I think it's still a definite maybe, @jamespa.

I can look at my historical figures and demonstrate clearly that my heat pump on its own is slightly cheaper to run than my old oil system, but that when combined with my solar PV/battery package that saving is significantly increased; it reduces my home's overall costs by about £1,000 annually. The whole solar PV/battery system cost about £7,500 to install so the payback for the whole thing is not an unfeasibly long time. How much of that is the battery? Good question, but eventually all I'm using it for is two things; to power the house during the summer nights (filled up by home-grown power since the PV can cover the day and have enough extra to fill the battery) and at other times to avoid us having to import from the grid during the expensive period (the 4pm-7pm stretch). Those requirements only need a fairly modest battery hence a modest price tag but the benefits are tangible.

The fact the inverter is controlled by Home Assistant (which also captures carbon intensity data for my geographic region) also allows me to be more picky as to when I fill it up if I need to charge from grid. It's not a precise science but I'm comfortable with the combination of manually overseen automation.

Given all that, I'm satisfied I have demonstrated to myself a good business case for including a battery in my setup on the basis of my situation, my costs, my power generation and usage and my preferences. In other words, it works for me. I certainly wouldn't want to draw any conclusions from that to apply to anyone else but I don't think I'm an edge case. Nonetheless, if you can't see a justification then it's not the right decision for you and I certainly wouldn't encourage you to spend.

I started off thinking of a battery need as to provide all 24hrs of electricity usage. But that not the right approach for us and since the battery already exists and was bought with more PV it is a sunk cost to be best used.

I find it personally very satisfying to see the solar being more than the total house use in the daytime and that needs a battery since the sun /shadow cycle would never align with the ashp cycle.  It is virtually impossible to model that other than statistically /Monte Carlo analysis and the pain to do that is too high.

At the daily level I modified the spreadsheet which MdeP wrote to go with this article https://protonsforbreakfast.wordpress.com/2023/11/01/heat-pumps-cop-envy-is-pointless/ to make it fit our last years gas bill, then with dynamic pricing due to battery been used up and round trip efficiency. You need to do your own modifications since my spreadsheet models are never well documented. With a single 9.5kWh battery, 7kW ashp and house use the average cost is 25% more than the lowest cosy rate. So there was no purpose of adding a further battery to use only the lowest rate.

But it was a considerable saving over std rate and that (from memory) would give a rough pay-back time of 10years. However OVO charges you 15p per kWh (for only Vaillant ashps) which doesn’t require a battery to achieve that. Their terms can be onerous though so you’re not comparing on equal terms. 
It’s the solar which makes a battery make sense and the combination over the whole year. 

Posted by: @majordennisbloodnok

↑

I can look at my historical figures and demonstrate clearly that my heat pump on its own is slightly cheaper to run than my old oil system, but that when combined with my solar PV/battery package that saving is significantly increased; it reduces my home's overall costs by about £1,000 annually. The whole solar PV/battery system cost about £7,500 to install so the payback for the whole thing is not an unfeasibly long time.

Ditto Major. 2x6.5kW Growatt batteries timed to charge on 2 of 3 low rate periods with Cosy Octopus each day. There's a third unused time slot on both the Growatt App and Cosy, which we've not needed this season yet. Cosy has 8 hrs of low rate energy each day in 3 periods, so even a modest battery storage capacity can leverage the advantage of that. I would advocate getting the largest BESS capacity you can comfortably afford however.

We shifted 85% of import to lowest rate during the heating season Oct-Apr when we import 85% of our annual energy consumption. During the summer we're largely self-sufficient or small net exporters with a modest 3.6kW solar array and BESS.

For us the batteries were an afterthought to the Solar PV array, and an additional £5K investment, but a total game changer in terms of reducing our energy bills. We're £1K a year now all-electric with the house heated all day via ASHP, whereas we were over £2K before with an oil boiler sparsely used morning and evening and a cold house at other times.

BESS should pay for itself in 5 years, but it wasn't purchased with any specific ROI in mind, neither was the Solar PV or ASHP - more because we felt all were the right thing to do. We still feel that,  and the house is sooooo comfortable & warm now 🙂

Thanks, @judith and @allyfish. However, @jamespa’s point still holds true. If he can’t see a justification in his set of circumstances, going ahead with a battery is not the right thing to do. My point is just that it is right for plenty of others; horses for courses.

Posted by: @jamespa

↑

How to get from here to the binary decision 'should I get a battery given that there is no financial business case' still escapes me.  I rather have the impression from what you say that the answer is maybe, and maybe not, we just don't know (and currently don't have the information infrastructure to know?

It does depend a lot on whether you have your own micro-generation.
For most people that would be solar panels; but a micro wind-turbine or hydro-turbine would be better because they produce more generation in the winter months.

It's micro-generation and future ToU tariffs which contribute most to the case for storage batteries.

I do have a fair idea of the direction in which tariffs need to move in order to get us to decarbonisation of the electricity grid by 2030.
But that direction gets thwarted by Government.
NESO really needs to get a move on, and force through the required decisions based on science.

Unfortunately civil servants themselves are advising ministers about future energy based on incorrect assumptions.

I'm about to reply to DESNZ regarding a Technical Appraisal they sent me which still relies on opinion and 'assurances' they've been given by the Energy Sector.
My response will, of course, have mathematical modelling based on cold hard facts!

