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Wiring solar panels in series adds their voltages while the current stays the same; wiring them in parallel adds their currents while the voltage stays the same. Series is usually better with an MPPT charge controller and long wire runs. Parallel is better with a PWM controller or where panels get partial shade. Many systems combine both.
Below we walk through both with the actual specs of a 100W panel, show the two limits you must check before wiring anything, and answer the common questions: which is better, how to tell how yours are wired, and how to connect six panels.
| Series | Parallel | |
|---|---|---|
| How it connects | Positive of one panel to negative of the next | All positives together, all negatives together |
| Voltage | Adds up | Stays at one panel's voltage |
| Current (amps) | Stays at one panel's current | Adds up |
| Wire size | Thinner wire, less voltage loss | Thicker wire needed |
| Shade | One shaded panel drags the string down | Shade on one panel mostly affects only that panel |
| Controller | Needs MPPT | Works with PWM or MPPT |
| Extra parts | None | Branch connectors, and fuses with 3 or more strings |
Here are the real numbers using our MEGA 100, rated at 18.6V and 5.38A at maximum power, 22.8V open circuit, and 5.78A short circuit.
Two MEGA 100s in series:
Two MEGA 100s in parallel:
Same 200 watts either way. What changes is the voltage and current your wire and controller have to handle.
Power lost in wire grows with the square of the current. Halve the current and you cut wire losses to a quarter. That is the big advantage of series: higher voltage, lower current, so you can run thinner wire over a longer distance, from a ground mount to the shed or from the roof down to the battery bay, and lose less along the way.
An MPPT controller converts that higher panel voltage down to the battery's charging voltage and turns the difference into extra charging current. It also needs the panel voltage to stay a few volts above the battery's charging voltage to work at all, and series strings give it that headroom on hot days, early mornings, and cloudy afternoons. That is why our MPPT vs PWM guide recommends MPPT for anything over about 200W.
You have a PWM controller. A PWM controller connects the panels straight to the battery, so it cannot use extra voltage. Put two 12V-class panels in series on a 12V PWM system and the extra voltage is simply wasted. With PWM, keep 12V-class panels in parallel.
Some panels get shade. In a series string, current flows through every panel in turn, so a shaded panel limits the whole string. Bypass diodes in each panel's junction box soften the hit, but a shaded panel still costs more in series than it does in parallel, where the unshaded panels keep producing at full current.
You want low voltage for safety or code reasons. A parallel array stays near one panel's voltage, which keeps things simple in small mobile systems.
The trade-off: parallel current adds up fast. Four MEGA 100s in parallel put out about 21.5A, which needs heavier wire, branch connectors to combine the leads, and a controller rated for that current.
1. Your controller's maximum PV input voltage, in the cold. A panel's open circuit voltage rises as temperature drops, and the coldest morning of the year is when it peaks. The National Electrical Code includes correction factors up to 1.25 for very cold climates, so a safe habit is to multiply your string's open circuit voltage by 1.25 and stay under the controller's limit.
Example with a 100V MPPT controller and MEGA 100 panels: 22.8V x 1.25 = 28.5V per panel in extreme cold. Three in series reach about 85.5V, safely under 100V. Four in series could reach about 114V and damage the controller. So three is the maximum per string on a 100V controller.
2. Your controller's current rating. Add the short circuit current of the strings in parallel and size the controller with margin. Our charge controller sizing guide gives you the formula.
Larger arrays combine both: build several identical series strings, then connect the strings in parallel. Four MEGA 100s as two strings of two (written 2S2P) give about 37.2V at 10.76A, 400W. You keep voltage high enough for an efficient MPPT harvest and current low enough for reasonable wire, and a shaded panel only drags down its own string.
The rules for series-parallel are simple: every string must have the same number of panels, and the same panel model, so the strings run at the same voltage.
It depends on your controller's voltage limit. With six MEGA 100s:
Why fuses at three strings? If one string faults, the others can push their combined current backward through it. With two strings that current stays within what a panel can handle, but with three or more it can exceed the panel's maximum series fuse rating, so each string gets a fuse.
Sometimes. In series, current must match, because the string runs at the current of its weakest panel. A 100W panel wired in series with a 200W panel drags the 200W panel down to about half its output.
In parallel, voltage must match. Panels with similar operating voltage combine well even if their wattage differs. Our MEGA 100 (18.6V) and MEGA 200 (18.4V) are close enough to parallel together, and each delivers close to its full rating. So if you want to add a 200W panel to an existing 100W panel, parallel is the way to do it.
Three quick checks:
Is it better to hook solar panels up in series or parallel? With an MPPT controller, series or series-parallel is usually better because it cuts wire losses and keeps voltage up in poor light. With a PWM controller or partial shade, parallel is better.
Does series or parallel produce more power? Neither changes the panels' total watts. Series loses less power in the wire and handles low light better with MPPT; parallel loses less power when one panel is shaded.
How do I know if my solar panels are wired in series or parallel? Trace the leads, count the wires at the controller, or measure the array's open circuit voltage and compare it to one panel's rating.
How can I connect 6 solar panels in series and parallel? Two strings of three (3S2P) is the usual layout on a 100V controller with 12V-class panels. Check the cold open circuit voltage against your controller's limit first.
Can I mix 100W and 200W solar panels? Yes, in parallel, if their operating voltages are similar. Do not mix them in the same series string.
Wiring a new array? Shop solar panels and charge controllers, or call our team at 888-855-7286 with your panels and controller and we will check the string math with you. Planning an RV roof? See our best solar panels for RV guide.
This guide is general information, not electrical or professional installation advice. Always follow the panel and controller manuals and local electrical codes, use properly rated wire, fuses, and disconnects, and have a qualified electrician install or inspect grid-connected and high-voltage systems.
Reviewed by the Krato Power team. Questions? Reach us at 888-855-7286.