Mår power plant

The power plant uses water from watercourses in the municipality and has a catchment area totalling 770 square kilometres with a mean annual inflow of 560 million cubic metres. The development of the power plant was planned and initiated during World War II, but was first commissioned in 1948.

The height of fall from the inlet in Lower Grottetjørn Lake is 820 metres. The staircase up through the 1,250-metre-long penstock shaft inside the mountain has 3,875 steps, making it one of the world's longest wooden staircases.

The power plant has five generating units equipped with Pelton turbines.

The regulated water area for Mår power plant is in the Skien watercourse and includes the reservoirs Mårvatn, Kallhovd, Gøyst, Strengen and Grotte. These have a combined holding capacity of about 580 million cubic metres of water, sufficient for the production of about 1 TWh of power.

Mår dam is one of the few dams in Norway made of natural stone.

In 1949, local painter and artist Henry Kittilsen was commissioned to decorate the end wall of the machine room. It ended up being one of Norway's largest frescoes, at 180 square metres. The painting, a map showing the regulated area, is painted directly on the wall.