Another input on correlation of low price with green fuel (or lack of it) is Octopus green days https://energy-stats.uk/octopus-greener-days/

This is a screen capture of the last 50days against 3 tariffs

@judith And then there is Cosy (correlation of greeness not actually in evidence then) Cosy is a TOU tariff but may or may not be greenish! Cheapest/greenest? times being 04:00 - 07:00 and 13:00 - 16:00 and 22:00 - 24:00 every-day-of-the-week. The dominant no-go time in all the tariffs is that ‘homecoming and cook the dinner time of 17:00 - 20:00 when I assume, it is very not-green regardless of the weather! Regards, Toodles.

Cosy is a construct to win over ashp owners and if you compare it to the agile prices (again as shown by energy stats) you can see how they fit it into the price profile. Over the last few weeks it been lower than the market price derived agile many times.

The offered price is a commercial decision by Octopus and they may be thinking they pitched it too low so far this season.

@judith At present, this ASHP owner has been won over by O.E.’s Cosy tariff. I recently saw another scheme that is being extended to include integration of Tesla Powerwall kit; so they will offer Intelligent Flux where Kraken controls import and export at a common rate (sounds similar to the original Tesla scheme to me) but with integrated Kraken masterminding everything.

I think this may be a useful scheme during times of export but paying more per kWh during the heating season with little solar to export sounds less attractive than sticking with Cosy and exporting with Outgoing Fixed to me. I have written to O.E. for clarification as I would like to assist the grid if I can but, not if I am going to put additional wear and tear on the battery without financial compensation for doing so.

Rewards, Toodles.

Posted by: @toodles

↑

they will offer Intelligent Flux where Kraken controls import and export at a common rate [...] but with integrated Kraken masterminding everything.

That's a similar approach to the Demand Side Response (DSR) proposals from DESNZ in their consultation on Delivering a Safe and Secure Electricity System.
That was Part-2 of the Consultation, sub-titled "Implementation".

Their starting point is that GB will experience regular Demand peaks which cannot be matched by Supply (generation + storage).
That premise is illustrated in the consultation with the Load being a domestic heat pump, and the excess demand being the existing early-evening peak.

There was no underlying evidence presented that the daily demand-peak was a reasonable scenario,
nor that demand would outstrip supply during any possible future scenario.

National Grid ESO told Parliament that their main focus was on energy storage for periods in excess of 200 hours, which is a very different strategy.

The possibility of flattening the peak wasn't considered as an alternative.
That might be because the early-evening peak-demand period is greater in areas with less generation and storage... London (Westminster) being the prime example.

The DESNZ Proposal is for consumers to sign up to a scheme whereby a third-party DSR-Agent would use encrypted commands over the internet to turn off the home heat-pump.
For this, the householder would receive financial compensation.

I raised counterpoints to these proposals on a number of different levels, such as:

• the proposal lacks resilience; the internet communication path is susceptible to a DDoS attack without even bothering to hack the Agent's systems
• the choice of a heat-pump as an appropriate load to switch off isn't well thought through. Domestic heat-pumps will be operating continuously, and are not therefore contributors to a Demand-Peak.
• re-starting heat-pumps would itself cause a demand peak. Attempting to do so randomly on a national basis would still cause overloads at local substations
• the cost of electricity to start a heat pump and bring the house back to working temperature is significant. The financial compensation would need to be high enough to cover that additional demand as well as the DSR-Agents' fees
• stopping heat-pumps increases risks of legionella bacteria in the DHW tank
• a communications system failure could leave heat-pumps switched off without the "switch on" command being issued

Sending DSR commands to prevent charging of storage batteries or re-charging EVs during Demand Peaks would be better illustrations,
but such practice is unlikely due to ToU tariffs. We already re-charge when it's cheaper to do so.

In short, I dislike imposing a broadcast command and control system on top of our electricity supplies, whether it's Octopus' Kraken or OVO's Flex.

If any such DSR strategy were actually required, then it should be implemented using the Auxiliary Load Control System (ALCS) for which each Smart Meter has 5 channels available.
The national Smart Meter Network is secure and independent of the internet.

I think most of your criticism of the denz proposal makes sense to me although I can see why turning off heat pumps is attractive.  Houses are large storage systems that already exist, typically storing half a day or more of heat energy.  It's difficult to ignore that.  The cost of recovery could be mitigated by pre loading to raise the house temperature above the design temperature, but I agree resilience and security must be very high.

Posted by: @jamespa

↑

The cost of recovery could be mitigated by pre loading to raise the house temperature above the design temperature,

It couldn't unless the UK Government was able to persuade HP manufacturers to allow digital access to their control electronics...
effectively opening a port to the internet through which commands can be sent.

The DESNZ proposal is for crude access to the mains incomer.

Perhaps I should also point out that the Proposal includes data capture which is supplied onward to NESO by a licensed DSR-Agent.
That is intended to be used to bring generation on-stream and supply statistical analysis of our electricity supply system.

Government contracts for companies to develop control and database software on this scale are not known for their ability to

• operate effectively
• stick within budget

For comparison purposes Britain has 'merely' 550,000 electricity local substations.
Less than a couple of hundred have ever been monitored, and none have the capability to receive commands and act on them.

The DNOs know that such a system could never be financially justified.

So why would DESNZ imagine that it's sufficiently beneficial and viable to create an even bigger mechanism to handle DSR for every home with a Smart Meter? 😲