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Chapter 9 Solar And Wind Power & Battery Storage
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Solar Energy Fusion takes place in the core and takes a million years for a photon of light to reach the surface
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Produces electricity during daylight hours when most needed
Solar Energy Produces electricity during daylight hours when most needed More reliable than wind because sun rises and sets on schedule Cut significantly by clouds and by sun being near horizon Seasonal (winter sun does not rise as high as summer sun) Sun’s ultraviolet light
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In the 5th Century, the Greeks incorporated passive solar design in their buildings by allowing the southern sun to penetrate interiors for warmth in the winter
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In 212 BCE, Archimedes focused sunlight with polished bronze shields on a Roman fleet attacking Syracuse and succeeded in setting ships afire
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Justinian Code ( ) included laws regarding “sun rights” to ensure that houses and buildings had continued access to sunlight after their construction
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Energy from sun tapped by: Minimal cloud cover (deserts)
Solar thermal heaters Solar thermal electricity Solar photo voltaic electricity (PV) Red areas best for extracting solar power Minimal cloud cover (deserts)
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Solar heaters take heat of sun and warms water that can be used as hot water for washing clothes, showers, or heating a home Solar heating units being built and installed rooftops of developing nations for home hot water such as India, Egypt, and others by local entrepreneurs
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Thermal solar energy totaled 269 GW in 2012 vs 40 GW solar photovoltaic in 2010
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Installing roof top solar thermal hot water heaters a cottage industry in Egypt and elsewhere
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Solar Thermal Capacity (Gigawatts)
Figure 9.1 Solar Thermal Capacity (Gigawatts)
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First solar power plant to produce steam
“Eventually industry will no longer find in Europe the resources to satisfy its prodigious expansion... Coal will undoubtedly be used up. What will industry do then?” Augustin Mouchot ( ) First solar power plant to produce steam
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In 1912 Frank Shuman ( ) built parabolic solar collectors near Nile River to run steam-pumps to irrigate desert land Wanted to build 20,000 square miles (!) of reflectors
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Solar Thermal Power Plant Design
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Historical Development Solar Thermal Electricity Capacity (Gigawatts)
Figure 9.2 Historical Development Solar Thermal Electricity Capacity (Gigawatts)
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Solar Thermal Energy for Electricity Generation
Solar Power Tower A circular field array of heliostats (large mirrors) individually tracks the sun The heliostats focus sunlight on a central receiver which heats molten salt that via heat exchanger feeds steam to generator to produce electricity
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Natural gas or bio fuel by night
Trestin Bio (Hybrid) Solar by day Natural gas or bio fuel by night
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SolarReserve Thermal tower 600’ in Nevada Surrounded by 10,000 mirrors sized as large as billboards 110 MW output Molten salt stores energy which can be converted to electricity on demand—more reliable than solar panels
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Trough-shaped parabolic mirrors automatically follow the sun and focus the sun’s rays at 30 to 60 times their normal intensity on a receiver pipe filled with synthetic oil—heat exchanger to produce steam to generate electricity
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Thermal solar electricity plants under construction/development
(19,777 MW Total) Parabolic Trough Power Tower Dish CSP – Concentrated Solar Power
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Installed cost solar thermal plants: $5.80 per watt
Dark Day for Solar Thermal: Solar Trust Switches 500MW Power Plant to PV In 2011, including above, 3 gigawatts of solar thermal electricity generating projects have been converted to PV projects Installed cost solar thermal plants: $5.80 per watt As consequence of falling manufacturing cost of solar panels Installed cost of utility-scale PV installation: $3.40 per watt Source: and
