My Tesla Powerwall was £8k fitted but I did wait a year for delivery.
I regard the battery as key to the success of the solar throughout the year so really need to look at the combined cost of £17k.
I also think it’s a mistake to just concentrate on the warranty period e.g. I have friends who have had the same PV system for 20 years.
My Tesla is programmed to charge from solar and then the grid at off peak. The dishwasher and washing machine also run during off peak hours. The storage cooker also gets a boost off peak. So the house rarely runs on peak rate electricity.
Likewise, the PHEV only charges on surplus solar or off peak.
We use approximately 6500 kWh per annum in the house and about 750kWh for the PHEV.
The battery means that from April to September we should be using significantly reduced grid power but we haven’t been through a year yet.
So an estimate would be -
No solar or battery = 7250kWh x 34p = £2465 (assuming the cost of electricity doesn’t rise, I’m betting it will).
5 months at Feb rate of grid use would be approx 1670 kWh.
1670 x 12p = £200
Then say 7 months averaging 50% less would be approx £140
So, saving is approx £2465-£200 -£140 = approx £2100 per annum which gives system payback of approx 8 years.
Allowing 25% contingency would give 10years payback on the system.
In all honesty I didn’t think about payback, at the time of ordering interest rates were rock bottom and I couldn’t think of a better annual return on £17k.
