Balancing the Load

Spotlight on fast-ramping energy storage systems

India has an ambitious goal of installing 225 GW of renewable energy, including 175 GW of solar and wind by 2022. Analysts expect that the country will achieve at least 175 GW, though this will put a strain on the already creaking grid infrastructure. Therefore, the recent rush to add energy storage capacity in renewable energy plants is the most likely reaction to the increasing renewable energy integration.

Renewable energy systems face issues such as periods of excess and shortage in electricity generation. Solar energy systems work best in bright sunlight while hydropower systems work only when there is water and wind energy systems when there is wind. So, the problem faced by countries today pertains to the storage of excess energy, or the reduction of demand during periods of low generation, or both.

Energy storage provides a myriad of benefits along with cost savings. Large-scale energy storage allows the electrical system to run more efficiently, which means lower prices and lower emissions, and more reliable power. Traditional energy sources such as coal- and gas-based power plants have to be ramped up or down as demand fluctuates, and are almost never operating at peak performance. This means that energy not only costs more, but also pollutes more. And the slow ramp-up time of these bulk generation facilities means they cannot respond to spikes in demand in real time, potentially leading to brownouts and poor power quality.

With energy storage solutions, renewable technologies can continue to power the grid even when the sun has set and the air is still, levelling out jumps in output to create a continuous, reliable stream of power throughout the day. Storage technologies also improve the quality of power through frequency regulation, allowing companies to produce power when it is cheapest and most efficient, and providing an uninterruptible source of power for critical infrastructure and services.

Types of energy storage

Energy storage systems consist of an array of technological approaches that can be covered under the following categories:

  • Solid state batteries: A range of electrochemical storage solutions, including advanced chemistry batteries and capacitors
  • Flow batteries: Batteries that store energy directly in the electrolyte solution for longer cycle life and quick response times
  • Flywheels: Mechanical devices that harness rotational energy to deliver instantaneous electricity
  • Compressed air energy storage: Utilising compressed air to create a potent energy reserve
  • Thermal: Capturing heat and cold to create energy on demand
  • Pumped hydropower: Creating large-scale reservoirs of energy with water

Pumped storage hydroelectricity (PSH) is used by power systems for load balancing. Pumped storage systems use cheap electricity to transport water from a downhill lake to an uphill lake. They regenerate electricity when it is required using turbines just like the ones in hydropower stations.

These systems store the gravitational potential energy of water pumped from a lower elevation reservoir to a higher elevation. Low-cost surplus off-peak electric power is typically used to run the pumps. During periods of high electricity demand, the stored water is released through turbines to produce electric power. Pumped storage systems store energy from intermittent sources (such as solar, wind and other renewables), or excess electricity from continuous baseload sources (such as coal or nuclear) for periods of higher demand. The reservoirs used with pumped storage are quite small when compared to conventional hydroelectric dams of similar power capacity, and generating periods are often less than half a day.

Pumped storage is the largest form of grid energy storage. As reported by the United States Department of Energy Global Energy Storage Database, PSH accounted for over 95 per cent of all active storage installations worldwide as of 2017, with a total installed nameplate capacity of over 184 GW, of which about 25 GW is in the US. The energy efficiency of PSH is 70-80 per cent, with some sources claiming up to 87 per cent.

The main disadvantage of PSH is that a special site is required for its development, with both geographical height and water availability. Suitable sites are therefore likely to be in hilly or mountainous regions, thus potentially in areas of outstanding natural beauty, creating social and ecological issues. Many recently proposed projects, at least in the US, have avoided highly sensitive or scenic areas, while some have proposed to take advantage of “brownfield” locations such as unused mines.

