To be sure, when talking about solar panels, 800W is the nominal/nameplate capacity. That's how much it generates when conditions are perfect and the sun is shining straight down on them. Most of the time an 800W installation will produce rather less than that.
You'd need rather more panels (and/or some combination with batteries) to hit 900W output constantly. (on the other hand, do you need 900W constantly, or is that peak usage? A battery might be able to handle that.) That said, solar panels are probably a lot more efficient in Indonesia than they are in Germany. Since you're in/near the tropics, perhaps 1500-2000W nameplate capacity could cover your 900W? See if you can get a local expert do the maths for you.
You'd need rather more panels (and/or some combination with batteries) to hit 900W output constantly. (on the other hand, do you need 900W constantly, or is that peak usage? A battery might be able to handle that.) That said, solar panels are probably a lot more efficient in Indonesia than they are in Germany. Since you're in/near the tropics, perhaps 1500-2000W nameplate capacity could cover your 900W? See if you can get a local expert do the maths for you.