Sretna nova godina 2012!

Happy new year 2012!

Alles Gute für das Neue Jahr 2012!

Feliz año nuevo 2012!

CROATIAN CENTER of RENEWABLE ENERGY SOURCES (CCRES) 

POWER-GEN Middle East 2012

Under the Patronage of His Excellency Dr. Mohamed bin Saleh Al-Sada, Minister of Energy and Industry

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CROATIAN CENTER of RENEWABLE ENERGY SOURCES GIVES YOU AN OPPORTUNITY TO DISCOVER NEW TECHNOLOGIES FOR OPERATONAL FLEXIBILITY & EMISSIONS CONTROL IN THE MIDDLE EAST CLICK HERE to register for Middle East's premier POWER conference

HIGH-LEVEL INTERNATIONAL SPEAKERS

POWER-GEN Middle East 2012 will feature a wealth of knowledge and experience offering insights into new power technologies to achieve cleaner plant operation through emissions control, greater operational flexibility and efficient design and operation by renowned specialist professionals from around the globe.

Confirmed chairs and speakers to date include:

♦ Adnan M. Fakro, Deputy Chief Executive Distribution and Customer Services, Electricity & Water Authority, Kingdom of Bahrain

♦ Raad Al-Haris, Deputy Minister of Electricity, Iraq Ministry of Electricity, Iraq

♦ Jamal Al Ebrahim Al Khalaf, Executive Managing Director, Qatar Power Co., Qatar

♦ Aref Hasan Abdulla, Board Director, Deputy General Manager, ADWEA (Al Mirfa Power Co.), U.A.E.

♦ Fouad A.Sheikh Abdulla, Station Manager, SPWS, Electricity & Water Authority, Kingdom of Bahrain

♦ Vauhini Telikapalli, Director-Product Development-Carbon Capture and Storage Business, Alstom Power, Switzerland

♦ Andrew Baxter, Product Manager, GE, USA

♦ Alessandro Clerici, Chair of Study Group "Energy Resources and Technologies", WEC, Italy

♦ Willibald Fischer, Program Director 8000H, Siemens AG Energy, Germany

♦ Emad Ragaban, Bus Development, Saudi Aramco, Kingdom of Saudi Arabia

♦ Sayed Hassein Miri, Process & Chemical Expert, Mapna Group Company, Iran

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UP-TO-DATE CONFERENCE TOPICS

The event will look at  why advanced power technologies are recognized as an ecological and economic necessity and are increasingly being practiced globally around the world.

The conference comprises dedicated technical tracks that focus on advanced technologies to achieve fuel and cost efficiency covering such topics as:

♦ Boiler Technologies - a look at efficient design and operation of boilers and HRSGs that will offer plant operations insight into state-of-the art plant technology

♦ Technologies for Operational Flexibility - informed perspectives on how power plants can achieve greater operation flexibility including industrial cogeneration and grid stability applications, combined cycle power plants, recent developments in gas turbine fuel flexibility and optimizing power generation life-cycle cost

♦ Renewables & Environmental Technologies - insights into cleaner ways towards plant operation through emissions control technologies and green power solutions including solar combined cycles and seawater FGD technology

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EVENT SNAPSHOT

♦ From 6-8 February 2012, POWER-GEN Middle East 2012 will bring together representatives within the power industry from across the globe to explore the latest technologies to meet regulatory standards as well as practical solutions to address the increasing rise in demand for power associated with rapid population and economic growth

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♦ Find our about important issues and developments in the power industry as the demand for power becomes an increasingly important issue in many regions around the world

♦ Discover why power resource allocation is one the most urgent and pressing issues for the region to secure a sufficient power supply for the future

♦ Learn how the very latest power treatments and technologies are emerging as vital solutions to the region’s and the world’s power challenges

POWER DEMANDS - QUICK FACTS

♦ The Middle East and North African economies are becoming some of the most exciting of any emerging markets. With a young demographic structure, and with solid earnings and economic growth, the region’s investment opportunities have grown enormously over the past decade

♦ To meet an estimated six to 10 per cent annual surge in demand for power, which is around eight gigawatts of additional capacity generation, GCC countries are projected to invest more than $300 billion in some 20 energy projects by 2020

♦ Qatar will be one of the main drivers of this ambitious power generation drive in the GCC with an investment of $125 billion in new energy projects

♦ With demand for electricity already growing by 14 per cent respectively over the last two years, Qatar's 10-year plan will focus on developing distribution networks, and increasing production and maintenance of electricity cables

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Wind Mapping

 

Management of Meteorological Variables and Wind Mapping

INTRODUCTION

Once established the feasibility for the installation of wind farms in a determined country or region from the political, legal and economic point of view, the next step is to deeply study the geographic region about which the wind potential is intended to be analyzed.
In order to determine which region is the most adequate to start the studies, what must be known is the distribution of the atmospheric capes in the area, the direction or main directions of the winds and the local conditions of the area, as the obstacles (buildings, trees, etc.), the ground surface and the orography of the area. In the present conditions of the Argentine Republic, such study must be based on reports or previous analyses which could be available or which have to be done, on reports by the National Meteorological Service and satellite images, among others. It is important to say that nowadays there is not a unique wind map of the Argentine Republic, which would be the basic instrument for any kind of consult or preliminary study. The analysis of this generic information with which we count on at present only gives a generic data and it must be considered as such.
It is also advisable to count on the local assessment of a meteorologist, who can give a better interpretation as regards historic values of the region, wind tendencies, pressure, average temperature and humidity, as well as data concerning the meteorological phenomena which usually take place in the area (such as rain and/or snow storms, extreme temperatures, strong winds, etc.)
Once this preliminary study has been done a series of processes must be followed so as to know the area in detail and which, finally, allow to get a scientific and meteorologically sustained answer to the question How much wind can we expect in the determined area?
So as to answer the previous question, it must be taken into account that the wind conditions for an area are defined by the wind profiles of this area, the average wind speed and direction, the wind speed distribution and direction, and the wind daylight and seasonal patterns.

