As India transitions from fossil fuels to renewable energy (RE) sources, Battery Energy Storage Systems (BESS) become essential to give reliable power through out the year. Multiple technologies are needed for energy storage to accommodate daily and seasonal variations in energy generation. The BESS can be classified as short-duration discharge (SDS), long-duration discharge (LDS), and cross-season storage (CSS). SDS accommodates daily variations with high round-trip efficiency (RTE). In contrast, LDS should be energy density to provide power for no generation days. CSS should have minimal self-discharge to store excess energy in summer and utilize it in winter/monsoon.

We used a Li-ion battery with high RTE as SDS, and we developed a Zn-air battery as LDS/CSS with a high energy density of 600 Wh/l and energy storage as Zinc with minimal self-discharge.

The current challenge with Li-ion batteries is their safety analysis for grid storage applications. At CHL, New Rummy Game, we built a micro-grid with a 10 kW solar panel with a 2 kW peak load and 28 kWh of NMC Li-ion batteries. We have been running this microgrid for 18 months and analyzed various parameters to evaluate its feasibility as SDS. Also, we have built a battery lifetime and safety test rig (BLAST-r) to perform thermal runaway experiments and analyze Li-ion battery safety.

For LDS and CSS, existing options are hydro-pumped storage systems and hydrogen electrolyzer + fuel cell systems. Both technologies are mature but expensive. In our lab, we have developed a mechanically rechargeable zinc-air battery module+ recharging unit, which is low-cost. We have developed innovative designs for the high utilization of Zinc (95%), the high energy density (600 Wh/l) of the Zn-air battery module, and the redeposition of highly dense Zinc from discharge products using solar PV.

These Li-ion and Zn-air battery technologies are complementary to each other as SDS and LDS/CSS. If we solve the existing challenges, a hybrid of these BESS can provide a storage option for uninterrupted power from RE.