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Up the current: How to connect solar panels in parallel in 5 steps

When you build your own solar system, the question of how to connect the panels always pops up. When a system is small and there is a threat of shading, a parallel connection is a reasonable choice. This type of wiring is a bit complex, that’s why we’ll teach you how to connect solar panels in parallel in this article.

Parallel connections are common in small systems

Solar panels are wired in parallel when you want to increase the total current output in a system. The currents from panels add up, while the same voltage remains low.

Here are some scenarios where you might choose to wire solar panels in parallel:

1. Shade mitigation. When panels are connected in parallel, they are independent of one another. This means that when a solar panel is shaded, it doesn’t affect the others like it does when an array is wired in series.
2. High current systems. Sometimes you need to charge batteries or operate devices that require a higher current than what a single solar panel can produce. Connecting multiple panels in parallel allows you to achieve the required current.
3. PWM controller. If you have a simple PWM controller in your system, you might need to wire panels in parallel to make use of it. A PWM controller is only viable when the voltage in your system is slightly higher than the voltage of a battery.

Wiring solar panels in parallel is common in small off-grid systems, such as RV and boat systems. Shading is common in these scenarios. The parts of a system are close together so energy losses are tolerable. Parallel wiring requires thick wires and addons like branch connectors and combiner boxes. When a system gets big, it becomes costly and difficult to use parallel configuration.

Parallel wiring is more expensive

The biggest drawbacks of parallel connection are wiring complexity and costs. High current in the system means you’ll need thicker wires. Wiring is more difficult because you’ll need branch connectors and/or combiner boxes. Electricians also add inline fuses to protect the equipment from high currents.

Parallel wiring allows you to save money when choosing a controller though. The system’s output voltage will match the panel with the lowest voltage rating. If the system’s voltage is equal or only a couple of volts higher than the voltage of a battery, you can use a cheap PWM controller instead of an MPPT controller.

Wiring solar panels in parallel in 5 steps

Connecting solar panels in parallel means joining the positive (+) terminals of all the panels together and connecting the negative (-) terminals of all the panels together. In comparison to a series connection, this requires branch connectors or a combiner box. Here is how to connect solar panels in parallel:

Step 1: Prepare the equipment

Gather all your equipment: solar panels, cables, connectors, branch connectors or a combiner box, duct tape, wire cutters and strippers. The wires from the combiner box or branch connectors usually go to a charge controller. 

Decide on the placement of your solar panels on the roof or ground. Ensure they are positioned to receive maximum sunlight exposure throughout the day. Place the solar panels side by side in the desired arrangement. Ensure there is enough space between each panel for easy cable connection.

Solar panels should have matching voltage and current ratings. Mismatched panels can lead to imbalances in the system, reducing overall performance. The system’s output voltage will match the panel with the lowest voltage rating. 

Cover the panels with cardboard or a blanket so that you don’t work with the voltage going through the wires

Step 2: Prepare the cables

Male and female MC4 connectors

Each solar panel has two cables coming out of the junction box: a positive (+) cable and a negative (-) cable. The cable either ends with a connector or you have you add one yourself. Usually, male and female MC4 connectors are used. You can learn how to replace a connector in our article on types of solar connectors.

Before connecting, make sure you know which cable is positive and which one is negative. As a rule, the female MC4 connector is attached to the positive lead, but it’s better to make sure. Look for the markings — positive cable is usually red and negative is black. Alternatively, use a voltmeter.  

Step 3: Connect cables to branch connector or combiner box

To join the cables together, you can use branch connectors. The most popular options are 2-to-1, 3-to-1 and 4-to-1 types, but you can find even 6-to-1 connectors.

Take all the positive cables from the solar panels and connect them to an appropriate set of branch connectors. For instance, two cables with female MC4 connectors should go to a male part of 2-1 set of branch connectors. Then take all the negative cables from the solar panels and connect them together using the suitable connectors.

When you connect three solar panels in parallel or more, it’s recommended to add a set of MC4 in-line fuses to each positive cable. The fuses go in-between cables from solar panels and branch connectors

When the current output gets high, a combiner box is a safer option. Most MC4 branches are rated for 30A. If the Isc values of your panels combined go over the maximum current for branch connectors, use a combiner box instead. 

Isc stands for ‘short-circuit current’. It’s the maximum current that a panel can produce when its terminals are directly connected together without any external load

The idea remains the same with a combiner box: run the positive and negative cable bundles from the solar panels to the box. It will consolidate the cables into a single set of positive and negative cables that will go to the charge controller or the rest of the system.

Step 4: Connect to Charge Controller 

Take the positive cable from the combiner box or a branch connector that combines positive cables from panels. Connect it to the positive input of the charge controller. Similarly, take the combined negative cable bundle and connect it to the negative input of the controller or the rest of your solar system.

Step 5: Check the connections and test the system

Ensure that all the connections are secure and properly tightened. Use appropriate cable clips and conduits to protect the cables and connections from environmental elements. Color code your wires with duct tape if you haven’t already. Mark the positive cable with red color and the negative one with black.

Before putting the system into full operation, conduct a test. Use a multimeter to measure the current and the voltage. Remember: when you connect solar panels in parallel, currents from panels add up whereas the voltage stays low.

Andrey Gorichenski
Senior Editor

Andrey had been a news editor and freelance writer for a number of medias before joining A1SolarStore team. Climate change and its impact on people's lives has always been among his interests and it partially explains his degree in Philosophy and Ethics.

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