DEVELOPMENT

It must be considered that to determine the period in which the measurement in the area will be done, the lasting of that period depends on the kind of project that is intended to be carried out. If the intention is to develop a complete wind map of a region, it must be considered the measurement taking for at least 10 years (i.e., long-term); otherwise, if it is a preliminary analysis of the wind resource, it must be considered the realization of the measurement, at least, for a year in its initial phase (i.e., short and medium-term).
After this, the quantity and setting of the anemometers to be installed must be defined, taking into account that it is advisable the average surface monitored by each anemometer to be of 2500 km². Technically, it is recommended the use of head anemometers, calibrated every 6 months in a  certified wind tunnel. Once calibrated and installed the anemometers in the region, it is advisable that they work, for their optimal performance, during nearly 4 weeks before the measurement starts, without their data to be considered for the study which has to be done. These data, must only be taken into account so as to be able to study the correct equipment calibration and the acquisition process of data, as well as the correct functioning of the electronic equipments of meteorological measurement and data store.
Calibrating the anemometers every 6 months and doing a bimonthly follow-up of each of them in the field during the data collection period, will minimize the error introduction or the loss of data. The errors in this kind of wind study must be understood as a very complex factor and can lead to the complete failure of the whole wind project. Taking into account that the energy found in the wind is proportional to the cubic wind speed (E~V³) and that, according to Betz’s law, theoretically the 59.3% of the wind energy can be extracted, the measurement that are done on the “wind resource” must be very accurate and free of possible errors.
Considering that the wind which is further from the surface has more speed and less turbulence, due to the fact that it is not affected by obstacles from the land, it is advisable to carry out the measurement as high as the standards allow. In general, it is advisable to carry out in the same spot two measurements at different heights, at 10 and at 30 meters, though measurements have been done with meteorological masts placed even at 50 or 100 meters high.
Once the measurement network of meteorological data has been installed on the land, the analysis of the air turbulence must be carried out. This analysis must be done measurement the vertical movement of the air (through the use of ultrasound anemometers), as well as the air temperature.
It is important to take into account the density of the air in the region, due to the fact that the air density in warmer regions lowers, and in colder regions it increases. It must be considered that it is better for the production of wind energy regions in which the air density is as high as possible, i.e., regions with cold temperatures (example: Argentina Patagonic region).
Air Density in Normal Conditions of Pressure and Temperature: 1.225 Kg. /m³.

Normal Conditions of Pressure and Temperature: 1013 hP and 20˚C (NCPT)

Data Collection and Processing

Considering that the meteorological data obtained is the “raw material” of the project and having used anemometric stations properly calibrated, installed and verified, the processing phase must begin, having a clear idea of what information must be obtained when this phase ends.
Because of that, and before the data processing, it is important to define adequate policies and protocols which allow to manipulate the information and to process it with highest levels of security and efficiency:

• It is advisable to establish the frequency for the data collection in the electronic equipments of the anemometers in 1 Hz.
• The meteorological values obtained must be averaged every 10 minutes (some anemometers allow to do this average internally).
• The policies of getting, collecting and transmitting the data coming from the anemometers installed in the measurement field must be defined.

It will be essential to do height extrapolations, which allow to estimate the winds that finally will be used for the wind electric energy production[5]. To extrapolate the winds there are two different equations:

1. Hellmann’s equation:

This equation allows to extrapolate the winds at a second height (h₂) though it is usually used only as an approximation.

v = wind speed
h = height above the ground [m]
α = Hellmann’s Exponent (For example: in Germany α=0.16)

2. Logarithmic Profile equation:

This equation must be applied only on average values, not on individual values, and must be used with measurements that imply long-term periods.

v = wind speed [m/s]
h = height from the ground [m]
d = thickness of the moving cape [m]
Z₀ = ground surface

So as to be conservative, in the analysis and interpretation of any of these equations, an error margin of +/- 10% must be considered.

The data processing in the first phase implies to obtain :

1. Weibull’s Curve.

f = density of frequency
v = wind speed (center of class) [m/s]
A = scale parameter [m/s]
c = shape parameter (note: c is k)

There is a relationship between Weibull’s parameters and the mean wind speed:

Increasing parameter c of Weibull with the height (empiric) Weibull c₂ = c₁ + 0.008 (h₂ – h₁)

2. Study of wind drafts

3. Maximum and minimum wind speeds

4. Compass card of the region

EVALUATION OF THE WIND RESOURCE

What is a wind map:

It is a representation of the magnitude and the direction of the winds of a region in graphic form, using cartography with a scale and determined symbolism.

