Is Solar Parallel Connection Better Than Wiring Solar Panels in Series?

etting up a well-performing and efficient solar system isn’t just about the quality of solar equipment but also about how adequately all the elements are interconnected. For example, it might come as a surprise for solar newbies that there isn’t just one way of wiring solar panels together. And what's more, the type of PV panel wiring is a critical factor not only in achieving maximum PV panel efficiency but also ensuring safe operation. Keep reading down below for everything you need to know about panel wiring, including what wiring type will work best for your PV panel system.

PV panel basics: voltage and amperage of solar panels

Before delving deeper into PV panel wiring, there are two physical concepts we need to clarify, namely, voltage and amperage. So it’s time to brush up on your electricity knowledge.

Despite voltage and amperage being both measures of electrical current, they do not mean the same thing. Voltage is the measure of potential energy between two points in an electric field. As one point has more charge than another, the pressure between them provides the “push” that forces charged electrons to move through a circuit. Voltage is measured in volts and represented by the letter “V.”

The second term we’ll use today is amperage – the strength of electrical current flow. Basically, it is the number of electrons passing a certain point in a system in a certain amount of time. Amperage is expressed in amperes, often shortened to “amps.”

One of the best analogies to voltage and amperage would be a flow of water in a hose. Water flows only if there is a pressure difference, moving from high- to low-pressure regions until the difference levels out. Electric current (amperage) is equivalent to water flow, while voltage is equivalent to water pressure pushing the water through the hose.

There is an important rule on the subject: lower voltages (i.e. lower pressure) require more current running through the wire to “push through” the same electrical power. Inversely, higher voltages can transmit more power without requiring as much current, so if the voltage is increased, less current is needed to supply the same amount of power.

And with that out of the way, let's get into PV panel wiring and discuss wiring types in detail.

Series wiring of solar panels

The principle difference between the series or parallel wiring of PV panels is the output voltage and current. Similar to a battery, each solar panel has a positive and a negative terminal. Wiring solar panels in series mean that the positive terminal of each panel is connected to the negative terminal of the next panel (similar to outdoor string lights).

As previously explained, lower voltages mean higher currents and vice versa. When you wire photovoltaic panels in series, their voltages add up, but their amperage stays the same for all the panels. This means voltage values grow with every added panel while the total current generated by the system remains low.

By the way, the series connection is used for wiring photovoltaic cells within a panel. Each cell increases the overall voltage output of the panel, keeping the amperage the same. The optimum voltage of a single cell under load is approximately 0.5 volts at 25 degrees Celsius, generating a current of around 3 amps in the full sun. Consequently, a typical residential panel has a peak voltage rating of 16 volts (this voltage is reduced in PV systems to be suitable for 12V battery charging). Still, the amperage remains at around 3 amps.

The same happens when wiring solar panels in series. Suppose you have four panels with a rated voltage of 12 volts and a rated amperage of 5 amps. When connected in series, the total installation will supply 42 volts and 5 amps.

Pros of wiring solar panels in series

So what advantages can wiring panels in series offer? First, this configuration is easier for PV installers, as it requires little personnel training and minimizes the chances of incorrect wiring.

Another considerable advantage is lower power losses. This allows long wire runs of 20 feet or more (for example, from PV panels on the roof to the inverter) without losing much electricity. Additionally, these wires can be cheaper and less thick because they carry much lower current.

Cons of wiring solar panels in series

However, wiring solar panels in series has a fair amount of drawbacks. First, the series connection is less reliable: since the entire system is connected by one single wire, the whole system will be affected if this wire fails.

Another disadvantage is vulnerability to shading. When a cloud or any nearby obstruction shades a single panel in the series, the efficiency and output of other panels will drop. Shading can be an even bigger issue because a shaded panel causes an increase in internal resistance, creating so-called hotspots – zones with an increased temperature that may eventually lead to fires.

And finally, wiring solar panels in series requires an efficient MPPT controller, which is quite expensive.

Solar panel parallel wiring

Unlike series connection, solar panel parallel wiring implies connecting the positive terminal of one panel to the positive terminal of the next panel and, likewise, the negative terminal of one panel to the negative of the next panel. As a result, in a solar parallel configuration, all positive terminals are wired together, and all negative terminals are wired together.

A solar panel parallel works opposite to series wiring in terms of voltage and current. When you connect solar panels in series, the system’s amperage increases, but the voltage remains the same. So if you connect four panels supplying 12 volts and 5 amps each, the entire array will deliver 12 volts and 20 amps.

Pros of solar parallel connection

Now let’s look at some advantages of solar parallel configuration. One of them is that solar panel parallel systems are less affected by shading. In case one photovoltaic panel is shaded, the performance of other panels in the array won’t change because the solar parallel connection means every unit is independent from the others.

Solar parallel connection is also considered safer because you don’t have high voltages running on your roof. On top of that, for such a panel system, you can buy a PWM controller that costs considerably less than an MPPT option. However, the MPPT controller will work with this wiring configuration as well.

Cons of solar parallel connection

As for the disadvantages of solar panel parallel wiring, low voltages mean higher current values resulting in higher electrical losses and, therefore, poorer performance of your PV system.

Additionally, a higher current in solar panel parallel systems requires more cable, and the cable has to be thicker than in a series connection to endure higher amperages. And lastly, solar parallel systems are more expensive and difficult to install.

Combining solar panel parallel and series wiring

Sometimes it is impossible to achieve the needed voltage and current with neither a series nor parallel connection. When wiring solar panels in series, there is a risk of increasing the voltage limit. And in the solar parallel connection, you can exceed the current limit while not delivering the maximum possible power.

Combining the two types implies making strings (i.e., series connections of several modules) and wiring them in parallel with the other strings. The idea is to add up the voltage of each panel and leave the amperage the same within the string, but then also add up the amperage of each string after connecting the strings in parallel. This method allows for obtaining the benefits of both series and parallel configurations.

So is solar parallel wiring better for PB systems? Often, but not always.

There's no definitive answer to whether solar parallel connection is better than writing the panels in series. Solar panel parallel is ideal for shaded locations and generally safer than series configuration. However, when higher voltages and minimum power losses are desired, a series connection can be a better choice.