Design, implementation and evaluation of a directly water cooled photovoltaic- thermal system
- Authors: Mtunzi, Busiso
- Date: 2013
- Subjects: Sensitivity analysis -- Photovoltaic thermal system (PV/T) , Solar utilization -- Carbon emission
- Language: English
- Type: Thesis , Doctoral , PhD (Physics)
- Identifier: vital:11597 , http://hdl.handle.net/10353/d1016198 , Sensitivity analysis -- Photovoltaic thermal system (PV/T) , Solar utilization -- Carbon emission
- Description: This research project was based on the Design, Implementation and Evaluation of a Photovoltaic Water heating system in South Africa, Eastern Cape Province. The purpose of the study was to design and investigate the scientific and economic contribution of direct water cooling on the photovoltaic module. The method involved performance comparison of two photovoltaic modules, one naturally cooled (M1) and the other, direct water cooled module (M2). Module M2 was used to produce warm water and electricity, hence, a hybrid system. The study focused on comparing the modules’ efficiency, power output and their performance. The temperatures attained by water through cooling the module were monitored as well as the electrical energy generated. A data logger and a low cost I/V characteristic system were used for data collection for a full year. The data were then used for performance analysis of the modules. The results of the study revealed that the directly water cooled module could operate at a higher electrical efficiency for 87% of the day and initially produced 3.63% more electrical energy each day. This was found to be true for the first three months after installation. In the remaining months to the end of the year M2 was found to have more losses as compared to M1 as evidenced by the modules’ performance ratios. The directly water cooled module also showed an energy saving efficiency of 61%. A solar utilization of 47.93% was found for M2 while 8.77% was found for M1. Economically, the project was found to be viable and the payback period of the directly cooled module (M2) system was found to be 9.8 years. Energy economics showed that the system was more sensitive to the price changes and to the energy output as compared to other inputs such as operation and maintenance and years of operation. A generation cost of R0.84/kWh from the system was found and when compared to the potential revenue of R1.18 per kWh, the system was found to enable households to make a profit of 40.5 %. Use of such a system was also found to be able to contribute 9.55% towards carbon emission reduction each year. From these results, it was concluded that a directly cooled photovoltaic/thermal heating (PV/T) system is possible and that it can be of much help in terms of warm water and electricity provision.
- Full Text:
- Date Issued: 2013
- Authors: Mtunzi, Busiso
- Date: 2013
- Subjects: Sensitivity analysis -- Photovoltaic thermal system (PV/T) , Solar utilization -- Carbon emission
- Language: English
- Type: Thesis , Doctoral , PhD (Physics)
- Identifier: vital:11597 , http://hdl.handle.net/10353/d1016198 , Sensitivity analysis -- Photovoltaic thermal system (PV/T) , Solar utilization -- Carbon emission
- Description: This research project was based on the Design, Implementation and Evaluation of a Photovoltaic Water heating system in South Africa, Eastern Cape Province. The purpose of the study was to design and investigate the scientific and economic contribution of direct water cooling on the photovoltaic module. The method involved performance comparison of two photovoltaic modules, one naturally cooled (M1) and the other, direct water cooled module (M2). Module M2 was used to produce warm water and electricity, hence, a hybrid system. The study focused on comparing the modules’ efficiency, power output and their performance. The temperatures attained by water through cooling the module were monitored as well as the electrical energy generated. A data logger and a low cost I/V characteristic system were used for data collection for a full year. The data were then used for performance analysis of the modules. The results of the study revealed that the directly water cooled module could operate at a higher electrical efficiency for 87% of the day and initially produced 3.63% more electrical energy each day. This was found to be true for the first three months after installation. In the remaining months to the end of the year M2 was found to have more losses as compared to M1 as evidenced by the modules’ performance ratios. The directly water cooled module also showed an energy saving efficiency of 61%. A solar utilization of 47.93% was found for M2 while 8.77% was found for M1. Economically, the project was found to be viable and the payback period of the directly cooled module (M2) system was found to be 9.8 years. Energy economics showed that the system was more sensitive to the price changes and to the energy output as compared to other inputs such as operation and maintenance and years of operation. A generation cost of R0.84/kWh from the system was found and when compared to the potential revenue of R1.18 per kWh, the system was found to enable households to make a profit of 40.5 %. Use of such a system was also found to be able to contribute 9.55% towards carbon emission reduction each year. From these results, it was concluded that a directly cooled photovoltaic/thermal heating (PV/T) system is possible and that it can be of much help in terms of warm water and electricity provision.
