A set of mirrors mounted on the cliffside some 400 meters above the town will reflect sunlight down into the center of town.
The mirrors will track the sun through the day, powered by wind and solar energy.
Rjukan was one of the first Hydro sites when the company was established early in the 20th century. One of Hydro's founders, Sam Eyde, got the idea for mirrors about 100 years ago, following up on a letter to the editor in the local newspaper by a sun-starved employee.
"Eyde managed to accomplish a lot in his time, but we have to say that this is one of the few ideas he wasn't able to see through. Now we're making it happen," says Øystein Haugan, heritage coordinator for the area, which is on the UNESCO global heritage site list.
"In Eyde's mind, nothing was too grand – not even a mirror measuring 100 square meters."
The mirror components were recently lifted into place by helicopter and the preparations are about complete.
Come October, the residents of Rjukan will have a brighter perspective on the coming winter.