Wind Energy Exam 1-4

where does wind come from?

air movement in response to pressure gradients or differences

what causes pressure differences?

uneven solar heating of the earth’s surface; coriolis effect; wind circles along lines of constant pressure

how does the coriolis effect change air movement?

air moving toward the poles veers to the east while heading to the equation veers to the west

what is full dynamical downscaling?

analyzing wind patterns from a global, regional, and local perspective; a complete collection of wind patterns using an atmospheric mesoscale model

what are the key characteristics of the wind?

the temporal dimension, the spatial dimension; wind probability distribution function; air density; icing frequency

what aspect of the temporal dimension is measured in very short time scale (seconds)?

the domain of turbulence

what aspect of the temporal dimension is measured in short time scale (minutes-hours)?

wind direction and magnitude

what aspect of the temporal dimension is measured in mid time scale (12-14 hours)?

daily wind patterns associated with solar heating

what aspect of the temporal dimension is measured in long term scale (1-7 days)?

weather fronts

what aspect of the temporal dimension is measured in seasons scale (months)?

winter or wet seasons are traditionally considered more windy

what aspect of the temporal dimension is measured annually (1-10 years)?

hemispheric and global climate oscillations

for wind power plants projects, what is the spatial dimension of interest?

100m - 10km

for wind integration analysis, what is the spatial dimension of interest?

a wider range (up to 1000-10,000 km)

capacity factor equation

CF (%) = Annual production (MWh)/ 8760 x Installed Capacity (MW)

full load hours equation

FLH = capacity factor * 8760

what is the order of surfaces in terms of increasing roughness parameter?

water, field, town, forest

what is the order of surfaces in terms of increasing wind speed?

forest, town, field, water

how are the roughness and wind speed related?

inversely related, as roughness decreases the wind speed increases

wind speed equation

U(z) = u/k [ln z/z0 - psy]

(u = wind speed, z = height, z0= roughness length, u = friction velocity, k = von karmen constant ~0.4, psy = atmos. stability function)

what are the steps of a wind resource assessment campaign?

wind resource assessment, permitting, financing/due diligence, construction, operation and decommissioning

what are the components of a wind resources assesssment?

site identification, resource monitoring, wind resource analysis

what goes into site identification?

surveying a large region; using public data bases/resource maps; considering market conditions, capacity. constructability, etc.

what goes into resource monitoring?

involves measurement and characterization of wind to verify whether a sufficient resource exists to justify further investigation and to compare and rank different candidates

what goes into the wind resource analysis?

description of the wind resource at all relevant temporal and spatial scales to support the optimal placement and estimate energy production

what are some wind monitoring measurement instrumentation?

sonic anemometer, cup anemometer, wind vane, data logger

what is important for wind monitoring?

tower number and placement, instrument height, tower instrumentation

what are the steps for data analysis and resource assessment?

data validation, characterizing the observed wind resource, estimating the resource at hub height, climate adjustment process, wind flow modelling, uncertainties

mean wind speed equation

v = (1/N) sum(vi)

wind shear or rate of change in horizontal speed with height equation

v2 = v1 * log(h2/z0)/log(h1/z0)

((z0 is the surface roughness length)

turbulence intensity equation

T = standard deviation/ mean

wind power density equation

WPD = 1/2N * sum(pi x vi³)

air density equation

rho = P/RT = (353.05/T)*e^(-0.03417 * z/T)

speed frequency distribution and weibull parameters equation

p(v) = (k/A) x (v/A) ^ (k-1) x e^-(v/A)^k

what is also used to calculate wind shear?

wind power law

wind power law equation

v2/v1 = (h2/h1)^alpha

(alpha is wind shear exponent)

what is one benefit of computational fluid dynamics wind resource mapping?

estimating the wind resource and the effect of other turbines, wake effect

what is the annual energy production composed of?

wind speed distribution at hub height and the wind turbine power curve

what is the potential energy yield composed of?

gross energy yield at each site and the wind turbine wake modelling

who was the first wind turbine pioneer?

charles f. brush

who was the found father of the ‘theory’?

paul la cour

who made the first AC- wind turbine?

johannes juul

what are some of the wind turbine manufacturers

vestas, siemens, goldwind, GE, united power

what are some horizontal axis turbines (HAWT)?

triple bladed, multi-rotor, sail wing, counter rotating blades

what are vertical axis turbine (VAWT)?

drag (savonious, plates, cupped), lift (turbine, giro-mill), combinations (airfoil), deflector

what are the main components of a WECS structure?

nacelle, yaw mechanism, power cables, tower, grid-connected transformer, foundation, door, ladder

what are the main components of the nacelle?

rotor hub, blade tip, blade pitch, rotor blade, gearbox, low speed shaft, rotor brake, high speed shaft, coupling, generator, power converter

what is the standard for WECSs?

IEC 61400

what are the top blade manufactures?

LM wind power, tecsis technology, TPI composites, Sinomatech wind power blade company

what are the main mechanical components of WECS?

pitch, drive train- gearbox, yaw system, brakes, tower, foundation

what is the pitch system?

modifies the angle of attack of the blades in order to capture more or less power, used as aerodynamic brake

what is the purpose of the gearbox?

adapts turbine and generator speeds

what are the top gearbox manufactures?

windenergy AG, ZF wind power, Moventas, bosch rexroth

what is the purpose of the yaw drive?

orientates the nacelle and the turbine towards the wind

what are the types of WECS towers?

tubular steel tower, tubular concrete, lattice tower, three-legged tower, guy-wired pole tower

how is tower height related to blade radius?

tower height is approximately equal to blade radius + 40% (stiffness is a critical factor)

who are the top tower manufactureres?

DS SM, bladt industry, Titan group, CS wind corp.

what are the main electrical components of WECS?

generator, power converter, transformer, cables, switches and protection

what is the purpose of a generator?

convert mechanical energy into electrical power

what are the kinds of WECS generators?

induction generator (squirrel cage), doubly-fed induction generator (DFIG), synchronous generator

what are the top generator manufacturers?

ABB, siemen, ingeteam, elin motoren

what is the purpose of a transformer?

steps-up the generator voltage to transport the generated power with a lower current, therefore lower losses

what is the purpose of power electronics converters?

used to control the generator torque; couples fully/partially the generator magnitudes to the grid

given a stand still plate perpendicular to the wind speed, what is known about the forces?

large drag force, but not power (no motion)

given a moving plate perpendicular to wind speed, what is known about the forces?

less drag force at plate; Power = D*V (due to plate motion with speed V); speed seen from the plate is lower

given a stand still plate tilted to wind speed, what is known about the forces?

less drag force than perpendicular plate; lift force appears; no power

what is necessary to curve the streamlines to create lift in an airfoil?

a pressure gradient dP/dr = rho * V² / r

(r is the curvature of the streamline; V is the speed)

what creates a lift force?

the aerodynamic shape of the blade which changes the wind’s pressure field on the bottom and top of the blade

what is the relative wind velocity when the blade rotates?

the vector sum of the wind speed and the rotational speed of the airfoil seen from the blade

tip speed ratio equation

TSR = gamma = rotational speed x radius / wind velocity at blades = omega * R/ U

power in the wind equation

P = ½ x rho x area x U³

maximum theoretical usable power

P = ½ x rho x area x U³ x 16/27

Power equation

P = ½ x rho x area x U³ x Cp(TSR, angle)

what is the angle of relative wind equation

angle of attack + pitch