3. Electronic Theses and Dissertations (ETDs) - All submissions
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Item Simulation of a hot mirror parabolic trough solar collector receiver(2018) Kaluba, Victor SiulutaParabolic trough solar collectors (PTSC) are currently the most mature solar collecting technology, applied commercially for electricity generation. High input temperature in power plants are desired for improved efficiency and help reduce electricity costs. However, at high temperatures, heat losses through radiation increase significantly. Thermal radiation transfer is the dominant heat loss mechanism in PTSC receivers operating at high temperatures. In existing systems, the radiation losses are reduced by using a selective absorber coating placed on the absorber pipe. It has optical properties that suppress infrared radiation (IR) emissions. The material absorbs well in the solar wavelength range (0.3 to 2.5 um ) but emits poorly in the infrared (IR) wavelength range. However, the material degrades at temperatures beyond 400oC resulting in high IR emission. This study developed a theoretical framework to characterize a different approach, alternative to the selective coating in reducing heat losses. This is the use of a hot mirror coating in a PTSC receiver. The coating is placed on the inner surface of the glass cover to reflect infrared radiation emanating from the absorber pipe back for reabsorption. The hot mirror is transparent to solar radiation and reflective in the wavelengths above 2.5 um. The formulations developed described the thermal interactions in a hot mirror coated PTSC receiver. To describe the heat loss reduction mechanisms, the study modelled theoretically the long range thermal radiation interactions inside the receiver unit. The model used discretization of the active surfaces to account for all the dominant radiation interactions. Different simulations scenarios were done to predict receiver performance. The performance of various candidates for hot mirror coating (ITO, Gold and Silver) were investigated. The effects of variation of some hot mirror optical parameters on overall plant efficiency was also investigated. The simulation was validated using other simulation works and experimental data. The results showed a close match with a discrepancy of 0.7%. High HTF temperatures were attained using hot mirrors. ITO gave the highest HTF temperature. The hot mirror thermal stability is not compromised since the glass cover stays cooler than the absorber pipe (< 400oC). The glass cover temperatures were far less than the absorber pipe temperatures. Even with the higher temperature of ITO (500oC), the glass cover never reached above 400oC. Solar transmissivity for the hot mirror materials is as important as the need for high HTF out temperatures.Item Investigating the feasibility & impact of a solar array for Wits West Campus by using historical solar and power data(2016) Singh, AjeshniThis dissertation uses historical electrical consumption/load and actual solar radiation data to design a solar array for the University of the Witwatersrand’s West Campus. The array must meet the campus’s minimum demand as selling excess generated power back to the utility is not possible at this stage. The financial and spatial impact of adjusting the size of the array, design losses and cloud cover are also investigated. In addition to this, the influence on the payback period of financial variables such as taxes, electricity and start-up costs are also explored. The solar array system design process starts by determining the amount of power that the array must produce or supplement. Thereafter, load estimates and electrical consumption figures that are provided by utility bills or measured with load monitoring equipment are analysed. Furthermore, system losses are factored in which ultimately increases the size of the array. Once all the input variables are analysed, the amount of available solar radiation in the area where the array will be installed is required to determine the amount of energy that the array can produce. Several free databases with this information are available but it is found that this data over predicts the availability of solar radiation. The University has been monitoring the electrical consumption of West Campus since 2012 and solar radiation data is also available for this site. Comparing the satellite derived and measured datasets found that the ground monitored data is 25 % more accurate and therefore better suited for designing a solar array. Individually adjusting the design and financial variables changes the payback period between 3 – 17 %. Combining all the variables can reduce the payback of option 1 from 9.6 years to 6.1 years. Clear legislation needs to be developed for the uptake of renewable energy resources and supported by better rebates for renewable users and harsher taxes for non-renewable users. Should legislation change and if additional capital is available, a larger array will benefit the University more and should be installed as the difference between payback periods is not significant. This is mainly due to decreased costs associated with a higher yield. The financial benefits of a larger array will also be more lucrative if better rebates are enforced.Item Biologging as a method to remotely detect orientation to solar radiation in black and blue wildebeest(2015-04-17) Botha, AristaAnimals can shift their orientation to solar radiation to adjust the amount of body surface area that is exposed to solar radiation, thereby manipulating the amount of radiant heat they absorb from their environment. This behaviour is especially important in animals that need to graze out in the open during the day, such as wild ungulates. All previous studies of orientation to solar radiation in animals have relied on visual observations. The problem with visual observations is that animal behaviour, including animal orientation, can be affected by human presence. Therefore I set out to develop a remote technique to detect and quantify orientation to solar radiation in wildebeest to eliminate the need of a human observer. I hypothesised that if an animal was orientated perpendicular to solar radiation, the side facing the sun would be hotter than the opposite side. In contrast, if the animal was orientated parallel to solar radiation I hypothesised that both sides will have a similar temperature. To test my hypothesis, temperature-sensitive data loggers were implanted subcutaneously into free-ranging black (Connochaetes gnou) and blue wildebeest (Connochaetes taurinus) from Mokala National Park and their orientation to solar radiation was determined visually. I found that when wildebeest were orientated perpendicular to solar radiation, there was a greater difference between the left and right subcutaneous temperature than when wildebeest were orientated parallel to solar radiation (t7=2.5, p=0.04). However, using subcutaneous temperature difference on its own to predict orientation to solar radiation could not account for how the previous orientation to solar radiation of wildebeest affected subcutaneous temperature patterns. Therefore, I designed a prediction model incorporating both subcutaneous temperature difference and rate of change in subcutaneous temperature difference to determine orientation to solar radiation. The prediction model was accurate more often than expected by chance (60 %), but there were many factors other than solar radiation that influenced subcutaneous temperature, which reduced the accuracy of the remote technique. Further research is necessary to improve the remote technique before it can be successfully used to study orientation to solar radiation. However, my study shows, for the first time, the potential of using subcutaneous temperatures to remotely detect orientation to solar radiation in ungulates. A remote technique to study orientation to solar radiation will be a great advantage for future studies on thermoregulatory behaviour. Because behavioural responses are likely to be an animal’s first defence against increased heat loads resulting from climate change, studying behavioural thermoregulation could provide important information for conservation and management decisions.