A dissertation submitted to the Faculty of Engineering and the Built Environment, University of the Witwatersrand, Johannesburg, in fulfillment of the requirements for the degree of Doctor of Philosophy in Engineering, October 2017 / The dwindling fossil reserves coupled with environmental pollution necessitate the search for clean and sustainable energy resources. Biohydrogen is emerging as a suitable alternative to fossil fuels and has received considerable attention in recent years due to its economic, social, and environmental benefits. However, the industrial application of biohydrogen has been hindered by low yield. Therefore, development of novel techniques to enhance the yield is of immense importance towards large-scale production of biohydrogen. Thus, this research effort explored various options to enhance the yield of biohydrogen during dark fermentation process. Some options explored included (i) the utilization of feedstocks from the agricultural, industrial and municipal sectors, (ii) parametric optimization of biohydrogen production, (iii) investigation of biohydrogen production using metal ions and nitrogen gas sparging, and (iv) assessing the feasibility of biohydrogen scale-up study to pave the way for pilot-scale development. Solid biowaste feedstocks consisting of apple, bread, brewery residue, cabbage, corn-cob, mango, mealie-pap, pear, potato, and sugarcane were investigated for dark fermentative biohydrogen production using anaerobic mixed sludge. The experimental results showed that substrates which are rich in carbohydrates are suitable for dark fermentative biohydrogen-producing bacteria. Consequently, a maximum biohydrogen fraction of 43.98, 40.32 and 38.12% with a corresponding cumulative biohydrogen yield of 278.36, 238.32 and 215.69 mL H2/g total volatile solids (TVS) was obtained using potato, cabbage, and brewery wastes, respectively. Based on these results, potato waste was chosen as a suitable substrate for subsequent biohydrogen production studies. Parametric optimization was carried out on biohydrogen production via dark fermentation using potato waste as the substrate. Effects of operating variables such as pH, temperature, fermentation time, and substrate concentration were investigated via response surface methodology (RSM) approach using a two-level-four factor (24) central composite design (CCD). The obtained predictive model (statistical model) was used to explain the main and interaction effects of the considered variables on biohydrogen production. In addition, the model was employed in the optimization of the operating conditions. Consequently, a secondorder polynomial regression with a coefficient of determination (R2) of 0.99 was obtained and used in the explanation and optimization of operating variables. The optimum operating conditions for biohydrogen production were 39.56 g/L, 5.56, 37.87 oC and 82.58 h for potato waste concentration, pH, temperature and fermentation time, respectively, with a corresponding biohydrogen yield of 68.54 mL H2/g TVS. These results were then validated experimentally and a high biohydrogen yield of 79.43 mL H2/g TVS indicating a 15.9% increase was obtained. Furthermore, the optimized fermentation conditions were applied in the scale-up study of biohydrogen production that employed anaerobic mixed bacteria (sludge) which was immobilized in calcium alginate beads. A biohydrogen fraction of 56.38% with a concomitant yield of 298.11 mL H2/g TVS was achieved from the scale-up study. The research also investigated the influence of metal ions (Fe2+, Ca2+, Mg2+ and Ni2+) on biohydrogen production from suspended and immobilized cells of anaerobic mixed sludge using the established optimal operating conditions. A maximum biohydrogen fraction of 45.21% and a corresponding yield of 292.8 mL H2/g TVS was achieved in fermentation using Fe2+ (1000 mg/L) and immobilized cells. The yield was 1.3 times higher than that of suspended cultures. The effect of nitrogen gas sparging on biohydrogen conversion efficiency (via suspended and immobilized cells) was studied as well. Cell immobilization and nitrogen gas sparging were effective for biohydrogen production enhancement. A maximum biohydrogen fraction of 56.98% corresponding to a biohydrogen yield of 294.83 mL H2/g TVS was obtained in a batch process using nitrogen gas sparging with immobilized cultures. The yield was 1.8 and 2.5 times higher than that of nitrogen gas sparged and non-sparged suspended cell system, respectively. Understanding the functional role of microorganisms that actively participate in dark fermentation process could provide in-depth information for the metabolic enhancement of biohydrogen-producing pathways. Therefore, the microbial composition in the fermentation medium of the optimal substrate (potato waste) was examined using PCR-based 16S rRNA approach. Microbial inventory analysis confirmed the presence of Clostridium species which are the dominant biohydrogen-producing bacteria. The results obtained from this research demonstrated the potential of producing biohydrogen using South African solid biowaste effluents. These feedstocks are advantageous in biohydrogen production because they are highly accessible, rich in nutritional content, and cause huge environmental concerns. Furthermore, optimization techniques using these feedstocks will play a pivotal role towards large-scale production of biohydrogen by increasing throughput and reducing the substrate costs which accounts for approximately 60% of the overall costs. The findings from this research also provide a solid basis for further scale-up and techno-economic studies. Such studies are necessary to evaluate the competitiveness of this technology with the traditional processes of hydrogen production. In summary, the findings from this research effort have been communicated to researchers in the area of biohydrogen process development in the form of peer-reviewed international scientific publications and conference proceedings, and could provide a platform for developing an economic biohydrogen scaled-up process. / CK2018

