How to Size Solar Panels for Off-Grid 12V / 24V Systems
Sizing an off-grid solar setup requires balancing daily energy usage against available sunlight (Peak Sun Hours). A common mistake is using total daylight hours (e.g. 10 hours of sun) instead of Peak Sun Hours (PSH), which measures the equivalent hours of 1,000 W/m² solar intensity.
The Solar Sizing Formula
Daily_Energy_Required_Wh = Appliance_Wh_per_Day × Safety_Buffer
Required_Solar_Watts = Daily_Energy_Required_Wh / Peak_Sun_Hours
MPPT_Current_Rating_Amps = Installed_Solar_Watts / Battery_Float_Voltage
Required_Solar_Watts = Daily_Energy_Required_Wh / Peak_Sun_Hours
MPPT_Current_Rating_Amps = Installed_Solar_Watts / Battery_Float_Voltage
Why Roof-Mounted Panels Require a Higher Buffer
When solar panels are mounted flat on a campervan, caravan, or boat roof, they rarely face the sun at the optimal perpendicular 90° angle. Furthermore, heat build-up under vehicle roofs reduces solar cell efficiency by approximately 0.4% per °C above 25°C. For this reason, a 25% to 35% buffer is essential to ensure your batteries stay charged during cloudy periods.