The main objective of this paper is to show the economic and environmental benefits that can be attained through the coupling of borehole thermal energy storage (BTES) and combined heat and power (CHP). The subject of this investigation is the University of Massachusetts CHP District Heating System. Energy prices are significantly higher during the winter months due to the limited supply of natural gas. This dearth not only increases operating costs but also emissions, due to the need to burn ultra low sulfur diesel (ULSD). The application of a TES system to a CHP plant allows the plant to deviate from the required thermal load in order to operate in a more economically and environmentally optimal manner. TES systems are charged by a heat input when there is excess or inexpensive energy, this heat is then stored and discharged when it is needed. The scope of this paper is to present a TRNSYS model of a BTES system that is designed using actual operational data from the campus CHP plant. The TRNSYS model predicts that a BTES efficiency of 88% is reached after 4 years of operation. It is concluded that the application of BTES to CHP enables greater flexibility in the operation of the CHP plant. Such flexibility can allow the system to produce more energy in low demand periods. This operational attribute leads to significantly reduced operating costs and emissions as it enables the replacement of ULSD or liquefied natural gas (LNG) with natural gas.

The cost and fuel economy of hybrid electrical vehicles (HEVs) are significantly dependent on the power-train energy storage system (ESS). A series HEV with a minimal all-electric mode (AEM) permits minimizing the size and cost of the ESS. This manuscript, pursuing the minimal size tactic, introduces a bandwidth based methodology for designing an efficient ESS. First, for a mid-size reference vehicle, a parametric study is carried out over various minimal-size ESSs, both hybrid (HESS) and non-hybrid (ESS), for finding the highest fuel economy. The results show that a specific type of high power battery with 4.5 kWh capacity can be selected as the winning candidate to study for further minimization. In a second study, following the twin goals of maximizing Fuel Economy (FE) and improving consumer acceptance, a sports car class Series-HEV (SHEV) was considered as a potential application which requires even more ESS minimization. The challenge with this vehicle is to reduce the ESS size compared to 4.5 kWh, because the available space allocation is only one fourth of the allowed battery size in the mid-size study by volume. Therefore, an advanced bandwidth-based controller is developed that allows a hybridized Subaru BRZ model to be realized with a light ESS. The result allows a SHEV to be realized with 1.13 kWh ESS capacity. In a third study, the objective is to find optimum SHEV designs with minimal AEM assumption which cover the design space between the fuel economies in the mid-size car study and the sports car study. Maximizing FE while minimizing ESS cost is more aligned with customer acceptance in the current state of market. The techniques applied to manage the power flow between energy sources of the power-train significantly affect the results of this optimization. A Pareto Frontier, including ESS cost and FE, for a SHEV with limited AEM, is introduced using an advanced bandwidth-based control strategy teamed up with duty ratio control. This controller allows the series hybrid’s advantage of tightly managing engine efficiency to be extended to lighter ESS, as compared to the size of the ESS in available products in the market.

No description available.

Energy storage systems such as batteries and supercapacitors store electrical energy in the form of chemical energy and release it when required. Among the various electrode materials, manganese oxides (MnOx) are promising electrode materials for these devices. Despite its outstanding theoretical capacitance, Mn-based oxide electrodes have several limitations that impede their electrochemical performance. Understanding how the charges are efficiently stored in the electrodes or across the electrode/electrolyte interface is crucial for developing advanced electrode material in the field of energy storage applications. The goal of my thesis is to develop and apply synchrotron-based scanning transmission X-ray microscopy (STXM) to investigate changes in the oxidation state of Mn and their spatial distributions in MnOx electrodes in the context of energy storage and release. To achieve high- precision qualitative and quantitative STXM identification and mapping of different MnOx species, calibrated and high-quality reference Mn 2p and O 1s NEXAFS (near edge X-ray absorption fine structure) spectra were measured. In collaboration with Wenjuan Yang and her PhD supervisor, Prof. Igor Zhitomirsky, I performed ex-situ STXM studies on Mn3O4-based supercapacitor electrode materials to investigate the influence of different synthesis methods and activation protocols on the charging behavior and capacitance performance. In collaboration with Pablo Ingino and his supervisor, Prof. Martin Obst (Bayreuth University), and my colleague, Dr. Chunyang Zhang, I helped develop a three-electrode, microfluidic-based flow electrochemical device for in-situ STXM. This device was used to electrodeposit MnO2 on the working electrode (WE) and track the oxidation state and morphological changes by STXM while scanning the potential of the cell in different electrolyte pH. The in-situ STXM studies showed a spontaneous reduction of the initially deposited MnO2 resulting from the local pH change at the WE. Additionally, a significant change from a quasi-uniform MnO2 film to a dendritic MnO2 structure was observed at oxidative potential. This dendritic growth resulted from dissolution/redeposition of MnO2 during charging/discharging processes, indicating a partial reversibility of dissoluble Mn species. The ex-situ and in-situ STXM studies I performed provide mechanistic insights that will help further improve Mn oxides-based electrodes and their applications as energy storage devices. / Thesis / Doctor of Philosophy (PhD)