Kinds of data needed

The data which is needed to draw the wind map of a region are of varied source and, depending on the method applied to do the job, they will have to be of different kind, having each method their compulsory data entry well defined. In this way, at the moment of developing the wind map which data is available must be reveled and in what way they can be used to apply which method.
Nevertheless, and not considering the method to be applied, the data necessary for the mapping can be summarized in the following list:

• Anemometric measurement or surface measurement.
• Orographic data.
• Topographic data.
• Data of land use/natural coverage.
• Satellite images.

The data measured on surface is of vital importance, due to the fact that it can be used to obtain the wind map of a region as well as to validate the results obtained through other methods which do not use measurements as entrance. On the other side, the surface data is still the most accurate at the moment of doing the project.

PARTS OF A WIND MAP

Data

The most frequent data represented on the map for a determined height are the mean wind speed (measured in m/s), the mean wind direction (expressed in arrows or characteristic symbols of plotting in meteorology), the mean energy density (measured in W/m²), the frequencies distribution, the compasses cards, the Weibull (A y k) parameters, the studies on wind drafts and the studies of turbulence, among others. Besides, the results must present not only the average historic data, but also the seasonal regimens and the daylight and night cycles of the resource.
There is another data which is used as entrance for the wind map models, but which can become very useful to be used and represented as a summary of the outcome. These are the ground surface map, the land use and vegetal coverage map, and topographic maps.
All these data will be represented at different heights, being nowadays the most common 30 and 50 m; though there are also atlases which represent the information at 10, 25, 30, 50, 75, 80, 100, 125 and 200 m. Really, once the calculus have been done and knowing how the wind profile behaves for an area, the values can be easily extrapolated in height through methods as the ones mentioned above.
Wind classes definition: Whatever the data represented on the wind map is, the objective is always the same: to reveal the wind potential in an area.

One of the data which is usually represented is the quantity of energy than can be obtained from a region.
This is measured in W/m² and there is a table of equivalencies between the wind speed and power, which is used in the USA, called Wind Class [1].

Models

In order to build wind maps data and models are needed. The models will be all those processes (programs, algorithms, methods) which allow to draw the wind behavior and distribution in an area or given region.
Once determined which ones will be the models to use and collected all the necessary data to feed the model, both things combine to become a wind map. In some cases, the models can be combined between themselves to get a more accurate result.
Kinds of climatic scales and their models: The models can be of macro scale, known as synoptic scale (more than 2000 km); meso scale (2 to 2000 km) or micro scale (up to the 2 km).
The most commonly used for the wind resource evaluation are those of meso and micro scale, both of them can be used separated or in combination. In general, the most common experiences are those in which both models are used together.
Generally, the models used –independently of the scale- can be of numerical or statistic type. In the case of the numerical models, are based in a group of more or less complex equations which model the physics reality of the climatic phenomena.
On the other side there are statistic models, which are characterized for applying principles of statistics and probabilities to solve the problem of how winds behave. Some of these methods are based on principles of traditional statistics and others use modern techniques of artificial intelligence, for example.
General numerical models: the numerical models can be classified in three different categories according to the way in how they model the reality (accuracy with which their equations model the physics behavior of the winds).

• Solving the fundamental equation models.
• Simplified physics models.
• Statistics analysis models.

Solving the fundamental equation models

These are models which solve the general equation of the flux movement of Navier-Stokes [3]. They include the description of the topography, of effects of the surface ground, they allow to model complex thermal effects and use geographic information, through the GIS systems. These are called meso scale models.
They allow the atmospheric representation or simulation in greater detail, at the same time they allow the modeling of a wider area than the rest of the numerical methods. These consider all –or almost all- the important meteorological phenomena. On the other side, they do not depend on data measured on surface. Known examples: KAMM (Karlsruhe Atmospheric Mesoscale Model, from the homonym university in Germany), MM5 (Mesoscale Model version 5 of NCAR/Penn - National Center for Atmospheric Research/ Pennsylvania), ETA (generated model every 12 hours created by the NCEP - National Center for Environmental Prediction and used by the National Meteorological Service of the Argentine republic) and MatMeso, among others.
At the same time, this kind of model requires the use of other methods so as to achieve a greater resolution and surface measurement if it is wished to validate that the outcome of the method is correct in all the cases.

Classification of the  meso scale phenomena(Fujita, 1986)

• Alfa Mesoscale (a): they have a dimension of between 200 and 2000 km with phenomena which can last between 6 hours and 2 days, as small hurricanes and weak anticyclones.
• Beta Mesoscale (b), which counts with sizes of between 20 and 200 Km. lasting between 30 minutes and 6 hours; there can be fields of local winds, mountain winds, breezes from the continent and the sea, connective complexes of meso scale and big electric storms.
• Gamma Mesoscale (c) of an estimated size of between 2 and 20 km, lasting between 3 and 30 minutes, representing phenomena like most of the electric storms and big size tornados.

In order to achieve a collection of wind resource data using a meso scale method the following steps must be followed: first, wind data and measures must be collected in height. In general, measurements of radio sound are used, though the measurements on surface can be considered to calibrate the model and estimate errors. The model is executed to simulate the winds of 10 to 15 years and, depending on the power of the calculus available and the region to be modeled, the resulting grid ca be between 1 and 5 Km. It is also possible to obtain a greater accuracy if a micro scale model is executed or one which allows a greater resolution within each point of the grid, for example the WAsP or WindMAP. After the execution of the model, the map of the wind resource is traced. In this map the data mentioned above can be represented.

