Evaluation of the suitably of proposed site for construction of photovoltaic solar facility at Kakamas in the Northern Cape of South Africa

Abstract

Solar energy development is experiencing significant growth due to national interest in increasing energy efficiency, reducing dependence on fossil fuels, increasing domestic energy production, and curbing greenhouse gas emissions. Northern Cape is generally known to be one of the preferred areas for the generation of solar energy in South Africa, and even in the world, due to its abundant solar radiation. Although this area has abundant potential for solar power generation, not all the areas are suitable for construction of solar plant facilities especially those that are prone to sand storm and dust accumulation. Consequently, site evaluation is very crucial for planning, design and construction of the solar facility. The main objective of this study was to determine the suitability of a proposed site at Kakamas in the Northern Cape for construction of a photovoltaic solar facility. The specific objectives of this research were to assess and establish all the geotechnical aspects that may have an impact on the development of the site, to explore the surface conditions at the proposed site and to establish the soil properties and comment on the use of the on-site soils in the construction of the solar facility. Other specific objectives included to determine the variability of ground conditions and effects of such variability on the proposed development and to provide foundation recommendations for the design and construction of the solar facility. In order to obtain this information, methods such as desktop studies, geological survey, soil survey, magnetic survey and soil profiling were employed to obtain information about the geotechnical aspects of the study area and properties of the on-site soil. Field tests such as cone penetration and resistivity survey and laboratory tests such as foundation indicator test, California Bearing Ratio, pH and permeability test were also performed in order to determine the engineering, behavioral and hydraulic properties of the soil. The results of the geologic and magnetic survey indicated that the study area is underlain by mainly igneous and metamorphic rocks such as gneiss, quartzite, pegmatite, gneiss and calcrete. The results of the soil profiling and the resistivity survey showed that the study area is comprised of sandy soil with either two or three horizons while the cone penetration results revealed high variable soil consistency and stiffness which ranged from very loose to very stiff soils. The particle size distribution, atterberg limits and grading modulus indicated that the study area is characterized mainly by dry, cohesionless and non-plastic to slightly plastic coarse-grained sandy soil with sand content ranging from 71- 96%. From the CBR results, it was found that the soils in the study area generally classifies as G6 material and can be used as base, sub base and backfilling material in accordance with the TRH 14 specifications. The permeability test results indicated moderately permeable sandy silt soils with coefficient of permeability ranging between 1x10-3 to 8x10-3 cm/sec and ground water was encountered at 1.3 m depth. The material excavatability indicated variable material on site ranging from soft calcretes with soft excavation to highly competent material such as quartz and dorbank which require hard excavation while the side wall stability of trial pits indicated stable pit walls during the investigation giving an indication of stability of long pit excavations. The foundation analysis showed that driven piles and earth screws are the ideal foundation types for this site and that the site is generally suitable for construction of the solar facility provided all the recommendations are implemented.