My thoughts:
switching to an Octopus export tariff to replace the deemed export is worth the risk
Questionable whether Decent Price for Export will be persistent. As more PV is installed maybe there will be less incentive to pay a good price for Export (you allude to this later in the thread ...) but its put me off doing it ... I am more focused on using everything I can generate, and taking the 50% deemed export FIT
In winter, the ASHP will often use more than one Powerwall can provide just charging once per day.
Solar PV is going to do next-to-nothing for you in Winter (I am sure you know that, so just mentioning)
How do you prioritise Powerwall and car charging?
I have a lot more panels than you, I have to charge car at same time as PowerWall - 'coz once PowerWall is full I have more than 7KW of generation (on good days, Natch!) and that would require that both EVs are available for charging
The problem I have with Tesla's AI for how much overnight charge level to attain (based on prediction of "tomorrows sun") is that it has no idea how much I need for the cars. So it charges to, say, 50% because tomorrow will be sunny - but I wanted PowerWall to 100% because I was planning to put all PV into the cars.
So, for me, I want a system where I say (roughly) how many miles each car is going to do for the next few days, and when they will be parked at home (available for PV charging) / away, and then have the API-stuff attempt best-fit (charge cars to 90%, maybe even 95%, if a journey is imminent, but be content with 50% car-charge if planned journeys are only local). For most people (with, say, 16 panels or less) maybe this is irrelevant as there isn't enough PV generation to need to try to be clever.
I use time based over winter Oct-Apr and self powered the rest of the year.
Me too. I have to remember when it changes over, in Spring, because it stops being Tesla's responsibility to charge PW overnight and discharge during the day ... and is now my responsibility!
When the days are still "a bit short" the time between Sun-Down and Off-Peak start (and again in the morning from Off-Peak end to Sun-up and PV generation exceeding household usage), which needs support from Batteries, is more of a challenge than in mid summer when the PV is generating from 6AM to 7PM (and I have 100% at 7PM then I have no difficulty surviving from 7PM to 6AM on battery - as my night usage is lower than my day usage)
total cost would then be in excess of 10 years of our current electricity bill... maybe I need some different man maths
You could use my man Maths ... I'm afraid that is just "JFDI".
But ... having used that algorithm
and spent a fortune for each early-adopter Eco thing I have done, I have been fortunate that all of them paid off. Extra PowerWall, extra PV Panels ... Putin decided he needed to annex Ukraine and price of Leccy skyrocketed and (I thought at the time) there was a very real risk of rolling power cuts. And you would not have been able to get a PowerWall installed in a reasonable timeframe for love-nor-money. Glad I did every single Eco thing that I have done.
setting the backup reserve to current percentage will "pause the battery" at a guess
Yup.
In case useful to O/P: first thing in morning my Reserve is changed to 45% (calculated as being enough, just, from 6PM to start of Off Peak). If there is decent sun (in Winter) I will get to 6PM with considerably more than 45%. At 6PM reserve is reduced to 0%. So rather than running a permanent 10%/whatever reserve, I run down from 45% "in the evening". On some miserable, rainy, winter days I am drawing from grid (e.g. lunchtime-to-6PM battery is holding reserve at 45%). I think this is kinder to the grid (I stop using Grid when it gets busy in the evening), and if I get a power cut earlier in the day I have a much more decent reserve than an arbitrary "10%". If my battery runs to 0% when Off Peak starts, and we then have a power cut, I'm tucked up in bed and not too bothered. A 10% reserve would only give me a couple of hours anyway, so I would still wake up to "nothing"
It would be nice to run heat pump entirely on off-peak electricity…
Insulate the house and run the Heat Pump thermostat "a bit high" overnight.
My house will lose 1C if I turn everything off and go away for the weekend, in mid-winter. So "overheat on Off Peak" would be entirely viable for me (except I don't have a heat pump !)
, has anyone measured or calculated the degradation of their Powerwall battery? 
)
github.com
