So if remembers correctly, a 800 watt inverter divided by 240 euro volts would provide 3.3 amps. Then we reduced that by 10% because of connections, length of wire runs and other mysteries. This gives you an idea what can be powered.
Say you use a 12volt deep cycle battery with a 105 Amp Hour rating. Which means your battery will be as dead as a door nail in 105 hours at 1 amp per hour.
To determine the minimum drain on your battery the inverter causes when pushing 3.3 amps (full output). Take 800w divided by 12 volts and that inverter is drawing a minimum of 66 amps an hour. Something like that will only give you a little over an hour of use at full output before your battery dies.
Two 400 watt solar panels and a lot of clear sunny days ought to keep things going quite nicely.
If it’s a 24 volt battery it gets better.
At least I think so, I could be wrong I haven’t had to mess with 12 volt stuff and inverters for 20 plus years