This thesis discusses the importance of tidal turbine support structures through analytical and computational modelling. A head-driven analytical channel model was first developed to determine the sensitivity of the flow to the presence and type of support structures. It showed that there was a significant potential reduction in farm power output even when only considering approximate force coefficients for rotor and support structure. To confirm these findings, computational simulations were performed on a full-scale turbine to obtain more accurate force coefficients considering full rotor-support structure interactions. The flow interaction effects between the rotor and its support structure were studied using Computational Fluid Dynamics (CFD) for different support structure shapes for a range of tidal velocities including the power-capping zone. The integrated rotor force coefficients were higher in the presence of the cylindrical support structure than the elliptical support due to the higher opposing thrust from the cylinder in the channel redirecting the flow and increasing the flow velocity over the top half of the rotor. The presence of rotor caused a drop in the stream-wise forces on the support structure. The amplitude of the stream-wise sectional forces along the support structure height was lower in the case of an elliptical than a circular cylinder due to more streamlined shape of the ellipse. At device scale, the computational model was used to study the turbine performance in the power-capping zone by pitching the blades to feather. The influence of pitch-to- feather power-capping strategy was examined by studying the forces and angle of attack on the turbine blades, and the wake at three different blade pitch angles. Increasing blade pitch angle resulted in a significant drop in the average load on the blade. Also since the tidal channel flow has a shear in its velocity profile, the influence of shear on turbine performance was studied by comparing it to the same turbine in a uniform flow. The analytical channel flow model was used to investigate the characteristics of tidal stream energy extraction for large tidal farms deployed in tidal channels with specific focus on the limitations to realizable farm power due to turbine support structure drag and constraints on volume flow rate reduction. The force coefficients dataset from computational modelling was used to obtain a better estimate of the farm power output. Support structures were seen to contribute significantly to the overall resistive force in the channel and thus reduce the overall flow rates in the channel, leading to losses in realizable power. Over a wide range of channel characteristics, realistic levels of support structure drag lead to up to a 10% reduction in realizable power, and an associated reduction in the number of turbines that can be economically installed.

Global efforts to address climate change have recently introduced a new source of fatality risk to bats, from wind turbines. Bat fatalities have now been confirmed in varying magnitudes at wind energy facilities around the world. Research at large turbines and wind farms has started to produce a knowledge base regarding impacts upon bats, though many questions remain. Little, however, is known about risk levels at small and medium scale wind turbines. Equally, research regarding the impacts of turbines in the UK is limited. This thesis examines the impacts of small and medium scale wind turbines upon bats. Planning records of wind turbines in Wales and south west (SW) England were reviewed. Approved planning applications for single and double turbine sites were found to greatly outnumber those for larger scale wind farms. The large majority of single and double turbine approvals were also for small turbines. The potential impacts of turbine presence and density on current bat roost populations and population changes were analysed, finding no impact. An estimate of bat fatality rates at small and medium turbines was calculated, using a trained search dog to locate carcasses. An average fatality rate between 0.81 and 15.15 turbine-1 year-1 was estimated. The higher rate accounted for uncertainty in the monitoring protocol. Only 3 bat carcasses were however observed across all monitored turbines, suggesting more stringent monitoring would likely confirm a lower maximum annual fatality rate. Bat activity levels were also compared between the turbine location and differing habitat types. A disturbance effect was consequently identified in proximity to turbines during high wind speeds. Finally moderating influences of environmental weather and habitat conditions upon bat activity were confirmed. Social Network Analysis (SNA) methods were used to analyse bat movement networks within a small grid of bat detectors centred on each turbine. Associations were identified between bats’ movement routes and habitat structures present at sites, highlighting vulnerabilities to disruption. Furthermore bats actively used the turbine area, potentially for foraging purposes. Finally by assessing bats’ activity levels in response to a turbine noise playback experiment, small turbine noise was found to have no impact upon bat activity. Planning guidance regarding bats and small and medium turbines is highlighted as a priority for policy development.

