is under £2900. So hopefully that might work out about £1000 less than the price you were quoted for the fully installed price - i.e. a comparable price to the FOX installation but with some more oomph on the inverter's output.

Alpha 5.0kW ESS Hybrid Inverter + IP65 10.1 kWh Battery Bundle

Achieve true energy independence with AlphaESS, a leading global specialist in intelligent battery energy storage systems (BESS). Since 2012, AlphaESS has engineered innovative solutions designed to maximize your solar PV system's potential. AlphaESS systems allow you to efficiently store your...

www.cityplumbing.co.uk

Would a 5kW inverter mean a G99 required? Especially if you plan to sell back to the grid.

 

[Everest]

Would a 5kW inverter mean a G99 required?

Yes. But IME that's no big deal. Bit more paperwork for the installers, but they do that every day