We would recommend a 6Kw Inverter to run most houses and 10kw of storage is a good start as most homes consume between 8 - 20kw per day.
With this system you will charge the storage batteries during the day from the solar panels and top up at night using the cheap tariff using the stored power and solar input during the day.
You can add more batteries at any time in the future.as well as giving you the option to add more solar panels to increase the savings (Subject to room)
Average price including installation will be around £8,500.00 excluding scaffolding costs. (no vat payable)