Certified Energy Auditor Certification Renewable Energy Systems 2 — Questions and Answers
Question 1: What does 'peak sun hours' mean as used in PV system sizing?
- The hours of the day when solar panels produce their highest instantaneous output
- The equivalent number of hours per day with solar irradiance at exactly 1000 W/m² (Correct answer)
- The total daily sunlight hours from sunrise to sunset at a specific location
- The hours of daylight minus cloud cover hours at a given location
Correct answer: The equivalent number of hours per day with solar irradiance at exactly 1000 W/m²
Peak sun hours represent the equivalent number of hours per day that a location receives solar irradiance of 1000 W/m² (STC conditions), and are used to estimate daily PV energy production.
Question 2: For a fixed-tilt PV installation in the continental US, what is the general rule for maximizing annual energy production?
- Set tilt angle equal to local latitude, oriented toward true south (Correct answer)
- Set tilt angle to 45° regardless of location, oriented toward magnetic south
- Install panels horizontally (0° tilt) to maximize diffuse radiation capture
- Set tilt angle equal to latitude minus 15°, oriented toward the east
Correct answer: Set tilt angle equal to local latitude, oriented toward true south
Setting the tilt angle equal to the local latitude and orienting panels toward true south maximizes annual solar energy capture for fixed installations in the Northern Hemisphere.
Question 3: What is the typical annual degradation rate of crystalline silicon PV modules?
- 0.5% per year (Correct answer)
- 2.0% per year
- 5.0% per year
- 10.0% per year
Correct answer: 0.5% per year
High-quality crystalline silicon PV modules typically degrade at approximately 0.5% per year, retaining about 80–87% of rated output at the end of a 25–40 year lifetime.
Question 4: Which inverter technology is best suited for maximizing energy harvest when individual PV panels may experience partial shading?
- Central string inverter
- Large central inverter
- Microinverter or DC power optimizer (Correct answer)
- Line-interactive UPS inverter
Correct answer: Microinverter or DC power optimizer
Microinverters and DC optimizers perform maximum power point tracking (MPPT) at the individual panel level, preventing one shaded panel from degrading the output of the entire string.
Question 5: A rooftop PV system is rated at 50 kW STC. Using a derate factor of 0.80 and 5 peak sun hours per day, what is the estimated daily energy production?
- 250 kWh/day
- 200 kWh/day (Correct answer)
- 150 kWh/day
- 400 kWh/day
Correct answer: 200 kWh/day
Daily production = 50 kW × 0.80 derate factor × 5 peak sun hours = 200 kWh/day.
Question 6: What is the primary function of a Maximum Power Point Tracker (MPPT) in a PV system?
- To prevent the PV system from exceeding the utility interconnection power limit
- To continuously adjust operating voltage to extract maximum power from PV panels (Correct answer)
- To monitor and report peak power output for manufacturer warranty compliance
- To regulate battery charging voltage in off-grid systems only
Correct answer: To continuously adjust operating voltage to extract maximum power from PV panels
An MPPT continuously adjusts the electrical operating point of PV modules to ensure they operate at the voltage-current combination that produces maximum power under varying irradiance and temperature conditions.
Question 7: In evaluating a solar thermal system for domestic hot water, what does the 'solar fraction' indicate?
- The percentage of roof area covered by solar collectors
- The proportion of total hot water energy demand supplied by the solar thermal system (Correct answer)
- The ratio of useful heat collected to total solar radiation incident on the collector
- The fraction of sunlight hours when the system operates above its minimum threshold temperature
Correct answer: The proportion of total hot water energy demand supplied by the solar thermal system
Solar fraction is the percentage of a building's total hot water (or space heating) energy demand provided by the solar thermal system, with the remainder supplied by a conventional backup source.
Certified Energy Auditor Certification Renewable Energy Systems 2
What does 'peak sun hours' mean as used in PV system sizing?