A 2 m² PV panel receives 800 W/m² at 20% efficiency. Estimate output.
A 320 W
B 160 W
C 800 W
D 1600 W
Answer: A. 320 W. Power is irradiance times area times efficiency: 800 times 2 times 0.20 equals 320 W, before system losses.
Four PV modules rated 40 V each are connected in series. Find string voltage.
A 40 V
B 80 V
C 160 V
D 200 V
Answer: C. 160 V. Series-connected module voltages add, so four modules at 40 V each give 160 V.
Three identical 5 A PV strings are connected in parallel. Find total current.
A 5 A
B 15 A
C 10 A
D 20 A
Answer: B. 15 A. Parallel string currents add, giving three times 5 A or 15 A at the common operating voltage.
A PV array outputs 240 W at 30 V. Find current.
A 4 A
B 8 A
C 6 A
D 12 A
Answer: B. 8 A. Electrical power equals voltage times current, so 240 W divided by 30 V is 8 A.
A 1 kW PV module has a -0.4%/°C power coefficient. Estimate power 25°C hotter.
A 900 W
B 800 W
C 950 W
D 1000 W
Answer: A. 900 W. A 25°C rise produces about a 10 percent reduction at -0.4 percent per degree, leaving about 900 W.
A 100 kW plant generates 150 MWh in one year. Approximate capacity factor.
A 8.6 percent
B 25 percent
C 17.1 percent
D 50 percent
Answer: C. 17.1 percent. The annual rated-energy maximum is 100 kW times 8760 hours, or 876 MWh; 150 divided by 876 is about 17.1 percent.
Below rated operation, what happens to ideal wind power if speed doubles?
A It doubles
B It quadruples
C It increases sixfold
D It increases eightfold
Answer: D. It increases eightfold. Wind kinetic power is proportional to wind speed cubed, so doubling speed multiplies the available power by eight.
A wind rotor has a 10 m radius. Approximate swept area.
A 314 m²
B 31.4 m²
C 100 m²
D 628 m²
Answer: A. 314 m². Swept area is πr squared; π times 10 squared is about 314 square metres.
What is the Betz-limit maximum fraction of wind power?
A 1 over 2
B 16 over 27
C 3 over 4
D 1 over 1
Answer: B. 16 over 27. The ideal Betz limit is 16/27, approximately 59.3 percent of the kinetic power in the undisturbed wind.
A hydro plant has Q 10 m³/s, head 5 m, and efficiency 0.8. Estimate output.
A 98 kW
B 392 kW
C 245 kW
D 490 kW
Answer: B. 392 kW. Using P equals rho g Q H eta gives 1000 times 9.81 times 10 times 5 times 0.8, about 392 kW.
After a P&O voltage step, measured PV power falls. What should it do next?
A Keep stepping same way
B Disconnect the inverter
C Short the PV array
D Reverse perturbation direction
Answer: D. Reverse perturbation direction. Perturb-and-observe reverses the perturbation direction when the measured power decreases, steering back toward the maximum-power point.
At the PV maximum-power point, what relation holds for incremental conductance?
A dI/dV equals minus I/V
B dI/dV equals I/V
C dI/dV equals zero
D I/V equals zero
Answer: A. dI/dV equals minus I/V. Since dP/dV equals I plus V dI/dV and is zero at the maximum, dI/dV equals negative I divided by V.
Why can partial shading create multiple PV power peaks?
A Wind speed changes suddenly
B Bypass paths alter string curve
C Grid frequency doubles
D Battery voltage becomes zero
Answer: B. Bypass paths alter string curve. Bypass diodes change which cell substrings conduct under shade, producing a multi-peaked array power-voltage curve.
How does a grid-connected inverter exchange active power?
A Changes water head
B Changes module temperature
C Controls synchronized current
D Moves turbine yaw
Answer: C. Controls synchronized current. A grid-connected inverter controls current synchronized to the grid; its in-phase component controls active-power exchange.
Why is battery round-trip efficiency below 100%?
A Energy is created
B Voltage cannot change
C Cells store all input
D Charging and conversion losses
Answer: D. Charging and conversion losses. Losses occur in electrochemical charging and discharging, power conversion, wiring and thermal management.
What defines an islanded microgrid operating condition?
A All sources are shut down
B Grid frequency is infinite
C Local grid section is disconnected
D Only PV modules remain
Answer: C. Local grid section is disconnected. An islanded microgrid is electrically separated from the main grid while local sources and loads continue operating.
A storage system supplies 10 kW for 4 hours. Required usable energy is?
A 40 kWh
B 2.5 kWh
C 14 kWh
D 400 kWh
Answer: A. 40 kWh. Energy equals power times duration, so 10 kW times 4 hours is 40 kWh before reserve and conversion allowances.
What does solar thermal collector orientation mainly optimize?
A Grid phase angle
B Wind rotor torque
C Battery cycle count
D Incident solar energy capture
Answer: D. Incident solar energy capture. Collector tilt and orientation are selected to capture useful solar radiation for the intended site and season.
What does variable-speed wind control often optimize below rated power?
A Tip-speed ratio
B Battery C-rate
C Hydro head
D Grid pole count
Answer: A. Tip-speed ratio. Changing rotor speed helps maintain a near-optimal tip-speed ratio and aerodynamic power coefficient as wind speed changes.
How does feedstock moisture affect biomass conversion?
A Raises silicon voltage
B Increases wind shear
C Can lower usable heating value
D Sets grid phase
Answer: C. Can lower usable heating value. Moisture consumes energy during heating and evaporation, reducing useful energy available per unit of wet feedstock.
Why do evacuated-tube collectors reduce heat loss?
A Higher wind speed
B Larger grid current
C Reduced convective heat transfer
D Lower fluid flow
Answer: C. Reduced convective heat transfer. The evacuated space limits gas conduction and convection between the absorber and outer tube.
What drives hydropower output for fixed efficiency?
A PV temperature only
B Wind pitch only
C Battery voltage only
D Flow rate and head
Answer: D. Flow rate and head. Hydraulic power is proportional to water density, gravity, flow rate and head.
What is a common reason for multiple renewable sources in a hybrid plant?
A Remove all controls
B Improve supply complementarity
C Guarantee constant weather
D Eliminate conversion losses
Answer: B. Improve supply complementarity. Different resource profiles can complement one another and improve supply, although they do not guarantee firm output.
What does a renewable forecast help a grid operator schedule?
A Blade material
B PV cell doping
C Penstock diameter
D Balancing resources
Answer: D. Balancing resources. Forecasts help schedule reserves, flexible generation and storage to balance expected renewable output and uncertainty.
Why does PV output fall when irradiance falls?
A Photocurrent decreases
B Wind torque decreases
C Hydro head rises
D Grid frequency drops
Answer: A. Photocurrent decreases. Lower irradiance produces less photocurrent, usually reducing array current and available power.