RES Midterm #2 2018
First concept of energy extracted from a moving fluid
(1) Energy conversion. Some of the kinetic energy initially the fluid passing through the turbine is converted to rotational energy (work) which is then converted to electrical energy.
Second concept of energy extracted from a moving fluid
(2) The turbine can not take all of the velocity (KE) from the fluid
Third concept of energy extracted from a moving fluid
(3) The mass flow in to a turbine has to be equal to mass flow out.
What is the percentage of bird mortalities by wind turbine?
0.1-0.2%
How can you protect turbines from over-speeds?
1. Aerodynamic brake flaps 2. Feather blades
What are some concerns of the visual impact of wind turbines?
1. Aesthetics regarding the landscape are individual opinions It often depends on a variety of complex social and psychological parameters In Wisconsin, there is more of a preference for onshore over offshore wind.
What are some negatives to wind energy?
1. Bird/bat mortalities 2. Visual impact 3. Noise 4. Flickering of light during sunset/sunrise 5. Electromagnetic interference
What is the cause of bat mortality with regards to wind turbines?
1. Blunt-force trauma 2. Barotrauma (flying into lower pressure vortex from rotating blades) 3. Fatality rates are variable 4. Highest numbers fall during migration periods
The following are characteristics of an off-shore wind farm compared to the same wind farm on land (select all that apply).
1. Capital costs are higher 2. Average annual wind speeds are higher
Why do wind speeds vary?
1. Geography 2. Topography 3. Seasons
What kinds of wind circulation cell patterns are there?
1. Hadley cell (trade winds) 2. Ferrel cell 3. Polar cell
What type of wind turbine has the maximum efficiency?
1. High-speed two blade (.45) 2. Darrieus (.35) 3. Savonius (vertical axis) (.30) 4. Dutch four-arm (.18) 5. American multi-blade (.15)
What are some benefits of off-shore wind?
1. Increase in flora and fauna around foundations, supporting reef-structures 2. Higher energy capacity
What are disadvantages of wind?
1. Intermittency issues 2. Price > conventional sources 3. NIMBY concerns
What are some positives to wind energy?
1. No air pollution 2. No carbon emissions 3. No water use 4. High energy ratio 5. Efficient land use
What are some micro-processes that affect wind availability?
1. Sea Breezes 2. Mountain breezes, valleys, canyons (help focus/concentrate the wind into a certain area)
What are the losses of Betz Limit caused by?
1. Some of the wind not going through the hoop (going around) 2. Wind exiting the blade cannot be slowed to zero velocity 3. Aerodynamic drag 4. Frictional losses from high velocity/ turbulence
Why are wind turbines on high towers?
1. The closer to the earth you are, the less wind. 2. There is less turbulence the higher you go 3. There is less blade fatigue
What are factors affecting wind shear?
1. Trees, buildings, hills, topography 2. Turbulence takes energy from turbine
What are some concerns of off-shore wind?
1.Noise echo from the wind turbine can affect whales and dolphins. 2.Higher capital costs
What is the most common distance of measuring wind speed?
10 meters above a flat surface
What is the total potential wind capacity in the United States?
10,640,080 MW
What is the average commercial turbine efficiency?
10-45%
What is the current annual increase in wind power capacity?
15-25%
What is the approximate range of capacity factors for wind power sites?
20% to 40%
What is the average U.S. electrical consumption?
3,758,992 GWh
What is the total potential wind generation in the United States?
30,949,523 GWh
What is the conversion efficiency (power coefficient) from power in the wind to power output from the blades for a modern highly engineered horizontal axis high-tip-speed two blade wind turbine?
35%-45%
If you were standing 150 meters from a modern wind turbine, the noise level from the turbine would be about,
45 dB(a) or comparable to the background noise level inside a house.
What is the Wisconsin requirement on the noise generated by wind turbines?
50 db(A) during the day and 45 db(A) during the night at a setback distance of 380 m
What is the Wisconsin rule regarding the noise levels of wind turbines?
50dBA during the day, 45dBA at night *Whispering: 20dBA Community buildings and non-participating residences must be at least 380 meters away from the turbine.
How much can utility-scale turbines achieve from the Betz limit?
75-80%
What are direct drive wind turbines?
A horizontal turbine. The rotor is directly connected to the generator. This makes the rotational speed higher and the turbine noisier. The speed is also very variable. There usually is a much narrower range of wind speeds that these operate at. Typical for small diameter (<4ft.) low power (<10kW) turbines Have a lower efficiency than larger turbines
What is a turbine?
A large structure with several spinning blades (usually three) that are connected to an electromagnetic generator that creates electricity when the wind causes the blades to spin.
