Off-Grid Solar System Sizing Calculator | Evergreen Off-Grid DIY Tool

Evergreen Off-Grid, LLC
Off-Grid Solar Sizing Calculator
Enter a design location or peak-sun-hours value, add your loads, select a battery-autonomy target, and set design margins. The tool estimates the PV array, inverter, MPPT charge controller, LiFePO₄ battery bank, battery BMS capability, and key battery-side DC wiring.
1) Location & System Preferences
For year-round off-grid use, use the lowest-production design month—not an annual average.
Autonomy is the time the battery can serve the loads with little or no solar input, so it is intentionally separate from peak sun hours.
The calculator prefers one controller when possible and recommends multiple only above this limit.
Location note: Lower peak sun hours increase the PV array required to replace daily energy. They do not directly change a user-selected “zero-solar” autonomy period. Local weather, winter solar, temperature, snow cover, and acceptable generator use should inform the autonomy selected.
Ampacity note: This tool uses a simplified copper-conductor ampacity ladder for preliminary guidance. Always verify conductor ampacity, temperature corrections, terminal ratings, voltage drop, overcurrent protection, and local code requirements.
2) Add Your Loads
Enter item name, quantity, watts, and hours per day. Leave watts blank to use a rough name-based estimate. Energy estimates for some cycling loads include a duty factor. Peak load conservatively assumes all entered loads may operate at once.
Item Qty Watts Hours/Day Daily Wh
Start with lights, refrigeration, computers, network gear, pumps, and other daily loads.
Results & Recommendations
All modeled capacity checks passed within the limits of this preliminary calculator.
Load Summary
Daily Energy
Peak Load
PSH Used
Solar & Power Hardware
Based on daily energy, design PSH, an overall production factor, and the selected PV design margin.
Continuous rating is selected above the conservative simultaneous peak. Surge is shown as a preliminary estimate only.
This is battery-side controller output current. Actual controller selection must also verify PV-array Voc, Isc, stringing, temperature, and controller input limits.
Auto-selected from estimated peak power and daily energy unless manually overridden.
Battery Bank
Battery storage is based on selected autonomy, inverter efficiency, battery discharge efficiency, usable depth of discharge, and battery reserve. It does not shrink automatically in a sunnier location because autonomy assumes little or no solar contribution.
Assumes an AC-heavy load profile, 90% inverter efficiency, 97% battery discharge efficiency, and 80% maximum design depth of discharge.
Example uses 12.8 V, 100 Ah LiFePO₄ modules. Confirm manufacturer series/parallel limits and use matched batteries, busbars, overcurrent protection, and equal-current-path wiring.
Compares estimated inverter DC current with the combined continuous BMS current of the parallel battery strings.
Installed capacity is rounded up to complete 12.8 V, 100 Ah modules.
Wiring & Protection Overview
The controller-current result is the MPPT-to-battery output circuit, not the PV-array input circuit. PV-input conductor and overcurrent sizing require module Isc, string count, series configuration, temperature-corrected Voc, and equipment ratings.
Reliability note: This is a preliminary energy-balance and autonomy calculator, not an hourly weather simulation. It does not model consecutive cloudy days, seasonal state of charge, snow cover, shading, battery temperature, generator operation, or loss-of-load probability.
Disclaimer: This calculator is provided for informational and educational purposes only. Results are estimates based on user inputs and simplified assumptions. Actual requirements vary with site conditions, equipment, manufacturer instructions, installation methods, and applicable codes. Consult qualified professionals and the authority having jurisdiction. Evergreen Off-Grid, LLC assumes no liability for design choices, installation errors, or damages arising from use of this tool.