Over the last few decades, the demand for electricity has grown considerably in India and many other developing countries. In 2018, India’s annual gross electricity generation reached 1486.5 TWh, with about 79% of this generation produced from fossil fuel combustion.
The volume of carbon emissions created by such combustion has negative implications for the environment. To address these growing concerns, India has set itself aggressive renewable energy targets, including generating more than 30 percent of its electricity from renewable resources by 2030.
However, the intermittent nature of renewables poses several challenges for utilities, namely in terms of load balance, grid stability and security. Many solutions have been put forward to remedy this, including using demand-side management and strengthening grid infrastructure.
Another promising approach is Energy Storage (ES). As well as mitigating the intermittent nature of renewables, ES offers multiple additional benefits. These include providing back-up services during power outages, meeting peak electrical load demands, offering time-varying energy management, meeting remote and vehicle load needs and enabling smart grids.
There are six types of ES technology available: mechanical, electrochemical, electrical, thermochemical, chemical and thermal (see diagram below). The choice of technology mainly depends on cost and how it’s being applied to the grid ie. whether it’s for load management, power quality or back-up services.
The grid ES market is big and expected to grow further as renewables become more widely used. Navigant Consulting reported that the global market for grid-scale ES is expected to grow from the $675 million annually that it was in 2014 to $15.6 billion annually by 2024.
As of now, the dominant ES technology for grid application is pumped hydro, which has an installed capacity of about 135G W globally, equating to 96 percent of installed ES technology. The quick response of pumped hydro makes it suitable for frequency regulation, but it requires lengthy construction time and high capital investment.
In India about 2.6 GW of pumped hydro plants are already in operation while another 3.1 GW is under construction after long delays. Proposals for another 8.9 GW are still awaiting approval, hindered by cost, time and numerous social and environmental clearances.
Other ES grid applications include flywheels, compressed air and electrochemical batteries. Though their relative share is small, demand for them is set to grow quickly thanks to new developments in battery technology.
Earlier this year, Tata Power launched its first grid-scale battery-based energy storage system in Delhi, with an installed capacity of 10 MW. More recently, the Indian government has floated several tenders for grid-based battery energy storage technologies.
Battery usage varies depending on whether it’s for residential, industrial or commercial purposes. For residential consumers, batteries are used as back-up to address power outages and mostly have a capacity of less than 5 kW. Lead acid batteries are the most widely-used rechargeable kind, and are often seen in rooftop solar installations.
For industrial consumers, the demand for battery-led ES storage is smaller because power outages are scheduled and planned. Standby diesel generators are generally used for back-ups where needed, with ES reserved for critical loads.
The preference in the commercial sector is for low maintenance batteries, especially from smaller commercial units. Telecom towers, petrol pumps, academic institutions, medical centres and rural banks tend to use solar systems with battery back-up.
Another kind of battery technology is Lithium-Ion, largely used in laptops and cellphones. With electric vehicles now on the rise, there’s now an even greater demand for Lithium-Ion batteries. Offering high energy density and lightweight design,a typical lithium-ion battery can store 150 watt-hours of electricity in 1 kg of battery. This is six times higher than a typical lead acid battery, which can store only 25 watt-hours per kg.Nevertheless, Lithium-Ion is expensive and can degrade quickly.
Meanwhile, other new battery technologies are entering the market, such as nickel-cadmium and sodium-sulphur, plus flow batteries like vanadium redox and zinc bromine. Current commercial scale applications remain limited though.