A heliostat is a device that reflects the sun’s rays to a stationary object. There are two different types of heliostat serial and parallel type. The most used is the serial type of heliostat with Azimuthal-Elevation(Az-El) drive. The parallel heliostat includes two or more actuators to accommodate for the movement, one such design is heliostat with Hydraulic Infinite Linear Actuator (HILA). In this design, the mirror assembly is supported by two HILA’s and a universal joint. The mirror thus has three support points making it a parallel heliostat. This thesis work includes setting up the geometry of the new concept for160 m2reflector area and formulating kinematics and optics equations for calculating the lengths of the actuators and rotations at the universal joint. For structural analysis, the application of wind loads on the structure in the form of pressure is calculated and the structure is designed to satisfy the deflection requirements of 2 mRads at a maximum allowable wind speed of 22 m/s. The symmetric structure is modelled and checked for deflection requirements in Ansys Workbench. The reaction forces are calculated which are then used for topology optimization of the base structure, which is performed Trinitas. When there is an established design for the heliostat with HILA benchmarking is done by designing a scaled-down model for 25 m2 and comparing it with pre-existing results for Az-El type heliostats in literature.

The boundary concentrated finite element method is a variant of the hp-version of the FEM that is particularly suited for the numerical treatment of elliptic boundary value problems with smooth coefficients and boundary conditions with low regularity or non-smooth geometries. In this paper we consider the case of the discretization of a Dirichlet problem with exact solution $u \in H^{1+\delta}(\Omega)$ and investigate the local error in various norms. We show that for a $\beta > 0$ these norms behave as $O(N^{−\delta−\beta})$, where $N$ denotes the dimension of the underlying finite element space. Furthermore, we present a new Gauss-Lobatto based interpolation operator that is adapted to the case non-uniform polynomial degree distributions.

Solar Tower Power Plants with thermal energy storage are a promising technology for dispatchable renewable energy in the near future. Storage integration makes possible to shift the electricity production to more profitable peak hours. Usually two tanks are used to store cold and hot fluids, but this means both higher related investment costs and difficulties during the operation of the variable volume tanks. Another solution can be a single tank thermocline storage in a multi-layered configuration. In such tank both latent and sensible fillers are employed to decrease the related cost by up to 30% and maintain high efficiencies.  The Master thesis hereby presented describes the modelling and implementation of a thermocline-like multi-layered single tank storage in a STPP. The research work presents a comprehensive methodology to determine under which market structures such devices can outperform the more conventional two tank storage systems. As a first step the single tank is modelled by means of differential energy conservation equations. Secondly the tank geometrical design parameters and materials are taken accordingly with the applications taken into consideration. Both the steady state and dynamic models have been implemented in an existing techno-economic tool developed in KTH, in the CSP division (DYESOPT). The results show that under current cost estimates and technical limitations the multi-layered solid PCM storage concept is a better solution when peaking operating strategies are desired, as it is the case for the two-tier South African tariff scheme. In this case the IRR of an optimal designed power plant can be decreased by 2.1%. However, if a continuous operation is considered, the technology is not always preferred over the two tank solution, yet is a cheaper alternative with optimized power plants. As a result the obtained LCOE can be decreased by 2.4%.