- Full Text:
- Date Issued: 2013
Development of corona-based power supplies for remote repeater stations for overhead HVDC power transmission systems
- Authors: Kaseke, R
- Date: 2012
- Language: English
- Type: Thesis , Doctoral , PhD (Physics)
- Identifier: vital:11595 , http://hdl.handle.net/10353/d1006787
- Description: More and more people worldwide are becoming “carbon conscious”. This means they are becoming increasingly aware of the imminent adverse effects of global warming. Of late there has been an urgent drive for governments to be on the forefront of all carbon mitigation initiatives. One such drive involves the United Nations Framework Convention on Climate Change whose parties have been meeting regularly under the banner of Conference of Parties (COP) since 1995. At this conference, parties to the convention review progress made in dealing with climate change. Also key to the deliberations in such meetings are better ways of developing cleaner “carbon free” energy sources. Energy sources of this nature are commonly known as renewable energy sources. In essence global energy trends are constantly moving towards development of more renewable energy sources. It is an undeniable fact that some of viable renewable energy sources especially those with bulk capacity are usually located remotely from load centers. This inevitable reality necessitates the construction of long distance bulk power transmission corridors to link generation sites with load centers. Due to its many inherent advantages over High Voltage Alternate Current (HVAC) for long distance power transmission, High Voltage Direct Current (HVDC) is gradually winning the favor of many utilities. In fact, recent advances in HVDC technology have encouraged many utilities to explore the possibility of harnessing remotely located renewable energy sources which would have otherwise not been viable with HVAC transmission. Through the unfortunate and inevitable phenomenon known as corona effect, overhead HVDC conductors suffer real power losses to the air dielectric surrounding them. Through corona, part of the energy carried on the transmission line is expended through ionization and movement of charges in the air dielectric. This study combined physics, mathematical as well engineering concepts to review corona phenomenon around HVDC lines with specific emphasis on space charge generation and motion within ionized DC fields as well as the influence of temperature on corona discharge or power loss. Also, unlike HVAC, performance of an HVDC system relies heavily on the availability of a reliable and robust telecommunication system. One of the key ways of ensuring reliability of a telecommunication system is by making sure that reliable power supplies are in place to power remote repeater stations. A novel concept of quasi-autonomous corona-based power supply (or QC power supply in short) that works on the principle of magnetohydrodymic (MHD) power generation was developed. A small scale experiment was then designed to assess the feasibility of such power supplies. The experiment was conducted with DC supply of a maximum rated voltage of 30 kVDC and generated up to 6 VDC at an optimum ambient temperature of 23°C. These results have confirmed that with further development QC power supplies have the potential of proving reliable power to remotely located repeaters or any other small critical loads along the stretch of the HVDC transmission line. Practical HVDC transmission systems operate voltages in the excess of 500 kV. By linear extrapolation of the above mentioned results; one would expect to yield up to 100-, 120- and 160-VDC from a 500-, 600- and 800- kV HVDC system, respectively. Although the study succeeded in conceptualizing a CMHD idea upon which the novel QC power supply was developed, quite extensive and rigorous design, modeling, prototyping and experimentation processes are still required before the first QC power supply can be commissioned on a practical HVDC line
- Full Text:
- Date Issued: 2012
- Authors: Kaseke, R
- Date: 2012
- Language: English
- Type: Thesis , Doctoral , PhD (Physics)
- Identifier: vital:11595 , http://hdl.handle.net/10353/d1006787
- Description: More and more people worldwide are becoming “carbon conscious”. This means they are becoming increasingly aware of the imminent adverse effects of global warming. Of late there has been an urgent drive for governments to be on the forefront of all carbon mitigation initiatives. One such drive involves the United Nations Framework Convention on Climate Change whose parties have been meeting regularly under the banner of Conference of Parties (COP) since 1995. At this conference, parties to the convention review progress made in dealing with climate change. Also key to the deliberations in such meetings are better ways of developing cleaner “carbon free” energy sources. Energy sources of this nature are commonly known as renewable energy sources. In essence global energy trends are constantly moving towards development of more renewable energy sources. It is an undeniable fact that some of viable renewable energy sources especially those with bulk capacity are usually located remotely from load centers. This inevitable reality necessitates the construction of long distance bulk power transmission corridors to link generation sites with load centers. Due to its many inherent advantages