The Powerbuoy was originally deployed in October 2008, 1.6km off the coast at a depth of 30m.
The power produced during the initial phase of testing was said to be in line with expectations.
The system works by extracting the natural energy of ocean waves using patented technology in electronics, energy conversion and computer controls to respond to different ocean conditions.
The additional funding from the US Navy is expected to support upgrades and testing of the system to improve its durability.
According to the company, work on the project will make use of local Hawaiian subcontractors for the installation, test and servicing of the systems.
OPT will also work alongside ocean engineering company, Sound and Sea Technology, to review system upgrades.
The project has already undergone an environment impact assessment to investigate potential damage to the seabed, fish, other sea organisms and sea quality.
This resulted in a Finding of No Significant Impact (FONSI).
Mark Draper, chief executive of OPT, said: ‘This project reflects the ongoing commitment of the US Navy to renewable energy generation and sustainable development.
‘It furthers the long-standing partnership which OPT has had with the US Navy in developing our core Powerbuoy technology.
‘Our success to date owes much to this shared commitment to renewable energy, and we expect to leverage this programme in the commercial expansion of our business internationally.’