Transmission System Planning Under Uncertainties Including Renewable Penetration Regime in Indian Context

Indian electricity demand is growing at an accelerated pace. It is expected that electricity demand of the country shall reach to about 150 GW by year 2022. To meet growing demand and to reduce supply-demand gap, there is a need for large capacity addition through conventional as well as renewable energy sources. India is bestowed with abundant renewable potential. Govt. of India has set an ambitious plan for establishing about 175 GW renewable generation capacity by 2022 including 100 GW of Solar, 65 GW wind and 10 GW other renewable sources.

Increasing renewable penetration presents numerous challenges to the system planner as well as grid operator. From transmission system planner perspective, differences in gestation period of renewable generation and transmission, uncertainties in development of Renewable generation complexes, no firm beneficiaries at the development stage of generation project are key challenges. In India, above uncertainties have been addressed through series of measures including a proactive initiative viz. evolution of Green Energy Corridors, where transmission for high potential renewable zones was planned in anticipation of subsequent Renewable development. Green Energy Corridors comprises Intra state transmission system i.e. transmission facility from Renewable generation projects to the state grid network at 132 kV/220 kV/400 kV level within the host state as well as at Inter state transmission system (ISTS) for transfer of power across the states.

For evolution of Green Energy Corridors, integrated system study were conducted which were developed based on capacities and transmission available/anticipated during study time frames for national grid including various high capacity transmission corridors as a whole. Thereafter maximized Renewable dispatch scenarios as well as various other sensitivity scenarios like peak demand, off peak demand scenarios were developed. Study of historical patterns such as demand patterns, wind & solar generation patterns over the days/season in various regions were also taken into account while building above scenarios. The study involved State wise Renewable Purchase Obligations (RPO) requirements both solar, nonsolar to generate Renewable Surplus/deficit situation across each control area (state). With above inputs, detailed simulations were carried out in PSS/E software for all India transmission system to evolve Intra and Inter state transmission as part of Green Energy Corridors.

In order to integrate high quantum of renewable energy, it is necessary to introduce more flexibility into system. Considering envisaged Renewable penetration scenarios, balancing studies were also carried out using “Net Load” methodology for different RE scenario viz. Base case/moderate as well as accelerated (175 GW target) RE scenario and typical ramping requirements were studied. Results revealed that ramping requirement in accelerated renewable scenario vis-a-vis its base case scenario is about 25% and 87% higher respectively for 2018–19 and 2021–22 scenario, which is quite significant.

Because of the low capacity utilization factor of the renewable resources, network utilization of the sub transmission level for renewable evacuation is lower than that of strongly interconnected transmission network at national level. This leads to higher tariff for transmission network dedicated to renewable system. To rationalize the tariff to facilitate renewable integration, an innovative financing scheme has been evolved for Green Energy Corridors

This paper deliberates considerations for transmission system planning under above mentioned uncertainties in Indian context and also presents the methodology to develop infrastructure to facilitate large scale renewable generation into the grid. Paper also discusses ramping requirement as well as implementation plans of Renewable energy management centers (REMCs). Innovative financing strategy to encourage high penetration of renewables, transmission charges sharing mechanism etc. are also discussed.