Energy is integral to the quality of life of any society. However, meeting the demand for energy sustainably is the main challenge facing humanity. In general, non-renewable energy resources are used to supply the ever increasing energy demand. However, the extraction and processing of these resources is accompanied by the production of wastes which are a health hazard and impact negatively on climate change. Considering the finite nature of non-renewable sources, the environmental concerns which are associated with their usage and ensuring energy security, renewable energy sources have been brought in the energy supply chain. Wind energy is one of the renewable energy sources which has been supplying electrical energy to the ever increasing energy demand of humanity. Wind energy technology is a mature technology which over and above the bare (conventional) wind turbine technology has seen the development of duct augmented wind turbines. Ducts are used to encase wind turbine rotors to augment the power output of wind turbines especially in low wind speed areas. Though the technology has been under study for decades now, research indicates that there is no known model to estimate the power output of a diffuser augmented wind turbine. This thesis presents the development of the conical Diffuser Augmented Wind Turbine (DAWT) power output estimation model and its validation.

PV systems in practice experience excessive thermal energy dissipation that is inseparable from the photo-electric conversion process. The temperature of PV cells under continuous illumination can approach 40°C above ambient, causing a drop in the electrical performance of about 30%. The significance of elevated temperature on PV cells inspired various thermal management techniques to improve the operating temperature of the cells and hence their conversion efficiency. Hybrid PV/Thermal (PV/T) collectors that can supply both electrical and thermal energy are attractive twofold solution, being able to cool the PV cells and thus improving the electrical power output as well as collecting the thermal energy by-product for practical utilization. The challenges present on the performance of PV systems due to elevated operating temperature is considered the research problem within this work. In this research, an integrated hybrid heat pipe-based PV/Thermoelectric (PV/TEG) collector is proposed and investigated theoretically and experimentally. The hybrid collector considers modular integration of a PV absorber rated at 170W with surface area of 1.3 m2 serving as power generator as well as thermal absorber. Five heat pipes serving as the heat transport mediums were attached to the rear of the module to extract excessive heat accumulating on the PV cells. The extracted heat is transferred via boiling-condensation cycle within the heat pipe to a bank of TEG modules consisting of five 40 mm x 40 mm modules, each attached to the condenser section of each heat pipe. In principle, the incorporation of heat pipe-TEG thermal waste recovery assembly allow further power generation adopting the Seebeck phenomena of Thermoelectric modules. A theoretical numerical analysis of the collector proposed is conducted through derivation of differential equations for the energy exchange within the system components based on energy balance concepts while applying explicit finite difference numerical approach for solutions. The models developed are integrated into MATLAB/SIMULINK environment to assess the cooling capability of the integrated collector as well as the addition power generation through thermal waste heat recovery. The practical performance of the collector proposed is determined experimentally allowing for validation of the simulation model, hence, a testing rig is constructed based on the system requirements and operating principles. Reduction in the PV cell temperature of about 8°C, which account for about 16% reduction in the PV cell temperature response compared to a conventional PV module under identical conditions is attained. In terms of the power output available from the PV cells, enhanced power performance of additional 5.8W is observed, contributing to an increase of 4% when compared with a PV module. The overall energy conversion efficiency of the integrated collector was observed to be steady at about 11% compared to that of the conventional PV module (9.5%) even at high ambient temperature and low wind speeds. Parametric analysis to assess the performance enhancements associated to the number of heat pipes attached to the PV module is conducted. Increasing the number of heat pipes attached to 15 pipes permits improved thermal management of the PV cells realised by further 7.5% reduction in the PV module temperature in addition to electrical output power improvement of 5%.

Issues from global warming with increased CO2 emissions have been to a main concern over world. As an example in the UK, the energy demand in the domestic sector has risen by 17% in 2010 compared with that of 1970. Applying renewable energy is widely agreed to be the most effective and promising way to solve the problem where solar energy and photovoltaic technology have been greatly developing from the last century. Photovoltaic combines with Phase Change Material (PV/PCM) system is a hybrid solar system which uses phase change material to reduce the PV temperature and to store energy for other applications. This thesis aims to investigate the performance of a designed building integrated photovoltaic thermal system (BIPVT) with PCM as thermal storage for building applications. The research objectives are to increase the building integrated photovoltaic (BIPV) efficiency by incorporating PCM while utilising the stored heat in PCM for controlling indoor conditions and reduce the total building energy consumption. The research starts with solar energy convection technologies including solar thermal and solar photovoltaic. Then a combined technology named photovoltaic thermal system (PVT) was introduced and discussed. Research work on a different type of PVT using water and air as thermal energy medium was further reviewed and discussed. An analytical approach investigation was presented on a PVT system and the results were used to design the experiment work on PV/PCM configuration. Experiments have been carried out on a prototype PV/PCM air system using monocrystalline photovoltaic modules. Transient simulations of the system performance have also been performed using a commercial computational fluid dynamics (CFD) package based on the finite volume method. The results from simulation were validated by comparing with experimental results. The results indicated that PCM is effective in limiting temperature rise in PV device and the heat from PCM can enhance night ventilation and decrease the building energy consumption to achieve indoor thermal comfort for certain periods of time. An entire building energy simulation with designed PV/PCM air system was also carried out under real weather condition of Nottingham, UK and Shanghai, China. The result also shows a market potential of PV/PCM system and a payback time of 11 years in the UK condition if using electrical heater.