As energy systems shift away from fossil-fuel based electricity, the non-dispatchability of renewable energy converters (REC) continue to stress the grid infrastructure and conventional thermal generating units. These hybrid electricity systems require energy storage systems to buffer the variabilities of electricity supply and demand. Regenerative air energy storage (RAES) is an emerging technology that shows promise to overcome the barriers of REC variability. RAES uses a novel compressor/expander that approaches isothermal operation by spraying water into the piston/cylinder to absorb/release heat. RAES can be sized for power and energy independently, and has a high round-trip efficiency that can be boosted using low grade waste heat. Because of its novelty, new numerical models are necessary to investigate the sizing and performance of RAES systems. In this thesis a numerical simulation tool is developed to allow flexible and intuitive analysis of a range of hybrid energy systems involving RAES.

Sweden is only utilizing half of the available excess heat. To utilize more of the excess heat a seasonal thermal energy storage could be implemented to store excessed heat from the summer when the demand is lower to the winter when the demand is higher. This can be achieved by an integration of a seasonal thermal energy storage to the district heating system. A seasonal thermal energy storage may also reduce the need of the system’s peak load, which often is economically costly and adversely affect the environment. The purpose of the paper is to investigate the possibility for Skövde Värmeverk to implement a seasonal thermal storage. The paper is performed by a literature collection and calculations are made by software programs. The result shows that it is technically possible to implement a pit thermal energy storage and a borhole thermal energy storage, but no outcome shows a profitability within 20 years. A pit thermal energy storage can replace the system’s peak load up to 79 percent and a borhole thermal energy storage up to 2,8 percent. The most suitable case for Skövde Värmeverk is to install a pit thermal energy storage with a storage capacity of 4 GWh.

