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I traditionally take Physics 8 to the cave as a lab. I also invite Physics 6. It’s fun!
I’ll pay for it!
Last tour of the day starts at 4:00. Tentatively scheduled for 4:00 Friday, April 23. A typical driver can get to the park from Physics in 35 minutes, if traffic is light. Allow time for buying tickets!
Who wants to go to the cave? Want to bring a sibling/friend/spouse?
April 19Alternative
Energy
April 21Global Warming
April 26Student Talks
April 28Student Talks
May 3Student Talks
May 5Student Talks
Physics 6 Schedule
How many folk singers does it take to change a light bulb?
answer after four slides
Your Talks
April 26 (4 students)Darryl ColemanFrank Keehn & David SaundersCourtney Pitts
The class period is 75 minutes (4:00-5:15). You are allotted 10 minutes if presenting alone, 15 minutes if two are presenting, 20 minutes if three are presenting. If talks end early, I will lecture.
April 28 (10 Students)Kelsey HansenLisa HasslerAndrew LottAlexandra McCormickMelony MeierSara MitchellAlly NissenElizabeth RusinkoSuzanne SimpsonChristina Wilson
Your Talks
The class period is 75 minutes (4:00-5:15). You are allotted 10 minutes if presenting alone, 15 minutes if two are presenting, 20 minutes if three are presenting. If talks end early, I will lecture.
May 3 (5 students)Sarah GrantAmanda McBeeFareedah WashingtonDanielle WarcholDebra Wielms
May 5 (5 students)Jazmine BellD Naya MimsDrew SkylesJosh Smith
Grading Your Talks
Tentative grading sheet:
environment-related topic (0-3)scientific evidence presented (0-5)effort by presenter to evaluate evidence (0-4)talk organized and flowed logically (0-5)evidence of thought on part of presenter (0-5)good effort and enthusiasm (0-3)
total (0-25)
Thursday is Earth Day
Activities at Havener Center, 11 am – 3 pm.
Write down on a piece of paper and hand in at break... what do you think of when you hear the term “solar energy?” Just the first example that comes to mind, please!
How many folk singers does it take to change a light bulb?Two: one to change the bulb, and one to write a song about how good the old light bulb was.
E=mc2
We saw earlier that matter is the “stuff” the universe is made of.
Einstein says “No, the ‘stuff’ of the universe is mass-energy.”Mass and energy are two different manifestations of one phenomenon.
Energy is not conserved. Mass-energy is conserved.
Energy content of one gram of mass:E=(1x10-3 kg)(3x108 m/s)2=9x1013 joules
E=90,000,000,000,000 joules
Enough energy to last you several thousand years!
Nuclear Energy
No time this semester!
The Sun
“Every day, the sun radiates (sends out) an enormous amount of energy – in fact, it radiates more energy in one second than the world has used since time began.” (Sorry, I closed the web page before I copied the link.)Optimistic, but useless trivia. I’ll explain.
This is more useful:
“The fraction of the energy from the sun that reaches the earth in just one day is enough to cover the energy use of the world in a whole year.”
“However, not all the energy of the sun that reaches the earth can be used effectively.”
Alternative Energy Sources
Forces Do Work
Strong
Weak
Electromagnetic
Gravitational
Most of the energy we use—that I can think of—is “nuclear” in origin.
“Nuclear”
E=mc2 gravity
solar “nuclear”
geothermal
fission
fission
geothermal
solar thermalsolar electricity
wind
biomass conversion
fossil
hydroelectric
ocean thermal
tidal
Renewable: e.g., we use energy from the sun today, and it gives us more tomorrow.
“Solar” energy comes from nuclear reactions in the sun!
wind
solar thermalsolar electricity
biomass conversionhydroelectric
ocean thermal
tidal
Remember this figure?
Renewable: means we use energy from the sun today, and it gives us more tomorrow. The “fuels” for the other energy sources are finite! (So is the sun’s fuel, but not on the scale of human lifetimes.)
Past and projected world energy consumption (DOE):
Here today, gone tomorrow.
Here today, here tomorrow.
Today’s lecture is not about energy we’re “using up.”
It’s about energy that is replenished by the sun.
