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Questions and Answers
What does the power generated by a wind turbine depend on?
What does the power generated by a wind turbine depend on?
The mass flow of air through the blades is independent of the blade diameter.
The mass flow of air through the blades is independent of the blade diameter.
False
What is the equation for the work extracted from the change in kinetic energy of the wind?
What is the equation for the work extracted from the change in kinetic energy of the wind?
wout = (V12 - V22) / 2
What is the capacity factor of wind turbines based on variability of wind speed?
What is the capacity factor of wind turbines based on variability of wind speed?
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The area available for energy extraction in a wind turbine is determined by the length of the ______.
The area available for energy extraction in a wind turbine is determined by the length of the ______.
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Wind turbines are designed to operate efficiently at constant wind speeds only.
Wind turbines are designed to operate efficiently at constant wind speeds only.
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Match the components of a wind turbine with their functions:
Match the components of a wind turbine with their functions:
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What is the theoretical power formula for wind calculated as P = 1/2 ρ A v^3 represented in a different form?
What is the theoretical power formula for wind calculated as P = 1/2 ρ A v^3 represented in a different form?
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The density of air is usually _____ kg/m3.
The density of air is usually _____ kg/m3.
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Match the following terms with their definitions:
Match the following terms with their definitions:
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Which turbine is most suitable for very high pressure heads greater than 1000 ft?
Which turbine is most suitable for very high pressure heads greater than 1000 ft?
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The majority of pressure loss in a reaction turbine occurs in the fixed blades.
The majority of pressure loss in a reaction turbine occurs in the fixed blades.
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What is the function of the stationary guide vanes in reaction turbines?
What is the function of the stationary guide vanes in reaction turbines?
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The _____ turbines are typically used for large installations with high flow rates.
The _____ turbines are typically used for large installations with high flow rates.
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Match the following turbines with their characteristics:
Match the following turbines with their characteristics:
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What is the optimum ratio VR that maximizes power produced?
What is the optimum ratio VR that maximizes power produced?
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What primarily causes surface winds on Earth?
What primarily causes surface winds on Earth?
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The maximum kinetic energy that can be converted to work output by a wind turbine is 39%.
The maximum kinetic energy that can be converted to work output by a wind turbine is 39%.
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Mechanical energy from wind turbines has been used for electricity production since around 500-900 AD.
Mechanical energy from wind turbines has been used for electricity production since around 500-900 AD.
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What does the power coefficient (Cp) represent?
What does the power coefficient (Cp) represent?
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What are the key features of a turbine blade as perfected in early European mills?
What are the key features of a turbine blade as perfected in early European mills?
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The power output of a wind turbine is dependent on the __________.
The power output of a wind turbine is dependent on the __________.
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The first wind turbines were of _______ axis orientation.
The first wind turbines were of _______ axis orientation.
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What is the relationship between blade sweep and power?
What is the relationship between blade sweep and power?
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Which of the following is NOT a component of a modern wind turbine?
Which of the following is NOT a component of a modern wind turbine?
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Match the historical wind energy applications with their uses:
Match the historical wind energy applications with their uses:
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Where are the ideal locations for wind farms?
Where are the ideal locations for wind farms?
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Local heating and cooling effects do not play a significant role in the development of wind patterns.
Local heating and cooling effects do not play a significant role in the development of wind patterns.
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Actual power coefficients can exceed the theoretical maximum of 0.593.
Actual power coefficients can exceed the theoretical maximum of 0.593.
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Modern wind turbines are primarily of _______ axis configuration.
Modern wind turbines are primarily of _______ axis configuration.
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What is the average solar irradiance on the Earth's surface?
What is the average solar irradiance on the Earth's surface?
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Solar energy can be harnessed only through active solar collectors.
Solar energy can be harnessed only through active solar collectors.
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What percentage of the US electricity needs could potentially be supplied by solar energy by 2050?
What percentage of the US electricity needs could potentially be supplied by solar energy by 2050?
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The US may require __________ in subsidies between 2011 and 2050 to make solar energy cost-competitive.
The US may require __________ in subsidies between 2011 and 2050 to make solar energy cost-competitive.
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What is one limitation of solar energy mentioned?
What is one limitation of solar energy mentioned?
