MPPT is basically an algorithm and implemented through a combination of software hardware and electronics in any inverter or solar controller.
It helps ensure that the output of the solar panel or array or solar sequence is at its peak / maximum. This is done through a continuous power tracking methodology to be installed at the optimum power point of the solar panels.
The maximum power of a solar module varies with the solar radiation, the ambient temperature and the temperature of the cell. The objective of the MPPT system is to test the output of the photovoltaic modules and apply the adequate resistance to obtain the maximum power for any given solar radiation and total environmental conditions.
How MPPT is applied to solar circuits
When a load is directly connected to the solar panel, the operating point of the panel will rarely be at maximum power. The impedance seen by the panel is derived from the operating point of the solar panel. Thus varying the impedance seen by the panel, the operating point can be moved to the point of maximum energy. Since the panels are c.c. devices, the DC-DC converters must be used to transform the impedance of one circuit (source) to the other circuit (load).
In a particular impedance (or duty ratio) the operating point will be at the point of maximum energy transfer. The I-V curve of the panel can vary considerably with variations in atmospheric conditions such as glare and temperature. Therefore it is not feasible to set the duty ratio with such dynamically changing operating conditions. On the hardware side the MPPT technology is implemented by means of DC-DC conversion technology with high switching frequencies typically in the range of 15 to 80 kHz.
This high switching frequency has the advantage of being more efficient. To achieve the best result and an optimal ratio of efficiency, performance and reliability, a very careful design is required. There is also a software and a microcontroller to control the entire process and continually search for the most optimal solar power point in the array. On this front there are several methods to achieve MPPT technology. Some of the commonly used are:
- Disturb and observe
- Incremental conductance
- Current sweep
- Constant voltage
Unique solar module
A PV module is a device of constant current type. As shown in a typical voltage of the PV module versus the current curve, the current remains relatively constant over a wide voltage range. Conventional PV regulators essentially connect the PV array directly to the battery when the battery is discharged.
When a 75-watt module is directly connected to a 12-volt battery charge, the module still provides approximately the same current. But, because the output voltage is now 12 volts instead of 17 volts, the power output of the module is artificially limited and the 75W module only delivers 53 watts. This wastes 22 watts of available energy.
The MPPT technology of the solar charger controller works in a very different way. Under these conditions, the solar charger controller calculates the maximum power voltage (V) in which the PV module delivers the maximum power, in this case 17 volts. MPPT operates the 17-volt module that extracts the maximum available power from the module. The solar charger controller continuously recalculates the maximum power voltage as the operating conditions change.
The input power of the maximum power tracking controller, in this case 75 watts, powers a switching type power converter that reduces the input of 17 volts to the battery voltage at the output. The full 75 watts that are now delivered at 12 volts would produce a current of 6.25 amps. An increase in the load current of 1.8 amps or 40% is achieved by converting the 22 watts that would have been wasted into usable load current. Note that this example assumes 100% efficiency to illustrate the principle of operation.
MPPT technology helps to generate the maximum power from the solar modules / solar array. In fact, that is the reason why MPPT technology is now the common standard in all types of solar-TIE network inverters and also the standard for larger battery-based inverters.