Solution for low power factor in solar power system installation

The reduction of power factor is a common issue encountered when connecting grid-tied solar power systems to the electrical systems of operational factories. A low power factor leads to increased energy losses, wear and tear on conducting equipment, transformers, adverse effects on the national grid, and potential penalties for low power factor from power suppliers.

1. Causes of decreased power factor

• The existing power factor correction system of factory is insufficient to correct the power factor when integrating the grid-tied solar power system.
• Power factor correction capacitor rating of the factory’s power factor correction system is too large, making the capacitor control ineffective (adding a capacitor results in excess, removing it leads to a deficiency).
• The power factor correction controller lacks support functionality when the grid-tied solar power system operates. The capacitor control panel cannot accurately determine the direction of the grid current supplied to the load or returned to the grid to control the capacitor closing accurately.
• The grid connection point of the grid-tied solar power system is located below CT (Current Transformer) position of the power factor correction controller.

*** Example problem

• Consider the case of a factory without a solar power system:

The factory operates without a grid-tied solar power system, with 100% of the electricity obtained from grid.

• Consider the case of installed solar power system: solar power system only generates Active Power (P)

In the scenario where the factory’s power consumption remains constant (P=100kW and Q=32.9kVAr), if the factory installs a solar power system generating active power (P) of 60kW with a power factor (cos phi) equal to 1, only the active power (P) drawn from the grid is reduced due to the support from the solar power system. At this point, the active power (P) drawn from the grid is only 40kW, while the reactive power (Q) drawn from the grid remains unchanged at 32.9kVAr. This results in reducing the power factor (cos phi) of the system to 0.77.

2. Handling the issue of reduced power factor when solar power system is in operation

2.1. Setting up solar power system to generate both P and Q with a fixed power factor of 0.95

– Configure solar power system to generate power with an appropriate power factor so that inverters produce both active power (P) and reactive power (Q), reducing the amount of active power (P) and reactive power (Q) drawn from the grid. Thus, the power factor (cos phi) is maintained as in the initial state when the solar power system was not installed.

– Advantages: Easy to implement, no need to change the grid connection point or relocate CT position of the capacitor bank controller.

– Disadvantages: Affects electricity generation as solar power system generates a certain amount of reactive power (Q), reducing the Performance Ratio (PR) of solar power system.

2.2. Setting the power factor parameter to 0.99, selecting Four-Quadrant operation mode for the capacitor bank controller:

– Adjust the setting parameter Set cos phi for the capacitor bank controller with a power factor value of 0.99 and enable the Four-Quadrant mode. The Four-Quadrant mode allows the capacitor bank controller to operate in both power absorption and generation modes. Ensure the correct polarity of the CT for this mode to function properly; if the polarity is incorrect, this function will not work. The capacitor bank controller will close multiple stages of capacitors to generate more reactive power, thus enhancing the reactive power (cos phi) value of the power system.

– In case the capacitor bank system is still insufficient to raise the power factor of the system to 0.9, further calculations are needed to consider additional capacitor installation.

– Advantages: Easy to implement.

– Disadvantages: The capacitor capacity may not be sufficient to increase the power factor (cos phi) of the power system to 0.9, or the capacitor bank size may be too large and not flexible enough, potentially affecting the optimal control of capacitor bank stages.

3.1. Adjusting the grid connection point of the solar power system for suitability

– The inappropriate grid connection point is a primary cause of the reduced power factor (cos phi) phenomenon in the solar power system.

– Adjusting the grid connection point above the CT of the capacitor bank controller or moving the CT of the capacitor bank controller below the grid connection point of the solar power system will address the issue of reduced power factor (cos phi) when the solar power system is connected to the grid.

– Advantages: Solves the problem of reduced power factor (cos phi) without affecting the electricity generation of the solar power system.

– Disadvantages: Difficulty in changing the grid connection point or the position of the CT of the capacitor bank controller.

 We can observe that:

• The solar power system acts as a source, not a load, so it does not consume reactive power (Q).
• To avoid the reduction of the power factor (cos phi) of the plant after installing the solar power system, consider the following:

– Collect sufficient information about the capacitor bank system (capacity, number of capacitor bank stages), the power factor of the plant at different times, and the corresponding stages of the capacitor bank that are closed concerning the power factor at that time.

– Thoroughly survey the grid connection point of the solar power system to see if the grid connection point is above the CT of the capacitor bank controller. If, due to unavoidable circumstances, the grid connection point of the solar power system cannot be above the CT of the capacitor bank controller, consider the solutions mentioned above.

For further consultation on comprehensive and effective solar power solutions, please contact DAT Group’s Hotline at 1800 6567 (free of charge) for 24/7 assistance.