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 at night using the cheap tariff and then using the stored power during the day.
You can add more batteries at any time in the future.as well as giving you the option to add solar panels to charge the batteries during the day.
Average price including installation will be around £5,500.00 (no vat payable)