Boondocking Power Calculator

This calculator sizes an off-grid solar and battery setup from three usage numbers and a battery chemistry choice. Battery Type has the single largest real effect on Battery Bank Size of anything in this calculator, even though a small nudge to it can't show that: switching from the default Lithium/LiFePO4 (80% depth of discharge) to Lead-Acid (50%) raises Battery Bank Size from 938 Ah to 1,500 Ah at the default usage -- 60% more capacity needed, because a lead-acid bank can't be drained as deeply without shortening its life. Daily Energy Usage and Days Off-Grid move Battery Bank Size by an identical proportion, since both are pure linear multipliers of the same battery-sizing formula. Daily Energy Usage and Peak Sun Hours have an exactly equal and opposite effect on Solar Array Size, since one sits in the numerator and the other in the denominator of the same ratio -- Days Off-Grid and Battery Type play no role in solar sizing at all, since panels only need to replenish one day's usage, not the whole trip.

Estimated System Cost tells a more surprising story than Battery Bank Size alone: despite needing a much bigger bank, Lead-Acid actually costs less overall ($1,800 vs. $2,307 at the default usage), because it's cheap enough per amp-hour to more than offset the extra capacity required. Daily Energy Usage has the largest effect on System Cost of the three numeric inputs, since it scales both the battery and solar halves of the cost together. This is a rough sizing estimate -- it doesn't account for charge controller losses beyond the flat 80% system efficiency, battery temperature effects, or cloudy-day reserve margin.