You’re allowed to use the solar on the roof before buying from the grid which will save you tons on most days. The UK grid operates on marginal pricing so if you buy from the grid the highest price provider dictates the price.

This essentially means that you pay the peaker plant nat gas price for electricity where every MWh hits pretty hard on the bill. To recoup the investment in the UK, especially with the interconnectors inside the Eurostar tunnel, is pretty easy and a decentralised grid allows the UK to skip building a lot of power lines for energy that’s used locally.