Survey of wind power potential for wind-based electricity at Makambako, Iringa Tanzania

The potential for wind-generated electricity is examined using 22 months wind data collected from a prospective site located in the southern highlands of Tanzania. While the data for the year 2001 was from March to December that of 2002 was for all the twelve months of the year.Characteristics of monthly and annual wind speed and direction are systematically investigated based on hourly time-series data using Windographer software. The Weibull shape factors k corresponding to a height of 50 m were found to be 3.10 and 3.80 while the scale factors c were 11.06 and 12.27 m/s for the years 2001 and 2002, respectively. The wind power potential at the location is established to be substantially high as the mean power density and energy content at the site are 8,788 and 6,839 W/m2, and 78,986 and 59,908 kWh/m2/yr, respectively, for the years2001 and 2002. The large difference between the mean values for the two years is due to the fact that the set of data for first year was for a period of 10 months while that of the later year was for 12 months

Prediction of Wind Power Density for Electricity Generation at Makambako, Tanzania Using Auto-Regression Integrated Moving Average (ARIMA) Model

Wind speed data used in this study were from Makambako and were recorded at a height of 10 m. In the analysis, the data were extrapolated to 80 m above ground level and wind speed from July to November were found to have an average value of 17.58 m/s. November was found to be the windiest month for the whole duration while the calm month was found to be March. The wind power density was found to be highest in the month of November for the whole study duration. The months of July to November have higher wind power density ranging from 1,739.00 W/m2/month to 12,244.35 W/m2/month at 80 m above ground level while the remaining months have values below the mentioned range. The findings of this study have shown that among five predictions, three showed acceptable predictions of 90.40%, 96.38% and 73.42%, one showing a fair prediction of 65.90% while the fifth one giving unacceptable prediction of 28.83%. It is proposed that ARIMA model be used to predict wind speed for other months apart from March 2009 and November for the years 2009, 2010, 2013 and 2016 that were predicted in this study.Keywords: ARIMA model; average wind speed; prediction; wind power density

Assessment of wind energy potential for eletricity generation in Setchet, Hanang, Tanzania

Tanzania depends heavily on hydropower for her electricity demand and experiences power shortage during the dry seasons. Wind energy is proposed as an alternative source of electricity to the fossil fuel generators during the dry season, the latter are normally used to supplement the shortfall in hydro-electricity generation. Fossil fuel generators produce emissions that are toxic and as such degrade the environment. Wind speed data from a site called Setchet is used to illustrate that the available wind energy can be harvested to generate electricity that can supplement the shortfall of electricity. The windy season, which is from July to November, coincides with the dry season. The annual average wind speed is 8.3 m/s, a value that is sufficient to generate electricity. Wind energy that can be harvested from this annual average wind speed is 2.30X103 kwh per year. It is suggested that by generating electricity from wind, the already limited hydrological resources in the country could be used for irrigation schemes instead of channelling them for developing new hydropower plants. Tanz. J. Sci. Vol. 28(2) 2002: 27-3

Determination of the power law exponent for southern highlands of Tanzania

The 1/7th power law is among the methods that have been used to extrapolate wind speed to the hub heights of wind turbines from the measuring levels. However, it tends to underestimate the actual long-term average wind speeds. In this paper, the power law exponent for Makambako, a site located in the southern highland zone of Tanzania, was established using wind speeds measured at heights Z1=2 m and Z2=7 m. The average power law exponent obtained at the test site was 0.47, a value that is substantially higher than the 1/7th power law exponent. It is low during the dry season and high during the rainy season. Values of the exponent higher than the overall mean were observed during the night while lower values were detected during the daytime. The overall mean value of the exponent determined from this trial site can be used to project wind speed to desired heights in areas with similar topographical features especially those in the southern highlands of Tanzania, in which the experimental site is situated. Tanzania Journal of Science Vol. 32 (1) 2006: pp. 103-10

Comparison of accuracies in techniques for evaluating wind power density

Wind power is among important renewable sources of energy. In order to know the magnitude of wind power, appropriate techniques for evaluating it need to be investigated. Apart from the standard formula that can be used to evaluate wind power density at a site there are two more techniques namely power law exponent and Weibull two-parameter density function. However the accuracy of the latter two methods relative to the standard one has not yet been investigated. The main objective of this paper is to compare accuracies of these techniques. The wind power densities were calculated using standard formula, Weibull model as well as exponential factor of power law. The annual average of wind power density evaluated using the standard formula at the test site is 623 W/m2 while the values estimated using power law exponent and Weibull model are respectively, 629 W/m2 and 615 W/m2. The correlation coefficients between the standard method and the other two methods were found to be respectively, 0.996 and 1.000. These correlations are high enough to warrant that each one can be used to evaluate wind energy density at site with sufficiently high accuracy.Keywords: Annual average, Wind power density, Power law exponent, Weibull mode

