Battery Bank Sizing
The battery bank is the heart of an off-grid system and usually the biggest cost. Undersize it and you run the generator constantly; oversize it and you waste money on unused capacity. Sizing is a calculation, not a guess.
Chemistry changes the math
Lithium iron phosphate (LiFePO4) can be discharged to 80% or more of capacity and lasts thousands of cycles. Lead-acid should rarely go below 50% depth of discharge if you want reasonable lifespan. The same daily load therefore needs a much larger lead bank than lithium bank — the calculator applies the right limits per chemistry.
Autonomy and temperature
Autonomy days are how long the bank runs with no sun. Two to three days is common. Cold temperatures reduce usable capacity, especially for lead — the calculator applies environmental derating so a cold winter morning does not leave you dark.
Common questions
Lithium or lead?
Lithium costs more up front but lasts longer and discharges deeper, usually winning on lifetime cost. Lead suits tight budgets if sized correctly. Verify with your supplier.
What does "usable kWh" mean?
Nominal capacity minus the portion you cannot safely use (the depth-of-discharge limit). Usable kWh is the number that matters for your daily load.