When it comes to smaller solar power systems, like those found on campervans or off-grid cabins, it’s best to wire your solar panels in series. This raises the efficiency of the solar array and requires less hardware/circuit protection. However, there are some situations where you will need to use parallel connections.
In this article we’ll explain when and how to use each configuration.
Why you should wire your solar panels in series
When designing a solar array, we have the option to wire our solar panels in series or in parallel. In general, it’s best to keep our panels in series as much as possible. Wiring in series provides many advantages like:
It’s smart to avoid wiring solar panels in parallel because we run into a few disadvantages like:
If you’re designing a small solar power system, select a charge controller with a high enough input voltage, in order to allow the solar panels to be wired in series. We discuss this in more detail in the next section.
How to wire solar panels in series
To wire solar panels in series simply take one positive(+) terminal and connect it to the negative(-) of the next solar panel. Continue this until all panels are connected in one row. This is called a “series string”.
The number of solar panels we can wire in series is limited by the charge controller we choose. Remember in this configuration we are adding the solar panel voltages together. The max voltage of our string must stay atleast 20% below the max input voltage of the charge controller.
To accurately calculate our max string voltage, we need to look at the back of our solar panels for a Voc rating.
This is the voltage your panel can create without a load attached. In other words, the physical maximum voltage this panel can produce.
Typically “12-Volt solar panel” has a Voc of around 20-Volt, + or – a couple of volts.
Once you know the Voc of your panels, add them all together together (you should be using identical solar panels) and add at least 20% as a safety margin. This number is the minimum input voltage of your charge controller. You can always use a larger charge controller, just never smaller.
There is a bit more to consider when selecting your charge controller and designing a solar array. We’ll cover this in more detail in an upcoming article. Feel free to email us if you need some help with your system design.
When to Wire Solar Panels in Parallel
When you plan to build a larger solar array you may need to use parallel connections to keep the voltage under the charge controller’s max input voltage. To do this you can wire your solar panels into multiple, equal-sized strings. Then wire these strings together in parallel.
The amperage of each string will be added together in this configuration. This will affect the required cable size for the main cables that feed into our charge controller. The higher the amperage, the larger your cable must be. Read our wiring guide to learn how to size cable and wire the easy way.
In the following diagram we have a charge controller that can accept a maximum of 80-Volt, and we want to connect 9 solar panels to it. If we were to wire these solar panels in series, we would have an array capable of producing 120-Volt. This would exceed the charge controller’s max input.
Instead we do the following:
- First we divide our 9 solar panels into equal-sized groups.
- Next we wire each group of solar panels in series. This will raise their voltage up to 60-Volt, while their amperage will remain the same.
- Finally we wire each string together in parallel with one another. Now the amperage will add together, creating 15-Amp, but the voltage will remain at 60-Volt.
A very important thing to remember is, when we wire solar panels in parallel, amperage increases. If there is a short circuit between strings, and string amperage is high enough, this will cause a fire. To avoid this, each string must be protected by a fuse or circuit breaker. This is standard procedure in large solar arrays that require mixed configurations.
To provide circuit protection you can purchase an appropriately sized inline mc4 fuse or PV combiner box. If you’re not sure which size fuse to install, you can read our Guide to Fuse Selection.
Why series is especially important for camper and RV solar systems
Solar panels need to point directly at the sun to gather as much sunlight as possible.
Solar panels mounted on a camper or RV usually point straight up. This causes a lot of sunlight to reflect off of the panel in the morning and evening.
So unless the sun is directly above our solar array, we’ll have weak current production.
Weak current production can cause the solar panel voltage to drop below the battery voltage, meaning you won’t charge your battery.
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12-Volt batteries are typically charged with 14-Volts. So if we’re using a 20-Volt solar array, we have only a 6-Volts range to charge our battery. That means voltage can very easily fall below 14-Volts.
When we use a higher voltage solar array we make it easier to stay above our battery voltage, even if the current production is relatively weak. This means that earlier in the morning, later in the evening, or even on cloudy days we still have a chance to produce power.
Summary
We learned that it’s important to keep our solar panels in series to raise their efficiency and reduce the cost and complexity of our solar array. We also learned that there are situations where we are forced to use parallel connections, like when our charge controller has a limited input voltage.
If you’re still deciding which solar panels you’ll use for your system, check out our Campervan Solar Panel Guide. It pays to invest in quality solar panels and not all panels are suitable to mobile solar systems. In our solar panel guide we give a brief summary of which solar panels you should be considering.
We hope this article clears up some of the confusion, if you still have questions however, please feel free to send us an email!
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