MSE Energy

variability

China 282 GW

USA 118 GW

Germany 62 GW

some regions are more suitable but it also depends on politics

wind kinetic energy => rotor kinetic energy => generator from kinetic to electric energy

force on a plane is a pressure ovr a certain area (dynamic pressure, like holding your hand out of a driving car, rho " velocity^2 = pressure)

P~U^3

almost no power is harvested at low velocity but at high velocity a lot of power is generated

sun heats erath surface with intensity that depends on latitude

energy from sun is constant but some areas are more exposed than others

differences in air temperature and density drive wind forces

atmospheric air circulation is organized in 3 cells with internal circulation, from equator to poles: hadley cell, ferrel cell, polarcell; rise at equator and between ferrel and polar; remember corriolis => clock wise in northern hemisphere

those are the main driving forces, they are always there, additionally some local meteorological pheonomena but those are minor

Westerlies in north Europe, additionally presence of sea increases speeds locally => stable and strong winds hit fast

depends on average wind velocity

higher altitude = increased wind forces and speed

Excellent: > 6 m/s at 10 m height

the higher the wind speed at hub height, the better the resource class, better turbines can withstand more turbulence, also a measure of cost

best class (high wind, high turbulence): 10 m/s at hub heigt + can withstand 70 m/s gust (but it will not run anymore at this speed)

you want a regular terrain BEFORE your wind turbine, top of hill is nice; avoid turbulences before your turbine

you want a wind that is regular in direction and speed

more locally: influenced by opstacles like trees or buildings, if turbulence: less efficient and more vibration = more noise

so you want to be away from obstacles to have undisturbed laminar flow

avoid surface roughness like forest or cities = sea is nice

fluid in contact with a surface, is at rest, then the further from the surface the more the speed increases until it reaches undistrubed max velocity U_infinity

boundary layer defninition for undisturbed flow: thickness until velocity = 99% of U_infinity = inviscid region

turbulence makes increase lesss steep = higher velocity closer to ground but maybe lower overall velocity

left: in a valley: very constant wind directions high speeds

right: mountain top, high variability of directions and speeds

extracts kinetic energy out of wind

slows down wind but does not stop it

only that part of the air that passes through rotor disc is affected

Cp: ratio of power that wind turbine can extract and total power of wind

Cp max = Betz limit = 26/27, independent of kind of turbines etc. some turbines might come closer to Betz limit than others; assume infinite number of blades, incompressible fluid, no losses, steady state

even thoug velocity is ^3 and has a big impact, power will decrease on a mountain top compared to sea level due to density difference

= ratio between blade tip velocity and wind velocity

if TSR > 1 => blade is moved by aerodynamic lift like an airplane

TSR < 1 => blade is moved mainly by aerodynamic drag

high TSR = higher efficiency, higher noise levels, higher construction complexity

vertical axis wind turbines: omni direction, easy to mount at ground level; no tower needes; low rotation speed; no gearbox needed, less noise; some self starting problems; drag devices only capture 15% of energy, Darrieus up to 40%; no large scale commercial applications

horizontal axis wind turbines: fewer blades = higher tip speeds; optimum tip speed ratio approx 8, > 4 blades = loss of efficiency; normal efficiency 30%; lower cut-in wind speeds than vertical turbines

aerodynamic drag = lift induced drag (like airplane) + parasitic drag

parasitic drag = sikin friciton + pressure drag

drag is influenced by shape, viscous forces and surface, and lif that cerates vortices that increase drag

drag is key for stability of wind turbine

Wake losses: mechanical energy lost in wind turbine wake, especially at low TSR rates

Aerodynamic drag, even though it rotates the blades, it also dissipates energy, increases at higher TSR rates

finite number of blades; lowers the whole curve with regards to Betz limit

E.g. Eolienne: high number of blades => should be closer to Betz, but then resistance against wind increases => pole must be stronger etc = more losses => comprimize on number of blades and solidity

turbulences after blades

the first windmill will influence the following windmills due to wake, some energy will be lost in the wake and is not available for the second turbine

power vs wind speed, S-shape starting at cut in speed, reaches plateau at rated output speed, stop at cut out speed

cut in speed: no engagement below, you can overcome the rosistance but you cannot harvest power yet, no rotation

rated output power: max power, e.g at 14 m/s rated output speed

cut out speed: when turbine is turned so it has low exposure to wind to avoid structural damage (usually at 25 m/s)

depends on rotor area, type of aerofoil, number and shape of blades, cut in speed, TSR, speed of rotation, Cp, gearing and generator efficiency

savoinius: vertical, low efficiency, low TSR

Eolienne: horizontal, CP up to 0.3, low TSR

Darrieus: vertical, Cp up to 0.4, low to medium TSR <4 to 7

3 wings: horizontal, Cp uo to almost 0.5, TSR 5 - 11,

vertical axis turbine (like a vertical eye shape), driven by lift of wing profile

+ : gear box and generator on the ground

- not self starting, low power harvest, a lot of rotation close t oground where velocities are low

vertical axis, wings are just placed vertically on radial holding arms

technically simpler than Darreius, less costly but low efficiency;

hard to start and can have problems running in steady state

vertical axis, only drag forces, no lift (TSR < 1)

S shape with overlapping opening in middle or closed S shape

+ simple design, rotor is not sensitive to wind direction, easy self starting

sharf torque is pulsating and with sign inversion => So best place two savonius rotors one on top of each other with blades 90° shifted => steady rotation

Efficiency Savonius 19-23; Darrieus: 30-40

Power density W/m^2: S 175; D 470

Noise: S none; D 70 dBA

Vibrations: S none, D yes

RPM limit: S none, D yes

Start: S auto, D not auto

newest up to 260 m (Eiffel tower: 324 m)

blades are attached to hub

blade angle can  be adapted by pitch bearings

main shaft bearings brings rotation into nacelle by georbox => to generator and transformer

generator and transformer are on top in the nacelle

nacelle is fixed on pole by yaw bearings

nacelle is rotated by a motor, not by wind!

are usually hollow, mady by multiple different composite materials, (resin, fibre, wood, metal, ..)

=> light materials => low inertia => larger discs possible => harvest more energy

low provision for clean source of energy

no GHG emissions

locations

compatible with other land uses

reduction of costly transport of electricity

national security

conservation of water

reduced destructive mining

short commissioning time

cost effective

creation of jobs and local resources

intermittency of wind

good sites are often remote

noise pollution

aeshetics

turbine blades can damage wildlife

frequency of light and shadows

shortage of rare element (neodymium) which is needed for turbine magnets

high initial costs

no storage capabilities

wind turbine run at approx 50 dBA, inside a car is approx 80 dBA

noise is reduced quickly when distance to turbine increases

a few wind parks, some big single plants with > 1000 kW (mostly in valleys and mountains); Mont Crosin probably biggest, Jura 16 wind turbines

many small single plants (eher im Mittelland, on hills)

good wind quality (constant in speed and directions, few surface roughnesses etc)

high wind velocity

maximum power output of a plant

meaningful, but should be used with consideration and context