Sample Exam
(from summer 2001)
1. (10 points) Cite at least five fundamentally different types of energy and give at least ten different examples of how energy can be interconverted from one to another.
2. (10 points) Compare and contrast solar energy with one other type of renewable energy in terms of relative advantages and disadvantages.
3. (10 points) Distinguish between energy and power and give examples of each, including specific units of measurement that might be used for each.
Draw an approximate power curve for a solar cell, using voltage and current as the axes. Indicate where the optimum power would be obtained.
4. (10 points) Imagine a space station with a solar array measuring 10 meters by 10 meters.
In full sunlight, how much solar energy is impinging on the array?
If it can be converted to electricity at 20% efficiency, how much electric power is generated?
After this electricity is used, what becomes of the energy? Give at least two examples, for example, if the electricity is used for lighting or for running a scientific instrument.
On earth, a commercial solar array of the same size won’t do as well in generating electricity. Give at least two reasons why not.
5. (10 points) Trace all the types of energy involved in the experiment that used solar cells to run small fans.
Design an experiment that could do the exact reverse process in which wind energy turns on a light.
6. (20 points) Answer all the questions in any TWO of the following four sections, but DO NOT select the section that was covered by your group.
a) Basic Science
Describe the difference between a metal, a semiconductor, and an insulator, both in terms of their measurable properties, their physical appearance, and their basic structure at the atomic level. Why does the structure lead to the characteristic properties?
Describe the difference between n-type and p-type silicon. Why are both needed for a solar cell?
6. b) Implementation
What are the basic components of a simple solar cooker, and how does it work?
What are the relative advantages and disadvantages of having a solar system with or without a grid-tie? With or without a battery system?
6. c) Politics/Economics
Describe rural electrification.
Indicate a country that has a strong alternate energy program and describe how this commitment is manifested in government policies.
What is the state of Oregon's policy on solar rights?
6. d) Education
Describe specific examples of how solar energy activities can be worked into middle and high school classes in earth science, physical science, biology, chemistry, and physics.
What are the strategic benefits of implementing small units rather than a revised curriculum?
7. (10 points) The diagram below indicates possible orientations of the solar panels that we will install on the patio. Assume we can arrange to have the panels facing any direction (i.e., any degree of North/South or East/West). Also assume that we may have the panels flat (horizontal = 0°) or tilted at an angle of either 30°, 60°, or 90° (vertical).
One possible plan for moving the panels during the day is diagrammed. The direction on the compass is the direction the panels would be facing, and the tilt angles are changed at the dotted lines.
What parts of the diagram correspond to morning, noon, and afternoon?
Why are there different tilt angles at different times of the day?
Is this plan for a summer or winter day? How can you tell?
What aspects would be different in the opposite season?
8. (10 points) Give a personal view of what the future energy usage may be (or should be) in the United States in terms of renewable and nonrenewable energy resources.
9. (10 points) Think up and answer any question you wish had been asked on this exam.
Like Olympic sports, there’s a difficulty scale and a performance scale that combine for the total score.
Potentially Useful Information
1. Units of Light Energy
The Solar Constant
energy arriving from the sun just outside the earth's atmosphere
1.94 cal/cm2 min
19.4 kcal/m2 min
81.2 kJ/m2 min // 1 cal = 4.186 J
1.35 kJ/m2 sec
1.35 kW/m2 // 1 watt = 1 J/sec // 1 watt = 1 volt x 1 amp
1.42 BTU/m2 sec // 1 BTU = 1.05 kJ
32.5 kWh/m2 day
1.1 x 105 BTU/m2 day
area conversions: 1 m2 = 10.76 ft2
1 acre = 4047 m2 = 43,560 ft2
2. Atmospheric Attenuation of Intensity
caused by absorptions and scattering
AM units (one air mass unit = one atmosphere thickness penetrated perpendicularly)
AM 0 outside atmosphere
(Solar Constant = 1.35 kW/m2)
AM 1 at earth's surface, sun directly overhead
(Solar Constant reduced to about 1.0 kW/m2 = 100 mW/cm2 )
AM 2 at earth's surface, sun at 30o angle
(Solar Constant reduced to about 0.75 kW/m2)
3. Annualized Worldwide Averages
there are major differences in solar intensity caused by:
daily cycle (day and night)
geographic location (solar angle)
seasonal cycle (earth’s tilt)
weather, cloud cover
global average -- worldwide solar radiation averaged over a full year:
0.2 kW/m2 (about 15% of the Solar Constant)
