What they are referring to is... and I quote...
"Picture yourself in pristine lagoons and allow the power of the sun, tides and wind to replenish your cruising. Motor away from distant fuel docks of unknown diesel quality without bating an eye. Remove your portion from our oil burden while silently cruising into distant harbors. Live the Solidnav shift, change your world. "
This is charging a battery, then running constant loss on the battery, and no-doubt having to compete with the sort of energy delivery I calculated.
Where does the energy I describe come from?...
There is just not enough energy stored in the battery bank, this side of sanity.
You do not yet understand how these systems work. They do not need the batteries to see the reduced fuel costs and the use of batteries can remove the need for diesel.
The Solidnav system recommends using windmill generator, solar, tow drogue generator, and regenerative power under sail, to achieve the "Solidnav Shift" with no diesel. If you are sailing away from the diesel pumps you can be charging the batteries. That would be the same battery bank you could use to run other, or all, electrical items on the boat.
This "Regenerative power" is produced whenever the system is on, and the boat is under sail, moving fast enough to cause the propeller to rotate. This rotation causes the electric motor to act as a generator. You can adjust how much charging occurs once you are above the minimum speed required to generate.
This means that if winds are light you might discharge the bank to add to the sailboats speed and then recharge later when the wind picks up. It would be a different way of sailing which I expect would take some getting used to.
And the assumptions you used for your calculations are incorrect which is why your calculations and understanding appear insane. A little more research should have you seeing why these drive systems are so much more efficient. Maybe start here: solidnav.com/faqs.htm