When wiring multiple solar panels together in a system, you have two choices: series and parallel. Which one suits you depends mainly on your application. Let's look at the differences and when each method is best.
What's the difference? Solar panels in series or parallel
The main difference between wiring solar panels in series or parallel is the output voltage and current. When you wire multiple panels in series, their output voltages add together and their output current stays the same. Wire those same panels in parallel and their output currents add together while the voltage stays the same.
Series solar panel wiring
Voltage and amps in series
To wire solar panels in series, connect the positive terminal on the first panel to the negative terminal on the next, and so on down the string. The resulting voltage is the sum of all the panel voltages in the series, while the total current equals the output current of a single panel.
For example, three 18-volt, 6-amp panels wired in series give an output of 54 volts (18V + 18V + 18V), yet the output current is still 6 amps.
What it's best for
Series wiring is optimal in unshaded conditions. If shade covers a single panel in a series array, it drags down the whole string's output — every panel in a series connection is critical.
Parallel solar panel wiring
Voltage and amps in parallel
To wire solar panels in parallel, connect all the positive terminals together, then do the same for the negatives. The resulting current is the sum of all the panel amperages in the array, while the total voltage equals the output voltage of a single panel.
For example, three 18-volt, 6-amp panels wired in parallel give an output of 18 amps (6A + 6A + 6A), yet the output voltage is still 18 volts.
What it's best for
Panels in parallel operate independently of one another, which makes parallel the better option in mixed-light conditions. If shade covers one or two panels, the rest of the array keeps generating as expected.
Parallel arrays also suit low-voltage systems running a lower-cost PWM controller. Because parallel wiring doesn't change the total output voltage, if your panel output voltage already matches your nominal battery charging voltage you can increase charging current without needing to regulate the voltage down.
Series or parallel — which is better?
It genuinely depends on the application.
Series is often preferred if you spend most of your time in unshaded locations. A series array is more efficient and performs better at the start and end of the day, and under cloud.
Take three panels wired in series with a maximum output voltage of 54-60 volts. That array only needs to operate at around 25% capacity to push a charge into your batteries — far easier to achieve late in the day or under cloud. Note that a setup like this requires an MPPT charge controller to work.
Parallel is not a bad option. MPPT controllers cost more and can be overkill for small portable setups. For a small low-voltage system on a caravan or boat that sees variable light, parallel works well and pairs happily with a lower-cost PWM charge controller.
Mixing panel types
The examples above assume identical panels, which is ideal but not a strict requirement. Mixing panels from different manufacturers with different electrical ratings is possible, with some important guidelines.
If you are wiring your array in series, all panels should share the same current rating. The voltages will still add together, but the current output will be limited to the lowest-rated panel in the string.
If you are wiring in parallel, panels should share the same voltage rating. The currents add together, but a voltage mismatch will drag the array down to the lowest panel's voltage.
Need a hand sizing your system?
Townsville Wholesale Batteries can spec the right array, controller and battery bank for your setup. Browse our Victron solar panels and SmartSolar MPPT controllers, or call us on 0459 364 303 for advice.