Anion intercalation in the graphite positive electrode of a dual-ion battery requires high potential (> 4.3 V vs Li+/Li), which aggravates parasitic reactions involving electrolyte decomposition and Al corrosion, manifesting in poor coulombic efficiency, cycle life, and quick self-discharge. This study aims to investigate the stability of anion-intercalated graphite electrodes in a 4 M solution of lithium bis(fluorosulfonyl)imide (LiFSI) in ethyl methyl carbonate (EMC) using both in-situ and ex-situ Raman spectroscopy. The concentrated electrolyte is essential as it limits parasitic reactions at the cathode-electrolyte interface (CEI) occurring in parallel to anion intercalation. Using electrochemical methods including cyclic voltammetry, and post-mortem electron microscopy it was confirmed that the Al current collector is largely stable at potentials as high as 5.2 V in the electrolyte under consideration; no dissolved Al species were detected using EDX characterization. Results from the cyclic voltammetry study also indicate that parasitic reactions can be mitigated when the cut-off potential is limited to 5.0 V leading to higher coulombic efficiency (CE = 94 %) and more stable discharge capacity (85.17 mAh g-1). However, extending the potential to 5.1 and 5.2 V results in the discharge capacity increasing by almost 20 mAh g-1, though at the expense of the coulombic efficiency, which decreases from 94 to 76 %. Upon raising the cut-off potential to 5.3 V, the CE significantly decreased (20.62 %) as a result of extensive solvent decomposition ultimately leading to much quicker capacity fading.  Based on SEM images taken after 50 cycles, graphite particles did not sustain any structural or morphological change during cycling regardless of the cut-off potentials applied. Further tests were conducted on Li-graphite DIBs using galvanostatic methods in the range from 3 to 5 V, and at different specific currents (20, 50, and 100 mA g-1). Though the cells exhibited good performance in terms of capacity retention, and cycle life at all currents, the coulombic efficiency tended to decrease as the test currents were lowered. This observation confirms the presence of parasitic reactions which are only visible when the experimental timescale is sufficiently long. At 50 and 100 mA g-1, the CE reached > 98 % which further verifies the kinetic aspect of electrolyte decomposition reactions. It is evident that self-discharge sustained in the course of open-circuit potential (OCP) relaxation of the fully charged cell can reveal the stability of the electrolyte and the anion-intercalated graphite. Raman spectroscopy measurements conducted in-situ and ex-situ on graphite electrodes charged and discharged to a series of potential cut-offs reveal the existence of self-discharge leading to extraction of anions from the graphite particles. This was demonstrated through the spectral appearance of E2g2(i) band next to E2g2(b) band at a fully intercalated state, as opposed to the in-situ spectrum, which only showed one intercalated band (E2g2(b)). It can be concluded that concentrated electrolytes (such as 4 M LiFSI in EMC) only provide kinetic stability and are unable to entirely inhibit parasitic reactions at the interface. This further highlights the need for electrolyte additives that can create a more stable interfacial passivation layer on the positive electrode so that more reversible anion intercalation can be attained.

In response to the extensive energy demands on national and global levels, concentrated solar power (CSP) plants are designed to harness and convert solar energy to electricity. For such green energy application, robust, reliable and durable materials for CSP constructions are required. The corrosion resistance is among many parameters to consider in these thermalelectrical stations such as for pipes and storage tanks in CSP. In this investigation, the corrosion behavior of AISI 304 stainless steel (18 wt. % Cr, 8 wt. % Ni) with the heat transfer fluid, also known as solar salt, has been examined. The ternary eutectic salt mixture with the composition, 53 wt. % KNO3, 40 wt. % NaNO2, and 7 wt. % NaNO3, that melts at 142°C, has a potential use in CSP as a heat transfer fluid. The solar salt was prepared for this corrosion study from reagent grades of high purity nitrites and nitrates. Samples of AISI 304 stainless steel were sectioned from a sheet stock of the alloy and exposed to solar salt at 530°C in air at 1 atmospheric pressure. After test intervals of 250, 500, and 750 hours in total immersion condition, AISI 304 stainless steel samples have developed a scale of corrosion products made up of multiple oxides. X-ray diffraction and scanning electron microscopy with X-ray energy-dispersive spectroscopy were employed to examine the extent of corrosion and identify the corrosion products. Transmission electron microscopy was used to verify the corrosion products identity via electron diffraction patterns. Oxides of iron were found to be the primary corrosion products in the presence of the molten alkali nitrates-nitrite salt mixture because of the dissolution of the protective chromium oxide (Cr2O3) scale formed on AISI 304 stainless steel coupons. The corrosion scale was uniform in thickness and made up of sodium iron oxide (NaFeO2), iron oxide, hematite (Fe2O3), and chromium-iron oxide (Cr,Fe)2O3 solid solution. The latter was iv found near the AISI 304 stainless steel. This indicates that the scale formed, particularly on the upper layers with presence of sodium iron oxide and iron oxide, hematite, is protective, and forms an effective barrier against penetration of fused solar salt. At the alloy interface with the bulk corrosion scale, the corrosion process induced a compositional modification in the grains located at the interface. There are iron rich and iron depleted grains at the interface if compared to the nominal iron content of the alloy. The mode of attack is identified as uniform at the test temperature of 530°C, showing a parabolic behavior with a parabolic rate constant (Kp) equals to (m2 /sec). By extrapolation, annual corrosion rate is estimated to reach 0.784 mils per year. Corrosion behavior of AISI 304 stainless steel is discussed in terms of thermodynamics and reaction paths.