In hot climate areas, the electrical load in a building spikes, but not by the same amount daily due to various conditions. In order to cover the hottest day of the year, large cooling systems are installed, but are not fully utilized during all hot summer days. As a result, the investments in these cooling systems cannot be fully justified. A solution for more optimal use of the building cooling system is presented in this dissertation using Cool Thermal Energy Storage (CTES) deployed at a district level. Such CTES systems are charged overnight and the cool charge is dispatched as cool air during the day. The integration of the CTES helps to downsize the otherwise large cooling systems designed for the hottest day of the year. This reduces the capital costs of installing large cooling systems. However, one important question remains - how much of the CTES should be charged during the night, such that the cooling load for the next day is fully met and at the same time the CTES charge is fully utilized during the day. The solution presented in this dissertation integrated the CTES with Photovoltaics (PV) power forecasting and building load forecasting at a district level for a more optimal charge/discharge management. A district comprises several buildings of different load profiles, all connected to the same cooling system with central CTES. The use of forecasting for both the PV and the building cooling load allows the building operator to more accurately determine how much of the CTES should be charged during the night, such that the cooling system and CTES can meet the cooling demand for the next day. Using this approach, the CTES would be optimally sized, and utilized more efficiently during the day. At the same time, peak load savings are achieved, thus benefiting an electric utility company. The district presented in this dissertation comprises PV panels and three types of buildings – a mosque, a clinic and an office building. In order to have a good estimation for the required CTES charge for the next day, reliable forecasts for the PV panel outputs and the electrical load of the three buildings are required. In the model developed for the current work, dust was introduced as a new input feature in all of the forecasting models to improve the models' accuracy. Dust levels play an important role in PV output forecasts in areas with high and variable dust values. The overall solution used both the PV panel forecasts and the building load forecasts to estimate the CTES charge for the next day. The presented method was tested against the baseline method with no forecasting system. Multiple scenarios were conducted with different cooling system sizes and different CTES capacities. Research findings indicated that the presented method utilized the CTES charge more efficiently than the baseline method. This led to more savings in the energy consumption at the district level. / Doctor of Philosophy / In hot weather areas around the world, the electrical load in a building spikes because of the cooling load, but not by the same amount daily due to various conditions. In order to meet the demand of the hottest day of the year, large cooling systems are installed. However, these large systems are not fully utilized during all hot summer days. As a result, the investments in these cooling systems cannot be fully justified. A solution for more optimal use of the building cooling system is presented in this dissertation using Cool Thermal Energy Storage (CTES) deployed at a district level. Such CTES systems are charged overnight and the cool charge is dispatched as cool air during the day. The integration of the CTES helps to downsize the otherwise large cooling systems designed for the hottest day of the year. This reduces the capital costs of installing large cooling systems. However, one important question remains - how much of the CTES should be charged during the night, such that the cooling load for the next day is fully met and at the same time the CTES charge is fully utilized during the day. The solution presented in this dissertation integrated the CTES with Photovoltaics (PV) power forecasting and building load forecasting at a district level for a more optimal charge/discharge management. A district comprises several buildings all connected to the same cooling system with central CTES. The use of the forecasting for both the PV and the building cooling load allows the building operator to more accurately determine how much of the CTES should be charged during the night, such that the cooling system and CTES can meet the cooling demand for the next day. Using this approach, the CTES would be optimally sized and utilized more efficiently. At the same time, peak load is lowered, thus benefiting an electric utility company.

The design of nanoparticles in mesoporous supports is explored through synthetic strategies of electrophoretic deposition and electroless deposition with application towards energy storage. Electrophoretic deposition of nanoparticles into a mesoporous thin film is examined using charged nanocrystals in a low-permittivity solvent. To provide a basis for the deposition, the mechanism of particle charging in a low-permittivity solvent was studied. Dispersions of carbon black particles in toluene with an anionic surfactant were characterized using differential-phase optical coherence tomography with close electrode spacing to measure the electrophoretic mobility. The particle charge in concentrated dispersions was found to decrease as a function of increasing surfactant concentration. Partitioning of cations between the surfactant-laden particle surface and micelle cores in the double-layer was found to govern the dynamics of particle charging. Subsequently, charged Au nanocrystals were deposited by electrophoresis within perpendicular mesochannels of a TiO2 support. High loadings of 21 wt% Au with good dispersion were achieved within the mesoporous TiO2 support using electrophoretic deposition, which would otherwise be inhibited by the weak nanocrystal-support interaction. According to a modified Fokker-Planck equation, the mean penetration depth of a single nanocrystal inside of the perpendicular pores was found to be dependent on the electric field strength, electrophoretic mobility, pore diameter, nanocrystal size, and local deposition rate constant. Nanocomposites for electrochemical capacitors were designed via electroless deposition of redox-active MnO2 in a high surface area mesoporous carbon support. Disordered mesoporous carbon supports with a pore size of ~8 nm were used both in amorphous (AMC) and graphitic (GMC) form, with a ~1000-fold larger conductivity for GMC. High loadings of 30 wt% MnO2 were achieved in the AMC in the form of ~1 nm thick domains, which were highly dispersed throughout the support. Oxidation of the GMC was necessary to facilitate wetting and deposition of the MnO2 precursor in order to achieve high loadings of 35 wt% MnO2 with ~1 nm thickness. High gravimetric MnO2 pseudocapacitances of >500 F/gMnO2 were achieved at low loadings and low scan rate of 2 mV/s for both carbon supports. However, at high scan rates ≥100 mV/s, the MnO2 pseudocapacitance is twofold larger for MnO2/GMC, relative to MnO2/AMC. Sodium ion diffusion throughout both MnO2/AMC and MnO2/GMC was shown to be facile. For the GMC versus AMC support, the higher MnO2 pseudocapacitance is attributed to the higher electronic conductivity, which facilitates electron transport to the MnO2 domains. / text

