There are two ways of doing it. The first is the suck it and see method where you hope the bloke that installed it was an expert and got things at least partly correct.
The second and far more scientifically-correct way is to list all your appliances with their current draw and an estimate of how many hours each day you are likely to use them. This calculation is done in Amp-hours, often abbreviated Ah. Ampere is capitalized because he was a real person and h is lower case because it isn't a person. I only mention it because some knowledgible people get upset if units are not correct while most so-called experts don't know the different.
So
TV set -- 2 Amps x 2 hours (per day) = 4ah (per day) [Its all per day so I will leave that off]
Water Pump -- 5A x 0.5h = 2.5Ah
Lighting -- 2A x 5h = 10Ah
Computer -- 6A x 2h = 12Ah
Microwave (via the
inverter) 100A x 0.1h = 10Ah
So total per day is 4+2.5+10+12+10 = say 40Ah
How many Ah does your FULLY CHARGED
battery hold?
say 100Ah
BUT you should only take out HALF of this energy otherwise your
battery life will be short. So this means you have 50Ah to play with and you use 40Ah per day -- SO if it is raining or you are north of almost anywhere in central Europe and your
solar panels are doing nothing except keeping part of the roof paint from weathering, you can stay for a bit more than 24 hours safely and maybe if you don't use the microwave, you can extend your stay to 2 nights.
How big is your
solar panel? Normally rated in Watts just to confuse everyone and to hide the fact that
solar panel ratings are one of the biggest legally sanctioned frauds around.
Lets say 100Watts. Everyone knows that Volts x Amps = Watts so since we have a 12V
battery system then OBVIOUSLY 12 x A = 100 so your panel will put out 8.5 amps any time the sun happens to be shining. Great! 8.5Amps X 8 hours of sunlight = 68Ah pumped back into the
battery every day. WooHoo, you can sell some power to the bloke next door and wild camp forever.
If only.
It is true that if that
solar panel is flashed with a light intensity of 1000Watts per square metre for no longer than about 20 milliseconds then the panel will produce energy at the rate of 100W during that brief time. So working on 15Volts which is the voltage at which maximum power transfer takes place (not 12, sorry), the panel will put out 100/15 - say about 7 amps. Then because your panels are flat on the roof you lose another 10 to 30% power production, and you are say in Finland in winter where there is no sun, the actual peak output might be closer to zero even on a good day. The sun only shines for 2 hours in winter so 2 x close to zero is pretty close to Zero.
In Spain in Summer you may be able to produce more than enough power to wild camp until your water runs out or you have to empty your tanks, but really, you are likely to be short-changed for power even during good weather.
The other complicating factor is if you drive every couple of days for at least a couple of hours, the vehicle alternator will be able to recharge the leisure
battery to about 75% of its full capacity. With a bit of messing around and a long drive and using AGM batteries, you can get close to 100% but not normally. So the day after you have driven, you only have 75%-50% of the
battery available so if you get no
solar input, you have to drive each day to keep things topped up and even then, since
solar may not be too reliable, the end result is that the
battery charge gets lower and lower each day. Bad for the
battery, especially if it is not charged up promptly.
Now you have a generator. That has a convenient "
battery charger" output so that will charge up the
battery because it puts out 8Amps. Sorry, but usually it is a fixed voltage peaking out at about 13.7V and that will just not charge a
battery up beyond about 65% in any reasonable time. Even if it did, you would need to run it for something close to 4 hours a day to do much good.
If you have a good quality 3 stage charger that puts out say 20 amps then 3 hours would be close to enough time to get the
Battery close to 100% charged - whether from generator or campground 220V supply.
etc
etc
etc.
It's all too difficult because the best you can do is work on averages and they just don't work very well in the real world.
And this mess that I've created above (deliberately) is why the smart posters said to try it and see what happens with your particular set up and your particular lifestyle. As they wisely said -- you need to know exactly how big your
battery is and whether it is in good condition (because bad handling over just one winter - or even on one short vacation - will completely wreck a
battery) and how big your
solar panel is and what loads you are going to run abnd for how long and what other means of charging the
battery is on board.
And blah, blah blah ...
