Wellhead Power Plants

Abstract

Wellhead power plants have been around for many decades in the geothermal industry. With the rapid expansion of the industry in Eastern Africa for the last decade the demand for wellhead power plants has increased. The modularity and simplicity of wellhead power plant allow for accelerated construction time and shorter time period from drilling completion to power production. Cost of a wellhead power plant is also similar to a large scale unit connecting multiple wells. However, the simplicity of the wellhead power plant affects its efficiency and ultimately the utilization of the geothermal resource. Another approach has been to use wellhead power plants for early generation in a geothermal field and replace them with a large scale power plant when enough steam has been secured and then mobilize the wellhead power plants to a new location. These two approaches influence the selection between technologies used for the wellhead generator, i.e. condensing flash, back pressure flash or an ORC type binary cycle. The article analyses cost of the wellhead power plants and cost scaling for early estimates as well as installation and mobilization time for the different power plant technologies. The analysis aims to assist geothermal developers in creating a geothermal field development plant taking into account possible use of wellhead power plant, large scale plants or a combination of both. For best results the strategy for wellhead power plants should be made clear from the beginning of field development. The strategy involves deciding whether the units shall be portable and thus temporary or permanent as this effects the size and in some cases the technology selected.