SECURING FUTURE ELECTRICITY SUPPLY

Switzerland aims at developing hydro storage power plants as efficient and flexible assets, to address fluctuating power demands and peaks in a financially and environmentally efficient manner.

Kraftwerk Linth-Limmern (KLL) AG—a partnership between Axpo Power AG and the Glarus cantonal authority—was seeking a way to extend its hydroelectric power production. At the time, the Linth-Limmern hydropower plant, located in the heart of Switzerland in Linthal and operated by KLL, was generating 450 MW (it has since been upgraded to generate 520 MW).

KLL awarded GE a contract in 2008 to provide four new 250MW variable speed pump turbines, four 280MVA variable speed motor generators and power electronics.

The variable speed hydro storage technology proposed to KLL is the latest hydro innovation developed by GE, thanks to its R&D work on asynchronous-motor technology. It allows utilities to regulate the power in pumping mode (storage), when fixed speed only provides regulation in turbine mode (production). To generate electricity, KLL opens the main inlet valves and lets the water run down from Lake Mutt to Lake Limmern which is 630m lower in the valley. However, if power demand drops, the plant is able to pump it from Lake Limmern back up to Lake Mutt.

Thanks to the added flexibility that variable speed offers, utilities are able to react fast and capture the lucrative sweet spots when prices of electricity are highest.

POWER AT THE FLIP OF A SWITCH

End of 2017, GE successfully handed over the Linth-Limmern hydro storage plant to KLL marking the completion of the overall certification process of the four new 250MW units.

The new hydro storage units extend the current 520MW hydropower complex to generate 1,520MW of renewable electricity, which is as powerful as a nuclear power plant. Most importantly, Linth-Limmern acts as a giant natural battery. It can store up to 34GWh, the equivalent of 340,000 fully charged electric cars.

GE’s variable speed hydro storage technology enables KLL to monitor the level of excess electricity in the grid and send the right amount in whatever direction it is needed, all with an overall cycle efficiency of more than 80%. It gives the Swiss network great levels of stability and flexibility. Only 120 seconds are needed to start-up the plant and 270 seconds to switch from pump to turbine mode.

The Linth-Limmern power plant is GE’s first variable speed hydro storage plant connected to the grid.