Wiring 12V Solar Panels in Parallel vs Series

Wiring 12V Solar Panels in Parallel vs Series

Solar Panel Wiring:  Which is better - Parallel or Series?

So you are interested in setting up your own DIY solar panel array to charge your batteries.  Perhaps you want to use portable solar panels for RV or Marine batteries, or establish a DIY portable solar power generator kit to power RV appliances such as a Dometic CoolFreeze Portable cooler, a TV, lights, cooktop, etc.  After reviewing Solar Generators vs. Portable Solar Power Banks and estimating your PV wattage requirements using our solar calculators, you recognize that a single 12v 100W solar panel may not quite be sufficient to meet your needs, so you consider adding additional portable solar panels ranging from 50W-100W, or more. 

How should you wire the portable solar panels together?  If you are purchasing a portable solar panel kit that includes more than one solar panel along with a charge controller, you should always follow the installation and wiring instructions that come with your kit. Taking measures to wire these panels contrary to instructions may have significant negative consequences, considering the fact that your included charge controller is a primary determining factor on wiring solar panels in parallel vs. in a series.  Pulse Width Modulation (PWM) charge controllers are used to wire solar panels in parallel, whereas Maximum Power Point Tracking (MPPT) charge controllers are more flexible, and are needed to wire solar panels in a series.

If, however, you are a DIY’er who is assembling your own solar charge kit by selecting your own components, you will want to consider a few facts when deciding to wire your solar panels in parallel vs. a series.  Your choice will affect the current flow and solar panel efficiencies, and each has its own pros and cons.  Let’s explore them.

Wiring solar panels in parallel

Wiring 12V solar panels in parallel generally keeps the voltage the same, and you obtain a higher amperage current. Each solar panel must have an identical voltage rating, and your solar charge controller must be able accommodate total system amperage. If you have 2 portable 12V solar panels rated at 5 amps, connecting these 12V portable solar panels in parallel will yield a maximum of 12 volts and 10 amps of power under peak sun.

The biggest advantage to parallel RV solar panel wiring is that each panel is connected to every other component, and if one 12V solar panel should for some reason experience a failure, the other 12V solar panel will continue to produce solar power. When connecting two or more solar panels in parallel, you end up with less shading effect. That means you may experience better solar panel charge activity under partial shaded conditions. On the other hand, under those situations you may also experience voltage instability, which can drag down your overall solar panel performance. If your cables are strong and not excessively long (preventing loss of energy conversion), voltage drop becomes less of a concern.

Multiple parallel 12V solar panel wiring arrangements require thicker, shorter wires equipped to handle heavier amp loads, which is fairly typical for DIY solar panel arrangements. It would be extremely costly and difficult to achieve for large rooftop solar installations. 

Wiring solar panels in a series

When connecting two or more solar panels in a series, your amp charge is stable, while your voltage multiplies.  If you have two 12V solar panels each rated at 5 amps, you will retain the 5 amps but would get a 24 volt charge.  You must be careful not to exceed the maximum (battery) system voltage.  In other words, this arrangement will require an MPPT solar charge controller, which is configured to “step down” voltage in cases where you are only charging a single 12 volt battery.  Or, you would need to have two 12V batteries, also wired in a series, to establish the 24 voltage for this portable solar power “generator” combination to work. 

The benefits of wiring solar panels in a series is that this configuration yields less voltage dropping during a charge cycle, which ultimately yields fastest, most efficient solar panel charge time.  Another benefit of wiring in a series is that the length of your connecting wires is less of a concern in terms of lost energy efficiency.  That’s why most rooftop solar panel installations are wired in a series. 

At the same time, recognize that wiring 12V solar panels in a series means that each panel is only connected to the one before/after it. Think of it like a string of Christmas tree lights. If a circuit is ever disconnected at any point, no current will flow. More specifically, if one of your panels experiences partial shade, the entire system’s solar energy production is likely to drop quite a bit, unless each panel is independently connected to its own solar charge controller. With that solution, your set-up costs just increased, and you are better off reverting to parallel solar panel wiring. On the other hand, if your solar power generation needs are time sensitive, wiring your portable 12V solar panels in a series may be right for you after all. Everything about solar power set-up has its trade-offs. 

Multiple batteries

What if you have more than one battery? Should you wire them in parallel or a series? Again, there are pros and cons to each. Wiring batteries in parallel increases power, whereas wiring batteries in a series increases voltage. If you choose to wire your solar panels in a series, thereby increasing the peak voltage, you should ideally also wire your batteries in a series accordingly, or make sure to use an MPPT controller to step down the voltage as needed. 

That said, the more batteries you add, the more flexibility you have with establishing desired amps out and voltage of your self-designed solar powered system.  For example, one could take six 12V batteries, wire three batteries in parallel (2x) and then wire the two sets of three batteries together in a series.  This gives you 2x the voltage (24V) and 3x the power, the amperage of which would depend on the battery specifications.

Still have a question? Need a little DIY solar assistance? Please drop us a line and we will get back to you shortly. Be sure to leave us detailed information on the equipment that you are using, or are considering to purchase, so that we can best answer your questions.

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