Abstract

The increasing penetration of distributed renewable generation and the electrification of end uses are making flexibility procurement a critical requirement for distribution system operators (DSOs). This has led to the emergence of local flexibility markets (LFMs) across several countries, where DSOs procure active power regulation services through technology-neutral competitive auctions. This paper presents an optimization framework based on mixed-integer linear programming to determine the optimal power capacity that a user should reserve when participating in a LFM. The model explicitly accounts for the electricity bill structure and enables the joint provision of explicit and implicit flexibility. The proposed approach is applied to a real multi-energy microgrid participating in the LFM established by Unareti within the MiNDFlex pilot project, where the DSO conducts monthly forward auctions to secure upward flexibility capacity. Results show that, in the absence of a battery energy storage system, participation in the market is not economically viable, as the revenues from flexibility services fail to offset the increase in electricity consumption and associated bill components. Conversely, when storage is available, participation becomes profitable: under average October 2025 auction prices for reserve availability (475.5 k€/MW/y) and service activation (57.6 €/MWh), the configuration with storage achieves a net economic gain of 31.8 k€ per month. These findings highlight the importance of accounting for implicit flexibility signals embedded in electricity tariffs and the pivotal role of storage in enhancing the economic profitability of participation in LFMs.

Abstract

In this study, thermal performance of anincreasing-pressure endothermic power cycle (IPEPC) has been numerically investigated. In the IPEPC, a downhole heat exchanger (DHE) is used to replace atraditional evaporatoron the ground. Matching relationships amongfour key parameters (DHEinlet pressure, DHElength, geothermal water temperature, and geothermal water mass flow rate) and the working fluid mass flow rateare quantitatively analyzed.The research results indicate that, when the DHE inlet pressure is 3.7MPa and the geothermal water temperature is 95°C, the optimal working fluid mass flow rate is 9kg/s, corresponding to amaximum net poweroutputof 45.11kW. When the geothermal water temperature is 130°C, the optimal working fluid mass flow rate is 9.5kg/s, withamaximum net power outputof111.7kW. As the geothermal water mass flow rate increases, the optimal working fluid mass flow rateincreases synchronously, and the net power output under this matched operating condition also shows an upward trend. Under the conditionthatthe working fluid mass flow rate is low (ranging from 3to 6kg/s), using a shorter DHE length results in a better thermal performance.When theworking fluid mass flow rateis high (ranging from 6to 12 kg/s), using a longer DHE is an effective way to increase the net power output.The findings of this study provide theoretical guidance for IPEPC system optimization and engineeringdesign.

Abstract

For CAES (Compressed Air Energy Storage) system, using underground wellbore as storage spaces for compressed air can utilize the heat of underground reservoirs, thus achieving the increase in the production temperature of the air during the energy release stage, thereby improving the efficiency of the system. In this study, a combined underground wellbore CAES and heating (W-CAESH) thermodynamic cycle is put forward, and the performance of this system is investigated. Based on the theory of local thermal equilibrium, the actual gas state equation, and thermodynamic theory, heat transfer in the reservoir and the thermo-dynamic cycle performance are simulated. First, the heat transfer between the compressed air and Hot Dry Rock (HDR) reservoir is investigated. Then the power generating and energy storage performance are analyzed. Finally, the overall performance of energy storage and heating is evaluated in different operating conditions. Results indicate that the Round-Trip Efficiency (RTE) of the wellbore CAES is 55.93–62.25%, which is increased 15~20% compared the conventional CAES systems. When heating load is considered, the overall efficiency of this system is about 96.17%–97.47% as mass flow rate varies between 10–20 kg/s, and the overall efficiency rises with compressed-air mass flow.

