How to wire solar panels
Wiring solar panels together, also called stringing, requires an understanding of how different configurations affect the solar array’s performance.
Voltage that exceeds what the inverter allows will limit production and possibly even the inverter’s life. Too little voltage, and the solar system won’t perform to expectations, as the inverter won’t work until “start voltage” kicks in. Shaded cells can also impact voltage. Growing foliage, nearby construction of tall buildings, chimneys or protruding pipes can all cause shade over panels, so you need to keep that in mind.
Solar panel wire types
Before you can create an electrical circuit, you need to settle on the appropriate solar system wires. This will enable the current to flow in the circuit to the inverter, which will transform the DC power to AC. Before deploying any solar PV system, check your local electrical codes, which regulate electrical installations in your area. Also, note: the National Electrical Code (NEC) prohibits using regular cables in your solar panel installation.
You need solar panel cables and wires designed specifically for the job at hand. Panel-wiring cable resists high-temperatures, flames, UV rays and moisture. You’ll also find that cables for solar panel array wiring last much longer than regular cables – between 25 and 30 years.
There are two types of wires:
- Single wire
- Stranded wire
A single wire is obvious – just one wire – while a stranded wire is multi-stranded. Stranded solar wires are larger than single wires. The current typically flows on the external part of the wire, which means stranded wires’ conductivity is better, as there’s more wire surface. They’re also flexible and durable – exactly what you want for wiring multiple solar panels and their components. Multi-stranded wires will also ensure reliable connections.
Minimising voltage drop
You’ll need different wires to connect:
- Solar panels to the main inverter
- Inverter to the batteries
- The batteries to the battery bank and/or the inverter directly to the electric grid
When current flows through an electrical circuit, some voltage loss, called voltage drop, will occur due to resistance in the wires. This voltage drop reduces the solar array’s production and the longer the wire run, the more resistance. If you’re designing a PV system, give consideration to solar power wiring. Keep voltage drop to a minimum so that your array performs as close as possible to its peak rated output. Industry best practice considers voltage drop at 3% or less as acceptable, though you should aim for below 2% if it’s not too impractical.
To reduce the voltage drop in grid systems:
- Minimise the length of the solar system wiring run.
- Be strategic in the inverter placement. AC wiring from the inverter to service panel is often more vulnerable to voltage drop than high voltage DC wiring that run from the panels to the inverter or controller. Battery storage systems should be within 20-30 feet, and the charge controller should be mounted within a yard or metre of the batteries. If the DC voltage from the solar array is:
- Higher than the utility service panel: install the inverter closer to the utility service panel.
- Lower than the utility service panel: install the inverter closer to the solar array.
- Use a larger wire size. The bigger the wire, the less resistance.
- Design your system with higher voltage, which will also reduce resistance.
Solar panel wiring: series vs parallel
Are solar panels wired in series or parallel? That depends on what you’re trying to achieve. Wiring solar panels in series increases the array’s voltage while keeping the amperage the same. Wiring solar panels in parallel increases the amperage but keeps the voltage the same.
How to wire solar panels in series
Series wiring is typically done for a grid-connected inverter or charge controller that requires 24 volts or more.
Solar panels are similar to batteries in that they have two terminals: positive and negative. A series connection is made by connecting the positive terminal of one panel to the negative terminal of another. Connecting at least two solar panels in this manner becomes a PV source circuit.
Which wire is positive on solar panels?
Solar panel wires and connectors work together to make the job easier. Use MC4 connectors, which have a locking mechanism, making them ideal for outdoor environments. If you’re an installer, the modules you’re working with will most likely have been manufactured with this connector attached to the junction box on the back of the panel. The junction box will contain two wires:
- One wire is the DC positive (+): this solar DC wiring is typically for the female MC4 connector
- The other is the DC negative (-): this is for the male connector
By series wiring the panels together, you’re left with a single positive and negative connection. The voltages of each individual solar panel add up together to give the array’s total output voltage:
- Let’s say a 60-cell panel as shown above produces 30 volts at 7.25 amps
- In series wiring, we’re looking at a total output of 150 volts (30 volts x 5 panels), at 7.25 amps
Although our example is about identical panels, panels with different power ratings can also be series wired. With different power ratings, the amperage will vary panel to panel as well. Let’s say the highest panel is 4 ampere and the lowest is 1. In this scenario, the overall amperage will be restricted to the lowest value, which is 1 ampere, which is incredibly inefficient.
The advantage of series wiring is that electricity transfers easily over long distances. The disadvantage: if just one panel becomes shaded or covered with leaves or other debris, it impacts the entire string – you won’t see much production.
How to wire solar panels in parallel
Parallel wiring of panels requires that the positive terminal from one panel is connected to the positive terminal of another. Also, the negative terminal from one panel is connected to the negative terminal of another panel. The result is a single positive and negative connection to link to your regulator and batteries.
This works the opposite of series wiring. With parallel wiring, the amperage adds up together while the voltage stays the same. The advantage of parallel wiring is that a shaded or covered panel does not affect the rest of the string.
Like series, you can also parallel wire different types of solar panels. The currents add up together, but the problem is that your system has to adjust to the lowest voltage. While parallel wiring panels with different power ratings is possible, it’s not a good idea due to the inefficiency your system will experience. Only parallel wire panels that have the same voltage.
How to wire 12v solar panels to 24v batteries
Wiring two solar panels together in series is the route to take in this scenario, as the solar wiring diagram shows.
- Connect the positive terminal of one panel to the negative terminal of the other panel.
- Connect the negative terminal of the first panel and the positive terminal of the second panel and connect to the corresponding terminals in solar regulator’s input.
- The solar regulator will detect the panels and start to charge the battery during sunlight.
Solar panels wired in series and parallel
Wiring solar panels in parallel or series doesn’t have to be an either/or proposition. To generate the maximum amount of power, wiring solar panels in series and parallel is possible, though it is complex. This is a normal configuration for large installations. The ability to configure series-parallel depends on the maximum possible total output voltage and output current of the solar array. In turn, these are limited by the maximum possible total input voltage and input current of the charge controller if an off-grid system, or an inverter, if you’re dealing with a grid-tied system.
To do this wiring, make two sets of PV panels and connect them in series. Then, connect the two sets of series-connected solar panels in parallel to the charge connector.
Basic solar wiring diagram
This solar system wiring diagram depicts an off-grid scenario where the solar panels are series wired. Grid-tied solar systems don’t need batteries and therefore, don’t need charge controllers, which monitor the current. The purpose of the charge controller is to ensure the batteries don’t over charge.
On-grid solar panel wiring diagram
In this PV system wiring diagram, the panels are series wired. On-grid systems need DC and AC disconnects in case power has to be shut off immediately.
Solar combiner box wiring diagram
Solar panel combiner boxes are commonly used to combine solar panels into a bus. Essentially, these are junction boxes designed for the wiring used in PV systems. Large systems rely on combiners, but they’re helpful in small PV systems, enabling easier wiring and monitoring.
What else should you know?
Learn more about the components of a solar PV system that you’ll need:
If you’re new to the solar PV industry, we recommend you learn the basics in What is photovoltaic solar power?
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