A Compound Parabolic Concentrator (CPC) is investigated for capturing and focusing sun rays onto ... more A Compound Parabolic Concentrator (CPC) is investigated for capturing and focusing sun rays onto an absorber, for conversion of solar radiation to heat. CPCs are cost-effective as they do not need solar tracking, only requiring tilting of the concentrator at intermediate times during a day. In this study, a 3D CPC with reflecting surfaces is strongly simplified by using only two sets of 4 flat mirrors (upper and lower mirrors) arranged in such a way that they form a quadratic funnel. A cylindrical heat absorber made of aluminum is positioned at the base of the funnel and the system is insulated to reduce the heat losses from the system. The purpose of the heat storage is to accumulate heat at sufficient temperatures for cooking. The idea is that a concentrator can be positioned over the heat storage and be replaced by an insulating cover after the heat storage has been charged. Tests with a CPC system is presented here, with test results in outdoor conditions in Trondheim, Norway during the months of May and June. The heat storage reached temperatures of about 135 °C at solar radiation conditions of 500–700 W/m2, higher temperatures are to be expected with improved insulation and at sun conditions closer to equator. Previous separate cooking tests have been successfully demonstrated on a similar cylinder for initial heat storage temperatures of 220 °C. A computational model which was tuned to the 220 °C case showed that even an initial temperature of 140 °C can be sufficient for boiling water although at modest amounts of about 1 l.
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.
Linköping electronic conference proceedings, Oct 28, 2022
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, placed inside the CPC. The ray tracing methodology is presented together with the results of the interceptions on the cylindrical absorber using the discretized CPC. Results show the effect of tilting the discretized CPC is not very strong as the interception values are slightly reduced and the curves a little bit not symmetric around the normal sun angles.
Tanzania Journal of Engeering and Technology, Feb 28, 2023
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 pot can be placed and left on the top of the cylinder. When the energy is depleted, the beans should be ready cooked.
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 ...
A Compound Parabolic Concentrator (CPC) is investigated for capturing and focusing sun rays onto ... more A Compound Parabolic Concentrator (CPC) is investigated for capturing and focusing sun rays onto an absorber, for conversion of solar radiation to heat. CPCs are cost-effective as they do not need solar tracking, only requiring tilting of the concentrator at intermediate times during a day. In this study, a 3D CPC with reflecting surfaces is strongly simplified by using only two sets of 4 flat mirrors (upper and lower mirrors) arranged in such a way that they form a quadratic funnel. A cylindrical heat absorber made of aluminum is positioned at the base of the funnel and the system is insulated to reduce the heat losses from the system. The purpose of the heat storage is to accumulate heat at sufficient temperatures for cooking. The idea is that a concentrator can be positioned over the heat storage and be replaced by an insulating cover after the heat storage has been charged. Tests with a CPC system is presented here, with test results in outdoor conditions in Trondheim, Norway during the months of May and June. The heat storage reached temperatures of about 135 °C at solar radiation conditions of 500–700 W/m2, higher temperatures are to be expected with improved insulation and at sun conditions closer to equator. Previous separate cooking tests have been successfully demonstrated on a similar cylinder for initial heat storage temperatures of 220 °C. A computational model which was tuned to the 220 °C case showed that even an initial temperature of 140 °C can be sufficient for boiling water although at modest amounts of about 1 l.
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.
Linköping electronic conference proceedings, Oct 28, 2022
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, placed inside the CPC. The ray tracing methodology is presented together with the results of the interceptions on the cylindrical absorber using the discretized CPC. Results show the effect of tilting the discretized CPC is not very strong as the interception values are slightly reduced and the curves a little bit not symmetric around the normal sun angles.
Tanzania Journal of Engeering and Technology, Feb 28, 2023
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 pot can be placed and left on the top of the cylinder. When the energy is depleted, the beans should be ready cooked.
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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Papers by Casiana Lwiwa
equator. Previous separate cooking tests have been successfully demonstrated on a similar cylinder for initial heat storage temperatures of 220 °C. A computational model which was tuned to the 220 °C case showed that even an initial temperature of 140 °C can be sufficient for boiling water although at modest amounts of about 1 l.
equator. Previous separate cooking tests have been successfully demonstrated on a similar cylinder for initial heat storage temperatures of 220 °C. A computational model which was tuned to the 220 °C case showed that even an initial temperature of 140 °C can be sufficient for boiling water although at modest amounts of about 1 l.