Wind and Wave Power

Tressa Naylor, Maggie Noun, Maia Johnson, Samantha Gagnon,

Madeline Stevens

Introduction

Wave and Wind power are important power sources to consider. Both sources are completely renewable, and would benefit our environment as a whole. Usable energy can be derived with different systems and generators that the presentation will cover. However, some problems can ensue with these types of energy because both wind and waves are out of human control and are dependent on the atmosphere.

About Wind Turbines

Wind is a form of solar energy, caused by the uneven heating of the atmosphere by the sun, irregularities of earth's surface, and the earth's rotation. Wind turbines harvest motion energy from the wind flow to make electricity. Wind Turbines convert kinetic energy in wind into mechanical power. The turbines have propeller blades that power the generator with moving air and supplying electrical current. Turbines are the opposite of a fan because they produce energy rather than use it. There are a few varieties, the major ones consisting of horizontal axis and vertical axis. Some main parts include the blades, drive train, rotor, and the tower that supports it.

Example of a Horizontal-axis

wind turbine

Vertical-axis

wind turbine

Basic Features of a Wind Turbine

1. Blades

2. Rotor 3. Pitch

4. Brake

5. Low-speed shaft 6. Gear bolt 7. Generator 8. Controller 9. Anemometer (measures wind speed) 10. Wind vane

11. Nacelle

12. High-speed shaft 13. Yaw drive 14. Yaw motor 15. Motor

More Helpful Images

Effects of different wind speeds on the turbine

The first wind speed is the start up speed, where the machine doesn't fully operate yet. Cut-in windspeed is when the rotor can be loaded. Rated windspeed is the optimum machine run, furling windspeed is the speed where the machine can be turned out of the wind to avoid damage, and and the maximum design windspeed is when the machine could be damaged. A small generator can produce 120/240 V for domestic use, and 12/24 for battery charging. Large generators produce three phase electricity. An important part is the tail vane that keeps the rotor turned towards the wind or out of it depending on whether it will be damaged.

The Key Parts of the Turbine

-Rotor blades - act as barriers to the wind. When the wind makes the blades move, it transfers some of its energy to the rotor. -Shaft - The wind-turbine shaft is connected to the center of the rotor. The rotor spins

which causes to the shaft to spin too. The rotor transfers its mechanical, rotational energy to the shaft, which enters an electrical generator on the other side. -Generator - uses electromagnetic induction to produce electrical voltage. Generating voltage is to generate current. A simple generator consists of magnets and a conductor. The conductor is usually a coiled wire, and in the generator, the shaft connects to an line of permanent magnets that surrounds the coil of wire. In electromagnetic induction, if you have a conductor surrounded by magnets, and one of those parts is rotating around the other, it creates voltage in the conductor. Basically, after the rotor spins the shaft, the shaft spins the assembly of magnets, creating voltage in the coil of wire. That voltage drives electrical current through power lines for distribution.

Efficiency of Wind Generators

Scientists generally strive to create machines that are 100% efficient. However, a 100% efficient wind generator could not exist. Wind generators work by slowing down the wind and converting the wind's kinetic energy into mechanical energy. (see diagram on next slide) According to the First Law of Thermodynamics, the energy put into the system must equal the energy coming out of the system. If a wind generator was 100% efficient, it would slow down the air going into it by 100%, and would take all of the energy from the air, which is not possible. Therefore, a wind generator must always be less than 100% efficient.

A diagram of how energy is conserved in wind turbines and generators:

Power Coefficient (Cp)

As stated before, the power efficiency can never reach 100%. The next slide describes the real world maximum efficiency through Betz's law.

The power coefficient is measure of the efficiency of the wind generator.

Betz Limit Albert Betz was a German Physicist. He worked at the University of Gottingen Aerodynamics Laboratory.

In 1919, he discovered the "Betz Limit" or "Betz Law" that the

maximum efficiency of a wind generator is 59.3% or 16/27. This limit is not dependent on the design of an individual wind generator. See next slide for illustration of Betz Limit

Betz's law is the theoretical maximum efficiency; it has never been reached. Real world wind generators have only about 35-40% efficiency. Due to other variables, though, the efficiency often falls between 10-30% efficiency. Vertical Axis Wind Turbines generally have a higher power efficiency than Horizontal Axis Wind Turbines.

Other facts and nuggets about Wind Generator Power and Efficiency:

Solve Problems Involving Wind Power

How To Calculate the Power

P= (½)(air density)(swept area)(wind velocity)3

Swept Area= π*r² r= radius of turbine blade

Important Variables

Air density

Swept Area

Wind Velocity

Example Situation

A wind turbine has a blade with a diameter of 2 meters and on this current day the wind velocity is 14 mph. The elevation is at sea level so the air density is 1.23 kg per cubic meter. What is the magnitude of the power produced?

