The objective of this paper is to sketch, in a general context, influences on construction of
wind power plants and problems associated with them when choosing the right area for their
construction

Lukášek, Jan

Škorpil, Jan

DSpace at University of West Bohemia

51707-IC-1-2005-1-CZ-ERASMUS-IPUC-381WIND POWER ENERGY - INTERACTION OF THE ATMOSPHERE WITH THE ENVIRONMENTJan Lukášek, Jan Škorpil,ABSTRACTThe objective of this paper is to sketch, in a general context, influences on construction ofwind power plants and problems associated with them when choosing the right area for theirconstruction.1. INTRODUCTIONA turning wind power plant must belong to a few sights that delight every favourer ofalternative energy sources.This sight rarely appears to an observer in the Czech countryside and it is therefore consideredmore as a rarity if not a curiosity. This situation is partly caused in general awareness of laityeven specialists by not very well embodied knowledge of options of the alternative sourcesuse but also by weather conditions in the Czech basin. None of these two situations isfavourable. This paper, however, is not aimed at increasing knowledge of general public inthe field of alternative sources but on the contrary, it is focused on a very specific field,namely on the problems of wind power plants installation.When building a wind power plant, the only decision is alpha and omega - the right choice ofthe place. The right place for the construction of a wind power plant provides good energyprofits, few dead plates on account of unfavourable environmental conditions, briefly asatisfactorily operating project. On the contrary a wrong choice of the place leads slowly butnecessarily to fairly big financial losses. The Czech Republic does not have as convenientconditions for the use of wind energy as for example coastal countries (Denmark, GreatBritain), nevertheless there exist good areas in our country where it is profitably possible toinstall wind power plants. How to find out whether the area which seems to be good for theconstruction of a plant is really the right one?2. INFLUENCE OF THE ENVIRONMENTThis question can be answered by experts in the field of wind power energy. They usevery sophisticated mathematical models by the estimation of wind energy in a specific area.Even though those are well developed models, it is necessary to stress the word estimation onbehalf of externality. In despite of well developed models, everything is only a calculation, nomeasurement. In this field the same way as in other fields, the following thesis is valid:Calculation is as accurate as input values are. Have a more detailed look at the mentionedinput values which are related to the successful choice of the place.Flow represents a motion of mass particles which make the atmospheric mass. Thisvariable motion can be described by two values, namely by speed and direction. Theenvironment surely has an influence on speed and direction values.Air move is influenced in ground layers most markedly by the following items:− features of ground− cover of groundLook briefly what the mentioned terms mean.3.FEATURES OF GROUNDThe term "orography" is known better than "features of ground". Orography is a wordcompound of two words. "Oros" is a Latin word indicating a barrier or a hill, "graphis" meansa line or graphite.51707-IC-1-2005-1-CZ-ERASMUS-IPUC-382To the orography there can be included features and gradient of ground, which mean physicaldemonstrations of the environment risen from long time lasting geologic processes.Altitudinal inequality of the environment results in the change in direction and speed of airmass in the ground layer. The nearer the ground we are, the more significant the change is.Ground roughness can be divided into positive (hill, mountain, etc.) or negative (valley, steep,etc.) types. Interaction of these both basic types with the atmosphere has an effect on the flow.In general we can say that wind medium speed is changed above the roughnesses of thepositive even negative type. The speed change size is influenced above all by the geometry ofa barrier. The principle of speed increase and decrease can be explained by so calledaerodynamic action of an object. If any roughness is in the way of air flow, the flow willchange its dynamics and thereby the speed will change as well. The further from the groundwe are, the smaller influence the orography has. There is no surprise that the importance oforography influence grows up with the growing altitude of ground roughness. What exactlyhappens if the flow meets ground roughness? The flow collides with a barrier, loses itsdynamics and in result of it the motion is slowed down. Not only flow slowing down canhappen but also the contrary effect.We all may know wind speed increasing on a hill. The shape of a hill generates places withdifferent air density. The biggest concentration is on the top of a hill. At the moment whenflow gets behind a hill top, it means to the area with smaller space limitation, expansion andinternal pressure decrease is reached. As a result the wind speed immensely increases. Thiswind increase is in English literature called Speed-up effect. From above mentioned it resultsthat the highest speeds cannot be expected on the windward side before or on hill tops but asfar as behind the hill top on the leeside. This result is not valid every time, it depends verymuch also on the side slope, wind speed, temperature of the environment and other factors.Orography in itself essentially influences behaviour of the ground layer of the atmosphere.Let´s describe one of the special orographic cases - a barrier. Everything what markedlysurmounts surrounding ground and cannot be classified as a ground roughness is classified asa barrier of flow. It is possible to say that the barrier is in many cases an object of man-madeorigin, e.g. a