At the SSCA Gam in the Rhode River south of Annapolis, the featured speaker Nigel Calder presented a wealth of data on power management which he, and others, have collected and analyzed.
Most shocking was the real
costs of recharging your batteries from either main engine or from onboard generators. I won't get into specifics here, but suffice it to say that we all tend to WAY WAY WAY underestimate the real costs. If you factor in the cost of POL (fuel, oil, etc.), the amortization cost of running an internal combustion engine, the most efficient "window" for charging, engine/generator loading, etc., etc., you will find that the real costs are enormous for most of us in the way we use our boats.
One takeaway...the most important one: if you're using modern AGM or TPPL or gelled batteries, the best thing you can do to cut costs from engine-driven charging is to fit the largest alternator you can. Also, fit the largest solar panels you can. Wind generators are good -- especially in windy places -- but they require maintenance, while solar panels are like the energizer bunny that just keeps on giving...for at least 20 years.
: MORE ONBOARD CHARGING CAPACITY = LOWER OVERALL OPERATING COSTS
If you have AGMs or TPPL batteries aboard, the likelihood is that you cannot possibly fit all the charging capacity which would be desirable.
So, do the best you can: put the largest alternator/battery charger/solar panels aboard you can reasonably accommodate.