| 1. |
- Benavente Araoz, Fabian Andres, et al.
(författare)
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An Aging Study of NCA/Si-Graphite Lithium-Ion Cells for Off-Grid Photovoltaic Systems in Bolivia
- 2021
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Ingår i: Journal of the Electrochemical Society. - : IOP Publishing Ltd. - 0013-4651 .- 1945-7111. ; 168:10
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Tidskriftsartikel (refereegranskat)abstract
- Performance and aging of lithium-ion 18650 cylindrical cells containing NCA and Si-graphite composite electrodes are investigated during long-term low current rate (∼0.1C) cycling protocol resembling charge/discharge profile of off-grid photovoltaic battery system. The cells are cycled within 30% and 75% state-of-charge ranges (SOC) with low, middle and high cut-off voltages. Electrochemical impedance spectroscopy data of full cylindrical cells exhibit severe aging for cells that have been cycled at higher cut-off voltage of 4.2 V. Symmetric cell impedance from each electrode shows that aging of NCA is dominant over aging of Si-graphite. Using a Newman-based impedance model, the NCA symmetrical cells' impedance spectra are parameterized to evaluate the aging modes. The resulting parameterization confirms increased particles' surface film resistance due to possible electrolyte oxidation and tortuosity increase at high cut-off voltages. Cycling the cells with middle and low cut-off voltages causes few significant changes when compared to calendar-aged samples. This opens up the possibility to significantly increase battery lifetime for small photovoltaic battery systems in rural areas of Bolivia. © 2021 The Author(s).
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| 2. |
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| 3. |
- Benavente Araoz, Fabian Andres, 1985-, et al.
(författare)
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Effect of Partial Cycling of NCA/Graphite Cylindrical Cells in Different SOC Intervals
- 2020
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Ingår i: Journal of the Electrochemical Society. - : Institute of Physics Publishing. - 0013-4651 .- 1945-7111. ; 167:4
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Tidskriftsartikel (refereegranskat)abstract
- A quasi-realistic aging test of NCA/graphite lithium-ion 18650 cylindrical cells is performed during a long-term low c-rate cycling and using a new protocol for testing and studying the aging. This to emulate a characteristic charge/discharge profile of off-grid PV-battery systems. The cells were partially cycled at four different cut-off voltages and two state of charge ranges (ΔSOC) for 1000 and 700 cycles over 24 months. Differential voltage analysis shows that a combination of loss of active material (LAM) and loss of lithium inventory (LLI) are the causes of capacity loss. Cells cycled with high cut-off voltages and wide ΔSOC (20% to 95%) were severely affected by material degradation and electrode shift. High cut-off voltage and narrow ΔSOC (65% to 95%) caused greater electrode degradation but negligible cell unbalance. Cell impedance is observed to increase in both cells. Cells cycled with middle to low cut-off voltages and narrow ΔSOC (35%-65% and 20% to 50%) had comparable degradation rates to calendar-aged cells. Cycling NCA/graphite cells with low c-rate and high cut-off voltages will degrade the electrode in the same way high c-rate would do. However, low c-rate at low and middle cut-off voltages greatly decrease cell degradation compared to similar conditions at middle to high c-rate, therefore increasing battery lifetime. © 2020 The Author(s).
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| 4. |
- Benavente Araoz, Fabian Andres, 1985-, et al.
(författare)
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Evaluation of the battery lifetime impact on PV systems techno-economic design
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Battery cycle life is a determining factor to enable the sustainability and reliability of off-grid photovoltaic (PV)/battery systems installed in rural communities. External circumstances such as remote localization and disperse distribution of communities, make the replacement and/or maintenance of battery systems with short cycle life rather difficult. Using experimental data of capacity retention from lithium-ion commercial batteries, we calculate the optimized loss of power supply probability (LPSP) and life cycle cost (LCC) for three applications operating in three locations of Bolivia. PV power and battery capacity design are estimated through optimization under the influence of suppressed demand. Optimization results show favorable LCCs when the location offers high solar irradiance in general. Suppressed demand has a marked impact on LPSP for cases where battery cycle life is limited due to aging. This is more evident for the household case, where the seasonal effect on the solar irradiance profile is considered. For the school and health center applications, a uniform load profile has positive impacts on the resulting LCC values.
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| 5. |
- Benavente Araoz, Fabian Andres, et al.
