12.mt midterm review of renewable energy frank r. leslie, b. s. e. e., m. s. space technology...
TRANSCRIPT
12.MT Midterm Review of Renewable Energy
Frank R. Leslie, B. S. E. E., M. S. Space Technology
2/23/2010, Rev. 2.0
fleslie @fit.edu; (321) 674-7377
www.fit.edu/~fleslie
Some of the more important points
12 Overview of the Review
These slides are intended to provide the most important aspects of each of the sessions of the course
Equations should be provided at the end, but you are responsible for knowing how to find them and how to use them
Some sections may not be fully complete at this time when other lecturers used transparencies
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12.1 Introduction
The introduction at RE01 has a synopsis of the general content of the whole course and should be studied for the test
Not all sessions are treated equally here, but reflect what I believe to be most important in the renewable energy field and with general energy issues
I have concentrated on the conclusions of each session and may not have completed the one or two pages of the “condensed” version from the original files
Look at http://my.fit.edu/~fleslie/CourseRE/ClassPres/classpresentations.htm
to select those files
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12.2a Current Events
“Light sweet” crude oil futures changed from $26/42-gallon barrel (4/26/2003) to about $34/bbl (2/19/2009)OPEC production cut-backs affect the global marketChina and India increasing demand; price up
Key issues affecting the economy are the prices of gasoline and natural gasGasoline affects the price of goods delivered by
truck, and diesel oil for trains and ships tends to parallel this price, also affecting farming and food
Natural gas is used for home heating and for the large utility plants built for natural gas or being converted to use it (lower pollution)
Hydrogen made from NG will increase the price
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12.2b Pollution
Air and water pollution continue to drive the costs of energy production
There are other costs outside of the cost to consumers known as “externalities”Military defense of oil sources (Iraq, etc.)Public health costs of respiratory and other
diseases caused by pollutantsRoad traffic caused by oil truck transportation, and
resultant exhaust fumes, which cause more ailments
Renewable energies usually cause less pollution than conventional fuelsMaking the converter also uses energy and may
cause some transient pollution090219
12.2b Conclusion: Pollution
Combustion energy sources emit pollutants NOx, SOx, VOCs, etc. plus CO2, a green house gas (GHG)
Nuclear plants might rarely emit accidental releases of radioactivity, but safe designs reduce this chance
Wind and solar energy doesn’t pollute, but there may have been pollution from the making of the equipment
Laws effect and enforce plant changes to reduce pollution; they remove economic incentives to pollute
Emissions credit trading may help reduce pollution since there is an economic incentive to clean up
During the Iraq War, Hussein did not have time to set oil wells on fire as in the Persian Gulf War of 1991
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12.3 Climate Change
Climate change is controversial, as many or most scientists believe that increased combustion of fuels by civilization and industry releases green house gases (like CO2) that change the earth’s temperature balance
The level of atmospheric CO2 and population have both grown over the last 150 years; is one the cause of the other?A classic statistics example is that the sales of
liquor and the number of Baptist ministers (who presumably claim to eschew alcohol) are correlated
They are correlated to the increasing population, not necessarily to each other! Be wary!
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12.3 Climate Change
An argument is made that most of the World’s scientists agree that global warming is caused by mankind
In somewhat earlier days, “most” scientists agreed that the earth was flat, and only “extremists” thought otherwise! Koreshans believed that we lived in the middle and the stars were in the center
Science is not democracy, and “most” doesn’t make right! Public opinion doesn’t determine science
About 1950, there was concern about global coolingOn the other hand, now glaciers are melting and
receding over a period of years indicating a warmer weather change
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12.4 Fuel: Hydrogen
There is much talk of the “Hydrogen Economy”, where hydrogen (an energy carrier) will replace fossil fuelsSee Amory Lovins, Rocky Mountain Institute for early
espousal of the concept; Joe Romm for the oppositeThere are no hydrogen wells, so hydrogen isn’t a fuel
in the usual sense, but an energy carrierTo get hydrogen, electrolysis of water, pyrolysis of
fossil fuels, or bacterial action is requiredNuclear and fossil fuel base-load power plants
produce energy to support the lowest daily load or moreThis cycle peaks in mid-afternoon and/or
dinnertime and is lowest at 3 a.m.If the electrolysis is done off-peak, is the resultant
hydrogen clean? Depends upon energy source
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12.4 Fuel
Fossil fuels are of limited extent: known, suspected, and possible
Hubbert predicted the depletion of oil in the US about 1970 (it peaked in 1974)
World oil production may peak about 2005 to 2020
After the peak, lots of money chasing a diminished supply increases the price (has the price increased?)
