Rezzalasco – Sondalo Hydroelectric Power Plant

Rezzalasco Sondalo

The Rezzalasco hydroelectric power plant, located in Val di Rezzalo in the Municipality of Sondalo in the Province of Sondrio, taps into the waters of the stream of the same name, a left tributary of the Adda River. The plant rests along the course of the Rezzalasco stream at 1,385 m.a.s.l., up to the collection work at 950 m.a.s.l., the restitution point of the turbine waterfeed.
The plant consists of a waterbed intake comprised of a collection crosspiece made of reinforced concrete for the derivation of the waters, two settling tanks and a surge tank for the conveyance of the waters coming from the penstock. The water intake then extends entirely to the right side of the stream and allows up to a maximum capacity of 1,755 l/s for the derivation of the water.
The steel penstock, used for the conveyance of the waters to the main building, has a DN of 1,100 mm and flows entirely to the right of Val di Rezzalo, for a total length of approximately 2,580 ml.
The main building, located at approximately 959 m.a.s.l., was constructed entirely in reinforced concrete. Particular attention was given to the external finishing works using local stone and wood. The machine rooms, the control panel room and the local transformers are housed inside. Three Pelton turbine-generator groups were installed, which produce an average of 24/26 Mw annually, with a nominal jump of 428 m.

Rezzalasco Sondalo

The restitution of the turbine feedwater to the Rezzalasco stream occurs thanks to an underground discharge channel, which from the main building reaches the streambed, for a total length of approximately 75 ml.

The delivery and connection to the national network of the electrical energy produced involved the implementation of a 1.5 km electrical line and the relative delivery room near the existing main Sondalo power station.

The contract involved all the phases of the planning/definitive/executive and the supervision and accounting of the job with the exception of the planning regarding the aspect relative to the dimensioning of the electromechanical works. Particular attention was given to identify the ideal layout of the penstock and, above all, the choice of optimal solutions as far as the migration techniques of the penstock itself.