PV string sizing calculator

Check temperature-corrected module voltage against inverter limits, and parallel-string current against one tracker’s ratings.

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10per string
2on one tracker
MPPT windowHot Vmp: 353.8 VCold Vmp: 471.5 VCold Voc: 549 VDC limit 600 V

Shaded MPPT window: 200–550 V. Dashed line: 600 V absolute limit. Lines from top: hot Vmp, cold Vmp, cold Voc.

  • Cold open-circuit voltageWithin limit549 V
  • Hot MPP voltageWithin limit353.8 V
  • Cold MPP voltageWithin limit471.5 V
  • Operating currentWithin limit25 A
  • Short-circuit currentWithin limit27.5 A

Edit modules or strings to see the voltage and current checks change. The form below contains every design assumption.

Example values
Module data at 25°C
V
V
%/°C

Use the voltage coefficient, not the power coefficient.

%/°C
A
A
Temperature and arrangement
°C

Cell temperature can exceed ambient temperature.

°C

Illustrative factor. Set from your manufacturer and applicable design rules; not a universal code factor.

One inverter tracker
V
V
V
A
A

String screening

Within entered limits

10 modules × 2 parallel strings on one tracker.

Modules per string from voltage limits
6–10
Maximum strings from current limits
2

Screening only. Startup voltage, power rating, tolerances, bifacial gain, irradiance and local installation rules need separate checks.

How it’s calculated
  1. Cold module Voc = Voc × [1 + βVoc × (Tcold − 25)]=50 × [1 + -0.0028 × (-10 − 25)]=54.9 V
  2. Hot module Vmp = Vmp × [1 + βVmp × (Thot − 25)]=42 × [1 + -0.0035 × (70 − 25)]=35.39 V

This arrangement meets the five entered voltage and current limits.

Tip: No current temperature model is included; the current multiplier must cover the design conditions you intend to screen.

Method and boundaries

Cold Voc protects the inverter’s absolute DC input limit. Cold and hot Vmp screen the operating voltage window. A string can remain below the absolute maximum yet fall outside the MPPT window. Check the rated-power window and startup requirements separately when the manufacturer distinguishes them.

Keep absolute voltage separate from MPPT

Cold Voc protects the inverter’s absolute DC input limit. Cold and hot Vmp screen the operating voltage window. A string can remain below the absolute maximum yet fall outside the MPPT window. Check the rated-power window and startup requirements separately when the manufacturer distinguishes them.

Use cell temperature and the right coefficient

The linear correction uses the module voltage at 25°C and its voltage temperature coefficient in percent per degree Celsius. Enter the separate Voc and Vmp coefficients from the module documentation. A power coefficient is not a Vmp coefficient. Cell temperature can be substantially above ambient air temperature in sunshine.

Parallel strings add current

Series-connected modules add voltage; identical parallel strings add current. Enter operating and short-circuit limits for one tracker rather than an inverter-wide sum. The current multiplier is a deliberate design assumption for irradiance and other corrections. Its example value is not a universal electrical-code requirement.

PV string sizing examples

Ten modules inside the entered limits

Cold open-circuit voltage is 549 V and hot maximum-power voltage is 353.85 V. Operating current with two strings and the entered multiplier is 25 A. The result is Within entered limits. This describes only the five checks, not installation approval.

String screening Within entered limits Open in the calculator

One more module exceeds the DC limit

Eleven modules give 603.9 V cold open-circuit voltage against a 600 V limit. The result is Outside entered limits even though the operating voltages may still fall inside the MPPT window.

String screening Outside entered limits Open in the calculator

Questions about PV string sizing

Can a passing result approve the installation?

No. It screens only the entered limits. Protection, conductor ratings, module tolerances, startup voltage, DC power, mounting conditions and local installation rules remain separate checks.

Why are there two voltage coefficients?

Open-circuit voltage and maximum-power voltage do not necessarily change at the same rate with temperature. Use the module manufacturer’s values for each.

Does this choose a module or inverter for me?

No. Enter verified datasheet limits for the specific equipment and operating conditions. The displayed minimum and maximum module counts are an intersection of voltage constraints, not a catalogue recommendation. The current check is independent and can rule out a parallel arrangement even when its voltage is acceptable.

Limits of this result

  • Checks apply to identical modules and strings on a single tracker, using linear voltage-temperature coefficients relative to 25°C.
  • A passing result is not an installation approval. Check startup voltage, power rating, module tolerances, bifacial gain, protection, cables and local requirements separately.
  • No current temperature model is included; the current multiplier must cover the design conditions you intend to screen.

Related guides

Sources

  1. Requirements for PV modules per input (opens in a new tab) SMA, accessed 2026-10-01
  2. Planning of a PV Generator, sections 3.2.1 and 3.2.2 (opens in a new tab) (PDF) SMA, accessed 2026-10-01