Solar Panels
What’s the Difference? Solar Panels: Series or Parallel
The main difference between wiring solar panels in series or parallel is the output voltage and current. When you wire multiple panels in series, their output voltages add together, and their output current remains the same. Conversely, when you wire numerous solar panels in parallel, their output currents add together, but their output voltages stay the same.
Let’s take a closer look at how this works and how to wire panels in series and parallel.
Series Solar Panel Wiring
Voltage and Amps in Series
To wire solar panels in series, connect the positive terminal on the first panel to the negative terminal on the next, and so on. The resulting voltage will be the sum of all of the panel voltages in the series. However, the total current will be equal to the output current of a single panel.
For example, in the graphic above, we have three 18-volt, 6-amp panels wired in series. The output voltage is 54 volts (18V + 18V + 18V = 54V), yet the output current is still 6 amps.
What It’s Best For
Solar panels in series are optimal in unshaded conditions. If shade covers a single panel of your series array, it will bring down the whole system’s power output. Each panel in a series connection is critical.
Solar panels in series are also best if you need a low-amperage system. To calculate the output power of a solar system, multiply the voltage by the current. If you have a higher voltage system, your amperage will be lower. Lower amperage allows you to use smaller gauge wires which are less expensive and easier to work with.
One important thing to know is that you will need to use an MPPT charge controller when wiring your panels in series. MPPT charge controllers regulate the voltage and current from the solar panels to match the battery bank’s voltage without sacrificing power. If you use a PWM controller, the battery will pull the total panel array voltage down to match it, and you will lose a lot of power.
Parallel Solar Panel Wiring
Voltage and Amps in Parallel
To wire solar panels in parallel, connect all of the positive terminals on each panel together and then do the same for the negative terminals. The resulting current will be the sum of all of the panel amperages in the parallel array. However, the total voltage will be equal to the output voltage of a single panel.
For example, in the graphic above, we have three 18-volt, 6-amp panels wired in parallel. The output current is 18 amps (6A + 6A + 6A = 18A), yet the output voltage is still 18 volts.
What It’s Best For
Solar panels in parallel operate independently of one another and therefore are the best option for mixed-light conditions. If shade covers one or two of your panels, the remaining panels in the array will continue to generate power as expected.
Parallel solar arrays are also ideal when you want a low voltage system using a lower-cost PWM controller. Again, wiring multiple solar panels in parallel doesn’t change the total output voltage. So, if your panel output voltage matches your nominal battery charging voltage, a parallel array allows you to increase your output charging current without needing to regulate the voltage.
Solar Panels: Series or Parallel, Which is Better?
Now that we understand the difference between wiring solar panels in series vs. parallel, we can talk about which option is better. So, should you wire your solar panels in series or parallel? Well, again, it truly depends on your application.
Connecting your solar panels in series is often preferred if you’re able to spend most of your time in unshaded locations. The main reason for this is that your solar panel system will be more efficient and will perform better at the beginning and end of the day and when it’s cloudy. Here’s why.
Batteries require a higher voltage than their nominal voltage to charge. For example, our lithium batteries need 14.4 volts to start charging. Most solar panels in the 100-watt range have an output voltage between 18-20 volts. To reach the 14.4 volts required to charge your batteries, solar panels in parallel would need to be operating at 75% capacity or more.
However, if you were to wire three of these same panels in series, the maximum output voltage would be 54-60 volts. This would mean your panel array would only need to operate at around 25% capacity to provide a charge to your batteries. Operating at 25% capacity is much easier to achieve even late in the day or on cloudy days. It is important to remember that you will need an MPPT charge controller for a system like this to work.
Wiring your solar panels in parallel is not necessarily a bad option. MPPT charge controllers are expensive and may be overkill for small portable applications. If you have a small low-voltage system for an RV or boat that might be in variable lighting conditions, a parallel system may be a great option. Systems like this will work great with a lower-cost PWM charge controller, which will save you money.