Topic 8: Wind Energy

Components of a Wind turbine

-Foundation -Tower -Rotor -Nacelle -Gearbox -high speed shaft -Generator -Control system -Yaw mechanism -Brakes

Types of offshore wind turbine foundations

-Gravity based support -Monopile support structure -Tripod support structure

Turbine characteristics

-rotor diameter up to 120 m -Hub height up to 120 m -Peak electrical up to 8 MW now up to 10 MW forseen Cut in windspeed typically 3 to 4 m/s Rated windspeed typically 15 m/s Cut out windspeed typically 25 m/s Maximum Efficiency achieved at 11 m/s typically

Tell me about the land requirements for a 1,000MW(e) power plant.

-turbines are generally spaced 3 rotor diameters apart within rows, and the rows are spaced 10 rotor diameters apart -the spacing can vary depending on the type of land and the location of the wind farm -Land required: 50-150km2 Nuclear plant only requires 1-4km2

Efficiency of a Wind turbine

1. Aerodynamic efficiency (ratio of mechanical power of the rotor to wind power) 2. Mechanical efficiency (ratio of mechanical power of the generator axis to the mechanical power of the rotor axis) 3. Electrical efficiency (ratio of electrical power fed into the grid to the mechanical power of the generator axis) -Betz' law 59.3% efficiency lost by turbine slowing down when 2/3 of its original speed Real turbine peak value 44% average 25% -Atypical mechanical efficiency is 96 to 99% -Atypical electrical efficiency is 96 to 97%

What are the steps involved in the design and building of an onshore wind farm?

1. Understand Your Wind Resource 2. Determine Proximity to Existing Transmission Lines 3. Secure Access to Land 4. Establish Access to Capital 5. Identify Reliable Power Purchaser or Market 6. Address Sitting and Project Feasibility Considerations 7. Understand Wind Energy's Economics 8. Obtain Zoning and Permitting Expertise 9. Selection of Turbine 10. Secure Agreement to Meet Operating and Maintenance Needs

What is Betz's law?

Betz, a German physicist, in 1919, theoretically determined that a wind turbine can only convert 16/27 (59.3%) of the kinetic energy of the wind into mechanical energy by turning a rotor - 'Betz Limit', it is the maximum efficiency of a wind turbine

What is the difference between availability factor and capacity factor?

Capacity factor: the actual energy output for the year divided by the energy output if the turbine operated at its rated power output for the entire year. -your average energy output / the maximum energy output capable of the system. Most systems are not operating at the full level capacity Availability Factor: Reliability issues and maintenance, scheduled or unscheduled. Other factors include the design of the installation, its location, the type of electricity production and with it either the fuel being used or, for renewable energy, the local weather conditions ranging from 20% to 40%

When we think about the cost distribution of various components of a wind power system, what averaged % of total cost do the actual turbines account for?

For onshore systems: the turbines account for 64-84% of the cost. For offshore systems: the percent of turbine cost is around 44-50% of the total cost (higher maintenance and installation fees outweigh the turbine cost). In general, offshore turbine systems cost around 20% more than onshore systems.

Weibull distribution function

Gives us the probability of a windspeed a curing per unit of wind speed intervals

Wind turbines can be divided into two categories based on the axis about which the turbine rotates. What are these called, and how are they defined?

Horizontal Axis: The blades of horizontal-axis wind turbines spin in a vertical plane. During rotation, blades move more rapidly over one side, creating a low pressure area behind the blades and a high pressure area in front of it. The difference between these two pressures creates a force which causes blades to spin Vertical Axis: The blades of vertical-axis wind turbines spin in a horizontal plane. VAWTs have the main rotor shaft running vertically. -Allows generator and gearbox to be placed on the bottom, requiring no central tower to support the turbine. Allows the turbine to be oriented in any direction. Requires lower and more turbulent air, resulting in lower energy.

Wind can be unreliable in some locations. What are the consequences of this effect on a power company's generating capacity?

