PeteSpencer wrote:interesting but in effect meaningless without knowing the total cost of the installation which I'd imagine you'd prefer to keep to yourself.
Ours was £7k all in for 4.1kW system, including passive provision for batteries, but no batteries.
Cheapest quote for comparable spec was £5.8k - but I wanted to go with someone with multiple local recommendations.
I've modelled payback time, but it's glorified guesswork without knowing future electricity prices.
The standard model for our location is that I should get 3560kWh of annual generation.
The standard model assumes I will use 49% and export 51%
The standard model assumes that both import and export rates will rise by 6% per annum from current values of 29p/15p.
That gives me a payback of around 7.5 years*
My personal view is that it is likely overstating the cost of electricity; we know it is coming down to 27p/kwh in October. An alternative view of the model assuming a flat average of 25p/kwh import and 10p export, and that I'm likely to use > 60%, not the 49% assumed gives a 10 year payback*. If I buy an electric car, then I might be able to push consumption to 75%, and get payback down to 9 years*.
* both ignoring any costs of repairs or maintenance.
In summary, I don't think you would do it for financial reasons alone.