In this study, we analyze the quantile dependence for green bond returns and renewable energy stock returns with three major asset classes: corporate bonds, stocks and oil. Furthermore, we control the dependence structure for technology, uncertainties as well as lag structures and time-varying effects. We apply the cross-quantilogram developed by Han et al. (2016) that allows us to study the dependence structures between two time series in arbitrary quantiles. The results led us to three key findings: 1) The returns of thegreen bond market are tail-dependent on the returns of both long and short-term maturities for the corporate bond market but are not dependent on the stock market nor the oil market. The tail-dependence indicates that while investors may hold green bonds due to moral incentives, it is not enough during times of turbulence. Further, the dependence structures are short-lived. 2)The renewable energy market is dependent on oil returns of similar quantiles, suggesting that renewable energy substitutes oil when oil prices increase. However, renewable energy does not influence the oil market, indicating that oil is not a substitutional energy source for renewable energy driven firms. Renewable energy stocks are further highly dependent on the returns of the general stock market but are not influenced by the returns on the corporate bond market. 3) The dependence of both renewable energy and green bonds with the asset markets are time-varying. Our overall results obtained by this paper provides information that could help facilitate new investment allocations towards green investments. Further, the results may have immediate and important implications for investors. For those in the corporate bond market, adding green bonds does not add diversification benefits during turbulence. Similarly, renewable energy stock does not add diversification benefits to investors in the oil or stock market.

In 2015, the United Nations developed 17 goals to work towards sustainable development by 2030. Among these goals, goal number seven focuses on providing clean and affordable energy for all, to solve problems such as poverty and to reduce greenhouse gas emissions around the world. In Sub-Saharan Africa, 600 million people live without access to electricity. Furthermore, millions of people in Sub-Sharan Africa die each year because of indoor air pollution that comes from combustible and inefficient energy solutions. Because of these issues, social enterprises are a vital component to be able to work towards providing renewable energy solutions and efficient cooking solutions to households in Sub-Saharan Africa. This thesis analyses social enterprises working within the renewable energy sector in Sub-Saharan Africa, and investigates what a social enterprise must do to succeed. To answer this question, the authors carried out interviews to identify the factors that contribute to success and barriers that prevent the success of social enterprises active within the mentioned sector and region. The answers from the interviews were later on compared with findings from existing literature discussed in a literature review. Social enterprises in Sub-Saharan Africa that works within the renewable energy sector must work together with local employees to access knowledge about external factors that could engender barriers. Other barriers that a social enterprise might encounter are linked to profitability and affordability, and what the business is primarily focusing on achieving.    Social networks and financial institutions are of importance for social enterprises to succeed in Sub-Saharan Africa. Furthermore, by providing excellent customer service together with having the right abilities and knowledge, a social enterprise will have a higher chance of success. One of the most critical variables when aiming for success in the renewable energy sector in Sub-Saharan Africa is to have a well thought out business model before entering a new target market. This thesis concludes that the identified success factors and barriers, along with the explanation behind them, can be used as guidelines for future social enterprises that want to establish in the renewable energy sector in Sub-Sharan Africa.

