I'm interested in finding out if the hitherto uneconomic?? landscape, regarding home batteries has shifted and if anyone has first hand experience of them.
My lucrative three year electricity contract ends in 3 months and I'm number crunching with new tariffs e.g. EV, Economy7, and I thought I'd throw home batteries into the mix.

I have a 10 kw battery now 3 years old. Calculations as to whether worthwhile was borderline but now that they have down quite markedly the last 12 months or so they make more sense than ever. What the battery gives you is flexibility and becoming more so as the night time tariffs can allow you to charge your battery (particularly valuable in winter time) at cheap rate to use at premium rate time. You need to get a system that allows you to control when you want to charge it up. My inverter does not allow me to do that I have to switch it to charge manually. I need to do that after 11.30 pm and it will switch off when full. The beauty of it off course is that should it be sunny next day and solar tops up what you have used then export will kick in and you will get a return on it depending on your tariff. I pay 7p at night on an EV tariff and get 15p for export during day. So a no brainer. If you have got a very smart system then you can get the system to discharge to the grid at premium export rate a friend of mine does that. The newer battery systems can be very flexible and have built in inverters with gateways that give and very fast switch over if your grid outages. I have not looked into them in detail but from what I have gleamed they look a very attractive option.

Posted By: owlmanAge; both boiler and me however, means I have to plan for change.

Yeah - me too, getting old sucks!

Posted By: owlmanfit an "Open Energy Monitor" do get an idea of which circuits are using power and when to decide if e.g. Economy 7 could be the way to go, my gut reaction is yes it would.

With an EV I thought that the Octopus EV tariff at 7.5p/kWh. was the go to package.

Oner here we are lucky having guaranteed for the next 9 years annual reconciliation so the grid acts as my inter-seasonal 'battery' hence no point in a battery or sophisticated time of use software. The providers don't like annual reconciliation and if you get a grant for PV then you get monthly reconciliation. (And the current grants mandate a battery as well),

Fwiw this year the Octopus Agile tariff has averaged 10-15p for twenty hours each day (daytime often cheaper than overnight, occasionally very cheap or free) and 30p+ for the peak 4pm-8pm period.

Power can be exported anytime for 15p so self-consumption doesn't pay.

Way forward for us seems to be to work out what loads can and cannot be shifted away from evening peak period (cooking, lights, a little space heating and TV). Then work out how much £ would be saved by storing up cheap-period electricity to use during the evening.

Batteries have got a lot cheaper but still doesn't seem worthwhile as a standalone project, maybe better if done as part of a big change like fitting PV.


Some other changes seen in US and Europe and likely here:

1) growth of very cheap renewables dominating the grid for some hours each day, but gas required at other times, gas generators pricing very high to cover their whole day's costs during fewer hours online. Leads to large price swings (the 'duck curve'). Good for home battery owners.

2) rapid installation of utility-scale grid batteries to profit from 1). This evens out the highs and lows so bad for home battery owners.

It's windy and bright today and there's plenty of renewables. Maybe today is an example of what the coming years will look like, as more renewable generation is built out in UK.

Electricity is free or negative-price all through today until 4pm-7pm, when it peaks up to 20p. (On octopus Agile)

A battery could store free power for use in the evening, saving 20p per kWh of battery capacity

Let's assume that happens 200 days/year for 10 years, giving lifetime savings of 200x10x20p = ~£400 per kWh.

That's still not quite enough to recoup the standalone install costs, afaict, around £500-£900 per kWh.



Good question why more people haven't yet got smart tariffs.
Istm the 'energy price cap' in recent years has been a big delay on smart tariffs, as the price cap is set at a fixed p per kWh and doesn't give savings from time shifting. It also drove lots of smaller/innovative energy companies bust, so we consolidated back to the 'Big Six'. And a minority of people still don't have ToU meters.

If you DIY a system it can be way cheaper than that. The kit prices have really fallen recently. 5KW of PV panels is under £1000. £800-1300 for an inverter. £2000 for 14kWh of battery (Fogstar). Plus incidentals which is maybe £300.

