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15Статья поступила в редакцию 22.02.10. Ред. рег. № 727
The article has entered in publishing office 22.02.10. Ed. reg. No. 727
УДК 620.91
СОЛНЕЧНОЕ ИЗЛУЧЕНИЕ В ТОГО К.А. Амоу, С. Оуро-Джобо, К. Напо
Лаборатория солнечной энергетики, Кафедра возобновляемых источников энергии UNESCO (L.E.S), Факультет естественных наук (CUER) Университета Ломе-Того BP: 1515, Ломе-Того, тел.: (228) 2255094; e-mail: mapkamou@yahoo.fr
Заключение совета рецензентов: 09.03.10 Заключение совета экспертов: 15.03.10 Принято к публикации: 18.03.10
На протяжении шести лет на трех станциях наблюдения на географической территории Того проводились измерения интенсивности солнечного излучения и продолжительности солнечного сияния. Статистический анализ данных об интенсивности солнечного излучения и продолжительности солнечного сияния был выполнен в рамках проектов по определению потока солнечной фотогальванической или тепловой энергии. Ограничения, налагаемые физической моделью, заставляют использовать данные наземных измерений. В результате исследований и обработки данных по станциям в городах Ломе, Атакпаме и Манго было установлено, что дневное значение интенсивности солнечного излучения составляет 4,39 кВт/м2 при среднеквадратическом отклонении 1,13 в Ломе, 4,81 кВт/м при среднеквадратическом отклонении 0,92 в Атакпаме и 5,45 кВт/м2 при среднеквадратическом отклонении 1,00 в Манго.
Ключевые слова: интенсивность солнечного излучения, продолжительность солнечного сияния, доля излучения, среднее значение, срединное значение, среднеквадратическое отклонение.
SOLAR IRRADIATION IN TOGO K.A. Amou, S. Ouro-Djobo, K. Napo
Laboratoire sur l'Energie Solaire(L.E.S), Chaire Unesco sur les Energies Renouvelables(CUER), Faculté des Sciences,
Université de Lomé-Togo BP: 1515, tel: 2255094; e-mail: mapkamou@yahoo.fr
Referred: 09.03.10 Expertise: 15.03.10 Accepted: 18.03.10
In three localities of the Togolese geographical space, solar irradiation and sunshine duration are measured during a six year period. A statistical study of the solar radiation and sunshine duration data is made in seen evaluation of the solar irradiation within the framework of the projects solar photovoltaic or thermal. The limits of the physical models thus compel to have recourse to data of ground. After having studied and analyzed the data of Lomé, Atakpamé and Mango, the results show that the daily average of solar irradiation is of 4.39 kW/m2 with a standard deviation of 1.13 in Lomé, 4.81 kW/m in Atakpamé with a standard deviation of 0.92 and 5.45 kW/m2 in Mango with a standard deviation of 1.00.
Key words: solar irradiation, sunshine duration, fraction of shinning, average, median, standard deviation.
Organization: Université de Lomé, Faculté des Sciences, Chaire de l'UNESCO sur les Energies Renouvelables, Laboratoire sur l'Energie Solaire.
Education: Bachelor of Science degree in physics in 2004, master's degree in material science in 2006 at the Université de Lomé. I am preparing my PHD degree.
Experience: Scientific research project, member of Laboratoire sur l'Energie Solaire of Université de Lomé, ATER (Attaché Temporaire pour l'Enseignement et la Recherche) of Université de Lomé since January 2008.
Main range of scientific interests: renewable energy, solar energy, optoelectronic thin films and its applications.
Apélété Amou
S. Ouro-Djobo
Organization: Université de Lomé, Faculté des Sciences, Chaire de l'UNESCO sur les Energies Renouvelables, Laboratoire sur l'Energie Solaire.
Education: Bachelor degree in Electronic in 1994 at the University of Lille, master's degree in Systems and Electronic option in 1995 at the University Clermont-Ferrand II, PhD degree in 2001 at the University of Nantes.
Experience: Lecturer at University of Lomé since 2002, Maîtres Assistant since 2005 and member of Laboratoire sur l'Energie Solaire of Université de Lomé. Working on the characterization of Togo solar irradiation project, drying Agricultural products and thin films grown by chemical bath deposition for photovoltaic applications.