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Heated fluid transfers its heat to a gas such as hydrogen or helium to power a Stirling engine similar in construction to an internal combustion engine, or to a Brayton engine similar to a gas turbine engine (referred to as a micro-turbine). In neither case is there combustion; the engines run off the energy of the heated gas and drive an electricity generator—efficiency of 30% highest of all solar thermal power plants No water needed as in power towers and parabolic mirror systems Power output limited <5 MW and too sophisticated compared to PV
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First to study photovoltaic effect
Edmund Becquerel ( ) First to study photovoltaic effect
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Charles Fritts ( ) First working model of a solar cell in 1883 who coated a semiconductor (selenium) with a thin layer of gold in 1883 to produce the first working first photovoltaic (PV) solar cell
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Solar Photovoltaic (PV) Solar Power
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Historical Development of Solar Power (Gigawatts)
Figure 9.3 Historical Development of Solar Power (Gigawatts)
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Commercial solar panels require mechanical support and have an efficiency of around 18%
Energy output over lifetime of service vs energy input during manufacture and installation is a factor of 4 (for wind it is 80)
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Solar Panel Park or Farm
Once built, energy free and virtually maintenance free for 25 years
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Building a solar panel park
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Installed costs falling rapidly
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Cost of grid electricity rising, but cost of solar electricity declining
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Table 9.1 Economic Analysis of Actual Solar Energy System
Aggregate Savings (Costs) Over 25 Year Life of Project Avoided Electricity Purchases $2,415,000 Avoided Transformer Losses $50,000 Estimated Sales of Electricity Back to Utility First Four Years Only $315,000 Maintenance of Solar System and Roof ($110,000) Aggregate Savings $2,670,000 Cost of System Net of Rebate $1,145,000 Internal Rate of Return over 25 Year Period 8.3%
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Solar PV Power (Gigawatts)
Figure 9.4 Solar PV Power (Gigawatts)
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Required $/kWh versus $/W Installed Cost
Figure 9.5 Required $/kWh versus $/W Installed Cost
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Energy Source for New US Power Plants in 2013 (Gigawatts)
Figure 9.6 Energy Source for New US Power Plants in 2013 (Gigawatts)
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Thin solar film can be applied directly without need for panel support
Efficiency around 12%, less than solar panels
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Thin film solar panels being applied directly to the roof
Intent is to have thin film solar roofing material that can substitute for conventional roofing material
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Solar and wind and biofuel projects helping to bring electricity to isolated parts of the world not connected to an electricity grid Require batteries to store electricity when sun is not shining, but provides power during peak (daylight) periods
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Four Primary Applications for PV Power Systems
Off-grid domestic system: provide electricity to households and villages not connected to the utility electricity network Off-grid nondomestic installations: first commercial application such as telecommunication, satellite, and navigation aids Grid-connected distributed PV systems: provide power to a grid-connected customer. Grid-connected centralized systems: perform the functions of centralized power stations
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But desert locations have disadvantages:
Dust or sand accumulations must be removed from solar panels—generally using water Wind with sand grains scour solar panel surfaces reducing their efficiency if not protected by glass Some locations are maintenance-free without scouring
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Solar Power Updraft Tower
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Integrating solar and hydro power
Sun tracking solar panel installations floating on calm waters of hydro electric power reservoirs Solar power utilizes under-utilized hydro electrical system (avg output hydro plant 40%) Solar power peaks along with daily demand peak augments hydropower output saves reservoir water for when it is more needed Prototype installation being built in India
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Good news: solar output peaks during peak demand for electricity