How does the power density of wind (W/m2) at 50 meters elevation above the earth's surface compare to the power density at 10 meters above the earths surface?
About double
How much energy do existing and proposed wind projects in Wisconsin create?
Approximately 650 MW
What is the shut-down wind speed?
At this point, it is not safe to operate, so the turbine shuts down.
What is the maximum theoretical power conversion efficiency of the wind?
Betz Limit = 0.59 *So in order to calculate the total power, you have to multiply the power output by Betz Limit to get its maximum potential
What is the land use intensity for various energy productions and conservation techniques?
Biodiesel from soy: 894 Electricity from biomass: 534.4 Ethanol from cellulose: 455.9 Ethanol from corn: 347.1 Ethanol from sugarcane: 285.6 Wind: 72.6 Hydropower: 54.0 Petroleum: 44.7 Solar PV: 36.9 Natural gas: 18.6 Solar Thermal: 15.3 Coal: 9.7 Geothermal: 7.5 Nuclear: 2.4
Where is the highest bird mortality rate by wind farm located?
Buffalo Mountain, TN
Where are the Santa Ana winds located?
California
The area of the USA with the best wind resource is:
Central States
What country leads the world in installed wind energy capacity, with the US a distant second?
China
Which of the following are potential downsides (perceived, and some that are true) to implementing wind energy, that need to be accounted for when planning and siting wind farms?
Concerns of visual impacts Electromagnetic interference Noise considerations Bat and bird mortality Shadow flicker due to rotating turbine blades
What is the mass flow rate?
Cross-sectional area x velocity x density [m^2] x [m/s] x [kg/m^3] = [kg/s]
How do you calculate (annual total) energy from the wind?
Energy = Power x Time *Power depends on wind speed and the conversion efficiency **Time is estimated using an annual average wind speed and statistical distribution of wind speeds over time
What is Wind Energy?
Energy derived from wind by converting the air's motion into mechanical energy.
What time in a given day are wind speeds generally the greatest?
From around 8am to 7pm.
In what direction does air move?
From high pressure (cold) to low pressure areas (warm).
What are verbal axis wind turbines? (VAWT)
Generally less common wind turbines. They can use wind from any direction without the need for positioning the device. The generator is down on the ground, simplifying the tower. Some require a motor to get started, particularly the larger ones. The lower wind speed at ground-level limits power generation.. Overall efficiency is low.
While larger turbine blades can extract more energy from the wind resource, what is a typical downside to consider (select the best answer)?
Greater propensity for high-speed wind damage
What are the efficiencies of various wind turbines?
Highspeed 2 or 3 blade: .4-.47 Darrieus: .23-.35 Savonius: 0-.31 Dutch four-arm: .12-.16 American multi blade: 0-.15
Wind turbine size ranges:
Home: 10kW (100ft or 35m) Business: 100kW to 200kW Wind Farms: 500kW, 1.6MW, 3MW Offshore: 6MW
What is the energy output to input ratio of types of renewable resources?
Hydro: 40-200 Wind: 10-80 Nuclear: 12-35 Coal: 10-30 Natural Gas: 0-25 Biomass: 0-20 Solar: 0-15 **The higher the number, the better.
Fifth concept of energy extracted from a moving fluid
If the velocity is reduced and the mass flow rate is the same, then something has to give Such as: 1. Area increase (if not constrained in pipe) 2. Density decreases (if a gas) 3. Pressure decreases
When are wind speeds the greatest in Madison, WI?
In the winter months
What is a shadow flicker with regards to wind turbines?
Is a shadow cast by the turning blades during low sun angles in the morning or evening. Wisconsin rule: cannot cause more than 30 hours per year of shadow flicker at a nonparticipating residence or community building.
What is the (BASIC) formula of Kinetic Energy?
K.E. = (1/2)mV^2 m= mass (kg) V = velocity (m/s) Energy (Joules) = kg(m^2)/S^2
What is formula for the total POWER in Wind?
K.E. = (1/2)pAV^3 p = air density (1.239 kg/m^3) A = cross sectional area of the hoop V = velocity
What kind of energy is wind energy?
Kinetic Energy
What is a wind farm?
Large, high-tech turbines grouped together into wind power plants that generate a capacity that ranges from a few MW to hundreds of MW Requires transmission lines to move electricity to the energy market
What are lift type modern wind turbines?
Lift results from pressure differences between the upper and lower surfaces of an airfoil (Bernoulli effect: faster airflow = lower pressure) Looking to maximize lift and minimize drag
MODULE 6 WIND
MODULE 6 WIND
MODULE 7 WIND (2)
MODULE 7 WIND (2)
What was wind energy traditionally used for?
Milling grain and pumping water.
