Dong has asked the turbine manufacturer Siemens to carry out a retrofit on the turbine blades, which should boost turbine output by up to 1.5%.
The developer said this would be equivalent to installing two further turbines at the 91-turbine site, off the coast of Blavandshuk, southern Denmark.
Siemens installed its SWT-2.3-93 turbines at Horns Rev, which came online in 2009. Dong said the turbines had been designed for onshore use and with 2004 technology.
Michael Simmelsgaard, head of wind power operations at Dong, explained that blades have since developed to become more suited to an offshore environment.
"The technical upgrade that we now perform is part of what can be expected when working with a technology that is still making significant technological progress," he said.
In 2014, Horns Rev 2 had a capacity factor of 51.8% with 96.9% availability. A spokesperson for Dong said the project was producing electricity as expected but a boost to production was "attractive".
All of the turbines will be brought onshore for the upgrade work. Siemens will install aerodynamic components to increase output and repair leading edge corrosion on the blades.
Operations will start from spring to 2015 and is expected to be finished by summer 2016.
It is not the first major work to be carried out at the project. In 2010, Dong was part of a group of companies set up to investigate a fault with offshore monopiles. A design flaw with the grouting connection in the earlier monopiles caused some transition pieces to slip. Dong admitted the Horns Rev 2 project had been affected by the fault.