One of the main challenges in order to make electric cars competitive with gas-powered cars is in the improvement of the electric power system. Although many of the energy sources currently used in electric vehicles have sufficientlyhigh specific energy, their applicability is limited due to low specific power. It would therefore be advantageous to create a driveline with the main energy storage separated from a smaller energy buffer, designed to have high power capabilities and to withstand frequent and deep discharge cycles. It has been found that rotating kinetic energy storage in flywheels is very well suited for this type of application. A composite shell, comprising an inner part made of glassfiber and an outer part made of carbonfiber, was analyzed analytically and numerically, designed, and constructed. The shell was fitted onto a metallic rotor using shrinkfitting. The cost of the shell, and the complexity of assembly, was reduced by winding the glass- and carbonfiber consecutively on a mandrel, and curing the complete assembly simultaneously. Thereby, the shell obtained an internal segmentation, without the need for fitting several concentric parts onto each other. The radial stress inside the composite shell was kept compressive thanks to a novel approach of using the permanent magnets of the integrated electric machine to provide radial mechanical load during rotation. Two thrust bearing units (one upper and one lower) comprising one segmented unit with the permanent magnets in a cylindrical Halbach configuration and one non-segmented unit in a up/down configuration were optimized, constructed and tested. Each thrust bearing unit generated 1040 N of repelling force, and a positive axial stiffness of 169 N/mm at the nominal airgap of 5 mm.  Two radial active magnetic bearings (one upper and one lower) were optimized, constructed and tested. By parameterizing the shape of the actuators, a numerical optimization of force over resistive loss from the bias currentcould be performed. The optimized shape of the electromagnets was produced by watercutting sheets of laminated steel. A maximum current stiffness of120 N/A at a bias current of 1.5 A was achieved.

In the transition from traditional power plants to more environmentally friendly alternatives will generate a need for more flexibility in production, transmission and consumption. Energy storage can be provide the flexibility that are required to continue to have a robust and stable electrical system. The purpose of this report is to give an overview of the electrical energy storage technologies. The classification of energy storage technologies used in this report is mechanical, chemical and electrical. In these three categories were ten different technologies presented with function, advantages, disadvantages, degree of maturity and research area for each technology. The distribution between the globally operational energy storage technologies were presented. Also the framework and regulations for actors to own and operate an energy storage in Sweden. This review was complemented with a case study about connecting a lithium ion battery system to a wind farm. The case investigated the profitability for 20 MW wind farm with a 12 MW and 18 MWh energy storage system for a five and ten-year period. The utilization of the storage was optimized with \textit{What's best} for three different investment cost. The review were done in order to answer: what is the futures energy storage technology?, what applications can be replaced by energy storage for an electricity producer? and what will the effects be of the new actor Aggregator? The result from comparing three different prices for lithium ion batteries resulted in a non-profit scenario for all the cases in a five-year period. There were a maximum, minimum and predicted futuristic price, which generated a loss of 731, 220 and 76.6 MSEK for respective case. Only the futuristic price for a ten-year period indicated an profit. The conclusion that can be drawn from this case study is that energy storage is too expensive and the extra income from utilization of the energy storage is not enough to motivate an energy storage investment. There are not a single technology that possesses all of the required properties for the applications. In the future there will be a combination of technologies to cover all the applications. For the seasonal storage pumped hydro and compressed air are most promising technologies. The flywheels and supercapacitors can contribute with short powerful burst of energy that are needed for power quality and operating reserves. For the more wide range application such as power fleet optimization and integrate the renewable energy production, batteries in form of lithium ion battery and sodium-sulfur battery will most probably be used. For electricity producers energy storage can replace existing solutions. Instead of using diesel generators for black start services, an battery can be used. Also the power quality could be enhanced with batteries acting as filters. The process can be more utilized in a more efficient way with an energy storage. The aggregator actor gathers small variable load from e.g several houses and participate on the electricity market. This actor will level out the differences in power demand during the day. It will reduce the losses and reduce the need for grid investments in both the transmission and distribution networks. It would also generate more available frequency reserves and probably change how the market is paying for the generated benefits.