The acquisition means Aquila now has an installed capacity of 650MW worth of wind projects.
It owns the 65MW Högkölen project and 148MW Lehtirova site in Sweden, and holds the majority stake in the 150MW Midtfjellet wind farms in Norway.
The Kappel project, on the island of Lolland off the east coast of Denmark, came online in March and comprises six Vestas V117 3.6MW turbines and a V126 3.6MW machine.
Dong Energy originally owned the site, but sold it to Danish company European Energy in 2013 before construction. European Energy will continue to manage the park on behalf of Aquila.
The investment firm also holds stakes in hydropower and solar PV projects.