ENVS 350 MidTerm Exam
Name: _______________________________
Student ID:_________________________
This exam consists of 12 short/medium answer questions. Questions are
either worth 10, 15 or 20 points.
There are a total of 160 points available on the exam.
Write Legibly and Carefully - Sloppily prepared exams will receive
a point deduction. Take your time on this exam, there is no reason
to hurry through it.
In all of the questions below, please confine your answers to the space
that is provided for that question. For any numerical question,
be sure to show your work, don't just write down an answer.
10 Point Questions
- Explain how levelized costs are determined.
Need to discuss
- capital costs
- fixed costs
- variable costs
Product is then metered at relevant rate over the lifetime of the facility
- Explain how a basic electrical generator works to produce
electricity.
Need to discuss
- stationary magnets
- rotating coil or loop of wire
- produces an alternating current of electricity
- faster the crank turns, the more electricity is generated
- You have just purchased your whizbang new age healing device. This device generates designer ions that immediately reduce your level of stress. You really know nothing about this device other than a label on it which says "Plug me in - I require 5 amps of current". Over the course of 24 hours, how many total KWHs of energy has this device used. If you pay 10 cents per KWH, what is your monthly energy bill for this device?
- determine Wattage: 5 x 120 = 600 Watts
- 600 Watts x 24 hours is 14.4 KWH
- 10 centers per KWH = $1.44 per day x 30 = about 45$ per month
- Describe the basic operation of a Photovolatic (PV) cell and what limites
its overall operating efficiency.
- photons have sufficient energy to move electrons from the valence band
to the conductor band in some material
- once in the conductor band the material is now a semi-conductor
- silicon is the material of choice
- as the material heats up collisions between the free charge and the silicon
nuclei in the lattice increase and so the internal resistance of the material
increases and its ability to carry a current decreases
- Explain why hydroelectric power historically delivered the lowest price of
electricity to the consumer compared to any other technology.
- low operational and mainteance costs
- no fuel needed
- most of the capital cost was historically borne by the government which
then licenses the facility for electricity delivery
- Explain why wind produced electricity is projected to have the lowest levelized cost of any renewable energy technology.
Need to discuss
- capital costs for wind are moderate
- fixed costs are very low
- variable costs are really non-existant
- MW footprint on the land is increasing: scaleable technology!
15 Point Questions
- Discuss the good points as well as some shortcomings of the Energy Independence
and Security Act of 2007.
Good points:
- well at least its something
- biofuel yield goal is reaonsable
- general principlesaer okay
Shortcomings:
- too little; too late; not fast enough
- incand bulb target should be now; not 2020
- ramp up of average fuel economy is way too slow
- reduced carbon footprints of buildings is physically unreasonable
- Explain the parallel between the "energy dilemma" in the 1930s and
our current situation.
- running out of fossil energy now; back then wanted a subsititute for
dirty coal
- we need large scale renewable energy projects; back then it was hydro
- we need improved infrastructure
- we need government initiated large scale wind and solar now that will
create jobs/opportunity in a similar way that the hydro and other public
works projects (e.g. roads, bridges, etc) did in the
1930s.
- Your best friend's eccentric Uncle insists that there are 60,000
Megawatts of harnassable wind power available on the Oregon Coast if you
simply placed one wind turbine for every 5 miles of Oregon coastline. Show
whether or not this claim is credible.
Essential Elements:
- Coastline is 400-500 miles long
- 80 - 100 turbines
- max Tubine capacity is about 5 MW
so at most this is 500 MW (if wind blows all the time) nowhere near 60,000 !!!
- Explain why tranmission lines must operate at
fairly high voltage and what infrastructure is used to step down those voltages.
Need to discuss
- Ohms Law: V = IR
- Power = VI I2R
- Power losses through heat dissipitation therefore scale as current
squared. At constant Power if one increases V one lowers I and correspondly I2 lowers considerably.
- a network of substations ratchets the high voltage down in stages
- transformers using variable numbers of coils are the agent which acts
to step down the voltage
20 Point Questions
- Energy History of Washington State:
Five phases
- Coal (1870-1915) - transport to san francisco via steamers; transport to
steamers via human labor, trams, etc.
- Slow growth of hydro: 1900-1930; starts with Mossyrock dam and 8 dams
are built during this period for total output of about 1000 MW
- Federally initiated growth of hydro (1935-1975) ramp up to 25,000 MW
via large dams on Columbia and Snak
- 1970 - 1985: Failed attempt to build 5 nuclear power plants
- 1970 - now: Renewal of coal via the Centralia Coal Power plant; large
source of pollution in the PNW
- Describe how a solar concentrator system works and what some of its limitations might be?
Need to discuss
- how light is concentrated (e.g. mirrors, lens)
- what you put at focal point (solar sterling engine, heating oil, or even PV cells)
- if heating oil (parabolic trough) it mixes with water to produce steam so that's how the electricity gets out
- for solar thermal, container of molten salts stays heated, that mixes with water to make steam
Limitations:
- requires large land use
- low individual unit capacity
- heat damage to components may limit lifetime
- restricted to very sunny areas as well as direct sunlight in some cases