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TEKNIK PENGUKURAN POTENSI ENERGI ANGIN Malik Ibrochim Bidang Konversi Energi Dirgantara LAPAN

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WIND CAUSED Wind is caused by differences in pressure. When a difference in pressure exists, the air is accelerated from higher to lower pressure difference in pressure Near the Earth's surface, friction causes the wind to be slower than it would be otherwise. Surface friction also causes winds to blow more inward into low pressure areas. [1]friction [1]

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Overview: Wind Wind speed measurements provide local data to estimate wind power available – “Local” means where the turbine will stand Wind power/energy computations yield estimates of energy available at the anemometer Statistical processing is required to estimate accurately for the long term

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12.1 About This Presentation Anemometers Wind Data Processing Site Wind Variations Wind Power Wind Energy

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Anemometers Anemometers measure the speed and direction of the wind as a function of time Spinning cups or propeller Ultrasonic reflection (Doppler) Sodar (Sound detection and ranging with a large horn) Radar Drift balloons Etc. Wind data are usually collected at ten-minute rate and averaged for recording Gust studies are occasionally used, and require sampling at a higher rate to avoid significant information loss (4 pts/gust) Spectral analysis indicates the frequency components of the wind structure and permits sampling frequency selection to minimize loss

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PERALATAN UKUR POTENSI ENERGI ANGIN

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DIAGRAM ALUR PENENTUAN KECEPATAN ANGIN DAN DURASI OPTIMUM

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Wind Data Processing Serial data from a datalogger must be validated to detect errors, omissions, or equipment malfunctions These data are usually produced in a text (.TXT) format Specialized computer codes may read the data or an export function used to produce a txt output file Statistical analysis is used to detect anomalies, peaks and nulls (lulls in wind jargon), and determine the distribution of the speeds and directions Frequency analysis with the Fast Fourier Transform (FFT) will show where the energy lies and its probability Cepstral analysis shows the periodicities Graphic analysis displays the results for visual interpretation

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Local Site Wind Availability Once a region of persistent winds is located, an area of interest is defined by local reconnaissance, land inquiries made, etc. Since trees act to block the wind or cause turbulence, a distance to the nearest tree of less than feet will significantly impact the free wind A wind rose for that area will define the principal directions of arrival; seek local advice as to storm history as well; look for flagging of vegetation Place an anemometer or small temporary turbine about 20 ft away from the intended tower site so that the anemometer can be retained there when the main turbine is installed; choose the direction of least likely wind

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Wind Variation Since wind velocity (speed and direction) varies over a year and over many years, long-term data are required The velocities may be estimated using one year’s data or climate (long-term weather data) may be obtained from climate agencies While wind direction varies, most wind turbines will track in azimuth (yaw) to maximize the energy extracted, and wind arrival direction knowledge is more important in determining upwind blockage or obstruction The wind speed, average, one-minute gust, and extreme, is sufficient for most energy assessment purposes The top 30% of the wind speed regime will provide ~70% of the energy

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Wind Speed Variation In a time series of wind speed data, there will be many different values of speed For convenience, the speeds are usually divided into “bins”, or ranges of speed, e.g., 0-1 mph, 1+ to 4 mph,..., mph, etc. The ranges vary, but since there are many samples in a year, there can be many ranges in the process The number of samples that fall within a bin can be plotted as a histogram versus the wind speed ranges A line drawn through the top of the histogram bars approximates a continuous function that is similar to a Weibull Function, or in a more simple case, a Rayleigh Function

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Wind Speed Variation This Weibull probability curve shows the variation for a site with a 6.5 m/s mean wind and a shape factor of 2; the higher the factor, the more peaked or pointed Notice that the mean is not the most common; that is the mode, and the median is in the middle of the data The shape factor of 2.0 reveals that this is the Rayleigh probability as well Usually it’s a little windy, sometimes it’s calm, and in storms, the wind blows hard but not for long A probability curve (p.d.f.) is just a way to express this mathematically If the wind values are integrated, a distribution curve results

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Wind Speed Power Density Not all wind power can be extracted or wind would stop The Betz Limit of 59.3% is the theoretical maximum Turbines approach 40% from the rotor, but the mechanical and electrical losses may take 20% of the rotor output Grey = total power Blue = useable power Red = turbine power output 0 to 25 m/s on abscissa

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TINJAUAN PUSTAKA: c = 1,12 *KEC.ANGIN RATA-RATA( 1,5 ≤ k ≤ 4 ) h = f(u)t/2( Jam ) PARAMETER WEIBULL

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Bulan Nilai Kecepatan Angin (m/det) σ Lama waktu Pengamatan (menit) Parameter Weibull MaksMinc k Januari3,316,41,10, ,4 4,0 Februari3,216,81,10, Maret3,417,21,20, April2,919,90,90, Mei2,814,10,70, Juni2,815,30,90, Juli3,216,80,90, Agustus3,318,71,10, September3,115,71,10, Oktober2,819,11,00, Nopember2,715,70,90, Desember3,018,30, Rata-rata3,017,00,8 Total lama waktu pengamatan (menit) Nilai kecepatan angin rata-rata, standar deviasi, lamanya waktu pengamatan dan nilai parameter distribusi Weibull c dan k untuk wilayah Palu Sulawesi Tengah dengan ketinggian 30 meter HASIL DAN PEMBAHASAN KURVAKURVA

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V (bin)Weibull f(u) %V E E E E E E E E E E E E E E E E E E E E E E-290 FUNGSI PROBABILITAS WEIBULL UNTUK MASING-MASING KEC.ANGIN GRAFIKGRAFIK

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KURVA PROBABILITAS DISTRIBUSI WEIBULL vs KECEPATAN ANGIN TABEL WEIBULL

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GRAFIK DURASI

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12.1 Conclusion: Wind Theory The theory of wind energy is based upon fluid flow, so it also applies to water turbines (832 times the density) While anemometers provide wind speed and usually direction, data processing converts the raw data into usable information Because of the surface drag layer of the atmosphere, placing the anemometer at a “standard” height of 10 meters above the ground is important; airport anemometer heights often historically differ from 10 meters For turbine placement, the anemometer should be at turbine hub height The average of the speeds is not the same as the correct average of the speed cubes! The energy extracted by a turbine is the summation of (each speed cubed times the time that it persisted)

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TERIMA KASIH

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