REP Geothermal and Hydropower 3 — Questions and Answers
Question 1: Which factor most directly determines the power output of a hydropower turbine?
- Water temperature and dissolved oxygen content
- Net hydraulic head and volumetric flow rate (Correct answer)
- Distance from the reservoir to the powerhouse
- Turbine blade material and surface roughness
Correct answer: Net hydraulic head and volumetric flow rate
Hydropower output (P = ρgQHη) is primarily governed by net hydraulic head (H) and volumetric flow rate (Q), along with water density and turbine efficiency.
Question 2: In the context of geothermal energy, what is 'reinjection' and why is it practiced?
- Adding chemical inhibitors to prevent scale buildup in pipes
- Returning spent geothermal brine to the reservoir to sustain pressure and reduce surface disposal (Correct answer)
- Injecting fresh water to cool the turbine exhaust steam
- Pumping natural gas into the reservoir to maintain fluid mobility
Correct answer: Returning spent geothermal brine to the reservoir to sustain pressure and reduce surface disposal
Reinjection returns cooled geothermal brine back into the reservoir, maintaining reservoir pressure, extending field life, and minimizing surface disposal of mineral-laden fluid.
Question 3: A Kaplan turbine is preferred over a Francis turbine for which site condition?
- High head (above 200 m) with low flow
- Low head (below 40 m) with high flow and variable flow rates (Correct answer)
- Medium head (40–200 m) with constant flow
- Very high head (above 500 m) with seasonal flow variation
Correct answer: Low head (below 40 m) with high flow and variable flow rates
Kaplan turbines have adjustable runner blades suited for low-head, high-flow sites with variable discharge, maintaining efficiency across a wide range of flow conditions.
Question 4: What is the significance of the 'capacity factor' for a hydropower plant?
- The ratio of actual energy generated to maximum possible energy at full capacity over a period (Correct answer)
- The maximum allowable turbine speed before cavitation occurs
- The percentage of reservoir storage volume available for power generation
- The fraction of installed capacity that serves base-load versus peaking demand
Correct answer: The ratio of actual energy generated to maximum possible energy at full capacity over a period
Capacity factor is the ratio of actual annual energy output to the theoretical maximum if the plant ran at full nameplate capacity continuously, reflecting real-world hydrology and operational constraints.
Question 5: Which U.S. federal agency is primarily responsible for licensing non-federal hydropower projects?
- Bureau of Reclamation (BOR)
- Army Corps of Engineers (USACE)
- Federal Energy Regulatory Commission (FERC) (Correct answer)
- Environmental Protection Agency (EPA)
Correct answer: Federal Energy Regulatory Commission (FERC)
FERC issues licenses and exemptions for non-federal hydropower projects under the Federal Power Act, overseeing project construction, operation, and environmental conditions.
Question 6: Cavitation in hydropower turbines is most likely to occur under which operating condition?
- High head operation with reduced flow
- Low local pressure causing water to vaporize near turbine blades (Correct answer)
- Excessive generator reactive power causing rotor heating
- High sediment concentration increasing water density
Correct answer: Low local pressure causing water to vaporize near turbine blades
Cavitation occurs when local pressure at the turbine runner drops below the vapor pressure of water, forming vapor bubbles that collapse violently and erode turbine components.
Question 7: What is the approximate global average geothermal heat flux at the Earth's surface?
- 0.065 W/m² (Correct answer)
- 6.5 W/m²
- 65 W/m²
- 650 W/m²
Correct answer: 0.065 W/m²
The global average geothermal heat flux is approximately 0.065 W/m² (65 mW/m²), far less than solar irradiance but sufficient for exploitation in high-gradient volcanic and tectonic zones.
REP Geothermal and Hydropower 3
Which factor most directly determines the power output of a hydropower turbine?