Main range of scientific interests: renewable energy, solar energy, product drying and optoelectronic thin films and its applications.
Publications: 10 articles and communications.
International Scientific Journal for Alternative Energy and Ecology № 2 (82) 2010
© Scientific Technical Centre «TATA», 2010
Kossi Napo
Organization: Université de Lomé, Faculté des Sciences, Chaire de l'UNESCO sur les Energies Renouvelables, Laboratoire sur l'Energie Solaire.
Education: Master degree in physic in 1982 at University of Abidjan (Côte d'Ivoire), DEA in material sciences in 1983 at University of Nantes, First PhD degree in 1986 at university of Nantes, Second PhD degree in 1998 at University of Nantes and Université de Lomé.
Experience: Lecturer at Université de Lomé since 2003, Person in charge of PhD training program in material science at Université de Lomé, National coordinator of UNITWIN of UNESCO at Université de Lomé, Senior associate of ICTP (Italy), member of scientific committee of Université de Lomé.
Main range of scientific interests: renewable energy, solar energy, thin film research, optoelectronic and electronic thin films applications.
Publication: 20 papers in international and national scientific journal, 10 oral communications and 5 posters.
Introduction
With the implementation of policy to fight climate change and exhaustion of the irradiations of fossil energy, solar energy knows a renewal of topicality in all its crenels of application: photovoltaic and thermic. The accurate evaluation of the local irradiation is a precondition to the assembly of projects on the ground. Whether it is about the selection of a site or a zone for the installation of a project, dimensioning of a photovoltaic system or follow-up of performances of the solar systems, the data of radiant exposure are essential for dimensioning and to meet the energy needs. This paper aims to place at the disposal of private individuals, researchers and companies, of the reliable data of sunning usable in Togo. The determination of the space and temporal distribution of the solar irradiation require a statistical study. This study cannot be made without the examination of the distribution of the traditional statistical variables. This is why in the first time a certain number of parameters will be examined: the first quartile, the third quartile, the median, the average, the expectation and the standard deviation will make it possible to have an outline of the distribution. Then the analysis results and of the curves will make it possible to release the characteristics of the distribution and that of the cumulative frequencies. But before that, some definitions must be recalled.
Some definitions and orders of magnitude
The solar radiation or illumination is the flow of power per unit of area which arrives on a surface at a moment. It is expressed in W/m2. In addition to the nature of receiving surface and the moment concerned, it is important to specify the type of radiation considered: direct (coming from the sun), diffuse (coming from the solar vault, other than the circumsolar zone) total (nap of direct and diffuse), reflected by the ground (a plan inclined compared to the horizontal one receives a component of radiation reflected by its close environment, according to the coefficient of reflection of the ground or albedo) [1]. Maximum global solar
radiation is about 1000 W/m2 under the most favorable conditions (clear sky, surface correctly directed compared to the sun). Integration over a certain period of time, solar radiation leads to energy per unit of area, called radiant exposure (irradiation), expressed in kW-h/m2. It is essential to specify always well, when one speaks about radiant exposure, to which time interval one refers (time, daily, monthly, annual or different. One frequently presents the data of solar radiation (as in this paper) in the form of monthly averages of the daily exposure. In this paper we will use the sunning or solar irradiation in W/m2. The S/So is the ratio of the sunshine duration measured in hour and of the maximum possible sunshine duration except for atmosphere for a given place. Taking into account the variability of the solar irradiation on different scale from time and space, it is necessary to rather precisely estimate the irradiation of a site before any study of establishment of a solar installation. This is why in Togo on three sites of the geographical space of the country which are Lomé, Atakpamé and Mango, the solar irradiation is measured since 2002 with devices of the type LICOR [2].
Methodology of measurement and data of study
The measurement of the solar radiation in Togo is carried out starting from pyranometers LI200 and recorded by power stations of acquisition LI1400.
The principle of this pyranometer is based on the measurement of the density flux of the solar radiation which passes by the horizontal plane of a surface of known surface. It comprises a photovoltaic sensor with calibrated silicon so that it converts this density flux into output power of intensity I, which is proportional to it. The value of this density flux is measured out of W /m2 and the error to the measures is lower than 5%.[3] Once established in the three localities which are Lomé, Atakpamé and Mango, measurements were taken, which enabled us to constitute a data bank treated. This bank consisted of the monthly, time data and day laborers of the sunning. Data used for this study of the data of time total sunning over the period 2002 to 2007 for the three
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stations and of sunshine duration for the station of Lomé alone during the same period. We present in Fig. 1, the map of Togo showing his position in Africa and the positions of the three towns.
Рис. 1. Карта Того с указанием его расположения в Африке и местонахождения городов, где находятся станции Fig. 1. Map of Togo showing his position in Africa and the positions of the station's towns
Statistic studies of data
Fraction of sunshine duration and solar irradiation
From the data of sunshine duration measured in Lomé and data of maximum possible sunshine duration calculated, the fraction of sunshine duration over all the period of measurements is calculated. Then, the frequencies corresponding to the various classes were calculated, which allowed to obtain the average values for each month. These frequencies also have allowed us to calculate the expectation, the variance and the standard deviation for each month as well as the total values of these parameters over the period 2002-2007. It should be noted that we do not have the values of sunshine duration for the towns of Atakpamé and of Mango, thus the fraction of sunshine duration relates to Lomé only.
The values of the hourly solar radiation are the raw data which are collect from the power stations LI-1400. These data were treated in order to obtain the values of the global solar irradiation for each day. The study is made from these daily values. After having gathered them by class; the classes of the quartiles and the median were given for each city. Then, the frequencies corresponding to the various classes were calculated, which led to obtaining average values of the global solar irradiation for each month. These frequencies also have allowed us to calculate the expectation, the variance and the standard deviation for each month as well as the global values of these parameters over the period 2002-2007. The results of this study are presented in Tables 1 to 8.
Таблица 1
Распределение дневной продолжительности солнечного сияния по классу, 1 квартилю, 3 квартилю и срединному значению (Ломе)
Table 1
Distribution of the daily sunshine duration by class, 1st, 3rd quartile and median (Lomé)
Fraction sunshine duration [0-0,1] [0,1-0,2] [0,2-0,3] [0,3-0,4] [0,4-0,5] [0,5-0,6] [0,6-0,7] [0,7-0,8] [0,8-0,9] [0,9-1] 1st quartile Median 3rd quartile
January 21 13 8 12 11 26 37 26 1 0 [0,2-0,3] [0,5-0,6] [0,6-0,7]
February 6 6 4 11 14 22 39 30 8 0 [0,4-0,5] [0,6-0,7] [0,7-0,8]
March 11 5 6 11 9 31 34 37 12 0 [0,4-0,5] [0,6-0,7] [0,7-0,8]
April 13 7 9 12 12 12 17 36 32 1 [0,3-0,4] [0,6-0,7] [0,7-0,8]
May 22 10 9 11 10 13 17 28 28 7 [0,2-0,3[ [0,6-0,7] [0,7-0,8]
June 33 11 6 8 14 10 12 12 11 3 [0-0,1] [0,4-0,5] [0,6-0,7]
July 24 10 10 14 15 10 19 8 12 2 [0,1-0,2] [0,4-0,5] [0,6-0,7]
August 22 16 15 20 13 10 13 10 5 0 [0,1-0,2] [0,3-0,4] [0,5-0,6]
September 13 8 15 15 16 16 10 16 11 0 [0,2-0,3[ [0,4-0,5] [0,6-0,7]
October 18 1 5 3 17 17 26 28 39 1 [0,4-0,5] [0,6-0,7] [0,8-0,9]
November 3 0 7 6 12 14 27 40 40 1 [0,5-0,6] [0,7-0,8] [0,8-0,9]
December 0 1 7 3 16 21 33 60 14 0 [0,5-0,6] [0,6-0,7] [0,7-0,8]
2002-2007 186 88 101 126 159 202 284 331 213 15 [0,3-0,4] [0,5-0,6] [0,7-0,8]
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© Scientific Technical Centre «TATA», 2010
Таблица 2
Среднее, математическое ожидание и среднеквадратическое отклонение для дневной продолжительности солнечного сияния в Ломе
Table 2
Average, hope and standard deviation of the daily sunshine duration in Lomé
Months Jan Feb March April May June July August Sept Oct Nov Dec 2оо2-2оо7
Effective 155j Щ 156j 151j 155j Щ 124j 124j 12Üj 155j 150j 155j 1705j
Average о,47 о,57 о,56 о,57 о,53 о,4о о,43 о,37 о,46 о,бо о,66 о,65 о,53
