MPPT Charge Controllers or Maximum Power Point Tracking Charge Controllers are a type of charge controllers that track the power output by the solar panels to generate the maximum power from the system.
What are PWM and MPPT charge controllers
There are two type of charge controllers commonly used in PV power systems,
- Pulse-width Modulation (PWM) and
- Multiple Power Point Tracking (MPPT).
PWM charge controller
- A PWM charge controller is a switch that operates between the solar panel array and the battery
- Its main function is to reduce the voltage of the solar panel array close to that of the battery to ensure that the battery is properly charged. In other words, they restrict the solar panel voltage to the battery voltage by reducing the Vmp down to the batteries system voltage with no change in the current.
- Due to the nature of their work mechanism, PWM charge controllers cannot use the maximum power produced by the PV system and so their efficiency is low and around 80% as compared to the MPPT Chare controllers.
- On the other hand an MPPT controller allows maximum power to be harvested from the panels.
- The basics of an MPPT Solar Charge Controller is to optimize the efficiency of the charge controller employed in a Solar photovoltaic system.
What is an MPPT Charge Controller?
- The MPPT charge controller ensures that the loads receive maximum current to be used by quickly charging the battery.
- Maximum power point could be understood as an ideal voltage at which the maximum power is delivered to the loads, with minimum losses. This is also commonly referred to as peak power voltage.
What is the maximum power point (MPP)?
- The maximum power point (MPP) is the point on a current voltage (I-V) curve at which the solar PV device generates the largest power output i.e. where the product of current intensity (I) and voltage (V) is maximum on the I-V curve.
- The MPP may change due to external factors such as temperature, light conditions and workmanship of the device.
- In order to ensure maximum power output (Pmax) of a solar PV device in view of these external factors, maximum power output trackers (MPPT) may be operated to regulate the resistance of the device.
How do MPPT charge controllers work?
We know the fact that the voltage of the battery varies with its charge content.
As current flows from a high potential to low potential, the steeper the gradient or voltage difference, the greater is the flow of current.
This potential gradient could be made steeper by two ways:
- By increasing the output voltage of the Solar Panel
- By decreasing the voltage of the battery (i.e discharging the battery)
Using increased panel voltage to deliver maximum power
Now batteries could only be charged if the output voltage of the solar panel is greater than that of the batteries, to facilitate a flow of current from the panel to the battery.
The output voltage of the panel depends on different factors, including the weather (irradiance). On a sunny day the output voltage may be higher than the rated output voltage, while during a cloudy day the output voltage is probably less.
Normal controllers do not have the capacity to utilize this higher output voltage to deliver more power. However MPPT charge controllers have the ability to adjust the voltage in order to get a boost of current during times of peak demand in such conditions.
MPPT delivers higher than rated charge to the battery as they can adjust the voltage to current ratio.
Using battery voltage for delivering maximum power
Current and Voltage are inversely proportional to each other. In other words, if the current increases, the voltage drops and vice versa.
By lowering the current by introducing some resistance in the path of the current, the MPPT charge controller can boost up the voltage.
This voltage to current ratio adjustment is called Maximum power point tracking. MPPT typically increases the current to the battery by approximately 25% to 30%.
Important to keep in mind is that a 80% discharged battery will charge faster than a 50% discharged battery.
The reason for this is that when the battery starts to discharge, its voltage also reduces. The larger the gap between the solar panel output voltage and the battery voltage, the more current will flow into the battery, and the faster the battery will be charged.
Combined techniques for optimum battery charging
The PWM charge controller is suitable for small systems. It provides a low-cost solution and is normally used when the solar cell temperature is between 45°C and 75°C.
MPPT system is normally used when the PV array voltage is substantially higher than the battery voltage. It is the best solution for higher power systems. The MPPT charge controller also provides substantially more power when the solar cell temperature is below 45°C or above 75°C, or when irradiance is very low.
MPPT charge controllers use both principles mentioned above to deliver the maximum amount of power.
This type of solar charge controllers come pre-programmed with adjustable set-points which can be edited and adjusted according to your needs.
So dont hesitate to go for MPPT charge controllers even if if have pay a slightly higher price.