In order to do that I need to over-provision my solar panels. Solar panels remain a lot cheaper than batteries, so for me at least it makes sense to get a lot of solar panels and only a few "hours" worth of batteries.
Let's assume that some sunny days I have an extra KW of power generation for ~8 hours. On overcast days I probably don't have any extra power, unless I'm not at home and can shut everything down.
What can I use the waste electricity for?