While renewable energy capacity is growing at a fast pace, transmission-related issues have been hampering further progress in recent times. There is a mismatch in the construction timelines between transmission capacity addition and renewable energy capacity addition. While renewables have a very short gestation period, transmission projects take much longer. Further, transmission planning can start only after renewable energy bids have closed in order to get an idea about the location of the new capacity. Hence, transmission systems need to match this growing demand, which would otherwise delay renewable energy grid integration.
Impact of rising renewables on the grid
The penetration of renewable energy into the grid has improved in the past few years and is expected to increase further over the coming years. Currently, the level of penetration stands at around 21 per cent in terms of capacity, with over 80 GW of renewables installed so far. Renewable energy generation capacity is expected to grow at a compound annual growth rate of around 14.9 per cent per annum during the 2019-30 period provided the target of 175 GW by 2022 is attained. Due to high penetration of solar energy, the grid is expected to witness high ramp-down and ramp-up requirements. Solar generation increases during morning hours, and falls in early evening (4-6 p.m.). If renewable energy penetration is around 30 per cent, the level of required balancing reserves will be 48-50 GW. In the 2022 renewable energy scenario, the total balancing reserves required during the evening ramp is expected to be 60 GW. Thus, synchronisation between different energy sources will be needed to maintain grid stability. Greater flexibility and controllability will be required in such situations. Therefore, the need for balancing reserves will also arise to enable quick discharge and storage.
Transmission infrastructure for renewables: GEC I and II
The green energy corridors project are at various stages of development and implementation. Green Energy Corridors (GEC) I (interstate) and GEC II (Transmission Scheme for Ultra Mega Solar Power Parks) are the transmission schemes that have evolved and have been deliberated upon in the respective regional standing committee meetings. They have been agreed as system strengthening schemes to address the current transmission system challenges.
GEC I involves the setting up of transmission lines of around 3,200 ckt. km and six substations with a total capacity of 17,000 MVA. Most of the schemes under GEC I have been commissioned. Meanwhile, GEC II entails putting in place the transmission systems for evacuation from 34 ultra mega solar power plants of capacity totalling 20 GW. Out of this, the evacuation of power from 13 solar parks (totalling 9.2 GW capacity) has been identified through the inter-state transmission system. The power ministry has assigned Powergrid the task of taking up the implementation of transmission systems for eight solar parks (7.2 GW), comprising transmission lines of 1,870 ckt. km and five substations of 13,500 MVA.
In order to ensure system stability and grid security, 11 renewable energy management centres are being set up at the regional, state and national levels. Further, 14 static synchronous compensators (11,350 MVAr), four static VAR compensators (2,500 MVAr) as well as 48 fixed series capacitors (FSCs) and thyristor-controlled series compensators are also planned to be deployed.
Renewable energy zones by 2022
The central government has approved transmission schemes for renewable energy zones (REZs) with a potential capacity of 66.5 GW to be achieved by 2022. The proposed transmission schemes will be implemented in two phases. Phase I will involve renewable energy capacity of 28 GW at an investment of Rs 168 billion. Phase II will take care of the remaining 38.5 GW renewable energy capacity at an investment of Rs 264 billion. Phase I is further divided into two parts. Part 1 will be taken up in Rajasthan (8.9 GW) and Gujarat (3.5 GW) at Rs 101.35 billion investment, and will be completed by September 2020 and December 2020 respectively. Under Part 2, the transmission scheme will be taken up upon receipt of long-term access (LTA) applications (15.5 GW) at an investment of Rs 66.65 billion.
The demand for energy storage is expected to reach a cumulative battery requirement of 120 GWh during 2017-20, 970 GWh during 2020-25 and 2,410 GWh during 2025-30. The market size is expected to be in the range of Rs 1.17 million – Rs 1.71 million by 2030. Globally, South Australia has deployed a mega battery energy storage project of 100 MW/129 MWh (lithium-ion), Japan has a 50 MW/300 MWh (sodium sulphate) project and California a 20 MW/80 MWh (lithium-ion) project. Besides, there are numerous other energy storage system projects deployed worldwide.
In India, Powergrid is implementing a 1 MW capacity pilot project based on battery energy storage in Puducherry. The technologies used include advance lead acid 500 kW/250 kWh and lithium-ion 500 kW/250 kWh. This project will help understand the aspects of commercial feasibility. On its successful implementation, the project will act as a case study for future large-scale installations. One of the major challenges for the transmission segment is that the gestation period of renewable generation projects is less than that for transmission projects. Moreover, LTA application is required for taking up the implementation of renewable energy transmission projects. Another major hurdle is the variability experienced during power generation from renewables and this calls for the need to have balancing reserves in place. Quick ramp-up is required through pumped storage, hydro and gas in order to manage renewable energy variability.
That said, robust transmission is required for the integration of renewables to get to a zero-carbon emission environment. This requires greater flexibility, controllability and observability in the current transmission system. Also, energy storage needs to be considered for the optimisation of transmission assets. Last, further capacity building is needed to address the current challenges and ensure the smooth integration of renewables into the grid.
With inputs from a presentation by Dr Subir Sen, COO, CTU Planning and Smart Grid, Powergrid, at a recent Power Line conference