Over the decades, several different power retention methods have been devised to capture and store energy so that it can be fed back to the grid when it is most needed to produce enough energy to meet the ever-fluctuating demands on 

electric grid. These are what we call Energy storage systems.

Energy Storage System (ESS) is a device or group of devices assembled that is to convert the electrical energy from power systems and store energy in order to supply electrical energy at a later time when needed. An ESS helps to effectively use and manage the electrical energy also expect the benefit of stable electricity supply and cost reduction. Examples of these systems include flywheels, solid-state batteries, ultracapacitor or supercapacitor, pumped hydroelectric storage dams.

By 2021, South Africa had started The Eskom Distributed Battery Energy Storage Systems project which involves the development of 360 MW storage system (equivalent to 1440 MWh with 4 hours storage per day) at various Eskom distribution sites in several provinces including Western Cape, Eastern Cape, Northern Cape and KwaZulu Natal. The aim of the project is to stabilize the grid in the country and to reduce rotational load shedding and energy curtailment by significant values.

References

Energy Storage System (ESS) and Battery

https://www.theprojectdefinition.com/p-energy-storage-system-ess-and-battery/

An overview of 6 energy storage methods

https://www.windpowerengineering.com/an-overview-of-6-energy-storage-methods/

South Africa - Eskom Distributed Battery Energy Storage Project - Project Appraisal Report

https://www.afdb.org/en/documents/south-africa-eskom-distributed-battery-energy-storage-project-project-appraisal-report