Solar string voltage calculator (series & parallel)
Check that your solar panels wired in series and parallel stay under your charge controller's max PV voltage on the coldest day, and see array voltage, current and watts.
Results
| Cold-weather string Voc | 74.1 V |
|---|---|
| Within controller limit? | Yes (74% of limit) |
| String Vmp (operating voltage) | 55.5 V |
| Array short-circuit current | 11.5 A |
| Array rated power | 600 W |
About this calculator
Solar panel voltage rises as panels get colder. A string that sits comfortably below your MPPT controller's voltage limit on a summer afternoon can exceed it on a clear, freezing morning, which is exactly when the sun first hits cold panels. Overvoltage is the most common way people destroy charge controllers.
This calculator applies your panel's temperature coefficient to the record low temperature at your site. You get the worst-case string voltage, plus the array's operating voltage, current and power for whatever series and parallel layout you choose.
How to use it
- Copy Voc, Vmp, Isc and the Voc temperature coefficient from the panel's datasheet or label.
- Enter how many panels you'll wire in series per string and how many strings in parallel.
- Enter the coldest temperature the site has ever recorded, not the average winter low.
- Confirm the cold Voc is below your controller's maximum PV input voltage, ideally with 5-10% margin.
The formula
Cold Voc = Voc × panels in series × [1 + (coefficient ÷ 100) × (Tmin°C − 25)].
Example: three panels at 22.5 V, −0.28 %/°C, at −10 °C: 67.5 × (1 + 0.0028 × 35) ≈ 74.1 V.
Series wiring adds voltage. Parallel wiring adds current. Array watts = panel W × total panels.
Worked example (default values)
Inputs
| Panel rated power | 200 W |
|---|---|
| Panel open-circuit voltage (Voc) | 22.5 V |
| Panel max-power voltage (Vmp) | 18.5 V |
| Panel short-circuit current (Isc) | 11.5 A |
| Panels in series per string | 3 |
| Parallel strings | 1 |
| Record low temperature at the site | 14 °F |
| Voc temperature coefficient | -0.28 %/°C |
| Controller max PV input voltage | 100 V |
| Battery bank voltage | 12.8 V |
Results
| Cold-weather string Voc | 74.1 V |
|---|---|
| Within controller limit? | Yes (74% of limit) |
| String Vmp (operating voltage) | 55.5 V |
| Array short-circuit current | 11.5 A |
| Array rated power | 600 W |
Tips and common mistakes
Series or parallel? Series keeps current low, so thinner cable and less loss over long runs, and MPPT controllers work best with a higher input voltage. Parallel tolerates partial shading better, because one shaded panel doesn't drag down a whole string. Many RV setups use 2-3 panels in series, then parallel those strings.
Mixing panels: panels within a series string should have matching current (Imp). Strings in parallel should have matching voltage (Vmp).
Frequently asked questions
How many solar panels can I put in series?
As many as you can while the cold-weather Voc stays below the controller's max PV voltage. For a 100 V controller and 22.5 V panels, that's usually 3 in cold climates and sometimes 4 in warm ones. Check with the calculator.
Why does voltage go up in the cold?
Silicon cells produce higher voltage at lower temperature, typically 0.25-0.35% more per °C below 25 °C.
Does Isc matter for the controller?
Yes. Many MPPT controllers also list a maximum PV short-circuit current. Parallel strings add to it.
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Estimates for planning only, based on the assumptions shown. Real-world performance varies with equipment, temperature and installation. Updated October 19, 2026. See our methodology.