The demand for modern energy services is increasing rapidly. Solar energy has the potential to meet a significant share of the world’s energy request. Solar energy is one of the cleanest renewable forms with little or no effect on the environment. The concentrating solar power is one of the methods to harvest sun’s energy. Concentrating solar power has the advantage of easier energy storage compared to photovoltaic systems. However, the cost of energy generated by those systems is higher than conventional energy sources. It is necessary to improve the performance of concentrating solar power to make them cost competitive. Moreover, few countries such as Saudi Arabia are moving from energy based on fossil fuel to renewable energy, therefore, improving the performance of concentrating solar systems and reducing their cost is considered to emulate photovoltaic systems. This research aims to develop an innovative design of parabolic trough solar collector that uses magnetic nanofluids as a heat transfer fluid to enhance the thermal efficiency compared to conventional parabolic trough. Based on past researches, new parabolic trough design is then proposed and investigated. Ferromagnetic nanoparticles dispersed in common heat transfer fluids (ferrofluids) exhibit better thermos-physical properties compared to the base fluids. By applying the right magnetic intensity and magnetic field direction, the thermal conductivity of the fluid increased higher than typical nanofluids. Moreover, the ferrofluids exhibit excellent optical properties. The external magnetic source is installed to alter the thermo-physical properties of the fluid. This thesis is comprised of four studies including two experimental studies, one heat transfer analysis, and one economic and environmental study. A small scale parabolic trough collector was manufactured and assembled at the laboratory based on the British Standards. A steady-state method was used to measure the performance of the parabolic trough collector in corresponding studies. The performance of the ferrofluids as a heat transfer fluid was compared to the base fluid. The two experimental studies differ in the absorber used. The two absorbers used were a conventional non-direct absorber and a direct absorber without a selective surface that allows ferrofluids to absorb the incoming solar irradiation directly. The effects of nanoparticle concentration, anti-foaming, external magnetic field intensity were investigated. The volume fraction of nanoparticles was 0.05%, 0.25%, and 0.75%. Three different magnetic field intensities were investigated, 3.14 mT, 6.28 mT, and 10.47 mT. Using ferrofluids to enhance the heat transfer performance the efficiency of the ferrofluids solar collector was compared to the based fluid (water). The results show that the parabolic trough solar collector in the experiment has similar performance of flat-plate solar collectors. The efficiency of the collector improved when ferrofluids water used compared to water. Ferrofluids with low concentration improved the performance of the solar collector. The ferrofluids showed much better performance at higher reduced temperature with lower overall heat loss coefficient. Due to the non-Newtonian behaviour of the fluid, increasing the volume fraction of particles will suppress the enhancement. The pH of ferrofluids influences the behaviour of the fluid. pH values higher than 5 showed a Newtonian behaviour of the fluid. In the presence of magnetic field, the performance of the solar collector enhanced further. By increasing the magnetic field intensity, the absorbed energy parameter increased, and at higher magnetic field intensity, the rate of enhancement decreases due to the magnetic saturation of ferrofluids. In this study, the performance of non-direct absorption receiver was better than the direct absorption receiver. However, the performance of the collector with a direct absorption receiver and using ferrofluids in the presence of the external magnetic field in some cases was higher than the performance of non-direct receiver with water as heat transfer medium. The performance of ferrofluids based parabolic trough collector was theoretically investigated. The correlation, equations, and specifications used in the model were discussed in detail. The model was used to study two different parabolic trough designs. First, the parabolic trough was validated with the experimental results of AZTRAK platform. The results of the model show a good agreement with the experimental data. Thereafter, nanoparticles were added to the heat transfer fluid, and the performance of the collector with and without the presence of external magnetic field was determined. The performance of the collector did not change a lot unless the external magnetic field was present. Moreover, the effect of the glass envelope on the performance was observed. A glass cover with vacuum in the annulus has higher performance and less thermal loss. Second, the model was used to study the performance of the test rig ferrofluids based parabolic trough. The performance of the parabolic trough was first considered as concentrating collector and then as a non-concentrating collector. With the lack of an external magnetic field, the efficiency changed slightly, wherein the presence of the external magnetic field the performances of the collector enhanced and showed higher performances. In General, the presence of the magnetic field showed promising enhancement. Economic and environmental effects of using ferrofluids based solar collector compared to a flat-plate collector for household water heating systems. Results show that the ferrofluids based parabolic trough has lower payback period and higher economic saving at its useful life end than a flat-plate solar collector. The ferrofluids based collector has higher embodied energy and pollution offsets tan flat-plate collector. Moreover, if 50% insertion of ferrofluids based parabolic trough for domestic hot water could be achieved in Tabuk over 83,750 metric Ton of CO2 could be eliminated.

