How many panels per string? Voc, Vmp and temperature in practice

September 29, 2026 · 6 min read · Danilo Nascimento

See how to work out the minimum and maximum panels per string from Voc, Vmp and temperature in four example scenarios, and test your own data in the calculator.

Temperature changes the voltage

This article applies, in complete examples, what solar panels in series and parallel explains: the number of panels in a string has a minimum and a maximum, and both depend on temperature. In the cold the panel voltage rises; in the heat it falls.

54.8 VVoc of one panel at −15 °C (49.5 V at 25 °C)

47.3 VVmp of one panel at −15 °C (41.5 V at 25 °C)

35.0 VVmp of one panel with the cell at 70 °C

That is why the calculation uses the worst case for each limit: the highest possible voltage (cold) against the inverter limit, and the lowest possible voltage (heat) against the start of the MPPT range.

The data that goes into the calculation

Panel Voc and Vmp

datasheet

Voc is the no-load voltage; Vmp is the voltage at the maximum power point. Both are given at 25 °C, under test conditions.

Temperature coefficients

datasheet

In %/°C. Voc usually has about −0.27 %/°C and Vmp about −0.35 %/°C: Vmp varies more.

Site temperatures

climate

The lowest air temperature (a cold dawn) for Voc, and the hot cell temperature, well above the air, for Vmp.

Maximum voltage and MPPT

inverter

The absolute input limit, which Voc must never exceed, and the range in which the inverter tracks maximum power.

The two calculations

With panels of 49.5 V Voc and 41.5 V Vmp, a 600 V inverter with an MPPT range of 160 to 550 V, at a site that reaches −15 °C and with cells at 70 °C in summer:

600 Vinverter maximum voltage÷54.8 VVoc per panel in the cold=10.9 → 10maximum, always round down

160 Vstart of the MPPT range÷35.0 VVmp per panel in the heat=4.6 → 5minimum, always round up

The string can have 5 to 10 panels. In practice choose a value with some margin from both limits, so you do not depend on an extreme day.

Four scenarios

The same panel calls for different numbers depending on the climate and the inverter. Here is the maximum number of panels in each case:

Maximum panels per string (the minimum is between 5 and 6)

Cold site: lowest temperature −15 °C5 to 10

Standard: lowest 0 °C, cell at 70 °C5 to 11

Hot site: lowest 10 °C, cell at 75 °C5 to 11

500 V inverter with 200 to 450 V MPPT6 to 9

Test your own numbers

Replace the data with that of your panel’s and inverter’s datasheets and with your site’s temperatures. The calculator shows the voltage at each extreme, the panel range and whether the chosen number meets the stated voltage limits.

Common mistakes

Do

Use the site’s lowest temperature for Voc and the hot cell for Vmp
Round the maximum down and the minimum up
Use the Vmp coefficient from the datasheet, not only the Voc one
Confirm the limits with the inverter manufacturer

Avoid

Add up the voltages at 25 °C and stop there
Push the Voc right up to the inverter limit: a cold morning may exceed it
Forget that the cell heats up well above the air temperature
Mix different panels in the same string

Draw it in Editor Solar

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A string of 10 panels at a cold site: the cold Voc stays below the inverter limit and the hot Vmp stays inside the MPPT range.

Try it: Change the number of panels to 11 and redo the cold Voc calculation: does the string still respect the inverter’s 600 V? Write the result in the diagram text.

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