Simplified physics models

They use a more reduced group of equations and –due to this- they model a smaller quantity of climatic phenomena. They are used to trace wind maps in low or medium complexity surfaces, getting maps equally useful and accurate, but requiring a lot lower potential of calculus. The advantages of this kind of methods are that they function with anemometric seasonal data of surface, with no need of height data and, besides, they are ideal for low complexity surfaces.
As a counterpart, their disadvantages are that they do not model the reality completely, they can only represent some aspects of the wind behavior and other meteorological variables. Then, they are not capable of modeling complex meteorological phenomena, but very important ones, as the breeze from the sea or the continent, or the wind produced by thermal effects, like the mountain winds; they do not take into account the splitting of the air flux produced by the irregular surface. It depends on anemometric measurements on surface, what implies that if the measurements are not enough or they are done in a wrong way, the model will generate an incorrect result. The anemometric non reliable measurements can not be used without using correction techniques which can introduce new errors in the calculus.

Models based on GIS

These kind of models are based on completely different functioning principles. For their functioning they use wind measurements in height which are extrapolated to low altitude. Moreover, they are based on the GIS (Geographical Information System) technology for the collection of data and the drawing of the part of the region to be analyzed.
In 1995 the NREL - National Renewable Energy Laboratory started to develop a new method of wind mapping based on the GIS technology. The model is called WRAM (Wind Resource Assessment Model). It produces maps of great quality and was used to develop the wind maps of several union states (North Dakota, South Dakota and Vermont; part of Minnesota, Iowa and Nebraska); apart from several international atlases like Dominican Republic, Mongolia,  Philippines and regions of Chile, China, Indonesia y Mexico. This method needs of wind values previously calculated and, really, it is no other thing than a method of representation, more than of calculus.

Models from the point of view of the principles

From the point of view of the physic-mathematics principles, the numericalal models are classified in:

• Based on the Jackson-Hunt’s theory
• Based on the uniform mass model

In the first case, these models tend to satisfy the Navier-Stokes’ equations [3]. Their basic characteristic is the description of two fundamental principles: the mass conservation and the moment conservation. Due to this, this kind of model is very sophisticated and has a very good output: an error among the 8 and the 10%.
In the case of the models based on the mass uniform model, they only describe (different from the previous ones) the mass conservation. They are less sophisticated and has a similar output –under determined conditions- to the most complex models. Examples of this kind of model are the WindMAP and the WAsP.
It can be deduced from the description of both models that the mass conservation principle is the most important determinant of the wind variation, always referring to surfaces of low or moderated complexity.

Graphics of the combined models

The graphic shows the steps to develop a wind map using a meso scale method and one of micro scale together, as the Wind Atlas style.

EXAMPLES OF THE MOST KNOWN MODELS

• KAMM (Karlsruhe Atmospheric Mesoscale Model) [meso scale] [4]
• Wind Atlas Analysis and Application Program (WAsP) [Simplified] [4]
• MesoMAP [meso scale] [7]
• WRAM Method [GIS] [8]
• WindMAP [Simplified] [7]
• WindSCAPE [Mix]: Raptor [micro] + TAPM [meso]

WIND MAP EXAMPLE: EUROPE

WIND MAP EXAMPLE: EUROPE OFFSHORE

WIND MAP EXAMPLE: DENMARK

CONCLUSIONS

One must be conservative in the interpretation not only of the data obtained as a consequence of the measurements done in the field by the measurement equipments but also with the extrapolations which are done, in height as well as on the surface. It is convenient to estimate between a 10% and a 20% less in the obtained data, and with those values to do the calculus and estimations.
Finally, the report of the “wind potential” of the region must present a technical and meteorologically sustained detail of the following information:

• The preliminary analysis of the region. (In this case it is advisable to count with the wind map of the country)
• Equipment installation process.
• Wind Mapping.
• Results and final report.

It does not matter what kind of wind project will be started, the evaluation phase of the potential of a region is one of the most important ones. According to its result the feasibility or not of a future project will be determined; also which is the best place within a region to establish a new wind complex.
The wind maps (atlas, resource evaluations, or whatever name they are assigned) are fundamental instruments to start any work of planning the installation of a wind farm. But all of them depend, at the same time, on fundamental incomes which will allow their creation: the meteorological data, of whatever kind they are.

REFERENCES

1. [1]. Wind Energy Danish Assoc. WindPower.org. Wind class standard definitions “Wind Class”. 11/Feb/2004,  <http://www.windpower.org/es/stat/unitsw.htm>
2. [2]. Brower, M., B. Bailey, and J. Zack. The New US Wind Resource Atlas [cdrom]. In: European Wind Energy Conference & Exhibition 2003. [Madrid], European Wind Energy Association, 2003.
3. [3]. Cambridge University Press. Foundations of Fluid Mechanics. Navier-Stokes Equations [on line]. 14/Aug/2004. <http://www.navier-stokes.net/>
4. [4]. Frank, H. P., O. Rathmann, N. G. Mortensen, and L. Landberg. The Numericalal Wind Atlas: The KAMM/WasP Method. [Roskilde, Denmark]: Information Service Department, RisØ National Laboratory, June 2001.
5. [5]. Gasch, R., and J. Twele. Wind Power Plants. Fundamentals, Design, Construction and Operation. [Berlin, Germany]: Solarpraxis AG, 2002.
6. [6]. Manwell, J. F., J. G. McGowen, and A. L. Rogers. Wind Energy Explained: Theory, Design and Application. [West Sussex, England]: John Wiley & Sons Ltd, 2002.
7. [7]. Brazil Mining and Energy Ministry. Mapas do Potencial Eólico Anual [cdrom]. In: Atlas Do Potencial Eólico Brasileiro. [Brasilia, Federative Republic of Brazil], e-dea Technologies/ Christianne Steil, 2001.
8. [8]. Nielsen, J., S. Innis, and K. Pollock. Renewable Energy Atlas of the West. <http://www.EnergyAtlas.org>
9. [9]. RisØ National Laboratory. Wind Energy Department.    Wind Resource Atlas for Denmark. [Denmark]: 23/Jan/2004. <http://www.risoe.dk>

