Cong Nam Truong

Bio: Cong Nam Truong is an academic researcher from Technische Universität München. The author has contributed to research in topics: Battery (electricity) & Photovoltaic system. The author has an hindex of 8, co-authored 18 publications receiving 487 citations.

Economics of Residential Photovoltaic Battery Systems in Germany: The Case of Tesla’s Powerwall

Abstract: Residential photovoltaic (PV) battery systems increase households’ electricity self-consumption using rooftop PV systems and thus reduce the electricity bill. High investment costs of battery systems, however, prevent positive financial returns for most present residential battery installations in Germany. Tesla Motors, Inc. (Palo Alto, CA, USA) announced a novel battery system—the Powerwall—for only about 25% of the current German average market price. According to Tesla’s CEO Elon Musk, Germany is one of the key markets for their product. He has, however, not given numbers to support his statement. In this paper, we analyze the economic benefit of the Powerwall for end-users with respect to various influencing parameters: electricity price, aging characteristics of the batteries, topology of battery system coupling, subsidy schemes, and retrofitting of existing PV systems. Simulations show that three key-factors strongly influence economics: the price gap between electricity price and remuneration rate, the battery system’s investment cost, and the usable battery capacity. We reveal under which conditions a positive return on invest can be achieved and outline that the Powerwall could be a worthwhile investment in multiple, but not all, scenarios investigated. Resulting trends are generally transferrable to other home storage products.

Economic Optimization of Component Sizing for Residential Battery Storage Systems

Abstract: Battery energy storage systems (BESS) coupled with rooftop-mounted residential photovoltaic (PV) generation, designated as PV-BESS, draw increasing attention and market penetration as more and more such systems become available. The manifold BESS deployed to date rely on a variety of different battery technologies, show a great variation of battery size, and power electronics dimensioning. However, given today’s high investment costs of BESS, a well-matched design and adequate sizing of the storage systems are prerequisites to allow profitability for the end-user. The economic viability of a PV-BESS depends also on the battery operation, storage technology, and aging of the system. In this paper, a general method for comprehensive PV-BESS techno-economic analysis and optimization is presented and applied to the state-of-art PV-BESS to determine its optimal parameters. Using a linear optimization method, a cost-optimal sizing of the battery and power electronics is derived based on solar energy availability and local demand. At the same time, the power flow optimization reveals the best storage operation patterns considering a trade-off between energy purchase, feed-in remuneration, and battery aging. Using up to date technology-specific aging information and the investment cost of battery and inverter systems, three mature battery chemistries are compared; a lead-acid (PbA) system and two lithium-ion systems, one with lithium-iron-phosphate (LFP) and another with lithium-nickel-manganese-cobalt (NMC) cathode. The results show that different storage technology and component sizing provide the best economic performances, depending on the scenario of load demand and PV generation.

Evaluation of grid-level adaptability for stationary battery energy storage system applications in Europe

Abstract: This work discusses the grid-level suitability for stationary battery energy storage systems based on lithium ion technology in general, focusing on the integration of such systems in the low-voltage grid-level in Europe. The vast majority of recent research regarding stationary battery storage systems focuses on single-electricity-grid voltage levels, whereas the interaction of different electricity grid-levels has been widely neglected. Challenges in distribution grids mostly originate from the quantity of challenges in low-voltage grids, stationary battery energy storage systems that are operated in low-voltage grids may reduce these challenges. Therefore, this work investigates stationary battery energy storage systems installed in low-voltage grids and their effects on superimposed grid-levels. Simulation results show that grid challenges, addressed by battery storage systems in low-voltage grids, have positive multiplicative impacts on upper grid levels, reducing local grid demand and lowering power peak stress. A proposal is presented for a low-voltage grid battery storage system that can be operated to fulfill the aforementioned functionality and yield the benefits via a multi-purpose or multi-tasking battery storage system.

