Thanks, my impression is also that investing in a larger battery (if you are not tied into an expensive battery system) is currently the best solution for people combining EV with a heatpump. 

Hopefully grid storage will be added, enabling new tariffs that can work with small batteries.  

Other considerations if adding a battery... do you want EPS? Emergency Power Supply may or may not be important to you. Ideally fully automated for whole home? But like everything it comes at a cost e.g. Tesla Powerwall or similar

I was lucky that I could add EPS for a very reasonable cost, as below. Solax, Sunsynk/Deye and Victron hybrid inverters have similar capabilities. 

The key for this type of systems is to use batteries with compatible BMS (in practice, same BMS). 

My back of the envelope calculations suggest that we could run our whole house that consumes 8000 kWh per annum (including EV and an heat pump) on an average of about 20p even without solar and batteries. It's still more than double what it costs with our solar and battery setup and being on Octopus Go, but the Eco7 option would be considerably cheaper than being on a SVT.

Remember to check inverter charge/discharge rates. Ideally you want a higher rate to maximise .... 

Other considerations if adding a battery... do you want EPS? Emergency Power Supply may or may not be important to you. Ideally fully automated for whole home? But like everything it comes at a cost e.g. Tesla Powerwall or similar

I actually think the fix for many people would just be a bigger battery but it's all about timescales and if someone tricked you into a product tied to overpriced vendor specific batteries or not. If you've got the flexibility then big batteries seem to be the winner with an EV tariff, dunno about agile.

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I'm thinking by adding a HP we may be best going onto agile and use havenwise to optimise and then having our EV charger +appliances still set to run overnight, but manually adjust it on exceptional days - maybe introduce a bit of automation to cap/alert on high/low pricing.

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Particularly interested to hear from anyone with an ev+heat pump but no solar battery and people using havenwise with agile, as I'm very finger in the air on what to expect my heat pump's p/kwh to end up being.

This one still seems to be a very relevant topic. 

I had a look but cannot find any good all year round tariffs for people using an EV (charged overnight), with a heatpump? Assuming a small energy storage battery. Would people agree the best solution is still to go for an EV tariff and temporarily switch to something like Cosy around the winter months? 

It does not seem realistic to aim to run even an oversized heatpump mostly overnight..

Battery storage has been immensely useful though. We were on Octopus cosy initially when we installed the heat pump. But, then we doubled the battery capacity in the summer. So, Octopus Go is the best tariff all year around. Now we are averaging about 12 p per kWh during a relatively cold November and kind of mild but also odd very cold days in December. I predict around 15 p per kWh average for January and February, then go back to 8.5 p from March to October.

The engineer booked to do my (next) heatloss is heatgeek elite and has various systems on open monitor with an average scop >4. 

The original heatloss I went through in early 2023 was precisely to get emitters sized correctly before I went through a major refurb where the aim was to be heat pump ready at the end.

Our boiler is giving up unexpectedly early. I hadn't anticipated needing to do this for another few years. Maybe given political climate I'll be glad of doing this sooner than planned.

You've probably already seen on the forum that too big is almost as bad as too small.

To be honest, this is one of my main concerns. Instinct tells me my downstairs ufh, at 100m centred pipes, is currently oversized Vs rads upstairs. As previously mentioned though I'm skeptical of the true flow temp being 30c and I know the flow rate is faster than I'd get off a hp without any boost, so hoping this levels the field by reducing energy going in.

The only thing I would personally not see as negotiable is the need for checking and double checking the quotes not just for cost but for the installers' ability to justify each design choice. In particular:

• The heat loss calculation must be carried out properly and the results made available to you.
• The heat emitters must be verified to be compatible with the ideal flow temperatures for a heat pump, and suited to the rooms they're in. Your preparation here will have been invaluable.
• The heat pump must be appropriately sized for the house and available heat emitters. You've probably already seen on the forum that too big is almost as bad as too small.
• View with serious suspicion anyone who tries to insist on a buffer tank in the design. Pound to a penny, it's not needed and will reduce efficiency.

I know I'm banging a drum that's been hit many a time before here, but if you want to see that 3.8 SCoP, this is the best chance of doing so.

