Power grid operators around the world have been experiencing challenges in operating the grid with the increasing penetration of Variable Generation (VG) sources like Solar PV and Wind. Variability in one form of generation must always be compensated with other modes of generation at all times to ensure grid stability. There is a need for the Indian Grid architecture to sustain and support a consequent increase in ramping requirements due to the renewable energy (RE) target of 175GW by the year 2022 enunciated by the Government of India. The Electricity demand is inherently variable. External Lighting demand does not come up in the day, Air conditioning demand is higher in summer, etc. The process of increasing generation to meet the demand is referred to as Ramping in the conventional parlance. With the onset of Solar/ Wind, it should be noted that variability is introduced in supply side too due to the inherent intermittency of electricity generation in VG sources. Power grid operators in India currently can choose to meet the ramping needs through conventional generation technologies like Coal, Natural Gas, Hydro, solar, wind, Biomass plants, etc. 60% of the installed generation capacity on the Indian power grid is thermal generation using coal as fuel.
These coal plants, most of which are based on sub-critical coal technologies, are designed to operate primarily as baseload units and are not fully capable of quickly ramping up and down to fulfill demand-spikes or supply-shortfalls. Using these sub-critical coal plants to meet the ramping requirements may result in a severe drop in the overall thermal efficiency of the coal plants leading to increased carbon emissions per unit of power generated that may offset some of the benefit gained through installing Solar PV plants. Sub-critical coal plants may also incur additional maintenance costs due to the wear and tear created by the daily ramping cycles to which these plants will be prone to.
At this juncture, it is essential to juxtapose the fact that India has over 26 GW of natural gas plants constituting about 8.5% of the total installed capacity that has been operating only around 20% capacity factor over the last 3 years due to chronic natural gas unavailability. Also, while India has high Hydropower generation potential, the water availability during summer peak load periods and siltation during monsoon may somewhat limit the availability of Hydro generation to meet any accelerated ramping needs. The problem of lack of sufficient ramping capability on the system (also referred to as flexibility) therefore
may not only make the slow acting thermal units (primarily coal-based power plants) economically unviable but also result in curtailment of renewable generation to keep the grid stable. The nature of the problem mandates the architecture to feature embedded flexibility to allow a higher penetration of renewables on the grid.
While Demand Side flexibility enhancing paradigms like Time-of-use and Demand Response programs do exist, it is also feasible to infuse flexibility into the system through supply side (generation) technologies that will facilitate the scaling of VG sources with lesser friction to adoption from consumers. The Supply side flexibility can be introduced into the system by having generation resources that are capable of quickly starting up from zero to any required output value within minutes. Such a generator should also be capable of multiple starts and stops a day and should have a dispatchable output. Three major technology streams: Flexibility from Coal generation, Flexibility from Natural Gas generation and Flexibility from Renewable and Emerging Technologies (RT/ET option) can be considered as solution alternatives to the ramping problem, that are available for the policymakers to build the needed generation flexibility into the system.
Natural gas is generally considered as the bridge fuel for the world economy to move from carbon-intensive coal to zero-carbon energy production. This is because GHG emissions from Natural gas are about 65% lower than those of coal plants. Also, the thermal efficiency of Natural gas (upwards of 50%- 60%) is much higher than the Coal plants (33%). However, power generation from Natural gas needs massive capital investments into both the gas power plants as well as the storage and transportation infrastructure for the gas. Considering only the capital investments required to build gas plants, our work has shown that the Natural Gas alternative is inferior to both the flexible coal option as well as RT/ET option. In addition, Natural gas infrastructure typically has a life of 30-60 years. This means any new gas plant build today will continue to operate through 2050 and beyond. Investing in the Natural gas may create a carbon lock cycle in India, especially from high RE integration into the grid perspective that may be detrimental to the goal of quickly moving towards zero carbon future. Given the paucity of Natural gas resources, India would have to rely on imports for its power production resulting in potential energy security issues.
The ramping need on the system can also be met through a combination of renewable resources like Hydro and biomass as well as energy storage technologies. India has a total hydro potential of 148 GW out of which 44 GW has been installed. India also has about 20 GW of biomass potential with 5 GW currently installed. Biomass is generally considered to have a similar ramping capability as coal. Technology improvements and retrofits of existing biomass plants will be able to yield some improvements in the ramping capability. Hydro & other renewable power generation contributes to ~30% footprint in the installed generation capacity. Excessive reliance on this alternative might not suffice to meet the full ramping requirements once VG sources start operating at scale. Energy storage technologies both at the grid and domestic level have had promising developments in the past decade. There are several other emerging technologies like Solar Power with storage, off-shore wind generation, microgrids, and smartgrids, etc. that utilize a combination of supply side and demand side technologies to provide ramping capabilities on the grid. But it should be noted that adopting this alternative would imply large- scale greenfield investments apart from the issue that actual generation potential, costs, and technology readiness are still under evaluation in the majority of these futuristic technologies.
Taking into cognizance, the fact that India has abundant coal reserves and a vast amount of coal capacity already built on the system, retrofitting existing coal option seems to have very attractive returns. It is also important to note that except for 52 GW of Thermal power capacity that will be obsolete for any retrofitting after 2027, the remnant capacity can easily be upgraded for supporting flexible generation. Given that the installed capacity is sunk cost, using this capacity to meet the daily ramping requirements seems to be the most viable and feasible among all other alternatives.Considering incremental capital costs, incremental fuel costs and additional carbon emissions across each of the options, we recommend that the optimal
path for India to integrate ambitious RE capacity into the national power grid would be to rely on flexible coal plants as the bridge to directly leapfrog into the renewable energy-heavy grid. For this to come to fruition, the Coal generation technology needs to quickly move from the concept of Coal serving as base-load plants to coal plants being equipped to play the role of Peaker plants. Concomitantly, India’s power policy requires to promptly operationalize other Renewable & Emerging technologies like the off-shore wind that have complementarity to Solar PV profile as well as energy storage technologies like pumped hydro, battery storage, etc. Making the load responsive to grid requirements through the use of smartgrid and deep energy efficiency technologies will also go a long way in achieving ambitious renewable energy goals on the grid.
Written by Prof Amit Garg and Rajeev Annuluru
Prof. Amit Garg is a faculty with the Public Systems Group at IIM Ahmedabad. He is currently the Chair for Fellow Programme in Management at IIMA. Rajeev (PGPX 2016-17) graduated from IIM Ahmedabad. This article is based on the research undertaken by the authors.