Financial details of the deal have not been disclosed.
The facilities that will be part of the transaction are Bryson, Franklin and Mission hydro stations in the Nantahala area; and the Tuxedo and Gaston Shoals hydro stations in the Green/Broad River Basin.
They have a combined generation capacity of 18.7MW.
Duke Energy Carolinas Regulated Renewables vice-president Randy Herrin said: “This sale will deliver long-term benefits for our customers and shareholders.
“Through this transaction, the plants will continue to serve our customers with clean renewable energy, but at a lower cost.”
The energy company has also agreed to purchase the energy generated by these facilities for five years through power purchase agreements with Northbrook Energy.
Northbrook Energy president Chuck Ahlrichs said: “Northbrook is pleased with the opportunity to supplement its renewable hydroelectric portfolio in the Carolinas and leverage its local operating efficiencies.
“Nearly 22 years after our first purchase of hydropower assets from Duke Energy, we are excited to build on our success in the region by expanding employment opportunities and proffering hydropower’s baseload capabilities in support of the region’s demonstrated desire to deploy intermittent renewables such as wind and solar.”
Independent power producer Northbrook Energy operates hydro assets in 12 states, including the Carolinas.
The company has partnered with New Energy Capital Partners to finance the acquisition.
Subject to approval from the US Federal Energy Regulatory Commission (FERC) and other state regulatory approvals, the transaction is expected to complete during the first quarter of next year.
Following the FERC approval, the hydroelectric licences will be transferred to Northbrook Energy.