Bad news: peak is short-lived and overcast skies significantly reduce output
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Suppose that sunlight can be modeled by the following probability distribution for the indicated time of day
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The discrete probability associated with each hour of the day can be taken off the probability distribution The conversion to MW-Hrs is the ratio that 15.4% is maximum output of 1 MW-Hr
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Without cloud cover, the capacity of a 1 MW solar panel installation
compared to a 1 MW coal fired generator is 6.49/22.8 or 28% Suppose there is a 60% chance of cloudless days and 40% of cloudy days Total overcast sky: power output 30%
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Output reflects 60% chance of no cloudiness
Mean output of 5.55 when compared to coal plant is 24%
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Future Directions Sun Catalytix Silicon solar cell has different catalytic materials bonded onto its two sides—needs no external wires or control circuits to operate. Paced in a container of water and exposed to sunlight, it quickly begins to generate streams of oxygen bubbles from one side and hydrogen bubbles from the other Costly and inefficient (2.5%) at present
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Joule Unlimited Specially genetically modified organisms can directly convert waste water, CO2, and sunlight to diesel and ethanol with no intervening steps
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Xtreme Concentrated Photovoltaics, XCPV
(SUNRGI Corp) Tracks sun and uses magnifying glass to focus light on PV cells needs cooling—37% efficiency over 17% nominal efficiency
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Applying nanotechnology to solar panels
Tiny nanospheres silica covered with silicon—silica removed with hydrofluoric acid Light trapped within spheres markedly increases efficiency of thin film solar
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Technological Goals Increase efficiency from 20% to 50% or more Sharply reduce manufacturing costs/solar output If successful, will bring solar power into mainstream of power generation
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Wind Wind results from differences in air temperature, density, and pressure from uneven solar heating of the earth’s surface Like ocean currents, wind currents act as giant heat exchangers: Cooling the tropics Warming the poles Consistent winds: Through passages between mountains (California) Alongside mountain chains (east side of Rockies) Coastlines where sea breezes and land breezes alternate between day and night (NJ and DE) Offshore waters (Europe)
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Wind Energy: Long Exploited
5000 BC in Egypt Egyptians dug canals to haul food and stone from inland sources to Nile River not unlike our interstate highway system
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Age of Exploration Triangular sail invented in Arabian waters key to tacking into wind Model of Columbus’ Sailing Vessel
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Clipper Ships: End of an Era
America’s response to British steamships Lasted only a few decades Doomed by: Reliability of coal propulsion Suez Canal shortening voyage for steam ships Europe to Asia Lesson: Cannot stop technological progress!
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Horizontal Windmill (Primary rotating axis is horizontal)
Gearing necessary to translate to vertical axis to turn grindstones to convert wheat to flour Historically speaking, many societies incapable of technically changing direction of power axis Holland created by building dikes to keep back the sea and thousands of windmills to pump out the water
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Modern Vertical Wind Turbines (Vertical Axes)
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Long history of windmills in development of the West
Little surface water Windmills pumped water for humans and animals Water for steam locomotives Later generated electricity for isolated farm homes
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Wind turbine development mainly financed by government programs
Wind turbine farms depend on various tax credits and grants Favorable wind locations normally in isolated areas and require building long distance transmission lines to population centers Government inducements include requiring utilities to have a set percentage of power supplies being renewable and allowing higher rates to be charged to customers
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Total US potential wind capacity
Hub distance 80 meters: 10,500 GW 100 meters: 12,125 GW Current capacity: GW Capacity factor: % Sufficient to power the US Plains states Average wind speed of 9 m/s 9*3.3 ft/m * 3600 sec/hour/5280 ft/mile 20.2 mph average!
