BTR EnerjiPV string size calculator: cold Voc, hot Vmp and the MPPT window
Enter your module and inverter values and see the longest and shortest safe string. No sign-up, and the values you enter stay in your browser.
Module
Inverter and temperature
Check the values: Vmp must be below Voc, the coefficient negative, and the MPPT lower limit below the upper limit.
This inverter gives no safe range with this module: the shortest string is longer than the longest string. Consider another inverter voltage class or module.
Tracker tables that fit:
How is it calculated?
- Longest string: the module's open-circuit voltage at the lowest temperature must not exceed the inverter's maximum DC voltage. Cold Vmp must also stay within the MPPT upper limit.
- Shortest string: Vmp drops on a hot cell in summer and must not fall below the MPPT lower limit.
- Temperature effect: Voc = Voc,STC + β × Voc,STC × (T − 25). Vmp is assumed to change with the same V/°C slope.
The defaults are for a 710 W module (JKM710N) and a 1500 V inverter class; enter your own datasheet values. Our simulator uses the same formulas. The default design temperature is −10 °C; if your site is colder, enter your own value.
Worked example and charts: 1500 V string sizing and cold Voc. The list of fitting tables follows the rule that a table divides into whole strings (such as 1P56 = 2 × 28).
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Frequently asked questions
Which design temperature should I enter?
The lowest daytime temperature at the site. Voltage only appears with light, so night-time values are not needed. Without local data, −10 °C is a common starting point; cold climates need a lower value.
What happens if the 1500 V limit is exceeded?
The inverter and module voltage ratings are exceeded; equipment can be damaged and warranty cover may be disputed. That is why the longest string is set by cold Voc.
Why does the shortest string matter?
Voltage falls as the module heats up in summer. If the string is too short, voltage drops below the MPPT lower limit and the inverter curtails or stops.
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These calculators are for preliminary design and are not binding; verify final design with equipment datasheets and site data.