The author of the article has a smart battery which (as far as I can tell) outputs 460 watts of power [1] - whereas and a fan oven can use up 2.5kW†, a kettle 3kW, a shower 8.5kW.

So unfortunately you'll be importing electricity from the grid sometimes anyway, if you want to shower or cook when it's dark.

[1] https://www.moixa.com/solar-battery/wp-content/uploads/2018/...

†When the thermostat is turned on, that is. So the average consumption over an hour of operation will be lower.