As a homeowner who is just learning about solar energy options, it is easy to get confused with all the technical terms you might read or hear about.

Your installer is likely to mention different ways that arrays of solar panels are wired. And your first thought might be that it does not matter how they are wired. Likely, you just want the panels to produce the energy to power your home. However, depending on your home, how your panels are wired does matter. It impacts the performance of your system and your choice of inverter.

The better your solar system performs, the better your savings and your return on investment.

Here are answers to some of the common questions customers ask about wiring solar panels that can help you have a better understanding of the pros and cons of wiring in series or in parallel.

What does it mean to wire solar panels in series?

When an installer connects your solar panels in a series, he is wiring each panel to the next. This creates a string circuit. The wire running from the panel's negative terminal is connected to the next panel's positive terminal and so forth down the line for one path of current for a continuous, closed loop.

Back of solar panels - wiring between solar panels

Wiring between solar panels (back of solar panels)

The important difference between wiring panels in series or in parallel is that electrically it affects the voltage and amperage of the resultant circuit.

In a series circuit you sum the voltage of each panel to get the overall voltage of the array. However, the amperage of the overall circuit stays the same stays the same.

What does Wiring panels in Parallel mean?

Wiring solar panels in a parallel fashion is a little bit more complicated. Instead of connecting each panel to the next, each panel is connected to a centralized wire coming from your roof. There is one wire for connecting the wires from all the positive terminals and one wire for the wires from the negative terminals.

With panels connected in parallel the voltage of the overall circuit stays the same as the voltage for each panel but the amperage of the overall circuit is the sum of the amperage of each solar panel.

Parallel solar panels amperage connection

Parallel solar panels: 5A + 5A + 5A + 5A = Total 20 Ampersand + 12 Volt

How do solar panels wired in series compare to solar panels wired in parallel?

To understand how wiring in series works in comparison to how parallel wiring works, let’s think for a moment about how Christmas lights used to work. If a bulb burned out, came loose from its socket or broke, the entire string refused to light up. This was because the lights were wired in a series. You would have to locate the problem bulb and replace it or reseat it to get the string of lights to work again. Today, most Christmas lights feature a form of parallel wiring that allows for strings of lights to stay lit even when there is one troublemaker in the string.

Series wired circuits for solar panels work in a similar way. If for some reason there is a problem with the connection of one panel in the series, the entire circuit fails. Meanwhile, one defective panel or loose wire in a parallel wired circuit will not stop the rest from operating.

In practice how solar panels are wired today depends on the type of inverter that is being used.

Wiring solar panels when using a string inverter

When using a string inverter. the string inverter will have a rated voltage window that it need from the solar panels to operate and also a rated current that the inverter can operate with. Remember string inverters have MPP trackers in them that vary current and voltage to produce maximum power and so when designing these machines they need to have a range of what voltage and current will be receiving from the solar array.

In most crystalline solar panels the open circuit voltage is around 40 Volts and for most string inverters the voltage window is between 300 to 500 volts. This would mean that when designing a system you could have between 8 and 12 twelve panels in series.

However, often an array might be larger than 12 panels and so it is common to actually have two strings of 8 or 9 panels in series but then have two strings to be in parallel.

The diagram below only has four panels in each string but it is an example of this type of wiring.

2 rows of 4 solar panels. Positive and Negative connection to controller

Which wiring works better – series or parallel?

In theory, parallel wiring is a better option for many electrical applications because it allows for continuous operation of the panels that are not malfunctioning. But, it is not always the best choice for all applications. When designing your solar system, your installer might decide that series wiring is better suited for your application or he might choose a hybrid approach by series wiring some panels and parallel wiring others.

When designing your solar system, a critical balance of voltage and amperage needs to be achieved for it to perform at its best. This is where mixing parallel circuits with series circuits is beneficial. When solar panels are wired in a series, voltage is additive, but the amperage stays the same. For example, if you have five panels that are 12 volts and 5 amps each, an array that is series wired would have 60 volts and 5 amps. But if you parallel wired those same five panels the amperage would be additive, while the voltage remains the same. Therefore, you would have 12 volts and 25 amps instead.

Can you add more solar panels to your existing system?

This is a question you should ask so that your system is designed taking future expansion needs into account. Going with a full installation from the start is always best when installing a residential solar system. Using a solar calculator helps estimate your solar system costs and power needs to accurately determine how many panels you should have in your system. However, if you were limited with your budget, or underestimated your future power needs, you could be considering adding more panels to your existing system.

The problem is that most existing systems are not designed for expansion. If your power inverter was oversized to accommodate future expansion, the possibility of an expansion improves. But you may also need to upgrade your older system’s components to current standards to make it code compliant with new components that are required by the 2011 NEC.

Another problem may be matching new panels to older ones, and not necessarily for aesthetic purposes. If your panels were wired in a series, your existing series string might not allow for much expansion. This is because its maximum circuit voltage limits how many panels can be added in. For example, your older panels could be 80-watt, 12V, while today panels with 200W or more that are 30V to 60V are more common.

Does the use of micro-inverters or optimizers change how solar panels are wired?

The use of micro-inverters or optimizers in the scheme of your solar system can help avoid inverter-size limitations that string inverters have. Your system can be expanded one panel at a time by giving it its own inverter by connecting it to a micro-inverter. This can be done with existing string inverters that are maxed out provided that additional solar panels are wired in on the AC side of the string inverter.

How do you connect solar panels to the grid?

Another consideration between series wired and parallel wired is the amount of wires that are used to connect the solar system into the grid. A series wired circuit will use a single wire to connect. Meanwhile, a parallel wired system will have multiple wires to connect it into the grid.

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