Phill,  I would like to add a few corrections.

12*100 = 1200w*2 = 2400w is the max energy he can store in those two batteries.

Also, the 100Ah label on many batteries could be misleading, it depends on the manufacturer (you need to reach the sheets), if it says 100Ah C100 it means it's only capable of providing 100Ah if discharged over a period of 100 hours, so a 100ah C100 battery could very well be just 80Ah C10.

Also, most batteries will have the highest number of cycles when the depth of discharge doesn't go past 50%, going 100% on the battery will probably kill it in a few hundred cycles, I think for the average battery you find the market if you go near 100% DoD you will hardly get 300-400 cycles on the battery which means for daily use, every year he will need to get a new set of batteries.

To keep this pretty simple, if you want to achieve max economic gain from the setup, you need to account for the following:

1- 20% power loss from the DC<>AC conversation (which means the total power you can store is 2,400w a day (hopefully will get your two batteries fully charged)
2- Use no more than 50-60% of the battery capacity to get a good number of cycles, so anywhere between 50-60Wh

If you need to use a miner that needs more than 50-60W, you are going to need to increase the size of your charger (be it a solar pannel or wind turbine or whatever) and the size of your batteries.