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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?
Physics 6 Schedule How many folk singers does it take to change a light bulb? answer after four slides
Your Talks April 28 (10 Students) Kelsey Hansen Lisa Hassler Andrew Lott Alexandra McCormick Melony Meier Sara Mitchell Ally Nissen Elizabeth Rusinko Suzanne Simpson Christina Wilson April 26 (4 students) Darryl Coleman Frank Keehn & David Saunders Courtney 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.
Your Talks May 5 (5 students) Jazmine Bell D Naya Mims Drew Skyles Josh Smith May 3 (5 students) Sarah Grant Amanda McBee Fareedah Washington Danielle Warchol Debra Wielms 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.
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 “Nuclear” Weak Electromagnetic Gravitational Most of the energy we use—that I can think of—is “nuclear” in origin.
E=mc2 gravity solar “nuclear” geothermal geothermal wind wind fission tidal tidal fossil fission solar thermal solar thermal “Solar” energy comes from nuclear reactions in the sun! solar electricity solar electricity biomass conversion biomass conversion Renewable: e.g., we use energy from the sun today, and it gives us more tomorrow. hydroelectric hydroelectric ocean thermal ocean thermal
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…
Solar Photovoltaic Energy If so, you were thinking of “solar photovoltaic energy.” According to the DOE: “Photovoltaic devices use semiconducting materials to convert sunlight directly into electricity.” “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.” “Nevertheless, almost all U.S. regions have useful solar resources that can be accessed.”
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.”
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: This is an approximation to the actual solar spectrum. Silicon (common solar cell material) “needs” 1.1 eV photons. The wavelength of such a photon is about 1100 nanometers. 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).
From http://www.solarserver.de/lexikon/solarzelle-e.html: 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)
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. Actually, your electric bill is reduced by the amount of energy you provided—or maybe some fraction thereof. 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.
From http://www.dsireusa.org/: “Missouri House Bill 1402, passed in 2002, provides for the interconnection of wind, biomass, fuel cell and photovoltaic systems up to 100 kW.” “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 Thermal Energy Heat for your home:
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 hectare Castor 1413 Sunflower 952 Safflower 779 Palm 5950 Soy 446 Coconut 2689 Algae 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. How is this solar energy? We’ve already dammed most of the good sites. The tree-huggers will fight to prevent dams elsewhere.
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)