Hope о,47 о,57 о,56 о,57 о,53 о,4о о,43 о,37 о,46 о,бо о,66 о,65 о,53
Variance о,об о,о4 о,о5 о,о7 о,о9 о,о9 о,о7 о,об о,об о,о7 о,о4 о,о2 о,об
Standard deviation о,24 о,2о о,22 о,26 о,зо о,зо о,26 о,24 о,24 о,26 о,2о о,14 о,24
Таблица 3
Распределение дневной интенсивности солнечного излучения по классу, 1 квартилю, 3 квартилю
и срединному значению (Ломе)
Table 3
Distribution of the daily sunning by class, 1st, 3rd quartile and median (Lomé)
Sunning (kW/m2) [о-1] [1-2] [2-3] [3-4] [4-5] [5-6] [6-7] [7-В] [В-9] 1st quartile Median 3rd quartile
January о 5 14 В9 35 4 о о о [3-4] [3-4] [4-5]
February 2 2 1 2В 47 31 2 о о [3-4] [4-5] [5-6]
March о о 4 2о 2В 43 6 о о [4-5] [4-5] [5-6]
April о 3 5 9 1В 37 17 о о [4-5] [5-6] [5-6]
May о 6 12 В 19 36 14 о о [3-4] [5-6] [5-6]
June 2 16 14 23 25 27 3 о о [2-3] [4-5] [5-6]
July 1 В 17 22 3В 23 о 1 о [3-4] [4-5] [4-5]
August о 5 15 31 21 1В 2 о о [3-4] [3-4] [4-5]
September о 5 9 2о 19 27 9 1 о [3-4] [4-5] [5-6]
October 1 5 6 12 22 43 2о о о [4-5] [5-6] [5-6]
November о о 3 1о 47 55 5 о о [4-5] [5-6] [5-6]
December о о 4 23 В1 В о о о [4-5] [4-5] [4-5]
2002-2007 6 55 1 о4 295 4оо 352 7В 2 о [3-4] [4-5] [5-6]
Таблица 4
Среднее, математическое ожидание и среднеквадратическое отклонение для суммарной дневной интенсивности солнечного излучения в Ломе
Table 4
Average, hope and standard deviation of the daily total sunning in Lomé
Month Jan Feb March April May June July August Sept Oct Nov Dec 2оо2-2оо7
Manpower 147j 113j B9j 95j Щ Щ 92j 90j Щ Щ 116j 1292j
Average 3,63 4,42 4,77 4,9B 4,65 3,B3 3,97 3,91 4,44 4,B7 4,91 4,3о 4,39
Hope 3,63 4,42 4,77 4,9B 4,65 3,B3 3,97 3,91 4,44 4,B7 4,91 4,3о 4,39
Variance о,56 1,о6 о,95 1,5B 2,1 о 2,22 1,63 1,42 1,92 1,BB о,64 о,37 1,36
Standard deviation о,75 1,о3 о,97 1,26 1,45 1,49 1,2B 1,19 1,39 1,37 о,Во о,6о 1,13
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Таблица 5
Распределение дневной продолжительности солнечного сияния по классу, 1 квартилю, 3 квартилю и срединному значению (Атакпаме)
Table 5
Distribution of the daily sunning by class, 1st, 3rd quartile and median (Atakpame)
Sunning (kW/m2) [0-1] [1-2] [2-3] [3-4] [4-5] [5-6] [6-7] [7-8] [8-9] 1st quartile Median 3rd quartile
January 0 0 3 17 52 20 0 0 0 [4-5] [4-5] [4-5]
February 0 0 3 5 33 42 6 0 0 [4-5] [5-6] [5-6]
March 0 1 1 3 23 54 26 0 0 [4-5] [5-6] [5-6]
April 0 2 2 16 21 74 42 1 0 [4-5] [5-6] [6-7]
May 1 1 4 8 27 56 34 0 0 [4-5] [5-6] [6-7]
June 1 2 6 11 36 54 18 1 0 [4-5] [5-6] [5-6]
July 0 3 14 40 43 20 3 0 0 [3-4] [4-5] [4-5]
August 0 3 27 54 30 12 1 0 0 [3-4] [3-4] [4-5]
September 1 4 8 32 51 45 5 0 0 [3-4] [4-5] [5-6]
October 0 2 2 13 29 76 8 0 0 [4-5] [5-6] [5-6]
November 0 0 0 2 20 72 11 0 0 [5-6] [5-6] [5-6]
December 0 0 0 9 84 31 0 0 0 [4-5] [4-5] [5-6]
2002-2007 3 18 70 210 449 556 154 2 0 [4-5] [4-5] [5-6]
Таблица 6
Среднее, математическое ожидание и среднеквадратическое отклонение для суммарной дневной интенсивности солнечного излучения в Атакпаме
Table 6
Average, hope and standard deviation of the daily total sunning in Atakpame
Month Jan Feb March April May June July August Sept Oct Nov Dec 2002-2007
Manpower 92j 89j 108j 158j 131j 129j 123j 127j 146j 130j 105j 124j 1473j
Average 2002-2007 4,47 4,98 5,41 5,35 5,27 4,97 4,09 3,69 4,44 5,03 5,38 4,68 4,81
Hope 4,47 4,98 5,41 5,35 5,27 4,97 4,09 3,69 4,44 5,03 5,38 4,68 4,81
Variance 0,53 0,70 0,79 1,12 1,25 1,37 1,09 0,96 1,24 0,85 0,36 0,29 0,88
Standard deviation 0,73 0,84 0,89 1,06 1,12 1,17 1,04 0,98 1,11 0,92 0,60 0,54 0,92
Таблица 7