This study provides an insight into the fundamentals of PV performance enhancement under different environmental conditions. The study also presents a new concept of PCM integrated PVT system which has a better performance from both electrical and thermal perspectives. The study employs both analytical and computational techniques to investigate the PV performance under the effect of different parameters such as wind speed, solar radiation level, ambient temperature and additional cooling condition. A parametric analysis of the PCM is also carried out under different solar radiation level, water inlet temperature and flow speed. Additional analysis regarding to the effects of PCM’s thermal physical properties against its thermal performance is also presented. A validation analysis is carried out prior to the parametric analysis to ascertain the reliability of the CFD models used, the prediction result of the CFD model is compared with analytical calculations as well as data from literature. The study found that the active water cooling is the best solution which can provide guaranteed performance enhancement regardless effects of ambient conditions. The novel PVT-PCM system is found to have a noticeable electrical performance enhancement over conventional PV panel as well as having the ability to store a significant amount of thermal energy. It is found that the PVT-PCM system has much lower PV cell temperature (maximum temperature reduction of 36.5°C and 38.3°C respectively) compared to conventional PV systems when used in both Nottingham and Shanghai area, hence provide up to 5.4kWh (5.7kWh in Shanghai) more energy per unit module. The stored thermal energy could be utilized to provide moderate heating to air and/or water. The air preheated by PVT-PCM system could satisfy space heating requirement during April to October in Nottingham without any additional energy consumption. On the other hand, the preheated water could reduce boiler heating energy from up to 20% and 41% respectively for Nottingham and Shanghai climate. The overall performance benefits of the proposed PVT-PCM system could be greater if used in hotter climates. Finally, a cost analysis was carried to prove the whole system is financially feasible for use in both climates of Nottingham and Shanghai with a discounted payback period of 10.67 and 12.83 years respectively.

The emergence of decentralized energy resources has brought numerous novel and advanced designs of efficient power generation systems with utilisation of renewable energy for locally provided, sustainable and cost-effective energy production. The micro trigeneration system has been a highly anticipated solution to fulfil domestic energy requirements, allowing simultaneous generation of electricity, heating and cooling from one primary source. As a matter of fact, the micro trigeneration system is still under research and development stage, with limited available demonstrations around the world. Current laboratory experimental and simulation studies mainly focus on integrations of mature technologies, whereas many promising alternatives have not been widely explored, for example organic Rankine cycle (ORC) and liquid desiccant cooling technology. The main aim of this thesis is to technically develop and evaluate a novel micro trigeneration system with a combination of scroll-based ORC and membrane-based liquid desiccant cooling (MLDC). In principle, the micro trigeneration system provides highly efficient energy conversion in a decentralized manner, as the scroll-based ORC has superior abilities in generating electricity and providing sufficient thermal output that matches the low-temperature regeneration requirement of the liquid desiccant in the MLDC. In terms of system sustainability, compact linear Fresnel reflectors (CLFR) can be one option of the primary energy source for the micro trigeneration system. A comprehensive literature review has demonstrated that no work has been conducted previously on such a system. In this thesis, the possibility of integrating CLFR to power generation systems has been firstly investigated and a detailed optical design of the CLFR-hybrid system has been conducted through geometrical modelling and experimental work. Results demonstrate that the CLFR-hybrid system with polar orientation is feasible to efficiently convert the absorbed solar energy into thermal energy, which thereby can be utilised for powering the micro trigeneration system. The concept of the novel micro trigeneration system with scroll-based ORC and MLDC has been critically examined and energy performance of the two main components, namely scroll-based ORC and MLDC have been evaluated respectively through both theoretical modelling and experimental work. Experimental tests show that the scroll-based ORC electric output of 564.5W, scroll expander isentropic and volumetric efficiencies of 78% and 83% are achievable at a 1kW capacity. In terms of MLDC, experimental results indicate the importance of system mass balance between the membrane-based dehumidifier and regenerator for continuous operation. Under the steady operating condition of MLDC, a supply air temperature of 20.4°C with dehumidification effectiveness of 0.3 and system COP of 0.70 are attainable at calcium chloride (CaCl2) solution concentration of 36%. Simulations based on a validated and comprehensive system model demonstrate the feasibility of pairing the scroll-based ORC and MLDC for the microre trigeneration system. The exhaust heat from the scroll-based ORC effectively fulfils the regeneration requirement of the MLDC. The inclusion of MLDC facilitates the micro trigeneration system overall efficiency with an increase of approximately 35.49%, compared to that of ORC-based separate power generation. Theoretical results show that the proposed micro trigeneration system has the overall system efficiencies of 38.96% in cogeneration mode and 41.23% in trigeneration mode. The thesis makes contribution to the knowledge of micro trigeneration technology, distributed power generation, energy conversion and air conditioning. Moreover, the presented parametric studies of CLFR, ORC and MLDC can be employed for designing and optimizing the relevant individual components. Regarding the future work, this thesis recommends more in-depth system modelling with a combination of CLFR, ORC and MLDC, logic optimisation of the micro trigeneration system and comprehensive field trial testing of the micro trigeneration system in building context.