Let’s talk about some sources of that renewable energy.I’ll bet when many people hear “what do you think of when you hear the term ‘solar energy?’ ” they think of something like this…
If so, you were thinking of “solar photovoltaic energy.”
According to the DOE: “Photovoltaic devices use semiconducting materials to convert sunlight directly into electricity.”
“Nevertheless, almost all U.S. regions have useful solar resources that can be accessed.”
“Solar radiation, which is nearly constant outside the Earth's atmosphere, varies with changing atmospheric conditions (clouds and dust) and the changing position of the Earth relative to the sun.”
Solar Photovoltaic Energy
Solar photovoltaic energy involves direct conversion of sunlight into electricity.
When a photon of light strikes a conductor, it may provide enough energy to “liberate” an electron from an atom.If the conductor is a metal, the extra “free” electron will rapidly be “consumed” by an atom has lost an electron.If the material is a semiconductor, an electron-hole pair may be formed.
From howstuffworks.
If you connect this semiconductor material to an external circuit, it delivers an electric potential, just like a battery.
If you get the feeling I didn’t explain this very thoroughly, I didn’t. You need to study quantum mechanics to understand.“I think that I can safely say that nobody understands quantum mechanics.”—Richard Feynman, Nobel Prize-winning quantum theorist
If you connect this semiconductor material to an external circuit, it delivers an electric potential, just like a battery…
…except as long as the sun shines, the solar cell supplies energy.
The solar cell voltage depends on the solar cell material.
1.1 V (silicon) 1.6 V
About 1.5 volts is “typical.”
You have to maximize the amount of light that reaches layers D and E.
Difficulties to overcome:
The obvious one: you only generate electricity while the sun shines.
You have to find a way to store your energy. Batteries? Passive storage?
Net metering (discussed in a couple of slides) lets you use the nations electrical grid like a giant battery.You put energy into the grid while the sun shines on you, and use somebody else’s energy when the sun shines on them.
The Laursen’s 57 kW residential system.
Difficulties to overcome:Silicon (common solar cell material) “needs” 1.1 eV photons.The wavelength of such a photon is about 1100 nanometers.
This is an approximation to the actual solar spectrum.
Lower-energy photons can’t deposit their energy in silicon.Higher-energy photons “waste” all of their energy except for the 1.1 eV.
Efficiency also decreases with temperature (and these things are going to get hot).
Efficiency of a solar cell made of single-crystal silicon: about 24 % (laboratory) and 14 to 17 % (production). (expensive)
Efficiency of a solar cell made of polycrystalline silicon: about 18 % (laboratory) and 13 to 17 % (production). (cheaper)
Efficiency of a solar cell made of amorphous silicon: about 13 % (laboratory) and 5 to 7 % (production). (cheapest)
From http://www.solarserver.de/lexikon/solarzelle-e.html:
Solution: “stack” solar cells made of different materials.
Silicon, gallium, arsenic, phosphorus, indium, aluminum—do any of these elements make you nervous?
Solution: find a full-spectrum solar photovoltaic material.http://www.lbl.gov/msd/PIs/Walukiewicz/02/02_8_Full_Solar_Spectrum.html http://www.lbl.gov/Science-Articles/Archive/MSD-full-spectrum-solar-cell.html
Net Metering
“In 34 states, consumers can install small, grid-connected renewable energy systems to reduce their electricity bills using a protocol called net metering.” (http://www.ases.org/)You plug your energy system into the power grid and start charging the electric companies for your power.
Remember, I told you about this when we were talking about perpetual motion machines? It’s not quite as good as selling power, but it still is worth money.
Actually, your electric bill is reduced by the amount of energy you provided—or maybe some fraction thereof.
“Missouri House Bill 1402, passed in 2002, provides for the interconnection of wind, biomass, fuel cell and photovoltaic systems up to 100 kW.”
From http://www.dsireusa.org/:
“Although the bill refers to this arrangement as ‘net metering,’ this is not actually the case. Rather, it is net billing: Any generation that that is fed back to the grid is credited on the next bill at the avoided cost rate, not the retail rate as in true net metering.”
“Net excess generation at the end of the month is also credited at the avoided cost rate on the following month’s bill. A utility does not have to enroll qualifying customer-generators beyond 10 MW or 0.1% of the utility's peak load for the previous year.”
