Answer: A. Matches array operating voltage. A DC-DC converter can adjust the PV operating point and interface the array with a DC bus or battery.
What does perturb-and-observe MPPT do?
A Changes blade pitch only
B Perturbs voltage, checks power
C Measures water flow
D Disconnects the array
Answer: B. Perturbs voltage, checks power. Perturb-and-observe changes the PV operating voltage and observes whether output power rises or falls to choose the next direction.
At the PV maximum-power point, what is true locally?
A Current is always zero
B Voltage is always zero
C dP over dV equals zero
D dP over dV is infinite
Answer: C. dP over dV equals zero. At a smooth maximum of the power-voltage curve, the local derivative of power with respect to voltage is zero.
What should a grid-connected inverter synchronize with?
A Wind blade pitch
B Grid voltage and frequency
C Battery chemistry
D Water turbine speed
Answer: B. Grid voltage and frequency. A grid-connected inverter synchronizes its output waveform with the grid voltage and frequency before power exchange.
What does anti-islanding protection detect?
A Low solar irradiance
B Unintended isolated grid section
C Battery full charge
D Excess wind speed
Answer: B. Unintended isolated grid section. Anti-islanding protection stops or controls a distributed generator when a utility outage leaves a local island energized.
What is the purpose of a wind turbine yaw drive?
A Change generator frequency directly
B Cool the battery
C Adjust water flow
D Align rotor with wind
Answer: D. Align rotor with wind. Yaw control turns the nacelle to align the rotor with wind direction and reduce misalignment losses.
What is the optimum tip-speed ratio?
A Wind speed to tower height
B Generator voltage to current
C Blade speed to wind speed
D Rotor radius to blade mass
Answer: C. Blade speed to wind speed. Tip-speed ratio is blade-tip speed divided by wind speed; each turbine design has an efficient operating range.
What is the Betz limit for an ideal wind rotor?
A About 25 percent
B About 59.3 percent
C About 75 percent
D Exactly 100 percent
Answer: B. About 59.3 percent. The Betz limit states that an ideal turbine cannot extract more than 16/27, about 59.3 percent, of the wind's kinetic power.
What does pitch control usually do above rated wind speed?
A Raises tower height
B Increases grid frequency
C Stops battery charging always
D Limits aerodynamic power
Answer: D. Limits aerodynamic power. Blade pitch is adjusted to keep turbine power and rotor speed within rated limits in strong winds.
What does a wind turbine yaw controller use to orient the nacelle?
A PV cell voltage
B Hydro head sensor
C Battery state of charge
D Wind direction measurement
Answer: D. Wind direction measurement. A wind-direction sensor provides the yaw controller with information about the direction of the incoming wind.
What can anaerobic digestion produce from wet organic waste?
A Solar-grade silicon
B Hydrogen only
C Biogas and digestate
D Wind turbine blades
Answer: C. Biogas and digestate. Anaerobic digestion produces a methane-rich biogas and a nutrient-containing digestate from biodegradable feedstocks.
What is biomass gasification?
A Direct cell conversion
B Water pumped uphill
C Partial oxidation to producer gas
D Wind-to-AC conversion
Answer: C. Partial oxidation to producer gas. Gasification converts carbonaceous feedstock into a combustible gas using limited oxygen or steam at elevated temperature.
What is a run-of-river hydro plant designed to use?
A Available river flow
B Large pumped storage reservoir
C Ocean wave motion
D Geothermal steam only
Answer: A. Available river flow. Run-of-river plants generate using available river flow, usually with limited water storage.
What does pumped hydro storage do?
A Pumps water uphill for storage
B Creates new renewable fuel
C Stores wind in blades
D Converts PV cells to heat
Answer: A. Pumps water uphill for storage. Pumped hydro uses surplus electricity to pump water to a higher reservoir, then generates electricity as it flows back down.
What does a battery charge controller help regulate?
A Wind direction
B Turbine blade length
C Battery charging and protection
D Grid pole count
Answer: C. Battery charging and protection. A charge controller manages charging conditions and protects a battery from unsafe overcharge or discharge.
What is state of charge?
A Remaining stored-energy fraction
B Grid voltage quality
C Turbine rotor speed
D Solar irradiance level
Answer: A. Remaining stored-energy fraction. State of charge estimates the remaining usable charge or energy in a storage device relative to its capacity.
A 100 kW plant produces 175.2 MWh in a year. Approximate capacity factor?
A 10 percent
B 40 percent
C 80 percent
D 20 percent
Answer: D. 20 percent. Rated annual energy is 100 kW times 8760 hours, or 876 MWh; 175.2 divided by 876 is 20 percent.
What is renewable curtailment?
A Reducing available generation
B Increasing turbine head
C Charging a battery fully
D Raising inverter frequency
Answer: A. Reducing available generation. Curtailment intentionally reduces renewable output, often when grid, transmission or balancing limits prevent accepting all available power.
Why are forecasts useful for variable renewables?
A Change module polarity
B Set turbine foundation depth
C Plan balancing and reserves
D Eliminate all outages
Answer: C. Plan balancing and reserves. Generation forecasts help operators schedule reserves, storage and other resources to balance variable renewable output.
What is a common advantage of a hybrid PV-wind system?
A No need for controls
B Complementary generation profiles
C Unlimited firm output
D Zero storage losses
Answer: B. Complementary generation profiles. Solar and wind output can complement one another over time, though actual benefits depend on local resource patterns.
What role can storage provide to a microgrid?
A Create additional sunlight
B Shift energy across time
C Increase water head
D Change blade pitch
Answer: B. Shift energy across time. Storage can absorb surplus generation and supply energy later, helping balance a microgrid.
What does a grid-following inverter use to track grid phase?
A Phase-locked loop
B Yaw position sensor
C Hydro governor
D Battery fuse
Answer: A. Phase-locked loop. A phase-locked loop estimates grid phase and frequency for synchronization and current control.
What does a bypass diode protect in a shaded PV module?
A Windings from overspeed
B Battery from cold
C Turbine from yaw error
D Cell substring from hot spots
Answer: D. Cell substring from hot spots. A bypass diode gives current a path around a shaded cell substring and limits reverse-bias heating.
What often limits PV output during partial shading?
A Current mismatch across modules
B Wind speed cubed
C Water head only
D Battery pole count
Answer: A. Current mismatch across modules. Series-connected modules share current, so a shaded module can constrain string output and create multiple local power peaks.
What is the main grid interface for a variable-frequency wind generator?
A Solar thermal receiver
B Penstock valve
C Biogas digester
D Power electronic converter
Answer: D. Power electronic converter. A power electronic converter conditions variable generator output for grid voltage and frequency requirements.