Hydroelectric power station. Hydroelectric power (HEP) stations rely on water flow turning electricity generating turbines. As the flow of water is effectively endless, HEP stations cost very little to run once started. The water is said to be a renewable energy source, as it is not a finite resource such as oil. HEP stations do not pollute the environment as there are no waste products. This power station, at Sultartangi, Iceland, has dammed the Thjorsa and Tungnaa rivers. It was opened in 1998, and contains two 60 Megawatt generators. Photographed in 2003.