The full cost of Prime Minister Malcolm Turnbull's Snowy Hydro expansion could hit nearly $12 billion by the time the project is built and the federal government negotiates a buyout of NSW and Victoria's stake in the scheme.

But the cost blowout, revealed in a new feasibility study, has failed to dampen the Coalition's enthusiasm, with Environment and Energy Minister Josh Frydenberg on Thursday promising the technically challenging undertaking "will go ahead and Australians will be better off for it".

The study found the project was viable and could be switched on within seven years, contributing enough new electricity to power hundreds of thousands of homes and businesses as Australia's energy network transitions from coal to renewables.

However Snowy Hydro Limited refused to release three key chapters of the study covering commercial projections, business modelling and detailed cost estimates, citing commercial sensitivities.