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Match the following solar energy harnessing methods with their descriptions:
Match the following solar energy harnessing methods with their descriptions:
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To harness solar energy effectively, buildings should have designs that maximize __________ exposure.
To harness solar energy effectively, buildings should have designs that maximize __________ exposure.
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What area in the US would be needed to supply 69% of its electricity from solar energy by 2050?
What area in the US would be needed to supply 69% of its electricity from solar energy by 2050?
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Study Notes
Renewable Energy Sources
- Renewable energy sources rely on natural environmental energy, not finite resources. They are effectively infinite.
- Renewables typically have: ubiquitous energy sources, low power density, and intermittent energy fluxes.
- Ultimately, all renewable energy (excluding tidal/geothermal) derives from the Sun. Examples: solar, wind (from thermal gradients), and photosynthesis to make fossil fuels. Geothermal energy comes from Earth's core radioactivity and tidal energy comes from the Moon's gravity.
Renewable Energy Sources - Examples
- Hydro power including conventional hydroelectric dams and tidal barrages & turbines
- Wave power
- Pumped Storage
- Wind power (onshore and offshore)
- Solar power (photovoltaic cells and collectors)
- Geothermal
- Biomass & hydrogen
- Fuel cells
Technologies fitting into overall energy generation
- Technologies are connected into an overall generation scheme. In the diagram, the different technologies that use the outputs from the others.
Typical Power Densities
| Source | Area | Heat (W/m²) | Work (W/m²) |
|---|---|---|---|
| Solar PV | Collectors | 150 | 20 |
| Photovoltaic | Cells | 30 | |
| Hydroelectric | Drainage basin | 0.01 | 40 |
| Wind | Turbine | 0.1 | 0.02 |
| Geothermal | Field | 0.5 | 0.1 |
| Biomass | Field | 10000* | |
| Ocean Tidal | Tidal pond | 1 | |
| Ocean Wave | Frontal area | 10000* |
- compare to a fossil or nuclear plant where we typically achieve > 100 kW/m²
Installed Capacity Cost
- Typical installed costs for each technology are shown. The target for most technology costs is ≤$100/MWhr or $1000/kW.
2007 - 2016 Installed Capacity Cost data
- Data are provided on installed capacity cost using different energy sources, comparing their efficiency based on capacity factor, variable O&M (including fuel) and levelized capital costs.
Hydro Power
- Hydro power extracts potential energy from water as it changes elevation. This is in diagrams of: Intake, Penstock, Turbine, Powerhouse, Transformer, Tailrace, Draft Tube, and Transmission Lines.
Hydro Power - Dams
- Examples of dams include Mactaquac Dam in Fredericton, Hoover Dam in Nevada and Three Gorges Dam in China. These are used in various hydro power applications.
Tidal Power
- Tidal barrages and tidal fences are described in diagram form.
- Tidal turbines are essentially underwater “wind” turbines that are used in operation and proposed. The example of East River in NYC is highlighted.
Tidal Concerns
- The “killing machine”. There are environmental concerns about potential tidal turbines.
Wave Power
- Wave power uses waves to drive turbines.
Pelamis
- Pelamis is a wave energy converter.
OTEC
- OTEC uses differences in temperature of ocean depths to generate power, with a Rankine cycle with ammonia in diagram shown.
Design Concepts OTEC
- Design concepts for 100 MWe OTEC power plant are given.
Thermodynamic properties of ammonia and seawater
- A table of thermodynamic properties is given for ammonia and seawater.
Calculate problems on OTEC
- Problems are given to calculate gross work, thermodynamic efficiency, pumping work & net efficiency, as well as a comment about feasibility.
Solar PV
- Solar radiation amounts 164 W/m2, can be used directly in energy production (with the exceptions of Nuclear, Tidal, and Geothermal energy sources).
Critical Factors of Solar PV
- Critical factors for PV technology (e.g. land area, thin film, installed cost) are covered in a table showing efficiency improvements over time.
Solar Energy
- Solar energy can be harnessed from active or passive solar collectors (flat plate collectors, building design to maximize heat inventory, and photovoltaic cells).
Concentrated Solar Power
- Using mirrors or flat-plate concentrators to increase light exposure allows for more efficient collecting of solar energy. Example is the parabolic trough, “power tower” arrangement.
