General recommendations for selecting the solar charge controller
The solar charge controller is the central component of an island system. It regulates the energy flow in the entire system and has a significant influence on the function and service life. A suitable solar charge controller must therefore be carefully selected. The cost share of the solar charge controller measured against the total costs of a stand-alone system is only 3 to 5 %. For the system, however, it is the most important component. A high-quality and reliable solar charge controller in a higher price class pays for itself very quickly, as it contributes significantly to a long battery life and thus significantly reduces the total costs of the system.
Steca solar charge controllers are available as professional hybrid shunt controllers, as serial charge controllers or as MPP trackers. Depending on the requirements of the application, the appropriate topology should be selected. Switching charge controllers such as shunt and serial charge controllers can only be used for 12 V systems in conjunction with 36-cell solar modules. For 24 V or 48 V systems, two 36-cell (24 V) or two 72-cell (48 V) solar modules must be serially connected to form a string. Serial charge controllers are well suited for small applications and solar home systems. For larger applications and hybrid systems, shunt regulators are recommended because they have lower power dissipation during charging. Due to their good electromagnetic compatibility, shunt controllers are also recommended for telecommunication applications. A solar charge controller with MPP tracking must be used if solar modules that are not made up of 36 or 72 cells are used. This includes most solar modules optimized for grid-connected systems and all thin-film modules. The lower the annual average temperature and the more important efficient charging at low battery charge levels, the more recommended it is to use an MPP tracker, even if standard 36-cell modules are used.
Design of the solar charge controller
When designing switching charge controllers, the short-circuit current (Isc) of the solar modules is the decisive variable (under STC conditions). Basically, KATEK Memmingen recommends to design the solar charge controller generously. The nominal current of the solar charge controller should be approx. 20 % higher than the sum of the short-circuit current of all connected solar modules.
If the solar charge controller is used in an application in which people live with the system, it is important that it has a large LC display that shows the operating states via symbols. In order to inform the user about the system and the way it is used, the solar charge controller should be equipped with an integrated energy meter. For purely technical applications, such as night lighting systems, a solar charge controller with a simple LED display is sufficient.
Cables and construction
To ensure a long life span it is important to use solid solar charge controllers and connect them to the battery with short, thick cables. The device should always be screwed directly above the battery on a non-flammable wall. It is important that there is enough free space around the solar charge controller so that it can be sufficiently cooled by the ambient air. In any case, the regulations in the operating instructions must be observed.
In applications with stand-alone inverters or in hybrid systems, it makes sense to use solar charge controllers with additional functions. A connection possibility to the stand-alone inverters for communication and coordination of the devices is a prerequisite for an effective inverter or hybrid system. Furthermore, special functions for energy management are of central importance in hybrid systems.