The problem here is that we're trying to assess future financial viability whilst doing the maths on ToU tariffs which have been introduced recently, over the last few years.

Would it help if I told you the tariffs which will exist in 2030, once NESO has taken the UK to full decarbonisation of electricity generation?

@toodles , @gary  Thanks.  Im developing a simple excel model that I can plug various tariffs into. 

I suspect that the Ovo 15p for heat pump consumption without a battery is unbeatable, but I also suspect it wont last.  Im also a bit suspicious about the longevity of tariffs which give a very cheap cheap rate, but of course if they only last a few years and pay off the battery in that time then its good enough!

Posted by: @transparent

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Would it help if I told you the tariffs which will exist in 2030, once NESO has taken the UK to full decarbonisation of electricity generation?

Yes, Im sceptical about the longevity of some of the more extreme current tarrifs and any info about likely future tarrifs would at least allow a faintly intelligent decision to be made

Posted by: @jamespa

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Im going through a similar process, working out a sensible battery setup with ASHP, electric car and 4kWp of PV.  I still cant get the finances to stack up.  Looking at agile prices by time of day with a bit of a bias towards the winter, it seems like I could perhaps get to an average unit cost of ~17p, compared to 23.4p which I get on a fixed price tarriff, provided I could store about 12hrs worth of energy.  With my heat pump working at 4kW output, which is where it will sit most of the time, that's 16kWh at a COP of 3.  So its the 19.5kWh battery at 7k for a saving of about 6.5p per kWh, perhaps £600 saving per year based on 10MWh/year which is a reasonable estimate including car, heat pump and base load. 

The payback for the capital is thus 12 years, and if I want a rate of return of say 3% on top (which I could get by putting the money in the bank) then its even longer, and anyway greater than the claimed battery lifetime. 

I've run the numbers with more detail extracted from meter reads, but get essentially the same result (so it's more transparent if expressed crudely).

If I had an environmental argument the payback is good enough for me and Id go for it, but I haven't heard one (yet). 

Have I got it wrong or do batteries just not make sense unless you buy cheaply and self install?

@jamespa, I'm not sure you necessarily need to store a whole 12 hours of energy, though. I know you've seen my figures and they are based on a 6kWh battery, but my aim is only really to tide my house over the expensive Agile period (4pm until between 7pm and 9pm depending). That alone brings our import average price down to the ballpark you're talking about, and the battery we've got more than covers that even in the winter. As a result, I'd be interested how your figures look if you recalculate around a more modest battery/inverter setup.

@gary  @toodles  @majordennisbloodnok Thanks for the comments. 

Im working up a  simple excel model to test various tariffs based on load from the major items and what % is at what price (which depends on whether there is a battery or not).  I will share it and any conclusions in the next few days. 

Its quite difficult to estimate how much storage one needs with agile (even if you have smart meter data, as I do), but with fixed time period tarrifs fairly easy.  I think I might model agile as something like a 4 step timed tarrif which is probably good enough both to get a handle on savings and the storage needed to optimise them.  7p/kWh (Octopus Go) sounds very attractive but if its only for 6 hrs per day you need a lot of storage to keep a heat pump, which is the major load, going for the remaining 18hrs.  You don't need a battery to charge the car during the cheap periods, that's just scheduling of the charging.  The battery is needed to deal with the things that you cant (or cant conveniently) schedule.

@transparent if you know anything about tarrif futures that would be much appreciated.  Id also appreciate your comment on whether there is in fact an environmental benefit of local storage.  I cant quite see it but maybe it does help enough with grid decarbonisation to help the environment.

I should've added a smiley after my comment.

There are a number of dominant criteria which affect how these future tariffs are constructed.

1: Political policy. The government has decided that Nodal (locational) Pricing is not to be made available to consumers, but will only operate on the wholesale market. That policy decision was made by the previous Sec of State for Energy on 12th March '24. But it's not well founded on the underlying science. At some point it will need to be reversed.

2: Grid capacity. The longest cable lengths on the electricity network are at the 11kV level. There is sufficient capacity to meet demand as we progress towards Net Zero, but only if we time-slice it to avoid demand peaks. Upgrading the 11kV network to continue meeting whatever consumer demands we make on it is beyond the financial reach of GB. It's equivalent to HS2 on steroids!

The map shows an anonymised area of rural England. The red lines are 11kV.
Each dot is a pole-mounted transformer. The larger blue ones carry only 2-phases (a split-phase' supply).

3: The reason for the classic overnight cheap-rate period is to prevent Closed Cycle Gas Turbine (CCGT) sites dropping into open-cycle mode, which is inefficient.
But if we decarbonise the grid, then those CCGT generators won't be there.

Moreover, electric transportation (privately-owned EVs and autonomous pods) will want to be recharged at night, whilst most of us are asleep.
NGET's mathematical modelling indicates that will increase overall demand by 10%.
That's not a large figure when viewed nationally, but unsustainable for the 11kV network.

4: Government (DESNZ), Ofgem and NESO are only considering money as the factor which controls when household demand rises and falls.
That's not just the range of ToU tariffs, but also by offering monetary compensation for household appliances being turned off remotely when demand is too high.
They call that Demand Side Response (DSR), and it featured in the DESNZ consultation (June'24) on Delivering a Smart & Secure Electricity System.

The proposed DSR model won't compensate households running heat-pumps off-grid from a storage battery.
That's a serious oversight because those households with batteries will contribute greater benefit to the grid than those who are compensated for a heat-pump being switched off for a couple of hours.

5: None of the Energy Suppliers has yet devised a strategy to offer ToU tariffs to households on Pay As You Go (PAYG) Smart Meters.
Not only is that a sizeable proportion of the population, but it encompasses many of those who live in Energy Poverty or on the Priority Services Register (PSR).
It would have a very great impact on national demand if those households had storage batteries and thus made zero demand on the grid during peak-use periods.

I could add several more. But I hope these provide an insight into the way future tariffs might be shaped.
The biggest problems are caused by government policy.
NESO will have to fight against political decision-making in order to impose a system of supply and demand based on sound science.

@jamespa Just some figures for context.  I have a 13.5kwh Powerwall and an 8.5kw heatpump and 7kwp solar, no gas.

Last year I imported 250kWh/8400kWh or 3% of my total import at peak time and exported 6800kWh.  That's excluding car charging that is all at offpeak

For half of the year the heat pump will only be doing DHW and a fair proportion of the remainder will be at a low level of output and wont be on continually.

I heat house in early hours offpeak downstairs only then heat pump will only come on in the afternoon/evening or not at all depending on OAT.

When it gets really cold in Dec/Jan and there is little solar I will run out of battery by lunchtime but this is only a very small proportion of the year.