CEA Renewable Energy Technologies 3 — Questions and Answers
Question 1: Which metric best describes the total electricity generated by a solar PV system over its lifetime relative to the energy used to manufacture and install it?
- Levelized cost of energy (LCOE)
- Energy payback ratio (EPR) (Correct answer)
- Capacity factor
- Power density
Correct answer: Energy payback ratio (EPR)
The energy payback ratio (EPR) compares lifetime energy output to embodied energy, indicating net energy gain from a PV system.
Question 2: In a wind turbine drivetrain, a gearbox-free direct-drive design eliminates the gearbox by using:
- Hydraulic fluid couplings
- A high-speed permanent magnet generator
- A low-speed permanent magnet generator with many pole pairs (Correct answer)
- Compressed air transmission
Correct answer: A low-speed permanent magnet generator with many pole pairs
Direct-drive turbines use low-speed permanent magnet generators with many pole pairs to match rotor RPM without mechanical gearing.
Question 3: What is the primary purpose of a power purchase agreement (PPA) in renewable energy project finance?
- Establish equipment warranties between manufacturer and installer
- Provide a long-term contract guaranteeing electricity sale price and volume (Correct answer)
- Set interconnection fees between the generator and grid operator
- Define renewable energy credit (REC) ownership rights
Correct answer: Provide a long-term contract guaranteeing electricity sale price and volume
A PPA is a long-term contract between an energy producer and buyer that locks in the price and volume of electricity sold, reducing revenue risk.
Question 4: What differentiates a parabolic trough CSP system from a power tower (central receiver) CSP system?
- Parabolic troughs use photovoltaic cells; power towers use steam turbines
- Parabolic troughs focus sunlight onto a linear receiver; power towers concentrate it onto a central point (Correct answer)
- Parabolic troughs operate at night; power towers only during the day
- Parabolic troughs require no tracking; power towers use two-axis tracking
Correct answer: Parabolic troughs focus sunlight onto a linear receiver; power towers concentrate it onto a central point
Parabolic troughs use curved mirrors to focus sunlight onto a linear tube receiver, while power towers use hundreds of heliostats to focus on a central point at higher temperatures.
Question 5: Which geothermal power plant type is best suited for lower-temperature hydrothermal resources (below 150°C)?
- Dry steam plant
- Flash steam plant
- Binary cycle plant (Correct answer)
- Enhanced geothermal system
Correct answer: Binary cycle plant
Binary cycle plants use a secondary working fluid with a lower boiling point, enabling power generation from lower-temperature geothermal resources.
Question 6: What is 'curtailment' in the context of renewable energy grid integration?
- Scheduled maintenance shutdown of renewable generators
- Forced reduction of output below available generation capacity (Correct answer)
- Gradual ramp-down at end of generator life
- Seasonal variation in renewable output
Correct answer: Forced reduction of output below available generation capacity
Curtailment occurs when grid operators force renewable generators to reduce output below what they could produce, typically due to transmission constraints or excess supply.
Question 7: In tidal stream energy systems, power output is proportional to water velocity raised to which power?
- First power (linear)
- Second power (squared)
- Third power (cubed) (Correct answer)
- Fourth power
Correct answer: Third power (cubed)
Like wind turbines, tidal stream turbines extract kinetic energy from moving fluid, and power is proportional to the cube of fluid velocity.
CEA Renewable Energy Technologies 3
Which metric best describes the total electricity generated by a solar PV system over its lifetime relative to the energy used to manufacture and install it?