Grunnåi Power Plant is located in Seljord municipality and is part of the power production system in the Skinsvassdraget watercourse.
The Grunnåi watercourse primarily runs through Seljord municipality in Telemark county. Its outlet is from the east side of the valley at Vallaråi river in Flatdal. The source of the watercourse is Slåkåvatn lake on Lifjell mountain. It is dammed up at the top of Grisejuvet where the intake is also located. The power plant was commissioned in 2006 and utilises a waterfall height of 387 metres.
In 2019, an extra generator was installed and increased the annual production to 66 GWh. The original generator has an installed capacity of 15.1 MW and an annual output of 55 GWh, while generator 2 has an installed capasity of 10.2 MW and an annual output of 11 GWh.
The new machine can facilitate research projects. It's possible to mount sensors on the impeller, and windows are fitted to the machine making it possible to look into the turbine during production.
The power plant has a very limited degree of regulation, which means it can be regarded as a run-of-the-river power plant. The reservoir of around 25 cubic metres is emptied in just over an hour during full-capacity production. The turbine is a five-nozzle Pelton turbine that is regulated by the water level in the intake reservoir and associated inflow.
Owners: Skagerak Kraft AS 55%, Vest-Telemark Kraftlag AS 15% and a group of landowners with a total of 30%.