Hourly wind velocity exceedence maps of Turkey

Transcription

1 Energy Conversion and Management 44 (2003) Hourly wind velocity exceedence maps of Turkey Ahmet Duran Sßahin * Energy Group, Department of Meteorology, Istanbul Technical University, Maslak 80626, Istanbul, Turkey Received 11 October 2001; accepted 7 February 2002 Abstract Risk analysis is one of the very important topics in engineering applications and scientific researches. In wind engineering, the possible extreme wind velocities constitute the basic targets in risk evaluations. In practice, lower extremes are significant for low energy generation possibilities and for power-cut risks, depending on the turbine type. However, upper extremes endanger the stability of the wind turbines. Additionally, the maxima of wind velocity variations have fundamental importance in engineering structural designs. Besides, from the meteorological point of view, maximum wind velocities directly relate to storms and thunderstorms. In this paper, wind velocity exceedence maps over 10, 12, 15 and 20 m/s are produced for Turkey, and the necessary interpretations are given. These maps show that especially the western part of Turkey and, particularly, coastal areas are risky locations for structural stability and wind erosion. Ó 2002 Elsevier Science Ltd. All rights reserved. Keywords: Risk analysis; Risk value; Structure; Wind energy; Wind velocity 1. Introduction As is well known, wind occurrences depend on different cooling and heating phenomena within the lower atmosphere and over the earth surfaces. These are called, in general, gradient winds. In addition, meteorological systems move from one place to another by generative wind velocities. Most of these winds occur under different pressure systems, which are called meteorological systems, and they are influenced to a certain extent by topographic conditions. It is this system of winds that gives rise to occasional extreme wind velocities. These conditions must be predicted prior to any wind farm planning, siting, design, operation and maintenance. Of course, if these * Tel.: ; fax: address: sahind@itu.edu.tr (A.D. Sßahin) /02/$ - see front matter Ó 2002 Elsevier Science Ltd. All rights reserved. PII: S (02)

2 550 A.D. Sßahin / Energy Conversion and Management 44 (2003) extreme values are known, then it is possible to arrive at a risk decision rather easily. Wind velocity risks have significance for construction of buildings, bridges, choosing settlement locations, predicting wind erosion and evaluation of optimum wind energy potentials. In wind energy researches, and especially in turbine design cut-in and cut-out velocities, risk levels must be searched [1 4]. For the extraction of extreme wind speeds, two methods are in current use. First, when a sufficiently long time series of meteorological data are available, it is possible to identify the individual storms, and then the method of independent storms should be adopted. Contrarily, in cases where the time series data is limited to annual largest values only, then the usual choice is the Gumbel Lieblien Blue method [5]. In practice, most often, many wind engineers use the Gumbel method as a procedure for analysing data without being familiar with its underlying theoretical basis. Both the theory and practice were described originally in the book by Gumbel [6], but this also contains a wealth of other information from which it is not easy to extract the material required. Additionally, Gumbel revisited extreme values statistics as applied to wind speed by Harris [7]. On the other hand, Sßen [3] took into account statistical investigation of wind energy reliability and its application to Turkey. Also, Sßahin and Sßen [8] looked at extreme wind speeds by a first order Markov-chain model. Additionally, the areal wind characteristics of the western and north western parts of Turkey are considered by Sßen and Sßahin [9,10]. They also searched the change of areal wind energy for all Turkey. Furthermore, Oztopal et al. [11] constructed maps of average wind energy for Turkey. However, in all these researches, no regional risk values were considered. Hence, it is the main purpose of this paper to present extreme velocity regional exceedence maps for Turkey. 2. Data and application In this paper, 68 wind speed measurement stations with five years hourly wind speed data are considered. The record interval of wind speed values is These stations have different characteristics from each other because of topographical and local climatological conditions. In Table 1, one can see the topographic characteristics of each station. First of all, the number of exceedence hours greater than or equal to a set of base wind speeds is calculated for each station. Herein, the base wind velocities are considered as 10, 12, 15 and 20 m/s. The number of exceedences are shown in Table 1. After that, maps of equal exceedences number contours are constructed at 10, 12and 15 m/s levels. For instance, Fig. 1a shows the 10 m/s base wind velocity exceedence number at unit intervals. It is apparent from this figure that some locations have dark colours, whereas others have either gray or white colours. As a rule of thumb, dark locations include fragment exceedences, gray regions are intermediate locations and white areas are non-exceedence domains. In other words, dark locations are rich in wind energy generation potential but care should be taken for structural stability. On the other hand, the white parts are not suitable for wind energy generation over 10 m/s. It is evident that the wind potential areas at 10 m/s velocity with dark and gray colours are completely reliable regions, but white areas are very unreliable, i.e risky. Some stations do not have any risk groups at the 10 m/s level, such as at the Giresun, Rize, Bolu, Cß ankırı, Sivas, Agri, Musß, Aydın, Urfa, Hakkari, Adana and Antakya locations. Generally, these stations are