The Comparative Analysis of the Performances of Four and Six Pole Pairs Permanent Magnet Synchronous Generator

Wind power applications using multi-poles permanent magnet generators have become very attractive especially in small ratings. Low-speed multi-pole PM generators are maintenance-free and may be used in different climate conditions. Most of the low speed wind turbine generators presented is permanent magnet machines, which have advantages of high efficiency and reliability since there is no need of external excitation and conductor losses are removed from the rotor. From the study two types of PM AC generator are designed with 6 pole pairs and the other one with 4 pole pairs. These generators were designed and analysed using Maxwell software. The results were compared for the best performance determination. The 6 poles generator was found to have good power output with less Total Harmonic Distortion (THD) and high efficiency of over 92% that could be achieved at low wind speed of 2 m/s

Design of a Small Scale Wind Generator for Low Wind Speed Areas

Most small scale level wind turbine generators are directly driven system, variable speed, and partially connected power electronic converter system. Choice of such system is to avoid costs associated with gearbox. However, due to low wind speed in most of the tropical countries, synchronous generators with smaller or medium speed Permanent Magnet (PM) generator design found to be important and given high performance efficiency. In order to be able to harvest wind energy in off-grid population efficiently, there was a need to design a synchronous generator that can be able to operate under low wind speed, directly connected to the end user. Hence, the study designed a six pole pair wind turbine generator using permanent magnet (PM) model, using Maxwell two dimensions (2D) and Rotational Machine Expert (RMxrpt) software. The designed PM AC wind turbine generator worked with efficiency of 93% at rotational speed (rpm) range from 50 to 350 with maximum power output of 980 watts.Keywords: Pole Pairs, Performance Characteristics, Permanent Magnet Wind Generato

Analysis of Power Efficiency of a Direct-Driven Locally Fabricated Permanent Magnet Ac Generator for Small-Scale Wind Power Applications in Tanzania

The use of direct-driven permanent magnet alternating current (AC) generators offers the opportunity to reduced costs and increased system efficiency. This type of generator could be the best alternative for rural population whom are not connected to the national grid. To improve the design and efficiency of locally fabricated generators, it is imperative tocharacterize both their mechanical and electrical parameters. This paper presents the analysis of power efficiency of the synchronous permanent AC generator locally fabricated in Tanzania. In this case, load resistance and rotational speed are characterized using designed experiment. The output current and voltage of the generator were recorded simultaneously in each step change of load resistance and rotational speed. The output power and efficiency were then determined analytically. The results show that there is a linear relationship between voltage and rotational speed of the generator with and without load resistance. The results further indicated that out power is not linearly related to rotational speed. The generator•s power efficiency was found to be about 55% against both the output voltage and rotational speed

Fire regimes and variability in aboveground woody biomass in miombo woodland

This study combined a process-based ecosystem model with a fire regime model to understand the effect of changes in fire regime and climate pattern on woody plants of miombo woodland in African savanna. Miombo woodland covers wide areas in Africa and is subject to frequent anthropogenic fires. The model was developed based on observations of tree topkill rates in individual tree size classes for fire intensity and resprouting. Using current and near-future climate patterns, the model simulated the dynamics of miombo woodland for various fire return intervals and grass cover fractions, allowing fire intensity to be estimated. There was a significant relationship between aboveground woody biomass and long-term fire regimes. An abrupt increase in fire intensity and/or fire frequency applied as a model forcing led to reduced long-term average aboveground woody biomass and mean tree size. Fire intensity increased with increasing living grass biomass (which provides increased flammable fuel), thereby affecting the relationship between fire regime and tree size, creating a demographic bottleneck on the route to tree maturity. For the current fire regime in miombo woodland, with a fire return interval of about 1.6-3 years, the model-predicted fire intensity lower than 930-1700 kW m-1 is necessary to maintain today's aboveground woody biomass under current climate conditions. Future climate change was predicted to have a significant positive effect on woody plants in miombo woodland associated with elevated CO2 concentration and warming, allowing woody plants to survive more effectively against periodic fires