Necessity of Grid Connection Rules
The grid impact of an RPP depends on a number of factors such as technology of the plant, interconnection features/capabilities, and penetration level. The challenging features of RPP can be summarized as follows .
Variability and Uncertainty of Resources
Unlike customary nonrenewable resources, the output of solar, wind, and some hydro generation units fluctuates according to the availability of the primary resources (solar irradiance, wind velocity, and water head) that cannot be practically stored. These resources are considered variable and hence the output of RPP changes according to their availability. As a result, plant output from an RPP becomes variable and less predictable than a conventional plant . The intermittent and random characteristics of wind and PV power result in difficulties to attain reliable energy balance and resource assurance. As wind power peaks usually occur at load off-peak, the situation is exacerbated with widespread integration of wind turbines . It adversely influences the real power balance of the system and causes severe system frequency problems under certain circumstances.
Location of Plant
Because of the availability of resources, RPPs are often located in distant regions and hence require long transmission lines to deliver power to load centres. For example, it can be mentioned that large-scale PV plant requires enormous land area for harnessing enough power from solar irradiation. Similar justification is applicable for large-scale integration of wind turbines too. In offshore wind plants with lengthy submarine AC cables, high charging currents necessitate the injection of a large amount of apparent power. Quick and large variation of wind output causes swift changes in system voltages as well as in tie line flows. This phenomenon can ultimately lead to voltage instability issues and endanger the security of the power system .
Generation Technologies and System Condition
Generation technologies behind each RPP influence the voltage and frequency regulation capabilities, harmonic emissions, and protection coordination . Integration of large WPPs in a weak power system results in inadequate dispatch and balancing capabilities.
In order to address the above technical disputes while responding to the pressure of accommodating increased clean power sources, TSOs have to modify traditional planning methods and operational practices. The foremost attitude is that, wherever feasible, RPPs should have practical potentials comparable to conventional generators to support secured operation of the power system . The principal grid codes discussed in the present study have been presented in the next section.