The two signed an original agreement June 6 a year ago then terminated it, later replacing it with a memorandum of understanding in November.
This was a result of the requirement to restructure the financing of the Kidston Pumped Storage Hydro Project, Genex said.
The ASX-listed company is developing a solar, pumped hydro and wind project in Queensland across three stages, with the second stage the largest and most technically complex.
This new agreement "is largely on the same terms as the original SSA and provides for a conditional investment of up to A$25 million by way of a subscription for ordinary shares in Genex, with the proceeds to be principally applied towards Genex's equity funding component for the construction of the project." it said.
The subscription will be at the higher end of the five-day volume weighted average price of Genex shares at financial close or the date that is five days after close.
This is subject to a subscription price cap which gives JPower a minimum investment of 15% of the company's enlarged share capital and a maximum of 19.99%.
JPower will be able to nominate a director to the board of Genex. Shareholders must approve this at an extraordinary general meeting; the Foriegn Investment Review Board must also approve the transaction.
Genex has also made a Technical Services Agreement (TSA) with the Japanese company and it will provide "certain professional technical advisory services" for the multistage project",
The balance of the equity requirement will be funded by JPower's direct investment in the project, subject to a separate project equity investor process Genex outlined at the beginning of July.
"Genex is delighted with today's signing of the new Share Subscription Agreement with J-POWER, who are global experts in hydroelectric projects, including pumped storage," CEO James Harding said.
"The signing of the agreement today cements this relationship with J-POWER as a long-term partner to finance and provide technical assistance for the construction of the Project, and to work with Genex to further develop our renewable energy and storage portfolio."
Genex is up almost 5.8% today with shares worth 27.5c each.