This dissertation investigates the effects of autocorrelation on the performances of various sampling plans for control charts in detecting special causes that may produce sustained or transient shifts in the process mean and/or variance. Observations from the process are modeled as a first-order autoregressive process plus a random error. Combinations of two Shewhart control charts and combinations of two exponentially weighted moving average (EWMA) control charts based on both the original observations and on the process residuals are considered. Three types of sampling plans are investigated: samples of n = 1, samples of n > 1 observations taken together at one sampling point, or samples of n > 1 observations taken at different times. In comparing these sampling plans it is assumed that the sampling rate in terms of the number of observations per unit time is fixed, so taking samples of n = 1 allows more frequent plotting. The best overall performance of sampling plans for control charts in detecting both sustained and transient shifts in the process is obtained by taking samples of n = 1 and using an EWMA chart combination with a observations chart for mean and a residuals chart for variance. The Shewhart chart combination with the best overall performance, though inferior to the EWMA chart combination, is based on samples of n > 1 taken at different times and with a observations chart for mean and a residuals chart for variance. / Ph. D.

This thesis studies the brushless permanent magnet synchronous (BLPM) machine design for electric vehicle (EV) and hybrid electric vehicle (HEV) application. Different rotor topologies design, winding design, and multiphase designs are investigated and discussed. The Nissan Leaf interior permanent magnet (IPM) traction machine has been widely analyzed and there is much public domain data available for the machine. Hence, this machine is chosen as a representative benchmark design. First, the Nissan Leaf machine is analyzed via finite element analysis (FEA) and the results confirmed via published experimental test data. The procedure is then applied to all the following machine designs and results compared. Then the Nissan Leaf machine rotor is redesigned to satisfy the performance specification with sinusoidal phase current in the full range for the same performance specification and permanent magnet material. Afterword, a comparative study assessing the design and performance attributes of the Nissan Leaf IPM machine, when compared to a surface permanent magnet (SPM) machine designed within the main Nissan Leaf machine dimensional constraints. The study illustrates and concludes that both the IPM and SPM topologies have very similar capabilities with only subtle differences between the design options. The results highlight interesting manufacturing options and materials usage. The grain boundary diffusion processed (GBDP) magnets are proposed to reduce the rare earth material content in the permanent magnet machines, especially subject to high load and high temperature operating scenarios by preventing or reducing the onset of demagnetization. The design and analysis procedure of BLPM machine with GBDP magnets are put forward. In the end, the Nissan Leaf IPM machine is taken as an example to verify the analysis procedure. and the results illustrates that IPM machines with GBDP magnets can realize torque and maintain efficiency at high loads while being less prone to demagnetization. A new multi-phase synchronous reluctance machine (SRM) with good torque performance and conventional voltage source inverter is introduced for traction machine applications. Although the torque density is low compared with BLPM machine, the SRM machine gets rid of permanent magnets and achieve low torque ripple compared with switched reluctance machine when the asymmetric inverter is replaced with conventional voltage source inverter. The concentrated windings are designed and studied with both IPM and SPM rotor according to the Nissan Leaf machine requirements of performance and dimension to investigate how the concentrated windings affect the machine performance and manufacturability and cost. 9-, 12-, 15- slot concentrated windings’ stator share the same slot area with the Nissan Leaf machine distributed winding and the performance are evaluated and compared. Multi-phase concentrated windings machines with IPM and SPM rotor are designed and analyzed based on the Nissan Leaf machine specification and dimension constraints. The performance of 23-phase, 5-phase, 9-phase machine at low speed and top speed are studied and the advantages and disadvantages are compared in terms of torque quality, efficiency, and power electronic requirements. / Thesis / Doctor of Philosophy (PhD)

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A desirable feature of concentrated solar power (CSP) with integrated thermal energy storage (TES) unit is to provide electricity in a dispatchable manner during cloud transient and non-daylight hours. Latent heat thermal energy storage (LHTES) offers many advantages such as higher energy storage density, wider range of operating temperature and nearly isothermal heat transfer relative to sensible heat thermal energy storage (SHTES), which is the current standard for trough and tower CSP systems. Despite the advantages mentioned above, LHTES systems performance is often limited by low thermal conductivity of commonly used, low cost phase change materials (PCMs). Research and development of passive heat transfer devices, such as heat pipes (HPs) to enhance the heat transfer in the PCM has received considerable attention. Due to its high effective thermal conductivity, heat pipe can transport large amounts of heat with relatively small temperature difference. The objective of this research is to study the charging and discharging processes of heat pipe-assisted LHTES systems using computational fluid dynamics (CFD) and experimental testing to develop a method for more efficient energy storage system design. The results revealed that the heat pipe network configurations and the quantities of heat pipes integrated in a thermal energy storage system have a profound effect on the thermal response of the system. The optimal placement of heat pipes in the system can significantly enhance the thermal performance. It was also found that the inclusion of natural convection heat transfer in the CFD simulation of the system is necessary to have a realistic prediction of a latent heat thermal storage system performance. In addition, the effects of geometrical features and quantity of fins attached to the HPs have been studied. / Mechanical Engineering