Analysis and Optimization of Pulse Dynamics for Magnetic Stimulation

Abstract: Magnetic stimulation is a standard tool in brain research and has found important clinical applications in neurology, psychiatry, and rehabilitation. Whereas coil designs and the spatial field properties have been intensively studied in the literature, the temporal dynamics of the field has received less attention. Typically, the magnetic field waveform is determined by available device circuit topologies rather than by consideration of what is optimal for neural stimulation. This paper analyzes and optimizes the waveform dynamics using a nonlinear model of a mammalian axon. The optimization objective was to minimize the pulse energy loss. The energy loss drives power consumption and heating, which are the dominating limitations of magnetic stimulation. The optimization approach is based on a hybrid global-local method. Different coordinate systems for describing the continuous waveforms in a limited parameter space are defined for numerical stability. The optimization results suggest that there are waveforms with substantially higher efficiency than that of traditional pulse shapes. One class of optimal pulses is analyzed further. Although the coil voltage profile of these waveforms is almost rectangular, the corresponding current shape presents distinctive characteristics, such as a slow low-amplitude first phase which precedes the main pulse and reduces the losses. Representatives of this class of waveforms corresponding to different maximum voltages are linked by a nonlinear transformation. The main phase, however, scales with time only. As with conventional magnetic stimulation pulses, briefer pulses result in lower energy loss but require higher coil voltage than longer pulses.

Lithium-Ion Battery Storage for the Grid—A Review of Stationary Battery Storage System Design Tailored for Applications in Modern Power Grids

Abstract: Battery energy storage systems have gained increasing interest for serving grid support in various application tasks. In particular, systems based on lithium-ion batteries have evolved rapidly with a wide range of cell technologies and system architectures available on the market. On the application side, different tasks for storage deployment demand distinct properties of the storage system. This review aims to serve as a guideline for best choice of battery technology, system design and operation for lithium-ion based storage systems to match a specific system application. Starting with an overview to lithium-ion battery technologies and their characteristics with respect to performance and aging, the storage system design is analyzed in detail based on an evaluation of real-world projects. Typical storage system applications are grouped and classified with respect to the challenges posed to the battery system. Publicly available modeling tools for technical and economic analysis are presented. A brief analysis of optimization approaches aims to point out challenges and potential solution techniques for system sizing, positioning and dispatch operation. For all areas reviewed herein, expected improvements and possible future developments are highlighted. In order to extract the full potential of stationary battery storage systems and to enable increased profitability of systems, future research should aim to a holistic system level approach combining not only performance tuning on a battery cell level and careful analysis of the application requirements, but also consider a proper selection of storage sub-components as well as an optimized system operation strategy.

Exploring competitive features of stationary sodium ion batteries for electrochemical energy storage

Abstract: Owing to the excellent abundance and availability of sodium reserves, sodium ion batteries (NIBs) show great promise for meeting the material supply and cost demands of large-scale energy storage systems (ESSs) used for the application of renewable energy sources and smart grids. However, the cost advantages of stationary NIBs alone are not enough to ensure their commercial success. In this review, we summarize the emerging attractive characteristics of stationary NIBs, such as high-rate capability, all-climate operation, and full-battery recyclability. Together with inherent cost advantages, these merits have resulted in an excellent compatibility between stationary NIBs and large-scale ESSs that dictates their validity in practical applications. Representative electrode materials are highlighted to illustrate advances in corresponding features. The insights presented in this review can inspire further research interest into NIB design and serve as a guide for the application of NIBs in large-scale stationary energy storage.

Circular economy strategies for electric vehicle batteries reduce reliance on raw materials

Abstract: The wide adoption of lithium-ion batteries used in electric vehicles will require increased natural resources for the automotive industry. The expected rapid increase in batteries could result in new resource challenges and supply-chain risks. To strengthen the resilience and sustainability of automotive supply chains and reduce primary resource requirements, circular economy strategies are needed. Here we illustrate how these strategies can reduce the extraction of primary raw materials, that is, cobalt supplies. Material flow analysis is applied to understand current and future flows of cobalt embedded in electric vehicle batteries across the European Union. A reference scenario is presented and compared with four strategies: technology-driven substitution and technology-driven reduction of cobalt, new business models to stimulate battery reuse/recycling and policy-driven strategy to increase recycling. We find that new technologies provide the most promising strategies to reduce the reliance on cobalt substantially but could result in burden shifting such as an increase in nickel demand. To avoid the latter, technological developments should be combined with an efficient recycling system. We conclude that more-ambitious circular economy strategies, at both government and business levels, are urgently needed to address current and future resource challenges across the supply chain successfully. New battery chemistry can help reduce the reliance on Co for electric vehicles. However, to avoid burden shifting to other resources such as Ni, circular economy strategies with enhanced battery traceability and recycling could contribute substantially to the reduction of primary Co demand from the automotive industry.