As India’s installed renewable energy generation increases rapidly putting pressure on evacuation infrastructure, the Central Electricity Authority (CEA) has suggested creating two separate groups of thermal power plants (TPPs) to manage ramp-up and ramp-down operations.
Coal-based power plants are used to maintain base load and grid stability. During the day they have to ramp down power output to accommodate solar power. However, in the evening they have to ramp up output as RE generation declines. Constant ramp up and ramp down creates wear and tear in plant equipment like boilers and turbines.
The CEA recently deliberated with industry stakeholders on ramp rate compliance, scheduling methodology and equipment stress during flexible operations, which for a coal-based plant means ramping up or down the electricity output quickly as solar or wind power generation rises or falls.
They looked into practical challenges related to sudden ramp ups & ramp downs, scheduling methodology, Deviation Settlement Mechanism (DSM) implications and equipment stress during flexible operations.
To ensure large scale integration of renewable energy while minimising the adverse impact of low load operations on the grid, the CEA recommended avoiding consecutive ramp-ups and ramp-downs of the same plants. It suggested selecting one group of units for ramp-up and another group for ramp-down.
Here, the ramping schedules should be rotated among a pool of units or plants rather than assigned strictly according to the Merit Order. This will alleviate the stress exposure of individual TPPs and share the burden among a larger pool of units to preserve the overall health of the plants.
To reduce the operations and maintenance (O&M) costs of power plants and extend their operational life, the Authority suggested that a set of power plants shall ramp down to the Minimum Technical Load (55 per cent or 40 per cent) in the morning when solar generation increases, followed by minimum load operation during solar hours and then load ramp up in the evening when solar generation declines, or sufficient stabilisation time shall be provided before change in direction of ramp.
The Authority emphasised that frequent high-magnitude ramping — rather than low-load operation — is the primary cause of severe wear and tear in the units because coal units are increasingly being used for fine grid balancing.
When these load ramps occur consecutively, the unit lacks sufficient time to stabilise creating additional system disturbance and stress on critical components.
Another option suggested by the CEA for fine grid balancing is utilising hydro power plants, gas power plants, pump storage plants, and battery energy storage systems (BESS).
The suggestions are part of a report that has been prepared after consultations with NTPC, Damodar Valley Corporation, Bharat Heavy Electricals, Rajasthan Rajya Vidyut Utpadan Nigam, Grid Controller of India and Adani Power, among others.