Parallel wiring means connecting all the positive (+) poles of the panels and connecting all the negative (-) poles. This keeps the voltage constant, but increases the current flow to the controller.

Series wiring is to connect the positive (+) pole of one panel to the negative (-) pole of another panel, which will increase the voltage, but keep the current the same.

Which is the better method?

Tandem solar panels

• No fuses, easier and cheaper wiring.

• Higher voltage rather than current means higher system efficiency.

• Series connection works better in certain lighting conditions. Tandem wiring is adapted to cloudy or low-light conditions. If the panel gets sunlight that only outputs 13V, two panels connected in parallel will still not output enough voltage (13.8V) to charge the battery. If connected in series, you can get 26V and then step it down to get the proper charging voltage.

Connecting solar panels in parallel

• Most PWM controllers require parallel wiring. These charge controllers are rated for an input voltage just a little higher than the battery bank. So if you have two 18V panels in series wired to feed 36V into the PWM controller, the voltage above 13.8V will be filtered out by the controller.

• In some cases, such as when one panel is masked and the other is not, you won't lose much power compared to the series approach because you'll still get enough voltage.

• Larger wiring, fuses and connectors are required. If one panel is shorted, each panel must be fused at the connector splice. As the current increases, the wiring must be larger.

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