When fossil fuel prices exceed the cost of renewable energy, a shift will occur, slowly at first, then accelerating
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12.4.3 Fuels Conclusion
Fuel usage is determined by cost and convenience
Fuel density is critical for transportation
Cost of fossil fuels and nuclear energy will keep these in predominance for several decades
Renewable energy provides small contributions now, but diversity is critical as transition occurs
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12.5 Conservation and Efficiency
Conservation of energy is the cheapest way to cut energy costs, but there is a tradeoff against the benefits of using the energy
Automatic air conditioning thermostats can manage temperatures without human intervention, simplifying life while saving energy
Motion-sensor lights only use electricity when someone is moving in the field of view
The time to pay off the investment is zero, and savings begin immediately
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12.5 Conservation and Efficiency
Efficiency means getting the desired result for less money
Lighting must be bright enough for the task and not present when not neededBright local lighting is better than bright
general lighting since less power is neededCompact fluorescent lights (CFLs) produce
good light intensity with about 1/4 the powerTimers or motion detectors can turn off lights
when they are not neededBetter building insulation conserves heating in
winter and keeps summer heat out
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12.5.3 Cons. & Efficiency Conclusion
Conservation by reducing loads or shortening duration of use will save money, reduce pollution, and extend the time that fossil fuels last
Greater efficiency in generating, transmitting, and using energy will yield the same utility for lower cost
Energy not used reduces the urgency for utility plant construction
Efficient use of fuels will save still more money and prolong their economical use
While conservation and efficiency are valuable practices, they only delay the depletion of fossil fuels
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12.6 Prof. Odum, EROEI, and Emergy
Emergy addresses the amount of energy that is required to make energy conversion systems and to obtain and process the fuel for them
Energy Return on Energy Invested shows worth of an approach or product
This subject is “well-known, but only to a few”
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12.7 Thermal Systems
Steam boiler systems require fuel to heat the water, making steam for turbines that spin generators that produce electricity
Solar parabolic collectors have been developed to heat water into steam or to power Stirling engines
Simple flat plate collectors heat water for household or industrial use
Thermocouple systems generate low-voltage electricity from heat on metals of different types Used in radioactive thermal generators (RTGs)
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12.7.3 Conclusion
Thermal energy conversion remains the predominant use of fuel
Since these fuels are still perceived as cheap, there isn’t much clamor to change to renewables
As the price of conventional fuels increase and renewables decrease, a shift will occur
There must be a long overlapping period of the two technologies to permit development of renewable resources before conventional fuels become difficult to obtain at a reasonable price
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12.8 Coal
The most available and most inexpensive fuel in the US, coal has many pollution issues
The so-called “Clean Coal” program reduces pollution by washing the coal first, controlling burn temperature, and then cleaning the stack gases
Powerful marketing forces and lobbies clamor for maintaining coal predominance in the energy market
Many union jobs depend upon coal production and transport, thus many block-votes drive politicians to retain coal rather than fund the renewable energy area There aren’t many renewable energy unions
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12.8.3 Conclusion: Coal
Coal is the most abundant fuel in the United States and is estimated to last about 100 to 400 years
Coal will last several hundred years longer than oil or NG
Coal will continue to be a primary fuel close to coal mines
Coal is most suited to fixed energy plants; while mobile use requires oil or natural gas
Coal is cheap, and may be chemically processed to yield natural gas or hydrogen, but taking heat and water to do so
Is hydrogen clean (green) if it is processed from coal or coal-generated electricity?