building, chimney or another high construction.We are interested in barriers due to the similar reason as we were dealing with the abovementioned parameter of the environment. We are interested in the influence of a building onthe flow and direct connection with the rise of turbulent flow.To be able to define the influence of a barrier on the flow we must describe its evidentparameters well. It is not enough to define only proportions of the object. An importantparameter when investigating the influence on the flow form is e.g. surface permeability. It isa ratio of poruses surface to total surface of the object. If the surface permeability is high, thepermeability of the object is huge. For example an iron grate must have a smaller influence onthe form of ground-layer atmospheric flow than a stone wall of the same size. If we choose aninteresting wind place, we shouldavoid a place with a big barrier in itsneighbourhood. Anything elsecannot be worse for the wind powerplant operation than turbulent flow.In the area of  turbulent flowwind speed changes suddenly.Random speed changes have anegative impact on wind-millmotors. The place affected byturbulent flow goes up behind thebarrier approximately to triple of its51707-IC-1-2005-1-CZ-ERASMUS-IPUC-383height, so rotor near the barrier must be placed higher in order not to be subjected to beats andvibration whereby financial demands of construction of the power plant body tube grow up.The influence of turbulence becomes weak with the growing distance from the barrier.4. COVER OF GROUNDAnother but certainly indispensable is so called influence of ground cover. In technical,meteorological and building field the cover of ground is characterized by so called roughnessof ground. If it concerns the specification of categories in term of ground roughness, everycountry has developed its own table of roughnesses and uses different types of roughnessinfluences on the flow. These tables differ a little bit. The following table is used in the CzechRepublic.No. Classification Z0 [m]0  Seas or shores exposed to high sea 0,003I  Lakes or flat areas with insignificant green and no blocks 0,01II  Areas with low greens as grass and separated barriers (trees,buildings) whose distance is more than 20 heights of the barrier 0,05IIIAreas evenly covered by greens or buildings or with detachedbarriers whose distance is maximum 20 heights of the barrier (asvillages, suburbs, continual forest)0,3IV  Areas in which at least 15% of the surface is covered by buildingswhose average height is more than 15 metres 1,0This table contains data about the roughness made on the basis of the construction of so calledwind logarithmic vertical profile. This profile records vertical changes of wind speed causedby surface differences.=0ln)(zzuzuκz0 is surface roughness parameter, κ is „von Karman“  constant (κ ≈ 0,4) and u is dynamic(friction) speed. The assumption of the validity of the wind profile logarithmic definition is aneutral thermal stratification of the atmosphere (air temperature does not change with theincreasing altitude) with a small correction dedicated to the deviations from this basic stagecaused by instability of the atmosphere.What is the imagination of it?In the following picture thereis illustrated a vertical profileof the air at the moment whentransiting from a flat to roughsurface. As it is evident fromthis picture, during thetransition from grass to roughstony ground there happens aradical reduction of the windspeed not only in theneighbourhood of the groundbut subsequently also at higher51707-IC-1-2005-1-CZ-ERASMUS-IPUC-384levels. If we substitute roughness by e.g. grown forest, the change caused just by theroughness can achieve unexpectedly big values. Choosing the place of a wind power plantconstruction should take this influence into account as well. Certainly a bad choice will be toplace a power plant among grown trees, near the forest or on the meadow surrounded bygrown tree species from three sides.5. CONCLUSIONIs it possible to say what environment is the most suitable for wind power plants construction?The most interesting areas are medium steep unwooded shores, standalone unwooded hills,water levels... simply the places where nothing is in the way of flow and where acceptableflow acceleration happens due to appropriate conditions.The objective of this paper was not to describe all details about the relations of the flow ofatmospheric ground layer and landscape in a complex way but to show the fact howsignificant role is played by the right choice of the place of wind power plant construction.Only two most significant elements of all were shown here. By the right calculation of thesefactors during area choosing total energy and financial yield of wind power plants can besignificantly influenced.This paper was written under solving science project GAČR 102/06/0132   6. LITERATURE[1] RYCHETSKÝ, V.; JANOUŠEK, J.; PAVELKA, J.: Větrné motory a elektrárny,Vydavatelství ČVUT, Praha, 1997.[2]     LUKÁŠEK J., ŠKORPIL J.: Speed and unit power wind maps. In: Power engineering:         15th international expert meeting – Maribor: University of  Maribor, 2006 – ISBN  86-         435-0772-5[3]    MÉSZÁROS, A.:  Sustainable energy systém our futurem requirement. In: Distributed         Power Systéme 2004. Plzeň  ZČU 2004, ISBN 80-7043-283-7.Authors´ address:prof. Ing. Jan Škorpil, CScIng. Jan LukášekDepartment of Electric Power Engineering and EcologyUniversity of West Bohemia in PilsenUniverzitní 8306 14 PLZEN Czech RepublicE-mail: skorpil@kee.zcu.cz lukasekj@kee.zcu.cz

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Wind power energy: interaction of the atmosphere with the environment

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Wind power energy: interaction of the atmosphere with the environment

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