The two battery storage facilities installed in Tonga are complementary: the aim of the first 5 MWh / 10 MW battery is to improve the electricity grid's stability (regulating the voltage and frequency), while the second 23 MWh / 7 MW battery is designed to transfer the. . The two battery storage facilities installed in Tonga are complementary: the aim of the first 5 MWh / 10 MW battery is to improve the electricity grid's stability (regulating the voltage and frequency), while the second 23 MWh / 7 MW battery is designed to transfer the. . The two battery storage facilities installed in Tonga are complementary: the aim of the first 5 MWh / 10 MW battery is to improve the electricity grid's stability (regulating the voltage and frequency), while the second 23 MWh / 7 MW battery is designed to transfer the electrical load in order to. . nd shift to renewables. The project will deliver utility-scale storage systems to provide base load response and grid stability,paving the way for more renewable energy integration in the main island,while green mini-grids will be install electricity generation. The Government of Tonga has. . . 2MWh of energy storage. The ADB has approved a grant of US$12. 2 million for the Tonga Renewable Energy Project, through the much larger Pacific Renewable Energy Inves project, of 5 MW/10 MW. Both are scheduled for completion in t e third quarter of 2020.