Search Results (40)

Building-applied photovoltaics (BAPV) offer a practical retrofit pathway for the prefabricated social housing estates of Central and Eastern Europe. This study assesses the solar and photovoltaic potential of post-WW II housing districts in Poznań, Poland, through a multi-scale workflow spanning the city, district, and building levels. Measured municipal rooftop data for 336 residential buildings in four districts were combined with tree-inclusive parametric solar simulations, calibrated against the rooftop solar cadastre (normalized mean bias error of +0.4% after calibration), to select South Winogrady and two representative buildings. Three PV design scenarios were then evaluated in roof, facade, and combined configurations using a techno-economic model that incorporates manufacturer-warranted degradation, maintenance, inverter replacement, and a ±25% electricity price and installation cost sensitivity envelope. Roof configurations pay back in 6.6–7.2 years (30-year return on investment of 286–321%), facade systems are economically defensible only on the best-exposed surfaces (8.9–13.8 years), and all configurations remain profitable even under the pessimistic bounding case. ENVI-met simulations of the same scenarios show localized pedestrian-level reductions in the Universal Thermal Climate Index of up to 2.41 °C near the PV-equipped buildings, persisting under 2050 climate projections. The results provide a transferable evidence chain for prioritizing BAPV retrofits in standardized post-war housing stock. Full article

To address delayed roof fracture, severe stress concentration, and strong strata pressure under thick–hard roof conditions, this study investigated the 1014 mining face of Yushuquan Coal Mine. A staged thick-plate model incorporating boundary-condition degradation was established based on Mindlin–Reissner thick-plate theory to analyze the deformation and stress redistribution characteristics of the thick–hard roof during mining. The evolution mechanism of the stress-concentration shell was systematically studied through theoretical analysis, physical simulation, numerical simulation, and field application. The results show that, with mining advancement, the boundary constraints of the thick–hard roof gradually evolve from four-sided clamped support to four-sided simply supported conditions. Meanwhile, the high-stress zone migrates from the goaf boundary toward the central suspended roof region. The stress-concentration shell undergoes a dynamic process of formation, expansion, failure, and reconstruction, and its instability is the main driving mechanism of large-scale roof caving. The plastic zone expands upward in an inverted funnel shape, while acoustic emission signals increase significantly before roof instability and exhibit strong precursor characteristics. Based on the evolution characteristics of the stress-concentration shell, a three-stage coordinated blasting technology was proposed to regulate the overburden load-bearing structure. Field application shows that this method effectively reduces suspended roof distance, caving block size, surrounding rock deformation, and hydraulic support pressure, thereby improving roof stability and mining safety. The results provide theoretical and engineering references for stability control of thick–hard roofs under similar mining conditions. Full article

Rock bursts frequently occur in the fault group area in China, seriously restricting the safe and efficient production of coal mines. Based on field investigation, physical experiments, and numerical simulation, this study investigates the rupture types and spatial evolution of microseismic events during the excavation of working face through fault group areas in the TB Coal Mine, where the hard roof asymmetric is cut by faults. It reveals the cooperative instability mechanism of faults and hard roof, as well as the mechanisms of rock burst. Targeted rock burst prevention measures are proposed, including “roof blasting to cut off dynamic and static load transfer” and “coal blasting to reduce abutment stress”. The results demonstrate the following: (1) during mining in fault group areas, the synchronous activation of faults induces shear-type and high-energy microseismic events and the subsequent movement of hard roof, which has been cut by faults, forms asymmetric parallelograms and symmetric inverted trapezoids, and induces tensile-type and high-energy microseismic events. The synchronous activation of faults and the breaking of the hard roof are identified as the primary reason for high-energy microseismic events. (2) As the fault dip angle approaches 90º, the compressive strength of the fault-segmented hard roof strata decreases. Under synchronous activation of faults, roof failure concentrates in the central, right, and left sections for fault combinations with dip angles of 70° + 70°, 90° + 70°, and 110° + 70°, respectively. (3) Numerical simulations reveal two rock burst mechanisms in faults—hard roof systems: a forward “high dynamic stress and high static stress” type and a rear “low dynamic stress and high static stress “ type, which is consistent with in situ monitoring data. (4) For the three stages in which the 502 working face approaches, passes through, and mines away from the fault group area, a stress relief scheme combining roof blasting and coal blasting is proposed. Compared with the 501 working face, during the mining of the 502 working face, the total microseismic frequency and energy decreased by 71.9% and 87.9%, respectively, and the effectiveness of these measures is verified. Full article

