Modular Development of the Nesjavellir Power Plant for Flexibility

Abstract

In late 1986 Hitaveita Reykjavikur, nowadays Orkuveita Reykjavikur, decided to harness the high temperature geothermal field at Nesjavellir. This field is located some 30 km east of Reykjavik; see Figure 1. The Nesjavellir plant was intended to supply the city of Reykjavik and the annexing communities both with hot water for space heating and electricity for at least a period of 30 years and reach a fully developed capacity of about 100 MWe in electric and 300 MWt in thermal power. The plant will be expanded in harmony with increase in demand for heat and electricity. During this 30 years period the geothermal field is expected to change over time. According to reservoir modelling studies, the production fluid enthalpies will decrease gradually in the future. To achieve optimal thermal efficiency and flexibility during this development, both the process and the buildings are designed modular. The first stage of the plant was commissioned in 1990, with a thermal output of 100 MWt using the geothermal steam. The geothermal water was at the same time used in a pilot module to achieve operational experience with the Nesjavellir geothermal water. In 1994 the second stage of the power plant was commissioned, adding equipment to boost the output to 150 MWt. In late 1998, electricity generation started. Two condensing steam turbinegenerator units produce now 60 MWe. The cooling water from the condensers is heated further in geothermal water heat exchangers, to suit the district heating requirements. This paper describes the development of the plant, the design philosophy and the experienced gathered during the 10 years of operation.