Page 375 - Handbook of Energy Engineering Calculations

Compare the costs—installation and operating—of a 50-MW geothermal

plant with that of a conventional fossil-fuel-fired installation of the same
rating. Likewise, compare plant availability for each type. Brine available to
the geothermal plant free-flows at 4.3 million lb/h (1.95 million kg/h) at 450
2
lb/in (gage) at 450°F (3100 kPa at 232°C).

Calculation Procedure:

1. Estimate the cost of each type of plant
Assuming that the cost of constructing a geothermal plant (i.e., an electric-
generating station that uses steam or brine from the ground produced by

nature) is in the $1500 to $2000 per installed kW range. This cost includes all
associated equipment and the development of the well field from which the
steam or brine is obtained.
Using this cost range, the cost of a 50-MW geothermal station would be in
the range of: 50 MW × ($l500/kW) × 1000 = $75 million to 50 MW ×

($2000/kW) × 1000 = $100 million. Fossil-fuel-fired installations cost about
the same—i.e., $1500 to $2000 per installed kW. Therefore, the two types of
plants will have approximately the same installed cost.

Department of Energy (DOE) estimates give the average cost of
geothermal power at 5.7⊄/kWh. This compares with the average cost of
2.4⊄/kWh for fossil-fuel-based plants. Advances in geothermal technology
are expected to reduce the 5.7⊄ cost significantly over the next 40 years.
Because of the simplicity of geothermal plant design, maintenance

requirements are relatively low. Some modular plants even run unattended;
and because maintenance is limited, plant availability is high. In recent years
geothermal-plant availability averaged 97 percent. Thus, the maintenance

cost of the usual geothermal plant is lower than a conventional fossil-fuel
plant. Further, geothermal plants can meet new emission regulations with
little or no pollution-abatement equipment.

2. Choose the type of cycle to use
Tapping geothermal energy from liquid resources poses a number of

technical challenges—from drilling wells in a high-temperature environment
to excessive scaling and corrosion in plant equipment. But DOE-sponsored