Solar Photovoltaic Power Plants
See this web page for a list of the 50 largest, which range in output from 14 MW to 60 MW (in 2006, the 50 largest ranged from 0.5 MW to 4 MW; in 2008, the 50 largest ranged from 4 MW to 23 MW).
The top 15: all in Spain, Germany, or Portugal.
For comparison, a “typical” coal-fired power plant with an output of 1000 MW produces 17 times the power of the largest solar photovoltaic power plant.
Solar towers.
Pilot plant in Manzanares, Spain, operated for seven years between 1982 and 1989, and consistently generated 50kW.
A 200 MW power plant, enough to power 200,000 homes, with no fuel required and no emissions.
Planned for Australia.
Hot air flows up through the tower, past turbines, generating electricity. Animation here.
Biomass Conversion
From 2006 lecture. My opinions (briefly stated) on this:The idea is to convert plants into some kind of fuel (e.g. ethanol).
This is an example of harvesting solar energy.It will require energy to grow, harvest, and process the biomass.The laws of thermodynamics say you will never get as much energy out as you put in (but some of the energy input comes from the sun).
If you can minimize the fraction of energy expended by humans, it might become worthwhile. 2006: it takes 1.29 gallons of fossil fuel to make 1 gallon of ethanol from corn. Plus there are problems associated with transporting ethanol and burning it in internal combustion engines. Google “biomass conversion.”There will be emission questions related to the processing of biomass.
I see this as a method of producing alternative transportation fuels…
…which could save our economy…
…but I have not seen the data which tells me it will be a net source of energy.I am touching this topic only briefly because of lack of time... but I never promised that I would be unbiased.
Why did the gardener plant a light bulb?
Another biofuel option: switchgrass.
Native to the US, grows almost everywhere, requires little in the way of pesticides, good for the soil (adds organic matter), parts not used to produce ethanol can be burned in special stoves or to produce electricity.Not a net producer of CO2 (takes it up when growing, releases it when burned).Takes 1.5 gallons of fossil fuel to make a gallon of ethanol from switchgrass…or the ethanol from switchgrass produces 5 times the energy you put in…not sure who to believe here!Infrastructure to convert switchgrass to ethanol apparently does not exist yet.
Why did the gardener plant a light bulb?To grow a power plant.
Soybeans, sunflowers, wood cellulose are other options for producing ethanol.
There are a lot of numbers thrown around for the amount of energy that can be produced from “crops” such as these. Not easy to find a brief, nontechnical summary.
Hey, I’ve got an idea... if the oil we are taking out of the ground came from algae and similar organisms of long ago, why can’t we harvest algae of today for their oil?
Edited from http://www.oilgae.com/algae/oil/yield/yield.html The table below presents oil yields from various oilseeds and algae. There are significant variations in yields even within an individual oilseed depending on where it is grown, the specific variety/grade of the plant etc. Similarly, for algae there are significant variations between oil yields from different strains of algae. The data presented below are indicative in nature.
Crop Oil in Liters per hectareCastor 1413Sunflower 952Safflower 779Palm 5950Soy 446Coconut 2689Algae 100000
There is a major research project under way in our Mining and Nuclear Engineering Department on the use of algae to produce biodiesel.
Huh, Mining Engineering???
Missouri has lots of unused mines which could be used to grow racks and racks of algae for harvesting and converting to oil.
You need to provide the algae with light, so it requires electricity (if you want to grow algae underground), but the net energy gain could be huge.
Some “propaganda.” Positive article here, but one bothersome negative reader comment. The USDOE funded a 20-year program to study biodiesel from algae, but they shut it down in 1996. Final report is here.
Hydroelectric and Geothermal Energy
Remember this graph…
Why is hydroelectric energy projected to be flat?
When California had its electricity shortage, why couldn’t the Northwest states come to the rescue?
They were raising their electricity prices because they were experiencing a shortage of electricity.
Hydroelectricity requires a location where flowing water experiences a large decrease in height over a short distance.
We’ve already dammed most of the good sites. The tree-huggers will fight to prevent dams elsewhere.
How is this solar energy?
