Wiring solar panels in series increases the voltage while keeping the current the same. Wiring them in parallel keeps the voltage the same while adding the currents together. Series wiring suits MPPT charge controllers with a higher voltage input range. Parallel wiring is better when panels may be partially shaded or when your controller has a lower voltage limit.
Understanding the difference between series and parallel wiring is essential when designing a solar system. The choice affects which charge controller or inverter you can use, how shading impacts performance, and what cable sizes you need. This guide explains both configurations clearly and helps you decide which is right for your setup.
How Series Wiring Works
In a series string, panels are connected positive terminal to negative terminal in a chain. The result is that voltages add together while current stays constant at the level of a single panel.
For example, three 100W panels each rated at 20V open-circuit voltage (Voc) and 5A short-circuit current (Isc) wired in series produce:
- Voltage: 20V x 3 = 60V
- Current: 5A (unchanged)
The higher voltage is often preferred by MPPT charge controllers, which typically have a wider input voltage window (e.g. 12V to 100V) and can handle higher string voltages efficiently.
Advantages of series
- Higher voltage means lower current, which allows for thinner (and cheaper) cable runs between panels and controller
- Works well with most MPPT controllers designed for 24V or 48V battery systems
- Reduced resistive losses in cabling
Disadvantages of series
- Shading one panel in a series string reduces the output of the entire string, not just the shaded panel
- If one panel fails, the whole string is affected
- Total voltage must not exceed the charge controller or inverter's maximum input voltage
How Parallel Wiring Works
In a parallel configuration, all positive terminals connect together and all negative terminals connect together. Currents add up while voltage stays constant at the level of a single panel.
Using the same three 100W panels as above wired in parallel:
- Voltage: 20V (unchanged)
- Current: 5A x 3 = 15A
Advantages of parallel
- Partial shading of one panel does not drag down the others, only reducing total current slightly
- Works well with low-voltage systems (e.g. 12V battery banks with low-voltage charge controllers)
- Failure of one panel has minimal impact on the rest
Disadvantages of parallel
- Higher current requires thicker, more expensive cable
- May need a combiner box with fuses on each branch to protect against reverse current
- Voltage remains low, which is less efficient for long cable runs
Series-Parallel (Mixed) Configurations
For larger systems with many panels, a series-parallel combination is common. You create two or more series strings and then wire those strings in parallel. This increases both voltage and current in a controlled way, allowing you to match the combined array output to the controller's input range.
For example, two strings of three panels in series, then those strings wired in parallel, gives 60V and 10A rather than 60V at 5A (series-only) or 20V at 15A (parallel-only).
Which to Choose for Your System
12V battery systems
If you have a 12V battery bank and a basic PWM charge controller, parallel wiring keeps the voltage matched to the system. A PWM controller does not benefit from higher voltages in the way an MPPT controller does.
24V or 48V systems with MPPT
Series wiring is typically the better choice. Your MPPT controller can accept a higher input voltage and convert it efficiently. Check the controller's maximum input voltage and design your series string to stay safely below it, including the panels' temperature-adjusted Voc at cold temperatures (which is higher than the standard rating).
Shading is a concern
If some panels will regularly be in partial shade at different times (e.g. one panel gets shadow from a chimney), parallel wiring limits the damage. Alternatively, panel-level optimisers or microinverters can address shading in a series string without sacrificing the cabling efficiency benefits.
Safety Considerations
Before connecting panels in any configuration, check the following:
- Total string voltage (Voc x number of panels) must not exceed the charge controller or inverter's maximum PV input voltage
- Parallel strings carrying higher currents need appropriately rated fuses on each string positive lead
- Use MC4 connectors and UV-rated solar cable rated for the voltage and current involved
- Never disconnect panels from a charge controller under load. Always disconnect the load first, then the panels
If in doubt about your system design or cable sizing, consult a qualified solar installer or electrician before proceeding.
