The deal, which is subject to shareholder approval, will mean Marubeni will gain a 25 per cent holding in Mainstream, which has has recently applied for planning consent for a 450MW offshore wind farm in Scotland, Fife.
In addition, earlier this year Mainstream received a grid connection from National Grid for its Energy Bridge which will see Mainstream build and export 5,000MW of wind energy from Ireland to the UK starting in 2018.
As part of the agreement Marubeni has obtained the right to representation on the Mainstream board of directors alongside Barclays, which invested in the company in 2008.
Since its establishment five years ago, Mainstream has built a global pipeline of more than 19,000MW of wind and solar projects with plant currently in construction and operation in Ireland, South Africa, Chile and Canada.
Mainstream Renewable Power’s chief executive Eddie O’Connor, said: “This investment is a game-changer for Mainstream allowing us to focus on accelerating our project portfolios across a range of markets as well as entering into new strategic jurisdictions which present strong value opportunities for our business.
“Having grown our company in the midst of the global financial crises, this type of long-term strategic investment is true testament to the strength and experience of our team as well as the quality and spread of our global project portfolio.”