Energy storage is emerging as a critical requirement as the country moves towards smarter grids, renewable energy integration and greater uptake of electric vehicles (EVs). At the grid level, storage systems can be installed to address the resource variability issue associated with solar and wind power. Storage systems are essential to store surplus energy at the time of over-generation and feed this energy into the grid at the time of under-generation, thereby enabling better grid management through improved scheduling of power. Further, energy storage systems (in the form of Lithium-ion [Li-ion] batteries) are currently an EV’s most expensive and critical component. The manufacturing of these storage systems/batteries, therefore, presents a significant economic opportunity, given the government’s National E-Mobility Programme with a target of 100 per cent EVs by 2030.
The Indian battery energy storage market is currently dominated by lead-acid batteries, which are used by all categories of consumers for power back-up, as well as for running vehicles. However, due to limited depth of discharge, lower cycle life and other technical issues associated with these batteries, the market demand is shifting towards more advanced batteries like Li-ion, redox flow and sodium sulphate that can offer a longer cycle life and greater depth of discharge. In remote locations, small battery-based energy storage systems are being increasingly deployed alongside solar plants to resolve energy access issues.
In addition, hydropower pumped storage plants (PSPs) continue to be the oldest and the largest energy storage technology systems available for utilities. PSPs offer the unique advantage of acting as a load in the pump mode by raising the water to upper reservoir during times of surplus power and running in generating mode during times of deficit power situation in the grid. The country currently has an installed capacity of 4,786 MW of PSPs. Besides pumped hydro, there are several battery-based technologies currently prevalent in the storage space. Chief among these are solid-state batteries, flow batteries and flywheels.
Solid-state batteries use electrochemical cells that convert the stored chemical energy into electrical energy. The most common type of solid-state battery storage technology is the Li-ion battery, deployed for applications ranging from a few kWh in residential solar systems to providing ancillary services to the grid. Electrochemical capacitor (EC) batteries, meanwhile, physically store energy and have a very low response time with a nearly unlimited charge-discharge cycle. Considering that these have a relatively longer life cycle, EC batteries are typically suited for large-scale grid integration applications.
Nickel-cadmium (Ni-Cd) batteries can be found in some of the earlier storage systems and are typically used for stabilising wind power generation systems. The sodium-sulphur battery has also found application in energy storage technologies. It has a 90 per cent round trip efficiency, which has made it a preferred choice of energy operators in Japan, where it has been demonstrated at over 190 sites.
Flow batteries are rechargeable energy storage systems that can be instantaneously recharged by replacing the electrolyte liquid, while simultaneously recovering the spent material for re-energisation. These include redox flow batteries, iron-chromium, vanadium redox and zinc-bromine batteries.
Flywheel battery systems use kinetic energy stored in a rotating mass, which is discharged by drawing down the kinetic energy using the same motor generator. Low-speed flywheels use steel as the core rotating material with a speed of 10,000 rotations per minute (rpm). More advanced flywheels have achieved, high speed (about 100,000 rpm), high efficiency and low losses by using fibre glass resins or polymer materials with high tensile strength, and rotations in vacuum-like conditions to create minimum aerodynamic drag. These have extremely fast ramp and response rates and can go from full discharge to full charge in a few seconds. These advantages make the flywheel technology more preferred for energy service applications, power back-up, fast area regulation and frequency response.
The way forward
Indian utilities are taking gradual steps to deploy energy storage systems. A case in point is the commissioning of the country’s first grid-scale battery storage system (10 MW) by Tata Power, AES Corporation and Mitsubishi Corporation in Delhi in February 2019 based on Li-ion storage technology for the project. The Solar Energy Corporation of India has also launched solar and wind tenders entailing battery energy storage and more such tenders are expected in the future. As per NITI Aayog’s report, “India’s Energy Storage Mission” (November 2017), the market for EV batteries alone could be worth $300 billion from 2017 to 2030. Going forward, to meet the goal of large-scale deployment of EVs and smooth integration of renewables to the grid, India will require cutting-edge battery manufacturing technology and timely action to capture the fast-evolving technological landscape in energy storage.