Energy storage systems with Li-ion batteries are increasingly deployed to maintain a robust and resilient grid and facilitate the integration of renewable energy resources. However, appropriate selection of cells for different applications is difficult due to limited public data comparing the most commonly used off-the-shelf Li-ion chemistries under the same operating conditions. This article details a multi-year cycling study of commercial LiFePO4 (LFP), LiNixCoyAl1−x−yO2 (NCA), and LiNixMnyCo1−x−yO2 (NMC) cells, varying the discharge rate, depth of discharge (DOD), and environment temperature. The capacity and discharge energy retention, as well as the round-trip efficiency, were compared. Even when operated within manufacturer specifications, the range of cycling conditions had a profound effect on cell degradation, with time to reach 80% capacity varying by thousands of hours and cycle counts among cells of each chemistry. The degradation of cells in this study was compared to that of similar cells in previous studies to identify universal trends and to provide a standard deviation for performance. All cycling files have been made publicly available at batteryarchive.org, a recently developed repository for visualization and comparison of battery data, to facilitate future experimental and modeling efforts.

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The high penetration of utility interconnected photovoltaic (PV) inverters can affect the utility at the point of connnon coupling. Today's utility interconnection standards are evolving to allow voltage and frequency support, and voltage and frequency ride-through capability. With multi-MW-sized PV plants and multitudes of small connnercial and residential systems coming online each year, the interconnection standards are allowing distributed energy resource equipment to provide reactive power to supplement existing voltage-regulating devices and ridethrough voltage and frequency anomalies. These new interconnection requirements, coupled with the high de-toac ratios, are becoming more connnon with declining PV module costs and are changing the modes of operation for utility-interconnected PV systems. This report investigates the effects these modes of operation have on the inverter performance, array utilization, and power quality while focusing on conversion efficiency.

Lithium-ion batteries are a central technology to our daily lives with widespread use in mobile devices and electric vehicles. These batteries are also beginning to be widely used in electric grid infrastructure support applications which have stringent safety and reliability requirements. Typically, electrochemical performance data is not available for modelers to validate their simulations, mechanisms, and algorithms for lithium-ion battery performance and lifetime. In this paper, we report on the electrochemical performance of commercial 18650 cells at a variety of temperatures and discharge currents. We found that LiFePO 4 is temperature tolerant for discharge currents at or below 10 A whereas LiCoO 2 , LiNi x Co y Al 1-x-y O 2 , and LiNi 0.80 Mn 0.15 Co 0.05 O 2 exhibited optimal electrochemical performance when the temperature is maintained at 15 • C. LiNi x Co y Al 1-x-y O 2 showed signs of lithium plating at lower temperatures, evidenced by irreversible capacity loss and emergence of a high-voltage differential capacity peak. Furthermore, all cells need to be monitored for self-heating, as environment temperature and high discharge currents may elicit an unintended abuse condition. Overall, this study shows that lithium-ion batteries are highly application-specific and electrochemical behavior must be well understood for safe and reliable operation. Additionally, data collected in this study is available for anyone to download for further analysis and model validation. Lithium-ion batteries (LiBs) have become synonymous with portable electronics. The use of LiBs is expanding well beyond portable electronics into applications that require large energy and power capacities including electric vehicles, 1,2 and grid energy storage systems.3,4 However, with increasing system size and large scale deployments, safety issues associated with large LiB system failures are becoming important topics. [5][6][7][8] When determining the safety and reliability of an energy storage system (ESS), system performance and capacity loss are predictive parameters. For the successful implementation and commercial operation of utility class energy storage plants, safety and reliability define commercial feasibility and success. Despite a substantial body of research detailing the development of LiB technology, 9-19 detailed studies on the electrochemical performance as a function of application conditions have been limited. [20][21][22][23][24][25][26][27][28][29][30][31][32] When constructing an energy storage system, cells must be selected based on application-specific operation and performance characteristics. Application-specific cell-level requirements are highly unique and include operation temperatures and currents, stable output capacity and voltage, cell cycle or calendar life, and safety criteria. In support of this, cell manufacturers offer a wide variety of commercial cells that are designed to offer specific power and energy characteristics. Unfortunately, comparable information on electrochemical performance from c...

The inverter is still considered the weakest link in modern photovoltaic systems. Inverter failure can be classified into three major categories: manufacturing and quality control problems, inadequate design, and electrical component failure. It is often difficult to deconvolve the latter two of these, as electrical components can fail due to inadequate design or as a result of intrinsic defects. The aim of the current work is to utilize the extensive background in both inverter performance testing and component reliability found at Sandia National Laboratories to assess the role of component failures in PV performance and reliability. Although there is no consensus on the least reliable component in a modern inverter system, the IGBT is often blamed for failures and hence this was the first component we studied. A commercially available 600V, 60A, silicon IGBT found in common residential inverters was evaluated under normal and extreme operating conditions with DC and pulsed biasing schemes. Although most of the sample devices were robust even under extreme conditions, a few of the samples failed during operation well within the manufacturer-specified limits. Additionally, we have begun in situ monitoring of IGBTs as well as other components within an operating 700 W, single-phase inverter. The in situ testing will guide future device-level work since it allows us to understand the conditions that are experienced by inverter components in a realistic operating environment.