Solar panels in series and in parallel: understanding strings

September 28, 2026 · 6 min read · Danilo Nascimento

How series and parallel connections change module voltage and current, what a string is, how it relates to the MPPT and why cold weather matters.

What a string is

A string is a row of modules connected in series: the positive of one goes to the negative of the next. The logic is the same as with batteries.

Modules in series

Adds up the voltage

41.5 V
41.5 V
41.5 V
≈ 125 V

10 modules × 41.5 V ≈ 415 V
Current equal to that of one module (≈ 13 A)
Fewer cables to the inverter

Strings in parallel

Adds up the current

String 1
Combiner box
String 2

2 strings × 13 A ≈ 26 A
Voltage equal to that of one string
The strings must be identical

The numbers you need to know

49.5 VVoc: no-load voltage, the module’s highest

41.5 VVmp: working voltage (maximum power)

13.9 AIsc: short-circuit current under test conditions

≈ 495 VVoc of a 10-module string

Illustrative values, measured at standard test conditions (STC).

The MPPT window

The inverter looks for the maximum power point through its MPPT. There are two different limits: the string Vmp must stay within the MPPT range, in the heat and in the cold, and the Voc must never exceed the maximum input voltage, not even on the coldest day.

With 10 modules, the Vmp stays within the MPPT range from hot to cold, and the Voc stays below the inverter limit.

Why cold raises the voltage

Module voltage rises as the temperature drops. The manufacturer states by how much with the Voc temperature coefficient, around −0.25 to −0.30 %/°C. The Vmp varies more, close to −0.35 to −0.40 %/°C; if the datasheet does not give that value, the Pmax coefficient can serve as an approximation, but near the limit it can change the minimum number of modules (from −0.35 to −0.40 %/°C, one example goes from five to six). Prefer the Vmp coefficient from the datasheet and confirm the result with the inverter manufacturer.

Voc of one module (49.5 V at 25 °C; coefficient −0.27 %/°C)

−10 °C (harsh winter)54.2 V

0 °C (cold morning)52.8 V

25 °C (standard condition)49.5 V

50 °C (hot day)46.2 V

70 °C (roof in summer)43.5 V

Calculate your string

The number of modules is not free: it sits between a minimum, to reach the MPPT range in the heat, and a maximum, so as not to exceed the maximum voltage or leave the MPPT range in the cold. Try it with the data of your equipment.

Parallel strings and shading

Strings on the same input: same number and model of modules, same orientation and tilt
Roof with two slopes (east and west): use separate MPPT inputs
With three or more strings in parallel, string fuses are usually used, grouped in the combiner box (check the module data and the standard)

Drawing your array

The diagram below shows two strings combined in a combiner box and connected to the inverter. Use it as a starting point to draw your roof.

Draw it in Editor Solar

This is Editor Solar itself, already loaded with the diagram from this article. Move the equipment, edit labels, connect new parts and export to PNG, SVG or PDF. It is free and runs right in your browser.

Two strings of 10 modules combined in the combiner box and connected to the inverter.

Try it: Split the strings across two MPPT inputs: remove the combiner box, connect each string straight to the inverter and label the connections “MPPT 1” and “MPPT 2”.

Ready-made templates: On-grid diagram with microinverters

Open this diagram in the full editor ↗

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