REP Renewable Energy Technologies & Applications 2 — Questions and Answers
Question 1: What is the primary function of a Maximum Power Point Tracker (MPPT) in a PV system?
- Store excess solar energy in batteries
- Adjust the operating voltage to maximize power output (Correct answer)
- Convert DC power to AC power for grid use
- Monitor panel temperature and reduce current
Correct answer: Adjust the operating voltage to maximize power output
An MPPT continuously adjusts the electrical operating point of PV modules to extract the maximum available power under varying conditions.
Question 2: In a concentrating solar power (CSP) trough system, which fluid is most commonly used as the heat transfer medium?
- Water/steam
- Molten salt
- Synthetic oil (therminol) (Correct answer)
- Liquid sodium
Correct answer: Synthetic oil (therminol)
Parabolic trough CSP plants most commonly use synthetic oil (such as Therminol VP-1) as the heat transfer fluid between the collectors and the steam generator.
Question 3: Which wind turbine configuration is most commonly deployed in utility-scale onshore wind farms today?
- Vertical-axis Darrieus turbine
- Horizontal-axis, upwind, three-blade turbine (Correct answer)
- Horizontal-axis, downwind, two-blade turbine
- Savonius drag-type vertical-axis turbine
Correct answer: Horizontal-axis, upwind, three-blade turbine
The horizontal-axis upwind three-blade design dominates utility-scale installations due to its high efficiency, structural simplicity, and well-established supply chain.
Question 4: What does the 'capacity factor' of a renewable energy plant represent?
- The ratio of installed capacity to peak demand
- The percentage of time a plant operates at full rated output
- Actual energy produced divided by maximum possible energy over a period (Correct answer)
- The efficiency of converting fuel to electricity
Correct answer: Actual energy produced divided by maximum possible energy over a period
Capacity factor is actual energy generated divided by the energy that would be produced if the plant ran at full nameplate capacity for the entire period.
Question 5: Which geothermal resource type requires no water injection and uses naturally occurring steam directly to drive turbines?
- Hot dry rock (EGS)
- Binary cycle low-temperature
- Dry steam reservoir (Correct answer)
- Flash steam high-salinity
Correct answer: Dry steam reservoir
Dry steam resources, such as The Geysers in California, produce superheated steam directly from the reservoir that can be piped straight to steam turbines.
Question 6: In a run-of-river hydropower plant, what distinguishes it from a conventional reservoir-based plant?
- It uses tidal forces instead of river flow
- It relies on natural river flow with minimal water storage (Correct answer)
- It pumps water uphill during off-peak hours
- It generates power from rainwater harvested on rooftops
Correct answer: It relies on natural river flow with minimal water storage
Run-of-river plants divert a portion of river flow through turbines with little or no upstream storage, making output dependent on natural flow variability.
Question 7: What is the primary advantage of a doubly-fed induction generator (DFIG) in wind turbines compared to a fixed-speed induction generator?
- Zero maintenance requirements
- Variable-speed operation with partial-scale power converter (Correct answer)
- Higher tower height capability
- Direct DC output without inverter
Correct answer: Variable-speed operation with partial-scale power converter
DFIGs allow variable-speed operation by controlling rotor currents through a partial-scale converter (typically ~30% of rated power), reducing converter costs while improving energy capture.
REP Renewable Energy Technologies & Applications 2
What is the primary function of a Maximum Power Point Tracker (MPPT) in a PV system?