3 A.D. Sßahin / Energy Conversion and Management 44 (2003) Table 1 Station characteristics and exceedences numbers of each base levels Station characteristics Exceedences number Station name Latitude Longitude Height (m) 10 M/SN 12M/SN 15 M/SN 20 M/SN Inebolu Sinop Samsun Giresun Trabzon Rize Hopa Edirne Corlu Istanbul Bolu Cankiri Corum Tokat Sivas Erzincan Erzurum Agri Igdir Gokceada Bozcaada Canakkal Bursa Ankara Yozgat Gemerek Van Ayvalik Dikili Akhisar Afyon Kayseri Malatya Mus Siirt Izmir Cesme Kusadasi Aydin Isparta K.maras Urfa Mardin Diyarbakir Hakkari Bodrum (continued on next page)

4 552 A.D. Sßahin / Energy Conversion and Management 44 (2003) Table 1 (continued) Station characteristics Exceedences number Station name Latitude Longitude Height (m) 10 M/SN 12M/SN 15 M/SN 20 M/SN Dalaman Antalya Anamur Mersin Adana Iskender Uzunkopru Sile Akcakoca Ardahan Ipsala Divrigi Bergama Simav Cihanbeyli Aksaray Seydisehir Kozan Siverek Karaman Kilis Antakya located in central Anatolia, but the Giresun and Rize stations are at the coast of the Black Sea, whereas Adana and Antakya are near the Mediterranean coast of Turkey. In order to identify the most primary wind energy potential areas, coarser counter intervals, say 50, are adopted as shown in Fig. 1b, again for the 10 m/s wind velocity level. In this way, coarser intervals correspond to a pseudo-resolution decrease in the exceedence regional map. It is clear from Fig. 1b that hours of 10 m/s are more intensified at the western and northwestern parts of Turkey, including the Aegean coast, northern parts of eastern Anatolia and the eastern Black sea region. However, the greatest number of exceedences at 10 m/s is equal to 4400 at the Bozcaada station. This means that, during one year, 160 days have wind velocities greater than or equal 10 m/s. There are 1860 days in five years, and hence, nearly 10% of the days are risky for wind energy generation. For an efficient wind energy planning, design, operation and maintenance, these values are most desirable. Similar calculations and mappings can be prepared for other wind velocity levels. For instance, when 12m/s or greater values are considered, then Fig. 2a shows, at contour intervals of 1, the number of exceedences. Compared with Fig. 1a, this figure has more contours in the dark regions. The white locations in Fig. 1a have increased, and some of the dark locations became gray locations. Consequently, the risky parts in Turkey have increased in Fig. 2a. Especially, the western and some parts of the southern Marmara region with the southern part of the eastern Anatolia region enter into the non-risky region.

5 A.D. Sßahin / Energy Conversion and Management 44 (2003) Fig. 1. Map of 10 m/s exceedence numbers with (a) one interval counter lines and (b) 50 interval counter lines. Corresponding to the 50 interval contours of Fig. 1b, the 12m/s levels are shown in Fig. 2b where the wind potential generation safety locations are concentrated in the Agean region. Finally, another wind velocity level considered for wind generation exceedence number in this paper is 15 m/s. Similar maps are presented in Fig. 3a which shows the exceedence numbers for each station with one interval contours. In this figure, the exceedences of 15 m/s with one interval decrease rapidly in a similar way to Fig. 2a, and it is seen that the white areas are further increased. However, the locations with exceedences of 15 m/s fall into the safety part. On the other hand, Fig. 3b shows the exceedences of 15 m/s for each station at 10 counter intervals. On this map, only six stations have exceedences of 15 m/s, namely at Sinop, Cß orlu, Bozcaada, Cß anakkale, Van and Mersin locations. In addition, topographic effects are also examined. Firstly, the relation between altitude and maximum exceedence numbers of the stations are taken into consideration. It is seen in Fig. 4 that three different groups occur due to the altitude effect. The first group occurs at coastal stations,

