CHARGE REGULATOR – MPPT SOLAR CHARGER
The solar charge controller is the central element of a solar installation. It controls panel production while optimizing battery life. A suitable solar charge controller must therefore be carefully selected.
The charge regulator connects the solar panels with the batteries: it limits the current of the panels so as not to overload the batteries (and optimize their lifespan).
When selecting a charge controller, the short circuit current (Isc) of the solar panels is the essential characteristic. For MPPT charge regulators, two criteria are essential: on the one hand, the sum of the power in Wc of all the connected solar panels must not exceed
the maximum input power of the solar charge controller. On the other hand, the no-load voltage (Uoc) of all solar panels possibly connected in series must never exceed the maximum input voltage of the solar charge regulator.
RECOMMENDATIONS
Only 12V 36 cell or 24V 72 cell panels can be used with a PWM regulator!
All other configurations require the use of an MPPT regulator. For example, a 250W 60 cell panel, with a Vmp voltage of 30V cannot be used with a PWM regulator, an MPPT model, set at 12V, is necessary. In case of high temperature or low sunlight, the voltage Vmp of a solar panel drops drastically. With a voltage falling to 28V for example (+ 3% wiring losses), a 60-cell panel will not be able to properly recharge a 24V battery. This requires a voltage of 28.8v for a complete recharge, the battery would be damaged because it is never recharged to 100%.
General recommendations for selecting a regulator
In the case of MPPT charge regulators, one criterion is essential: The no-load voltage (Uoc) of all solar panels possibly connected in series must never exceed the maximum input voltage of the solar charge regulator. Caution should be exercised here, especially due to the temperature dependence of the no-load voltage of the solar panels. This tension actually increases when the temperature drops. Based on the lowest temperature in the application, the no-load voltage of the solar panel should be calculated using the temperature coefficient specified in the panel data sheet. The maximum input voltage of the solar charge controller must be higher than this voltage.
General recommendations for selecting a PWM regulator
When selecting a PWM charge controller, the short circuit current (Isc) of the solar panels is the essential characteristic. The manufacturer Steca recommends, for example, selecting the solar charge controller in large dimensions. The rated current of the solar charge controller should be approximately 20% higher than the sum of short-circuit current of all connected solar panels.
Choose a PWM or MPPT solar regulator?
The PWM solar charge controller is the preferred solution for:
- low cost installation
- a small installation
- when the temperature of the panels is moderate between 45°C and 75°C
The MPPT solar charge controller is the preferred solution for:
- when the temperature of the panels can be lower than 45°C or higher than 75°C
- when partial shading is a concern: the MPPT regulator will get more energy from the solar panels than a PWM regulator
- when you want to know the state of the batteries as well as the potential of the panels