This master thesis investigated how a hydrogen energy storage could be used anddimensioned to reduce the problem of power shortage in the local distributiongrid in Uppsala, Sweden. By implementing such a storage system in mobilityhouses, which are parking garages with integrated charging stations for electric vehicles and smart renewable energy solutions for power generation, the problem with power shortage could be decreased. The results showed that by integrating a hydrogen storage together with battery packs, it was possible to reduce power peaks in mobility houses. Further, it was clear that more power peaks facilitated the dimensioning of these type of systems. It was also shown that due to today's initial cost of hydrogen storages, the total savings related to a limited purchase of electricity from the grid were insignificant. It was therefore found that this type of hydrogen storage would not reduce costs in the short term for the mobility houses considered in this study. However, implementing a smaller kW storage could generate and improve knowledge in the hydrogen/hybrid field, which could facilitate the implementation of larger systems in the future. Furthermore, the results showed that it could be interesting to implement hydrogen storages on a bigger scale for municipalities or actors, who would want to reduce the power shortage in the local distribution grid.

The technical and scientific challenges to provide reliable sources energy for US and global economy are enormous tasks, and especially so when combined with strategic and recent economic concerns of the last five years. It is clear that as part of the mix of energy sources necessary to deal with these challenges, fuel cells technology will play critical or even a central role. The US Department of Energy, as well as a number of the national laboratories and academic institutions have been aware of the importance such technology for some time. Recently, car manufacturers, transportation experts, and even utilities are paying attention to this vital source of energy for the future. In this thesis, a review of the main fuel cell technologies is presented with the focus on the modeling, and control of one particular and promising fuel cell technology, aluminum air fuel cells. The basic principles of this fuel cell technology are presented. A major part of the study consists of a description of the electrochemistry of the process, modeling, and simulations of aluminum air FC using Matlab Simulink™. The controller design of the proposed model is also presented. In sequel, a power management unit is designed and analyzed as an alternative source of power. Thus, the system commutes between the fuel cell output and the alternative power source in order to fulfill a changing power load demand. Finally, a cost analysis and assessment of this technology for portable devices, conclusions and future recommendations are presented. / Includes bibliography. / Thesis (M.S.)--Florida Atlantic University, 2013.

Many issues related to the design and implementation of a maximum power point tracking (MPPT) converter as part of a photovoltaic (PV) system are addressed. To begin with, variations of the single diode model for a PV module are compared, to determine whether the simplest variation may be used for MPPT PV system modeling and analysis purposes. As part ot this determination, four different DC/DC converters are used in conjunction with these different PV models. This is to verify consistent behavior across the different PV models, as well as across the different converter topologies. Consistent results across the different PV models, will allow a simpler model to be used for simulation ana analysis. Consistent results with the different converters will verify that MPPT algorithms are converter independent. Next, MPPT algorithms are discussed. In particular,the differences between the perturb and observe, and the incremental conductance algorithms are explained and illustrated. A new MPPT algorithm is then proposed based on the deficiencies of the other algorithms. The proposed algorithm's parameters are optimized, and the results for different PV modules obtained. Realistic system losses are then considered, and their effect on the PV system is analyzed ; especially in regards to the MPPT algorithm. Finally, a PV system is implemented and the theoretical results, as well as the behavior of the newly proposed MPPT algorithm, are verified. / by Thomas Bennett. / Thesis (Ph.D.)--Florida Atlantic University, 2012. / Includes bibliography. / Mode of access: World Wide Web. / System requirements: Adobe Reader.