I've started a spreadsheet but not finished a proper analysis yet. For very low users like us it's hard to make it pay for itself because mostly we can just do arbitrage at maybe 5p/kWh overnight. (~70p a day minimum income.). And avoid importing at all outside 0-4am. So maybe save 18p/kWh on 3kWh each day in winter and 25p/kWh in summer. So maybe make/save £1.20/day on average so it might pay for itself in 4-5 years. The battery should last longer than that but paying £2000 for a 7-10yr asset to save £400/yr is not a massive incentive. It may work better in emissions terms: complete avoidance of electricity import avoiding 200Kg emissions , at an embodied carbon cost of maybe 1.4 tonnes. Just about break-even after 7 years. How much longer than that will the battery last?

So it has definitely moved from hopeless (on both carbon and financial fronts) to 'probably pays for itself'.

I'm probably going to get one but need to do a bit more work to convince myself it's worthwhile. If you have an HP or immersion heater, or other wise use more electricity (except EVs - they already have a battery) the numbers look better.

I'd prefer to just get a car and use the (massive) battery in that, but currently it's difficult to do. That should change soon.

I went ahead with a home battery install and I'm into my second month and so far I've managed to load shift all my home power incl. EV to the 5 hours @ overnight rate. This may change in the next couple of months if the weather worsens, we'll see.
I opted for 20kW of storage with the option to upgrade to 30kW in the future. So far it looks as if my monthly DD can be reduced by two thirds.
I've also made modifications to my 2000L accumulator tank attached to my log wood boiler and wet CH circuit, and I've re-arranged wiring circuitry to put in two 3kW immersions on timers to also run on overnight rates.

I don't know of BMZ are they high or low voltage, ( in the battery sense )? Could you not sell the BMZs and move to a different make, or is your inverter matched to them.

Posted By: owlmanI don't know of BMZ are they high or low voltage, ( in the battery sense )? Could you not sell the BMZs and move to a different make, or is your inverter matched to them.

BMZ are a German manufacturer it is nominally a 48v battery it is fully charged at 61V and about 52 v at 10% Inverter stops it going lower. I originally wanted 2 X 7kw but they were not available but I could add another 10 kW within 12 months. (something to do with degradation of the first would mean there would not be a balance between the two) but when I wanted to add to it the agent had stopped importing the battery and inverter so I am in no man's land. The thought I had, is to take out the current inverter and battery set up, they are designed to work together and have it as an off grid supply to my horticultural activity to power growing light and propagators. and get a Tessla 3 battery connected to my existing solar panels. At moment have to put that idea on back burner due to time and budget constraints.

I had a quick look at BMZ and their website is still showing UK representation.
Can't you get their head office to supply direct or maybe from one of their other subsidiaries e.g. Poland or France. Another 10kW is only about 100KG so a small pallet, there may be import costs but zero VAT rated.

Got no joy from BMZ just confirmed my battery will have aged too much to for another one but then that one has been discontinued anyway. I did ask what I could replace it with but got not comment. They make portable power stations and asked about that also, as I could make use of another one. Having had the surprise of low efficiency on one of the ones I have got I asked what efficiency I could expect but was told did not have efficiency figures. He did admit it was made in China for them, so have lost interest in that one.
Think will leave on the back burner for now got other stuff awaiting my attention. One option for future is to get a Tesla Powerwall 3 which has its inverter built in and move my current inverter and battery to my horticultural activities and put panels on the barn roof.

I suspect batteries are an area where the underlying technology & chemistry is changing so fast that you can't rely on being able to get identical parts for very long at all. I haven't figured out what that means for what to buy though?

Thanks, Tom.

EDF are running a "Sunday Saver" Plus a Christmas day scheme too.

"Shift your electricity usage from Monday to Friday, avoid peak times (4pm - 7pm), and get free electricity the following Sunday. You have four or five chances each month to meet your goal, so even if you miss it one week, there are more opportunities to smash your target the following week."

P.S. I tried to open this as a separate discussion, (6 times), but no joy.