Windmill's design and implementation aspects.

Szeidert, Iosif ; Prostean, Octavian ; Robu, Andreea 等

1. INTRODUCTION

The task of development and implementation of a certain wind farm site is an extremely complex job, which appeals interdisciplinary domains of engineering. (Heier, 1998) (Szeidert et. al., 2005) In technical literature, the analysis and design aspects of a wind farm are divided into two main separate parts: the resources and the constraints.

The main objective for the wind farm designer is to maximize the energy captured within the bounds placed on it by constraints, such as environmental and financial issues.

The main problem of using wind energy is the fact that this energy introduces significant uncertainty in operating of an energetic power system: it is variable and unpredictable (practically the energy presents a pumping character).

In this order of idea, the must be considered a suitable management for the uncertainties, there is required a higher flexibility in the energetic power system, either in the form of more flexible generation, demand or transmission between areas.

Nowadays, researchers are investigating the energetic power system impacts of wind power. Thus, the results on the costs of integration differ and comparisons are difficult to be conducted due to different methodology, data and tools used, as well as terminology and metrics in representing the results. The wind power must be considered always in relation with the other elements of the power system.

An in-depth review of the studies is needed to be able to draw realistic conclusions on the range of integration costs for wind power.

The design process for a wind farm must be iterative.

The design algorithm must establish at an early stage that there is a sufficient resource to make the project viable. Simultaneously, with this it is necessary to assess:

--Planning issues: ecology, landscape designations, visual influence, electromagnetic interference, sound (noise);

--Technical issues: grid connection, ground conditions and access which may affect the development and implementation of wind farms.

All previously mentioned issues may constrain the design of a wind farm and therefore must be early considered. After setting up the terms and constraints on the development, many aspects of the design process are solvable by using usual computational methods. In technical literature, a comprehensive methodology has been developed over the last few years using a number of sophisticated software packages.

These are mainly used to:

--Optimize the design of the wind farm,

--Calculate objective characteristics of the wind farm for use in the environmental assessment process,

--Predict the wind farm's yearly energy production.

Practically, the methodology links the various site, turbine, resources, environmental and economic issues together to produce an optimum and well defined solution under specified constraints.

Wind power energetic is one of the fastest growing electric power industries in the world. Current global installed capacity exceeds 25.000 MW with a projected growth rate of about 10.000 MW/year for the next five years. The phenomenal growth of this industry can be attributed to the fast progress made in wind turbine technology.

The actual technological progress has led to the development of turbines with high power capture efficiency. Nowadays, many wind farms produce electrical power at a Cost-of-Energy almost comparable to the one of coal and natural gas based power plants.

The studies on wind turbines development has been mainly focused on large wind turbines, due to economic reasons. Typical large wind turbines of today are massive structures with enormous blade spans (70-120m in diameter), tall towers (80-150m in height) with power ratings up to 5 MW.

Modern large wind turbines are endowed with sophisticated control systems which are organized to support several modes of operation such as start-up. shut-down, power production etc. During low wind speed operation, the goal is to maximize energy capture. However, in conditions where wind speeds are greater than the turbine's "rated" wind speed (usually around 10-13 m/s) the primary objective is to minimize fatigue loading of the turbine structure.

2. ISSUES REGARDING ENVIRONMENTAL IMPACT

One of the main issue regarding the environmental impact is the sound (noise) produced by the wind farms while functioning at site. Nowadays, it has become a standard procedure and requirement for manufacturers to quote the sound source power of their turbines together with the associated octave band analysis.

This approach is rapid and simple and can be used effectively for wind farm design. Unfortunately, in the case of sound (functioning noise), the precise values at any location are dependent on: the sound source power, the topography, ground cover, background sound levels and on air's quality.

In the analysis procedure, there must be adopted the sound envelope estimation.

Additionally to visual and sound implications of wind farms there are a number of other environmental, planning and energy issues that must be addressed, such as: EMI (electromagnetic interference problems), fauna/flora disturbances and other planning issues.

On national level, relevant issues should be national energy objectives such as the reduction of CO2 emissions problem, security of energy supply, local manufacturing potential and other related issues.

3. RESOURCE PLANNING--WIND SPEED

The energy production of a wind farm is very sensitive to wind speed. Therefore, an accurate estimate (as much as possible) of the long-term mean wind speed at a site must represent an important input to the financial assessment of a project. This fact can only be accurately achieved by making on-site wind speed measurements at a level close to the hub height of the wind turbine.

As there can be large seasonal variations in mean wind speed and annual variations in the order of up to 20%, data recorded over a period of several years is required to define the long-term values. An accurate estimate of long-term mean wind speed can, however, can be obtained from a short-term data set recorded on the site by additionally using concurrent and long-term data recorded at a nearby meteorological station.

