www.iteco.ch/Renewable Energy & Water/Project Selection/Small Hydropower in Mettental - Switzerland

Drinking water and energy from Mettental

small hydropower plant Mettental

One project – two uses: Hydropower and drinking water at Mettental Sachseln and highest ratio of water head to discharge in Switzerland

The community of Sachseln draws its drinking water from eight springs located in the upper part of the Mettental. As long ago as 1939 the community constructedan asbestos fibre-cement pipeline, fitted with nine pressure reduction shafts, to provide Sachseln with drinking water. A new dual use ultra high head hydro power-drinking water plant was constructed in 2004 to cope with the rising demand for domestic water supply. The plant was commissioned in March 2005.

Environmental friendly power and drinking water supply
The replacement of the old fibre-cement pipeline by a ductile cast-iron pipeline makes it possible to use the full 919 metre water head – a pressure of over 90 atmospheres at the turbine – for electricity production together with the provision of drinking water. More than one million kWh per year of environmental friendly electrical energy is produced for approximately 250 households. The power from the plant is fed into the regional power grid and the water, after discharge from the turbine, flows into the existing reservoir without any loss of quality.

Hydropower

Short construction period

Work on the 2.9 kilometre long penstock, following generally the route of the old pipeline, started on 12 July 2004. The water authority required that the supply of potable water to the community of Sachseln had to be maintained at all times during the construction period. A new plastic pipeline was laid at the same time as the steel penstock to provide water to alpine settlements (both mountain huts and livestock).

A storage pond of about 20,000 litres capacity was constructed close to the springs.The work in the steep and largely inaccessible terrain with variable ground conditions proved challenging to the contractor but within only two months the new pipes were laid, the pressure testing done and the terrain re-instated. The use of hydraulic excavators for the storage

pond and the trench for the penstock together with approximately 500 helicopter flights for transporting the pipes and other construction materials ensured that good progress was maintained during the project. A skilled construction crew and the use of the ductile cast iron flexible sleeve pipe system played key roles in achieving high production rates.

Turbine

A national trend-setting pilot project

ITECO carried out a feasibility study which showed that with only a relatively small flow and a large head it would be possible to produce electricity at a unit price of USD 0.12/kWh, a similar price to that paid by EW Obwalden (the regional supplier) for energy fed into the regional grid. As a result the Swiss Federal Office of Energy approved and sponsored this project – the first of its kind in Switzerland – and classified it as a pilot and demonstration project for high head small hydropower plants.

High-tech-turbine and bypass

With a very high head-discharge ratio the specially modified shape of the blades of the Pelton turbine (derived from experience gained on major hydro power plants) results in a high efficiency for this head flow ratio. Should the turbine shut down for any reason, a regulated pressure reduction valve acts as a bypass and ensures that a continual flow of drinking water is maintained. Water quality is maintained by doing away with all lubricating nipples and avoiding the use of hydraulic oil in the machinery.

Project main data

Design flow 40 l/sec
Gross/Net head 919 m (approx. 90 bar) / 880 m at full load (86 bar)
Average annual production 1.06 million kWh
Water utilised per year 580,000 cu m (energy produced 1.8 kWh per cu m of water)
Equipment Single nozzle, 300 kW Pelton turbine.
  3 phase synchronous generator,
  400V/370 kVA. 20 l/s regulated bypass capacity,
  2.9 km long ductile Cl penstock