In this post, we are going to discuss the 7 important Charge Controller functions in the off-grid /stand-alone Solar PV systems.
You will find that Photovoltaic modules are highly reliable and virtually maintenance free. But the modules alone do not solve customer power problems. Modules are usually connected to batteries to give power 24hrs a day.
Also Read: Primary functions of Battery
The Charge controller is the energy manager in a stand-alone SPV system, which ensures that the battery is cycled under conditions which do not reduce its ability to deliver its rated capacity over its expected lifetime.
Whenever batteries are included in a system, the additional facility must be built in, that will protect against overuse and that will information back to the user regarding the state of charge of the battery.
7 Important Charge Controller Functions:
Battery charge regulation and control of the energy produced by the PV array is a critical function in PV Systems.
Listed below are the 7 most important charge controller functions:
- Prevention of Battery Overcharge.
- Prevention of Battery Over Discharge.
- Status Information to System Users/Operators
- Load Control.
- Interface and Control backup energy sources
- Divert PV Energy to an Auxiliary Load
- Serve as Wiring Centre
Let’s get started.
1. Prevention of Battery Overcharge.
Charge regulation is the primary function of a battery charge controller, and perhaps teh single most important issue related to battery performance and life.
When the array is operating under good-to-excellent weather conditions, energy generated by the array often exceeds the electrical load demand. Current from the array will flow into the battery proportional to the irradiance, whether the battery needs charging or not.
If the battery is nearly full already, it will be overcharged. To prevent battery damage resulting from overcharge, a charge controller is used to protect the battery.
During overcharge, the voltage will rise, gassing will begin, the electrolyte will be lost, the internal heating will occur, and battery life will be reduced.
If left uncontrolled, the battery could lose almost all its electrolyte and be permanently damaged, and the loads could fail.
Charge controller prevents excessive battery overcharge by interrupting or limiting the current flow from the array to the battery when the battery becomes fully charged.
Charge regulation is most often accomplished by limiting battery voltage to a maximum value, often called as the Voltage Regulation(VR) Set Point.
2. Prevention of Battery Over Discharge
If you leave the loads ON too long, the battery can be over-discharged, The reaction of lead and lead dioxide will occur close to the lead grid material and weakens the bond between the active materials and the grid.
This can result in greater resistance and heat generation, loss of capacity and life will eventually occur.
Sometimes shallow cycling types of batteries are very difficult to recharge once they have severely discharged, especially with slow charge rates typical for remote photovoltaic systems( typically c/30or less).
If batteries are too deeply discharged, the voltage falls below the operating range of the loads and the loads will fail.
Over Discharge protection in charge controllers is usually accomplished by open-circuiting the connection between the battery and electrical load when the battery reaches a preset or adjustable Low Voltage Load Disconnect(LVD) Set point.
Most charge regulators also have an indicator light or alarm to alert the system user/operator to the load disconnect condition. Once the battery is recharged to a certain level, the loads are again reconnected to a battery.
3. Status Information to System Users/Operators
Nowadays charge controller used in Photovoltaic systems can provide status information on the operation of the system and the condition of the battery.
These features of controllers can allow users to intelligently manage their use of energy and gain a better understanding of how the system operates to fully utilize its potential.
Battery voltage and State of charge is a essential piece of information that can be indicated by the charge controllers.
Digital readout of exact battery voltage can also be provided for more sophisticated users. While random battery voltage can be provided, but the user must know how to interpret this information.
For example, the user must know at what voltage levels they should begin to reduce their energy usage, to prevent battery over discharge.
Other status information provided by charge controller are :
- Whether the array is charging the battery or not.
- Whether the array/ load is disconnected or not.
- Load currents
- Net battery amp-hours
4. Load Control
Some Charge controllers have optional features that allow regulation or control of PV System electrical load.
Most popular feature of load control is PV lighting system.This control can take place at Sunrise or Sunset as sensed by a photosensor or the array current or voltage output.
In other cases, the controller may have a timing function to cycle the load operation for a specified period or at a certain time of a day.
Sometimes load control functions may require adjustment and proper specification for the array type and site conditions such as temperature and background lighting.
Even when these features add to the extra cost and the complexity of the charge controller functions, they can greatly simplify the use and operation of the PV system.
5. Interface and Control backup energy sources
In Hybrid PV Power system using one or more backup energy sources in addition to the PV array. more advanced system control centers may be designed to interfere these alternate sources with PV systems.
One scenario would be a controller that activates a backup generator at low battery state of charge. The control center or charge controller would start the generator at a preset low battery voltage, and turn it off when the battery is recharged or reaches a higher voltage limit.
In some cases, stand-alone inverters used in Photovoltaic systems will start a backup generator or divert the loads to utility power when the battery reaches a low state of charge.
Once the battery has been recharged to a preset level, the loads are again connected to and powered by the battery bank.
6. Divert PV Energy to an Auxiliary Load
Batteries in Solar Photovoltaic systems are often fully recharged by the middle of the day during the summer.
The charge controller would normally disconnect the PV array to prevent battery overcharging, the array can continue to produce power for some other use. Some system controls include a diversion function.
When the battery bank is full, the array power is connected to another auxiliary load. There is no voltage control because there is no battery holding the voltage steady.
Typical Auxiliary loads used in PV systems are:
- Back up battery
- DC Water Pump
- A resistive element in the water heater
- A simple motor that operated without voltage regulation.
When the battery voltage falls, and array power is needed to run the regular loads, the auxiliary load will be disconnected from the PV array.
7. Serve as Wiring Centre
In most cases, the charge controller serves as the termination and connection point between the conductors leading to the various components in a Photovoltaic system.
For example, the charge regulator in a small residential lighting system has the PV array, battery, and load, all connected to the charge controller terminals.
A Fuse or Circuit breaker for array and battery protection can also be included in the regulator design.
Large PV systems generally have overcurrent protection and disconnect devices included as part of the control center. With these devices included in the system controller, the conductors leading to the PV array, battery and loads are connected at a centralized point in the system.
The Control centre may also be the principle grounding point in the system and include surge suppression devices.
With this centralized configuration for the system connection and controls, the installation, operation, and maintenance of the system are greatly simplified.
The above functions are the most important charge controller functions in a Photovoltaic system.
I would be happy to hear more about other Charge Controller Functions. Do share your thoughts what other Charge Controller Functions can be introduced in PV Systems in the comment section below.
References : GSES Standalone Photovoltaic Systems
Image Credit : Phocos