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Offshore wind farms can take advantage of
greater average wind speeds for greater output, but at a higher capital cost
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Europe: Annual Additions to Installed Offshore Wind Capacity (gW)
Figure 9.7 Europe: Annual Additions to Installed Offshore Wind Capacity (gW)
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2012 Offshore Installed Wind Turbines (gW)
Figure 9.8 2012 Offshore Installed Wind Turbines (gW)
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Wind farms are more price competitive than solar electricity and comparable to fossil fuel plants
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Global Installed Wind Power (gW)
Figure 9.9 Global Installed Wind Power (gW)
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2014 Wind Power Capacity by Nation (gW)
Figure 9.10 2014 Wind Power Capacity by Nation (gW)
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Table 9.2 World’s Largest Wind Turbine Manufacturers
Company Percent Market Share Description GE Energy (US) 15.5 16, mW installed plus 2.5 mW plus 4.1 mW built for offshore Vestas (Denmark) 14.0 43,000 turbines in 66 nations including 1.8 and 2.1 mW for onshore, 3 mW for low wind conditions plus 3 mW for offshore via MHI Vestas joint venture Siemens (Germany) 9.5 Market leader offshore turbines 2.3 mW, 3.6 mW and 6 mW with 150 meter diameter rotor Enercon (Germany) 8.2 20,000 turbines worldwide including 2 mW, 2.5 mW (light winds), 3 mW and 7.5 mW Suzlon Group (India) 7.4 21.5 gW of installed capacity including 2.1 mW for normal and light winds. German subsidiary is REpower mW Gamesa (Spain) 6.1 18 gW of installed capacity including 2 mW, 4.5 mW and 5 mW (offshore) Goldwind (China) 6.0 World’s leading manufacturer of permanent magnet direct drive turbines including 1.5 mW and 2.5 mW; other leading Chinese manufacturer is Sinovel
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Annual Market Forecast by Region 2013-2018 (gW)
Figure 9.11 Annual Market Forecast by Region (gW)
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Projected Growth of Wind Power (gW)
Figure 9.12 Projected Growth of Wind Power (gW)
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US States With More Than 2 gW Installed Wind Power
Figure 9.13 US States With More Than 2 gW Installed Wind Power
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California state requirements placed on utilities on renewable energy sources provided impetus for the first major wind farms
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California initiated concepts:
Renewable Portfolio Standard (RPS): utilities must provide certain percentage of their electricity from renewable energy sources—utilities select source on basis of lowest cost or may be directed to use a particular source Feed-in-Tariff (FIT): electricity charge by renewable energy sources must cover capital and operating costs— private investment is now feasible Often costs are subsidized either directly (investment subsidies) or indirectly (reduced taxation) If FIT is higher than rates for conventional electricity, consumers end up paying the difference
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China: Annual Installed and Cumulative Wind Power (gW)
Figure 9.14 China: Annual Installed and Cumulative Wind Power (gW)
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China’s Provinces
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Wind Power Capacity in Provinces of China (gW)
Figure 9.15 Wind Power Capacity in Provinces of China (gW)
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Daliang Wind Station outside Anxi in Gansu Province
Six wind farms each GW—enough to keep China in first place
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Nature of State Support Programs for Renewable Energy
Access laws to ensure access to transmission system Issuance of state bonds to help finance projects Construction and design criteria Contractor licensing and equipment certification State corporate, personal, property, and sales tax incentives Grants and loans Electricity production incentives Rebates on costs Required green power generation Renewable portfolio standards States have 1—18 individual green power policies
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Annual Additions to US Wind Power Capacity (gW)
Figure 9.16 Annual Additions to US Wind Power Capacity (gW) Highly addicted to wind subsidies
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A proposal: line the entire NJ and DE coastline with wind turbines will make both states electricity exporters to other states Shore has consistent land and sea breezes that alternate between night and day
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Government permits necessary for constructing wind farms (as with just about everything else) —wind farms off Cape Cod and Long Island killed by environmental objections during permitting process
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But one made it through the environmental hurdles: Deepwater Wind
First US offshore wind 30 mW, 5 turbine Block Island Wind Farm scheduled to be online in 2016 This should encourage building of other offshore wind farms
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Electricity drives motor that powers a fan— wind powers a fan (blades) to generate electricity
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Modern wind turbines – not always spinning like this –
actual output varies depending on location Best locale – highest average daylight hour wind speed
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Determining 1 MW wind turbine output given variation in wind speed
