It seems that when it’s sunny the panel produces about 150W which is enough to run the devices and charge the battery. Once the sun goes in, it stops providing power and the battery powers things until it runs out.
This is something I don’t understand – how to know when the battery is low, and when it’s “empty”. There’s a lot of dark arts involved, and I think the main trick is to just buy more batteries. Could also do with another panel to charge the batteries quicker, they don’t seem to remain full but I don’t know if this is because the inverter is drawing power, or because they’re not actually fully charged.
Think I’ll stick a power monitoring smart plug on the AC part and see what it does. I should probably monitor the actual current flow in and out of the battery using a current shunt. It feels a bit messy though, the battery cables are pretty thick.