Electricity needs when the grids down.

[Pete Grey]

If I had a large solar power bank I would reduce some of the needs, say lights all LED powered by batteries at night, and the central heating pump, when the panels aren’t charging.

In day time when the panels are working (21 panels should give a fare old wack), I would use timers to stager the times for the freezer and washing machine and probably also an immersion heater if possible. When NOT using 240volts I would charge the battery bank.

With 21 panels, most likely 180W = 3.8kW, If only 75% efficient 2.8kW - 11.5amps at 240volts.
If just 50% efficiency 1.9kW - 8amps, (240v), still very useful, but would need to schedule use.