Solar PV String & Array Sizing Calculator
Enter panel and inverter specifications to get the safe series string length with a temperature-corrected cold-day Voc check, MPPT window compliance, and total array kWp. Nothing uploaded.
Panel Specifications
Inverter Specifications
Design Conditions
String Sizing Results
Always verify the final design with a qualified electrician or solar designer. Cold-day Voc must never exceed the inverter maximum input voltage.
Learn more: PV string sizing for solar inverters
How many solar panels can go in series safely
The maximum number of panels in series is determined by the inverter's maximum input voltage. You multiply the open-circuit voltage (Voc) of one panel by the number of panels in series to get the total string voltage. That voltage at cold-day temperature must never exceed the inverter's maximum input voltage limit, or the inverter will be destroyed. This calculator accounts for the temperature coefficient of the panel - Voc gets higher in cold weather.
Understanding the cold-day Voc temperature coefficient
Solar panels have a negative temperature coefficient for voltage, typically around -0.28% per degree Celsius below 25°C standard test conditions. This means a panel rated 37V at 25°C will produce roughly 42-43V on a cold day at -10°C. The colder the weather, the higher the voltage. Your minimum expected temperature location determines the worst-case string voltage, which must not exceed the inverter maximum input voltage for safety.
The MPPT window and why it matters
The MPPT (Maximum Power Point Tracking) voltage window is the range within which an inverter extracts maximum power from the solar array. If your string voltage falls below the MPPT minimum, the inverter cannot start. If it falls above the MPPT maximum, the inverter clips output or switches off. The string's operating voltage at maximum power (Vmp) must sit comfortably within this window year-round for optimal energy harvest. Too many panels and you overshoot the window in summer; too few and you fall short in winter.
FAQ
What if my cold-day Voc exceeds the inverter maximum?
Do not install that string. Exceeding the maximum input voltage will damage the inverter permanently. Reduce the number of panels per string, or relocate to a warmer climate zone. Always verify your design with a qualified solar electrician before installation.
How do I know my panel's temperature coefficient?
Check the datasheet provided by the manufacturer. It is listed as a percentage per degree Celsius, usually in the electrical specifications section. Most modern panels are between -0.25% and -0.35% per °C. If you cannot find it, use -0.28% as a safe average.
Can I put multiple strings in parallel?
Yes - parallel strings add current, not voltage. Each string carries the same voltage, but currents add. The total current must not exceed the inverter's maximum input current. The calculator accounts for this when you enter the number of parallel strings.