Jan 7 (Reuters) - Blackstone Inc (BX.N) said on Friday it would invest about $3 billion in Invenergy Renewables Holdings Llc, the largest private renewable energy company in North America. The world"s largest manager of alternative assets such as private equity and real estate has been seeking to bolster its sustainability credentials as investors increasingly question companies on their impact on the environment and workers. Blackstone"s investment will provide capital to accelerate Invenergy"s renewables development activities, the company said in a statement. Canadian pension fund Caisse de dépôt et placement du Québec (CDPQ) and Invenergy management remain majority owners of the company, while Invenergy will continue as managing member. Blackstone said the investment was made through funds managed by Blackstone Infrastructure Partners.