(författare)
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Experimental Investigation and Electrochemical Modeling of Aging Mechanisms on NCA and Si-graphite Electrodes Harvested from Off-grid PV Lithium-ion Cells
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Performance and aging of lithium-ion 18650 cylindrical cells containing NCA and Si-graphite composite electrodes are investigated during a long-term cycling process applying low current rates and different state of charge (SOC) ranges and cut-off voltages. Firstly, electrochemical impedance spectroscopy (EIS) is used to periodically extract impedance data from cylindrical cells. Secondly, NCA and Si-graphite electrode samples are reassembled into symmetrical cells to separate the impedance contribution from NCA and Si-graphite. Finally, using a physics-based impedance model, the symmetrical cells’ impedance spectra are parameterized to evaluate the aging modes. We introduce an additional pseudo-dimension to the model to distribute double layer capacitances on electrode-electrolyte interface, combined with a probability distribution function for total volumetric current, to fit the depressed semicircle in EIS spectra. The parameterization results show that high cut-off voltages cause increased particles’ surface film resistance of the NCA electrode and tortuosity increase in its structure. In Si-graphite electrodes, high cut-off voltages combined with wide ΔSOC range lead to increased surface film resistance attributed to the SEI layer and local limitations in solid lithium intercalation. Cycling the cells with middle and low cut-off voltages causes few significant changes when compared to calendar-aged samples. This opens up the possibility to significant increase of battery lifetime for applications such as small PV-battery systems.
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| 6. |
- Benavente Araoz, Fabian Andres, et al.
(författare)
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Photovoltaic/battery system sizing for rural electrification in Bolivia : Considering the suppressed demand effect
- 2019
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Ingår i: Applied Energy. - : Elsevier BV. - 0306-2619 .- 1872-9118. ; 235, s. 519-528
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Tidskriftsartikel (refereegranskat)abstract
- Rural electrification programs usually do not consider the impact that the increment of demand has on the reliability of off-grid photovoltaic (PV)/battery systems. Based on meteorological data and electricity consumption profiles from the highlands of Bolivian Altiplano, this paper presents a modelling and simulation framework for analysing the performance and reliability of such systems. Reliability, as loss of power supply probability (LPSP), and cost were calculated using simulated PV power output and battery state of charge profiles. The effect of increasing the suppressed demand (SD) by 20% and 50% was studied to determine how reliable and resilient the system designs are. Simulations were performed for three rural application scenarios: a household, a school, and a health centre. Results for the household and school scenarios indicate that, to overcome the SD effect, it is more cost-effective to increase the PV power rather than to increase the battery capacity. However, with an increased PV-size, the battery ageing rate would be higher since the cycles are performed at high state of charge (SOC). For the health centre application, on the other hand, an increase in battery capacity prevents the risk of electricity blackouts while increasing the energy reliability of the system. These results provide important insights for the application design of off-grid PV-battery systems in rural electrification projects, enabling a more efficient and reliable source of electricity.
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| 7. |
- Zhang, Yang, et al.
(författare)
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Battery sizing and rule-based operation of grid-connected photovoltaic-battery system : A case study in Sweden
- 2017
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Ingår i: Energy Conversion and Management. - : Elsevier. - 0196-8904 .- 1879-2227. ; 133, s. 249-263
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Tidskriftsartikel (refereegranskat)abstract
- The optimal components design for grid-connected photovoltaic-battery systems should be determined with consideration of system operation. This study proposes a method to simultaneously optimize the battery capacity and rule-based operation strategy. The investigated photovoltaic-battery system is modeled using single diode photovoltaic model and Improved Shepherd battery model. Three rule-based operation strategies—including the conventional operation strategy, the dynamic price load shifting strategy, and the hybrid operation strategy—are designed and evaluated. The rule-based operation strategies introduce different operation parameters to run the system operation. multi-objective Genetic Algorithm is employed to optimize the decisional variables, including battery capacity and operation parameters, towards maximizing the system's Self Sufficiency Ratio and Net Present Value. The results indicate that employing battery with the conventional operation strategy is not profitable, although it increases Self Sufficiency Ratio. The dynamic price load shifting strategy has similar performance with the conventional operation strategy because the electricity price variation is not large enough. The proposed hybrid operation strategy outperforms other investigated strategies. When the battery capacity is lower than 72 kW h, Self Sufficiency Ratio and Net Present Value increase simultaneously with the battery capacity.
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