Technical Director INENSUS GMBH. 01 Wind Energy Basics 02 Components & functions of small wind turbines 03 Service and maintenance

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1 1 Energy - Basics & Technology 2 AGENDA 01 Energy Basics 02 Components & functions of small wind turbines 03 Service and maintenance 1

2 3 Energy source The sun Solar Energy Direct usage Solar energy Photovoltaic Solar collector Indirect usage Surrounding heat Passive heat usage with heat pumps Different heating of air mass wind energy power plants Ocean waves/ streams Wave energy Growth of plant Biomass fire fire Evaporation of water, rainfall on higher areas Hydropower Storage power station Running water 5 Comparison wind and hydro power Form of energy Formula energy Kinetic energy of the air in motion Hydro power Potential energy of the water Density of working fluid Energy density low high kg/m³ 1000 kg/m³ relationship quadratic linear 2

3 6 Rotor operating principle (1) No production Rotor 4 m/s 4 m/s 7 Rotor operating principle (2) Power production Rotor 1/3 * 4 m/s 4 m/s 3

4 8 Rotor operating principle (3) Energy of the air in motion kinetic energy P wind = = time 1 2 m t v 2 P wind P wind 1 = ρ A v 2 ( ) 2 1 = ρ A v 2 3 v Power depends on 1. Air density 2. Rotor surface 3. velocity (3 rd power) 9 Rotor operating principle (4) Limits of energy conversion Rotor Albert Betz: energie und ihre Ausnutzung durch mühlen (1926) Maximum utilization for lift-device rotors if v = 1 v 2 3 degree of harvesting 1 v 1 v 2 = c P, Betz 59% 4

5 10 Rotor operating principle (4a) Background Betz s Law assumption: massflow rotor wind : power : v m& P = = = ρ 1 4 v 1 + v 2 2 v 1 + v A 2 2 = 1 m& v 2 ρ 2 2 ( v ) 2 ( + v ) ( v v ) Av 1 power : P = ρ 0 A v Rotor operating principle (4b) Background Betz s Law P_/P_0 0,7 0,6 0,5 0,4 0,3 0,2 0,1 0,0 0,0 0,1 0,2 0,3 0,4 0,5 0,6 0,7 0,8 0,9 1,0 v_2/v_1 5

6 12 Technical usage system losses P WEC 59% = P wind cp, Betz η η 70 90% rotor 80 90% η generator 90 95% gearbox η 90 99% electronics Physically usable Aerodynamic and mechanic losses Electrical losses 13 Rotor types (1) drag devices Operating principle rotor blade evades the wind dragforce 2 = c 2 Av - Low rotor speed - Low efficiency + simple rotor blades + much torque at stand still Hau: kraftanlagen S ρ 6

7 14 Rotor types (2) lift devices lift force - Low torque at stand still - Complex and expensive rotor blades + high speed + good efficiency Rotor blade drag force 15 Rotor types (3) Savonius Rotor Also with more blades Rotor blades twisted or two rotors in one + good start-up behaviour + low noise (low rotor speed) + much torque from standstill - Expensive geared generator - Low efficiency 7

Self start-up only with more then 2 blades Alternatively: combination with Savonius or

8 17 Rotor types (4) Darrieus Rotor Lift force Lift force + low noise (low rotor speed) + no direction alignment necessary - More expensive generator - Expensive rotor construction - Self start-up only with more then 2 blades Alternatively: combination with Savonius or motor start-up - High inertia - Inefficient rotor surface usage 18 Rotor types (4a) Darrieus Rotor 8

9 19 Rotor types (4b) Darrieus Rotor 20 Rotor types (5) 3bladed horizontal axis + lightweight construction + simple generator connection + good usage of rotor surface + high speed generator - A bit more noise - direction alignment necessary - Low torque at stand still 9

10 21 Rotor types (5a) 3bladed horizontal axis 22 Rotor types (5b) 3bladed horizontal axis 10

