The increasing population and the rapid economic growth in South Africa have led to higher consumption of food resulting in the generation of large amounts of waste. In addition, South Africa has plenty of biomass from cattle, donkeys, horses, goats, pigs, chicken and sheep. However, anaerobic digestion could be an alternative solution for the utilization of these kinds of waste due to its environmental and economic benefits. Therefore, the main focus of the research was design, construct a field batch biogas digester, monitor its performance when fed with co-substrates and model the methane yield for an optimized mixing ratio.

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.

Miniaturisation has been the holy grail of mobile technology. The ability to move around with our gadgets, especially the ones for communication and entertainment, has been what semiconductor scientists have battled over the past decades. Miniaturisation brings about reduced consumption in power and ease of mobility. However, the main impediment to untethered mobility of our gadgets has been the lack of unlimited power supply. The battery had filled this gap for some time, but due to the increased functionalities of these mobile gadgets, increasing the battery capacity would increase the weight of the device considerably that it would eventually become too heavy to carry around. Moreover, the fact that these batteries need to be recharged means we are still not completely free of power cords. The advent of low powered micro-controllers and sensors has created a huge industry for more powerful devices that consume a lot less power. These devices have encouraged hardware designers to reduce the power consumption of the gadgets. This has encouraged the idea of wireless power transmission on another level. With lots of radio frequency energy all around us, from our cordless phones to the numerous mobile cell sites there has not been a better time to delve more into research on WPT. This study looks at the feasibilities of WPT in small device applications where very low power is consumed to carry out some important functionality. The work done here compared two rectifying circuits’ efficiencies and ways to improve on the overall efficiencies. The results obtained show that the full wave rectifier would be the better option when designing a WPT system as more power can be drawn from the rectenna. The load also had a great role as this determined the amount of power drawn from the circuitry.

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.

Abstract This study presents the characteristics of small-scale gravity waves in the mesosphere region as derived from the imaging riometer data at high altitude (~90 km) over SANAE (72˚S, 3˚W). Wavelet analysis and FFT (Fast Fourier transform) have been applied to extract short period gravity wave parameters for the year 2000. The horizontal wavelength, phase speed and observed period of gravity waves are typically 10-100 km, 5-60 m.s-1 and 3-60 minutes, respectively. The horizontal propagation direction is north-eastward throughout the year. This could probably be due to selective filtering by the zonal wind. Zonal and meridional winds in the region of the MLT (mesosphere and lower thermosphere) have been measured using HF radars at high latitudes in the southern hemisphere. Data from January 2000 to December 2003 have been used with the aim of investigating the characteristics of planetary wave activity at ~90 km. For SANAE and Halley stations, 2-, 5-, 10-, 16- and 20-day planetary waves are dominant in summer and winter. The results show the seasonal variations of the mean winds, which are caused by the internal variability of the quasi stationary planetary waves. Planetary wave coupling processes between UKMO assimilated and mesospheric data have also been investigated. The cross wavelet results show a strong coupling during winter months. The results suggest that planetary waves are generated at lower atmospheric heights and propagate upwards into mesospheric heights. However, not all observed disturbances in mesospheric heights can be explained by the propagation of planetary waves from lower atmospheric heights.

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

Abstract This thesis will present an investigation into the variability of the maximum height of the ionospheric F2 layer, hmF2, with hour, season and latitude over the South African region. The dependence of hmF2 on solar and magnetic activity is also investigated. Data from three South African stations, namely Madimbo (22.4 S, 26.5 E), Grahamstown (33.3 S, 26.5 E) and Louisvale (28.5 S, 21.2 E) were used in this study. Initial results indicate that hmF2 shows a larger variability around midnight than during daytime for all the seasons. Monthly median values for hmF2 were used in all cases to illustrate the variability, and the International Reference Ionosphere (IRI) model has been used to investigate hmF2 predictability over South Africa. This research represents the initial steps towards a predictive model for the hmF2 parameter, with the long term aim of developing a new global hmF2 predictive model for the IRI. It is believed that this work will contribute signi cantly towards this aim through the understanding of the hmF2 parameter over a region that has not previously been investigated.

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