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12.9 Oil and Natural Gas
Oil and the natural gas often found with it are of limited extent
Estimates of the remainder vary greatly since detection of more deposits is somewhat limited
Production in the United States peaked in 1974, resulting in oil imports as demand increased
World production will possibly peak in 2005 to 2010
Natural gas is a relatively clean-burning fuel and is the choice for new power plants
Competition for the diminishing supply will drive prices higher
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12.9 Natural Gas Decline
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12.9.3 Conclusion: Oil & Natural Gas
Oil is energy-dense and easy to transport and use, and thus it works well in vehicles
Many chemicals and materials are made from oil, thus burning it may restrict or prevent a better, higher use
Choices are made from the economics and cost of doing business
The future value of oil in ANWR is difficult to predict, but it will be far more valuable in constant dollars a hundred years from now than it is right now
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12.10 Nuclear Energy
Nuclear energy is not well understood by many; the mysteriousness leads to fear (and loathing)
Nuclear energy has many radioactive concerns in mining, preparation, transportation and disposal
At the end of the fuel cycle, the “spent” fuel must be dealt with to avoid a concentration of plutonium in the fuel that might be misused by terrorists
Yucca Mountain AZ will eventually be a storage site for spent fuel, yet the fuel must be taken there from many locations by rail or truckSome complain that storage must last 250,000
yearsHuman failure remains the largest concernMore outcry is raised about the possibility of nuclear
contamination than about the statistical health problems caused by fossil fuel plants
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12.10 Nuclear Energy
Future hydrogen may be produced by nuclear energy for electrolysis of water; is this what we want?
In many cases, what “we” want is instant gratification and cheap, not-a-care energy
The Age of Terrorism brings a new level of uncertainty to the problem, as the potential of attacks on nuclear plants cause widespread anxiety and outcry
If there were $1 billion of lawsuit payouts per year for plant errors, that much would have to be set aside each year $risk = $consequence * prob(consequence)Money spent to reduce the risk would cut the
amount needed as insurance premiums
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12.11.1 Solar Energy
Available solar energy changes with the seasons, thus collectors may need adjustment to receive maximum energy
There are four important astronomical epochs or transitions:The vernal equinox about Mar. 21 (equal day
and night hours)The summer solstice about Jun. 21 (longest day)The autumnal equinox about Sep. 23 (equal day
and night hours)The winter solstice about Dec. 22 (shortest day)These sometimes drift into an adjacent dateSolstices are extremes of angular sun travel
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12.11.1 Solar Energy
Since the earth axis is tilted 23.45 degrees from the plane of revolution, the Northern Hemisphere is tipped towards the sun in summer, which occurs because the sun’s rays strike more directly than in winter
Since the direction of the sun at solar noon changes throughout the year, a fixed collector works best if aimed parallel to the equatorial plane (latitude angle)The sun is too high in summer; too low in winter
Setting the collector angle to the latitude angle thus allows the sun angle to be equal and opposite at the solstices
To heat water in the winter, an extra tilt to the south of 15 degrees may be added since the cold air around the collector cools the collector in winter
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12.11 Conclusion: Solar Energy
Received solar energy varies widely as evidenced by climate records and vegetation (deserts and rain forests)
This variability affects the economic viability of a system
Solar energy systems are simple, robust, and easy to install
Solar modules are still expensive, approximately $3.50/W for large arrays to $14/W for small modules, depending upon size
Organic process might yield $0.20/W!?!? Installation adds another ~$5 per watt of cost
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12.11.2 Solar Electric
A PV module may produce 30 volts with no load, yet produce maximum power at ~17 volts
If it produces 17 volts and 5 amperes, the power is 17 * 5 = 85 watts (instantaneous power)
If it does this for 10 hours, the energy produced is 85 watts * 10 hours = 850 watt-hours (both the values and the units are multiplied)
If it produces 2040 watt-hours in one day (24 hours), the average power is 2040 watt-hours / 24 hours = 85 watts over that day including nighttime
Clearly (or cloudily), the average power varies with the weather
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12.11.2 Solar Electric: Batteries
Batteries are comprised of primary (nonrechargeable) and secondary (rechargeable) types
Only secondary batteries (groups of cells) are used for renewable energy work
