The project, worth a total of $16. 7 million USD, is jointly funded by the Asian Development Bank, Green Climate Fund, and the Government of Australia, and implemented by Tonga Power Limited with assistance from the Government of Tonga. The contractor for the project was. Battery Energy Storage Systems (BESS) is a technology developed for storing electricity with the underlying idea being that this stored energy can be utilized at a later time. 7 million of investment, with the wider TREP project costing just over US$50 million. The systems were commissioned. : 5 5 MW Avg. Load: 5 e manually scheduled value during a fault.