UNIVERSITY OF TORONTO, Department of Civil Engineering

Transcription

1 Name: Student #: UNIVERSITY OF TORONTO, Department of Civil Engineering CIV 380 Sustainable Energy Systems Midterm: Wednesday, March 6 th, :10 PM. The test is one hour and 50 minutes (110 minutes). Clearly show all calculations and state any assumptions. For the multiple choice questions, only one option is correct. Please keep qualitative answers concise and to the point A double-sided, hand-written aid sheet and a non-programmable calculator are allowed. No other aids are permitted. Please make sure your phone is turned off. Question Marks Marks Earned Total 50 Page 1 of 10

2 Question 1. Select the correct answer for the following questions. Note there is only one correct answer for each question. (5 marks) a) Generally, the GHG emissions associated with the combustion of natural gas are typically of that of coal combustion. I. One quarter II. One third III. One half IV. About the same b) Comparing ethanol with gasoline: one would expect ethanol to have a Energy Return on Investment (EROI) and a Fossil Fuel Ratio (FFR) compared to gasoline. I. Higher; Lower II. Higher; Higher III. Lower; Lower IV. Lower; Higher c) Base load electricity supply characteristics typically include: output; capacity factor, cost electricity source. I. Near-constant; High; Low II. Variable; High; Low III. Near-constant; Medium; Low IV. Variable; Medium; High d) Which one of the following would you expect to operate with the highest capacity factor in Ontario? I. Wind turbines II. Natural gas turbine III. Nuclear generating station IV. Coal plant e) The area under Hubbert s peak oil curve is representative of: I. The rate of resource extraction II. The total available resource III. Cumulative production IV. The total amount of reserves remaining Page 2 of 10

3 Question 2 (12 marks) Use point form and/or short calculations to answer the following questions be concise in your responses but ensure that each point is sufficiently elaborated. a) A ground-source heat pump uses a 5 horsepower (Hp) compressor operating at full load while transferring 50 kj of energy to/from groundwater each minute. What is the COP: i. If the purpose is to cool the building? (2 marks) ii. If the purpose is to heat the building? (2 marks) b) Briefly describe one advantage of distributed electricity generation compared to centralized electricity generation. (2 marks) Page 3 of 10

4 c) Why is the voltage of electricity traveling through transmission lines different from the voltage supplied at the household level? Include some basic calculations to show the benefit of changing the voltage of electricity traveling through transmission lines. (3 marks) d) Why is cogeneration more efficient than conventional generation methods? Explain concisely why cogeneration is often discussed in the context of climate change mitigation and greenhouse gas reduction technology. (3 marks) Page 4 of 10

5 Question 3 (18 marks) A coal fired electricity generation station (GS) has the following characteristics: Rated capacity: 900 MW Annual capacity factor: 75% Temperature at the combustion chamber: 900 C Temperature of the river that the waste heat is rejected to: 15 C Conversion efficiency of the power plant: 32% GS lifetime: 30 years Coal energy content: 35 GJ/tonne coal Coal composition: 80% carbon (by weight) Activity Materials and construction of GS Coal fuel cycle (activities included are; mining, transport of fuel to power plant) Operating and maintenance of GS Decommissioning of GS Energy Use 1.2 x 10 7 MJ/MW of rated capacity 6 GJ per 100 GJ of coal delivered to power plant 3.6 kj/kwh produced by GS 1.2 x MJ Use this information to answer following questions. a) Calculate the maximum theoretical efficiency of this generating station. (2 marks) b) State one reason for the difference between the actual efficiency and the maximum possible efficiency? (1 mark) Page 5 of 10

6 c) Calculate the amount of electricity generated per year (in GWh/year). (2 marks) d) Calculate the annual coal consumption of the generating station (in tonnes/year). (2 marks) e) Calculate the amount of wasted primary energy per year (in GJ/year). (2 marks) Page 6 of 10

7 f) Suppose a nearby facility uses 30% of the waste energy from this generating station for an industrial process. What is the overall power plant conversion efficiency of the combined electricity and process energy generation? (2 marks) g) Calculate the EROI of producing electricity and heat from the coal generating station (with cogeneration) and discuss the implications of this result. Ensure you show the calculation of each component of the equation. (5 marks) h) Briefly discuss the tradeoffs associated with retrofitting an existing coal-fired power plant to include carbon capture and storage. (2 marks) Page 7 of 10

8 Question 4 (10 marks) A 20m 2 photovoltaic (PV) array is installed on the roof of a house in Calgary. The average solar energy availability and average temperatures in Calgary and the efficiencies of the PV array are given in the table below. January - April May - August September December Solar energy availability 10.8 MJ/m 2 /day 21.6 MJ/m 2 /day 9 MJ/m 2 /day Number of days 120 days 123 days 122 days Average air temperature -4 C 15 C 1.5 C Efficiency of the PV power system 12.5% 10% 11% You may assume that the PV array is kept clean and is in full sun (no trees, etc. shading the panels) throughout the year. a) State a possible reason for the variation of the PV array efficiency in different periods of the year. (1 mark) b) Estimate the annual electricity generation of the PV power system (kwh/year) (3 marks) Page 8 of 10

9 c) The capital cost of the PV power system is $12,000. The annual fixed operating and maintenance cost (O&M) of the system is $150. Calculate the cost of electricity generated by the PV system (in $/kwh produced). Use a discount rate of 10% and a lifetime of 25 years. (3 marks) d) What is the optimal tilt angle for solar collectors? Explain what angle you would choose if you were designing a PV system that was i) connected to the grid ii) not connected to the grid (e.g., a remote cottage in northern Ontario, occupied year-round) (3 marks) Page 9 of 10

10 Question 5 (5 marks) Draw the well-to-wheel life cycle flow diagram for the following (include at least 5 steps): a) The production of an oil sands-derived fuel. b) The production of conventional oil c) Some claim that life cycle GHG emissions from the oil sands are 5-10% higher than conventional, while others claim that emissions are 3-5 times higher. Explain how these conflicting claims arise. (5 marks) Page 10 of 10