over High Voltage Alternate Current (HVAC) for long distance power transmission, High Voltage Direct Current (HVDC) is gradually winning the favor of many utilities. In fact, recent advances in HVDC technology have encouraged many utilities to explore the possibility of harnessing remotely located renewable energy sources which would have otherwise not been viable with HVAC transmission. Through the unfortunate and inevitable phenomenon known as corona effect, overhead HVDC conductors suffer real power losses to the air dielectric surrounding them. Through corona, part of the energy carried on the transmission line is expended through ionization and movement of charges in the air dielectric. This study combined physics, mathematical as well engineering concepts to review corona phenomenon around HVDC lines with specific emphasis on space charge generation and motion within ionized DC fields as well as the influence of temperature on corona discharge or power loss. Also, unlike HVAC, performance of an HVDC system relies heavily on the availability of a reliable and robust telecommunication system. One of the key ways of ensuring reliability of a telecommunication system is by making sure that reliable power supplies are in place to power remote repeater stations. A novel concept of quasi-autonomous corona-based power supply (or QC power supply in short) that works on the principle of magnetohydrodymic (MHD) power generation was developed. A small scale experiment was then designed to assess the feasibility of such power supplies. The experiment was conducted with DC supply of a maximum rated voltage of 30 kVDC and generated up to 6 VDC at an optimum ambient temperature of 23°C. These results have confirmed that with further development QC power supplies have the potential of proving reliable power to remotely located repeaters or any other small critical loads along the stretch of the HVDC transmission line. Practical HVDC transmission systems operate voltages in the excess of 500 kV. By linear extrapolation of the above mentioned results; one would expect to yield up to 100-, 120- and 160-VDC from a 500-, 600- and 800- kV HVDC system, respectively. Although the study succeeded in conceptualizing a CMHD idea upon which the novel QC power supply was developed, quite extensive and rigorous design, modeling, prototyping and experimentation processes are still required before the first QC power supply can be commissioned on a practical HVDC line
- Full Text:
- Date Issued: 2012
Implementation of a 150kva biomass gasifier system for community economic empowerment in South Africa
- Mamphweli, Ntshengedzeni Sampson
- Authors: Mamphweli, Ntshengedzeni Sampson
- Date: 2009
- Subjects: Rural development -- South Africa , Electric power distribution -- South Africa , Condensation , Rural electrification -- South Africa
- Language: English
- Type: Thesis , Doctoral , PhD (Physics)
- Identifier: vital:11591 , http://hdl.handle.net/10353/262 , Rural development -- South Africa , Electric power distribution -- South Africa , Condensation , Rural electrification -- South Africa
- Description: There is growing interest in research and development activities on biomass gasification technologies as an alternative to fossil fuels technologies. However not much has been done in terms of technology transfer, particularly in under-developed and developing countries such as South Africa. This is mainly because of the lack of resources such as funding. Most parts of the under-developed and developing countries fall within rural areas and semi-urban centers, which are endowed with biomass resources. South Africa has a number of sawmill operators who generate tons of biomass waste during processing of timber; the large proportion of this is burned in furnaces as a means for waste management while a very small proportion is collected and used by people in rural areas for cooking their food. The majority of people in rural areas of South Africa are either unemployed or cannot afford the current energy services. The main aim of this research was to establish the viability of electricity generation for community economic development through biomass gasification, specifically using the locally designed System Johansson Biomass Gasifier™ (SJBG), and to establish the efficiency of the gasifier and associated components with a view of developing strategies to enhance it. The study established the technical and economic feasibility of using the SJBG to generate low-cost electricity for community empowerment. The study also developed strategies to improve the particle collection efficiency of the cyclone. In addition to this, a low-cost gas and temperature monitoring system capable of monitoring gas and temperature at various points of the gasifier was developed. The system was built from three Non- Dispersive Infrared gas sensors, one Palladium/Nickel gas sensor and four type K thermocouples. The study also investigated the impact of fuel compartment condensates on gasifier conversion efficiency. This is an area that has not yet been well researched since much has been done on energy recovery using combined heat and power applications that do not utilize the energy in condensates because these are produced in the gasifier and drained with chemical energy stored in them. The study established that the condensates do not have a significant impact on efficiency.