A battery with a 300 ampere-hour capacity based upon 25 hours specified time can deliver 300 ampere-hours/25 hours = 12 amperes current to a load for 25 hours
For 30 hours, 10 A; for 100 hours, 3 A; etc.But these aren’t quite linear relations, and
lower currents yield even more ampere-hoursEngine-cranking currents of ~500 A are for 30
seconds periods
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12.11.2 Conclusion
Solar PV cells tend to lose capacity due to some darkening of the cover glass; use more area than needed to compensate
While PV is expensive at $3.50/W to $14/W, the low installation costs (~$5/W) reduce the overall cost as compared to a diesel generator
Research similar installations to gain understandingEvaluate intended loads closelyUse spreadsheets to change system parameters
readily Isolated remote sites have no alternative utility
power, and some assumptions are warranted
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12.11.3 Solar Thermal
Solar thermal energy for water heating is simply done with uncomplicated materials
To get higher temperatures (>180 degrees F), the sun’s rays must be concentrated on the collector
Parabolic simply-curved surfaces are inexpensive and increase the energy by the ratio of the sunlight interception area to the collector area
Paraboloidal surfaces are more expensive to make but increase the temperatures still further
The SEGS solar thermal plants near Barstow CA use long rows of parabolic reflectors to heat oil, which then heats water to steam and spins a turbine
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12.11.3.3 Conclusion: Solar Thermal
Solar thermal systems are cost effective at low temperatures
Solar water heaters are energy savers, but initial cost dissuades many from using them
Power tower (Solar Two) electricity cost is at $6/W peakNot competitive
Massive power tower yields 10 MWe, while a typical utility plant is 500 Mwe
Power towers aren’t likely to be economically practical
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12.12.1 Wind Energy
Expensive wind turbines require good assessment of the local site winds to determine where to place the turbine
A 10% increase in wind speed can yield a 30% increase in power
Obstructions that interrupt a smooth laminar flow of wind will greatly hamper power production
Long-term wind studies ensure an optimal positioning of a turbine
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12.12.1.1 Wind Energy
Distant forests will have little influence on wind speed while a nearby building will have a great influence
The width and height of a blocking object determines how much effect will occur
A flagpole upwind is cylindrical and narrow, thus the wind stream will reconverge 5 - 10 pole diameters behind the pole to resume smooth, fast flow as before
A rule of thumb is that the wind turbine should be 500 feet from the nearest object and at least 30 feet above it; rules vary
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12.12.1 Conclusion: Wind Resources 1
Wind resources vary greatly with latitude, season, and terrain
Extensive data and wind maps exist for wind prospecting
At the mesoscale level, topographic information is being used to create predictions of wind speed from widely scattered real data
Anemometers can be erected to obtain wind speeds in a likely locale
An alternative is to erect a small wind turbine to sample the energy and to help determine where a large turbine should be placed
Wind resources may be excellent, but there is much more to installing a turbine
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Wind energy is a statistical variable that is usually much more variable than sunshine
We traditionally quantify wind energy in “bins” of various speed ranges
A probability density function (p.d.f.; left) and cumulative distribution function (c.d.f.; right) define these variations and make revealing graphs
12.12.2 Wind Energy 2
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12.12.2.1 Wind Energy 2
The probability of a certain wind speed times the energy of that speed yields the probable energy; add each of these products to get the 100% probable energy
Proportional averaging means multiply the percent of time a value occurs by the value, sum each of these products to get the overall average (all of them =100%)Average = (A + B)/2 = (0.5 * A) + (0.5 * B) = (50%
*A) + (50% * B)So 20% * 10 + 80% * 40 = 2 + 32 = 34
For a wind problem, winds under ~6 mph cause zero output and don’t turn the rotor
The top 30% of the winds likely produce the majority of the energy
http://www.itl.nist.gov/div898/handbook/eda/section3/eda362.htm is a good statistics reference070226
12.12.2 Conclusion: Wind Theory
The theory of wind energy is based upon fluid flow, so it also applies to water turbines; water density is 832 times more
While anemometers provide wind speed and usually direction, data processing converts the data into information
Because of the surface boundary drag layer of the atmosphere, placing the anemometer at a “standard” height of 10 meters above the ground is important
Turbine anemometers are often placed at 150 meters above ground
The erroneous average of the speeds is not the same as the correct average of the speed cubes!