Solution

14 miles/hour= 6.25856 meters per second

Area=π(1)²=π

P=(1/2)(1.23)(π)(6.25856)³

P=474 Watts

Another Situation

One day you want to find out what the wind velocity is. You know that your wind turbine is producing power with a magnitude of 250 Watts. You are at sea level so once again the air density is 1.23 kg per cubic meter and the radius of the blade is 4 meters. Calculate the wind velocity with these given values.

Solution

A=π(4)²=16π

P=(1/2)(ρ)(A)(v)³ v=(P/(2*ρ*A))¹⁄ ³ v=(250/(2*1.23*16π))¹⁄ ³

v=1.26 meters per second

the Oscillating Water Column (OWC)

With new technology, more extensive research is being done to test the potential of harvesting energy from waves. OWC's use a combination of water and wind power, making the idea more complex than a wind or water turbine.

the Oscillating Water Column OWCs can be fixed to the seabed or harnessed to the shore; it must be able to be reached by waves at all times, even during tide changes. There are some locations with greater potential for wave power, including the western coast of Europe, the northern coast of the UK, and Pacific coastlines along North and South America, Southern Africa, Australia, and New Zealand. This is due to the wind currents that blow in these zones (the prevailing westerlies). Although this form of energy cannot be controlled and is solely based on the atmosphere, the waves that are caused by these winds can generally be predicted about five days in advanced. The Blue arrows

indicate the prevailing westerlies. We can see that they come from the west, proving that it would be most beneficial to place the OWC on the western shore to be subjected to the maximum number of consistent waves.

How an OWC Functions

The bottom of the structure is completely submerged and is open, allowing waves to flow in and out. [A]. The turbine is attached to a generator, which generates power. [D].

A water column is either a floating raft attached to the ocean floor with mooring lines, or stationary and built permanently the shore. Both function the same way.

The waves naturally flow into the column, compressing the air within. The air inside becomes a piston, moving back and forth with the motion of the waves. [B]. There is an air turbine at the exit of the column (generally a Wells Turbine), that spins with the rising internal air pressure. [C].

[A]

[B]

[C]

[D]

Wells Turbines Because the air in an OWC moves like a piston, the air must be able to escape through the turbine when compressed, and air must be able to return when the system expands again. As there are only two openings and one is blocked by water, the air must be able to exit and return through the same opening with the turbine.

This requires a certain type of turbine that maintains a unidirectional rotation, even when the movement of the air column reverses, to prevent the system from doing "negative work".

The Wells Turbine consists of aerofoils that are specifically designed to be symmetrical. The plane symmetry is in the plane of direction but perpendicular to the airstream, which allows the air to pass through the turbine from any direction, and the turbine will rotate continuously in one direction.

Floating OWC's

The Mighty Whale Prototype is 50 meters long and 30 meters wide. It is equipped with three air turbine generators. It is located in Gokasho Bay, Japan. It can be controlled with a remote from onshore. For this prototype, the energy produced is used to keep itself running instead of storing the energy as power. The world's first offshore floating wave OWC was created in 1998 by the Japan Marine Science and Technology Center.

There have been a number of floating OWC's and prototypes to test the new technology.

The Islay LIMPET The only permanent wave power station was designed and built by Wavegen in 2000. They were aided by researchers from the Queens University in Belfast, and was financially backed by the European Union. It is located in Portnahaven, Scotland, on the island of Islay (on the North Atlantic Ocean). It is called the Islay LIMPET (Land Installed Marine Powered Energy Transformer) or LIMPET 500. Two more stationary OWC projects have been approved by the Scottish Government, but are yet to be completed.

Islay, Scotland

Portnahaven

Problems Involving Wave Power

Power per unit length of a Wavefront The Equation for it is: PL =ρga2λ/4T

ρ is the density of the water (103 Kg/m3 ), a is the wave amplitude (half of the wave height), g is the gravitational constant (9.81 m/sec2), λ is the wave length of the oscillation and T is the period of the wave (how long it takes for one wave oscillation).

Power per unit length of a wavefront determines the available power for each wave.

Diagram of a Wave

Important Variables

Density Period

Amplitude

Wavelength

Example Problem

PL =ρga2λ/4T

You want to find the wavefront power with a wavelength of 100 meters. The period is 15 seconds and the amplitude is 7 feet. Use 10³kg/m³ as density. Using this data, find the wave power.

Solution

PL =ρga2λ/4T

P=((10³)(9.81)(7^2)(100))/((4)(15)) PL=801150 Watts = 801 kW

Another Example

The power of a wave is 190kW and the density of water is 10³kg/m³. The wavelength is 70 meters and the amplitude is 10 meters. Using this information, find the period in seconds.

