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 8: Operation and Maintenance 
Operation and maintenance can be divided into the O&M for the steam field (wells, pipelines, 
infrastructure, etc.) and the O&M of the power plant (turbine, generator, cooling system, substation, 
etc.). Proper maintenance of all facilities is crucial to ensure a high availability factor
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and capacity 
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Availability factor is defined as the amount of time that a power plant is able to produce electricity over a certain period, divided by the 
amount of the time in the period.

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G e o t h e r m a l H a n d b o o k : P l a n n i n g a n d F i n a n c i n g P o w e r G e n e r a t i o n 
factor
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for the power plant, and to ensure steady steam production from the geothermal wells. The 
particular plant depicted in Figure 2.5 has been in operation since 1977 and demonstrates a capacity 
factor of close to 100 percent.
The O&M for the steam field consists of cleaning existing wells, drilling new ones (make-up wells) from 
time to time to regain lost capacity, and maintaining other equipment in the field. Using the example of 
a 50 MW power plant unit, estimated costs for these activities are in the range of US$ 1 to 4 million per 
year, depending on fluid chemistry, geology, the quality of the wells, and other factors. 
For the power plant unit, the maintenance costs are often estimated at 1.5 to 2.5 percent of the 
investment (purchase price) of the power plant. These figures depend heavily on the chemical 
composition of the geothermal fluids (e.g., their acidity, corrosion, scaling potential, etc.). Using the 
50 MW power plant example, this implies that a turnkey 50 MW power plant, costing US$ 100 million, 
would need annual maintenance of US$ 1.5 to 2.5 million over an expected 30-year lifetime span.
Finally, a fully automated 50 MW geothermal plant would need a staff of approximately 20 well-trained 
personnel. Estimated operating costs (including taxes, wheeling charges, overhead, etc.) would range 
between US$ 1 and 4 million per year.
Based on the assumptions above, total O&M costs for a 50 MW power plant in a developing or 
developed country would be in the range of US$ 3.5 to 10.5 million per year. These costs can be 
translated into US$ 0.009 to 0.027 per generated kilowatt hour, based on a 90 percent capacity 
factor.
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