EMP Renewable Energy Systems 2 — Questions and Answers
Question 1: What is the primary purpose of a Maximum Power Point Tracker (MPPT) in a photovoltaic system?
- Limit current to prevent panel damage
- Continuously adjust the load impedance to maximize energy harvest (Correct answer)
- Convert AC power to DC for battery storage
- Monitor panel temperature and shut down if overheated
Correct answer: Continuously adjust the load impedance to maximize energy harvest
An MPPT controller dynamically adjusts the electrical operating point of PV modules so they always operate at peak power output regardless of varying irradiance or temperature.
Question 2: Which wind turbine configuration is most commonly used in utility-scale onshore wind farms?
- Vertical-axis Darrieus turbine
- Horizontal-axis upwind three-blade turbine (Correct answer)
- Horizontal-axis downwind two-blade turbine
- Savonius drag-type turbine
Correct answer: Horizontal-axis upwind three-blade turbine
The horizontal-axis upwind three-blade design dominates utility-scale wind because it offers the best balance of aerodynamic efficiency, structural reliability, and noise characteristics.
Question 3: A solar farm in the US Southwest produces 8 GWh annually from a 5 MW DC installation. What is its capacity factor?
- 12.3%
- 18.3% (Correct answer)
- 22.8%
- 26.4%
Correct answer: 18.3%
Capacity factor = 8,000 MWh ÷ (5 MW × 8,760 h) = 8,000 ÷ 43,800 ≈ 18.3%.
Question 4: In a geothermal binary cycle power plant, what fluid is used to drive the turbine?
- High-pressure steam extracted directly from the reservoir
- A low-boiling-point working fluid heated by geothermal brine (Correct answer)
- Compressed air heated by surface solar collectors
- Superheated water at reservoir temperature
Correct answer: A low-boiling-point working fluid heated by geothermal brine
Binary cycle plants use a secondary organic working fluid (e.g., isobutane) with a low boiling point, allowing electricity generation from moderate-temperature geothermal resources without flashing brine.
Question 5: Which metric best describes the ratio of usable energy output to total energy input over a renewable technology's lifetime?
- Levelized Cost of Energy (LCOE)
- Energy Return on Energy Invested (EROI) (Correct answer)
- Net Present Value (NPV)
- Internal Rate of Return (IRR)
Correct answer: Energy Return on Energy Invested (EROI)
EROI measures how many units of energy a technology delivers for every unit consumed during manufacturing, installation, operation, and decommissioning.
Question 6: What is the Betz limit, and what does it represent for wind turbines?
- Maximum structural loading a turbine blade can withstand
- Theoretical maximum aerodynamic efficiency of 59.3% for any wind turbine (Correct answer)
- Minimum wind speed required for turbine cut-in
- Regulatory noise limit for residential wind installations
Correct answer: Theoretical maximum aerodynamic efficiency of 59.3% for any wind turbine
The Betz limit (16/27 ≈ 59.3%) is the theoretical maximum fraction of kinetic energy that any turbine can extract from free-flowing wind, derived from conservation of momentum.
Question 7: Which interconnection standard must US distributed solar inverters typically comply with for anti-islanding protection?
- ANSI C84.1
- IEEE 1547 (Correct answer)
- NFPA 70E
- UL 508A
Correct answer: IEEE 1547
IEEE 1547 sets the US standard for interconnection of distributed energy resources, including mandatory anti-islanding functions that disconnect the inverter when grid power is lost.
EMP Renewable Energy Systems 2
What is the primary purpose of a Maximum Power Point Tracker (MPPT) in a photovoltaic system?