11 23 Rotor characteristics (1) tip speed ratio λ = blade tip speed wind speed Drag device λ < 1 Lift device λ > 1 Slow running λ < 2.5 Fast running λ > Rotor characteristics (2) comparison of rotor types 0,5 coefficient of power cp 0,4 0,3 0,2 0, tip speed ratio 11

12 25 Rotor characteristics (3) synthesis to power curve Power curve Rotor power [W] v=10 m/s v=12 m/s v=14 m/s v=8 m/s v=6 m/s v=4 m/s Rotor speed [rpm] [m/s] 26 Rotor characteristics (4) power curve Rated power power 3 ~v P P WEC Power limitation Technical losses Most frequent wind speeds speed [m/s] 12

13 27 What is my wind speed? Beaufort number v [m/s] v [km/h] Impact 1 < 1,6 < 5 Smoke drift indicates wind direction 2 < 3,4 < 11 Leaves rustle 3 < 5,5 < 19 Small twigs constantly moving 4 < 8,0 < 28 Dust and loose paper raised 5 < 10,8 < 38 Branches of moderate size move 6 < 13,9 < 49 Large branches in motion 7 < 17,2 < 61 Whole trees in motion 8 < 20,8 < 74 Some twigs broken from trees 9 < 24,5 < 88 Some branches break off trees 10 < 28,5 < 102 Trees are broken off or uprooted 11 < 32,7 < 117 Widespread damage to vegetation 12 > 32,7 > 117 Very widespread damage to vegetation 28 Annual average wind speed? frequency 30% 25% 20% 15% 10% 5% v=10m/s v=7,5m/s v=5m/s v=2,5m/s p [W/m²] specific power[w/m²] 0% wind speed [m/s] 13

14 29 Direction alignment Needed for plant with horizontal axis Most common technical solutions: 1. vane Rotor in front of the mast (upwind) 2. Rotor itself behind the mast (downwind) Electrical azimuth drive for rated power > 10kW Small side-rotor Problem Too small vanes not effective Airflow on downwind rotor disturbed by the mast 30 Limitation of rotor power (1) reducing the active rotor surface (furling) Rotor a 1. Lateral turning out of the wind 2. Vertical turning (helicopter position) Depending on rotor thrust Eccentric bearing Restoring force/device needed End stop and damping needed Problems Centrifugal forces delay furling Higher rotor speeds extremely slow down function Only coarse control 14

15 31 Limitation of rotor power (2) reducing the active rotor surface Rotor 1. Bending of rotor blades, restoring through own elastic force 2. More seldom with hinges and springs Only suitable for downwindrotors Active principle of an umbrella Faster as furling, bit better power control In some systems complicated mechanics 32 Limitation of rotor power (3) stall effect speed > maximum permissible wind speed: increasing of load on rotor -> slowing down of rotor speed Rotor blades are twisted along their axis and allow gradual stall from too steep angle of resulting wind speed vector Wikipedia Problem Generator needs additional reserve power Rotor blades need more careful design effort Loss of load or failure of electrical system causes failure of stall braking 15

16 33 Limitation of rotor power (4) active blade angle control pitch Active blade angle control Small wind turbines mostly use mechanical systems with centrifugal force depending on rotor speed with springs In some systems also in combination with rotor thrust Problem Mostly too expensive for small wind turbines Complicated mechanics Continuous control needed Lot of effort needed to fulfil safety requirements 34 Generator (1) Requirements & characteristics Extremely low startup- / cogging torque High efficiency at different speeds High torque in short-circuit (if generator part of the safety system) Low maintenance bearing Brushless construction Bearings capable to carry forces and weight from the rotor Stiff characteristic if active electronic power converter or soft characteristic if battery charging system Each generator can only generator AC-current, DC current from rectifier Only 3 phases allow constant torque and Wikipedia power per rotation Frequency of AC current proportional to rotor speed 16

17 35 Generator (2) Synchronous, salient-pole Wikipedia 36 Generator (3) Synchronous, non-salient pole Wikipedia 17