Abstract

This paper examined how critical climatic factors, specifically rainfall, temperature, and humidity, affect hydropower generation at the Kihansi Hydropower Plant in Tanzania. The analysis was based on data collected from 2010 to 2023, by using Principal Component Analysis, Pearson correlation, and multiple linear regression analysis, processed through SPSS software.
The PCA results revealed that rainfall, temperature, and humidity together explained 79.09% of the total variation in hydropower generation at the plant. Notably, rainfall and humidity alone accounted for 53.28%, while temperature contributed 25.94%. This means that changes in these climatic variables account for nearly 80% of the fluctuations in power generation, a critical insight for operational planning.
Pearson correlation analysis showed a strong positive relationship between rainfall and humidity (r = 0.541, p < 0.001), confirming that higher rainfall periods are typically accompanied by increased humidity, which influences water availability. The correlation between rainfall and temperature was weak and negative (r = -0.100, p = 0.198), while humidity and temperature showed no significant relationship (r = 0.030, p = 0.704). The multiple linear regression analysis shows that rainfall had a strong positive impact (β = 0.844, p < 0.001), with a 1 mm increase raising generation by 0.180 MW. Temperature showed a significant negative effect (β = -0.114, p = 0.002), where a 1°C rise reduced output by 2.180 MW due to higher evaporation. Humidity had a positive but insignificant effect (β = 0.041, p = 0.344). The model explained 78.5% of the total variance in hydropower generation (R² = 0.785). This confirms that rainfall is the most influential factor at Kihansi.

Abstract

The shared electric bicycles are increasingly used under the goal of “carbon neutrality,” but convenient charging remains a current challenge. This paper designs a large-area Wireless Power Transfer (WPT) system based on a rectangular single-turn coreless Transmitting coil, suitable for charging of multiple lightweight electric vehicles in public spaces. The system utilizes the transmitting coil to generate a uniform weak electromagnetic field, supporting flexible placement of the receiver and enabling charging of multiple devices, adhering to the ICNIRP (International Commission on Non-Ionizing Radiation Protection) “RF EMF Guidelines 2020” to ensure human electromagnetic safety. However, in a magnetic induction power transfer system, metal foreign objects, the vehicle body, and the number of device connections can affect changes in system parameters. To address detuning issues caused by multiple device connections and metallic foreign objects, a Switch-Controlled Capacitor (SCC) dynamic tuning technique is proposed to ensure stable and efficient system operation in the Zero Phase Angle (ZPA) state. The experiments achieved a transmission efficiency of 69.957% with a single load and 73.867% with two loads. Moreover, the results indicate that the transmission efficiency can be further enhanced by increasing the input power and the number of loads.

Abstract

The air starvation protocol is a common method for rapid activation of proton exchange membrane fuel cells (PEMFCs) due to its efficiency. However, its impact on the spatial uniformity of the membrane electrode assembly (MEA) performance remains poorly understood, as conventional methods only assess overall performance. This study proposes a novel methodology that correlates in-situ temperature distribution during activation with ex-situ electrochemical performance mapping to unravel this critical issue. During the air starvation activation of a 300 cm² MEA, the temperature was monitored in real-time at 11 strategic locations on the bipolar plates. Carefully divide the MEA into 3 samples of 5 cm² each, which are distributed along the direction of oxygen flow. Each segment underwent comprehensive electrochemical characterization including cyclic voltammetry (CV), linear sweep voltammetry (LSV), and electrochemical impedance spectroscopy (EIS).
The results revealed significant spatial heterogeneity. In-situ temperature monitoring identified pronounced thermal gradients: a maximum difference of 1.6°C within a single bipolar plate and 4.7°C across the 5-cell stack, consistently showing higher temperatures near the oxygen outlet Ex-situ analysis confirmed substantial performance inconsistency across the MEA. The electrochemical active specific surface area (ECSA) derived from CV varied by up to 61.9% between regions—peaking at the oxygen outlet (15.73 m²/g) and bottoming at the center (5.99 m²/g)—consistent with the local temperature fluctuations during activation.
Critically, an association was observed between the local temperature profiles during activation and the final electrochemical parameters. Areas with higher activation temperatures tended to exhibit different ECSA and mass transport properties, suggesting localized variations in the activation efficacy. This work provides valuable insights into the heterogeneous nature of the air starvation process and demonstrates how such inhomogeneity can lead to spatial performance inconsistencies in the MEA. Our findings suggest that future activation protocols could be improved by considering spatial uniformity to enhance overall MEA quality.

