As we transition toward a power grid that is increasingly based on renewable resources like solar and wind, the intelligent control of distributed energy resources (DERs) including photovoltaic (PV) arrays, controllable loads, energy storage, and plug-in electric vehicles (EVs) will be critical to realizing a power grid that can handle both the variability and unpredictability of renewable energy sources as well as increasing system complexity. Realizing such a decentralized and dynamic infrastructure will require the ability to solve large scale problems in real-time with hundreds of thousands of DERs simultaneously online. Because of the scale of the optimization problem, we use an iterative distributed algorithm previously developed in our group to operate each DER independently and autonomously within this environment. The algorithm is deployed within a framework that allows the microgrid to dynamically adapt to changes in the operating environment. Specifically, we consider a commercial site equipped with on-site PV generation, partially curtailable load, EV charge stations and a battery electric storage unit. The site operates as a small microgrid that can participate in the wholesale market on the power grid. We report results for simulations using real-data that demonstrate the ability of the optimization framework to respond dynamically in real-time to external conditions while maintaining the functional requirements of all DERs.

In this paper, we develop optimization and control methods for a grid-tied photovoltaic (PV) storage system. The storage component consists of two separate units, a large slower moving unit for energy shifting and arbitrage and a small rapid charging unit for smoothing. We use a Model Predictive Control (MPC) framework to allow the units to automatically and dynamically adapt to changes in PV output while responding to external system operator requests or price signals. At each time step, the system is modeled using convex objectives and constraints and solved to obtain a control schedule for the storage units across the MPC horizon. For each subsequent time step, the first step of the schedule is executed before repeating the optimization process to account for changes in the operating environment and predictions due to availability of additional information. We present simulation results that demonstrate the ability of this optimization framework to respond dynamically in real time to external price signals and provide increased system benefits including smoother power output while respecting and maintaining the functional requirements of the storage units and power converters.

This paper presents a methodology that has been developed by Electric Power Research Institute (EPR I) to perform the technical and cost/benefit analysis of realizing the potential solution opportunities of e nergy storage within distribution. The methodology develo ped was built in terms of identifying and characterizin g feeder contrainsts. Key elements of the overall methodology are presented in this paper. This methodology is now being tested through case studie s in several utility situations.Results from one example case study is presented in the paper.

Introduction A number of distributed energy trends add up to increased interest in microgrids. The objectives and value propositions include access to renewable resources for energy and environment, a more resilient electricity supply amidst storms, optimized energy use by local generation and by local control. Individually these objectives are already being served in various applications and with available distributed energy technologies. A prominent example is roof-top photovoltaic (PV) systems. Widely deployed and custom fit to end-user's sites these systems rely on the grid for balancing differences in output and demand. Also common, battery energy storage and standby generators protect critical processes in applications like hospitals and computer centers. Commercial combined heat and power (CHP) systems usually serve local heat requirements with power to the public grid as a byproduct. Nothing new here, but put them together with a grid connection and a control, and you have the makings of a microgrid. In concept microgrids employ an integrated approach that captures the benefits of several distributed resources. They may provide value to both producers and end users. It's a good concept, but still, the extent of adoption will depend on many factors such as renewable policies, the weather and the price of natural gas. Also future advancements in distributed energy technology and product options are expected to bring improved economics. Ease of grid integration will also be a critical factor in deployment. The challenge, and opportunity, is to create a safe and effective operational collaboration. Utilities can play an important role here. Considered from the broader system viewpoint, harnessing distributed resources can add both flexibility and resiliency to the electric power grid. This primer reviews the drivers for distributed resources and their extension into a microgrid configuration. It explores barriers and challenges for adoption including technical, economic and regulatory. Technologies expected to improve performance or support integration are identified. The primer touches on ownership and business models as well as the likely end-user candidates where a microgrid may contribute to uptime and overall energy efficiency. Finally, it discusses the future for microgrids and points out ways utilities can strategically incorporate them into the larger grid operations.

Power converters constructed from discrete components are difficult to mass produce, and their installation requires a significant labor cost for the proper interconnection among the panel, inverter, and grid. Several critical applications, such as portable power stations (for use on a battlefield or scientific expedition), will require key attributes from a photovoltaic (PV)-based power system, such as modularity, high reliability, and quick set-up time. Therefore, a paradigm shift in the design of the entire PV power system is needed to mitigate this need. To increase the converter reliability and portability, the active and passive elements of a power converter [especially capacitors and active switches such as metal-oxide-semiconductor field-effect transistors (MOSFETs), junction gate field-effect transistors (JFETs), or insulated-gate bipolar transistors (IGBTs)] could be embedded on the same substrate material used for fabricating the p-n junctions in the PV panel. To the authors' knowledge, there is no prior work in cell-level power conversion with embedded converters, and therefore this project idea could be considered "outside the box." A novel fabrication process along with experimental results are presented in this article, demonstrating the integration of PV cells and major components needed to build a power converter on the same substrate/wafer. Because of the cell-level power conversion, PV panels constructed from these cells are likely to be immune to partial shading and hot-spot effects. In addition, the effect of light exposure on converter switches has been analyzed to understand the converter behavior at various illumination levels. Simulation and experimental results have been provided to support this analysis. In addition to process-related challenges and issues, the justification of this integration is explained by achieving higher reliability, portability and complete modular construction for PV-based energy harvesting units.

The purpose of this work is to develop an evolutionary procedure to be used by Chemical Engineering students for the base-case design of a Vanadium Redox-Flow Battery. The design methodology is based on the work of Douglas (1985) and provides a profitability analysis at each decision level so that more profitable alternatives and directions can be indentified before additional time and effort is expended on an impractical design. Ultimately, a base case flow sheet and capital cost estimate are generated; this type of design activity as the work presented here is referred to as creation and analysis of a study level design.

This paper will describe work done at EPRI over the past several years in relation to energy storage and bulk power system integration of renewables. In particular, applications of energy storage and related functional requirements are described and technologies are summarized. Insights and lessons learned from various case studies are also examined, showing the impact of energy storage on bulk system integration of variable generation.

The increasing interest in energy storage for the grid can be attributed to multiple factors, including the capital costs of managing peak demands, the investments needed for grid reliability, and the integration of renewable energy sources. Although existing energy storage is dominated by pumped hydroelectric, there is the recognition that battery systems can offer a number of high-value opportunities, provided that lower costs can be obtained. The battery systems reviewed here include sodium-sulfur batteries that are commercially available for grid applications, redox-flow batteries that offer low cost, and lithium-ion batteries whose development for commercial electronics and electric vehicles is being applied to grid storage.

A new cell voltage equalizer topology for future plug-in hybrid electric vehicles (PHEV) or renewable energy storage has been proposed in this paper. This topology has fewer components compared to the conventional topologies found in the literatures, and therefore, it could reduce cost and fabrication complexity. This new circuit is based on a time shared fly-back converter, and any number of series connected cells could be used in a string without any apparent issues. Each cell in a string shares this converter during its allocated time slot provided by the microcontroller. In addition, dynamic allocations of the time slots are possible to achieve faster cell balancing, and the circuit dynamically distributes depleted charge among cells in a regenerative fashion - ensuring a very high efficiency. The prototype of a four-cell lithium-ion battery balancer circuit was designed and implemented. Simulation and experimental results are presented to verify the operation of the new topology.