Connected in parallel or series Higher number of poles for higher frequency at lower RPM

18 37 Generator (4) Synchronous, salient-pole with slip rings Wikipedia 38 Generator (5) winding connection ings connected in star or delta ings with several connections Connected in parallel or series Higher number of poles for higher frequency at lower RPM P = 1 : 3000 RPM P = 3 : 1000 RPM P = 5 : 600 RPM P = 10 : 300 RPM 18

19 39 Synchronous generator (1) single phase model U R X U P (n) No load voltage proportional to rotor speed n Loaded generator: Ohm losses (heat) from winding resistance with voltage drop Additional voltage drop from synchronous reactance X depending on frequency = rotor speed U P (n) defined by the magnetic circuitry Reaches a saturation level R and X defined by the winding and the air gap 40 Synchronous generator (2) synchronous permanently excited 3phase current Continuous power delivery Efficient energy transmission using 3 wires (enables long distances, saves additional return conductor for 1phase AC or DC) Robust and cheap generator design Permanently excited Generator braking capability at loss of external power supply No slip rings for excitation current -> no wearing parts Cogging torque at start-up may be problematic Rare metals for high power magnets getting rare and costly Magnets can demagnetize if heated above their Curie- Temperature (150 to 200 C) 19

20 41 Synchronous generator (3) synchronous permanently excited Idle voltage and frequency are proportional to rotor speed variable voltage at different wind speeds Variable frequency not problematic, rectification for further usage Adaptation of the load according to voltage or frequency required for optimum efficiency Voltage has a certain temperature dependency (±10%) Synchronous generator (4) measured open circuit voltage (example) Idle voltage AC and DC [V] V_AC V_DC y = 1,81x y = 1,34x Generator speed [rpm] 20

21 43 Gearbox Adaptation of relatively low rotor speed to generator speed Additional effort, allows smaller generator Problem Oil change / regular inspection of fill level Additional vibration from meshing Higher start-up-torque from stand still Start-up-behaviour depending on oil temperature 44 Brake Needed depending on safety concept if generator fails For stopping the rotor completely Different concepts operated by centrifugal force Operated by hydraulics / cable Electrically kept open -> stops automatically on grid loss Bi-stable electrically switched brake Not restored automatically after severe errors 21

22 45 Safety and control systems Rotor speed monitoring Generator monitoring Manual shutdown Emergency stopping Detection of vibration as result of unbalance or ice building up 46 Systems for battery charging (1) overview 3~ Main switch Charge controller inverter DC consumers rectifier Charge controller Battery 22

23 47 Systems for battery charging (2) operational principle G 3~ Generator rectifier battery 48 Systems for battery charging (3) summary Generator delivers 3~ AC current Variable frequency and variable voltage Generator in idle mode at low rotor speeds As soon as rectified generator voltage is higher then batter voltage, current flows to the battery Battery limits the rise of generator voltage Sufficient wind enables speeding up of the rotor, more current flows to the battery Generator operates like a bike dynamo, voltage is independent of generator speed Good loading of the rotor according to actual wind speed Battery is charged Overcharge damages the battery, hence wind charge controllers are mostly overcharge protectors dissipating surplus power Each rated battery voltage needs special generator winding and charge controller 23

stations Traffic control Research stations Pumping stations

24 49 Systems for battery charging (4) fields of operation Rural electrification Holiday flats caravans boats Weather stations Traffic control Research stations Pumping stations Base transceiver stations 50 Polyphase rectification Wikipedia 24

25 51 Simple battery charger (1) schematic 52 Simple battery charger (2) photo 25

53 Systems for feeding to the grid (1) overview source: www.sieb-meyer.de 1. Small wind turbine 2. Overvoltage protection 3. Disconnecting point 4.

