Work on Osen power station started in 1963. There is a 2.3 km long water transfer tunnel from the upper reservoir Nespervatn.
Osen power station lies in Sirdal Municipality in Vest-Agder. The municipality has a population of 1,831, and covers an area of 1,554 km², approximately 11% of which is water. Osen is one of seven power stations in the municipality.
The power station makes use of the 67-metre height difference between Nespervatn and Bjørnestadvantnet.
The reservoir has a capacity of 40 million m3.
Wikipedia, Agder Energi’s own data.