Ce travail de thèse concerne l’étude de la faisabilité des cycles organiques sous-critiques et supercritiques de Rankine pour la valorisation de rejets thermiques industriels à basse température. Dans un premier temps, un état de l’art des cycles ORC (acronyme anglais pour Organic Rankine Cycle) et leurs fluides de travail a été réalisé. Nous avons réalisé une comparaison préliminaire de plusieurs configurations à partir de la littérature scientifique. Dans un second temps, les méthodes d’analyse énergétique et exergétique ont été appliquées pour évaluer et optimiser les performances des cycles ORC. En effet, la seule méthode d’analyse énergétique n’est pas suffisante pour juger de la bonne utilisation du potentiel énergétique de la source de chaleur disponible correspondant à un rejet industrielle de chaleur (chaleur fatale). L’analyse exergétique, intervient en complément de l’analyse énergétique du système, afin de permettre de localiser les pertes des ressources énergétiques dans les différentes composantes du système et de déterminer leurs importances relatives et leurs causes. Une optimisation thermo-économique des installations de valorisation de rejets thermiques utilisant un cycle sous-critique ou supercritique de Rankine a été effectuée. Nos résultats montrent que la valorisation de rejets thermiques industriels à basse température (ex. source thermique de 150 °C) en utilisant un cycle ORC sous-critique est plus intéressante sur le plan énergétique que celle opérée en utilisant un cycle supercritique de Rankine. / This thesis concerns the feasibility study of subcritical and supercritical organic Rankine cycles for industrial waste heat recovery at relatively low temperature. Initially, a state of the art of ORCs (Organic Rankine Cycles) and their working fluids has been achieved. We conducted a preliminary comparison of several configurations from the scientific literature. In a second step, methods of energy and exergy analysis were applied to evaluate and optimize the performance of the ORCs. Indeed, sole energy analysis is not enough to access the proper use of the energy potential of the available heat source that corresponds to an industrial waste heat. Exergy analysis, in a complementary way to the energy analysis, enables us to locate the energy resources losses in the various components of the system and to determine their true magnitude and their causes. A thermo-economic optimization of waste heat recovery systems using a subcritical or supercritical Rankine cycle has been performed. According to the results, the industrial waste heat recovery at low temperature (e.g. heat source 150 ° C) using a subcritical ORC is more interesting on economic point of view than the system using a supercritical Rankine cycle

This study addresses the use of a Solar blind system (SBS) instead of ordinary glass used on windows of buildings. To investigate the effects of using an SBS for electricity energy generation a fictitious wooden house as a prototype, a real building needed to be constructed. The purpose of experimental studies is to measure the effect and asses the performance by examining the optimal angle of inclination and evaluating the profitability of SBS. To calculate the electricity energy generation by it is then expected that general renovations of a building will be used in the system. To perform the different scenario for each inclination angle, the simulation software PVsyst was used where the measurements are validated according to the simulation results to confirm that models are suitable and which inclination angles produced the most electricity. After the validation process, a financial assessment, and an annual electricity production of the system for a fictitious building where SBS is applied were performed. The result for the annual electricity production at different angles of inclination turned out to be 2457 kWh/year at 30, 2235 kWh/year at 60   and 1781 kWh/year at 90 . The optimal angle of inclination was 30  , which also has the highest electricity production compared to the other angles. Electricity production does not differ much with the inclination angle of 60. The simulation for the annual electricity production was examined for ten windows in opposite directions. The investment cost for the use of SBS was extraordinarily high, landing at 28,120 SEK/kW. The reason for this high investment cost is that it includes high material costs and that the area for SBS systems is low, which is 1,696 m². The reason is that the low area in m² leads to a lower electricity generation and the higher the area m² leads to higher electricity generation, which turns into affecting the profitability and electricity production.