The energy extracted by a turbine is the summation of (each speed cubed times the time that it persisted)
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12.12.3 Wind Turbines
Vertical axis turbines are simple but don’t work very wellThe wind forces reverse on the blades with each
half turn of the rotor and cause mechanical stress failure
Three-bladed horizontal axis turbines have good performance and appear to have the best future chances of success (common style works!)
The turbine power is proportional to the cube of the wind speed, thus a 20 mph wind has eight times the power of a 10 mph wind
This means a wind speed of 20 mph (eight times the power as 10 mph wind) for an hour yields the same energy as a 10 mph wind for eight hours!
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12.12.3.1 Wind Turbines
Large companies investing in renewable energy usually choose wind or solar as offering the best return on investment
Wind power is about one-fifth the solar cost per watt
Florida doesn’t have very high winds (ignoring hurricanes), yet GE Power Systems builds wind turbines near Pensacola, while FPL (formerly known as Florida Power and Light) is the largest owner of utility size wind turbines in the US
Many turbines were developed in Nordic countries
Europe has good ocean winds and strong incentives for renewable energy
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12.12.3.2 Conclusion: Wind Turbine Theory 1
The turbine rotor must be matched to the generator or alternator to maximize the extracted power at lowest cost
Although most turbines won’t rotate until the wind speed reaches 6 mph, there is no significant energy lost below this speed; remember the cube law?
If better placement (siting) can increase the wind speed by just 10%, the power increases by 33%
All parts must be designed to survive high winds, say 140 mph
Large turbines use yaw motors to aim the nacelle into the wind; small turbines steer by tail wind forces
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12.12.4 Wind Turbines 2
The exact site determines the annual power available
Rows of turbines are placed at right angles to the usual “power” wind direction so they don’t block each other
Rows are spaced some eight rotor diameters apart to allow wind speed to increase between rows
Turbines are often remotely controlled from a central operations site
Offshore turbines have free access to the unhindered wind from any direction and yield high energy over a year
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12.12.4.3 Conclusion: Wind Turbine Siting and Installation
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Turbine siting is somewhat of an art, but science is providing tools that speed site selection
Accurate siting strongly determines the economic and energy success of the system
Energy storage is likely to be in batteries for the foreseeable future; more exotic methods are slow in reaching a cost-effective market entry
Since wind energy is the fastest developing energy source, the economic fall of prices will speed its adoption where the wind is powerful
24 Conclusion: Review
This review synopsizes the key points of the Renewable Energy course, ENS4300 to mid-term
Study of this presentation provides a good starting point for mastering the mid-term test, but you will find study of the original presentations also is helpful
Where additional presenters assisted, you may need to study your class notes if no PowerPoint slides were available
Good luck on your exam!
Frank Leslie
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12.1 Some Interesting Facts
Earth’s axial tilt = 23.5 degrees (23.45)Earth-sun distance = 92 M miles = 92,955,820.5 miles = 149,597,892 kmEarth Equatorial Radius = 6378137 m (WGS-77)
Wind Turbine Power, P = ρ/2·A· U3 watts, where ρ (rho) is 1.225 kg/m3, A is area = π r2 m2, r= blade radius in m, U = wind speed in m/s.