Solution

PL =ρga2λ/4T

T=pga2λ/4P

PL=190kW=1.9*10⁵W

T=((10³)(9.81)(10^2)(70))/((4)(1.9*10⁵))

T=90.4 seconds

Sankey Diagrams

A Sankey diagram shows how energy is being transformed by using arrows where the thickness of the arrow represents how much energy there is being transformed or how much energy is going in. Sankey diagrams are used to show the proficiency inefficiency of a certain source of energy. Named after a man by the name of Captain Matthew Henry Phineas Riall Sankey. He first used this diagram to predict the energy efficiency in an ideal steam engine.

Sankey Diagrams

Efficient Wind Park

Wind Sankey Diagram

Betz's Law Losses: 40.7%

Electrical Generator Losses: 5-10%

Sub-systems losses: 5%

Availability Factor losses: 1-5%

Electrical Energy: 45-50%

Wave Sankey Diagram

Wave Sankey Diagram

A wave power generator relies on low-friction bearing material. If less energy is lost through friction, then more energy will be able to be used for electricity. Breakdown: Wave Power in: 100 units

Friction: 46 units

Electricity Lost: 12 units

Electricity: 42 units

Sources "Wind Energy Basics." Wind Energy EIS Public Information Center. Web. 6 Mar. 2012. <http://windeis.anl.gov/guide/basics/index.cfm>. "How Does a Wind Turbine Work?" Wind Program:. Web. 6 Mar. 2012. <http://www1.eere.energy.gov/wind/wind_animation.html>. "Wind Turbines." - Kinetic Wind Energy Generator Technology. Web. 6 Mar. 2012. <http://www.alternative-energy- news.info/technology/wind-power/wind-turbines/>. "Basic Features of a Wind Turbine." » » Etc4CA. Web. 6 Mar. 2012. <http://etc4ca.com/projects/basic-features-of-a-` wind-turbine/>. HowStuffWorks. Web. 6 Mar. 2012. <http://science.howstuffworks.com/environmental/green-science/wind-power1.htm>. "Battery and Energy Technologies." Hydroelectric Power Generation. Web. 08 Mar. 2012. <http://www.mpoweruk.com/hydro_power.htm>. House, Matthew. "Oscillating Water Column." Wikid Energy Funhouse. 22 Apr. 2009. Web. 7 Mar. 2012. <http://wiki.uiowa.edu/display/greenergy/Oscillating Water Column>. "Hydroelectric Power Generation." Battery and Energy Technologies. 2005. Web. 7 Mar. 2012. <http://www.mpoweruk.com/hydro_power.htm>. Johnson, Nicole, and Eric Olson. "What Is an OWC." Oscillating Water Column (OWC). 2010. Web. 7 Mar. 2012. <http://owcwaveenergy.weebly.com/>.

Sources (continued) http://www.esru.strath.ac.uk/EandE/Web_sites/01-02/RE_info/wave%20power.htm

http://practicalaction.org/docs/technical_information_service/wind_electricity_generation.pdf http://www.stormsurf.com/page2/tutorials/wavebasics.shtml "Understanding Coefficient of Power and Betz Limit." Kidwind Science Shack. Web. 9 Mar. 2012. <http://learn.kidwind.org/sites/default/files/betz_limit_0.pdf> Chiras, Dan with Sagrillo, Mick, and Woofenden, Ian. Power from the Wind. Text. 10 Mar. 2012.Canada: New Society Publishers, 2009. "Energy Degradation." PAC-IBPHYS. N.p., n.d. Web. 7 Mar 2012. <http://pac-ibphys.wikispaces.com/Energy degradation>. Koroneos C and E Katopodi. "Exergy analysis of the wind power hydrogen and electricity production.". Athens: Print. <http://ewec2006proceedings.info/allfiles2/0376_Ewec2006fullpaper.pdf>. "Who is this Sankey guy?." Sankey Diagrams. N.p., 12 Apr 2007. Web. 09 Mar 2012. <http://www.sankey-diagrams.com/who-is-this-sankey-guy/>. "Sankey Diagrams." Cyber Physics. N.p., n.d. Web. 05 Mar 2012. <http://www.cyberphysics.co.uk/general_pages/sankey/sankey.htm>. Michna, Paul. "Water Power Devices." Wave Power. Earth Science Australia. Web. 7 Mar. 2012. <http://earthsci.org/mineral/energy/wavpwr/wavepwr.html>. "Wave Power." Renewables in Scotland. May 2002. Web. 7 Mar. 2012. <http://www.esru.strath.ac.uk/EandE/Web_sites/01-02/RE_info/wave%20power.htm>. "Wells Turbine." Wikipedia. Wikimedia Foundation, 22 Feb. 2012. Web. 8 Mar. 2012. <http://en.wikipedia.org/wiki/Wells_turbine>.