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  1. 12.MT Midterm Review of Renewable Energy Some of the more important points Frank R. Leslie, B. S. E. E., M. S. Space Technology 2/23/2010, Rev. 2.0 fleslie; (321) 674-7377

  2. 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 040413

  3. 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 select those files 050428

  4. 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 market • China and India increasing demand; price up • Key issues affecting the economy are the prices of gasoline and natural gas • Gasoline 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 090219

  5. 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 pollutants • Road traffic caused by oil truck transportation, and resultant exhaust fumes, which cause more ailments • Renewable energies usually cause less pollution than conventional fuels • Making the converter also uses energy and may cause some transient pollution 090219

  6. 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 050428

  7. 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! 050428

  8. 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 cooling • On the other hand, now glaciers are melting and receding over a period of years indicating a warmer weather change 090219

  9. 12.4 Fuel: Hydrogen • There is much talk of the “Hydrogen Economy”, where hydrogen (an energy carrier) will replace fossil fuels • See Amory Lovins, Rocky Mountain Institute for early espousal of the concept; Joe Romm for the opposite • There are no hydrogen wells, so hydrogen isn’t a fuel in the usual sense, but an energy carrier • To get hydrogen, electrolysis of water, pyrolysis of fossil fuels, or bacterial action is required • Nuclear and fossil fuel base-load power plants produce energy to support the lowest daily load or more • This 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 090219

  10. 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 050428

  11. 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 050428

  12. 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 050428

  13. 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 needed • Bright local lighting is better than bright general lighting since less power is needed • Compact fluorescent lights (CFLs) produce good light intensity with about 1/4 the power • Timers or motion detectors can turn off lights when they are not needed • Better building insulation conserves heating in winter and keeps summer heat out 040413

  14. 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 040413

  15. 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” 070226

  16. 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) 050428

  17. 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 050428

  18. 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 050428

  19. 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? 070226

  20. 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 050428

  21. 12.9 Natural Gas Decline 030426

  22. 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 070226

  23. 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 truck • Some complain that storage must last 250,000 years • Human failure remains the largest concern • More outcry is raised about the possibility of nuclear contamination than about the statistical health problems caused by fossil fuel plants 070226

  24. 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 050428

  25. 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 date • Solstices are extremes of angular sun travel 070226

  26. 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 070226

  27. 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 070226

  28. 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 050428

  29. 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-hours • Engine-cranking currents of ~500 A are for 30 seconds periods 050428

  30. 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 understanding • Evaluate intended loads closely • Use spreadsheets to change system parameters readily • Isolated remote sites have no alternative utility power, and some assumptions are warranted 070226

  31. 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 070226

  32. 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 peak • Not competitive • Massive power tower yields 10 MWe, while a typical utility plant is 500 Mwe • Power towers aren’t likely to be economically practical 050428

  33. 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 030426

  34. 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 100223

  35. 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 050428

  36. 12.12.2 Wind Energy 2 • 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 050428 sum3fly.htm

  37. 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 • is a good statistics reference 070226

  38. 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) 070226

  39. 12.12.3 Wind Turbines • Vertical axis turbines are simple but don’t work very well • The 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 energy 070226

  40. 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 070226

  41. 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 070226

  42. 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 030427

  43. Conclusion: Wind Turbine Siting and Installation • 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 070226

  44. 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 070226

  45. 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)” • (from AWEA, the American Wind Energy Association) 030419

  46. 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.) 030419

  47. 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 reflection • Altitude of the sun = 90º -latitude + sun declination; azimuth is the horizontal angle clockwise from north • (declination is the varying solar latitude+/-23.45 degrees) 100223

  48. 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. 070226

  49. References: Websites, etc. Wind Energy elist Wind energy home powersite elist on geothermal energy PNNL wind energy map of CONUS Elist for wind energy experimenters Site devoted to the decline of energy and effects upon population Federal Energy Regulatory Commission on OTEC systems 070226