CEM Renewable Energy and Cogeneration 1 — Questions and Answers
Question 1: Combined Heat and Power (CHP) systems improve overall fuel efficiency compared to separate generation because they:
- Use two separate boilers operating in parallel
- Capture and utilize waste heat from electricity generation that would otherwise be rejected (Correct answer)
- Reduce electrical output to minimize heat production
- Use renewable fuel sources exclusively
Correct answer: Capture and utilize waste heat from electricity generation that would otherwise be rejected
CHP (cogeneration) recovers waste heat from prime movers (engines, turbines) for space heating, water heating, or industrial processes, achieving overall efficiencies of 65-85% versus 33% for separate generation.
Question 2: The capacity factor of a solar photovoltaic (PV) system represents:
- The peak wattage rating of the PV panels
- Actual annual energy output divided by the energy the system would produce at rated power continuously (Correct answer)
- The efficiency of the inverter at converting DC to AC
- The percentage of sunlight reflected by the panels
Correct answer: Actual annual energy output divided by the energy the system would produce at rated power continuously
Capacity factor accounts for daily and seasonal variation in solar irradiance; typical US PV systems have capacity factors of 15-25% depending on location and tilt.
Question 3: A wind turbine's power output varies with wind speed according to:
- A linear relationship (power ∝ speed)
- A cubic relationship (power ∝ speed³) (Correct answer)
- A square relationship (power ∝ speed²)
- An exponential relationship (power ∝ e^speed)
Correct answer: A cubic relationship (power ∝ speed³)
Wind turbine power output is proportional to the cube of wind speed; doubling wind speed increases power output by a factor of 8, making site wind resource critical.
Question 4: Net metering allows facilities with on-site generation to:
- Avoid all utility interconnection fees
- Credit excess electricity fed back to the grid against future consumption charges (Correct answer)
- Store surplus energy in on-site batteries without utility approval
- Sell electricity at wholesale rates to other customers
Correct answer: Credit excess electricity fed back to the grid against future consumption charges
Net metering policies allow on-site generators to bank excess kWh fed to the grid, offsetting future purchases at retail rates and improving the economics of distributed generation.
Question 5: A microturbine used in CHP applications differs from a reciprocating engine CHP unit in that microturbines:
- Produce higher-quality (higher-temperature) exhaust heat suitable for high-pressure steam
- Operate at very high RPM with fewer moving parts and produce lower-temperature exhaust heat (Correct answer)
- Only operate on natural gas and cannot use biogas
- Have higher electrical efficiency than large reciprocating engines
Correct answer: Operate at very high RPM with fewer moving parts and produce lower-temperature exhaust heat
Microturbines spin at 50,000-120,000 RPM with air bearings (no oil lubrication), have very few moving parts, and produce lower-temperature exhaust (450-600°F) suitable for hot water or low-pressure steam.
Question 6: The primary economic metric used to evaluate a renewable energy investment alongside payback period is:
- Fuel utilization efficiency (FUE)
- Internal Rate of Return (IRR) or Net Present Value (NPV) (Correct answer)
- Capacity factor normalized by latitude
- Annual equivalent operating hours
Correct answer: Internal Rate of Return (IRR) or Net Present Value (NPV)
IRR and NPV account for the time value of money across the project lifetime, providing a more complete financial picture than simple payback for long-lived renewable energy assets.
CEM Renewable Energy and Cogeneration 1
Combined Heat and Power (CHP) systems improve overall fuel efficiency compared to separate generation because they: