Access to electricity is poor in the Economic Community of West African States (ECOWAS). Concentrating Solar Power (CSP) presents better opportunities for increasing access to electricity and for diversifying sources of energy in the ECOWAS region; however, to date, except for Burkina Faso, no site evaluation pertaining to the region has ever been performed for CSP. This study provides potential assessment and site ranking for large-scale CSP projects in the ECOWAS region. It computes the nominal potential power and gives the corresponding energy yield with many scenarios. By considering only 1% of the suitable land area with daily DNI greater or equal to 5 kWh/m2, a land slope less or equal to 5% and distance to transmission line not more than 100 km, the study showed, for example, that West Africa has a potential nominal capacity of 21.3 GW for parabolic trough technology.
The Economic Community of West African States (ECOWAS) is a regional group of fifteen countries. Its mission is to promote economic integration in all fields of economic activity, particularly industry, transport, telecommunications, energy, agriculture, natural resources, commerce, monetary and financial questions, social and cultural matters.
The region has some of the lowest modern energy consumption rates in the world with average electricity consumption of 120 kWh/capita compared to the continental and global averages of 529 and 2570 kWh/capita respectively [
Although the share of oil products in ECOWAS’ energy balance remains modest, commercial energy consumption (electricity, oil products and gas) is highly oildependent. Power generation depends on 65% of fossil fuel [
For the purpose of our study, the region has been divided into three main climatic zones: the humid tropical southern coastal zone, the Sahel and the Sahara desert. The Sahel and the Sahara desert are characterized by low population density, scarce water resources and lack of transmission lines. They however receive abundant solar energy all year round; their mean daily solar radiation exceeds 5.5 kWh/m2 [
Selecting an appropriate site for concentrating power plant has been the subject of many studies. Azoumah et al. [
DNI and land slope were considered in all the studies while no study included water availability. The lack of detailed data in GIS format was pointed out by some of the authors as the main reason why the availability of water was not applied as a criterion.
Overlaying is the method used in this study. It is an important procedure in GIS analysis. It involves superimposing two or more map layers to produce a new map layer by combining diverse data sets; Overlay analysis is used to investigate geographic patterns and to determine locations that meet specific criteria. Criteria used in this study were sufficient DNI, proximity to transmission lines, low slope value. This approach was previously used by Charabi and Gastli [
†Low productivity lands include Moorlands and bushes, big formations of dense bushes, scarce bushes, Subdesert Xerosteppe, high altitude spaces with scarce vegetation, burnt areas. ‡“Solar park” is designated land for solar plants in the Southwest, with a lease fee of $200/acre/year. §Legacy of World War II and the Cold War which includes radioactive and chemical waste, environmental contamination, and hazardous material at over 100 sites across USA.
The DNI map in
ECOWAS has a total land area of 5,110,914 km2. This study reveals that 17% of that land area is endowed with an average daily DNI of 5.6 kWh/m2 while 38% enjoys an average daily DNI of 4.4 kWh/m2. 23% has an average daily DNI of 37 kWh/m2 and the remaining 22% records an average daily DNI value below 3 kWh/m2.
Land slope was derived from the Shuttle Radar Topography Mission (SRTM) 90 m digital elevation model [
DNI, land slope and proximity to transmission lines are crucial factors in selecting candidate site for a CSP
project. These three factors strongly influence the cost of the project. Electricity production by a CSP plant is approximately proportional to the DNI of the site, hence inversely proportional to the cost of electricity. For the land slope, a small gradient is desirable since it reduces cost associated with the civil work. Furthermore, the closeness of the site to a high voltage line will reduce not only power losses but also transmission cost.
Based on the obtained land area and using performance characteristics of some reference plants such as SEGS IX, PS 10 and PE I, the nominal capacity and the energy yield were then estimated.
Many studies (see
P1, A1 and represents respectively, the installed capacity of the reference plant, the land cover in which it was built and the DNI of the area where it is located.
Once potential power was known, the energy yield could then be computed through Equation (2) using the capacity factor of the reference plant.
SEGS IX, PS 10 and PE I were selected because of their commercial maturity.
