The function of a charge controller is to protect the battery bank from damage due to overloading and overcharging. Two solar panels are connected in series or parallel to a charge controller linking it to the battery bank. Assuming we have two standard-100 W (Watt) solar panels, each generating 20 V (volts) at 5 A (amps) charging a 12 V battery.
In series, the two solar panels generate 40 V at 5 A as the voltages add up for an output of 200 W. Wired in parallel, the current is added up, and the system will deliver 20 V at 10A for an output of 200 W. A charge controller regulates the current and voltage to the battery to 14 V at 14.28 A.
The charge controller will convert the power generated by the solar panels and adjust it to the requirements to charge the battery. A 12 V battery charges at 14 V; thus, the charge controller will adjust the output current to 14.28 A to deliver 200 W of power to the battery.
The input power in Watt will be balanced by the output power in Watt to suit the battery charge parameter.
We will look at the effects of the following criteria:
- Solar panel orientation; Series or Parallel
- Battery Bank Voltage
- Charge Controller Protection
Let’s look at how charge controllers protect and balance the power output from the solar panels to charge batteries and power loads.
Where Does The Charge Controller Fit Into A Solar System?
A solar panel cannot be linked directly to a battery or battery bank, as this will cause damage to the most expensive element of the solar system.
The main cost elements of a solar system are the battery bank and solar panels.
The solar panels are pretty rugged and are designed to be robust to survive up to thirty years of exposure to the elements. The battery bank is expensive but will not last as long as the solar panels.
Even modern Lithium Ion Phosphate batteries will last ten to twelve years before needing replacement. For older type flooded batteries, the lifespan is much shorter.
The charge controller is used to right-size the power generated by the solar panels to charge the battery under the most optimal input voltage and charge current parameters.
Once the battery nears full charge, the charge controller will lessen the charge rate to prevent the battery from overcharging and getting damage.
It is important to note that charge controllers are not used in solar systems tied to the grid but only where there is a battery bank to be charged. The primary role is to protect the battery bank by controlling the charge rate.
Some charge controllers also have DC load control, connecting DC applications to the charge controller.
The charge controller can thus manage the charging of the battery bank and the supply of DC power to DC applications connected to the charge controller.
When the solar panels do not generate power at nighttime, the charge controller will prevent power from flowing from the battery bank to the solar panels and only allow power to the DC loads.
Charge Controllers Manage Multi-Stage Charging Of Batteries
The charge controller will manage the power flow to the batteries by monitoring the batteries state of charge (SOC). If the SOC is low, the charge controller will allow the full flow of power to charge the batteries at the optimal voltage and charge current.
As the charge controller senses the batteries fill up, it will slow down the rate of flow to charge the batteries to prevent them from being overcharged and overheated. Overcharging will cause the electrolytes in the battery to boil off, damaging the battery and significantly shortening its lifespan.
As the charge controller detects that the battery SOC is full, it will continue to trickle-charge the battery to maintain its optimal SOC. This multi-stage charging is what a charge controller is designed to perform.
Multi-Stage Charging Key Points
- Bulk Charging – Send all the available power from the solar panel to the battery bank in optimal voltage and current.
- Absorption Charging – As the battery bank charge builds up, it regulates the voltage and the current to taper down to safe charging levels.
- Equalization Charging (Flooded Batteries) – The high voltage is maintained, and periodic boosts will agitate the electrolyte and level differences between cell voltages.
- Float Charging – Keeps the voltage to the battery low when the battery is fully charged.
Single Or Multiple Solar Panels Requires Charge Control
A charge controller must always be installed between a solar panel and a battery bank. Two solar panels can be connected in series or parallel to the charge controller to adjust the voltage and current at which the battery must be charged.
Batteries and battery banks can also be wired to be 12 V, 24V, 36V, and 48V systems. The charge controller will control the power coming from the solar panels in such a way as to optimize the charging conditions for the battery bank.
Standard Voltage Charge
The solar industry has standardized solar panels with 60 photovoltaic cells with a nominal voltage of 20 V.
The VOC is the “open circuit” voltage that you will measure directly from the solar panel using a Voltage-meter, and the Vmp is the “voltage at maximum power.”
Charge controllers will sense the voltage generated in ambient conditions and adjust it to suit the battery charging conditions. A solar panel will be more efficient in cold weather and generate more power.
The charge controlled will balance the solar-generated power from the solar panels to optimally charge the batteries.
What Are The Different Type Of Charge Controllers?
There are three charge controllers in use today, of which the Pulse Width Modulated (PWM) and the Maximum Power Point Tracking (MPPT) are the most widely used. Simple shunt-type charge controllers have become redundant due to limited functionality.
PWM charge controllers are much lower in cost than MPPT and are good for simple systems with similar voltage input and output. The PWM charge controller pulse charges the battery at the same voltage it receives from the solar panels.
To charge a 12 V battery, you must use a 12 V solar panel. To charge a 24 V battery bank (two 12 V batteries in series), you will require two 12 V solar panels in series. To charge a 48 V battery bank (four 12 V batteries in series), you need to wire four 12 V solar panels in series.
Ensure that the PWM charge controller is rated to handle the voltage of your battery bank system. The panel voltage must be in balance with the battery bank voltage.
How An MPPT Charge Controller Works
MPPT (Maximum Power Point Tracking) Charge Controllers are the most sophisticated and expensive, adding the most value to complex solar system setups. The MPPT tracks the optimum voltage/current ratio from the solar array.
An MPPT charge controller can increase charge controller efficiency by up to 30% over conventional PWM units, and more importantly, MPPT controllers can manage different input and output voltages.
MPPT charge controllers offer the best functionality when designing a solar system and higher voltages for long-distance power transmission when the solar panel array is far from the battery bank.