Energy Utilisation of Wind

Transcription

1 Ing. Pavel Dostál, Ph.D., Ostrava University 1 Energy Utilisation of Wind Choice of locality Energy and wind output Wind-power installations Wind-power installations: types and classification Basic parts of wind power stations Wind motors Wind motor accessories Pylons Safety of wind-power installations Choice of locality Economic utilisation of wind energy requires careful consideration about the location of a wind-power installation. The following are the most important factors influencing the flow and efficiency of wind energy: 1) Average wind speed 2) Wind flow frequency rate 3) Obstacles and how they influence the flow 4) Shape of wind-hit obstacle Average wind speed: Average wind speed in the Czech Republic is monitored and published by the Institute of Physics, the Academy of Sciences of the Czech Republic. Regional data are shown in the wind map. The figures are given as average annual speed in meters per second. Czech Republic Wind Map

2 Ing. Pavel Dostál, Ph.D., Ostrava University 2 Wind flow frequency of occurrence: To determine the output of a wind-power installation, average wind speed data are only an informative factor. The constant changing of the wind flow, which may occur even within very short intervals, requires that we also know the wind flow frequency of occurrence. Classic measurements taken every hour give us 8,760 values on average flow speeds a year. These data show the periods and speeds of wind flow and are used to draw a chart where the vertical axis expresses the wind frequency of occurrence and the horizontal axis the wind speed in meters per second. Wind speed frequency of occurrence chart for a given location Frequency of occurrence wind speed in locality 12 Frequency of occurrence in % Wind speed in m/s

3 Ing. Pavel Dostál, Ph.D., Ostrava University 3 Obstacles and how they influence the flow: The flow past an obstacle is affected by this obstacle a great deal. In particular, the obstacle reduces the speed of flow and affects its nature. How obstacles influence the wind flow 2 x vyska - double height vyska - height délka turbulenci je při rychlosti větru 8 12 m/s asi 20x delši než výška budovy - The turbulence length at wind speeds of 8 12 m/s is 20 times longer than the building height. Shape of a wind-hit obstacle Change in speed profile rychlostní profil - speed profile pozvolný vrch - gradual-slope hill stupňovitý vrch - stepped-slope hill zóna turbulence - turbulence zone oblast odtrženi - separation zone

4 Ing. Pavel Dostál, Ph.D., Ostrava University 4 Wind acceleration on a mounting ridge Wind-power installations Wind-power installations: basic types and classification 1. By axis of rotation Vertical axis installations

5 Ing. Pavel Dostál, Ph.D., Ostrava University 5 Horizontal axis installations 2. By rotor position Upwind installations vítr - wind Downwind installations Basic parts of wind power stations Wind motors these transform the wind kinetic energy to mechanical work. There are two basic working principles of wind motors mechanisms:

6 Ing. Pavel Dostál, Ph.D., Ostrava University 6 1. Resistance principle the exposed surface represents aerodynamic resistance to the wind flow, thus slowing the flow down and generating a force that is usually transformed to rotational motion. 2. Uplift principle the force acts across the direction of the air flow and is called uplift force. This category includes particularly propellers and wind wheels with horizontal axis of rotation. The blade section must have an uplift profile. To point 1) Resistance principle this principle is applied in cup anemometers, for instance, which are gauges to measure wind speed, or in Savonius rotors Cup anemometer and Savonius rotor To point 2) wheels. Uplift principle this category includes particularly propellers and wind Propellers In fact, propellers are wind motors with the highest possible efficiency. They consists of one to four blades; most common are two- or three-blade propellers. Propellers can have tip velocity ratio (the ratio of rotor blade tip speed to wind speed) equalling 10. However, the general rule is that this type of rotor reaches the maximum efficiency at tip velocity ratio 6. Compared to other wind motors, these tip velocity ratios are much higher and so propellers are called high-speed wind motors. Advantages of high-speed motors: Few blades, thus lower manufacturing costs than those of multi-blade rotors; The blade stress, caused by gusts of wind, is lower than that with other types of wind wheel because the blades are designed to much higher centrifugal forces. Disadvantages of high-speed motors: The initial torque generated by the propeller is very low, especially at low wind speeds, and so these machines either have a forced electrical start-up mechanism or have blades with adjustable longitudinal axis that are set in the initial position and re-adjusted to the working position after start-up.

7 Ing. Pavel Dostál, Ph.D., Ostrava University 7 Basic propeller types Vane wheels are low-speed wind motors usually consisting of vanes. The number of vanes is usually designed according to the wheel size and the required tip velocity ratio. The usual diameter of vane wheels is 5 8 meters. Unlike high-speed motors, these wheels reach the maximum efficiency at tip velocity ratio 1. The efficiency of low-speed motors is approximately 75% of that of high-speed motors. A dvantages of low-speed rotors More vanes give the rotor a greater start-up torque, so these rotors are almost ideal for water pumping, where the wind wheel rotor is directly linked to the pump. D isadvantages of low-speed rotors Unsuitable for power generation Only wind at speeds between 3 and 7 m/s can be utilised for generating energy Rotors are rather heavy because of steel bearing frames Significantly higher risk of wheel damage by gusts of wind Basic types of vane wheel

8 Ing. Pavel Dostál, Ph.D., Ostrava University 8 The moment factor curves of some rotor types by tip velocity ratio Wind motor accessories: 1) Body is the central constructional part of a wind power station. Under the safety cover of the body, there are a gearbox, brake, clutch, generator, bearings, and other machine parts necessary for the operation and mounting of the wind motor to the other constructional parts of the wind power station. 1) Gearbox Gearboxes are installed in wind power stations with great difference between the rotor nominal speed and the generator nominal speed, which is a common case from the practical point of view. Therefore, a gearing unit must be mounted between the wind motor rotor and the working machine to ensure the required speed. 1) Brake to regulate rotor speed or stop the rotor completely. Brakes are also useful for maintaining and servicing, when the rotor needs to be so secured that it could not rotate.

9 Ing. Pavel Dostál, Ph.D., Ostrava University 9 Wind direction alignment mechanism aligns the wind motor in the optimum upwind position so that the wind energy can be used best. In the past, there were no automatic alignment mechanisms and wind wheels had to be positioned manually, which is entirely insufficient for the maximum use of wind energy. Generator transforms the mechanical energy of wind to electrical energy. The concrete generator design must take into account how the generated electric power will be used. Arrangement of parts inside the body top down: BLADE HUB DISC BRAKE GEARBOX GENERATOR BODY FRAME FRAME PYLON Pylons Pylons are constructional parts that hold up the body and the rotor including all accessories necessary for the operation of a wind-power installation. The pylon design depends on the size and type of wind power station. Two pylon types, lattice and tubular pylons, are applied in wind power stations of high outputs. Tubular pylons are technologically more difficult to make than lattice pylons, but can house all control monitoring parts, unlike lattice pylons, which need to have a special rack. Today, the use of tubular pylons with small-size wind-power installations is gaining popularity. For such an application, thickwall tubes of large diameters are used.