- Full Text:
- Date Issued: 2009
- Authors: Mamphweli, Ntshengedzeni Sampson
- Date: 2009
- Subjects: Rural development -- South Africa , Electric power distribution -- South Africa , Condensation , Rural electrification -- South Africa
- Language: English
- Type: Thesis , Doctoral , PhD (Physics)
- Identifier: vital:11591 , http://hdl.handle.net/10353/262 , Rural development -- South Africa , Electric power distribution -- South Africa , Condensation , Rural electrification -- South Africa
- Description: There is growing interest in research and development activities on biomass gasification technologies as an alternative to fossil fuels technologies. However not much has been done in terms of technology transfer, particularly in under-developed and developing countries such as South Africa. This is mainly because of the lack of resources such as funding. Most parts of the under-developed and developing countries fall within rural areas and semi-urban centers, which are endowed with biomass resources. South Africa has a number of sawmill operators who generate tons of biomass waste during processing of timber; the large proportion of this is burned in furnaces as a means for waste management while a very small proportion is collected and used by people in rural areas for cooking their food. The majority of people in rural areas of South Africa are either unemployed or cannot afford the current energy services. The main aim of this research was to establish the viability of electricity generation for community economic development through biomass gasification, specifically using the locally designed System Johansson Biomass Gasifier™ (SJBG), and to establish the efficiency of the gasifier and associated components with a view of developing strategies to enhance it. The study established the technical and economic feasibility of using the SJBG to generate low-cost electricity for community empowerment. The study also developed strategies to improve the particle collection efficiency of the cyclone. In addition to this, a low-cost gas and temperature monitoring system capable of monitoring gas and temperature at various points of the gasifier was developed. The system was built from three Non- Dispersive Infrared gas sensors, one Palladium/Nickel gas sensor and four type K thermocouples. The study also investigated the impact of fuel compartment condensates on gasifier conversion efficiency. This is an area that has not yet been well researched since much has been done on energy recovery using combined heat and power applications that do not utilize the energy in condensates because these are produced in the gasifier and drained with chemical energy stored in them. The study established that the condensates do not have a significant impact on efficiency.
- Full Text:
- Date Issued: 2009
On the evaluation of spectral effects on photovoltaic modules performance parameters and hotspots in solar cells
- Authors: Simon, Michael
- Date: 2009
- Subjects: Photovoltaic cells , Energy dissipation , Electric power production , Photovoltaic power generation , Solar energy , Spectral energy distribution
- Language: English
- Type: Thesis , Doctoral , PhD (Physics)
- Identifier: vital:11593 , http://hdl.handle.net/10353/257 , Photovoltaic cells , Energy dissipation , Electric power production , Photovoltaic power generation , Solar energy , Spectral energy distribution
- Description: The performance of photovoltaic (PV) modules in terms of their ability to convert incident photon to electrical energy (efficiency) depends mostly on the spectral distribution of incident radiation from the sun. The incident spectrum finally perceived by the module depends strongly on the composition of the medium in which it has traveled. The composition of the earth’s atmosphere, which includes, amongst others, water vapour, gases such as carbon dioxide and oxygen, absorbs or scatters some of the sunlight. The incident solar spectrum is also modified by the diffuse aspect of radiation from the sky which strongly depends on aerosol concentration, cloudiness and local reflection of the earth’s surface. Although it is well known that the changes in outdoor spectrum affect device performance, little work has been conducted to support this theory. This is probably due to lack of spectral data or in certain instances where data is available, little knowledge of interpreting that data. The outdoor spectral data that one obtains in the field does not come clearly for just simple interpretation. Different analytical interpretation procedures have been proposed, all trying to explain and quantify the spectral influence on PV devices. In this study an assessment methodology for evaluating the effects of outdoor spectra on device performance parameters during the course of the day, seasons and or cloudy cover has been developed. The methodology consists of developing a device dependant concept, Weighted Useful Fraction (WUF) using the outdoor measured spectral data. For measuring PV