"Local issues, contractual issues, geological surprises, delay in decision making and poor risk-taking assessment have impacted the progress on the Subansiri project, which is now likely to cost nearly Rs 12,000 crore," a senior company official told PTI.
The project has been stalled since December 2011, after the local people raised issues related to its safety and downstream impact.
"Assam also wanted to increase its total share of power from the project," the official said, adding that the state was earlier granted 208 MW of electricity from the hydel station which has now increased to 300 MW.
Besides, the state is expected to get 25 MW or more free power from the plant which is likely to resume construction work next month. The project, earlier expected to be fully commissioned by December 2012, is now likely to be operational by December 2017.
"We are hopeful that the construction work on the project would start again from December, next month," the official said.
According to sources, the Power Ministry had a meeting with the state government earlier this month and achieved some breakthrough on the issues.
Once commissioned, Subansiri (250x8) will be India's biggest hydroelectric project. The project is located near North Lakhimpur on the border of Assam and Arunachal Pradesh.
The estimated annual energy generation from the project is 7,421 million units.
NHPC generates 5,702 MW electricity from 17 hydel stations in the country. As many as seven power stations with total capacity of 4,095 MW are under construction.