CEM Renewable Energy Systems 2 — Questions and Answers
Question 1: In a grid-tied solar PV system, what is the primary function of the inverter?
- Store excess solar energy in a battery bank for nighttime use
- Convert AC power from the utility grid to DC for the solar panels
- Convert DC power from solar panels into AC power compatible with the building and grid (Correct answer)
- Regulate water circulation in solar thermal collectors
Correct answer: Convert DC power from solar panels into AC power compatible with the building and grid
The inverter is the core power conversion device in a grid-tied PV system, converting variable DC output from the panels into AC power that matches grid voltage and frequency.
Question 2: What is the wind speed at which a wind turbine first begins generating electricity called?
- Rated speed
- Cut-in speed (Correct answer)
- Cut-out speed
- Survival speed
Correct answer: Cut-in speed
The cut-in speed is the minimum wind speed at which the turbine begins producing usable power; below this speed, wind energy is insufficient to overcome mechanical losses.
Question 3: Which type of solar thermal collector is most appropriate and cost-effective for low-temperature applications such as swimming pool heating?
- Parabolic trough concentrating collector
- Evacuated tube collector
- Unglazed flat-plate collector (Correct answer)
- Central receiver power tower
Correct answer: Unglazed flat-plate collector
Unglazed flat-plate collectors are simple, inexpensive, and well-suited for pool heating, which only requires raising water temperature a few degrees above ambient.
Question 4: What does the metric 'peak sun hours' represent for a solar installation site?
- Total hours per day that the sun is above the horizon
- Hours when solar panel surface temperature is highest
- The equivalent daily hours at 1,000 W/m² irradiance that delivers the same energy as actual daily solar radiation (Correct answer)
- The hours between 10 AM and 2 PM when solar output exceeds 80% of rated capacity
Correct answer: The equivalent daily hours at 1,000 W/m² irradiance that delivers the same energy as actual daily solar radiation
Peak sun hours normalize the daily solar resource by converting total daily irradiation into equivalent hours at the 1,000 W/m² standard test condition irradiance.
Question 5: Which statement best describes a biomass energy system?
- Converting kinetic energy of ocean waves into electricity via underwater turbines
- Combusting or thermochemically converting organic materials to produce heat or electricity (Correct answer)
- Using temperature differentials between deep and surface ocean water to generate power
- Producing hydrogen fuel from water using photocatalytic solar reactions
Correct answer: Combusting or thermochemically converting organic materials to produce heat or electricity
Biomass energy involves burning or thermochemically processing organic materials — such as wood, agricultural residues, or energy crops — to generate heat or electricity.
Question 6: What is the primary operational advantage of a run-of-river microhydro system compared to wind or solar installations?
- Zero noise or vibration output during operation
- Ability to generate consistent baseload power 24 hours a day from continuous water flow (Correct answer)
- Lower installed cost per kilowatt than any other renewable technology
- No civil works or water intake structure required
Correct answer: Ability to generate consistent baseload power 24 hours a day from continuous water flow
Microhydro systems produce reliable, near-continuous electricity as long as adequate stream flow is available, unlike solar and wind which are intermittent and weather-dependent.
Question 7: What is the primary purpose of a solar charge controller in a stand-alone off-grid PV system?
- Convert DC power from solar panels to AC power for loads
- Track the maximum power point of the solar array under varying conditions
- Regulate charging current to batteries and prevent overcharging or excessive discharge (Correct answer)
- Monitor and report grid frequency and voltage to the utility
Correct answer: Regulate charging current to batteries and prevent overcharging or excessive discharge
A charge controller manages current flow between the solar array and the battery bank, preventing overcharging that causes damage and over-discharging that reduces battery lifespan.
CEM Renewable Energy Systems 2
In a grid-tied solar PV system, what is the primary function of the inverter?