Agricultural/Bioengineering Renewable Energy 4 — Questions and Answers
Question 1: Which greenhouse gas has the highest global warming potential over a 100-year period relative to CO2?
- Nitrous oxide (N2O) (Correct answer)
- Methane (CH4)
- Carbon dioxide (CO2)
- Water vapor (H2O)
Correct answer: Nitrous oxide (N2O)
N2O has a GWP100 of ~265–298, higher than methane (~28–36), making it the most potent common agricultural GHG on this timescale.
Question 2: In a flat-plate solar collector used for crop drying, what material is typically used as the absorber plate to maximize heat absorption?
- Black-painted metal sheet (Correct answer)
- Clear glass
- White polycarbonate
- Aluminum foil
Correct answer: Black-painted metal sheet
A black-painted metal absorber maximizes solar radiation absorption across the spectrum while the selective coating minimizes re-radiation losses.
Question 3: What is the term for the ratio of electrical energy output to total solar energy input in a photovoltaic system?
- Module efficiency (Correct answer)
- Fill factor
- Open-circuit voltage ratio
- Performance ratio
Correct answer: Module efficiency
Module efficiency is the ratio of electrical power output to the solar irradiance × panel area, typically 15–22% for commercial silicon panels.
Question 4: A dairy farm produces 500 kg/day of manure with 8% total solids. Approximately how much biogas can be expected daily (assume 0.25 m³ biogas/kg VS, VS = 80% of TS)?
- 8 m³/day (Correct answer)
- 10 m³/day
- 40 m³/day
- 500 m³/day
Correct answer: 8 m³/day
VS = 500 × 0.08 × 0.80 = 32 kg VS/day; biogas = 32 × 0.25 = 8 m³/day.
Question 5: Which type of wind turbine is most commonly used in small-scale agricultural applications due to its self-starting capability in low winds?
- Horizontal-axis wind turbine (HAWT) (Correct answer)
- Savonius vertical-axis turbine
- Darrieus turbine
- Helical turbine
Correct answer: Horizontal-axis wind turbine (HAWT)
HAWTs dominate small-scale farm installations because they are efficient over a wide wind speed range and self-start reliably.
Question 6: What is 'co-digestion' in the context of agricultural anaerobic digesters?
- Combining multiple feedstocks (e.g., manure + food waste) to improve biogas yield (Correct answer)
- Digesting the same substrate in two sequential tanks
- Using two microbial inocula simultaneously
- Mixing biogas with natural gas before combustion
Correct answer: Combining multiple feedstocks (e.g., manure + food waste) to improve biogas yield
Co-digestion blends substrates with complementary nutrient ratios (C:N balance) and moisture content to enhance methane production and digester stability.
Question 7: In the context of renewable energy for irrigation, what is 'solar pumping'?
- Using PV panels to power electric water pumps directly (Correct answer)
- Heating water to drive steam turbines for pumping
- Using solar thermal energy to desalinate irrigation water
- Tracking groundwater levels using solar-powered sensors
Correct answer: Using PV panels to power electric water pumps directly
Solar pumping systems use photovoltaic electricity to run DC or AC pumps for irrigation, eliminating diesel fuel costs in remote areas.
Agricultural/Bioengineering Renewable Energy 4
Which greenhouse gas has the highest global warming potential over a 100-year period relative to CO2?