an area of responsibilty pertaining to helping issues that affect our enviroment eg solar energy , non-fossil based fuel like petrol , coal etc

In investing, a "portfolio" means the collection of securities (stocks and bonds) that you own. I think a "green portfolio" is an investment portfolio comprised of the stocks of "green" companies. That could either mean companies that are ecologically responsible, or companies that are in the business of providing "green" products and solutions. It sounds like a kind of "socially responsible investing," or SRI. _On the other hand..._ I just Googled and discovered "KKR Green Portfolio." KKR is a private equity company. They own a "portfolio" of businesses. Apparently "KKR Green Portfolio" is a management program that is intended to help all of the companies in this portfolio become better with respect to "greenhouse gas emissions, water, waste, priority chemicals, and forest resources."

If I had to guess, I'd say, it is a stock or investment portfolio that is making money or is active.