Balanced Generation

Optimising the power mix in medium and long-term scenarios

The Government of India has made a commitment to achieve 40 per cent of the cumulative installed electricity capacity from non-fossil fuel-based energy resources by 2030. It has also set a target to reduce the country’s emission intensity to 35 per cent by 2030, 33 per cent lower than the 2005 levels. To this end, the renewable energy roadmap for 2022 has been charted and projects are already being implemented on-ground. However, to make power accessible to and affordable for all, it needs to be scheduled and generated at the lowest possible cost.

A committee has been formed to decide on the optimal energy mix in power generation on both medium and long-term basis. The aim is to achieve energy autonomy and provide clean, affordable, reliable and sustainable power to all. The committee has issued a report to assess the generation mix required between 2022 and 2027, taking into account the Intended Nationally Determined Contribution (INDC) targets and an increased share of hydro power. In addition, the report discusses the flexible operation of thermal power plants for integrating 175 GW of renewable energy by 2022. Renewable Watch takes a look at the report’s findings with respect to the renewable energy sector.

Achieving optimal generation mix

The key focus of the report is on methods for the optimal generation of power. This is a pressing issue for any nation. Generation of power and its offtake need to be scheduled in such a manner that the costs are minimum and outputs are maximum. In most cases, power generation is optimised considering the costs associated with the operation of the existing and committed generating stations, as well as the levellised capital costs and operating costs of the new generating stations. Moreover, policy and regulatory constraints such as capacity addition targets, must-run status of renewable energy sources (RES), loss of load probability, reserve energy margins and emission limits have to be considered.

Based on the electricity demand assessed under the 19th Electric Power Survey and the renewable capacity addition target by 2022, generation mix studies for an optimum capacity mix have been carried out for the periods 2021-22 and 2026-27. This study has been done to support the National Electricity Plan and with the assumption that the renewable energy generation would be fully absorbed into the system without any curtailment. The study estimates that the peak power demand will be about 225.8 GW in 2021-22, for which 1,566 billion units (BUs) of electricity would be required. In 2026-27, the peak  demand is expected to rise to 298.8 GW, for which 2,047 BUs of electricity would be required. Hence, it is projected that between 2017 and 2022, 6,823 MW of hydro power, 25,545 MW of thermal, 3,300 MW of nuclear and 1,17,756 MW of renewable energy capacity will be installed in the country.

For the period 2022-27, two scenarios have been considered to meet power demands. In the first scenario, India’s current capacity addition targets have been analysed to match with the INDC targets. It has been observed that even with 1,25,000 MW of installed capacity from RES, that is, with a capacity addition of 100,000 MW during 2017-22 and 25,000 MW during 2022-27, as well as a committed capacity addition from hydro and nuclear, the INDC targets can be easily achieved.

The second case focuses on hydropower and considers a higher installed capacity of 80,000 MW by 2027. It has been found that in this scenario, 60 per cent of the installed capacity would come from non-fossil fuels while 40 per cent would come from fossil fuels. However, in this case, efforts have to be made on a war footing to timely harness the hydropower potential.

Thus, it is projected that the total share of renewable energy in the capacity mix will increase from 17 per cent in March 2017 to 44 per cent in March 2027, while the share of thermal power will reduce from 67 per cent to 43 per cent during the same period, which is in line with the government’s targets. However, energy generation from renewables will increase from 6 per cent in March 2017 to 23 per cent in March 2027, while the energy generation from thermal sources will reduce from 81 per cent in March 2017 to 60 per cent in March 2027. This shows that even though the share of installed renewable capacity will be the highest in 2027, most of the energy generation will still come from fossil-based sources.

Integration of renewable energy

Numerous studies have already established that there should be sufficient inertia in the power system to accommodate the variable renewable energy generation. To achieve this, conventional thermal power plants will need to become more flexible to step up or step down their output in a short time. The study finds that the gas-based units currently in operation can be suitable for this purpose. However, suitability for peaking operation will need to be studied on a case-to-case basis as it depends on the inspection schedules and start-up costs. Moreover, if coal-based capacity is considered for flexible operation, load-following costs will have to be accounted for. In addition, the operation of super-critical units at lower loads can move thermal power plants into the sub-critical range, which will result in a considerable loss of efficiency and subsequently, increase generation costs.

The study also shows that the gas-based combined cycle plants and hydropower plants contribute towards greater flexibility of the power grid. It has been observed that gas-based stations should be operated at low plant load factors (PLFs) so that they can be ramped up or down when required, instead of being completely shutdown and restarted again. Proper scheduling and utilisation of hydro power for providing secondary and tertiary frequency control (ancillary services), reactive power support, as well as black start services could also help in integrating renewable energy into the grid. Studies undertaken by Power System Operation Corporation Limited have revealed that power system balancing with 175 GW of renewable energy is achievable with the current 15-minute operational timescales and minimal renewable energy curtailment. However, reducing the minimum generation levels of large thermal plants would be essential for  lowering the renewable energy curtailment.

Emerging technologies

The report mentions technologies that have been or are being implemented in other parts of the world, and could be used to support India’s energy growth.

  • Ultra supercritical technology: These plants have greater efficiencies than supercritical and subcritical plants, and operate at steam pressures of 280 kg per centimetre square and temperatures of 600 oC. The technology is being adopted for the recently awarded, coal-based capacities in Madhya Pradesh.
  • Battery storage: Battery storage systems are being considered by most nations that have set ambitious renewable energy targets to assist grid balancing. To a certain extent, grid flexibility can be provided by energy storage systems due to their fast response. Other benefits such as small size, decreasing costs, reduced installation time, etc. have motivated India to consider battery storage systems. The report acknowledges that battery storage may soon  play a broader role in energy markets by moving from niche uses such as grid balancing to replacing thermal power generators for reliability, providing power-quality services, etc.
  • Electric vehicles (EVs): In its National Electric Mobility Mission Plan 2012, the government has envisaged that India would have 6 million EVs by 2020. The study assesses that while a higher EV penetration could lead to increased electricity demand; this demand would not be very significant. It is assumed that to serve the EV load, increased capacity additions would not be required as the demand would be confined to off-peak hours. In addition, EVs may help in utilising the solar energy during solar peak hours, thereby reducing the need for flexible operation of coal-based plants.

Outlook

The report observes that there is not much scope in optimising the generation mix by the year 2021-22, in light of the renewable energy targets, efforts in energy efficiency, energy requirements, availability of domestic gas, and existing and under construction power projects. However, generation can be optimised for the period 2022-2027 by either focusing on INDC targets or providing impetus to hydro power. The report concludes on the need for conventional generating plants to be flexible in order to meet the balancing and ramping requirements of the grid for accommodating the variable and uncertain renewable energy generation.

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