Configure system
Controller type
MPPT controllers are more efficient (93-99%) and can accept higher input voltages.
Panel specifications
Typically -0.25% to -0.35%. Found on panel datasheet.
Wiring configuration
Total panels: 4 (4 in series × 1 in parallel)
Battery & temperature
Coldest expected temp
Cold temps increase Voc. Use your location's record low.
Margin above cold weather Voc for the voltage rating. At least 5%, as in the project hub.
Controller requirements
Min voltage rating
228V Cold weather Voc: 216.8V
Peak output current
33.3A Controller clips if rated lower
WARNING Based on -10 °C
Use your area's record low. Pick a controller rated at or above the recommended rating. PWM controllers pass full array current: size them at 125% of Isc.
Safety and termsChecked at -10 °C, not your coldest morning. Set your area's record low to finish this check.
Array summary
Total 1,600W Voc 198.0V Cold 216.8V
Array summary
Total power
1,600W
Voc (STC)
198.0V
Voc (cold)
216.8V
Understanding charge controller sizing
MPPT vs PWM
MPPT
Higher efficiencyActively tracks the maximum power point, converting higher panel voltage to optimal charging current.
- Up to 10-30% more power vs PWM
- Flexible panel voltage selection
- 93-99% conversion efficiency
PWM
Lower costDirectly connects panels to batteries, requiring panel voltage to roughly match battery voltage.
- Simpler circuitry, lower price
- Panel Voc must match battery voltage
- 70-80% conversion efficiency
Key formulas
For MPPT
Min voltage rating
Array Voc × (1 + temp_coeff × (lowest_temp - 25°C)) × 1.05 or more, rounded up
Min current rating
(Total Array Watts / Battery Voltage) × 1.25
For PWM
Min voltage rating
Array Voc (panels must match battery voltage)
Min current rating
Total Isc × 1.25
Cold weather considerations
Cold weather matters. Solar panel voltage increases in cold weather. A typical temperature coefficient of -0.3%/°C means that at -10°C (compared to 25°C standard test conditions), Voc increases by about 10%.
Always size your controller for the coldest expected temperature.
Last updated: January 7, 2026
