Geothermal handbook: PlanninG and Financing power Generation t e c h n I c a L r e p o r t 2 / 2

Phase 6: Construction 
This phase comprises installation of the steam gathering system or SAGS (i.e., a system of steam 
pipelines from the well heads to the power plant and back for the reinjected fluids); the separators; the 
power plant with the turbine, generator, and the “cold end,” which consists of a condenser and needs 
either air (fan cooling) or water cooling (direct or by cooling tower). After utilization (expansion) of the 
steam, the cooled geothermal fluids are usually reinjected into the reservoir to be reheated and to 
maintain the pressure or avoid reservoir depletion. The electricity generated is sent to a substation and 
from there to the transmission grid.
Figure 2.5 shows the different components of a geothermal power plant and the plant’s most important 
equipment. Starting from the top, there are the geothermal wells, each with an access road and a 
drilling pad. Some of the wells are releasing steam (“blowing”)—possibly due to maintenance work, 
but all are connected via pipelines to the separator station (in the middle of the picture), where fluids 
are separated from steam. The pipelines are well insulated to minimize cooling of the fluids and steam 
over a distance of several kilometers. From the separator, the steam goes to the power plant turbines, 
while the water, which has the same temperature as the steam, gets reinjected into the reservoir 
by reinjection wells. The cooling towers are part of the condensing system, which condenses the 
remaining steam into fluids. The generated power is sent to the transmission grid through the attached 
substation.
For a 50 MW power plant unit, the costs for the construction phase of project development are, on a 
turnkey basis, usually in the range of US$ 1 to 2 million per megawatt installed. The cost estimates do 
not include the transmission line or the substation, which is needed to connect the power plant to the 
grid, as these costs can vary considerably from installation to installation.

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