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.

The hydrocarbon combustion process used to generate electricity releases harmful levels of Carbon, Sulfur and Nitrogen Oxides into the atmosphere. The alternative to environmentally toxic hydrocarbon based fuel, is electricity generated from solar powered microgrids. Solar photovoltaic microgrids represent a clean, renewable and economically viable energy alternative to hydrocarbon based fuel. The microgrid project outlined the specifications required to the charge the battery powered material handling vehicles at General Stamping & Metalworks. The project was designed to replace utility supplied electrical power with a solar microgrid to charge three lead acid type batteries. The solar microgrid project specifies the system requirements, equipment selection and installation methodology. Operational strategies for additional photovoltaic applications within the organization are discussed. Outlined in the report are the costs of installation and return on investment. The project was designed to demonstrate a practical application of microgrids within a manufacturing environment. The goal of the project was to design and build a small scale installation to provide a proof of concept. The overarching goal was to reduce the toxic emissions produced by utility supplied electrical power by installing a solar powered microgrid. The end result of the analysis was that photovoltaic powered microgrids represent a viable energy generating system for battery powered applications. However, based on the regional utility price of .092 $/kWh, the solar installation did not meet the organizations investment acceptance criteria.

Recent advances in innovative energy storage devices such as supercapacitors have made battery-supercapacitor hybrid energy storage systems technically attractive. However the field of hybrid energy storage system control is relatively new, involving the major challenge of developing control techniques optimised for improved battery-life or other performance metrics. This thesis presents the design and analysis of an actively controlled hybrid energy storage system. Detailed information is given regarding the system implementation and dynamic controls developed as a part of the research. Novel use of the sliding-mode or hysteretic current-controlled DC/DC converter is shown to provide a versatile and robust power electronic building block for the power-control hardware implementation. Current state of the art in the field has converged around a frequency-domain approach to the overall power sharing strategy within hybrid energy storage systems employing batteries and high-power, low-energy density storage such as supercapacitors, with benefits in terms of reduced battery current maxima and an (un-quantified) increase in battery life having been reported. This research extends previous studies by considering the frequency-domain approach in further detail and providing quantitative simulation results confirming how an estimated increase in battery cycle-life of ~18% can be achieved. A systematic simulation framework used for the development and assessment of novel hybrid energy storage system control strategies is described and demonstrated in the context of a remote wind power application. The hardware design of all systems considered is described in detail and demonstrated by experiment.

Fossil fuel will eventually become exhausted. Also, fossil fuels produce large amounts of carbon dioxide, which cannot only bring environment pollution, but can also cause global warming. Therefore, clean and renewable energy sources should be investigated. In this project, renewable wind power was considered. Wind energy is free, clean and available in large quantities, although it is difficult to use due to its stochastic variability. Energy storage can reduce this variability allowing energy production to match energy demand. In this study, different kinds of energy storage approaches were introduced, compared, and simulated by using half hourly wind data from the Met Office, UK, and half hourly load data from the University of Bath, UK. Hydrogen has higher mass energy density than all other energy storage methods. It is seen as a versatile energy carrier of the future, complementary to electricity and with the potential to replace fossil fuels due to its zero carbon emissions and abundance in nature. On the other hand, because hydrogen is the lightest element under normal conditions; the same amount of hydrogen must occupy a huge volume compared to other elements. The mature technology for converting hydrogen into electricity has high cost and low efficiency. These are big issues that limit the usage of hydrogen energy storage methods. Using wind and load data, a new algorithm was developed and used for sizing the wind turbine, and energy storage requirements. The traditional way to supply energy is distributing electricity, but in this PhD research, there are some discussions about a new method, hydrogen transport-hydrogen pipeline. From the results of the comparison and algorithm, a practical hydrogen energy storage system for the University of Bath network was proposed and designed. In the proposed design the energy from a wind turbine was directed to the load and the remaining excess power was used to produce hydrogen by water electrolysis. The hydrogen was stored in a high pressure compressed tank, and finally a hydrogen fuelled combined cycle gas turbine was used to convert the hydrogen to electricity. In this thesis, the dynamics of the complete hydrogen cycle energy storage and recovery mechanism are discussed, identifying potential applications such as power smoothing, peak lopping and extending power system controller ranges. The results of calculations of the payback time and revenue verify the feasibility of the designed hydrogen energy storage system. The main objective of the PhD was to design a practical hydrogen energy storage system for micro-grid applications. During this research, hydrogen energy storage was investigated to show that it does solve the problems arising from renewable energy.

