Wiring solar panels: Series or parallel?
How you wire your panels impacts the performance of your system, and determines the choice of inverter and charge controller.
First, let's remember that: W = V x A.
The important difference between wiring panels in series or in parallel is that 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. 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.
Wiring panels in series
When you connect your solar panels in a series, you are 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.
Series - wiring between solar panels (back of solar panels)
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.
Wiring panels in parallel
Instead of connecting each panel to the next, with a parallel connection, each panel is connected to a centralised wire. 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.
When installing a medium solar PV system, there will probably be a combination of parallel and series connections. You could for instance have 9 panels, with 3 strings of 3 panels. This means 3 panels in series, with 3 strings in parallel.
For this system, you could use a 150 V MPPT charge controller, as the Voltage is roughly 150 Volts (3 x 50 Volts of each panel in series), see picture below.
Series and Parallel wiring combined
Here you will find SunStore's Solar MPPT Charge Controllers.
How to compare series vs parallel?
In general, try to keep the Voltage of the PV array as high as possible (= more panels in series), so that the system will start working earlier. The system will start working if the Voltage of the array is higher than the voltage of the battery.
The lower the amperage, the less losses you have in your cables, so this also means more panels in series.
However, If for some reason there is a problem with the connection of one panel in a series connection, the entire circuit fails. Meanwhile, one defective panel or loose wire in a parallel wired circuit will not stop the rest from operating.
This is the same for shading of the panels; if the panels are wired in series and one panels gets shaded, the whole string stops producing yield, whereas this is not the case with parallel wiring.
The smaller the amount of Amperes through a wire, the smaller size wire you can use. When you wire panels in series, the amperes going through your wires is less compared to parallel wiring, so you can use thinner wires.
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.
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Adapted from https://www.solarreviews.com/blog/do-you-wire-solar-panels-series-or-parallel