Thanks, that makes a lot of sense. A single 9.5kWh is probably only slightly too small but should allow me to charge the battery and top up the car in the 6 hour IO window (I think). The almost 3 years faster payoff is more attractive and as you say is within the 10 year warranty.
The 13.5kWh of the Powerwall should more than cover average use. Fitter is due in a couple of hours to prepare a quote for that so will be able to compare prices.
Lots to think about.
It was a toss up between the Powerwall(s) and GivEnergy for me. I went with GivEnergy in the end. Mostly because of the cost of the battery size I needed and waiting time/ price / plus some extra flexibility.
I’ve been a bit unlucky and need some bits replacing and the GE customer service is slow but it’s in hand (think 3-5 weeks to 2 months). They didn’t argue that things need replacing but just slow to come out. Luckily I’ve been able to hobble along on half a system.
But that seems to be the industry norm.
The Powerewall is a very good option too and has its advantages and disadvantages, like them all. Seamless and Plays well with the rest of the Tesla kit but as it’s an AC system there are more conversion losses (3x conversions DC—> AC—>DC—>AC ~ 9% instead of ~ 3% with the GE hybrid kit for one conversion)
Do you know what your annual/ monthly usage is? You really need to have a rough idea. This will give you a much better idea of what size batteries you need. Do you have an EV? Heat pump? Etc? Future heat pump installation a near/distant possibility? You’ll want extra for that for sure.
In the last two weeks things have changed significantly with the addition of import rates of 7.5p and export rates at 15p (cough cough) So now it’s just fill ‘em up for 7.5p and solar generation and battery fills (which can be exported to grid at 15p) are giving you twice what you imported from grid up for. And all Solar export generated for free at 100% of the 15p
To give you a rough idea. We used 19,000 kW last year (4,500 was the car; Model Y ~ 13,000 miles worth) rest was the house. Paid about £6,500 last year for electricity it that would be £4,800 at todays 31p rate; Mostly high use in winter (old 3 storey Victorian semi with solid walls and crap insulation and the dreaded electric underfloor heating mats which seemed sleek and cool at the time
).
Should be about £1,000 this year. Plus/minus £400! Might be much less. Don’t know yet- only installed solar 2.5 months ago)
We’re on gas central heating and some underfloor. Which hasn’t been turned on yet.
Payback times are a bit of a red herring to be honest. One minute it’s 6 years, the next it’s 10 years, then it’s 12 years then something else.
Rates/ suppliers and import/ export tariffs come and go all the time, so it’s really hard to say “yeah - 8 year payback”. You’ll only truly know after the event. And if you rigorously geek out and keep track of it.
We went for 2x GIV 5.0 gen3 inverters and 4x 9.5kW batteries. 27x 420w panels Solar split over 4 non-ideal facing roofs. South, East, North. Probably we will generate about 6,000-7,000kW a year. TBC
Not trying to talk you into anything but if it’s borderline. Maybe go for the extra battery storage space. It’s 0% vat right now and you won’t be paying extra for installers to come out again and the extra 20% VAT next time.
I’ve never met anyone that said “yeah, you know what, I really should have got a bit less battery storage” same for solar panels.
Forums are full of people adding both extra panels and battery storage and wishing they had done it day one.
All that said if it’s only like 10% extra and you don’t plan to add a heat pump, extra EV’s etc then might not be worth it.
Let us know how you get on