"Large amounts of renewable energy generation are being introduced into modern power systems to decrease the environmental impact of power generation. Despite benefits, increased renewable energy penetration will likely create additional system instability and unpredictability. Increasing line capacity via redundancy of transmission networks and utilizing energy storage are two methods that can be used to increase transmission power system stability. This thesis investigates the economic effects of energy storage and line capacity in isolated test systems. Utilizing Powerworld Simulator, test systems based off two common industry test bed standards (WECC 9-bis, IEEE 14-bus) were built using scaled real-world generation and load data. Multiple Optimal Power Flow studies performed on the test systems with and without the addition of energy storage model revealed the incremental change in overall system cost of adding energy storage and highlighted the impact energy storage has on isolated systems with renewable energy."

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1980. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING. / Includes bibliographical references. / by James Raymond Downer. / M.S.

Properties such as chemical robustness, potential for synthetic tunability, and superior electron-accepting character describe the chromophore perylene-3,4,9,10-tetracarboxylic diimide (PDI) and have enabled its penetration into organic photovoltaics. The ability to extend what is already a large aromatic core allows for synthesis of graphene ribbon PDI oligomers. Functionalization with polar and ionic groups leads to liquid crystalline phases or immense supramolecular architectures. Significantly, PDI dianions can survive in water for two months with no decomposition, an important property for charge storage materials. We realized the potential of PDI as an efficient negative-side material for Redox Flow Batteries (RFBs). The synthetic tunability of PDI allowed for screening of several derivatives with side chains that enhanced solubility in polar solvents. The optimized molecule, PDI[TFSI]2, dissolved in acetonitrile up to 0.5 M. For the positive-side, we synthesized the ferrocene oil [Fc4] in high yield. The large hydrodynamic radii of PDI[TFSI]2 and [Fc4] preclude their ability to cross a size exclusion membrane, which is a cheap alternative to the typical RFB membranes. We show that this cellulose-based membrane can support high voltages in excess of 3 V and extreme temperatures (−20 to 110 °C). We assembled a cell with 0.4 M electron concentration with negligible capacity loss for over 450 cycles (>74 days). Such concentration and stability are among the highest values reported in redox flow batteries with organic electrolytes. Oxidative photocyclizations of PDI onto acenes administer regiochemistry that favors helical products, albeit with a small number of overlapping π-bonded atoms. We achieved an oxidative photocyclization of PDI onto phenanthrene to form the [7]helicenes PPDHa and PPDHb with 20 overlapping π-bonded atoms, as well as a partially planar molecule 5HPP. Higher temperature increases the ratio of PPDHa:5HPP. Calculations reveal that these molecules contain ~20 kcal/mol more strain than planar analogs, and single crystals show bending of the PDI units from their favored planarity. The PPDH molecules display a new electronic transition in their UV-Vis spectra that sets them apart from monomer PDI and other PDI helicenes. Spectroelectrochemical measurements confirm that PPDHb accepts four electrons. Compared to a naphthyl-fused PDI helicene with only 10 overlapping π-bonded atoms, the PPDH molecules have a heightened ability to delocalize the first added electron.

One of the main challenges in the implementation of renewable energy is the mismatch between supply and demand. Energy storage has been identified as one of the solutions to the mismatch problem. Among various storage technologies, thermal energy storage (TES) is foreseen to have a significant role to achieve a low carbon energy systems because of the large share of thermal energy demand and its relatively low cost. However, integrating TES into energy systems requires careful design and implementation since otherwise potential financial and environmental savings may not be achieved. Computational-based design tools are ubiquitous in the design process of modern energy systems and can be broadly categorised into two methodologies: optimisation and simulation. In both cases, designing an energy system with storage technology is significantly more complicated than those without, mainly due to the coupling of variables between time steps. This thesis is concerned with two facets of the application of TES in energy systems. First, the role of TES in improving the performance of renewable-based domestic heating systems. Second, the implementation of optimisation and simulation tools in the design of energy systems with integrated TES. They are addressed by examining two case studies that illustrate the spatial and temporal variance of energy systems: a single dwelling heat pump system with a hot water tank, and a solar district heating system with a borehole thermal energy storage. In the single dwelling case study, the technical and financial benefits of TES installation in a heat pump system are illustrated by the optimisation model. A simulation model which utilises the optimisation results is developed to assess the accuracy of the optimisation results and the potential interaction between the two methodologies. The solar district heating case study is utilised to highlight the potential of a time decomposition technique, the multiple time grids method, in reducing the computational time in the operational optimisation of the system. Furthermore, the case study is also employed to illustrate the potential of installing a similar system in the UK. The latter study was performed by developing a validated simulation model of the solar district heating system. The findings of the analyses reported in this thesis exemplify the potential of TES in a domestic and community-level heating system in the UK. They also provide a basis for recommendations on the improved use of optimisation and simulation tools in the design process of energy systems.

