Solar Charge Controllers

Solar energy is becoming a very common addition to many boat’s electrical systems as an alternative charging source for their battery bank.  Solar energy is harvested by photo-voltaic cells converting the light energy, photons, into direct current that can then be stored in a battery bank; however, like all charging sources it is important that the charge is controlled to prevent battery damage.  Some charge controllers appear to be complex electronic devices, while others appear to be quite simple, but all have important features and operating parameters that are important considerations that should not be taken for granted when choosing and installing a controller.

Some of the operating parameters and features are obvious and well publicized, while others are somewhat more covert.  The most basic consideration is the wattage rating of the controller, and ensuring that the controller can handle the wattage of the solar panel.  There is also a choice to be made in between the two common types of charge controller logistics: PWM ( Pulse Width Modulation ) or MPPT ( Maximum Power Point Tracking ); both perform about the same in warmer climates, but MPPT have been shown to do somewhat better in cooler conditions.  Some feature are visual like meters that display values that inform the user of important dynamics of the system, while other features, while equally as important, are somewhat obscured.

Some charge controllers require a battery differential as high as +5V from the solar panel to start a charge cycle.  This feature is added to some controllers to avoid constant and repeated “trickle charging” at low voltages that can lead to shortened battery life; lead acid batteries need some higher voltage charging to clean the plates of any lead sulfate crystals, and to avoid electrolyte stratification in flooded cells.  If a charge controller incorporates this protective feature it will be described in the installation and commissioning portion of the manual, so even if the device appears simple it is imperative check into the details.