Before each of the headrace tunnels from the Hálslón Reservoir or Ufsarlón Reservoir reach the underground power station, they both join to form a single combined headrace tunnel. The single headrace tunnel later splits into two long, diameter steel-lined penstocks (tunnels) and the water makes a rapid descent down a final vertical penstock into the power station. The underground Fljótsdalur Power Station contains six vertical-axis Francis turbine generators rated at 115 MW each. The power station has a combined capacity of 690 MW and discharge of (averages ) into the river Jökulsá í Fljótsdal via tailrace tunnels and canals. The power production of 4,600 GWh/year corresponds to a capacity factor of 76%, which is relatively high for a hydroelectric facility. Power produced is then transmitted to Alcoa's Fjarðaál aluminium smelter to the east in Reyðarfjörður.