6 554 A.D. Sßahin / Energy Conversion and Management 44 (2003) Fig. 2. Map of 12 m/s exceedence numbers with (a) one interval counter lines and (b) 50 interval counter lines. and they have the greatest exceedence numbers of high wind velocities. Behind this group there is a sharply separated area without exceedence number between 200 and 600 m altitude. As is shown in Fig. 4, the second exceedence number group occurred between 600 and 1200 m altitude where the high flat plateaux can be seen. After this region, there is a small group that occurred at high mountainous regions and deep valleys. There are at least 400 m differences between the second and third groups. In short, Fig. 4 shows that three altitude groups are important for wind energy generation and engineering design. In this study, the latitude effect is also considered in Fig. 5 which shows that the 38 north latitude separates the Turkish topography into two groups. In the first group, 21 stations are included with 41 stations at higher latitudes. Therefore, the high wind energy potential areas are

7 A.D. Sßahin / Energy Conversion and Management 44 (2003) Fig. 3. Map of 15 m/s exceedence numbers with (a) one interval counter lines and (b) 10 interval counter lines. located generally at high latitudes in Turkey. In Fig. 5, the first group of stations shows approximately the same exceedence numbers, but in the second group, there are homogeneous exceedence numbers. Especially, the highest wind velocity exceedence station in Bozcaada is in the second group in Fig. 5 but the first group in Fig Conclusions In this study, 68 major climate stations data are used from all over Turkey in order to see, regionally, the number of exceedences over the country. On the basis of these stations, three risk levels are considered and maps for each level are drawn. It is understood that most of the stations

8 556 A.D. Sßahin / Energy Conversion and Management 44 (2003) Fig. 4. Altitude effect on maximum wind velocity. Fig. 5. Latitude effect on maximum wind velocity. have exceedences frequently over 10 and 12m/s. These locations are considered as the safe spots for wind energy generation. Risky locations, from the stability point of view, have 15 m/s or greater wind velocity. There are 15 stations that fall into this group. Especially, the Bozcaada and Cß anakkale stations have high risks for construction buildings, bridges and wind erosion but are safe for wind energy production. In short, most of the wind power generation safe locations are along the Aegean coasts and partially at other coastal areas of the Black Sea and the Mediter-

9 A.D. Sßahin / Energy Conversion and Management 44 (2003) ranean Sea. In addition, altitude and latitude effects are considered, and it is seen that both topographic parameters have an essential role in the occurrences of maximum wind velocities. References [1] Justus CG, Hargraves WA, Yalcßin A. Nationwide assessment of potential output from wind-power generators. J Appl Meteorol 1976;15: [2] Justus CG, Mikheal A, Graber D. Methods for estimating wind speed frequency distribution. J Appl Meteorol 1978;17: [3] Sßen Z. Statistical investigation of wind energy reliability and its application. Renew Energy 1977;10:71 9. [4] Palutikof JP, Kelly PM, Davies TD. Impact of spatial and temporal wind speed variability on wind energy output. J Clim Appl Meteorol 1987;26: [5] Lieblein L. Efficient methods of extreme-value methodology report NBSIR Washington: National Bureau of Standards; [6] Gumbel EJ. Statistics of extremes. New York: Colombia University Press; [7] Harris RI. Gumbel re-visited- a new look at extreme value statistics applied to wind speeds. J Wind Eng Ind Aerodyn 1996;59:1 22. [8] Sßahin AD, Sßen Z. First order markov chain approach to wind speed modeling. Wind Eng Indust Aerodyn 2001;89(3 4): [9] Sßen Z, Sßahin AD. Regional assessment of wind power in western Turkey by the cumulative semivariogram method. Renew Energy 1997;12(2). [10] Sßen Z, Sßahin AD. Regional wind energy evaluation in some parts of Turkey. J Wind Eng Industl Aerodyn 1998;37(7): [11] Oztopal A, Sßahin AD, Akg un N, Sßen Z. On the regional wind energy potential of Turkey. Energy 2000;25:2.