For anybody not in my class who happens to be reading these notes:
How you interpret the term “tree-huggers” depends on your own personal baggage, doesn’t it?
Don’t automatically assume that I carry the same baggage!
—me
There are a few places on earth where thermal energy from below the ground escapes in large enough quantities to make it available for large-scale use.
What do you consider appropriate uses for these locations?
Wind Energy
Why do I classify wind energy as a subcategory of solar energy?
Five of the sixteen windmills at the Havøygavlen windmill park in Norway.
This windmill park generates about 40 MW of power (1/25 of a 1000 MW power plant).
The creator of the web site where I borrowed these pictures says:
“The dangerous wind power plant is surrounded by fencing, warning signs, and locked gates. Deadly high voltage electric lines run under foot and over head. Windmills can be seen lining the hills in the distance.”
“Clearly, the natural shape of the hills has been sacrificed for terraced foundations for the decrepit windmills. No one who sees this can claim they are better for the land, or much different in appearance, than oil derricks, which would be fewer and farther apart, and produce more energy.”Something else to think about: “Local wildlife researchers have received $2 million to find ways to reduce the number of birds killed each year by wind turbines.” (Santa Cruz Sentinel)
Here come some of my opinions again:
If there is coal or oil in the earth somewhere, humans will eventually go get it. Coal and oil are too valuable to leave in the earth.
If there is wind to be farmed, humans will eventually farm it. It’s too valuable not to farm.
I would rather not consider the scenarios under which coal is not mined and wind is not farmed.
Remember, my personal values may have something to say about coal mining and wind farming, but they are not relevant to the present discussion.
http://rredc.nrel.gov/wind/pubs/atlas/maps/chap2/2-01m.html
I can picture a giant windmill farm stretching across the Great Plains from Texas to the Canadian Border.
Borrowing heavily from the wonderful (although slightly old) Physics 162 course material at the University of Oregon:
Power that can be extracted from wind is proportional to wind speed cubed.
KE proportional to V2.
Amount of air proportional to V.
Power proportional to amount of air times KE, or V3.27 more times energy in 60 mph wind than in 20 mph wind!
Windmill efficiency is not 100%. Large structures impede wind flow (bad). High wind speed actually lowers mechanical efficiency.
To generate 10,000 KWH annual from a 20 mph wind that blows 10% of the time:
windmill area = 10,000 KWH/220 KHW per sq. meter = 45 sq meters
this is a circular disk of diameter about 8 meters
this is not completely out of the question for some homes
even a small windmill (2 meters) can be effective: 20 mph 10% of the time --> 2500 KWH
annually 40 mph 10% of the time --> 20000 KWH
annually 20 mph 50% of the time --> 12500 KWH
annually
4 small windmills at 20 mph 10% of the time --> 10000 KWH annually—would keep you powered up!
The hypothetical Great Plains Energy Project:
One turbine tower per square mile stretched out from Texas to Canada.
300,000 total towers. Each tower 850 feet high. (Important so as to get above friction induced by ground based obstacles.)
Each tower has 20 generators and is powered by a two blade propellor of diameter 50 feet.
Capacity of single tower is 500 KW capacity so total capacity is 150,000 Mega Watts (1/2 the US consumption--1998). Note, we already have 600,000 oil wells in the US and no one seems to mind.
Ocean Thermal Energy Conversion
Underwater windmills!
Out of time for today!
Hydrogen Power
Hydrogen…
“It's the most abundant element in the universe. It promises limitless supplies of pollution-free energy.”
As long as you don’t worry about the laws of thermodynamics.
H2 is a good way to transport energy from one place to another.
But the hydrogen in the “limitless supplies” in the ocean is in the form of H2O.
How are you going to get the H2 out of the H2O?
It takes energy. More than you get back when you burn the H2. Answer: nuclear power plants.
Hydrogen is not a source of “new” energy. It is a potentially good way to transport energy that is abundant in one location to another location where energy is less abundant.
http://www.enviromission.com.au/index1.htm solar tower
http://zebu.uoregon.edu/1998/phys162.html good links
http://carto.eu.org/article2489.html graphs
http://www.worldenergy.org/wec-geis/edc/
http://www.ases.org/ American Solar Energy Society
