Watts are a measure of power
, Wh and Ah are a measure of energy
(although Ah is hokey, since without specifying voltage you can't know the energy value, we just assume 12V in most cases).
So the 72W rating indicates that is takes 72W of power to run the unit. At 12V this is 6A of current
. If you run it for one hour then you have consumed 6Ah of energy (6A x 1 hour). So, for a 24-hour day you are looking at 6A x 24 hours = 144Ah of energy used every day.
Presuming your batteries are lead-acid the usable stored energy is about 50% of the rated capacity, or about 300Ah. So, you could run one unit for two days (300/144 ~2), or two units for one day (300/(144 x 2) ~1) before reaching the minimum desirable charge state on the batteries.
On the charging
side, so much depends on the solar installation
, the location, shading, etc. Making some gross generalizations, if everything is working perfectly you can probably see 4-5 hours equivalent of the rated output of your panels
, (you may see full power for an hour or two, 80% for another hour or two, and lower for the remainder of the day, but it works out to about 4-5 hours of full output).
If we use 5 hours then 560W x 5 hours = 2800Wh/day. Dividing by 12 to get Ah, the solar might be able to deliver 233Ah/day. At four hours equivalent you might get 187Ah/day.
To run one unit you need 144Ah/day, and you have maybe two days total reserve in the batteries. So, you might be able to run one unit, will depend on actual solar output, and how many sunless days in a row you might have.
That's a lot of generalizations on very little information, but you might be able to get away with one unit, certainly could not with two.