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Heat wave summer of 2015: a challenge for the hydroelectric power stations in the Alps

2015 was the second warmest summer since measurements began in 1864. The heat had a significant impact on electricity generation. Alpiq's storage power stations in the Alps were also affected. The vast quantities of meltwater last July had both positive and negative effects.

The hydropower stations in the lowlands suffered under the dry conditions during the summer of 2015. Simultaneously, as usual, the nuclear power stations were overhauled in summer and their production was lower. There was hardly any wind in Germany. And due to the extreme heat, solar modules became less efficient. However, in order to cool off, many people switched on their air conditioning systems and fans. This boosted electricity consumption. The consequence of this was higher prices for electricity, which over a period of several days increased to a price level that is usually only reached during winter.

Grande Dixence with record level water inflow

These conditions proved to be challenging for our storage power stations located high up in the mountains. The long heatwave caused an exceptionally high level of melting of the glaciers. The glacier meltwater filled the mountain lakes. An example of this is the Grande Dixence facility. In July 2015 it had a record inflow with 20 percent more water compared to the average value. The reservoir held 28 million cubic metres more water than usual, which is the equivalent of the annual electricity consumption of approximately 27,000 households. However, thanks to the availability and capacity of the Grande Dixence hydroelectric complex, this situation could easily be dealt with.

Overflow record at the Gebidem dam

The Electra Massa facility in the upper Valais region, which is operated by Alpiq, was also affected by the vast quantities of meltwater. In July, 46 percent more water flowed into the Gebidem reservoir from the Aletsch glacier than is normal during this month. Consequently, throughout July, the Bitsch power station was operated at full capacity, which corresponds to a turbine flow rate of 55 m3/s. At peak times, the water inflow considerably exceeded twice the maximum turbine flow rate. Although until the beginning of July Alpiq ensured that the water level of the reservoir was kept as low as possible, eventually the overflow of unused water amounted to the equivalent of 16.6 GWh. This unused water power corresponds to the annual consumption of 3,700 households – another, regrettably negative, record set during this extraordinary hot summer.