Download Ch.11 #1 - Academic Program Pages

Science Seminar
in
Energy Systems & Climate Change
Winter Week 1 – Thus. 12 Jan. 2012
The Evergreen St. College
Dr. E.J. Zita
[email protected]
Lab II Rm 2272
http://academic.evergreen.edu/curricular/energy/1112
What’s up today? Check the web!
What’s up next week?
Bookmark our SciSem homepage
Check details and updates on Moodle DAILY or WEEKLY
Science Seminar’s Moodle page
Let’s browse
Moodle
pageMoodle together
before the workshop…
Goals for today and tomorrow
TODAY: * Get onto Moodle
* Do the Intros & Teams Workshop
* Read Finkel, Sandoz, Olson
* Discuss Essays and Responses
TONIGHT and future: * upload your face to Moodle
* Read Sagan’s Baloney Detector article
* Use it with every reading (in and outside of Seminar)
* Integrate it into your essays (starting in 2 weekends)
Looking ahead
• Finish Big Coal this weekend
• start Cradle to Cradle
• Look at essays & responses on Energy Systems from
last quarter
• Do you know how to get on ES&CC Moodle site?
• Teams meet on Monday, post your PIQs
• Remember our new Seminar room Tuesday
• Did you print out your schedule? Check Moodle.
Break after workshop
3:00 Energy Systems on Sun & Electricity
Energy Systems & Climate Change
Sun & Electricity
Winter Week 1 – Thus. 12 Jan. 2012
The Evergreen St. College
Dr. E.J. Zita
[email protected]
Lab II Rm 2272
http://academic.evergreen.edu/curricular/energy/1112
Questions? Announcements? Logistics
• New Tuesday Seminar room: D 2109
• SignupSheets:
– Wolfson Sections
– Brief Reports
– Tuesday facilitators
• Announcements?
– Next Thursday? Food Summit Followup
– April: Green homes tour
Print out your syllabus / schedule
Solar Motion Demonstrators
Testing your hypotheses:
what key points and surprises did you find?
Sunrise is usually NE or SE, not due east
Sunrise and sunset are due E and W only at Equinox
(and on those dates, day and night are equally long at every latitude)
The north side of a house in Olympia can get sunshine in the morning
and evening all summer.
The Sun is never directly overhead in Olympia – only in the tropics,
and only one or two days a year.
The path of the Sun depends on your latitude.
The rising/setting locations depend on the time of year.
Day length and temperature change more at the poles.
You can find the length of the day with your model. More?
Q&A
Q: How does path of the Sun depend on your longitude?
A: It doesn’t – longitude simply fixes the timing of sunrise.
Q. Would patterns be reversed in the S. hemisphere? Yes.
Q: What are the different poles on Earth?
A: Earth’s spin axis points at the North Star (for a few centuries.)
The magnetic axis is offset 11°, and wanders randomly.
Q: What would the seasons be like if Earth’s rotational (spin) tilt
from its orbital plane was different than 23.5°?
A: More tilt → greater seasonal differences
Q: How is the brightness of sunlight affected by its incidence angle?
A: Steeper angle → dimmer sunlight.
Northern summer: intense sunlight
in N. America
Summer vs winter
Southern summer: intense sunlight
in the S. America
Rotation (spin) vs Orbit Axes
National Weather Service – online school for Global Weather
http://www.srh.noaa.gov/jetstream/global/global_intro.htm
Rotation vs Magnetic Axes
Boston University: Short course on Earth’s Magnetic Field
http://www.bu.edu/cism/cismdx/ref/Labs/2005_AFWA_ShortCourse/Lab03/refs/EarthMagneticField.pd
f
More questions & insights
about the motion of the Earth
and the variable Solar intensity?
There are long-termer effects, including
• sunspot cycles (decadal),
• Milankovitch cycles (26,000-100,000 yrs), and the
• slowly increasing luminosity of the Sun (billions of years)
Dependence of solar intensity on latitude
affects power installations
More on solar power tomorrow…
Let’s return to electricity for now
Wolfson Ch.11: Energy carriers
Q: How do the power losses from AC and DC lines
compare?
(Motivated by Solar Grand Plan
reading and need for new supergrid…)
Q: How do the power losses from
AC and DC lines compare?
Approach: Ploss = I2 R = (Psource/V)2 R (p.297), and
the average voltage amplitude is a bit lower for AC:
VAC 
VDC
2
Q: What’s another way to reduce
transmission losses?
Recall that Ploss = I2 R = (Psource/V)2 R
Right – reduce the current I by reducing the resistance, R.
The resistance is a property of the wires. How can we reduce R?
Ch.11 #1 For a given length of wire, resistance is inversely
proportional to the wire’s cross-sectional area. A utility is replacing a
115-kV transmission line with one using wire whose diameter is half
that of the line it’s replacing. At what voltage must the new line
operate if transmission losses are to stay the same?
Is this the right approach?
Will this increase or decrease the resistance R?
Resistance depends on the material
(r) and the dimensions of the wire
Ch.11 #1 For a given length of wire, resistance is inversely proportional to
the wire’s cross-sectional area. A utility is replacing a 115-kV transmission
line with one using wire whose diameter is half that of the line it’s
replacing. At what voltage must the new line operate if transmission losses
are to stay the same?
Will the voltage need to increase or
decrease to keep the line losses constant?
2
Ploss
 Psource 

 R
 V 
Ch.11 #1 For a given length of wire, resistance is inversely proportional to
the wire’s cross-sectional area. A utility is replacing a 115-kV transmission
line with one using wire whose diameter is half that of the line it’s
replacing. At what voltage must the new line operate if transmission losses
are to stay the same?
Ch.11 #1 For a given length of wire, resistance is inversely proportional to
the wire’s cross-sectional area. A utility is replacing a 115-kV transmission
line with one using wire whose diameter is half that of the line it’s
replacing. At what voltage must the new line operate if transmission losses
are to stay the same?
Ch.11 #5. In Example 11.2, find the voltage between the two ends of either wire—
that is, the voltage between power plant and city across either wire, not the voltage
between the two wires at the generator output. Answer for both choices of
transmission voltage.
Ch.11 #5. In Example 11.2, find the voltage between the two ends of either wire—
that is, the voltage between power plant and city across either wire, not the voltage
between the two wires at the generator output. Answer for both choices of
transmission voltage.
Looking ahead
• Let’s do Ch.11 #1 & 5 for HW next week.
• Friday: Wolfson Ch.9 Solar
– choose your sections on SignupSheets
– Brief Reports
• Weekend: start HW, read Big Coal (no essays yet)
• Tuesday:
– 1:00 Research updates & teams
– 3:00 Seminar: finish Big Coal
• Thursday: Food Summit followup (BulletinBoard)