Disadvantages of Low Power factor

Greater conductor size: To transfer or distribute a fixed amount of power at constant voltage, the conductor will have to carry more current at low power factor. These necessitate large conductor size.

Large copper losses: The large current at low power factor cause more I²R losses in all the elements of the supply system. This results in poor efficiency. 

Poor voltage regulation: The large current at low lagging power factor causes greater voltage drops in alternators, transformers, transmission lines and distributors. This results in reduced voltage available at the supply end, thus impairing the performance of utilisation devices. In order to keep the receiving end voltage within allowable limits, extra equipment (voltage regulators) is needed.

 Reduced handling capacity of system: The lagging power factor decreases the handling capacity of all the elements of the system. It is because the reactive component of current stops the full utilisation of installed capacity.