Eng. Luis Mariano Faiella
Eng. Alejandro J. Gesino
Research & Development Area
Argentine Wind Energy Association
www.argentinaeolica.org.ar

Croatian Center of Renewable Energy Sources (CCRES)

Wind Energy from antiquity until today

1. A brief history of the development of wind energy from antiquity until today

Since antiquity, mankind has been using wind energy; it is thus not a new idea. For centuries, windmills and watermills were the only source of motive power for a number of mechanical applications, some of which are even still used today.
Humans have been using wind energy in their daily work for some 4,000 years. Sails revolutionized seafaring, which no longer had to make do with muscle power. In 1700 B.C., King Hammurabi of Babylon used wind powered scoops to irrigate Mesopotamia.
Aside from pumps for irrigation or drainage, windmills were mostly used to ground grain. Thus, we still speak of "windmills" today, even when we are talking about machines that do not actually grind, such as sawmills and hammer mills.

Historical Dutch windmill, © Bundesverband WindEnergie e.V.

American windmill used for water pumping, © Bundesverband WindEnergie e.V.

But the wind turbines that generate electricity today are new and innovative. Their success story began with a few technical innovations, such as the use of synthetics to make rotor blades. Developments in the field of aerodynamics, mechanical/electrical engineering, control technology, and electronics provide the technical basis for wind turbines commonly used today.
Since 1980, wind turbines have been becoming larger and more efficient at rates otherwise only seen in computer technology.

2. The development of modern wind turbines since 1900

The major success story is wind turbines that generate electricity and feed it directly to the grid. They usually have two or three rotor blades, while horizontal axis, a nacelle with a rotor hub, gears, and a generator, all of which can be turned into and out of the wind. The rotor is positioned in front of the tower in the direction the wind is blowing (windward as opposed to leeward).
In 1920 and 1926, Albert Betz calculated the maximum wind turbine performance, now called the "Betz limit", and the optimal geometry of rotor blades.
In 1950, Professor Ulrich Hütter applied modern aerodynamics and modern fiber optics technology to the construction of rotor blades on the wind turbines in his experimental system.
Poul la Cour of Denmark developed a wind turbine that generated direct current. In 1958, one of his pupils named Johannes Juul developed the "Danish Concept," which allowed alternating current to be fed to the grid for the first time. This concept very quickly won over. Today, almost half of all wind turbines operate according to this principle.
In the 1980s, the Danes developed small turbines with a nominal output of 20 kW to 100 kW. Thanks to state subsidies, these turbines were set up on farms and on the coast to provide distributed power, with the excess power not consumed locally being fed to the power grid.

In other countries, research focused on large systems, two examples being NASA's research in the US or the German GroWiAn project. Unfortunately, these plans turned out to be too ambitious. After only a few hundred operating hours, tests at the research facilities were discontinued.

3. The physics of wind energy: what is the useful potential of wind energy?

Power is available from the kinetic energy of the mass of air moving in wind. The amount of energy that wind carries increases by a factor of two as its speed increases and is proportional to the mass of air that passes through the plane of the area swept by the rotors. As power is the product of energy (work) within a given time frame, the power of wind increases by a factor of three as the speed of wind increases. Because of the low density of air (P_air=1.25 kg / m3), the power density of wind is much lower than that of water power (P_water=1000 kg / m3), for instance. The power that can be harvested from wind is calculated in terms of the swept area -- for a horizontal axis wind turbine (HAWT), the area through which the rotor blades pass. As a result, if the diameter of the rotor blades is doubled, the power increases by a factor of four. If the wind speed then doubles, power increases by a factor of eight.
In 1920, Albert Betz demonstrated in his theory of the closed stream tube that a wind turbine can only convert a maximum of 16/27 or 59% of the energy in wind into electricity. This optimum performance cP is attained when a wind turbine's rotors slow the wind down by one third.
Current wind turbines convert up to 50% of energy in wind into electricity, thus coming very close to the theoretical limit.

4. Comparison of resistance and lift

Like some of these simple turbines with small output (up to 2 kW), historic windmills operate according to the principle of resistance. Here, a rotor with a vertical axis resists the wind, thus reducing wind speed. The maximum performance of such wind turbines is 12%. The performance of wind turbines based on the principle of lift is much greater at around 50% due to the relatively high lift-to-drag ratio.
The power coefficient (performance) of a wind turbine can be improved by optimizing the tip speed ratio (lambda), i.e. the ratio of wind velocity to the velocity of the tip of the rotor blade. If the tip speed ratio = 1, the rotor has many blades, generates great torque, and runs at slow speeds. If the tip speed ratio is higher, the rotor has few blades, generates less torque, and runs at higher velocity.
The performance of a rotor is not, however, relative to the number of rotor blades in principle (cf. Betz theory in the next section).

