Cheikh M. F. Kébé

Results of UHF radar observation of the nocturnal low-level jet for wind energy applications

We use two series of eight-month UHF radar observations collected during the dry and wet seasons of AMMA field campaign. The ultimate goal is to do preliminary work to know whether the lowest layers are suitable for wind energy applications. Surface wind is usually weak in West Africa, but the regular occurrence of a nocturnal low level jet (NLLJ) could provide interesting conditions for wind energy. This work is two-fold: it first aims at improving our knowledge about the NLLJ in West Africa regarding its structure and its variability during the year. Then, special attention is paid to the first 200 m agl, to study the possibility to use the sub-jet wind as a source of energy. A set of enhanced radio-soundings is taken to help to understand the dynamics and thermodynamics and to find a way to extrapolate the wind at low level, where the UHF radars do not provide data.

Lifetime assessment of a photovoltaic system using stochastic Petri nets

Abstract The lifetime estimation of photovoltaic (PV) systems is an important consideration in their life cycle. This paper presents a multi-level methodology to estimate the availability and the lifetime of a PV system using stochastic Petri networks and taking into account the time distribution to failure and to repair. The following components – module, wires, and inverter – are modeled with a Petri network. The evolution of the MTBF, availability, and outages over a 30-year period is simulated for different series/parallel configurations of connected PV modules. Findings are in agreement with reported experimental results, namely the evolution of the availability which tends to be near 96% for long times. Numerical results show that the highest MTBF is 3.2 years and the lowest outage is of 11.84 days/year, which are both obtained for the string configuration. The approach is interesting for the dimensioning of a PV plant or an installation.

Investigation of Degradation in Crystalline Silicon Photovoltaic Modules After 10 Years Exposition in Senegal by Infrared (IR) and Electroluminescence (EL)

The effects of a sub-Saharan coastal climate on PV modules degradation was studied in this paper. A Mono and a polycrystalline-silicone solar PV module exposed in Dakar, dry and coastal climate, at the extreme West of Senegal was studied. As first inspection in this region, the electrical parameters of two PV modules A and B operated during about 10 years, are measured under standard testing condition (STC) and their I-V characteristics were fitted. The initial I-V characteristics was performed under real conditions and translated to STC and compared to the measured I-V characteristics at standard test conditions (STC) obtained in PV Laboratory after exposition. After the operating years, the main important parameters of the studied PV modules: short-circuit current ISC, open circuit voltage UOC, maximum power PMPP, nominal current IMPP and Voltage VMPP are evaluated and then compared to the initial parameters obtained during initial exposition to estimate their degradation.

A Study of the Wind Potential in Climatic Zones of Chad

This paper focuses on the assessment of wind energy potential in the three climatic zones of Chad: the Saharan (north), the Sahel (center) and the Sudan (south) zones. For each zone, three representative meteorological locations were chosen and assessed based on satellite data provided by NASA. The data comes from MERRA (Modern-Era Retrospective Analysis for Research and Applications) and covers the period 2005–2014. The wind speed frequency distribution of locations was found by using Weibull distribution function. From this statistical data analysis, we found that the wind regime is different in the three regions. It is higher in the Saharan region (with annual mean wind speed of 5.78 m/s) followed by the Sahel (4.32 m/s) and Sudanian (3.7 m/s) regions. There are two distinct seasons in Chad: the dry and the rainy seasons with varying periods, with respect to the regions (2 months of rain in the Saharan zone vs 7 months in the Sudanian zone). For all regions the mean wind speed is higher in the dry season. Diurnal variations of mean wind speed show two regimes characterized respectively by high values in the early morning and the night and low values during the day. The corresponding power density was 193 w/m2, 76.15 w/m2 and 29.0 w/m2, resp. for the Saharan, Sahelian and Sudanian regions. The wind regimes are globally stable with dominant directions North-East (for Saharan region), East (Sahelian), South-Southwest (Sudanian).

Building Energy Audit in Nigeria: Some Guides for Energy Efficiency Building Regulations

Buildings account for a large proportion of total energy use in the world and that has surpassed all the other sector of the economy of most countries. There is a great need to gather better data on building energy performance and to be able to compare performance across locations and building typologies so that best practices can be more rapidly evolved. The question of how much energy the average Nigerian building consume is still an open ended one. This paper presents a synthesis of energy supplied and utilized in 105 buildings based on building energy audit, physical examination, onsite measurements and discussions with relevant stakeholders, conducted in three cities from different climatic belts of Nigeria. The aim was to draw a basic energy consumption profile of residential, commercial and institutional buildings. This survey found the preponderance of the use of energy inefficient products, inadequate utilization of daylighting, complete absence of building energy management systems, extremely low adoption of renewable energy systems and orienting building without due consideration to bioclimatic factors. This paper recommends policy changes that can be used to realise a large and feasible energy saving in new as well as existing buildings in Nigeria.

A Multivariate Regression Model for the Assessment of Solar Radiation in the Senegalese Territories

Senegal has a great solar potential, so it could be used to shift from a diesel-based power generation to cheaper renewable energy resources. To exploit this inexhaustible natural resource, the global horizontal irradiation remains one of the key parameters for any solar energy project at a given location. This work establishes a multiple linear regression approach to estimate the solar radiation in the Senegalese territories using the information of the global network of weather geostationary satellites (Meteosat and GOES), satellites database and the ground measurement data available in the website of the World Radiation Data Center (WRDC) as inputs to the model. Jointly a set of multivariate regression models, a statistical analysis between Meteonorm data and outputs of different linear combinations are presented in this work, which also gives the opportunity to appreciate the precision and consistency of each solar radiation model on different locations in the study area.

Study of the Correlation Between the Dust Density Accumulated on Photovoltaic Module’s Surface and Their Performance Characteristics Degradation

One of the major constraints related to the operating conditions of photovoltaic systems in the Sahelian environment is relative to the deposits of dust on the surface of the PV modules. Indeed, the Sahel is characterized by frequent and permanent sandstorm that impact on its strong solar potential. However, opinions are still divided on the significant impact of dust on photovoltaic modules production. This paper deals with the correlation between the density of deposited dust on the surface of crystalline silicon photovoltaic modules and the impact on their performances. This study is carried out on two different modules a monocrystalline and a polycrystalline technology. It focuses on the open-circuit voltage (VOC), the short-circuit current (Isc), the fill factor (FF) and more particularly on the maximum power (Pmax). This paper presents the methodology and the experimental study used to measure the environmental parameters (irradiation, temperature, and humidity), the density of deposited dust and the performance characteristics (ISC, VOC, FF and Pmax). Finally, the results of the correlation between the density of deposited dust and the performance characteristics of PV modules are presented.