Распределение дневной продолжительности солнечного сияния по классу, 1 квартилю, 3 квартилю и срединному значению (Манго)
Table 7
Distribution of the daily sunning by class, 1st, 3rd quartile and median (Mango)
Sunning (kW/m 2) [0-1] [1-2] [2-3] [3-4] [4-5] [5-6] [6-7] [7-8] [8-9] 1st quartile Median 3rd quartile
January 0 0 1 3 15 69 32 2 0 [5-6] [5-6] [6-7]
February 0 0 1 0 4 33 46 5 0 [5-6] [6-7] [6-7]
March 0 1 0 1 5 11 58 16 1 [6-7] [6-7] [6-7]
April 0 0 2 5 9 25 57 19 0 [5-6] [6-7] [6-7]
May 0 0 4 11 17 44 62 12 0 [5-6] [5-6] [6-7]
June 2 4 7 15 23 47 50 2 0 [4-5] [5-6] [6-7]
July 0 7 15 32 40 54 15 0 0 [3-4] [4-5] [5-6]
August 0 7 13 42 58 51 11 0 0 [3-4] [4-5] [5-6]
September 0 1 12 17 34 41 45 0 0 [4-5] [5-6] [6-7]
October 0 0 2 2 17 58 66 0 0 [5-6] [5-6] [6-7]
November 0 0 0 2 20 72 11 0 0 [5-6] [5-6] [5-6]
December 0 0 0 1 39 61 13 0 0 [4-5] [5-6] [5-6]
2002-2007 2 20 57 131 281 566 466 56 1 [4-5] [5-6] [6-7]
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Таблица 8
Среднее, математическое ожидание и среднеквадратическое отклонение для суммарной дневной интенсивности солнечного излучения в Манго
Table 8
Average, hope and standard deviation of the daily total sunning in Mango
Month Jan Feb March April May June July August Sept Oct Nov Dec 2002-2007
Manpower 122j B9j 93j 117j 150j 150j 163j 1B2j 150j 145j 105j 114j 15B0j
Average 5,6о 6,05 6,3B 6,10 5,73 5,19 4,51 4,41 5,0B 5,77 5,3B 5,25 5,45
Hope 5,6о 6,05 6,3B 6,10 5,73 5,19 4,51 4,41 5,0B 5,77 5,3B 5,25 5,45
Variance о,61 0,5B 0,90 1,1B 1,33 2,03 1,65 1,3B 1,63 0,6B 0,36 0,43 1,06
Standard deviation 0,7B 0,76 0,95 1,09 1,15 1,42 1,2B 1,17 1,2B 0,B2 0,60 0,66 1,00
Results analysis For Lomé
The analysis of Tables 1 and 3 shows that during June, July and August, the first quartile is lower than 0.2, 50% of the fractions lower than 0.5 and the third quartile lower than 0.7. In the same way June has the smallest value for the first quartile with regard to the daily total sunning. This means that in Lomé, these three months are those during which the fraction is weak compared to the others. Concerning the sunning, they also have values even if the less sunny month remains January. These facts are explained by the fact that during these three months, monsoon, a wind from south-west blows by sweeping the country of the South towards North. During these months, the sky is often covered all the day and the sun hardly appears. It is also about the great rain season in the southern Togo. On the contrary, October to December, on the one hand, and February until April on the other hand is characterized by a median class higher than 0.6 and whose third quartile is some time superior to 0,8 concerning the fraction of insolation. November remains the sunniest month in Lomé if the account of these two tables is taken. The dry season starts in Lomé as from November and that is accompanied with the progressive arrival of the harmattan. Harmattan being a dry and dusty wind, the sky is often charged with dust attenuating the solar radiation a little. The harmattan in January is the cause of the higher diminution of the sunning and thus the sunshine duration. Tables 2 and 4 enable us to know that the monthly median values of the fraction of insolation and sunning. The maximum is reached in April with a median value of 4,98 kW/m2/day. The expectation of variable x "value day laborer of the total sunning" is the median value of the possible values of variable xt balanced by frequencies pi. It is 4.39 kW/m2/day with a standard deviation (average fluctuation of the x t around the hope) of 1,13.
