6,894 research outputs found
Improving optimal control of grid-connected lithium-ion batteries through more accurate battery and degradation modelling
The increased deployment of intermittent renewable energy generators opens up
opportunities for grid-connected energy storage. Batteries offer significant
flexibility but are relatively expensive at present. Battery lifetime is a key
factor in the business case, and it depends on usage, but most techno-economic
analyses do not account for this. For the first time, this paper quantifies the
annual benefits of grid-connected batteries including realistic physical
dynamics and nonlinear electrochemical degradation. Three lithium-ion battery
models of increasing realism are formulated, and the predicted degradation of
each is compared with a large-scale experimental degradation data set
(Mat4Bat). A respective improvement in RMS capacity prediction error from 11\%
to 5\% is found by increasing the model accuracy. The three models are then
used within an optimal control algorithm to perform price arbitrage over one
year, including degradation. Results show that the revenue can be increased
substantially while degradation can be reduced by using more realistic models.
The estimated best case profit using a sophisticated model is a 175%
improvement compared with the simplest model. This illustrates that using a
simplistic battery model in a techno-economic assessment of grid-connected
batteries might substantially underestimate the business case and lead to
erroneous conclusions
Factoring the Cycle Aging Cost of Batteries Participating in Electricity Markets
When participating in electricity markets, owners of battery energy storage
systems must bid in such a way that their revenues will at least cover their
true cost of operation. Since cycle aging of battery cells represents a
substantial part of this operating cost, the cost of battery degradation must
be factored in these bids. However, existing models of battery degradation
either do not fit market clearing software or do not reflect the actual battery
aging mechanism. In this paper we model battery cycle aging using a piecewise
linear cost function, an approach that provides a close approximation of the
cycle aging mechanism of electrochemical batteries and can be incorporated
easily into existing market dispatch programs. By defining the marginal aging
cost of each battery cycle, we can assess the actual operating profitability of
batteries. A case study demonstrates the effectiveness of the proposed model in
maximizing the operating profit of a battery energy storage system taking part
in the ISO New England energy and reserve markets
Economic optimization of component sizing for residential battery storage systems
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.Web of Science107art. no. 83
Effects of cycling on lithium-ion battery hysteresis and overvoltage
Currently, lithium-ion batteries are widely used as energy storage systems for mobile applications.
However, a better understanding of their nature is still required to improve battery management
systems (BMS). Overvoltages and open-circuit voltage (OCV) hysteresis provide valuable information
regarding battery performance, but estimations of these parameters are generally inaccurate, leading
to errors in BMS. Studies on hysteresis are commonly avoided because the hysteresis depends on
the state of charge and degradation level and requires time-consuming measurements. We have
investigated hysteresis and overvoltages in Li(NiMnCo)O2/graphite and LiFePO4/graphite commercial
cells. Here we report a direct relationship between an increase in OCV hysteresis and an increase in
charge overvoltage when the cells are degraded by cycling. We fnd that the hysteresis is related to
difusion and increases with the formation of pure phases, being primarily related to the graphite
electrode. These fndings indicate that the graphite electrode is a determining factor for cell efciency.Peer ReviewedPostprint (published version
Optimal Regulation Response of Batteries Under Cycle Aging Mechanisms
When providing frequency regulation in a pay-for-performance market,
batteries need to carefully balance the trade-off between following regulation
signals and their degradation costs in real-time. Existing battery control
strategies either do not consider mismatch penalties in pay-for-performance
markets, or cannot accurately account for battery cycle aging mechanism during
operation. This paper derives an online control policy that minimizes a battery
owner's operating cost for providing frequency regulation in a
pay-for-performance market. The proposed policy considers an accurate
electrochemical battery cycle aging model, and is applicable to most types of
battery cells. It has a threshold structure, and achieves near-optimal
performance with respect to an offline controller that has complete future
information. We explicitly characterize this gap and show it is independent of
the duration of operation. Simulation results with both synthetic and real
regulation traces are conducted to illustrate the theoretical results
A 3D Framework for Characterizing Microstructure Evolution of Li-Ion Batteries
Lithium-ion batteries are commonly found in many modern consumer devices, ranging from portable computers and mobile phones to hybrid- and fully-electric vehicles. While improving efficiencies and increasing reliabilities are of critical importance for increasing market adoption of the technology, research on these topics is, to date, largely restricted to empirical observations and computational simulations. In the present study, it is proposed to use the modern technique of X-ray microscopy to characterize a sample of commercial 18650 cylindrical Li-ion batteries in both their pristine and aged states. By coupling this approach with 3D and 4D data analysis techniques, the present study aimed to create a research framework for characterizing the microstructure evolution leading to capacity fade in a commercial battery. The results indicated the unique capabilities of the microscopy technique to observe the evolution of these batteries under aging conditions, successfully developing a workflow for future research studies
Techno-Economic Analysis and Optimal Control of Battery Storage for Frequency Control Services, Applied to the German Market
Optimal investment in battery energy storage systems, taking into account
degradation, sizing and control, is crucial for the deployment of battery
storage, of which providing frequency control is one of the major applications.
In this paper, we present a holistic, data-driven framework to determine the
optimal investment, size and controller of a battery storage system providing
frequency control. We optimised the controller towards minimum degradation and
electricity costs over its lifetime, while ensuring the delivery of frequency
control services compliant with regulatory requirements. We adopted a detailed
battery model, considering the dynamics and degradation when exposed to actual
frequency data. Further, we used a stochastic optimisation objective while
constraining the probability on unavailability to deliver the frequency control
service. Through a thorough analysis, we were able to decrease the amount of
data needed and thereby decrease the execution time while keeping the
approximation error within limits. Using the proposed framework, we performed a
techno-economic analysis of a battery providing 1 MW capacity in the German
primary frequency control market. Results showed that a battery rated at 1.6
MW, 1.6 MWh has the highest net present value, yet this configuration is only
profitable if costs are low enough or in case future frequency control prices
do not decline too much. It transpires that calendar ageing drives battery
degradation, whereas cycle ageing has less impact.Comment: Submitted to Applied Energ
Advances in Repurposing and Recycling of Post-Vehicle-Application Lithium-Ion Batteries
Increased electrification of vehicles has increased the use of lithium-ion batteries for energy storage, and raised the issue of what to do with post-vehicle-application batteries. Three possibilities have been identified: 1) remanufacturing for intended reuse in vehicles; 2) repurposing for non-vehicle, stationary storage applications; and 3) recycling, extracting the precious metals, chemicals and other byproducts. Advances in repurposing and recycling are presented, along with a mathematical model that forecasts the manufacturing capacity needed for remanufacturing, repurposing, and recycling. Results obtained by simulating the model show that up to a 25% reduction in the need for new batteries can be achieved through remanufacturing, that the sum of repurposing and remanufacturing capacity is approximately constant across various scenarios encouraging the sharing of resources, and that the need for recycling capacity will be significant by 2030. A repurposing demonstration shows the use of post-vehicle-application batteries to support a semi-portable recycling platform. Energy is collected from solar panels, and dispensed to electrical devices as required. Recycling may be complicated: lithium-ion batteries produced by different manufacturers contain different active materials, particularly for the cathodes. In all cases, however, the collecting foils used in the anodes are copper, and in the cathodes are aluminum. A common recycling process using relatively low acid concentrations, low temperatures, and short time periods was developed and demonstrated
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