“P = 0.5 · ρ · A · Cp · V3 · Ng · Nb where:
P = power in watts (746 watts = 1 hp) (1,000 watts = 1 kilowatt)ρ = air density (about 1.225 kg/m3 at sea level, less higher up)A = rotor swept area, exposed to the wind (m2)Cp = Coefficient of performance (.59 {Betz limit} is the maximum theoretically possible, .35 for a good design) V = wind speed in meters/sec (20 mph = 9 m/s, or 2.24 mph = 1 m/s)Ng = generator efficiency (50% for car alternator, 80% or possibly more for a permanent magnet generator or grid-connected induction generator)Nb = gearbox/bearings efficiency (depends, could be as high as 95% if good)”
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12.2 Some Interesting Facts
Average wind power density, P/m2 = 6.1x10-4 v3 watt/m2, where v is m/s
Locations: Arctic Circle is 66.55º N; Big Blow, Texas is 31º N, 103.73º W; Colon, Panama is 9.7º N, 80º W; Cicely, Alaska is 66.55º N, 145º W; Florida Tech, Melbourne FL, 28.2º N, 80.6º W; Panama City, Panama 8.97º N, 79.53º W; Paris, France is 48.8º N, 2.33º E;
Area of sphere = 4 π r2 Volume of a sphere is 4/3 π r3
P=E*I=E2/R=I2R; E or V=IR Typical computer/monitor power is 150 watts. “Standard” 40 W
fluorescent ceiling lamps were/are being replaced by newer T8, 32 W lamps.
The Link Building power meter (SE corner) indicates a typical weekday power load to be 60 kW, and nights/weekends, it is 35 kW.
A copy machine is on only during office hours (8 to 5) weekdays and usually draws 190 W. When copying, it draws 900 W.
FPL charges $0.08/kWh for electricity (ignore demand charge and billing charge, taxes, etc.)
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12.3 Some Interesting Facts
Melbourne FL, Dec. 24-hour radiation on a horizontal surface is 150 W/m2 (?) and annual direct normal energy is 2.5 to 3.0 kWh/m2. Direct normal often is 1000W/m2
Air density is 1.225 kg/m3;Kinetic energy = 0.5 mv2 joules, where v is in m/s
K.E. also = p / (R·T), where p = pressure, T = Kelvin, and R = gas constant = 287.05 Joule/kg/K for air
Snell’s Law: Angle of Incidence = Angle of reflectionAltitude of the sun = 90º -latitude + sun declination;
azimuth is the horizontal angle clockwise from north (declination is the varying solar latitude+/-23.45
degrees)
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References: Books
Brower, Michael. Cool Energy. Cambridge MA: The MIT Press, 1992. 0-262-02349-0, TJ807.9.U6B76, 333.79’4’0973.
Duffie, John and William A. Beckman. Solar Engineering of Thermal Processes. NY: John Wiley & Sons, Inc., 920 pp., 1991
Gipe, Paul. Wind Energy for Home & Business. White River Junction, VT: Chelsea Green Pub. Co., 1993. 0-930031-64-4, TJ820.G57, 621.4’5
Patel, Mukund R. Wind and Solar Power Systems. Boca Raton: CRC Press, 1999, 351 pp. ISBN 0-8493-1605-7, TK1541.P38 1999, 621.31’2136
Sørensen, Bent. Renewable Energy, Second Edition. San Diego: Academic Press, 2000, 911 pp. ISBN 0-12-656152-4.
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References: Websites, etc.
[email protected]. Wind Energy [email protected]. Wind energy home powersite elistgeothermal.marin.org/ on geothermal energymailto:[email protected] rredc.nrel.gov/wind/pubs/atlas/maps/chap2/2-01m.html PNNL wind energy
map of CONUS [email protected]. Elist for wind energy experimenters
www.dieoff.org. Site devoted to the decline of energy and effects upon population
www.ferc.gov/ Federal Energy Regulatory Commissionwww.hawaii.gov/dbedt/ert/otec_hi.html#anchor349152 on OTEC systemstelosnet.com/wind/20th.htmlwww.google.com/search?q=%22renewable+energy+course%22solstice.crest.org/dataweb.usbr.gov/html/powerplant_selection.html
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