Offgrid Solar System Sizing Tool



This tool recommends solar and battery system sizes based on device power consumption and location.

Voltaic Systems Options

Device power consumption: .

equivalent sun: hours per day ( ), south facing, angled at °1

Solar Panel Performance in December

A power ratio of at least 1.5 is recommended.2
PanelPower Ratio
Power Available = Panel Power * Equivalent Sunlight Hours
Power Consumed = System Power * 24 hours

Battery Capacity

Batteries should be sized to run the device for at least 4 days with no sun in most situations.3
BatteryDays Runtime

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  1. We recommend angling the panel to produce the most power in the worst month of the year, typically December in the northern hemisphere.
  2. This accounts for system losses as well as extended days of below average sunlight. Increasing panel size beyond a 1.5 power ratio decreases risk of an outage. Shade or other obstructions may require larger panels.
  3. Most places experience a few long stretches of below average sunlight or temperatures below freezing. In these situations, the battery may receive little or no charge
  4. 1 watt(s) x 24 hours = 24 watt-hours per day
  5. To make calculations easier, we equate the sun's path across the sky to time spent directly in front of the solar panel, or equivalent direct hours.
  6. Power Ratio = Power Generated / Power Consumed
  7. Number of days the system could run on only a battery