Photovoltaic Cells
- The photoelectric effect (Albert Einstein) - releasing valence electrons from atoms using photons of suitable energy levels. P-type and n-type semiconductors generate the electricity.
Wind Power
- Surface winds result from solar radiation differences at different latitudes, this creates temperature differences leading to air density gradients leading to wind flow.
Wind Turbine Parts
- Main components in wind turbines: Rotor, Hub, Gearbox, Generator, Control unit, Tower.
Wind Power Output and Efficiency
- Power from wind turbines depends on wind speed, and these will obviously have minimum, or maximum wind speeds for efficient / safe energy production.
Wind Turbine Aerodynamics
- An ideal wind turbine ratio = 1/3rd between upstream & downstream wind velocity.
Theoretical and Actual Wind Power
- The theoretical power and actual power are different (e.g ideal theoretical power = 59%, actual power available = ~20-30%, based on variability in wind speed).
Wind Power Capacity
- Capacity factors for wind turbines are 20 - 30 %, meaning that the actual power produced over time is a fraction of the theoretical maximum sustained output.
Locations of Wind Power
- Good locations for wind farms are higher/high altitudes or near large bodies of water (mountainous regions).
Biomass Technologies
- Biomass is organic material with energy stored as carbohydrates from photosynthesis.
Biomass Sources
- Biomass sources for energy include: forests, stem wood, milling wastes, urban wastes, agriculture, food crops/residues, energy crops, algae, garbage, raw sewage, animal waste (manure), scraps, industrial waste, wood residues, mill sludge.
Biomass Energy Processes
- Biomass energy can be transformed via: Direct combustion; Co-firing (with fossil fuels); Gasification (producing syngas); Pyrolysis (no oxygen, leaving charcoal); Torrefaction (removing moisture and oxygen); Chemical Conversion (producing biofuels).
Chemical Conversion of Biomass
- Chemical conversion methods: Ethanol (corn, wheat, rice etc.) – used as a blending agent in conventional gasoline, Biodiesel (vegetable oils or waste cooking oils)
Biofuels from Algae and Microorganisms
- Algae can be used to produce organic oils in a photo-bioreactor.
Biogas
- Anaerobic digestion produces biogas; used in direct firing of power plants or upgrading to synthetic fuels.
Landfill Gas Systems
- Significant biogas from anaerobic decomposition in landfills. Landfill sites are designed for the collection of biogas.
Combined Heat and Power Systems (CHP)
- Biomass is used in Sweden for district heating and electricity production. Examples include calculating biomass for a generating station.
Major Geothermal Parameters
- Data on global geothermal power plants and their capacity and different types.
Geothermal Energy
- The heat in Earth's interior is a vast energy source (inaccessible or difficult to obtain / harness).
Geothermal Power Extraction
- Geothermal regions (e.g. tectonic plates & active volcanic regions) are areas of good geothermal power extraction.
- Water extraction is used in geothermal processes (water pumped into an injection well to produce steam, then goes back into a production well).
Hydraulic Fracturing
- Hydraulic fracturing (fracking) is used to extract steam in some geothermal power plants, it involves high pressure fluid injection into the rock to fracture it. Sand particles help keep the fractures open.
Geothermal Power Types
- Types of geothermal power plants are discussed: Dry/superheated steam directly to turbines; Single Flash geothermal plants; Double Flash; Binary Cycle
- Typical pictures of the processes are shown.
Environmental Impacts for Geothermal
- Off gases from geothermal reservoirs include H2S, SO2, CO2, NOx and Radon.
- Water/steam (from production wells) contains heavy metals, salts, potential hydrocarbons. Wastewater and brine solutions may carry these elements and affect the output and maintenance of the overall plant.
- Induced seismicity / earthquake potential, heat draw is considered non-renewable when heat extraction is at a faster rate than replenishment.
Notes on Feasibility for OTEC, Geothermal / other processes
- Feasibility statements / comments on costs, efficiency and other factors for the different technologies. The different technologies may require considerable infrastructure investment, maintenance cost, regulatory issues, etc which impacts the financial viability.
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Description
Test your knowledge on the principles of wind energy and the operation of wind turbines. This quiz covers topics like power generation, blade functions, and the theoretical formulas related to wind energy. Challenge yourself and see how much you really know about the mechanics behind harnessing wind power.