5. The aerodynamics of wind turbines

The power coefficient of a wind turbine's rotor blade is calculated according to the laws of airfoil theory. As with the wing of an airplane, air passing over a rotor blade creates an aerodynamic profile with low pressure above the wing, pulling the wing up, and overpressure below, pushing it up.
The difference in pressures exerts a lift on the wing vertical to the direction in which the wind is blowing and creates resistance in the direction of the wind (incident flow). For a wind turbine's rotor blade rotating around the rotor axis, the incident flow is the result of the geometric addition of wind velocity v and the circumferential speed u, which increases in linear fashion the longer the blade is. In other words, the lift exerted on the rotor blade is not only the result of wind velocity, but mostly out of the blade's own rotation. Speeds at the tip of the blade are thus very great. Current wind turbines have rotor tips travelling at velocities six times faster than the speed of the wind. The tip speed ratio is thus lambda = 6. The rotor tip can then be traveling at velocities of 60 m/s to 80 m/s.
The energy that the rotor harvests is equivalent to the lifting force in the swept area minus the resistance force in the swept area. The forces applied in the direction of the axis drive the rotor, which then not only harvests the energy of the wind, but also exerts a load on the tower and the foundation.
The Betz Theory allows us to calculate the optimal geometry of a rotor blade (thickness of blade and blade twisting).

6. Types of wind turbines

Wind turbines are categorized according to a number of criteria:
The position of the axis (horizontal or vertical) is obvious. Horizontal axis wind turbines (HAWTs) can be further divided into those with rotors rotating in front of the tower (windward) and those rotating behind the tower (leeward) vis-à-vis the direction of the wind. The tip speed ratio and the number of blades determine the response of the drive, and hence how the wind turbine can be used.
In modern wind turbines that generate electricity, there are different types of nacelles that turn on top of the tower to face the wind. There are turbines with gearboxes and without and nacelles whose components (bearings, gears, generator) are positioned separately or have multiple functions integrated in one component (bedding of rotor shaft in the gearbox).
Poles (generally guyed) are usually only used for small wind turbines (up to 10 kW). Free-standing towers are either steel or concrete tubular towers or pylons.

Modern wind turbines

Modern wind turbines are complex technical systems that combine the theoretical basics of a number of fields:
Aerodynamics, lightweight construction >> rotor blades, dynamics, overall system)
Mechanical and plant engineering >> machines with shafts, gearboxes, bearings, brakes, and tower
Electrical engineering >> generator, frequency converter, mains connection, electrical lines
Electronics, instrumentation and controls, and computer science >> system controls, remote monitoring, sensors
Construction engineering >> foundation, access roads
Meteorology >> design, yield

7. Concepts of wind turbines to generate electricity

At present, three concepts for the feed of electricity to the power grid dominate the market. The following table provides an overview of the differences and common ground between these types.

• The "Danish concept"
• The pitch concept with a synchronous generator
• The pitch concept with a doubly fed asynchronous generator

In the Danish concept, which completely dominated the market up to the mid-1990s, the asynchronous generator "naturally" limits power production in strong wind or gusts. It restricts the speed of the system to the frequency of the power grid, so that the rotor cannot turn faster when the wind blows stronger. In this concept, the rotor blades are designed to create turbulence at a certain wind velocity, preventing the lift from accelerating rotation any further even though the blades are not themselves pitched. Johannes Juul developed this concept.
The use of an asynchronous generator also eliminates the synchronization needed for a synchronous generator. In other words, the system is simple and robust.
The pitched concepts developed from 1990 to 2000 turn the rotor blades in and out of the wind along their axis. Depending on the wind velocity, the machines run at various speeds. The blades are turned out of the wind to limit power generation when the wind becomes too strong (above 12 m/s). The blades are only turned into the wind to start the system. Under normal conditions, the turbines are run at a set optimal angle for the best power generation, with the speed of rotation increasing until nominal output is attained. From then on, the pitch of the blades is activated to keep power production constant.
In the pitch concept with a synchronous generator (concept 2), a frequency converter ensures that the fluctuations in electricity caused by the changing speed of the turbine are nonetheless fed to the grid at the frequency of the grid.
In the concepts of a doubly fed asynchronous generator (concept 3), this is not necessary for all of the electricity generated, but rather only for the share coming from the generator's rotor. As this share only makes up around 40% of nominal output, the converter can be smaller.

8. From the drawing board to a working wind turbine

Wind turbines only appear to be simple constructions. There are many steps from the draft to construction before the turbine can begin generating environmentally friendly energy in the field.
Wind is not constant, so wind turbines do not always run at nominal output. The amount of energy generated is below the amount theoretically possible. One speaks of a capacity factor, which is the yearly yield in kilowatt-hours divided by the product of the wind turbine's nominal output and the 8,760 hours in a year.. Depending on the location, the capacity factor can range from 30% in coastal areas with great wind to around 18% at inland locations with less wind.
It is true that wind energy is not available at all times. However, the wind energy fed to the power grid does make up part of the baseload. The large number of wind turbines already installed in Germany (17,500 as of December 31, 2005) ensures that wind power is always being fed to the grid somewhere. Over large areas, some 10% of the nominal power of all wind turbines can be expected to be fed to the grid as constant output.