Stress evolution during overburden stabilization in non-pillar mining with roof-cutting and roadway formation (NMRRF) in inclined coal seams is highly complex due to the combined influence of seam dip angle and mining method. This study investigates the spatial stress evolution and structural stability of the overburden through numerical simulation and theoretical analysis. Results indicate that along the strike direction, the peak abutment pressure ahead of the working face decreases from the lower to the upper sections. As mining advances, the peak in the lower section shifts significantly forward, whereas changes in the middle and upper sections remain minimal. After advancing 150 m, upward expansion of the pressure-relief zone ceases, with the relief height in the lower goaf being smaller than that in the upper region. Along the dip direction, a pressure-relief zone forms in the roof and floor after 30 m of advancement, while stress concentration zones develop in the coal on both sides. With continued mining, the highest point of the pressure-relief zone gradually deviates from the central axis toward the upper section and eventually stabilizes within deeper strata at a certain distance from the axis. By 150 m of advancement, the relief zone peaks in the upper-middle section of the working face, and the height of the caved zone in the upper goaf exceeds that in the middle and lower parts. An asymmetric “inverted J-shaped” stress shell forms along the working face centerline, evolving into an overall asymmetric stress shell with its apex located in the upper goaf. A mechanical model of the overburden structure is established, yielding an expression for the three-dimensional stress shell morphology. Based on the stability mechanism of overburden movement and the failure modes of key block structures, support strategies for the mining face are proposed. The findings provide theoretical insights for non-pillar mining under similar geological conditions. Full article

Cities need photovoltaic (PV) systems to meet climate-neutral goals, yet dense urban forms and variable weather limit their output. This review synthesizes how machine learning (ML) models capture both static factors (orientation, roof, and façade geometry) and dynamic drivers (irradiance, transient shading, and meteorology) to predict and optimize urban PV performance. Following PRISMA 2020, we screened 111 records and analyzed 61 peer-reviewed studies (2020–2025), eight Horizon-Europe projects, as well as market reports. Deep learning models—mainly artificial and convolutional neural networks—typically reduce the mean absolute error by 10–30% (median ≈ 15%) compared with physical or empirical baselines, while random forests support transparent feature ranking. Short-term irradiance variability and local shading are the dominant dynamic drivers; roof shape and façade tilt lead the static set. Industry evidence aligns with these findings: ML-enabled inverters and module-level power electronics increase the measured annual yields by about 3–15%. A compact meta-analysis shows a pooled correlation of r ≈ 0.966 (R² ≈ 0.933; 95% CI 0.961–0.970) and a pooled log error ratio of −0.16 (≈15% relative error reduction), with moderate heterogeneity. Key gaps remain, such as limited data from equatorial megacities, sparse techno-economic or life-cycle metrics, and few validations under heavy soiling. We call for open datasets from multiple cities and climates, and for on-device ML (Tiny Machine Learning) with uncertainty reporting to support bankable, city-scale PV deployment.” Full article

This study investigates the asymmetric trade-off between cost and reliability in the optimal sizing of stand-alone Hybrid Renewable Energy Systems (HRESs) composed of photovoltaic panels (PV), wind turbines (WT), battery storage, a diesel generator (DG), and an inverter. The optimization is formulated as a multi-objective problem with Cost of Energy (CoE) and Loss of Power Supply Probability (LPSP) as conflicting objectives, highlighting that those small gains in reliability often require disproportionately higher costs. To ensure practical feasibility, the installation roof area limits both the number of PV panels, wind turbines, and batteries. Two metaheuristic algorithms—NSGA-II and MOPSO—are implemented in a Python-based framework with an Energy Management Strategy (EMS) to simulate operation under real-world load and resource profiles. Results show that MOPSO achieves the lowest CoE (0.159 USD/kWh) with moderate reliability (LPSP = 0.06), while NSGA-II attains a near-perfect reliability (LPSP = 0.0008) at a slightly higher cost (0.179 USD/kWh). Hypervolume (HV) analysis reveals that NSGA-II offers a more diverse Pareto front (HV = 0.04350 vs. 0.04336), demonstrating that explicitly accounting for asymmetric sensitivity between cost and reliability enhances the HRES design and that advanced optimization methods—particularly NSGA-II—can improve decision-making by revealing a wider range of viable trade-offs in complex energy systems. Full article