For Atakpamé
The analysis of Tables 5 and 6 shows that the class of the first quartile remains always higher than 0.3 for every month. This means that 75% of the values day
sunning are higher than 3 kW/m2/day for every month. August, July and September remain the less sunny months. These months are also characterized by the presence of monsoon and the rainy season, which decreases the sunning. The minimum is reached in August and it is the only month when the sunning is lower than 4 kW/m2/day. In November, the class of the first quartile is from [5-6], which is particularly high compared to the other months of the year. The sunniest months are March, April, May as well as October and November. Particularly for these months the average sunning is higher than 5 kW/m2/day. This period corresponds to the dry season with some rare rains. The maximum value is in general obtained in March with an average value of 5.41 kW/m2/day. The expectation of variable xt is 4.81 kW/m2/day with a standard deviation (average fluctuation of the x t around the hope) of 0.92.
For Mango
The analysis of the results at the level of Mango shows that from May through October, the first quartile is higher than 5 kW/m2/day. This means that 75% of the values are higher than 5 kW/m2/day. Also, February to April is particularly sunnier with values of the daily total sunning higher than 6 kW/m2. This is explained by the fact that from January to November, the harmattan is hard in the North with the intense fog reducing the visibility and source of attenuation of the solar radiation. The presence of dust in the air is a parameter of attenuation of the radiation during this period. This is why in spite of the absence of rain, nature remains a little dark during this period. On the other hand, from September to June, the rainy season and the presence of monsoon call for the presence of clouds. That causes a very often covered sky. The maximum value is in general obtained in March with an average value of 6.38 kW/m2/day. The expectation of variable x is of 5.45 kW/m2/day with a standard deviation (average fluctuation of the xt around the hope) of 1.00.
Comparisons of the data of the three cities
The data analysis shows that the sunning becomes more intense when one moves away from the equator.
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Thus it is higher in Atakpamé than in Lomé and more intense with Mango than in Atakpamé. These reports are of course observed in Fig. 2 which presents the curves of the monthly median values of the total sunning for the three cities. Sunning might be proportional to the distance from the city to the coast (or to the latitude) like the curve of the Fig. 3 shows it.
Рис. 2. Сравнение среднемесячных значений для трех городов (2002-2007) Fig. 2. Comparison of the monthly averages of the three cities (2002-2007)
Рис. 3. Интенсивность солнечного излучения в зависимости от расстояния до Ломе Fig. 3. Sunning according to the distance from Lomé
Before proposing an explanation to these observations, we will present initially the Table 9 summarizing their geographical positions.
Таблица 9
Характеристики городов, в которых проводились измерения
Table 9
Table gathering the characteristics of the measuring sites
Characteristic Lomé Atakpame Mango
Distance, from Lomé, km о Ш 5оо
Latitude об0Ю' Northern о7035' Northern ^22' Northern
Longitude оП5' East ого7' East оо028' East
Altitude, m i9,6Q 499,66 М4,7о
- Solar irradiation increases with the latitude because in the northern hemisphere days become longer when one tends towards the poles thus increasing the duration of sunning. This observation can be confirmed with the installations of other station in the country.