Screenshots show my most recent days usage of gas plus how often my upstairs has been calling for heat in December. DHW run is currently once a day, 2.30-3.30pm, but really could be done anytime of day.

"Try it and see" - you've given me confidence to do this. Will report back ok the outcomes.

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Actually, I don't; I would go with real world usage over theoretical every time. However, in the absence of any heat loss calculation guesstimates when I wrote what I did I could see your annual gas usage was about the same as my home's calculated heat loss and so I preferred my measured heat pump usage over your (as it seemed at the time) finger in the air estimate.

I would also point out that 16k kWh gas vs 3.8k kWh heat pump consumption is a ratio of about 4.2. If I had to go for a rule of thumb for heat pump performance over a whole year (energy in vs energy out, which is precisely what a SCoP value is), I'd want to err more towards a figure of 3 than 4; it's far better to overbudget than underbudget. Now your follow-up suggests an expected heat pump consumption of 5k kWh annually, that makes much better sense (3 x 5 = 15 which roughly equals 16k boiler figure).  

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Dishwasher and washing machine running overnight currently is no bother to us. The only real change in behaviour is pressing a button to delay starts and sometimes running the dishwasher on a half load where we would otherwise leave it until its full. The washing machine never runs at half loads! (2 kids under 3)

I think I agree with you on treating the optimisers as a tweak. Unfortunately that requires patience - a virtue I don't often have the patience for!

I also agree that comfort is the most important thing. My wife keeps me in check on that and an extra few quid on the direct debit is worth it to keep everyone comfortable.

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All sounds pretty reasonable to me.

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However..... We already have our house set to fixed temps (18c 24/7 upstairs, 20c downstairs with a 18.5c setback overnight). Our UFH throughout downstairs - with 100mm centres - also already runs at 30c* flow based off a mixer pre-manifold. Experience from the last 2 winters tells me on all but the coldest days (I'd estimate <30 days a year), the downstairs will generally heat up in the morning from 5am, the heating will overshoot it's 20c target and go to c.21c and not fall back below 20c without any additional energy until after we've gone to bed. The upstairs radiators have been on for an average of 45 mins a day over the last 30 days although flow to them is a guess as my current boiler doesn't give a readout. I'd guess 45c (I manually turn up once a fortnight for legionella). Basically, what I'm trying to say is that I suspect I could run a HP efficiently without being 24/7 - to the point where most usage could be offpeak - and tariff savings might trump SCOP savings and comfort wouldn't suffer.

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To be frank, we've had plenty of discussions here on the forum about savings from setbacks and setforwards with no significant consistent outcome. In that light, I would be surprised if what you're suggesting were true but I'm also well aware that each home is different and the characteristics of yours may yet fall outside what we've seen to date. No experiments you try once the heat pump is in will be irreversible so I'd suggest you simply try it and see. I'll also say that since you're running your boiler with rather heat pump friendly flow temperatures already, you're in a better situation than most for making predictions about your home with a heat pump installed.

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Final thing - interested that you say avoid Agile if no battery. I would have saved c£110 over the last year if I was on Agile vs OG with no behaviour change (agreed savings would have been a bit less if I was on IOG, but that's a long story). Is there something else I'm missing? I'm not particularly risk averse...

No, you're not missing anything; I am. The car in and of itself is a battery. I suspect that, if you separated out your energy consumption and time of use costs, you'd see that your non-EV outgoings would've been slightly more expensive over the last year with Agile but more than offset by the significant savings on the energy piled into the EV.

My point is that since I'm on Agile import, I know full well how expensive the peak times get. It can be quite alarming when the price per kWh hits the capped amount of £1, but knowing all our usage is coming from the battery that was filled up at perhaps a quarter of that is a big relief. You can, of course, avoid peak times with your EV, so all your predictions hang on whether you really can do some time-shifting of usage on your heat pump as you are hoping to. If not, your bills on the really cold days could be quite eye watering; the maximum I've seen in my time with a heat pump happened on 16th December 2022 when I saw a day's consumption hit 62.5 kWh (about 2.6kWh per hour, or a potential maximum of £7.80 for the three hour stretch between 4pm and 7pm if charged at the maximum allowed rate).

All that said, with Octopus you can swap between rates something like once a month so it costs relatively little to try out a few scenarios before settling on your preferred one.