Deep coalbed methane (CBM) is challenging to develop due to considerable burial depth, high ground stress, and complex geological structures. However, modeling deep CBM in complex formations and setting reasonable simulation parameters to obtain reasonable results still needs exploration. This study presents a comprehensive equivalent finite element modeling method for deep CBM. The method is based on the cohesive element with pore pressure of the zero-thickness (CEPPZ) model to simulate hydraulic fracture propagation and characterize the effects of bedding interfaces and natural fractures. Taking Ordo’s deep CBM in China as an example, a comprehensive equivalent model for hydraulic fracturing was developed for the limestone layer–coal seam–mudstone layer. Then, the filtration parameters of the CEPPZ model and the permeability parameters of the deep CBM reservoir matrix were inverted and calibrated using on-site data from fracturing tests. Finally, the propagation path of hydraulic fractures was simulated under varying ground stress, construction parameters, and perforation positions. The results show that the hydraulic fractures are more likely to expand into layers with low minimum horizontal stress; the effect of a sizable fluid injection rate on the increase in hydraulic fracture length is noticeable; the improvement effect on fracture length and area gradually weakens with the increased fracturing fluid volume and viscosity; and when directional roof limestone/floor mudstone layer perforation is used, and the appropriate perforation location is selected, hydraulic fractures can communicate the coal seam to form a roof limestone/floor mudstone layer indirect fracturing. The results can guide the efficient development of deep CBM, improving the human society’s energy structure. Full article

In order to examine the fracture development law of overlying strata in goafs and to reasonably lay out a high gas-drainage roadway under gob-side entry retaining with roadside filling, the 91–105 working face of the Wangzhuang Coal Mine was selected as the engineering case study. The failure laws and fracture development characteristics of the overlying strata in both the strike and dip directions using gob-side entry retaining and roadside filling were studied through rock mechanic tests and PFC numerical simulations. The optimal layout of the high gas-drainage roadway was determined through theoretical analysis and coupled Fluent–PFC numerical simulations, and on-site monitoring was conducted to evaluate the extraction effects. The results indicate that the first weighting interval of the 91–105 working face was 40 m, while the periodic weighting interval was approximately 14 m. The height of the falling zone was 14.4 m, and the height of the gas-conducting fracture zone was 40.7 m. In the dip direction, compared with coal pillar retaining, gob-side entry retaining with roadside filling formed an inverted trapezoid secondary breaking zone above the retaining roadway. Using this method, the span of the separation zone increased to 30 m, and the collapse angle decreased to 52°, resulting in a shift in the separation zone—the primary space for gas migration—toward the goaf. It was determined that the optimal location of the high gas-drainage roadway was 28 m above the coal roof and 30 m horizontally from the return air roadway. Compared with the 8105 working face, this position was 10 m closer toward the goaf. On-site gas extraction monitoring data indicate that, at this optimized position, the gas concentration in the high gas-drainage roadway increased by 22%, and the net gas flow increased by 18%. Full article

Ground-based movable roof construction offers advantages such as flexible adjustment, energy conservation, environmental protection, improved comfort, structural stability, and high space utilization. However, it faces technical challenges such as complex structure, high cost, and high maintenance expenses. This paper, based on the practical experience of the Hainan Lingshui Swimming Pool project, uses numerical calculations to analyze the mechanical characteristics of a ground-based movable roof’s track beam and roof structure. The results show that by using a two-point lifting method based on the center of gravity and structural characteristics, finite element simulations indicate that the top of the inverted L-shaped main beam deflects upward by 0.27 cm, and the cantilever end deflects downward by 2.08 cm. Under the combination of dead load + live load, the semi-ground-based roof has a mid-span deflection of 70 mm, with linear and nonlinear stability safety factors of 5.9 and 3.2, respectively. After optimizing the track beam, the deformation at 15 m did not meet the requirements, and the cost at 20 m was too high. Ultimately, a pile length of 18 m was selected. Full article

To address the challenges in the collaborative control of strong mine pressure and surface damage during fully mechanized shallow soft coal seam top-coal caving mining, this study takes the 22,031 working face of Xindeng (Zhengzhou, China) Coal Mine as the research background. By combining analytical modeling and discrete-element granular flow simulation, this research elucidates how overburden fractures evolve and how the ground surface responds throughout the mining of shallow, soft coal seams. This research shows that the mechanical model analysis based on plate theory indicates that the first fracture of the immediate roof occurs 0.5 m from the goaf side of the mined-out area. Numerical simulations demonstrate that when the working face advances 80 m, the mining-induced influence extends to the surface. The displacement field of the overburden undergoes a dynamic temporal evolution law following the sequence of “rectangle–trapezoid” → “hyperbola-like” → “trapezoid”. During the advancement of the working face, the fracture pattern of the overburden evolves from “rectangle–trapezoid” to “trapezoid”, and the affected range on the surface transforms from an “inverted trapezoid” to a “trapezoid”. This study ultimately clarifies the dynamic law of collaborative deformation between the overburden and the surface, providing a theoretical basis for the safe mining of shallow coal seams, the prevention of roof accidents, and the optimization of mining technology. Full article