The cost of energy and national power utility Eskom, is currently under heated debate after the cost of electricity has more than doubled over the past three years, with another five annual increases of 8% approved by the National Energy Regulator of South Africa. The state owned utility has a monopoly on electricity production in South Africa having sole ownership over the transmission and distribution of electricity. Eskom produces 95% of South Africa’s electricity, predominantly from coal fired power stations, which is one of the leading causes why the country is one of the highest carbon dioxide emitters in the world. The question of independent power production and the use of our abundant renewable resources for electricity generation have been at the forefront with critics arguing against the heavy increases absorbed by industry and consumers. Although the renewable energy space is a well discussed topic, it is not well scientifically documented from an economic standpoint. The primary objective is to determine if renewable energy is price competitive with Eskom, or non-renewable electricity generation, by not only looking at the current scenario but also the future price projection and point where renewable energy is on parity with the grid price. For this purpose the Levelised Cost of Energy calculation method was used. Four different measuring instruments were produced for each technology namely, biogas, biomass, solar and wind and a financial model developed to determine the levelised cost, taking into consideration more complex financial structures, tax incentives, revenues and costs associated with by-products. From the literature it is clear that wind and solar, on a large scale, are competitive with the levelised cost of Eskom’s new build coal power plants and particularly wind, is lower than the grid price in 2017. The empirical study focused on a smaller scale of 1 to 5 megawatt and concluded that the levelised cost of wind energy is lower than Medupi coal fired power plant, currently under construction. The study also determined that biogas and biomass, under certain conditions relating to feedstock costs, are able to compete with Medupi and offer real and sustainable benefits in long-term energy supply. / MBA, North-West University, Potchefstroom Campus, 2015

The cost of energy and national power utility Eskom, is currently under heated debate after the cost of electricity has more than doubled over the past three years, with another five annual increases of 8% approved by the National Energy Regulator of South Africa. The state owned utility has a monopoly on electricity production in South Africa having sole ownership over the transmission and distribution of electricity. Eskom produces 95% of South Africa’s electricity, predominantly from coal fired power stations, which is one of the leading causes why the country is one of the highest carbon dioxide emitters in the world. The question of independent power production and the use of our abundant renewable resources for electricity generation have been at the forefront with critics arguing against the heavy increases absorbed by industry and consumers. Although the renewable energy space is a well discussed topic, it is not well scientifically documented from an economic standpoint. The primary objective is to determine if renewable energy is price competitive with Eskom, or non-renewable electricity generation, by not only looking at the current scenario but also the future price projection and point where renewable energy is on parity with the grid price. For this purpose the Levelised Cost of Energy calculation method was used. Four different measuring instruments were produced for each technology namely, biogas, biomass, solar and wind and a financial model developed to determine the levelised cost, taking into consideration more complex financial structures, tax incentives, revenues and costs associated with by-products. From the literature it is clear that wind and solar, on a large scale, are competitive with the levelised cost of Eskom’s new build coal power plants and particularly wind, is lower than the grid price in 2017. The empirical study focused on a smaller scale of 1 to 5 megawatt and concluded that the levelised cost of wind energy is lower than Medupi coal fired power plant, currently under construction. The study also determined that biogas and biomass, under certain conditions relating to feedstock costs, are able to compete with Medupi and offer real and sustainable benefits in long-term energy supply. / MBA, North-West University, Potchefstroom Campus, 2015

