I suppose it depends on what battery you get I can only comment on the powerwall I had my first for 5 years before the inverter went and it was at 95% of it original capacity and it had been cycled full to empty pretty most days. 

New one was replaced under warranty only had it 2 months but it started with 15kwh it has lost 0.5kwh and is now steady at 14.5kwh only 13.5kwh is usable so has plenty of head room before it even gets below 100%.

The PW circled below have been discharged every day and are still at 90% capacity. 

Whether the math stacks up for your situation is very personal.  I charge up every night in the winter use all the battery and a bit of peak electricity in the depths of winter, once it hits March/Apr then heat overnight at cheap rate and use battery during day, export all PV.   

My electricity bill for 2024 was just under zero and that is running a EV at 5000 miles a year and a fully electric house, no gas.

To get the best return to will need to ditch the deemed export portion of your FIT that pays 50% generation at ~8p and go to metered export so you get 100% you export at 15p with Octopus.

My Export last year was worth just over £1000 my import 95% at off peak was £950

Nice data set Gary. Tesla clearly had a quality issue with the PW in 2019-20, in that many are showing  much reduced capacity even with few cycles. We were trying to buy one in 2020 but supply was an issue so we may have dodged that bullet.

Pressure to ship can often mean quality challenges IMHO

Where is the data from?

Here's my take on this with some rough maths that might require double checking. 

A decent 10kWh battery is rated for approx. 6,000 cycles at 90% depth-of-discharge (DoD). If you’re cycling it daily for tariff arbitrage, you’re looking at about 15 years before significant degradation in theory. Reality is harsher from what I've been told by battery installers – cold weather, partial cycles and calendar aging often cut that to 9-12 years. 

So the battery might only pay for itself just as it dies. There's also some talk of ToU tariffs being killed off in the years ahead which complicate the ROI maths further. For me, as things stand, batteries only make sense if you’re getting (or already have) an ASHP and solar – standalone, the ROI is a bit shaky.

@judith https://www.netzero.energy/content/2025-02/powerwall-analysis

Posted by: @editor

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There's also some talk of ToU tariffs being killed off in the years ahead

In what pub did you hear such talk?

@gary thanks for that link. A very useful analysis and I’m pleased to read the author’s view corresponds to my quick glance on it being some batches. The joys of being early adopters!

@editor &@transparent on a purely personal view TOU tariffs will exist as long as a competitive electricity market does, since it’s a way for a supplier to segment the market and differentiate themselves. Any pub conversation saying otherwise will be based on ‘winding up the mate’ who has spent most/relies most on their use. Or is a rumour put about by people who can’t/won’t get a smart meter.

Posted by: @transparent

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Posted by: @editor

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There's also some talk of ToU tariffs being killed off in the years ahead

In what pub did you hear such talk?

This came up in a podcast recording two months ago. After we’d stopped recording and were having an off-the-record chat. A panelist, who has close industry ties, mentioned that the ultra-cheap overnight rates (like those offered by Octopus Energy) were leading to significant financial losses, particularly for OE. The concern is that as more EVs, batteries and heat pumps take advantage of these rates, demand during those off-peak hours will rise, further straining the grid and increasing wholesale costs at those times.

The logical consequence? Rather than continuing to offer heavily discounted overnight electricity that leads to growing financial losses, suppliers might shift towards flatter, all-day tariffs... something more akin to OVO’s 15p/kWh ASHP tariff. If that happens, the days of sub-10p/kWh electricity in the early hours could be numbered.

Of course, nothing is set in stone, but it’s a conversation worth paying attention to, especially as the grid evolves and suppliers reassess how they price electricity in a changing energy landscape.

Posted by: @editor

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A panelist, who has close industry ties, mentioned that the ultra-cheap overnight rates (like those offered by Octopus Energy) were leading to significant financial losses, particularly for OE. The concern is that as more EVs, batteries and heat pumps take advantage of these rates, demand during those off-peak hours will rise, further straining the grid and increasing wholesale costs at those times.

Oh... well I agree with that analysis.

But I'll suggest that's very different from all ToU tariffs being killed off!

If the UK were to commit to no ToU Tariffs and no Nodal Pricing, then the entire grid would require upgrading to allow peak demand wherever and whenever.
That's never going to be viable.

It's not just financial losses for Suppliers which makes it difficult to substantiate keeping an overnight 'cheap rate' period.
Charging EVs at houses supplied with single-phase is also causing greater substation losses, and thermal degradation of underground Feed-Cables.

Posted by: @transparent

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Oh... well I agree with that analysis.

But I'll suggest that's very different from all ToU tariffs being killed off!

Agreed. Perhaps that was a bit overdramatic on my part. 🤣