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I can't get very sensible numbers out of considering investing in some batteries.

Fairly large usage with fairly large PV so starting at 10kWh of batteries and assuming I can utilise the full allowed DoD every morning from the nighttime electric and every evening from a full solar recharge. I can scale up if numbers work to an appropriate size but the best payback will be the first bought.

Day rate 24p/kWh
Night rate 20p/kWh.
SEG rate 12p/kWh.

£4000 for a 10kWh battery addition to existing hybrid inverters.


So, if I save 4p/kWh time shifting 10kWh onto night rate, that's £0.40/ day.
And if I save 12p/kWh using the daytime solar instead of exporting it, I can save, potentially, £1.20/day.

If I, for this very rough calculation, unrealistically assume I can do that 365days a year, that could save, probably £600 per year.

In this unrealistic world where I can utilise a battery completely, every day, payback of 6-7 years.

Is that about the gist of it? Or am I missing something?

It's going to be a relatively tiny battery that gets fully utilised every day though. Unless electricity costs jump or SEG price slumps, I don't reckon that it looks very appealing.

£4,000 for 10kWh is mental especially if there is an existing hybrid inverter? For 4k I'd be looking for 50kWh.

The day/night rates and export rates seem out of whack too. I can see why it's not appealing to you.

Sensible in, sensible out maybe?
I look at £1,200 for 15kWh diy+ 1/2 a grand for bits n bobs.
7p overnight rate
15p export
Any day rate will do but my mind has 24p in it as a default

Based on 5MWh import and 20% of that re exported.
7p&15p= £200 cost to me
24p flat = £1,200 cost to me

I was using this as a guide. Not essential it's solax/triple power but the inverters are so might as well.

https://midsummerwholesale.co.uk/buy/so ... fp-battery

Are they particularly overpriced? Or have I got the numbers wrong?

Regards electric prices, this is a business tariff. If you're used to home tariffs or have a different business usage they'll look odd. Ditto the SEG, octopus agile or their other home tarrifs don't apply unfortunately. Regarding export, 12p isn't too terrible, one other option is to organise a PPA, at our scale that'd be 6-8p

However, differences like that do explain why my numbers aren't working when others do

I was going to say almost the same as Joeboy, but ouch, just looked at the business E7 tariffs for Octopus, your actually on a good deal and your SEG rate makes batteries look very marginal.

Unless you like tinkering with stuff, which is half the fun.

Gareth J wrote: ↑Mon Jul 29, 2024 5:10 pm I was using this as a guide. Not essential it's solax/triple power but the inverters are so might as well.

https://midsummerwholesale.co.uk/buy/so ... fp-battery

Are they particularly overpriced? Or have I got the numbers wrong?

Regards electric prices, this is a business tariff. If you're used to home tariffs or have a different business usage they'll look odd. Ditto the SEG, octopus agile or their other home tarrifs don't apply unfortunately. Regarding export, 12p isn't too terrible, one other option is to organise a PPA, at our scale that'd be 6-8p

However, differences like that do explain why my numbers aren't working when others do

A reasonable way would be to chuck in (or have fitted) a couple of Pylontechs for a grand and a half, that gets ye 4.8kWh storage and a decent discharge rate. Then diy fit batteries from China to your hearts and wallets content. I don't know about business tarrifs so wouldn't offer advice there

nowty wrote: ↑Mon Jul 29, 2024 5:44 pm I was going to say almost the same as Joeboy, but ouch, just looked at the business E7 tariffs for Octopus, your actually on a good deal and your SEG rate makes batteries look very marginal.

Unless you like tinkering with stuff, which is half the fun.

Octopus were particularly poor. What was especially annoying was that all export tarrifs are unavailable except their SEG tarrif @4p.

Those prices quoted above (plus a hefty standing charge) just fixed. Unlike domestic, business tarrifs aren't capped. There was a time, when there were acute worries about gas shortages, that businesses were having to buy at £1 a unit. Ouch

Joeboy wrote: ↑Mon Jul 29, 2024 6:19 pm
A reasonable way would be to chuck in (or have fitted) a couple of Pylontechs for a grand and a half, that gets ye 4.8kWh storage and a decent discharge rate. Then diy fit batteries from China to your hearts and wallets content. I don't know about business tarrifs so wouldn't offer advice there

Not averse to using other bits and pieces but if doing DiY would really want it more or less plug and play.

Gareth J wrote: ↑Mon Jul 29, 2024 7:39 pm

Joeboy wrote: ↑Mon Jul 29, 2024 6:19 pm
A reasonable way would be to chuck in (or have fitted) a couple of Pylontechs for a grand and a half, that gets ye 4.8kWh storage and a decent discharge rate. Then diy fit batteries from China to your hearts and wallets content. I don't know about business tarrifs so wouldn't offer advice there

Not averse to using other bits and pieces but if doing DiY would really want it more or less plug and play.

Just an example who I've dealt with in the past. About as plug & play as ye get. I don't know if they're even the best per unit price available? In 6 years my pylontechs have been great.
https://www.itstechnologies.shop/collec ... 5jEALw_wcB

Hi Gareth, don't forget charging losses. So you might want to drop the night rate battery charging from your calcs, as the margins are very tight, assuming something like 10% losses.

Mart wrote: ↑Tue Jul 30, 2024 9:18 am Hi Gareth, don't forget charging losses. So you might want to drop the night rate battery charging from your calcs, as the margins are very tight, assuming something like 10% losses.

Yea, there will be losses to factor in left right and centre.

-Winter days where the inverters barely bother to wake up
-Slightly more marginal days where the batteries might rob the Eddis of their diversion electric to shift it onto night rate instead.
-Charging/Discharging losses for unexported electric too.
-Maintainance?
-Increased insurance?

I can't see it as a particularly exciting investment unfortunately, despite that I though l might - hence the hybrid inverters.

Our biggest electric expense is cooling (dairy farm). I should see how ice building compares cost /kWh.