Barometric distillation is an alternative method of producing fresh water by desalination. This proposed process evaporates saline water at low pressure and consequently low temperature; low pressure conditions are achieved by use of barometric columns and condensation is by direct contact with a supply of fresh water that will be augmented by the distillate. Low-temperature sources of heat, such as the cooling water rejected by electrical power generating facilities, can supply this system with the latent heat of evaporation. Experiments are presented that show successful distillation with a temperature difference between evaporator and condenser smaller than 10ê C. Accumulation of dissolved gases coming out of solution, a classic problem in lowpressure distillation, is indirectly measured using a gas-tension sensor. The results of these experiments are used in an analysis of the specific energy required by a production process capable of producing 15 liters per hour. With a 20ê C difference, and neglecting latent heat, this analysis yields a specific energy of 1.85 kilowatt-hour per cubic meter, consumed by water pumping and by removal of non-condensable gases. / by Eiki Martinson. / Thesis (M.S.C.S.)--Florida Atlantic University, 2010 / Includes bibliography. / Electronic reproduction. Boca Raton, Fla., 2010. Mode of access: World Wide Web.

The incorporation of an ejector refrigeration cycle with a high temperature PEM fuel cell (HT-PEMFC) presents a novel approach to combined heat and power (CHP) applications. An ejector refrigeration system (ERS) can enhance the flexibility of a CHP system by providing an additional means of utilizing the fuel cell waste heat besides domestic hot water (DHW) heating. This study looks into the performance gains that can be attained by incorporating ejector refrigeration with HT-PEMFC micro-CHP (mCHP) systems (1 to 5kWe). The effectiveness of the ERS in utilizing fuel cell waste heat is studied as is the relulting enhancement to overall system efficiency. A test rig specially constructed to evaluate an ERS under simulated HT-PEMFC conditions is used to test the concept and verify modeling predictions. In addition, two separate analytical models were constructed to simulate the ERS test rig and a HT-PEMFC/ERS mCHP system. The ERS test rig was simulated using a Matlab based model, while two residential sized HT-PEMFC/ERS mCHP systems were simulated using a Simulink model. Using U.S. Energy Information Administration (EIA) air conditioning and DHW load profiles, as well as data collected from a large residential monitoring study in Florida, the Simulink model provides the results in system efficiency gain associated with supporting residential space cooling and water heating loads. It was found that incorporation of an ERS increased the efficiency of a HT-PEMFC mCHP system by 8 t0 10 percentage points over just using the fuel cell waste heat for DHW. In addition, results from the Matlab ERS test rig model were shown to match well with experimental results. / by Michel Fuchs. / Thesis (Ph.D.)--Florida Atlantic University, 2012. / Includes bibliography. / Mode of access: World Wide Web. / System requirements: Adobe Reader.

