Compressed CO2 may be the answer to affordable long-term renewable energy storage: NTPC CMD Gurdeep Singh

Energy Dome

NTPC Ltd, India's biggest state-run power generator, is actively looking at scaling the use of compressed carbon dioxide for energy storage systems, according to Gurdeep Singh, the company's chairman and managing director (CMD).

"We have started working on compressed CO2 energy systems for long-term storage of renewable energy. For long-term, we currently has pumped storage systems, but they are location based. The good thing about compressed CO2 energy storage systems (CCESS) is that they can be built within the renewable energy parks," Singh said at the India Energy Week in New Delhi.

On January 29, NTPC Ltd announced that a CO2 battery with an energy storage capacity of 160 MWh will be set up at NTPC Kudgi, Karnataka. The project is spearheaded by NETRA, the R&D wing of NTPC, in collaboration with M/s Triveni Turbine Limited and M/s Energy Dome, Italy.

With numerous advantages such as a very long operational life (more than 25 years), no requirement for critical minerals like lithium and cobalt, topography agnosticism, minimal performance degradation and 100 percent depth of discharge, the Kudgi project is expected open new avenues in the field of electrical energy storage.

Unlike battery energy storage systems (BESS), which operate on electrochemistry, the CO2 battery is based on specialised electro-mechanical turbomachinery. It functions on a 'closed brayton thermodynamic cycle’ using anhydrous CO2 as the process fluid. The CO2 warms up, evaporates, and expands, turning a turbine to generate electricity. The charging and discharging of electricity occur by manipulating the physical parameters of CO2 from vapor to liquid state and vice versa.

Even as the cost of BESS is declining, NTPC does not plan to rely solely on it for energy storage. The cost of BESS for 4 hours just after sunset has now come down to about Rs 3.5 per unit. If it is for 2 hours, it has declined further to Rs 3.2. "Battery energy storage can be a solution for the short term, not just from the affordability point but also because of raw materials needed to making them," Singh said.

Unlike BESS, compressed CO2 energy storage systems do not need critical minerals such as lithium and cobalt. CESS uses only water, steel, and CO2. As per Energy Dome, the cost of the CESS can be as low as $50 per MWh.