The SWT-DD-130 turbines will have a rated capacity of 4.2MW and a 130-metre diameter rotor.
The 4.2MW models will be the highest capacity turbines installed in the country to date, the Norwegian Wind Energy Association said.
It is also the first time Siemens Gamesa’s SWT-DD-130 turbines have been ordered with a 4.2MW rating, the company said.
The manufacturer will also provide service and maintenance for the turbines for five years. Installation is scheduled to begin in summer 2019.
The Sørfjord site in the municipality of Tysfjord is only accessible by boat or helicopter, Siemens Gamesa said.
Hans Joern Rieks, CEO of North Europe, Middle East and Africa, at SGRE said: "We are proud to deliver the latest innovations from our onshore direct drive platform with the SWT-DD-130 to the Sørfjord Vindpark."
Fortum had acquired the 96.6MW site from Norwegian developers Nordkraft alongside the 32MW Nygårdsfjellet and 50MW Ånstadblåheia wind farms as part of a package deal in January.
The company is further looking to increase its portfolio in the Nordic countries and Russia, it said.
"This investment decision is a further step in the implementation of our wind growth strategy, in the perspective of building a sizeable scale portfolio in the Nordic area, said Philippe Stohr, vice president of wind power at Fortum.