The Delabole wind farm, which sits on the outskirts of one the highest villages in Cornwall, south west England, began generating electricity in 1991.
The package includes 9.6 million pounds in debt finance from the Co-operative Bank and 2.2 million pounds in equity from Good Energym, and will see the installation of four more effective Enercon turbines to replace the 10 Vestas ones, which are nearly 20 years old.
The project is expected to be completed by the end of 2010.
Upon completion, the wind farm's capacity is expected to rise some 2.5 times to around 9.2 megawatts, enough to power over 7,800 homes.
Good Energy shares were up 3 pence or 5.5 percent at 58 pence late on Monday.
(Reporting by Michael Szabo; Editing by Sue Thomas)