Solar Panel Wiring Diagrams: Series vs Parallel Explained

Whether you are building a small off-grid power system for a garden shed, a camper van solar setup, or a full rooftop installation, one of the first decisions you will face is how to wire your solar panels together: in series, in parallel, or a combination of both.

The wiring configuration you choose has significant consequences for the voltage, current, and behaviour of your system. This guide explains the differences clearly, with practical wiring examples and guidance on which configuration suits different charge controllers and inverters.

A Quick Refresher: Voltage, Current, and Power

Before diving into configurations, remember two things from basic electricity: In a series circuit, voltages add but current stays the same. In a parallel circuit, currents add but voltage stays the same. Power is always voltage multiplied by current (P = V x I).

A solar panel's electrical output is characterised by its open-circuit voltage (Voc), short-circuit current (Isc), maximum power point voltage (Vmp), and maximum power point current (Imp). For wiring calculations, we work with Vmp and Imp.

Example panel specifications: Vmp = 18V, Imp = 5.5A, Power = 18 x 5.5 = 99W (approximately 100W panel).

Series Wiring

How It Works

In a series configuration, the positive terminal of each panel connects to the negative terminal of the next. The result is that voltages add up while the current remains the same as a single panel.

Using our example panel (Vmp = 18V, Imp = 5.5A): With 2 panels in series: Vmp = 36V, Imp = 5.5A, Total power = 198W. With 4 panels in series: Vmp = 72V, Imp = 5.5A, Total power = 396W.

When to Use Series Wiring

Series wiring is ideal when you need higher voltage output — typically for MPPT charge controllers or grid-tie inverters that require input voltages above 24V or 48V. Higher voltage also means lower current for the same power, which reduces resistive losses in the cables connecting panels to the charge controller (thinner wire can be used, or the same wire carries less loss over long distances).

The Shading Problem

The critical drawback of series wiring is shading sensitivity. If even one cell in one panel of a series string is shaded, the current through the entire string is limited to the shaded cell's output. A single bird dropping, a passing cloud, or a chimney shadow can significantly reduce the output of all panels in the string.

Modern solutions include bypass diodes (built into most panels) which allow current to route around shaded cells, and power optimisers/microinverters which manage each panel independently.

Parallel Wiring

How It Works

In a parallel configuration, all panel positive terminals connect together (to the positive bus) and all negative terminals connect together (to the negative bus). Currents add while voltage remains the same as a single panel.

Using our example panel: With 2 panels in parallel: Vmp = 18V, Imp = 11A, Total power = 198W. With 4 panels in parallel: Vmp = 18V, Imp = 22A, Total power = 396W.

When to Use Parallel Wiring

Parallel wiring is suitable for systems using a PWM charge controller (which requires panel voltage to be close to battery voltage — typically 12V or 24V), or when the physical distance between panels and charge controller is short and cable losses are manageable.

Parallel wiring is more tolerant of shading on individual panels — if one panel is shaded, only that panel's output decreases, while the others continue producing at full capacity.

The Current Handling Challenge

The downside of parallel wiring is high current. Four 100W panels in parallel produce 22 amps — requiring heavier gauge cable and larger circuit breakers than a series configuration producing the same power at higher voltage. This increases cost, especially for runs of 5 metres or more.

Blocking diodes or fuses should be used in each parallel branch to prevent a high-output panel from reverse-charging a shaded or weaker panel. Most modern charge controllers have reverse current protection built in, but individual fuses per string are still good practice for safety.

Series-Parallel (Combination) Wiring

For larger systems with many panels, a combination approach achieves a balance of voltage and current. Panels are first wired in series to create strings, and then multiple strings are wired in parallel.

Example: 8 x 100W panels (Vmp = 18V, Imp = 5.5A). Wire into 2 strings of 4 panels each. Each string: Vmp = 72V, Imp = 5.5A. Two strings in parallel: Vmp = 72V, Imp = 11A, Total power = 792W.

This combination gives you the higher voltage needed for an MPPT controller or inverter while keeping current manageable. The strings must contain equal numbers of identical panels for balanced operation.

Matching Wiring to Your Charge Controller

PWM Charge Controllers

PWM (Pulse Width Modulation) controllers are simple, cheap, and effective for small systems. They regulate charging by rapidly switching the connection between panels and battery. Their input voltage range is typically 12–30V, which means your panel array voltage must be within this range. For a 12V battery system, use panels or series strings with Vmp around 17–22V. Parallel wiring is usually required to stay within the PWM controller's input range.

MPPT Charge Controllers

MPPT (Maximum Power Point Tracking) controllers are more sophisticated. They continuously find and operate at the panel array's maximum power point, converting higher input voltages down to the battery charging voltage with high efficiency (typically 93–97% efficient vs 70–80% for PWM). MPPT controllers accept a wide input voltage range (typically 12–100V or more depending on the model) and deliver maximum energy harvest — especially valuable in cold weather, partial shading, and non-optimal conditions.

MPPT controllers make series wiring practical and efficient. A 48V system using 4 panels in series (72V input) into an MPPT controller charging a 48V battery bank is a very common professional off-grid configuration.

Cable Sizing for Solar Systems

Cable sizing is critical for safety and efficiency. Undersized cables create resistive losses (wasted energy as heat) and can be a fire hazard. The key factors are maximum current, cable run length, and maximum acceptable voltage drop.

• For runs under 3 metres: 4mm squared cable is suitable for currents up to 25A.

• For runs 3–10 metres: 6mm squared cable for currents up to 25A.

• Use DC-rated cable (solar PV cable) for outdoor and in-panel applications — it is UV-resistant and rated for the operating conditions.

• Always use appropriately rated fuses or circuit breakers on both the positive and negative conductors between your solar array and charge controller.

Practical Wiring Tips

• Label all cables clearly — positive and negative, and which panel or string each belongs to.

• Use MC4 connectors (the standard weatherproof connector for solar panels) consistently. Never mix connector brands — they may not be mechanically or electrically compatible.

• Ensure all connections are tight. Loose connections create resistance, heat, and potential arcing.

• Use a DC multimeter to verify polarity before connecting to your charge controller. Reverse polarity can destroy an MPPT controller instantly.

• Install a DC disconnect switch between the array and charge controller for maintenance safety.

Conclusion

Series wiring increases voltage while keeping current the same — better for MPPT controllers and long cable runs. Parallel wiring increases current while keeping voltage the same — better for PWM controllers and shading tolerance. Series-parallel combinations offer the best of both for larger arrays.

The right configuration for your system depends on your charge controller specifications, battery bank voltage, number of panels, and physical layout. When in doubt, consult your charge controller's manual for recommended array voltage ranges.

For more solar project guides and hands-on wiring tutorials, visit the Circuit Diary Projects page. Explore more renewable energy content on the Circuit Diary Blog.