REP Geothermal and Hydropower 2 — Questions and Answers
Question 1: What is the primary environmental concern associated with geothermal power plants using open-loop hydrothermal systems?
- Emission of hydrogen sulfide (H₂S) gas (Correct answer)
- Excessive water vapor condensation
- Thermal runaway in turbines
- Increased seismic activity from steam injection
Correct answer: Emission of hydrogen sulfide (H₂S) gas
Open-loop hydrothermal systems release hydrogen sulfide (H₂S), a toxic gas naturally present in geothermal fluids, requiring scrubbing systems to meet air quality standards.
Question 2: A run-of-river hydropower project generates electricity without a large reservoir. What is the main trade-off compared to storage hydropower?
- Higher capital cost per MW installed
- Less predictable and dispatchable power output (Correct answer)
- Greater ecological disruption to fish habitat
- Lower turbine efficiency at rated flow
Correct answer: Less predictable and dispatchable power output
Run-of-river projects cannot store water, so generation fluctuates with natural streamflow, making output less predictable and limiting dispatchability compared to reservoir-based plants.
Question 3: In binary-cycle geothermal plants, what role does the working fluid (e.g., isobutane or isopentane) play?
- It is injected into the geothermal reservoir to increase pressure
- It absorbs heat from geothermal brine and vaporizes to drive a turbine (Correct answer)
- It cools the generator windings to prevent overheating
- It reacts chemically with minerals in the brine to purify the fluid
Correct answer: It absorbs heat from geothermal brine and vaporizes to drive a turbine
In binary-cycle plants, a secondary working fluid with a lower boiling point absorbs heat from geothermal brine via a heat exchanger, vaporizes, and drives a turbine before being condensed and recirculated.
Question 4: The penstock in a hydropower facility performs which function?
- Filters suspended sediment before water enters the turbine
- Conveys pressurized water from the forebay or reservoir to the turbine (Correct answer)
- Regulates downstream river flow for environmental compliance
- Converts turbine mechanical energy to electrical energy
Correct answer: Conveys pressurized water from the forebay or reservoir to the turbine
The penstock is a large pipe or conduit that carries water under pressure from the intake or forebay downhill to the turbine, converting potential energy into kinetic energy.
Question 5: Which geothermal resource type is characterized by temperatures above 150°C and is best suited for direct electricity generation?
- Ground-source heat pump fields
- High-enthalpy hydrothermal reservoirs (Correct answer)
- Low-temperature sedimentary aquifers
- Shallow soil thermal exchange zones
Correct answer: High-enthalpy hydrothermal reservoirs
High-enthalpy hydrothermal reservoirs with temperatures above 150°C contain sufficient thermal energy to flash steam or operate binary cycles for economical electricity generation.
Question 6: A pumped-storage hydropower facility consumes electricity during off-peak hours. What is the primary purpose of this operation?
- To irrigate agricultural land using surplus reservoir water
- To store energy by pumping water to an upper reservoir for later generation (Correct answer)
- To maintain minimum ecological flow downstream during dry periods
- To test turbine efficiency at various hydraulic head conditions
Correct answer: To store energy by pumping water to an upper reservoir for later generation
Pumped-storage hydropower uses off-peak surplus electricity to pump water uphill, storing gravitational potential energy that is later released through turbines during peak demand periods.
Question 7: What distinguishes Enhanced Geothermal Systems (EGS) from conventional geothermal power production?
- EGS plants use only solar thermal energy to supplement geothermal heat
- EGS creates or enhances permeability in hot dry rock through hydraulic stimulation (Correct answer)
- EGS extracts energy from shallow soil temperature gradients below 30°C
- EGS relies exclusively on naturally occurring steam vents at the surface
Correct answer: EGS creates or enhances permeability in hot dry rock through hydraulic stimulation
EGS artificially creates or enhances fractures in hot dry rock through hydraulic stimulation, enabling water circulation and heat extraction in areas lacking natural hydrothermal reservoirs.
REP Geothermal and Hydropower 2
What is the primary environmental concern associated with geothermal power plants using open-loop hydrothermal systems?