What I am trying to say, is that since you have to recharge to 100% once a month anyway, (needs 15+ volts on disconnected batts for a time) your solar is only affecting whether you can go that long or have to do it more often.
Start with the guy doing a week on batts and not having to recharge till he gets home. With some solar he could do longer. But he can't do longer than a month no matter how much solar he has. Now he needs to get to 15+volts on disconnected batts (somehow) to get them to 100%.
So to me, solar is just a way to extend the time between needed recharges to 100% up to a max of one month in time.
