WIND SPEED DISTRIBUTION, ESTIMATION OF THE WIND SHEAR EXPONENT AND THE ROUGHNESS PARAMETER FOR JUJA-KENYA
Saoke C*1., Kamau J.N1. and Kinyua R1
Department of Physics
Jomo Kenyatta University of Agriculture and Technology, Nairobi-Kenya
E-mail: winsaoke@gmail.com
ABSTRACT
Wind is a source of clean and alternative form of power production. Juja area (1° 10′ S, 37° 7′ E) in Kenya is growing very fast and being a University town is likely to become one of the economic hubs of Kiambu County and the greater Nairobi metropolis. This area also experiences frequent blackouts due to over reliance on electricity from the nationally connected grid, this despite the fact that it is highly endowed with adequate wind flow which can be locally harnessed to supplement power production and reduce over reliance on generators as backups. In spite of this potential, the lack of adequate site specific data information that enables informed choice on site selection, turbine selection, expected power output and turbine design still remains a challenge to the exploitation of this wind resource. This research paper provides a to study the wind speed variation through statistical data description of the Juja wind speed and the Weibull distribution model developed from the measured wind speeds applied to estimate the wind power density of the site. The wind speeds were analyzed and the wind characterized based on short term (three months) measured hourly series data of daily wind speeds at 13 m and 20 m heights. Analysis of wind data included daily wind data which were calculated to represent; the mean wind speed, diurnal variations, daily variations as well as the monthly variations. The wind speed frequency distribution at the 20 m was determined and the mean wind speed found to be 5.04 m/s with a standard deviation of 2.59. The average wind speeds at the two heights (13 m and 20 m) were used to calculate the wind shear exponent and the roughness parameter for Juja; this was found to be 0.16 and 0.048 m respectively. Using the calculated shear exponent, an extrapolation of the speeds was done to higher heights of up to 150 m. Maximum speed obtained at the 150 m height was 8.4 m/s during the month of October, these results provides a clear understanding of Juja’s energy potential and the localized wind parameter characteristics which are necessary for matching the machine characteristics to the local wind regime.
Keywords: Wind speed, wind shear exponent, roughness parameter, wind speed distribution