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!

The longer gusts are very important for high energy070226

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.

awea-windnet@yahoogroups.com. Wind Energy elistawea-wind-home@yahoogroups.com. Wind energy home powersite elistgeothermal.marin.org/ on geothermal energymailto:energyresources@egroups.com rredc.nrel.gov/wind/pubs/atlas/maps/chap2/2-01m.html PNNL wind energy

map of CONUS windenergyexperimenter@yahoogroups.com. 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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