You are probably looking at £1,000 – £1,500 for the scaffolding on a three storey house, fortunately our installation was on a bungalow so no requirement for scaffolding.
We recently paid £4,900 in March for a 12 panel 4.4 kW system with a Solis Invertor 10 year HIES Government backed warranty, we paid 5% VAT, installations are now zero rate VAT, the company I used unfortunately are a old established family based firm in Stafford, they would not take any payment until the works was completed and commissioned.
Realistically you should be looking around £6,500 (including scaffolding £1,500) for a 12 panel JA 390 kW system with a Solis 4.4 kW invertor and additional £3,600 for a 6.3kW Solax battery.
Unfortunately I have suffered a brain injury and occasionally I get confused and often say the wrong thing.