The changing role of various energy sources in meeting the power demand is driving India’s energy transition. In the coming years, the share of renewables in the energy mix is expected to increase significantly leading to a decline in the share of coal and oil, while the share of gas is likely to remain constant. Gas-based power will be used more for meeting the peak demand than the baseload demand. Over the past decade, gas-based installed capacity has increased from 14.8 GW in 2008 to 25 GW in March 2019, recording a growth of around 67 per cent. However, the plant load factor has decreased from about 60 per cent to 22 per cent during the same period. Gas-based power generation has also reduced from 73 billion units (BUs) in 2008-09 to 50 BUs in 2018-19. The key challenges facing the gas-based power segment in India are dwindling domestic gas supplies as well as taxation and regulatory issues. Measures are being taken to address these challenges. In the coming years, gas-based power plants will emerge as one of the peaking power options in view of the large-scale renewable capacity addition programme.
Peaking power opportunities
As per the National Electricity Plan 2018, the peak power demand in 2021-22 and 2026-27 is expected to increase to 226 GW and 299 GW, respectively, from the current level of 175 GW. To meet this peak load, a net load ramp of around 500 MW per minute (for 15-30 minutes) will be required during the winter months from November to February in 2022. A recent study by Power System Operation Corporation has concluded that a ramp rate of 300 MW per minute must be provided by coal and gas based power plants. Of this, more than one fifth is expected to come from gas-based power stations. While there are other sources for meeting the peak power demand, including storage-based hydropower plants, thermal storage and battery storage systems, gas-based units require the least amount of time for start-up and the least amount of energy per MW. This stands true for both open cycle gas turbines (OCGTs) and combined cycle gas turbines (CCGTs).
Benefits of gas-based power
Gas-based power plants offer several advantages as peaking plants. They allow quick ramping, offer black start facilities (the process of restoring power in the event of a total or partial shutdown of the grid without relying on the recovery of the external electricity transmission system), relieve network constraints, and provide increased flexibility. Gas power plants can operate at as low as 10-20 per cent of the related load in open cycle mode. Combined cycle gas plants are suitable for providing primary frequency response as they can produce up to ±15 per cent of the gas turbine rated load (± 10 per cent combined cycle rated load) as primary response in 10 seconds and full stabilised response within the first 30 seconds. Besides, gas is a clean energy source next to renewable energy sources. Gas-based plants emit NOx emissions as low as 25 parts per million (ppm), which can be reduced to 15 ppm with the use of new technology. Domestic gas-based power also provides an economical option with a variable cost of Rs 2.5-Rs 3 per unit, much lower than the peak hour price of electricity on the exchanges.
Challenges and the way forward
The flexibilisation of gas-based power plants increases the operations and maintenance costs while reducing efficiency. The use of new technologies though can prevent inefficiencies. In combined cycle mode, the turbine takes two to three hours to get started. Till then, it can be operated in open cycle mode. With the increasing integration of renewable energy into the national power grid, the role of gas-based power in flexible and peaking operations is also increasing. Apart from priority allocation of domestic gas, which will be the basic requirement for supporting the operations of gas-based plants, a number of policy and regulatory changes are needed. These pertain to the declaration of availability, the scheduling mechanism, and modifications in the gas supply contracts providing flexibility to power producers in terms of gas delivery rate and time. Suitable compensation mechanisms need to be in place to support the peaking operation of gas stations along with modifications in the operating norms. A uniform taxation policy should be introduced to make gas-based power generation economical in all states.