Series, Parallel, and Series-Parallel Circuits in PV Arrays

Why Circuit Configuration Matters in PV Arrays

Every PV array is a combination of individual modules connected together to reach the voltage and current levels a system needs. The way those modules are wired—series, parallel, or a mix of both—determines what voltage and current the array produces. Understanding these configurations is not just academic: sizing a string incorrectly can damage an inverter, produce no power at all, or create a serious safety hazard. NABCEP exam content and field practice both require you to predict and verify these values before energizing any circuit.

Series Circuits: Adding Voltage

When modules are wired in series, the positive terminal of one module connects to the negative terminal of the next. Electrons have only one path through the circuit, so the same current flows through every module.

Key rules for a series string:

• Total open-circuit voltage (Voc) = sum of individual module Voc values
• Total short-circuit current (Isc) = Isc of a single module (unchanged)
• Total power = Voc(total) × Isc

For example, three 12 V / 1 A modules in series produce 36 V and 1 A. Whenever one module in a series string is shaded or fails, current through the entire string drops because there is only one current path.

Parallel Circuits: Adding Current

When modules are wired in parallel, all positive terminals connect together and all negative terminals connect together. Each module has its own current path back to the load.

Key rules for a parallel bank:

• Total Voc = Voc of a single module (unchanged)
• Total Isc = sum of individual module Isc values
• Total power = Voc × Isc(total)

Two 12 V / 1 A modules in parallel produce 12 V and 2 A. A failed or shaded module reduces total current but does not kill output entirely—the remaining modules still conduct.

Series-Parallel (Series-Parallel) Arrays

Real residential and commercial arrays combine both configurations. A common shorthand is mSmP, where m is the number of modules per string (series) and the second m is the number of strings (parallel). A 2S2P array has two strings of two modules each.

Key rules for a series-parallel array:

• Total Voc = Voc(one module) × number of modules in series
• Total Isc = Isc(one module) × number of parallel strings
• Total power = Voc(array) × Isc(array)

For 12 V / 1 A modules in a 2S2P configuration: Voc = 24 V, Isc = 2 A, power = 48 W.

Measuring with a Digital Multimeter

A digital multimeter (DMM) is your primary diagnostic tool in this lab. Two measurements matter most:

• Voc (open-circuit voltage): Set DMM to DC volts, leave the circuit output unloaded (open), and place probes across the output terminals. Polarity matters—red probe to positive, black to negative. A negative reading means reversed polarity, not a damaged meter.
• Isc (short-circuit current): Set DMM to DC amps (or milliamps for low-current simulators), then connect the DMM in series with the circuit as the only load. On low-voltage trainers this is safe; never short high-voltage field arrays.

Record both the predicted value and the measured value in your lab log. A result within ±5% of prediction is acceptable and confirms your wiring is correct.

Diagnosing Faults: Reversed Polarity

A reversed module in a series string is one of the most common wiring faults in the field. When one module is flipped, its voltage subtracts from the string instead of adding. For three 12 V modules in series, one reversed module yields 12 V + 12 V − 12 V = 12 V at the output instead of 36 V.

To locate a reversed module:

1. Measure Voc of the complete string—if it is lower than expected, suspect a reversed module.

2. Working safely with a partner, measure voltage across each module individually while the string is open-circuit.

3. A module showing a negative voltage reading (red probe at its positive label) is wired backward.

4. Correct the connection and re-measure the string Voc.

Document every step in your lab log. Troubleshooting is a professional skill graded as seriously as correct predictions.

Safety for This Lab

• Safety glasses must be on before any circuit is built. Flying terminal clips are a real hazard.
• Insulated gloves (Class 00 minimum for these low-voltage trainers) are required whenever you are connecting or disconnecting live circuits.
• The trainer boards in this lab are low-voltage (12 V nominal), but good habits here carry over to field systems that can exceed 600 V DC.
• Lockout/tagout (LOTO): Even on trainers, disconnect power before reconfiguring wiring. Form the habit now—a 600 V DC array does not forgive lapses.
• Inspect every jumper cable for damaged insulation before use. Set damaged cables aside and notify the instructor.
• Never exceed the current rating of the DMM's fused input. Check the fuse rating before measuring current.
• No food or drink at the workstation.