Intermittency of wind: 1.The production of electricity by many projects during off-peak hours, which I had to over generation problems 2. When's power as a non-dispatchable must take resource, transmission line overlords 3.Shifts in power generations among fleets of wind turbines, can cause voltage collapse within a winter project -The intermittency issue could be addressed by having back up generation, and smart grid design that allow areas with larger wind resources to spread their power capabilities over larger geographic areas

Impacts of wind farm on the weather and climate

Large wind farms have a noticeable effect on regional winds, changing heat, moisture in atmosphere, and surface air temperature in the region

Wind turbine aerodynamics

Not a pushing force like a lift of an airplane wing that makes rotor rotate High pressure in front low pressure behind

Variable speed generators

Rotation rate of rotor varies with wind speed from 8 rpm to 16 rpm • Results in less stress on the structure and more uniform variation in power output (issues in wind energy) • Requires more complex electronics and gearbox to always produce electricity at the fixed grid frequency

Synchronous Generators(not as common for wind)

Synchronous generators are controllable by governors which monitor system frequency and adjust prime mover input to bring correction to frequency movements synchronous machine's rotor is closely coupled to the power system and therefore available for immediate conversion to power

How doe we express the kinetic energy (KE) of the air stream?

The amount of energy captured by the rotor depends on the density of the air, the rotor area, and the wind speed KE = 1/2mv2 = 1/2 Pa Va2 where, m is the mass of the moving air, Pa is the density of the air, and Va is the volume of the air parcel Units are joules

Discuss noise generation from wind turbines.

The danger of hearing damage from wind turbine low-frequency emissions is remote to non- existent. However, the annoyance is often connected with the periodic nature of the emitted sounds rather than the frequency of the acoustic energy At 500 m it could mage from a quiet bedroom (35dB) to a busy road at 5km/h(45dB) sound intensity decreases rapidly with distance from the source. In town it would be quiet but in rural areas it might be the most significant source of noise

What is the wake effect and how does it occur?

The interference of a turbine by a downwind from another turbine is called the ____________ This occurs when wind turbines are closely spaced. This is important because the closer the turbines, the stronger the effect; Thus, you want them spread out. But consequently, the further the wind turbines are spread out, the more land you require for the windfarm.

Capacity factor for wind

This is the mean power output of the turbine divided by the peak power output

Characteristics of wind

Variation of mean wind speed with height Variation of turbulence intensity with height

Asynchronous induction generators

When the rotor of the generator rotates faster than the stator, a strong current is induced in the rotor • The harder one cranks on the rotor, the more power that is transferred as electromagnetic force to the stator, converted to electricity, and fed to the grid • The difference in the rotation speed between no power and peak power is about 1%, but this slip reduces stress on the rotor and smoothes out power variations

Offshore wind farms

When turbines mounted on the seabed and water up to 50 m deep double or triple the cost of onshore wind turbine

Describe the forces and factors that shape the occurrence of wind (see sec 1.2, Vol 2).

Wind blows due to the uneven heating of the atmosphere by the sun, the irregularities of the earth's surface, and rotation of the earth. Wind flow patterns depend on the earth's terrain, oceans, and vegetative coverage. Locally, buildings, plants and mountains control the wind pattern and also the speed.

Is there a limitation on how deep a wind turbine could be installed in the sea?

Wind turbines may be mounted on the seabed in water up to 50 m deep. As could be assumed, the costs increase dramatically as depth to sea floor and distance from land increase.

Tall towers on a horizontal turbine. Advantages and disadvantages?

advantages: • better stability of the structure. • The ability to pitch the rotor blades in a storm minimizes the damage. The use of a tall tower allows access to stronger wind in sites with wind sheer and placement on uneven land. • The manufacturing cost can be less because of higher production volume, larger sizes and, in general, higher capacity factors and efficiencies. Disadvantages: • tall towers and long blades (up to 180 ft long) are difficult to transport, • higher install costs, and • higher maintenance costs.

Rated output power and rated ouput wind speed

typically somewhere between 12 and 17 m/s, the power output reaches the limit that the electrical generator is capable of.