- The climatic anomaly of the southern of Togo is another factor acting on the solar irradiation in Lomé making it weak.
- The two rainy seasons presence in the south of Togo (May-July and September-October) whereas in the North only one rainy season causes a drop in the sunning in the South of the country.
- The presence of moisture when one tends towards the equator is also another attenuating factor of the radiation whereas when one tends towards the tropics, the air is dry.
Temporal evolution of the sunning in Togo
This study will make it possible to know how the daily sunning evolves as we evolve in time. With this intention, we will use the comparative curves of the sunning of the various years of measurements. We will take into account that the years when the data are complete. The Fig. 4, 5 and 6 present the variation of the sunning for each station during the various years.
Рис. 4. Сравнение срединных среднемесячных значений дневной интенсивности солнечного излучения (2003, 2004 и 2007) в Ломе Fig. 4. Comparison of the monthly median values of the daily solar irradiation (2003, 2004 and 2007) in Lomé
These various observations made on the behavior of the solar irradiation in Togo are explained by the following facts:
Рис. 5. Сравнение срединных среднемесячных значений дневной интенсивности солнечного излучения (2002, 2003,
2004 и 2007) в Атакпаме Fig. 5. Comparison of the monthly median values of the daily solar irradiation (2002, 2003, 2004 and 2007) in Atakpamé
International Scientific Journal for Alternative Energy and Ecology № 2 (82) 2010
© Scientific Technical Centre «TATA», 2010
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Рис. 6. Сравнение срединных среднемесячных значений дневной интенсивности солнечного излучения (2004, 2005 и 2007) в Манго Fig. 6. Comparison of the monthly median values of the daily solar irradiation (2004, 2005 and 2007) in Mango
It seems that the sunning decreases in Lomé when we move in time referring to Fig. 4. This observation is not also visible on the Fig. 6, even if it is pointed out from June to December. On the other hand for Atakpamé, this phenomenon is not visible at all. It should be noted also that the minima and the maxima are obtained almost during the same months for all the three cities. We can note a great fluctuation of the values of Lomé compared to those of the other cities. The standard deviation obtained with Atakpamé is the weakest 0.92 compared with 1.13 in Lomé thus proving the less important variation of the sunning during the various years for Atakpamé. It is to be noticed that during these last years, the climate in Togo has undergone an involving change of big and regular rains, which was not case, before this phenomenon could be the cause of the reduction in the value of the sunning in Lomé.
Conclusion
Measurements of the solar irradiation in Togo enable us to better understand the solar radiation arriving on the ground. Consequently, we can provide for the country available data of the solar irradiation credible in the form of charts or statistical data. This irradiation is 4.39 kw/m2 for Lomé, 4.81 kw/m2 for Atakpamé and of 5.45 kw/m2 in Mango with variable standard deviations between 0.92 and 1.13. This work will make it possible to ensure the reliability of the solar energy systems conceived like a better promotion of those near the consumers and to propose adequate models making it possible to simulate the solar irradiation in Togo.
References
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2. LI-1400datalogger Instrument manual LICOR, Publication Number 9807-122. July, 1998.
3. LI-COR Radiation Sensors, Instrument manual, LI-COR, Inc July, 1998.
4. Bertolo L., Bourges B. Données climatiques utilisées dans le Batiment. Techniques de l'ingenieur, Traité mécanique et chaleur B2015. Paris, 1992.
5. Bourges B. Climatic data handbook for Europe. Klower acad. publ. Dordrecht. Paris, 1992.
6. Chiron de la Casinière A. Le rayonnement solaire. Publibook. Paris, 2004.
7. Perrin de Brichambaut Ch., Vauge Ch. Le gisement solaire: évaluation de la ressource énergétique. Technique et Documentation (Lavoisier), 1982.
8. Scharmer K. et al The European solar radiation atlas (2 volumes+CD). Les presses de l'Ecole de Mines, Paris.
9. Mezino J. Le gisement solaire de l'Île de Réunion. Thèse, 1983.
МЕЖДУНАРОДНАЯ ВЫСТАВКА СОЛНЕЧНОЙ ЭНЕРГЕТИКИ И ФОТОВОЛЬТАИКИ SOLARCON KOREA 2010
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