Find the safe maximum panels per string for your state’s winter low temperature — the #1 inverter warranty issue in residential solar.
Selects default temperature coefficients below — you can fine-tune them.
From panel spec sheet — labeled “Voc”
Enter as negative (e.g., −0.30). Labeled “α(Voc)” or “Temp. coefficient of Voc”
From panel spec sheet — needed for MPPT minimum check
Labeled “α(Vmp)” or “Temp. coefficient of Vmp” — usually more negative than Voc coefficient
Max DC input voltage — from inverter specs
Minimum MPPT start voltage — from inverter specs
Max MPPT input voltage — usually = Vmax or slightly less
Auto-filled for Colorado. Override for your specific micro-climate.
String Sizing Result
✓ 11 Panels Per String — Safe
Max panels per string
11
A string of 11 panels is within NEC limits for your location. Cold-day string Voc: 553V out of 600V Vmax (47V safety margin, 7.9%). MPPT minimum satisfied: 353V ≥ 200V at peak heat.
Cold-Day Voc (Voltage Spike Risk)
At -18°C, Voc rises by 12.9%: 44.5V × 1.129 = 50.2V per panel
Formula: 44.5V × [1 + (-0.3%/°C) × (-18°C − 25°C)]
Maximum Panels per String (Vmax Limit)
floor(600V ÷ 50.2V) = 11 panels
String cold-day Voc: 553V (leaves 47V safety margin = 7.9% headroom)
Hot-Day Vmp (MPPT Minimum Check)
Cell temp at 38°C ambient: ~63°C. Vmp drops by 13.3%: 37V × 0.867 = 32.1V per panel
Minimum panels for MPPT start: ceil(200V ÷ 32.1V) = 7 panels
✓ Max string (11 panels) satisfies MPPT minimum
Recommended string length
11 panels
Cold-day string voltage
553V / 600V
7.9% headroom
For your panel Voc of 44.5V in Colorado (design min -18°C)
| Inverter Vmax | HJT −0.25%/°C | TOPCon −0.30%/°C | PERC −0.34%/°C | Legacy −0.40%/°C |
|---|---|---|---|---|
| 480V | 9 | 9 | 9 | 9 |
| 600V | 12 | 11 | 11 | 11 |
| 800V | 16 | 15 | 15 | 15 |
| 1000V | 20 | 19 | 19 | 19 |
Highlighted cell = your current selection. Values are maximum panels per string before temperature correction.
| Panel | Wattage | Voc | Vmp | α(Voc) | Tech |
|---|---|---|---|---|---|
| Jinko Tiger Neo ↗ | 430W | 48.8V | 40.9V | -0.29%/°C | TOPCon |
| LONGi Hi-MO 7 ↗ | 445W | 47.2V | 39.8V | -0.3%/°C | TOPCon |
| Trina Vertex S+ ↗ | 425W | 48.2V | 40.5V | -0.3%/°C | TOPCon |
| Q CELLS Q.PEAK DUO ↗ | 400W | 46.4V | 39V | -0.35%/°C | PERC |
| REC Alpha Pure-R ↗ | 430W | 43.3V | 36.9V | -0.24%/°C | HJT |
| Panasonic EverVolt HK ↗ | 430W | 43.5V | 36.7V | -0.24%/°C | HJT |
Click a row to load its specs into the calculator. Always verify against the official spec sheet for your exact panel model and wattage.
String Sizing Guide 2026
Detailed walkthrough of all formulas, NEC compliance, and examples
DC-to-AC Ratio Guide
How many panels vs. inverter capacity — clipping loss analysis
Wiring Guide 2026
Series vs. parallel wiring, wire gauge, rapid shutdown compliance
Microinverters vs. String
Avoid string sizing entirely — microinverters are one panel per inverter
Solar ROI Calculator
Payback period and 25-year savings by state
How to Compare Solar Quotes
Ask your installer to show you their string sizing calculation
This calculator uses simplified ASHRAE design temperatures and NOCT-based cell temperature estimates. Always verify with the actual panel spec sheet and your installer’s design software (Aurora Solar, PVSyst, or HelioScope). NEC 2023 Article 690 governs solar string sizing — your local AHJ may have additional requirements.