I Squared Capital, which controls a global $3.8 billion (€3.4bn) fund of which most of which is invested in the US, India and China, is in the process of closing a deal to buy the Belfast-based group from Arcapita.
Viridian sells electricity and gas to retail and business customers, and owns the Huntstown power station in north- west Dublin, as well as wind farms across the country.
I Squared is now likely to seek to tap economic growth and anticipated increase in power demand by acquiring more wind farms and introducing new generating and backup technologies to the market here.
In a signal it is here to stay, I Squared is also likely to try to expand Viridian into Britain.
Its investments around the world include renewable energy, turbines, a Boston power plant, water-treatment plants in China and toll roads in India.
I Squared will pay down debt which has weighed on Viridian for some time.
It has signalled that it expects that customers north and south will not lose out following the acquisition.
I Squared said Energia and Power NI have a combined 20% share of domestic electricity sales and 27% of the business electricity on an all-Ireland basis.
Sources said that I Squared was particularly impressed by Viridian’s growth into the retail market through Energia, which is currently being heavily advertised in the Republic.
Commission for Energy Regulation figures suggest Energia has plenty of room to grow: It accounts for about 4% of the retail household market by consumption in the Republic.
It competes with Electric Ireland on a share of almost 55% of the retail electricity market; SSE Airtricity on 19%; Bord Gáis Energy with a 16% share; and against PrePayPower, with a 5% share.
In the consumer gas market, Energia’s share had grown last year to over 5%, while Bord Gáis had a share of over 51%.
Electric Ireland controlled over 23.6% of the retail gas market, with market shares of almost 16% for SSE Airtricity, and 5% for Flogas. Arcapita had owned Viridian since late 2006.
Arcapita has owned Viridian since late 2006. Viridian chief executive Ian Thom said I Squared has shown how to expand energy firms around the world.
The company would also benefit from the fund’s “increased financial strength”, he said.