This study aims to evaluate the long-term variations of sunshine duration and to estimate its interaction with meteorogical parameters from 1950 to 2010 in Chad, Central Africa. The results show that Chad is the one of world's sunniest countries. Each year, Chad receives more than 3030.91 ± 176.33 hours of sunning corresponding to 8.9 hours daily. Likewise, a strong north-south gradient is noted over Chad. For instance, the daily insolation is 10 ± 0.41 hours in the north, 8.85 ± 1.1 hours in the center and 7.75 ± 1.8 hours in the south. Furthermore, there is a marked seasonality of sunshine duration with maximums in dry season and minimums during the rainy season. The lowest values of sunshine duration are found in August. On the contrary, maximums are recorded from November to February with values greater than 9.5 hours per day. Moreover, the annual anomalies study allowed determining three great periods in terms of sunshine variability in Chad. Firstly, the period between 1950 to 1970 (named humid period) is characterized by the lowest values of sunshine duration in Chad. Secondly, from 1970 and 1990, the region suffered an unprecedented drought which resulted in an increase of sunstroke duration in Chad. And finally, the period from 1990 to 2010 called the return period is characterized by a rapid year-to-year fluctuations of insolation duration. Unlike to surface temperature, we have also shown that there is a direct relation between the duration of insolation and the meteorological parameters such as precipitations and relative humidity.

In this work, we have produced biogas by co-digestion of cow dung and slaughterhouse wastewater under different climate temperatures in two countries: N'Djamena in Chad, a country of Central Africa and Dakar in Senegal, a country of West Africa. In a first approach, we put the cow dung in cans of 1.5 L, hermetically closed. The goal was to know how long you could produce biogas. Then we built a bio-digester to produce biogas for cooking. Each bio-digester was exposed to receive solar heat that varied between 27˚C to 41˚C in Chad and between 24˚C to 30˚C in Senegal. Influenced by the high temperature and a minimum residence time, the experiments showed that the N'Djamena test produced biogas more quickly than the Dakar test which, on the contrary, had a low temperature and a long residence time. The production of biogas began at the end of seven days with flammability on the twenty-first day for the bio-digester in Chad and after twenty-seven days with a flammability on the thirty-sixth day for the bio-digester of Senegal. The different digestates were valorised in fertilizers, bricks and green coal. Our research aims to meet the living conditions of the rural world specifically for women by reducing their work and thus allowing them to have more time to self-educate and educate their children.

The objective of this work is to evaluate the available solar potential at N'Djamena (12˚08N, 15˚04E) from 2017 to 2018. To achieve this goal, we used various datasets and model including: the in situ shortwave radiation (by pyranometer) measurement and sunshine duration (by Campbell-Stokes heliograph) obtained from N'Djamena station, observations from MODIS (aerosol optical depth (AOD) and precipitable water) satellite sensors, and simulations from Streamer radiative code. The results show the presence of a good available solar potential with an annual global potential of 4.71 kWh/m 2 /d. At the intra-seasonal time scale, there are two maximums for the global solar potential. The first maximum is registered in the month of March (spring) with value of 5.7 kWh/m 2 /d and the second in October (autumn) with value of 5.18 kWh/m 2 /d. However, the minimum of global potential is recorded in winter (from December to February) with values around 3.86 kWh/m 2 /d. Then, the measured global irradiation allowed validating the Streamer radiative transfer code with a score of more than 98%. Subsequently, this model was used to simulate direct normal and diffuse irradiation for several types of days (clear, dusty and cloudy days). An examination of the dust influence on solar radiation based on selected cases (AOD = 2.05) indicates a mean decrease of 3.33 and 3.17 kWh/m 2 /d, respectively, for the total and direct normal potential. This corresponds to an increase of the diffuse potential of 0.52 kWh/m 2 /d. Finally, an increase of 5.82 cm of precipitable water per day tends to decrease the overall potential of 0.73 kWh/m 2 /d and the direct normal potential of 1.74 kWh/m 2 /d. For this cloudy day, the potential has increased more than 0.89 kWh/m 2 /d.

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