| Abstract |
Stepwise development strategy is considered a suitable method for securing a cost effective way for the development of geothermal power plants. This strategy has been in use in Iceland for the last decade. Geothermal high-temperature fields are developed in steps of 20-30 MW. About 6 years are required for each step in the development. Parallel development of several fields in a country might be preferable, especially when a rapid increase of the generation capacity is required in that country. The capacity factor of geothermal power plants depends on the mix of power plants serving the electricity grid. Where geothermal power plants can be operated as base load, the capacity factor is usually in excess of 0.9. The investment cost of geothermal power plants is divided into the cost of surface equipment, including the cost of the plant and steam gathering system, and the cost of subsurface investment (drilling cost). The cost of surface equipment can be estimated with the same accuracy as other construction works at the surface (buildings, roads, and bridges), whereas higher uncertainty might be associated to the cost of drilling. Analyses of the surface cost of 5 power plants in Iceland shows that the investment cost is linear with the size in the range 20-60 MW. The surface cost is found to be about 1000 $/kW with a relative error of 10%. Stefanson (1992) has published a statistical study of the drilling results in 31 high-temperature fields in the world. By using these results of Stefansson, it is possible to estimate the expectation value and its limits of error for the subsurface investment in an arbritary geothermal field. |