26 53 Systems for feeding to the grid (1) overview source: 1. Small wind turbine 2. Overvoltage protection 3. Disconnecting point 4. Grid-tie inverter 5. Ballast resistor 6. Disconnecting point 7. Grid connection 54 Systems for feeding to the grid (2) electric energy conversion source: 26

27 55 Systems for feeding to the grid (3) summary Generator produces 3~ current Variable frequency and variable voltage AC current rectified Supply of the inverter at its minimum input voltage Feeding to the grid a.too low rectified generator voltage boosted to about 400V DC and inverted to 230V, 50Hz b.inversion of rectified generator voltage, transformation to higher grid voltage via transformer Permanent monitoring of grid parameters according to EN / VDE 0126, automatic disconnection required Alternative loading of the generator during grid monitoring before feeding to the grid and while grid errors required to prevent speeding up of the rotor 56 Systems for feeding to the grid (4) fields of operation Self supply Feeding to the house electrical system Energy consumption with the existing AC appliances Coincidence of generation and consumption is low Only operating of variable power consumers (mostly heating) can absorb surplus power All surplus power not consumed flows back to the grid without payment (normal electricity meters) Feeding to the grid according to various renewable energy legislation Separate electricity meter required Payment of the energy produced Additional costs for separate meter and annual metering costs Operation in isolated networks Off-grid system with battery, inverter, etc. only economical if no public utility available 27

28 57 Variable voltage generator constant grid voltage boost converter Wikipedia 58 Systems for water pumping Configuration Dray devices or western windmills directly drive piston pumps, simple system but relatively low overall efficiency Improvements in combination with highly efficient inverter controlled electric pumps with or without battery storage By-passing of the electricity storage problem by means of storing the pumped water 28

29 59 Systems for heating Overview Electrical heating Air heating Hot water production with electrical heating cartridges Problem: heat absorption capacity of water in heating systems is limited, rotor must shutdown before water starts boiling Direct connection of a heating resistor to the generator not possible, rotor will not start-up at all Electronic power controller needed Direct heat generation With a water brake instead of an electric generator Heating circuit with flow line and return line to/from the wind turbine Anti-freeze protection needed 60 Mast (1) Mechanical loads Load on the top of the mast from rotor thrust Maximum value for conventional rotors (EN ) Weight of the nacelle negligible (except erection) Resonance from generator and rotor blades For small horizontal axis wind turbines with 3 blades not problematic Free standing masts more susceptible than guyed masts Very strong induced force from vertical axis rotors Mostly not included in the scope of delivery for very small wind turbines Knowledge of the soil conditions 29

61 Mast (2) Overview Materials Steel Wood Concrete Design Free standing tubular Free standing lattice Guyed tube/lattice Foundation On/in ground

30 61 Mast (2) Overview Materials Steel Wood Concrete Design Free standing tubular Free standing lattice Guyed tube/lattice Foundation On/in ground on buildings (induced vibration!!!!) Erection With tilt up tower Several kinds of self erection With crane 62 Mast (3) Erection with tilt-up tower 30

63 Service and maintenance Small wind turbines are usually relatively maintenance free, but: Operator has to be permanently aware of risks Stop wind turbine before exceptionally high wind speeds

31 63 Service and maintenance Small wind turbines are usually relatively maintenance free, but: Operator has to be permanently aware of risks Stop wind turbine before exceptionally high wind speeds Regularly check: Twisted cables? Safety functions operational? Screws properly fixed? Bearings OK? Different noise from damaged or dirty rotor blades? Vibration? Oil leaks? CONTACT INENSUS GmbH Am Stollen 19 D Goslar Germany Tel +49 (5321) Fax +49 (5321) INENSUS West Africa S.A.R.L. 10, Avenue Faidherbe, B.P. 397 Dakar Sénégal 31

Small Wind Energy - International Standards. Small Wind Energy International Standards. Overview

1 Small Wind Energy - International Standards 2 Small Wind Energy - International Standards Overview EC machinery Directive IEC 61400-2 IEC 61400-11 IEC 61400-12-1 1 3 EC Machinery Directive (1) 2006/42/EC