<p>The topic of this thesis is the study of energy storage systems operating with wind power plants. The motivation for applying energy storage in this context is that wind power generation is intermittent and generally difficult to predict, and that good wind energy resources are often found in areas with limited grid capacity. Moreover, energy storage in the form of hydrogen makes it possible to provide clean fuel for transportation. The aim of this work has been to evaluate how local energy storage systems should be designed and operated in order to increase the penetration and value of wind power in the power system. Optimization models and sequential and probabilistic simulation models have been developed for this purpose.</p><p>Chapter 3 presents a sequential simulation model of a general windhydrogen energy system. Electrolytic hydrogen is used either as a fuel for transportation or for power generation in a stationary fuel cell. The model is useful for evaluating how hydrogen storage can increase the penetration of wind power in areas with limited or no transmission capacity to the main grid. The simulation model is combined with a cost model in order to study how component sizing and choice of operation strategy influence the performance and economics of the wind-hydrogen system. If the stored hydrogen is not used as a separate product, but merely as electrical energy storage, it should be evaluated against other and more energy efficient storage options such as pumped hydro and redox flow cells. A probabilistic model of a grid-connected wind power plant with a general energy storage unit is presented in chapter 4. The energy storage unit is applied for smoothing wind power fluctuations by providing a firm power output to the grid over a specific period. The method described in the chapter is based on the statistical properties of the wind speed and a general representation of the wind energy conversion system and the energy storage unit. This method allows us to compare different storage solutions.</p><p>In chapter 5, energy storage is evaluated as an alternative for increasing the value of wind power in a market-based power system. A method for optimal short-term scheduling of wind power with energy storage has been developed. The basic model employs a dynamic programming algorithm for the scheduling problem. Moreover, different variants of the scheduling problem based on linear programming are presented. During on-line operation, the energy storage is operated to minimize the deviation between the generation schedule and the actual power output of the wind-storage system. It is shown how stochastic dynamic programming can be applied for the on-line operation problem by explicitly taking into account wind forecast uncertainty. The model presented in chapter 6 extends and improves the linear programming model described in chapter 5. An operation strategy based on model predictive control is developed for effective management of uncertainties. The method is applied in a simulation model of a wind-hydrogen system that supplies the local demand for electricity and hydrogen. Utilization of fuel cell heat and electrolytic oxygen as by-products is also considered. Computer simulations show that the developed operation method is beneficial for grid-connected as well as for isolated systems. For isolated systems, the method makes it possible to minimize the usage of backup power and to ensure a secure supply of hydrogen fuel. For grid-connected wind-hydrogen systems, the method could be applied for maximizing the profit from operating in an electricity market.</p><p>Comprehensive simulation studies of different example systems have been carried out to obtain knowledge about the benefits and limitations of using energy storage in conjunction with wind power. In order to exploit the opportunities for energy storage in electricity markets, it is crucial that the electrical efficiency of the storage is as high as possible. Energy storage combined with wind power prediction tools makes it possible to take advantage of varying electricity prices as well as reduce imbalance costs. Simulation results show that the imbalance costs of wind power and the electricity price variations must be relatively high to justify the installation of a costly energy storage system. Energy storage is beneficial for wind power integration in power systems with high-cost regulating units, as well as in areas with weak grid connection.</p><p>Hydrogen can become an economically viable energy carrier and storage medium for wind energy if hydrogen is introduced into the transportation sector. It is emphasized that seasonal wind speed variations lead to high storage costs if compressed hydrogen tanks are used for long-term storage. Simulation results indicate that reductions in hydrogen storage costs are more important than obtaining low-cost and high-efficient fuel cells and electrolyzers. Furthermore, it will be important to make use of the flexibility that the hydrogen alternative offers regarding sizing, operation and possibly the utilization of oxygen and heat as by-products.</p><p>The main scientific contributions from this thesis are the development of</p><p>- a simulation model for estimating the cost and energy efficiency of wind-hydrogen systems,</p><p>- a probabilistic model for predicting the performance of a gridconnected wind power plant with energy storage,</p><p>- optimization models for increasing the value of wind power in electricity markets by the use of hydrogen storage and other energy storage solutions and the system knowledge about wind energy and energy storage that has been obtained by the use of these models.</p> / Paper 1 is reprinted with kind permission of ACTA Press. Paper 2 is reprinted with kind permission of Elsevier/ Science Direct. http://www.elsevier.com, http://www.sciencedirect.com Paper 3 is reprinted with kind permission of IEEE.