A motivação para o desenvolvimento desse trabalho surge em um momento em que se verifica uma participação cada vez mais significativa das fontes energéticas renováveis não convencionais no País. Não obstante, o cenário de evolução evidencia que o arcabouço regulatório e as regras de mercado não acompanharam as especificidades inerentes à exploração dessas fontes. Como consequência, temos um setor elétrico moldado para a exploração de usinas de grande porte, como hidrelétricas e termelétricas convencionais, cuja expansão aponta para modicidade tarifária baseada em preço de venda de energia calculado de forma isolada, sem considerar os custos indiretos e as externalidades de cada fonte. Por essa razão, para que se mantenha adequado ritmo de inserção na matriz energética, devem ser buscadas opções para que fontes renováveis não convencionais sejam cada vez mais competitivas na atual configuração do mercado energético. A contribuição dessa pesquisa, portanto, centra-se na identificação do comportamento energético complementar, com suporte de estudos e simulações envolvendo a sazonalidade na produção e as características particulares de cada fonte, permitindo incrementos de produção e receita, sem aumentar o risco de perdas. Tal ganho é possível em virtude das compensações energéticas feitas entre as diferentes fontes em um portfólio combinado, mitigando a receita em risco decorrente das variações que existem nos preços de curto prazo e na produção energética. As simulações foram divididas em três etapas, de forma evolutiva e complementar. A primeira considera quatro fontes distintas: biomassa, eólica, solar e pequena central hidrelétrica (PCH), combinadas em diferentes portfólios, com o objetivo de identificar o arranjo com maior receita, dada a probabilidade de valores abaixo de um mínimo estabelecido. A segunda analisa a complementação entre uma PCH e quatro diferentes parques eólicos com histórico de geração reconstituído a partir de velocidades de vento desde 1948, obtidas a partir de modelo de Mesoescala, caracterizando uma evolução em relação à primeira simulação, onde foram considerados dados determinísticos, além da utilização do CVaR como critério de risco. Finalmente, a última etapa considerou a entrada gradual de uma fonte renovável em um portfólio hidráulico existente, com o objetivo de analisar o comportamento do risco. / The motivation to write this thesis has arisen at a time when the participation of nonconventional renewable sources in the Brazilian electric energy matrix has become more significant. However, the scenario of the regulatory framework and market rules has not followed the specificity of the nature of these sources. Therefore, the electric sector is shaped for the exploitation of large power plants, such as the conventional hydro and thermal; at the same time, the expansion aims at tariff reduction based on energy selling prices alone, putting aside indirect costs and externalities of each source. In order to maintain a higher growth rate in the national electric matrix, nonconventional renewable sources must find alternatives to the current electric market. Therefore, the purpose of this study is to identify a complementary pattern for these sources by means of studying and simulating seasonality of energy production and specific features of each one. This allows revenues increase while mitigating risks in a scenario where spot prices and energy production vary greatly. Such gains are possible due to differences amongst each source considered in the simulations, compensating the results in a diversified portfolio. Simulations were divided into three stages and carried out in an evolutionary and complementary manner. The first stage involves four different renewable sources: biomass, wind, solar and small hydro power. All of these sources were combined in different portfolios in order to identify an arrangement that provides the best revenue giving an acceptance of risk, measured by probability of revenue under a minimum settled value. The second stage has analysed the complementation between a small hydro and four different fields of wind power plants. In addition, the wind generation data was a reconstruction of wind speed data validated since 1948, with the aid of Mesoescale Models; an evolution in comparison to the first stage, which has used deterministic information. Another improvement was that the risk was measured using the CVaR (Conditional Value at Risk). Finally, an increasing amount of renewable source was added into an existing hydraulic portfolio, in order to analyse the risk effects of the combination.

O presente trabalho apresenta e analisa cenários para os próximos anos para a expansão da demanda do etanol a base de cana de açúcar no Brasil, considerando a influência dos condicionantes envolvidos e os conseqüentes impactos , necessidades e alternativas futuras na logística de distribuição deste insumo energético no Brasil. Mais especificamente apresenta o histórico e a evolução da cultura da cana-de-açúcar no Brasil e nos principais países produtores e consumidores dos derivados da cana-de-açúcar, aspectos produtivos relacionados á produção de etanol. Apresenta ainda os condicionantes para a demanda do etanol produzido no Brasil e as necessidades decorrentes de infra-estrutura logística para a distribuição do etanol nos mercado interno e para exportação. / This present work presents and analyses different scenarios for the following years for the demand expansion of sugarcane ethanol in Brazil. It considers the influence of different drivers involved and the consequent impacts, needs and future alternatives for distribution logistics of this energy source in Brazil. More specifically, this work presents historical evolution of sugarcane culture in Brazil and in other main producers and consumers of sugarcane products, productive aspects related to ethanol production . It presents drivers to the demand expansion of the ethanol produced in Brazil and the related needs of infrastructure and logistics for the ethanol distribution in the Brazilian local market and export markets.