The solar PV modules are influenced by a variety of loss mechanisms by which the energy yield is affected. A PV system is the sum of individual PV modules which should ideally operate similarly, however, inhomogeneous soiling, mismatching, and degradation, which are the main focus in this study, lead to dissimilarities in PV modules operating behavior and thus, lead to losses which will be assessed intensively in terms of energy yield. The dissimilarities in PV modules are referred to the ambient conditions or the PV modules characteristics which result in different modules’ maximum power point (MPP) and thus, different currents generated by each PV modules which cause the mismatching. However, the weakest PV module current governs the string current, and the weakest string voltage governs the voltage. Power optimizers are electronic devices connected to the PV modules which adjust the voltages of the PV modules in order to obtain the same current as the weakest module and thus, extract the modules’ MPP. Hence, the overall performance of the PV plant is enhanced. On the other hand, the power optimizers add additional cost to the plant’s investment cost and thus, the extra energy yield achieved by utilizing the power optimizers must be sufficient to compensate the additional cost of the power optimizers. This is assessed by designing three systems, a reference system with SMA inverters, a system utilizes Tigo power optimizers and SMA inverters, and a system utilizes SolarEdge power optimizers and inverters. The study considers four different locations which are Borlänge, Madrid, Abu Dhabi, and New Delhi. An Excel model is created and validated to emulate the inhomogeneous soiling and to evaluate the economic feasibility of the power optimiz ers. The model’s inputs are obtained from PVsyst and the precipitation data is obtained from Meteoblue and SMHI database. The economic model is based on the relation between Levelized Cost of Electricity (LCOE) which will be used to derive the discount rate. Graphs representing the discounted payback period as a function of the feed-in tariff for different discount rates is created in order to obtain the discounted payback period. The amount of extra energy yielded by the Tigo and the SolarEdge systems is dependent on the soiling accumulated on the PV modules. Relative to the reference system, 6.5 % annual energy gain by the systems utilizing the power optimizers in soiling conditions, up to 2.1 % in the degradation conditions, and up to 9.7 % annual energy gain at 10 % mismatching rate. The extra energy yield is dependent on the location, however, the Tigo and the SolarEdge systems have yielded more energy than the reference system in all cases except one case when the mismatch losses is set to zero. The precipitation pattern is very influential, and a scare precipitation leads to a reduction in the energy yield, in this case, the Tigo and the SolarEdge systems overall performance is enhanced and the extra energy gain becomes greater. The Tigo system yield slightly more energy than the SolarEdge system in most cases, however, during the plant’s lifetime, the SolarEdge system could become more efficient than the Tigo system which is referred to the system’s sizing ratio. The degradation of the system or the soiling accumulation decreases the irradiation and thus, a slightly oversized PV array become suitable and deliver an optimal power to the inverters. The SolarEdge system is feasible in all scenarios in terms of LCOE and discounted payback period, although its slightly lower performance relative to the Tigo system, this is referred to its low initial cost in comparison to the other systems. The Tigo system is mostly infeasible although it yields more energy than the reference and the SolarEdge systems, this is referred iii to its relatively high initial cost. However, feed- in tariffs higher than 20 € cent / kWh make all systems payback within less than 10 years. The results have overall uncertainty within ± 6.5 % including PVsyst, Excel model, and the precipitation uncertainties. The uncertainty in the degradation and the mismatching calculations is limited to PVsyst uncertainty which is ± 5 %. The uncertainties in LCOE in the location of New Delhi, since it is the worst-case scenario, are 5.1 % and 4 % for the reference and the systems utilizing power optimizers, respectively. Consequently, accommodating the uncertainties to the benefits gained by utilizing power optimizers indicates that the energy gain would oscillate in the range of 6 % - 6.9 % for the soiling calculations, 2 % - 2.2 % for the degradation simulations, and 9.2 % - 10.2 % for the mismatching simulations at 10 % mismatchrate.

The aim of this thesis is to analyze the importance of coal-fired power plants on the market of electric energy, with emphasis on aspects that fundamentally affect their production. Coal-fired power plants belongs nowadays among socially unpopular source of electricity. In recent decades intensively growing interest groups that support state intervention and regulation of the energy sector. This is essentially a massive promotion of renewable energy sources at the expense of fossil fuel plants. Analysis of individual power sources shows that despite the current restrictive measures imposed on power plants burning fossil fuels, and especially coal-fired power plants, electricity produced from coal resources is still competitive, despite some drawbacks has many positive qualities. Coal-fired power plants produce higher amounts of greenhouse gases and other pollutants than other types of power plants. On the other hand, they are able to provide a stable supply of electricity to transmission network, and thus partially offset the high volatility of electricity supply from renewable energy sources. The price of electricity from coal-fired power plants could be considered as relatively low in comparison with other energy sources. The analysis shows that in terms of practical economic policy is not economically justified to reduce the proportion of coal-fired power plants in the total production of electricity.

Solar energy is one type of the most commonly used renewable energy sources. It can produce electricity and heat without creating any Greenhouse Gases (GHG). Sweden has set up the goal of 100% electricity generated by the renewable energy source by 2040 and chosen Gotland as a pioneer project for self-electricity supply by renewable energy sources by 2030. Taking the year 2017 as an example, the total electricity production of Gotland in 2017 was about 1080 GWh, a share of 621GWh imported from mainland Sweden, 457GWh produced by Gotland's local wind energy, 1.6GWh produced by local photovoltaic energy and a very small fraction produced by local hydropower. Gotland has a high potential for photovoltaic power. This quantitative research case study used data to collect and a building model to measure the potential electricity production by photovoltaic power at three locations in Visby, Höken, Castor and Skalbaggen. Further, an analysis of the current value of installing photovoltaic panels for a public housing company to increase the capacity of renewable energy to stimulate the target towards 100% electricity from renewable energy sources by 2040. The result indicated that the ratio of production/Consumption at Höken, Castor and Skalbaggen were 73%, 52% and 1000%. According to the calculation, the LCOE of Höken is around about 0.74 to 1.17 SEK/kWh. For Castor, it is from 0.73 to 1.16 SEK/ kWh due to the range of interest rates. For Skalbaggen, it is around 0.70 to 1.11 SEK/ kWh. However, since the current limitation from both technical and legislative sectors were not allowed to transfer electricity between the adjacent building. Further research is required on how to facilitate tenants' use of renewable electricity produced by public housing itself, as well as how to maximize the penetration of smart grids.

