23% is the efficiency of that generation of panel. In my opinion, those numbers shouldn't be put in front because (as you can see) it confuses people.
Lets say 1 meter of sun can produce 100 watts of power (I don't remember the actual number). If your panel was 25% efficient, you would need a 4 meter panel to get all the power.
Currently 18%-23% is as good as it gets. If you buy an older (last gen/used) panel or cheap one, your in the lower percentage. The newer better brands will be higher.
When they put out panel wattage numbers, their saying our panel produces 400 watts and is this big. The difference between 18%-23% is slight and you would have to compare side by side to see the difference.
When they say 400 watts, the number is taken from the panel being located somewhere in the artic (i think) where there's no inversion layer. That means the amount of power your panel will put out, will change around the world.
Currently on the west coast I get as much as 70% but I don't have a new generation fixed panel and the flex panels have a bit lower output (I have 2 fixed and 2 flex).
With those 400 watt panels, I would expect about 7 amp per so 28 amp total. Thats if its pointing at the sun which means your occasionally moving it during the day. If you left it pointing at the sun mid day, it will have low output morning and late afternoon.
My guess would be an average of 14-18 amp over the day. Calculate it with say 10 hours of sun and your average will be 140-180 amp hours.
The controller needs to be as close to the battery as possible.
