Difficult to be completely prescriptive without more detail but in general heat pumps are best operated 24*7 single zone without thermostats or trvs,  or something close to that.  15 active thermostats will likely be a disaster.

May I suggest you read the ABC guide to heat pumps in articles on this forum and look towards:

Operating 24*7

Turning all thermostats to several degrees above the desired temperature so they have no effect ie they are constantly on

Balancing the loops by adjusting the flow regulators to get the desired temperature diffences between rooms

Reducing the WC curve until the house is at the right temperature.

From there you might tweak a bit but you need to start with a largely open system otherwise you are highly likely to be crippled by short cycling.

@jamespa @chrish, as James has explained 24/7 is the heat pump mantra for when to run it. Now, I think Go offers you something like. ~6 hours at a low rate and the other ~18 are somewhat at an elevated rate -yes? No problem to run the heat pump during go hours and charging your battery at the same time. Will your battery provide sufficient juice when supplemented by your solar power to cover most of the other ~18 hours? I suspect you will need to use grid power at some point - does your control equipment allow you to select grid power or battery / solar to avoid the highest (3 or 4? hours) on the grid powering for heat pump or battery charging?

By using the power from the battery during the most expensive hours will help to keep your costs down. Furthermore, running the heat pump 24/7 and fine tuning the weather compensation settings is likely to be cheaper and provide more even and constant comfort levels than operating the heat pump only during the cheaper rate hours and having to boost the heating to provide sufficient heat to compensate for the heat losses during the 24 hours. 

You haven’t given any details of heat pump power or how much solar power you might reap during the winter months - solar provides the least energy when we need it most! Regards, Toodles.

I’ve got 5.4kW array, 9.6kWh battery, 5kW heat pump, EV and I’m on IOG.

The following works for me.

Battery is charged from grid every night from 0115 to 0530.  I export from 2230 to 0100.

For the heat pump, WC is on. House temp is set at 18C for most of the day, then I have set back of 17C from 2145 to 0130.

The house is always comfortable. 

Last January was the most expensive bill, worked out at 11p/kWh (bill £200).  I was doing a lot of mileage (2000 miles) so car was charged frequently, that will have brought average price /kWh down. The previous year with standard OG (no car just electric motorbike) average was 16p/kWh for Jan (bill £165)

G

We are on the Intelligent Octopus Go tariff.  We installed a heat pump in the summer and our solar panel and battery installation is almost complete.  Our current approach is to run the system at a constant 20C temperature 24 hours per day.  We use weather compensation and flow return valves on most radiators.  Bedrooms and one sunny lounge have TRVs, but they are all wide open.

The rationale for this is that it is coldest at night, so make the heat pump work hardest when the tariff is lowest.  I plan to use solar to power the house as much as possible and use the rest to charge the batteries.   In winter, charge the batteries at 7p per kWh and use them to power the home during the day when it is 28p per kWh.  Sell spare capacity to the grid at 15p per kWh and recharge at night when it is only 7p.

I have yet to learn how easy this will be in practice, as I hear Tesla Powerwall 3s do not have particularly sophisticated control software.

@grahamf I've started using the netzero app with the powerwall, which has added a lot over the stock Tesla app. If you're with Octopus, it can automatically charge the battery during the free electricity sessions.

@treewizard The only fly in the ointment is whether the automation facilities in NetZero will save you as much as the monthly subscription of ~£7. Regards, Toodles.

@toodles I didn't realize I was on a free trial, definitely not going to make the money back at £7 a month!  Will need to investigate doing this through home assistant instead.

@treewizard Yes, I like the extra facilities that NetZero offered over those available from the Tesla app; I felt that though better automation options were then available, the charge per month was rather more than any gain I could ever expect to make using them.☹️ Regards, Toodles.

@treewizard

Posted by: @treewizard

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I've started using the netzero app with the powerwall, which has added a lot over the stock Tesla app. If you're with Octopus, it can automatically charge the battery during the free electricity sessions.

Very interesting, thanks - although I have seen the follow-up explaining that the Netzero app costs £7 per month.

Do you know if third party or home grown automation apps affect the Tesla Powerwall warranty?

@grahamf I don't believe there's any issue with the warranty purely from using the app, as it's using the official third-party tesla API (you auth the app with your own Tesla account),  but it would depend how you use it.  e.g. if you're setting up the automations for arbitrage, then that might void the unlimited cycles. 

@treewizard

Posted by: @treewizard

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I don't believe there's any issue with the warranty purely from using the app, as it's using the official third-party tesla API

That's probably fine, provided as you say you don't mistreat it by very frequent cycling.