What is the standard tower for wind farms?
Monotube is the standard on large machines and the occasional small machine. Freestanding Lattice tower is used for mid-size turbines Small turbines are generally tilt-down towers (<20kW)
What is wind?
Moving air caused by differences in atmospheric pressure
What reduces avian mortality regarding wind turbines?
Newer, larger turbines and control strategies The cases where you have more bird mortalities is when you have smaller, faster turning turbines
What was the style of older turbines?
Older style's were drag type devices. It can never go faster than the wind, always a little bit slower.
Horizontal Axis Wind Turbine Design Solutions
One of the issues with HAWT is that the velocity changes among the blade (the tip turns faster than the base) One solution is twisted blades that changes the angle as you move away from the hub Another solution is adjustable pitch blades that adjust the angle of attack Another solution os flexible blades that absorb fluctuating wind force
What are challenges with wind turbines?
Problem of producing turbines that operate at high efficiency at low wind speeds Problem is that in order to capture more energy, you need higher towers and longer blades. Problem of fatigue failure of 'flapping blades' ICE!
What was the early application for wind power?
Pumping water (windmill) Charging batteries
Which of the following statistics is true about US wind power as compared to other countries?
Rank #2 in the world in cumulative capacity installed
What are some alternatives to reducing bat mortalities?
Shutting down at nights during bat migration periods Increasing cut-in speeds during migration periods: from 4m/s to 6.5m/s can lead to a 44-93% reduction in mortalities
Where does the wind come from?
Solar heating the earth's surface (aka the SUN!)
Where in Wisconsin is the best wind potential?
Southeastern Wisconsin and Northcentral Wisconsin (along the lake)
Where is off-shore wind potential in Wisconsin?
Southern Lake Michigan Has a 9700 MW potential of wind energy There is a public concern about the "purity-of-view"-shed
Where is wind in the United States?
The Great Plains (central U.S.) have high wind speeds along with the coastlines.
The power curve of a wind turbine gives us the useful power output of the turbine at a specific wind speed. If you have a wind turbine power cure, which of the following additional information will allow you to calculate the useful energy output of the wind turbine over the course of one year?
The annual distribution of wind speed (hours per year that the wind blows at each specific wind speed)
Wind farms generally have a favorable land-use intensity because (select the best answer):
The area under the turbines can be used for agriculture/ pasture
What is the rated power?
The maximum power output of the machine.
What is the cut-in wind speed?
The minimum wind velocity required for the turbine to operate at all
What is a major advantage of wind?
The production of electricity from wind had no direct CO2 emissions.
What does the efficiency depend on?
The ratio of tip velocity to the air velocity
How can wind turbines disturb electromagnetic waves?
The rotating turbines between the transmitter and receiver distort radio/TV signals Depends mainly on blade materials and the shape of tower TV signals can be distorted but affected viewers of surrounding area could be provided with cable service
What are newer type wind turbines?
There are lift turbines, airfoil turbines, that actually go faster than the wind. *More common*
Match the following wind turbine tower types to their potential applications:
Tilt-down: Small wind turbine Freestanding lattice: midsize turbine Monotube: midsize to large turbine
True/False: The Dutch four-arm is an example of a drag-type turbine
True
True/False: Wind energy recently passed hydroelectric power to become the number one source of renewable generating capacity (in 2016) with an installed capacity of >82,000 MW
True
True/False: Wind speeds are generally higher and have less turbulence off-shore, allowing greater energy production.
True
True/False: Windmills are typically drag-based whereas most modern turbines work on the principle of lift
True
What is the mechanism used to convert air motion into electricity?
Turbine
Where is the best off-shore wind location?
Up to 30m to 50m in water depth and at least 5km off-shore. *The further from the shore, the higher the wind.
How do scientists characterize wind availability?
Using a wind map
Adjusting for Hub Height using the Power Law
V2 = V1(H2/H1)^alpha alpha = Wind shear exponent 'typical' = 0.14 Ranges from 0.1 for very smooth and 0.4 to very rough
WIND POWER CALCULATIONS
WIND POWER CALCULATIONS
Fourth concept of energy extracted from a moving fluid
We can calculate the flow rate going into the turbine by the cross sectional area, velocity, and density
The power curve of a wind turbine shows the power output of the turbine over its range of operational wind-speed. The power output of a well designed wind turbine increases in which proportion to wind speed up to its maximum rated power output?
Wind Velocity^3
What is a sea breeze?
Wind that results from the seas ability to maintain temperature. Day-time land heating, sea is cool, therefore the wind flows toward the shore. Night-time land cools, sea is warmer, wind flows toward the sea.
Wind power availability at a specific site changes with:
time of day month of year year to year height above the ground