SEGS IX is one of the nine Solar Electric Generating Station (SEGS) plants in the Mojave Desert in California. The combined electric generating capacity of these plants, which use parabolic trough technology, is more than 350 megawatts. SEGS IX which started operation in 1991, is the largest individual trough plant (along with SEGS VIII); it has an auxiliary natural gas heater which provides backup capability during low and non-solar hours [
PS10 (Planta Solar 10) is the first solar central-receiver system producing grid-connected electricity in a commercial basis. The plant started operation in March 2007. It is based on Direct Steam Generation (DSG) and makes use of well proven technologies, like glass-metal heliostats, a pressurized water thermal storage system, and a saturated steam receiver and turbine. The plant’s thermal storage system has a 50-minute capacity at 50% load to handle cloud transients. PS10 is located in Seville, Spain [
PE I (Puerto Errado 1) is a solar thermal power plant located in southern Spain. It is based on linear Fresnel collector technology and has an electrical capacity of 1.4 MW. Since March 2009, it has been connected to the local grid and selling electricity to the local network provider. It is also based on Direct Steam generation (DSG) and produces saturated steam at temperatures of up to 300˚C [21,22].
In Tables 4 and 5, the first three columns contain conditions on DNI, land slope and distance to transmission lines respectively. Column 4 computes the land area that satisfies the conditions in the previous columns in square kilometers while column 6 gives same in percentage of ECOWAS total land area. Column 7 gives the corresponding average DNI in the area.
Parabolic Trough (PT), Central Receiver (CR) and Linear Fresnel (LF).
Figures 4 and 5 provide the potential capacity and the corresponding energy yield for the three reference CSP technologies. Many cases were envisaged. The high and medium DNI areas are mainly located in the Sahara and the Sahel zone of West Africa. Land use pattern in these zones can be extrapolated from the results of the study conducted by Azoumah et al. [
Considering only 1% of lands with daily DNI greater or equal to 5 kWh/m2 (about 0.17% of ECOWAS total land area),
It is to be noted that in 2009, the total installed electricity generating capacity in ECOWAS amounted to 11.4 GW (57.8% from thermal power stations and 42.2% from hydroelectric plants) [1,23]. The projected demand by 2023 will require an installed capacity of some 17 GW [
next study.
Figures 6 and 7 are sample maps showing results from overlaying the three maps which illustrate the DNI, the land slope and the transmission lines in the ECOWAS region. The sample maps serve as illustration; therefore, the maximum slope and the maximum distance to transmission lines were set to their lowest values of 1% and 20 km respectively (
In both maps, the high potential zone lies between Agadez and Arlit in northern Niger. It is located in the Sahara desert and is the host of an important uranium mining industry. There is an existing 132 kV voltage line in the region.
Northern Mali has good DNI but no transmission line is in existence or has been planned (refer to Figures 1 and 3). Building new transmission line as part of a CSP project is capital intensive. In order to illustrate the cost of transmission lines in West Africa, the 225-kV line connecting Bobo-dioulasso to Ouagadougou with a load carrying capacity of 120 MW has cost about US$290,000 per kilometre [
The high potential zone falls in the Sahara desert which is characterized by an important sand and dust deposit, lack of water and lack of transmission lines. Dustresistant, Waterless, dry cooling and small-scale CSP technology could be envisaged in this zone. The medium potential zone coincides with the Sahel which is a transition between the Sahara desert and the humid tropical southern coastal zone. The low potential zone corresponds to the humid tropical southern coastal zone which, unlike the first two zones has better water resources, less dust deposit and a better transmission network. Dust and sand deposit affect optical efficiency of the mirrors thus
causing overall output drop of the plant whilst high DNI implies better output. It must be interesting to conduct studies and to see whether the loss in overall plant performance due to deposition of dust in the high potential zone is not compensated with better optical efficiency in low-DNI but dust-free zone. This will be investigated in future work.
Concentrating Solar Power (CSP) Plants appear to be good candidate for increasing access to electricity in Africa and to improve people’s living conditions; however, with the exception of Northern Africa where extensive work is being conducted, potential assessment of CSP Plants in West Africa was yet to be done. This paper presented results of the potential assessment of Concentrating Solar Power for electricity generation in West Africa. The study considered only 1% of the suitable land area which met certain criteria and found that West Africa has a potential nominal capacity of 22.16 GW for Parabolic trough technology. This greatly exceeds the projected electricity demand of 17 GW by 2023 for the region. Of course, the study is worth within the accuracy limits of the data used. Further studies need to be conducted in order to ascertain the economic viability of such plants in the region.
The authors would like to express their gratitude to the African Studies Center of the University of Michigan and to the African Union through the CSP4Africa Project for their support in carrying out this work.