In the UK, there are four pumped storage facilities, which can together store 30 GWh of electricity. They are typically used to store excess electricity at night, then return it during the day, particularly during the peak demand period, which is a profitable business. The Dinorwig power station, inside a mountain in the Snowdonia national park in Wales, has enough capacity to restart the national grid in the event of a major failure. Dinorwig can switch on from 0 to 1.3 GW power in 12 seconds. The total energy that can be stored at the station is about 9 GWh. Its upper lake is about 500 metres above the lower, and the working volume of 7 million m3 flows at a maximum rate of 390 m3 per second, allowing power delivery of 1.7 GW for five hours. The efficiency of this storage system is 75 per cent. If all four pumped storage stations are switched on simultaneously, they can produce 2.8 GW. They can switch on extremely fast, coping with any slew rate that demand fluctuations or wind fluctuations could come up with. However, this capacity will not be enough to meet the country’s power demand if suddenly there is no wind.

Pumped storage systems should preferably be near large wind farms. To this end, a new artificial lake could be made in a hanging valley (across the mouth of which a dam would be built), terminating above the sea, with the sea being used as the lower lake. A pumped storage facility can also be put up in an underground chamber. A pumped-storage chamber 1 km below London has been proposed. By building more pumped storage systems, any country can increase its maximum energy storage.

A growing market

A next-generation smart grid without energy storage is like a computer without a hard drive. According to market research firm IHS, the global energy storage market is growing exponentially, and is expected to reach over 40 GW by 2022 from an initial installed base of only 0.34 GW in 2012 and 2013. An IMS Research report expects the solar storage market, which was less than $200 million in 2012, to catapult to over $25 billion by 2020. Flywheel and battery energy storage systems are operating in the competitive ancillary services power market, providing a ten times faster and more accurate response to a power dispatcher’s signals compared to power turbine generators.

US-based utility PJM Interconnection projects that a reduction of just 10-20 per cent in its frequency regulation capacity procurement through additional storage projects could result in savings of $25 million-$50 million for residential, commercial and industrial consumers. Meanwhile, the California Public Utilities Commission has approved a target for the state’s three largest investor-owned utilities, aggregators and other energy service providers to install 1.3 GW of energy storage capacity by 2020.

India’s first grid-scale battery energy storage system of 10 MW was set up in February 2019 at Tata Power Delhi Distribution’s Rohini substation. It is said to be South Asia’s largest. The project will provide grid stabilisation and protect the critical facilities of the company.

The grid-connected system, owned by AES and Mitsubishi Corporation, will make way for much wider adoption of grid-scale energy storage technology in India. At the launch of the system, Praveer Sinha, CEO and managing director, Tata Power, said, “Grid-scale energy storage will pave the way for ancillary market services, power quality management, effective renewable integration and peak load management of Indian grids.”

A fast-ramping energy storage system like this can be built within months to provide critical flexibility. Moreover, battery-based energy storage does not require water, or produce emissions from its operations, yet provides the flexibility and agility for integrating intermittent solar and wind energy resources into the electric grid. In contrast, technologies such as pumped hydro storage can take years to build and are highly dependent on geographical locations. The Solar Energy Corporation of India has already invited bids for over 200 GWh of storage connected to solar energy systems in Andhra Pradesh, Jammu & Kashmir, Lakshadweep and Himachal Pradesh.

In March 2019, the cabinet approved the National Mission on Transformative Mobility and Battery Storage, under which two-phase manufacturing programmes will be introduced across the country. The first will support the setting up of gigafactories for battery manufacturing across India, while the second will focus on electric vehicle manufacturing. The announcement came shortly after the Andhra Pradesh Economic Development Board signed an MoU with Urja Global for the manufacturing of lithium-ion batteries and electric vehicles. The initiative will see Urja Global investing $28.55 million in manufacturing centres across the state.

Battery-based energy storage allows electricity to be stored and delivered within milliseconds, reducing grid instability and enabling more energy to be captured and delivered on demand. Thus, it is best that the government promotes the deployment of these systems. Given the cost economics and the future energy requirements, battery-based storage may replace pumped storage as the primary energy storage technology and play a key role in realising India’s vision for a more sustainable energy future.

By Anita Khuller


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