Abstract

Although increasing the Proton exchange membrane fuel cells (PEMFCs) operating temperature to near the water-boiling-point enhances mass transport and reaction kinetics for automotive applications, the combined effects of elevated temperature and high current load significantly accelerate the degradation of key PEMFC components. This study performed 1,000 dynamic load cycles (DLC) based on the New European Driving Cycle (NEDC) on single cells (working area: 25 cm²) at operating temperatures of 75 °C and 95 °C. In-situ electrochemical tests—including polarization curves, electrochemical impedance spectroscopy (EIS), and cyclic voltammetry (CV)—were used to evaluate the degradation of PEMFC performance. Additionally, cross-assembling aged and fresh gas diffusion layers (GDLs) with corresponding catalyst coating membranes (CCMs) enabled quantitative separation of their respective contributions to performance degradation. The results show that voltage decays approximately linearly with cycling, with faster degradation at 95 °C than at 75 °C under identical loading conditions. At 2.0 A·cm⁻², the overall degradation rate increases from 17.58% at 75 °C to 28.45% at 95 °C. The electrochemically active surface area (ECSA) decreased by 42.92% at 75 °C and 55.26% at 95 °C, corresponding to a substantial increase in Rmt observed through EIS. Cross-assembly experiments showed that at 2.0 A·cm⁻², replacing only the GDL with an aged one (paired with a fresh CCM) reduced the output voltage to 0.49 V at 75 °C and 0.464 V at 95 °C—corresponding to decreases of 7.37% and 12.29%, respectively, compared to the initial values. In contrast, using aged CCMs with fresh GDLs resulted in greater voltage losses—11.68% at 75 °C and 22.69% at 95 °C—indicating that CCM degradation plays a more significant role in PEMFC performance decline at elevated temperatures.

Abstract

The Chunfeng Oilfield represents a typical shallow-buried, thin reservoir of extra-heavy oil. Following multiple rounds of steam huff and puff, the field faces challenges such as declining formation pressure, reduced heating radius, decreased periodic production, and a sharp increase in periodic water cut. This study utilizes geological data and production statistics from the Chunfeng Oilfield to design physical simulation experiments for various development methods following high-cycle steam huff and puff, grounded in similarity criteria. The research validates the temperature distribution characteristics and production dynamics associated with high-cycle steam huff and puff, allowing for a comparative analysis of temperature distribution and production dynamics across different development methods at various stages. The results indicate that the N2 and VR composite steam flooding exhibits the highest levels of steam chamber development, production duration, and recovery rates, achieving a stage recovery rate of 42.3%. These findings provide valuable insights for the development of shallow-thin extra-heavy oil reservoirs.

Abstract

With increasing demands for energy efficiency, plate heat exchangers have gained widespread application in heating and cooling pump systems due to their highly efficient and compact heat transfer performance. Addressing the limitations of traditional selection methods in terms of accuracy and adaptability, this paper proposes a hybrid prediction model integrating data-driven approaches with physical constraints. By incorporating the narrow point theory to define the physical boundaries of the heat transfer area and leveraging the non-linear fitting capabilities of neural networks, the method achieves high-precision prediction of the plate heat exchanger’s heat transfer area under various operating conditions. Further global optimisation of neural network weights and biases through genetic algorithms enhances the model’s generalisation capability and predictive performance. Results demonstrate that the maximum prediction error of the hybrid model, prior to optimisation, did not exceed 10.36%, reducing to below 7.97% post-optimisation. Overall accuracy improved by 11.9% compared to conventional methods. This approach provides effective support for the precise selection of plate heat exchangers and the optimised design of heating and cooling pump systems.

Abstract

This study investigates the suppression effect of CO₂ foam flooding on fluid channeling and its mechanism for enhancing oil displacement efficiency through two-dimensional visualization flat-plate experiments combined with image processing techniques to systematically analyze fluid distribution and sweep characteristics during the displacement process. The results indicate that CO₂ flooding is influenced by viscous fingering, achieving a sweep efficiency of only 31.8% with an oil saturation of 54.8%. In contrast, CO₂ foam flooding effectively seals high-permeability channels through the Jamin effect, redirecting fluid flow to low-permeability zones, significantly improving CO₂ sweep efficiency and displacement performance. Microscopic observations reveal that CO₂ foam consists of tiny bubbles, and their migration and sealing behaviors are the microscopic mechanisms underlying the improved macroscopic effects. This study provides visualization experimental evidence and quantitative evaluation methods for CO₂ foam flooding in suppressing channeling and enhancing oil recovery.