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Need to know wind variation at a locality
Suppose that historical data suggests that average speed is 15 mph that can be described by above probability distribution
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Assumed Wind Turbine Power Output
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If this were a coal plant at 95% output – 95% X 1 MW X 24 hours = 22
If this were a coal plant at 95% output – 95% X 1 MW X 24 hours = 22.8 MWH Hence wind turbine is operating 9.27/22.8 or 40% as same sized coal plant
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(multiday periods of calm winds)
Why effective output can be as low as 25% of installed capacity (multiday periods of calm winds)
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Wind turbines not considered reliable Requires a backup energy source in case wind stops blowing or blows too hard Reliability can be enhanced by having wind farms in diverse locations where probability of adverse wind conditions at all sites is low 2009 wind energy output: 340 TWh Power (divide by 24 hours/day and 365 days per year): 38.8 GW 2009 installed wind power capacity: GW Hence effective utilization: 25% vs 95% for coal and nuclear power
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The largest land turbine is Vestas 8 mW with blades 80 meters long (rotor diameter of 160 meters)
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Basic Dimensions of Boeing 747 Wing Span – 195 ft 8 in (59
Basic Dimensions of Boeing 747 Wing Span – 195 ft 8 in (59.6 m) Overall Length – 231 ft 10.2 in (70.6 m) Can fit comfortably within area swept by 80’ blade
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And so can Airbus 380! Max capacity 840 passengers Tip-to-tip wingspan 79.8 meters Length 73 meters
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Average onshore turbine: $1.8 mm/MW
Wind turbine: 76% Grid connection: % Foundation, construction: 7% Control systems, land, others: 8%
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Areva 5 MW wind turbine – blade 116 meters
Cut-in wind speed: 4 m/s ( 9 mph) Rated wind speed: 12 m/s (27 mph) Cut out wind speed: 25 m/s (56 mph)
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Hub distance estimated 150 meters or 500’ above ground
Either need helicopter for repairman to land on top Or climb ladder inside tubular support equivalent to a story building Maintenance can’t be cheap!
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New design proposed by Japanese
See Web site: /Japanese-Breakthrough-in-Wind-Turbine-Design
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Environmental Objections to Wind Farms
Ruins scenic coastlines and mountain areas by both wind turbines and transmission lines Swishing noise of blades Kills migratory birds (actually lowest cause of bird deaths) Bird kills from hitting automobiles and buildings and being caught by cats far, far higher Building large wind turbines with slow speed blades reduces swishing noise and birds have better chance to dodge blades
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Avoid building wind farms on bird migratory routes and use radar to stop turbines when birds are passing through wind farm
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Winds at night often better than at day, but do not need electricity
Pumped water storage facilities or other form of electrical storage both to enhance reliability of solar and wind and store night time wind generated electricity for day time use
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Lithium Ion Battery Bank
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8 mW of power capacity that can operate for 4 hours to produce 32 mWh stored in 600,000 lithium-ion battery cells
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Sodium Sulfide Batteries
Positive electrode (molten sulfur) separated from negative electrode (molten sodium) by a solid ceramic electrolyte through which only positive sodium ions can flow During discharge sodium and sulphur ions combine to form sodium polysulfides During the charge cycle sodium polysulfides converted back into sulphur ions and sodium ions Sodium ions flow back through the membrane and recharge the battery
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Various Types of Flow Batteries
The vanadium redox battery (VRB) exploits vanadium ability to exist in solution in four different oxidation states VRB has just one electroactive element instead of two
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Flywheel Energy Storage (FEES)
Works by accelerating a rotor (flywheel) to a very high speed and storing energy as rotational energy Energy added to system by increasing and energy extracted by decreasing flywheel's rotational speed
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Compressed Air Electricity Storage
Off peak electricity is used to compress air for storage in underground mines or caverns which can then be fed along with natural gas into a gas-turbine power plant Two to three times as much electricity can be produced for the same amount of natural gas from energy contained in compressed air
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Table 9.3 Performance of Storage Technologies
Type Power in mW Discharge Time Efficiency Percent Lifetime Years Storage Cost $/mW-hour Pumped storage 250-1,000 10 hrs 70-80 <30 $50-150 CAES 3-10 hrs 45-60 30 About $150 Flywheels <10 <15 min >85 20 NA Supercapacitors 10 <30 sec About 90 50 k cycles Vanadium RB 2-8 hrs 75 5-15 $ Lithium ion 5 <4 hrs 8-15 $ Lead battery 3-20 4-8 Sodium sulfur 30-35 4 hrs 80 15
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End of Chapter 9
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