I’m often asked about the best way to turn a marine solar system on and off—and whether doing so could damage the panels. Here are some key points to keep in mind:
Firstly, your solar controller is powered by your batteries, not by your solar panels. This means that disconnecting the controller from the battery bank is not the recommended way to shut down your solar system, as it would cause the controller to reset and reboot each time it loses power. Instead, the correct method to turn off your solar system is by interrupting the positive wire running from your solar array to the controller. A simple on/off switch or breaker in this positive line makes it easy to toggle the solar array without any risk of damaging your system.
There’s also an advantage to having this switch or breaker between the solar panels and the controller: it allows you to temporarily shut down the solar system to optimize battery charging from other sources, like your alternator. When charging from the alternator, you typically want all its output directed toward the battery bank for the fastest, most effective bulk charging. Some alternators, especially those with smart regulators, sense the battery bank’s charge state and apply either a bulk or a float charge based on that state. However, if your solar panels are connected and actively producing, the regulator will read the combined charge of both the battery and the solar array. This may give a false impression of a higher battery charge than there actually is, causing the alternator to switch prematurely to float mode. This same effect can occur with shore power chargers in some setups.
This situation only arises with certain combinations of alternator regulators, solar controllers, and shore chargers, so it might not always be an issue. As a general rule, if you want to be sure of getting maximum performance from your alternator or shore charger, open the solar breaker while they’re in use. Otherwise, feel free to experiment with your specific setup to see if any interference occurs. If not, you can leave the solar system on continuously, as we do.
