The charge controller is one of the most important elements of the solar power system. It is designed for efficient charging of batteries, deep discharge or overcharge protection. The right controller can boost the efficiency of your local power station by 25-30%, which is comparable to the use of additional solar modules or a wind turbine. The controller can be built into the inverter unit or installed separately.
Purpose of the controller:
- Switch of load between power sources and distribution of power flows, i.e. selecting the power sources to supply the system – sun, wind, battery or public grid;
- Improvement of battery charging efficiency;
- Prevention of battery deep discharge or overcharge;
- Display of battery charge level, amount of stored and used energy, voltage and amperage;
- Load switch on/off;
- Short-circuit protection, etc.
The controller is a small metallic box with indicators on it, very easy to install and adjust. There are three main types of controllers:
Application of these controllers is limited to solar panels as the battery is switched off by short-circuit when fully charged (short-circuit cannot damage solar panels). When battery voltage reaches 14.4V (rated battery voltage is 12V), the controller stops the battery charging. And vice versa, charging resumes when battery voltage drops to 12.5-13V. At the same time, when the maximum battery charge is below 60-70%, it will have an adverse effect on the lifespan of the battery, since their number and capacity should be 40-50% higher.
Actually, this type of controller is no longer in use in modern power systems, though some suppliers still offer it because of its low price. Most global manufacturers have switched to PWM and MPPT controllers because of their much higher efficiency.
PWM controllers (Pulse Width Modulation)
In contrast to ON/OFF controllers, PWM controllers use pulse width modulation of charge current allowing 100% battery charging. It is illustrated in the picture below:
Overall battery charging is split into 4 stages:
- Maximum current charging — the controller supplies all the current from the solar panel to the battery;
- When the battery terminal voltage reaches the specific level, the controller starts maintaining constant high voltage through current pulse width modulation, which helps to prevent battery overheating and gassing. Amperage gradually goes down along with rise in charge level;
- Equalization — most batteries with liquid electrolyte show better performance after periodical charging until it is gassing. Gas helps to agitate electrolyte from different parts of the battery thus cleaning electrolyte and balancing its structure and density;
- Charge maintenance — after full charge, solar panel voltage gradually slips to the level sufficient to maintain battery voltage. This prevents overcharging and helps to save power.
MPPT controllers (Maximum Power Point Tracking)
It is the most advanced and efficient type of controller. It can boost system efficiency by 25-30% in comparison with other controllers. Its operation is based on calculation of peak power point.
If you look at current-voltage characteristic of a solar panel, you can see that the number of voltage and amperage combinations is huge, but this correlation can give maximum capacity only at one point. Since current and voltage ratio is defined by circuit parameters, the controller can influence it and provide maximum capacity.
Most of NEOSUN Energy controllers are based on MPPT technology. It allows:
- To reduce losses when charging the battery and extend its service life;
- To optimize the system operation in case of partial solar module shading;
- To increase electricity production in cloudy weather and low light;
- To reduce the cable cross sections and increase the distance from the panel to the controller by increasing the input voltage.