An Expert Explains: Why battery storage is essential for a renewables-heavy electricity grid

Unlike traditional sources of energy which boast a consistent and predictable output, renewables come with the challenge of weather-based variability. This is why battery storage infrastructure is crucial in this regard

A large battery storage power station with a capacity of 6.24 MWh and an output of 5 megawatts in Eastern Switzerland. (Wikimedia Commons)

With India targeting to have half of its electric power capacity come from renewables by 2030, the resilience and stability of its power grid have never been more critical. Renewables, while essential for a sustainable future, come with their own set of challenges.

Foremost among these is the inherent variability of renewable energy sources like wind and solar. Unlike traditional energy sources that provide a consistent and predictable output, renewable energy generation fluctuates based on weather conditions, posing a risk to grid stability. The electricity grid, thus, needs to be equipped with additional flexibility that will allow power generation to be ramped up or down based on demand.

To this end, a separate market for grid-flexible resources, called the ancillary services market, will have to be set up. Such markets exist in all geographies where the share of renewable energy in the grid has breached the 15-20% mark (renewables make up roughly 10% of India’s energy portfolio at the moment).

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Ancillary Services

In absence of infrastructure that can store electricity in large amounts, it must be produced as it is used. The electricity grid responds to shifting demand to continuously generate and route electricity to where it is needed the most.

This is all fine when it comes to traditional energy sources, with their consistent and predictable output. However, fluctuations in scheduled dispatches of electricity generated from renewables could have an error of 3-5%. For an installed renewables capacity of 500 GW (as India plans to achieve by 2030), a 3% error would amount to a supply reduction of 15 GW, enough to cause a severe imbalance in the grid.

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Ancillary services provide quick, real-time adjustments to balance supply and demand of power. There are three kinds of ancillary services:

Primary services respond to fluctuations in real-time (less than a second), which makes them the most relevant in addressing imbalances in renewables-heavy grids. They can only be provided via hydroelectricity, and battery storage (more on that later).
Secondary services respond to fluctuations within 10-15 minutes. These comprise gas-based capacities.
Tertiary services take about 20-30 minutes to respond, and comprise thermal power plants, including the coal-fired plants that remain in use in India.

The Covid Example

To illustrate just how these services would work, it will be useful to recall the evening of April 5, 2020 during the first Covid-19 lockdown. Prime Minister Narendra Modi had called for a switching off of lights at 9 pm for 9 minutes. This led to a sudden load reduction of almost 15 GW at 9 pm, and a subsequent increase in load at 9.09 pm.

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A Power System Operation Corporation Ltd (POSOCO) report published after the event outlined how the grid was managed. The load reduction was carried out in a phased manner, a few minutes before 9 pm by reducing power generation from thermal, gas, and hydel sources by about 11 GW. At 9.10 pm, hydropower stations were ramped up to supply approximately 17.5 GW, enough to handle the sudden surge in demand.

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The unique characteristic of hydropower — the ability to instantly ramp up or down — was crucial in this regard. Gas and thermal power stations require 8-20 minutes to do the same. The only other resource with similar characteristics as hydropower in this regard is battery storage.

This is more so because unlike in the Covid-19 event, which was meticulously planned for in advance, real life situations may not serve any advance notice. For the 9 minute long event, POSOCO had assumed full control of hydropower resources in advance, effectively removing it from the energy market and operating it independently.

Need for Battery Storage

The deployment of Battery Energy Storage Systems (BESS) within the ancillary services market will be crucial as India’s grid becomes more renewables-heavy. This is because BESS is the fastest in responding to grid contingencies, and can transition from standby to full power in under a second. It can provide essential services such as frequency control, voltage regulation, congestion relief, peak shaving, power smoothing, and peak capacity support, making it an invaluable asset in the modern grid.

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The Global Energy Alliance for People and Planet (GEAPP) partnered with BSES Rajdhani Power Limited (BRPL) and IndiGrid to launch India’s first commercial-scale BESS pilot in New Delhi earlier this year. This 20MW/40MWh project (which can provide up to 20 MW of power for two hours) is designed to provide reliable power access to over 12,000 low-income consumers in Delhi.

The Central Electricity Regulatory Commission has identified the need for 4 GW of such capacities to ensure grid flexibility and stability. By 2031-32, India has estimated a storage requirement of 73.93 GW, a majority of which is expected to come from BESS.

Saurabh Kumar is Vice President — India at Global Energy Alliance for People and Planet (GEAPP)