The long-term mean wind speed will vary over the site and these variations will impose the design, implementation and the energy production of the wind farm (the economic issue). (Zinger & Muljadi, 1997)

4. ENERGY PRODUCTION (OUTPUT) OF THE WIND FARMS

The yearly energy production of a proposed wind farm can be forecasted by combining the wind farm power curve, net of the effect of topography, wake interaction and electrical losses, with the wind speed direction frequency table. Availability in excess of 90% is considered to be typical for a modern wind farm. There are continuously developed prediction techniques for the wind speed on site, for energy consumption, etc. Some, of them were studied also by the paper's authors, such as modern techniques based on the usage of recurrent neural networks. (Vasar et. al., 2007) (Heier, 1998)

5. ISSUES REGARDING THE COST MODELING

The cost-modeling task studies the costs of energy production of the wind farm that results from the design activities in several cases, as depicted in Fig.1. (Zinger & Muljadi, 1997)

The cost analysis procedure takes into consideration the economic parameters, environmental conditions, performance parameters and cost components in order to elaborate the afferent cost model.

[FIGURE 1 OMITTED]

6. INTEGRATED APPROACH.

In present, the design of wind farms is conducted by using, an integrated approach regarding the electrical and civil engineering permits the site design.

In the case of wind farms, the management software should take into consideration and solve the following issues:

--The EC (electromagnetic compatibility), the IEC standards;

--Switching and operating strategies;

--Protection strategies;

--Monitoring and diagnosis issues;

--The wind farm's effects over the national energy power networks. (Lewis & Garrad, 1994) (Reinebach, 2007)

7. CONCLUSION

Because of the complexity of wind farms there is quite difficult to define cost functions for the automatic optimization of concept or design parameters. Therefore, an optimization process of wind farm concepts should be considered to be solved by multidisciplinary design teams. The optimization procedure should start with a baseline, followed by an objective learning phase and a consistent combining phase. However, in the case of differences between concepts, the selection could be performed by considering other criteria. (Bauer et al., 2003) (Garrad et al., 1993)

The wind energy market is moving so fast that construction has outpaced the availability of construction-ready sites. This has forced owners with fixed turbine deliveries to develop, design and build often at the same time. A coordinated and experienced team of development, engineering and construction professionals under central leadership is critical to having these sites completed on time and on budget. There are many decisions that have to be taken in designing a modern wind turbine.

As a conclusion, the optimal wind turbine design for one specific site is not necessarily the optimal design for another site because the wind speed distribution varies between the sites. Similarly, the turbine with the highest efficiency is not mandatory to be the optimal turbine. It is possible for a less efficient wind turbine to have a lower cost of energy. (Szeidert et. al., 2005)

In conclusion, the paper deals with the main issues and aspects that occur in the design and implementation of wind farms.

8. REFERENCES

Bauer P., De Haan S.W.H., Dubois M.R. (2003) Introduction to wind energy and offshore problematic, PCIM 2003, Nuremberg, Germany, 20-22 May.

Garrad, A. D., Mercer, A. S., and Adams, B. M. (1993) An analytical approach to wind farm design, Report of Garrad Hassan & Partners Ltd, with Jenkins, N. R., University of Manchester Institute of Science and Technology.

Heier S. (1998) Wind energy conversion systems, John Wiley & Sons Inc., New York, 1998.

Lewis, P. E. and Garrad, A. D. (1994) Wind farm optimization, Proceedings, 16th British Wind Energy Association Conference, Sterling, 1994.

Reinebach D. (2007) A Coordinated Approach To Wind Farm Construction, North American Windpower Magazine, November 2007, www.nawindpower.com,Accessed: 2008-02-05

Szeidert I., Budisan N., Filip I., Szeidert R. (2005) Consideration and Perspectives about Wind Energy Usage in Romania, Simpozion Electrotehnica si Energetica, Zilele Academice Timisene, 26-27 mai 2005, ISBN: 973-625-2533, CD-ROM.

Vasar C., Szeidert I., Filip I., Prostean G. (2007). Short Term Electric Load Forecast with Artificial Neural Networks, Preprints of the 4th IFAC Conference on Management and Control of Production and Logistics (MCPL 2007), Sibiu, Sept. 27-30, 2007, ISBN 978-976-739-481-1, pag.443-450.

Zinger D.S., Muljadi E. (1997) Annualized wind energy improvement using variable speeds, Industrial & Commercial Power Systems technical Conference, 1997. Conference Records, Papers presented at the 1997 Annual Meeting, IEEE 1997, 11-16 May 1997, pp. 80-83.