Wind farm Sintfeld for electricity production, one of the largest wind farms in Germany, © WWEA e.V.

Sintfeld Wind Farm

This figure will rise even further once the offshore wind parks currently planned are finally built. The same holds true for additional wind turbines and other countries in Europe, which will also be feeding power to the European grid.
In other words, conventional central power plants can actually be decommissioned and replaced by renewable energy for good. Intelligence demand management systems and the development of forecast systems for wind conditions will also help reduce the need for conventional power plant capacity.

9. Controlled power: nominal capacity and control

If we speak of a 1.5 megawatt wind turbine, we are describing the generator's maximum output -- its nominal capacity. 1.5 megawatts is equivalent to 1500 kW or 2,039 horsepower. The turbine generates that much power at a specific wind velocity. This nominal wind velocity is generally between 11 and 15 m/s (equivalent to 40-54 km/h).
Wind turbines begin generating power at the cut-on speed of around 2.5-4 m/s and cut off at wind velocity of 25-34 m/s. Modern control technology is used when wind turbines are connected to the grid to ensure a “soft”, gradual transition. If the wind is too strong, output is reduced to ensure that a constant level of power is fed to the grid. Modern turbines also switch off slowly during storms to prevent power output from disappearing suddenly. This gradual transition helps prevent disturbances in transit grids.
Control
To prevent wind turbines from overloading and to ensure that they have constant output, part of the power has to be throttled when the wind velocity exceeds nominal wind velocity. The following two principles are the most commonly used methods of controlling power output:

• Stall control (aerodynamic turbulence): if the wind velocity exceeds a certain limit, the rotor blades are designed to cause a turbulence at the edge of the blade to limit speed. In active stall control, the pitch of the rotor blades can also be changed.
• Pitch control: Electronics and hydraulics are used to infinitely adjust the pitch of each blade. This reduces the lift, so that the rotor continues to generate power at nominal capacity even at high wind speeds.

With the kind permission of the German Wind Energy Association (BWE)
Croatian Center of Renewable Energy Sources (CCRES)

Merry Christmas

EPA Issues First National Standards for Mercury Pollution from Power Plants

 We did it!

  This past summer, we asked CCRES supporters to submit public comments to the EPA on the proposed Power Plant Mercury and Air Toxics Standards rule. Thousands of you responded.

According to the EPA, reduced emissions from this new air toxics rule will save as many as 17,000 American lives per year by 2015, and will prevent up to 120,000 cases of childhood asthma. On the rule that took 20 years to finalize, EPA Administrator Lisa P. Jackson said “by cutting emissions that are linked to developmental disorders and respiratory illnesses like asthma, these standards represent a major victory for clean air and public health – and especially for the health of our children.”  
CCRES Team

Release Date: 12/21/2011

WASHINGTON – The U.S. Environmental Protection Agency (EPA) has issued the Mercury and Air Toxics Standards, the first national standards to protect American families from power plant emissions of mercury and toxic air pollution like arsenic, acid gas, nickel, selenium, and cyanide. The standards will slash emissions of these dangerous pollutants by relying on widely available, proven pollution controls that are already in use at more than half of the nation’s coal-fired power plants.

EPA estimates that the new safeguards will prevent as many as 11,000 premature deaths and 4,700 heart attacks a year. The standards will also help America’s children grow up healthier – preventing 130,000 cases of childhood asthma symptoms and about 6,300 fewer cases of acute bronchitis among children each year.

"By cutting emissions that are linked to developmental disorders and respiratory illnesses like asthma, these standards represent a major victory for clean air and public health– and especially for the health of our children. With these standards that were two decades in the making, EPA is rounding out a year of incredible progress on clean air in America with another action that will benefit the American people for years to come," said EPA Administrator Lisa P. Jackson. "The Mercury and Air Toxics Standards will protect millions of families and children from harmful and costly air pollution and provide the American people with health benefits that far outweigh the costs of compliance."

“Since toxic air pollution from power plants can make people sick and cut lives short, the new Mercury and Air Toxics Standards are a huge victory for public health,” said Albert A. Rizzo, MD, national volunteer chair of the American Lung Association, and pulmonary and critical care physician in Newark, Delaware. “The Lung Association expects all oil and coal-fired power plants to act now to protect all Americans, especially our children, from the health risks imposed by these dangerous air pollutants.”

More than 20 years ago, a bipartisan Congress passed the 1990 Clean Air Act Amendments and mandated that EPA require control of toxic air pollutants including mercury. To meet this requirement, EPA worked extensively with stakeholders, including industry, to minimize cost and maximize flexibilities in these final standards. There were more than 900,000 public comments that helped inform the final standards being announced today. Part of this feedback encouraged EPA to ensure the standards focused on readily available and widely deployed pollution control technologies, that are not only manufactured by companies in the United States, but also support short-term and long-term jobs. EPA estimates that manufacturing, engineering, installing and maintaining the pollution controls to meet these standards will provide employment for thousands, potentially including 46,000 short-term construction jobs and 8,000 long-term utility jobs.

Power plants are the largest remaining source of several toxic air pollutants, including mercury, arsenic, cyanide, and a range of other dangerous pollutants, and are responsible for half of the mercury and over 75 percent of the acid gas emissions in the United States. Today, more than half of all coal-fired power plants already deploy pollution control technologies that will help them meet these achievable standards. Once final, these standards will level the playing field by ensuring the remaining plants – about 40 percent of all coal fired power plants - take similar steps to decrease dangerous pollutants.