module’s performance parameters, a current-voltage (I-V) tester was developed in order to monitor the performance of six different module technologies. The Gaussian distribution was used to interpret the data. For hot-spot analysis, different techniques were used, which include Infrared thermographic technique for identifying the hot-spots in the solar cells, SEM and EDX techniques. The AES technique was also used in order to identify other elements at hot-spots sites that could not be detected by the EDX technique. iii Results obtained indicate that multicrystalline modules performance is affected by the changes in the outdoor spectrum during summer or winter seasons. The modules prefer a spectrum characterized by WUF = 0.809 during summer season. This spectrum corresponds to AM 2.19 which is different from AM 1.5 used for device ratings. In winter, the mc-Si module’s WUF (0.7125) peaks at 13h00 at a value corresponding to AM 1.83. Although these devices have a wider wavelength range, they respond differently in real outdoor environment. Results for mono – Si module showed that the device performs best at WUF = 0.6457 which corresponds to AM 1.83 during summer season, while it operates optimally under a winter spectrum indicated by WUF of 0.5691 (AM2.58). The seasonal changes resulted in the shift in WUF during day time corresponding to the “preferred” spectrum. This shift indicates that these devices should be rated using AM values that correspond to the WUF values under which the device operates optimally. For poly-Si, it was also observed the WUF values are lower than the other two crystalline-Si counterparts. The pc-Si was observed to prefer a lower AM value indicated by WUF = 0.5813 during winter season while for summer it prefers a spectrum characterized by WUF = 0.5541 at AM 3.36. The performance of the single junction a-Si module degraded by 67 percent after an initial outdoor exposure of 16 kWh/m² while the HIT module did not exhibit the initial degradation regardless of their similarities in material composition. It was established that the WUF before degradation peaks at 15h00 at a value of 0.7130 corresponding to AM 4.50 while the WUF after degradation “prefers” the spectrum (WUF = 0.6578) experienced at 15h30 corresponding to AM value of 5.57. Comparing the before and after degradation scenarios of a-Si:H, it was observed that the device spends less time under the red spectrum which implies that the device “prefers” a full spectrum to operate optimally. The degradation of a-Si:H device revealed that the device spectral response was also shifted by a 7.7 percent after degradation. A higher percentage difference (61.8 percent) for spectral range for the HIT module is observed, but with no effects on device parameters. Seasonal changes (summer/winter) resulted in the outdoor spectrum of CuInSe2 to vary by WUF = 1.5 percent, which resulted in the decrease in Isc. This was ascertained by iv analyzing the percentage change in WUF and evaluating the corresponding change in Isc. The analysis showed that there was a large percentage difference of the module’s Isc as the outdoor spectrum changed during the course of the day. This confirmed that the 17 percent decrease in Isc was due to a WUF of 1.5 percent. In mc-Si solar cells used in this study, it was found that elemental composition across the entire solar cell was not homogenously distributed resulting in high concentration of transition metals which were detected at hot spot areas. The presence of transition metals causes hot-spot formation in crystalline solar cells. Although several transition elements exist at hot-spot regions, the presence of oxygen, carbon, iron and platinum was detected in high concentrations. From this study, it is highly recommended that transition elements and oxygen must be minimized so as to increase the life expectancy of these devices and improve overall systems reliability
- Full Text:
- Date Issued: 2009
- Authors: Simon, Michael
- Date: 2009
- Subjects: Photovoltaic cells , Energy dissipation , Electric power production , Photovoltaic power generation , Solar energy , Spectral energy distribution
- Language: English
- Type: Thesis , Doctoral , PhD (Physics)
- Identifier: vital:11593 , http://hdl.handle.net/10353/257 , Photovoltaic cells , Energy dissipation , Electric power production , Photovoltaic power generation , Solar energy , Spectral energy distribution