Key factors in using variable renewable energy to sustain crop growth were investigated using the Isle of Lewis as a case study. Methods investigated sought to exploit plants' abilities to accommodate a variable solar input by supplementing it with variable renewable energy. The extant solar resource on Lewis was characterised. The mean ratio of photosynthetically active radiation (PAR) to solar radiation (SR) (fE) recorded in 2010 was 0.458. fE was found to be significantly different between the first and last hour of daylight and 12:00 GMT (F, (2, 33) = 7.98, p<0.001) and between winter and summer months (F, (1, 10) = 20.86, p<0.001). This supports the suggestion that fE decreases as the atmospheric path length decreases. Significantly higher mean fE was also identified for the cloudiest days (F, (1, 22) = 6.22, p<0.05). Supplementing sunlight with intermittent, artificial illumination powered using wind energy significantly increased the growth of Brassica hirta. 53.26% of the additional dry weight produced using fixed diurnal illumination was achieved with 35% of the energy using this technique. The dry weight of B. hirta grown with illumination timed with tidal streams was not significantly different from that grown using fixed diurnal patterns. This is potentially important for the use of renewable energy for horticultural illumination. The possibility of using energy to prioritise lighting in well insulated growing structures and the compatibility of electricity production and horticultural demand on Lewis were considered. These findings support the direct use of variable renewable energy to sustain crop growth and promote the concept of using plants to store renewable energy. This is of potential benefit for problems of renewable energy intermittency, the predicted need to increase world food supply and providing economic opportunities for remote areas with a poor solar resource but good supplies of variable renewable energy.

With the Scottish Government's commitment to sourcing 100% of the national electricity demand from renewable sources by 2020, within the global framework of climate change mitigation, the potential of the marine environment around the Highlands and Islands Region of Scotland to add to Scotland's renewables portfolio has led to the expansion of the wave and tidal industries in recent years. Nevertheless, to date, there has been limited research conducted on the social systems around marine renewable energy development, excluding offshore wind. In answer to this deficit, this study explores a well-established concept within the academic arenas of business, health, and rural development, among others, of agents for change (AFCs), within the context of the rapidly emerging wave energy sector. Two case studies, Lewis in the Outer Hebrides, and Orkney, were chosen based on their localities and the interest that they have garnered from wave energy developers due to their high energy marine environments. A grounded approach was taken to data collection and a social power analysis was conducted in order to find AFCs working within or closely with the wave energy industry that were not part of structured or hierarchical organisations. One emergent theme was that there was a noteworthy barrier to wave energy development in the case studies and to the work that the agents for change were doing in the form of a complex dynamic between financial investments in the sector, national grid, national energy policy, and the technology itself. The agents for change were found to act as catalysts for the wave energy industry through their perseverance and visionary approach to development. The motivations of the AFCs is discussed and the shifting roles that they took as a project progresses is described and compared to other change process models, namely Lewin (1958) and Kotter (1995).