The topic of this thesis is the study of energy storage systems operating with wind power plants. The motivation for applying energy storage in this context is that wind power generation is intermittent and generally difficult to predict, and that good wind energy resources are often found in areas with limited grid capacity. Moreover, energy storage in the form of hydrogen makes it possible to provide clean fuel for transportation. The aim of this work has been to evaluate how local energy storage systems should be designed and operated in order to increase the penetration and value of wind power in the power system. Optimization models and sequential and probabilistic simulation models have been developed for this purpose. Chapter 3 presents a sequential simulation model of a general windhydrogen energy system. Electrolytic hydrogen is used either as a fuel for transportation or for power generation in a stationary fuel cell. The model is useful for evaluating how hydrogen storage can increase the penetration of wind power in areas with limited or no transmission capacity to the main grid. The simulation model is combined with a cost model in order to study how component sizing and choice of operation strategy influence the performance and economics of the wind-hydrogen system. If the stored hydrogen is not used as a separate product, but merely as electrical energy storage, it should be evaluated against other and more energy efficient storage options such as pumped hydro and redox flow cells. A probabilistic model of a grid-connected wind power plant with a general energy storage unit is presented in chapter 4. The energy storage unit is applied for smoothing wind power fluctuations by providing a firm power output to the grid over a specific period. The method described in the chapter is based on the statistical properties of the wind speed and a general representation of the wind energy conversion system and the energy storage unit. This method allows us to compare different storage solutions. In chapter 5, energy storage is evaluated as an alternative for increasing the value of wind power in a market-based power system. A method for optimal short-term scheduling of wind power with energy storage has been developed. The basic model employs a dynamic programming algorithm for the scheduling problem. Moreover, different variants of the scheduling problem based on linear programming are presented. During on-line operation, the energy storage is operated to minimize the deviation between the generation schedule and the actual power output of the wind-storage system. It is shown how stochastic dynamic programming can be applied for the on-line operation problem by explicitly taking into account wind forecast uncertainty. The model presented in chapter 6 extends and improves the linear programming model described in chapter 5. An operation strategy based on model predictive control is developed for effective management of uncertainties. The method is applied in a simulation model of a wind-hydrogen system that supplies the local demand for electricity and hydrogen. Utilization of fuel cell heat and electrolytic oxygen as by-products is also considered. Computer simulations show that the developed operation method is beneficial for grid-connected as well as for isolated systems. For isolated systems, the method makes it possible to minimize the usage of backup power and to ensure a secure supply of hydrogen fuel. For grid-connected wind-hydrogen systems, the method could be applied for maximizing the profit from operating in an electricity market. Comprehensive simulation studies of different example systems have been carried out to obtain knowledge about the benefits and limitations of using energy storage in conjunction with wind power. In order to exploit the opportunities for energy storage in electricity markets, it is crucial that the electrical efficiency of the storage is as high as possible. Energy storage combined with wind power prediction tools makes it possible to take advantage of varying electricity prices as well as reduce imbalance costs. Simulation results show that the imbalance costs of wind power and the electricity price variations must be relatively high to justify the installation of a costly energy storage system. Energy storage is beneficial for wind power integration in power systems with high-cost regulating units, as well as in areas with weak grid connection. Hydrogen can become an economically viable energy carrier and storage medium for wind energy if hydrogen is introduced into the transportation sector. It is emphasized that seasonal wind speed variations lead to high storage costs if compressed hydrogen tanks are used for long-term storage. Simulation results indicate that reductions in hydrogen storage costs are more important than obtaining low-cost and high-efficient fuel cells and electrolyzers. Furthermore, it will be important to make use of the flexibility that the hydrogen alternative offers regarding sizing, operation and possibly the utilization of oxygen and heat as by-products. The main scientific contributions from this thesis are the development of - a simulation model for estimating the cost and energy efficiency of wind-hydrogen systems, - a probabilistic model for predicting the performance of a gridconnected wind power plant with energy storage, - optimization models for increasing the value of wind power in electricity markets by the use of hydrogen storage and other energy storage solutions and the system knowledge about wind energy and energy storage that has been obtained by the use of these models. / Paper 1 is reprinted with kind permission of ACTA Press. Paper 2 is reprinted with kind permission of Elsevier/ Science Direct. http://www.elsevier.com, http://www.sciencedirect.com Paper 3 is reprinted with kind permission of IEEE.