- Description: The performance of photovoltaic (PV) modules in terms of their ability to convert incident photon to electrical energy (efficiency) depends mostly on the spectral distribution of incident radiation from the sun. The incident spectrum finally perceived by the module depends strongly on the composition of the medium in which it has traveled. The composition of the earth’s atmosphere, which includes, amongst others, water vapour, gases such as carbon dioxide and oxygen, absorbs or scatters some of the sunlight. The incident solar spectrum is also modified by the diffuse aspect of radiation from the sky which strongly depends on aerosol concentration, cloudiness and local reflection of the earth’s surface. Although it is well known that the changes in outdoor spectrum affect device performance, little work has been conducted to support this theory. This is probably due to lack of spectral data or in certain instances where data is available, little knowledge of interpreting that data. The outdoor spectral data that one obtains in the field does not come clearly for just simple interpretation. Different analytical interpretation procedures have been proposed, all trying to explain and quantify the spectral influence on PV devices. In this study an assessment methodology for evaluating the effects of outdoor spectra on device performance parameters during the course of the day, seasons and or cloudy cover has been developed. The methodology consists of developing a device dependant concept, Weighted Useful Fraction (WUF) using the outdoor measured spectral data. For measuring PV module’s performance parameters, a current-voltage (I-V) tester was developed in order to monitor the performance of six different module technologies. The Gaussian distribution was used to interpret the data. For hot-spot analysis, different techniques were used, which include Infrared thermographic technique for identifying the hot-spots in the solar cells, SEM and EDX techniques. The AES technique was also used in order to identify other elements at hot-spots sites that could not be detected by the EDX technique. iii Results obtained indicate that multicrystalline modules performance is affected by the changes in the outdoor spectrum during summer or winter seasons. The modules prefer a spectrum characterized by WUF = 0.809 during summer season. This spectrum corresponds to AM 2.19 which is different from AM 1.5 used for device ratings. In winter, the mc-Si module’s WUF (0.7125) peaks at 13h00 at a value corresponding to AM 1.83. Although these devices have a wider wavelength range, they respond differently in real outdoor environment. Results for mono – Si module showed that the device performs best at WUF = 0.6457 which corresponds to AM 1.83 during summer season, while it operates optimally under a winter spectrum indicated by WUF of 0.5691 (AM2.58). The seasonal changes resulted in the shift in WUF during day time corresponding to the “preferred” spectrum. This shift indicates that these devices should be rated using AM values that correspond to the WUF values under which the device operates optimally. For poly-Si, it was also observed the WUF values are lower than the other two crystalline-Si counterparts. The pc-Si was observed to prefer a lower AM value indicated by WUF = 0.5813 during winter season while for summer it prefers a spectrum characterized by WUF = 0.5541 at AM 3.36. The performance of the single junction a-Si module degraded by 67 percent after an initial outdoor exposure of 16 kWh/m² while the HIT module did not exhibit the initial degradation regardless of their similarities in material composition. It was established that the WUF before degradation peaks at 15h00 at a value of 0.7130 corresponding to AM 4.50 while the WUF after degradation “prefers” the spectrum (WUF = 0.6578) experienced at 15h30 corresponding to AM value of 5.57. Comparing the before and after degradation scenarios of a-Si:H, it was observed that the device spends less time under the red spectrum which implies that the device “prefers” a full spectrum to operate optimally. The degradation of a-Si:H device revealed that the device spectral response was also shifted by a 7.7 percent after degradation. A higher percentage difference (61.8 percent) for spectral range for the HIT module is observed, but with no effects on device parameters. Seasonal changes (summer/winter) resulted in the outdoor spectrum of CuInSe2 to vary by WUF = 1.5 percent, which resulted in the decrease in Isc. This was ascertained by iv analyzing the percentage change in WUF and evaluating the corresponding change in Isc. The analysis showed that there was a large percentage difference of the module’s Isc as the outdoor spectrum changed during the course of the day. This confirmed that the 17 percent decrease in Isc was due to a WUF of 1.5 percent. In mc-Si solar cells used in this study, it was found that elemental composition across the entire solar cell was not homogenously distributed resulting in high concentration of transition metals which were detected at hot spot areas. The presence of transition metals causes hot-spot formation in crystalline solar cells. Although several transition elements exist at hot-spot regions, the presence of oxygen, carbon, iron and platinum was detected in high concentrations. From this study, it is highly recommended that transition elements and oxygen must be minimized so as to increase the life expectancy of these devices and improve overall systems reliability
- Full Text:
- Date Issued: 2009
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