What size charge controller for my solar array?
Your charge controller sits between array and battery, and it has hard limits on three fronts: maximum PV input voltage, maximum input current, and rated charge current into the bank. Sizing means keeping your array inside all three across the whole temperature range your site sees.
Total panel wattage alone tells you very little. How the panels are wired - series versus parallel - determines the voltage and current the controller actually sees, and cold weather moves the voltage.
How it works
Voltage: string Voc rises as temperature falls (panel Voc temperature coefficients are negative), so the check that matters is worst-case cold-morning Voc against the controller's maximum input voltage. A string that is fine in July can exceed the limit in January.
Current and power: parallel strings add current against the controller's input limit, and the controller's rated charge current times battery voltage bounds how much array power it can actually use. Modest array oversizing is normal and manufacturers publish per-voltage array maximums; hard voltage and current limits, though, are never negotiable.
Common questions
MPPT or PWM?
MPPT converts excess array voltage into charging current and tolerates flexible string design; PWM effectively ties the array to battery voltage and wastes the difference. For anything beyond the smallest 12V systems, MPPT earns its price.
Why does cold weather raise panel voltage?
Solar cell voltage rises as cell temperature falls - the Voc temperature coefficient is negative. String sizing uses your site's design low temperature because the highest voltage of the year happens on the coldest clear morning.
Can my array wattage exceed the controller's rating?
Within the manufacturer's published array maximums, yes - the controller simply cannot exceed its charge current, so extra array mostly buys cloudy-day and shoulder-season harvest. Voltage and current input limits still bind absolutely.
What is a dual-tracker (multi-MPPT) controller for?
Independent inputs for arrays that differ - different orientations, shading, or panel types. Each tracker optimizes its own array instead of one compromise operating point.
String your actual panels against any controller in the builder and the cold-weather voltage, current, and charge-rate checks run live.
Open the builderThese guides are educational and qualitative on purpose - the numeric answers depend on your exact components, and the builder computes them with every formula shown. Always verify a final design with a licensed professional.