As part of the commitment to maximize flexibilities under the law, the standards are accompanied by a Presidential Memorandum that directs EPA to use tools provided in the Clean Air Act to implement the Mercury and Air Toxics Standards in a cost-effective manner that ensures electric reliability. For example, under these standards, EPA is not only providing the standard three years for compliance, but also encouraging permitting authorities to make a fourth year broadly available for technology installations, and if still more time is needed, providing a well-defined pathway to address any localized reliability problems should they arise.

Mercury has been shown to harm the nervous systems of children exposed in the womb, impairing thinking, learning and early development, and other pollutants that will be reduced by these standards can cause cancer, premature death, heart disease, and asthma.

The Mercury and Air Toxics Standards, which are being issued in response to a court deadline, are in keeping with President Obama’s Executive Order on regulatory reform. They are based on the latest data and provide industry significant flexibility in implementation through a phased-in approach and use of already existing technologies.

The standards also ensure that public health and economic benefits far outweigh costs of implementation. EPA estimates that for every dollar spent to reduce pollution from power plants, the American public will see up to $9 in health benefits. The total health and economic benefits of this standard are estimated to be as much as $90 billion annually.

The Mercury and Air Toxics Standards and the final Cross-State Air Pollution Rule, which was issued earlier this year, are the most significant steps to clean up pollution from power plant smokestacks since the Acid Rain Program of the 1990s.

Combined, the two rules are estimated to prevent up to 46,000 premature deaths, 540,000 asthma attacks among children, 24,500 emergency room visits and hospital admissions. The two programs are an investment in public health that will provide a total of up to $380 billion in return to American families in the form of longer, healthier lives and reduced health care costs.

More information: http://www.epa.gov/mats/

Croatian Center of Renewable Energy Sources (CCRES)

Solar Photovoltaic Electricity Empowering the World

Solar Photovoltaic Electricity Empowering the World

The European Photovoltaic Industry Association (EPIA) , Greenpeace International and Croatian Center of Renewable Energy Sources (CCRES) are pleased to present the 6th edition of the “Solar Generation 6: Solar Photovoltaic Electricity Empowering the World” report.

This report aims at providing a clear and comprehensible description of the current status of the developing photovoltaic power generation worldwide and its untapped potentials and growth prospects in the coming years.

Global evolution of PV installed capacity

During 2010, the photovoltaic (PV) market has shown unprecedented growth and wide deployment of this environmentally friendly source of power generation. On a global scale, approximately 15,000 MW of new PV installations have been added during 2010, amounting the entire PV capacity to almost 40,000 MW. This number has risen above the optimistic forecast contained in the report, and it also translates into investments of over 50 bn€ in 2010, again ahead of the report’s forecast.

Total of world cumulative PV installed capacity under three scenarios

The most impressive result is however the number of installations and consequently, the number of individuals, companies, and public entities participating in this development: nearly 2 million single PV installations produce photovoltaic power already today.

The cumulative electrical energy produced from global PV installations in 2010 equals more than half of the electricity demand in Greece, or the entire electricity demand in ten central African countries (Angola, Benin, Botswana, Cameroon, Congo, Cote d’Ivoire, Eritrea, Ethiopia, Gabon and Ghana).

The strong growth in PV installations is currently driven in particular by European countries, accounting for some 70% of the global market, followed by the promising key markets of North America, Japan, China and Australia. At the same time, the PV arena has importantly widened its number of participating countries and also increased their specific weight. Major new areas for development lie also in the Sunbelt region, in Africa, Middle East and in South America that is just starting to create new growth opportunities dedicated to covering local demand.

The major competitive advantages of PV technology lie in its versatility, i.e. the wide range of sizes and sites, resulting in proximity to electricity demand, in the value of its production profile concentrated during peak-load hours, and in its enormous potential for further cost reduction.

PV technology has reduced its unit costs to roughly one third of what it did 5 years ago, thanks to continuous technological progress, production efficiency and to its wide implementation. The trend of decreasing unit cost will continue in the future, just like in comparable industries such as semiconductors and TV screens. Adding to the important feature of integrated PV solutions in architecture in particular, the potential of further growth is simply enormous.

The 6th edition of the Solar Generation report combines different growth scenarios for global PV development and electricity demand until 2050. It is built on the results of several reference market studies in order to accurately forecast PV growth in the coming decades. In addition, the economic and social benefits of PV, such as employment and CO2 emissions reduction, are also analysed. With PV becoming a cost competitive solution for producing power, it will open up a variety of new markets and contribute more and more significantly to cover our future energy needs.

PV technology has all the potential to satisfy a double digit percentage of the electricity supply needs in all major regions of the world. Going forward, a share of over 20% of the world electricity demand in 2050 appears feasible, and opens a bright, clean and sunny future to all of us.

Total of world cumulative PV installed capacity under three scenarios

Reference for the future

This publication is the sixth edition of the reference global solar scenarios that have been established by the European Photovoltaic Industry Association and Greenpeace jointly for almost ten years. They provide well documented scenarios establishing the PV deployment potential worldwide by 2050.

The first edition of Solar Generation was published in 2001. Since then, each year, the actual global PV market has grown faster that the industry and Greenpeace had predicted.

Annual PV installed PV capacity

 

Croatian Center of Renewable Energy Sources (CCRES)