Southern African Sustainable Energy Conference, 2021
Solar concentrators can provide high temperature heat for cooking and frying and the thermal ener... more Solar concentrators can provide high temperature heat for cooking and frying and the thermal energy can be available at off-sun hours if a heat storage is included. A heat transfer loop is then required, between the absorbers of the concentrators and the heat storage units. A double reflector system has previously been tested for direct illumination of a heat storage, avoiding the heat transfer loop. As solar tracking is still required, a Compound Parabolic Concentrator (CPC) is here evaluated as an alternative. A stationary CPC can capture solar rays for quite wide acceptance angles. Ray tracing is used for assessment of a 3D CPC to illuminate the top part of a small scale heat storage, which is designed for capacity to cook 1-2 kg of beans. The storage has a 20 cm diameter aluminum top plate with conducting fins into a latent heat storage (Solar Salt Nitrate mixture with melting point 220°C). The storage has previously been charged with electric heating elements. The purpose of the ray tracing is to perform a sensitivity analysis on the dimensions of mirror tiles on the CPC surface. The results show that uniform tile sizes up to 15 cm gives quite similar interception ratios (less than 10% changes) compared with the smooth surface. Larger and non-uniform tiles discretized in terms of rings and sectors can give similar results.
Concentrating solar systems use reflective surfaces to concentrate sunlight onto a small area, wh... more Concentrating solar systems use reflective surfaces to concentrate sunlight onto a small area, where it is absorbed and converted to heat. Many classes of concentrating collectors such as Compound Parabolic Concentrators (CPCs), parabolic dish and parabolic trough are available, each with different concentrating ratio and maximum absorber temperature, depending on the type of applications. A simplified 3D Compound Parabolic Concentrator (CPC) with 2 rings and 4 sectors has been designed. The designed CPC is cost effective as it requires only 8 mirrors to cover the reflector surface. It does not require sun tracking, but have capability to accept incoming solar radiation over a relatively wide range of angles. For further capturing of the solar radiations, tilting of the CPC during a day can be made a few times. This study aims to model the discretized 3D CPC using the ray tracing, to optimize the CPC for achieving optimal interceptions on a 0.2 m diameter cylindrical absorber, place...
Alternative cooking energy to replace wood fuels is needed in the African context. Liquified Natu... more Alternative cooking energy to replace wood fuels is needed in the African context. Liquified Natural Gas (LNG) is a solution but is still based on burning fossil fuel. Electrical cookers can be an alternative as well. However, for off-grid systems this means electrical batteries are required, as the solar electricity from Photovoltaic (PV) panels is intermittent, and as cooking is also to be made after sunset. Heat storage technologies can provide solutions where available energy is stored in the form of heat for cooking when needed. The challenge is then to develop systems which are robust, safe, and technically simple. A very simple small-scale solution is demonstrated here, for the particular case of cooking beans. An insulated iron cylinder is heated, either in a solar concentrator or by PV-powered heating elements. The stored heat can then be calibrated to the cooking of a given volume of beans. After the cylinder has reached the calibrated temperature during the charging, the ...
Southern African Sustainable Energy Conference, 2021
Solar concentrators can provide high temperature heat for cooking and frying and the thermal ener... more Solar concentrators can provide high temperature heat for cooking and frying and the thermal energy can be available at off-sun hours if a heat storage is included. A heat transfer loop is then required, between the absorbers of the concentrators and the heat storage units. A double reflector system has previously been tested for direct illumination of a heat storage, avoiding the heat transfer loop. As solar tracking is still required, a Compound Parabolic Concentrator (CPC) is here evaluated as an alternative. A stationary CPC can capture solar rays for quite wide acceptance angles. Ray tracing is used for assessment of a 3D CPC to illuminate the top part of a small scale heat storage, which is designed for capacity to cook 1-2 kg of beans. The storage has a 20 cm diameter aluminum top plate with conducting fins into a latent heat storage (Solar Salt Nitrate mixture with melting point 220°C). The storage has previously been charged with electric heating elements. The purpose of the ray tracing is to perform a sensitivity analysis on the dimensions of mirror tiles on the CPC surface. The results show that uniform tile sizes up to 15 cm gives quite similar interception ratios (less than 10% changes) compared with the smooth surface. Larger and non-uniform tiles discretized in terms of rings and sectors can give similar results.
Concentrating solar systems use reflective surfaces to concentrate sunlight onto a small area, wh... more Concentrating solar systems use reflective surfaces to concentrate sunlight onto a small area, where it is absorbed and converted to heat. Many classes of concentrating collectors such as Compound Parabolic Concentrators (CPCs), parabolic dish and parabolic trough are available, each with different concentrating ratio and maximum absorber temperature, depending on the type of applications. A simplified 3D Compound Parabolic Concentrator (CPC) with 2 rings and 4 sectors has been designed. The designed CPC is cost effective as it requires only 8 mirrors to cover the reflector surface. It does not require sun tracking, but have capability to accept incoming solar radiation over a relatively wide range of angles. For further capturing of the solar radiations, tilting of the CPC during a day can be made a few times. This study aims to model the discretized 3D CPC using the ray tracing, to optimize the CPC for achieving optimal interceptions on a 0.2 m diameter cylindrical absorber, place...
Alternative cooking energy to replace wood fuels is needed in the African context. Liquified Natu... more Alternative cooking energy to replace wood fuels is needed in the African context. Liquified Natural Gas (LNG) is a solution but is still based on burning fossil fuel. Electrical cookers can be an alternative as well. However, for off-grid systems this means electrical batteries are required, as the solar electricity from Photovoltaic (PV) panels is intermittent, and as cooking is also to be made after sunset. Heat storage technologies can provide solutions where available energy is stored in the form of heat for cooking when needed. The challenge is then to develop systems which are robust, safe, and technically simple. A very simple small-scale solution is demonstrated here, for the particular case of cooking beans. An insulated iron cylinder is heated, either in a solar concentrator or by PV-powered heating elements. The stored heat can then be calibrated to the cooking of a given volume of beans. After the cylinder has reached the calibrated temperature during the charging, the ...
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