Offshore wind is rapidly growing and optimised grid connections are crucial for its success. Generally, costs and losses are higher for HVDC at short distances due to the converters, while HVAC costs and losses increase more rapidly with distance due to the ac cables. Hence, there is a breaking point over which HVDC becomes beneficial, which is important knowledge for grid connection design. Recent research and practice indicate increasing distances for the breaking point, enabled by the introduction of offshore reactive compensation substations (RCS) for HVAC. In the study, steady-state models of HVAC and modular-multilevel converter (MMC) based VSC HVDC systems up to 260 km have been simulated in the Matlab/Simulink based program EeFarm-II. For base case assumptions, the average loss breaking point is 80 km and the levelised cost breaking point is 229 km. The resulting breaking point with respect to levelised cost of energy (LCOE) is 205 km and with respect to net present value (NPV) 186 km, agreeing with the trend of increasing breaking points. Given the range of distances in literature, it is of interest to also investigate how the breaking point depends on assumptions on technical, practical and economic parameters. For the NPV breaking point: lifetime and interest rate have no impact, availability and cost of RCSs have low impact, electricity price has moderate impact, operation and maintenance (O&M) cost has high impact while investment cost and lead time have very high impact. This could be taken into consideration in offshore projects and in future research.

Meeting electricity demand and power shortage remains as a challenge to the people of the Gambia. As the country is undergoing tremendous electricity accessibility expansion [1], to secure the environment for the future generation, it is necessary to consider renewable energy to be the major source of electricity production, to be specific, solar energy. This is because the country experiences the radiation from the sun throughout the year, it is sustainable not only to our environment for the future generations, but also economically. However, due to the intermittent nature of most renewable energy technologies, it is cumbersome to rely on them 100 % as a primary source of electricity production. Nonetheless, with suitable storage technologies, combination of different renewable sources, and intercountry grid connections can enhance to overcome this challenge. In this thesis work, designed and techno economic evaluation was carried out for high PV penetration that will meet 50 % electricity demand of the Gambia in year 2040. Three scenarios were considered in this study, based on the Strategic Electricity Roadmap 2020 to 2040 [1]. These scenarios are high, universal access (AU), and low electricity demand. Economically, 50 % electricity supply to meet the demand is possible for all the three cases. Consideration was mainly put on four key figures, thus, levelized cost of electricity (LCOE), payback period (PBP), net present cost (NPC) and solar fraction (SF). To achieve 50 % SF for the high electricity demand scenario, LCOE and PBP are 0.129 $/kWh and 12 years respectively. As for AU electricity demand case, 50 % SF is achieved with 0.126 $/kWh and 10 years for LCOE and PBP respectively. For low electricity demand scenario, 0.127 $/kWh and 10 years for LCOE and PBP respectively for 50 % SF. However, the optimum design recommended by HomerPro were 45 % SF with LCOE of 0.126 $/kWh and PBP of 9 years for high electricity demand scenario. As for the AU electricity demand case, the optimum design is 48 % SF, LCOE of 0.125 $/kWh, and PBP of 9 years. In the last scenario, which is low electricity demand case, 46 % SF, 0.124 $/kWh LCOE, and 9 years PBP.

As part of efforts to curb the protracted electricity problem in Nigeria, the government enacted the National Renewable Energy and Energy Efficiency Policy (NREEEP) in 2014. Through this policy, the country plans to increase its electricity generation from renewables to 20% by 2030. This thesis investigates the economic feasibility of this lofty goal, and as well determine the best hybrid configuration for off-grid rural/remote power generation across the six geopolitical zones of Nigeria The economic feasibility results, using Long-range Energy Alternative Planning (LEAP) tool, show that the 20% renewables goal in the Nigerian power generation mix by 2030 is economically feasible but will require vast investment, appropriate supportive mechanisms, both fiscal and non-fiscal (especially for solar PV) and unalloyed commitment on the part of the government. Moreover, the techno-economic results with Hybrid Optimization Model for Electric Renewable (HOMER) reveal Small hydro/Solar PV/Diesel generator/Battery design as the most cost-effective combination for power supply in remote/rural areas of Nigeria. Findings also highlight the better performance of this system in terms of fuel consumption and GHGs emission reduction. Lastly, the study identifies factors influencing RE development, and offers strategic and policy suggestions to advance RE deployment in Nigeria.