The current pulsetech 24V solar products (which are used by the military, have an NSN number, etc) are rated at 6 watts, their 12V units range from 3-25 watts, as a rule of thumb a well placed fixed solar panel will generator 5-6 times its peak output rating in watts per day from a typical mid US location, a poorly angled or placed one will generate considerably less. While looking for information after buying one of these current generation 6 watt charger models on ebay a while back I found a military PDF reference that says this model is not always capable of keeping up with the self discharge rate on some of the larger truck batteries in some conditions, but did exceed the self discharge rate of batteries in all current MEP series generators. This test included a chart where they tested 4 of these solar chargers in various conditions somewhere in the souther U.S. (I think AL or GA). What this means is one of these solar chargers if well placed will keep all but the largest batteries fully charged in most conditions, but will do little to charge a drained battery.
Ike