This paper investigates the repeated disturbance of weakly cemented overburden rock caused by closely spaced coal seam mining, focusing on the effect of water infiltration on the strength degradation of weakly cemented mudstone. The study compares the fissure and fissure distribution characteristics of the overburden rock under seepage conditions. It also examines the dynamic evolution of seepage parameters during repeated mining and their impact on the overburden rock’s bearing capacity and structural stability. The findings are as follows: (1) After water infiltration, the clay mineral content in weakly cemented mudstone decreases, leading to a significant reduction in strength, increased microcrack development, and a moisture content increase from 0% to 3.27%. Uniaxial compressive strength decreases by 59.83%. (2) In the absence of seepage effects, the fissure development zone in the overburden rock changes from a positive trapezoidal shape to an inverted trapezoidal one, with a water-conducting channel forming first on the setup entry side. When seepage is considered, the fissure development in the weakly cemented overburden rock significantly increases, and the location of large-scale fissure initiation and expansion is advanced by 80 m. (3) During coal seam mining, excavation of the upper seam reduces the pore water pressure in the roof, causing the region of reduced pore pressure to shift from a trapezoidal to an “M” shape. As mining progresses to the lower seam, a seepage channel forms near the setup entry and expands. (4) Under repeated mining conditions, seepage field evolution in the overburden rock triggers the migration and transmission of formation water and pore pressure. The sustained influence of fissure water infiltration and seepage pressure accelerates the development of the water flowing fracture zone. As the overburden rock experiences renewed fracturing and caving, secondary fissure formation intensifies the movement of formation water. Consequently, the bearing capacity and water-resistance properties of the overburden rock are gradually degraded, significantly increasing the extent of structural damage within weakly cemented mining overburden rock. Full article

The thick ore bodies in the Xianglushan tungsten mine have been irregularly mined, forming a super large, connected irregular goaf group and tall, isolated irregular pillars inside. At the same time, there is a production capacity task of recovering residual and dangerous ore bodies. This poses the potential for serious ground-pressure disasters, such as roof caving, pillar collapse, and large-scale goaf collapse during mining. Based on the actual needs of the site, we established a microseismic monitoring system. After analyzing the mining and filling processes and their relationships, and, combined with the distribution characteristics of microseismic multiple parameters, we constructed a ground-pressure disaster warning mode and mechanism. We analyzed the stability of the goaf, further formed a warning system, and achieved disaster warning. In response to the current situation of the difficulty of early warning of ground pressure in the Xianglushan tungsten mine, continuous on-site monitoring of existing goaves, point pillars, and strip pillars, as well as analysis of stress changes during dynamic mining and filling processes, we explored scientific and reasonable early warning mechanisms and models, understanding the relationship between the changes in microseismic parameters during dynamic mining and filling processes and ground pressure, studying and improving the reliability of underground microseismic monitoring and early warning, and achieved the internal connection between building early warning systems and the prevention of ground-pressure disasters. The results indicate that the mining and filling process of the ore body is the main factor in maintaining a stable and balanced distribution of underground ground pressure in mining engineering. Microseismic monitoring can invert the evolution of ground pressure and form a feedback system with ground-pressure warning, achieving mine safety management. Full article

The deeper penetration of renewables in the energy mix is an intense requirement in order to reduce global carbon dioxide emissions. In addition, new technologies are being developed, such as electric mobility and Distributed Generation (DG) in urban areas. However, the unpredictable fluctuations in energy generation from roof-installed PVs and the switching operation of their inverters greatly aggravate the already-present grid quality problems. In this paper, the Smart Boiler (SB) concept for grid quality improvement is presented. Furthermore, its experimental verification is implemented on a flexible testbed that accurately emulates several realistic scenarios for the low voltage distribution grid, under complex operating conditions. The proposed low-cost electronic kit, which contains a converter of fairly simple topology and requires connection to the internet, is used to upgrade conventional domestic boilers to smart devices. The SB automatically regulate the local reactive power flow, helping to stabilize the voltage level and suppress the grid current harmonic content, with both services provided in a matter of seconds. The higher the active power consumed and the denser the SB cluster, the wider the beneficial impact on the affected network area. While this service is provided, excess energy generated by PVs is temporarily stored as heat in the boiler tanks, given the users’ hot water consumption habits. The whole application, as a powerful demand-side management tool, proves beneficial for both the network operator and the end-user, especially when self-consumption is desirable in order to achieve a Nearly Zero Energy Building. Full article

Bayan Obo is a well-known polymetallic deposit containing significant quantities of rare earth elements, niobium, thorium, and iron. However, the epoch in which mineralization occurred and the mineralization process are still debated due to the complex nature of its mineralization and geological evolution. Inadequate geophysical exploration has further contributed to this lack of clarity surrounding critical issues, such as the deep link between the main orebody and the eastern orebody, the form and distribution of the extensive dolomite, and the geologic structures in the area. Therefore, we implemented the time-domain controlled-source electromagnetic method (CSEM) to acquire electrical structures at depths down to 2.5 km between the Main and Eastern mines. According to the inverted resistivity structure, in conjunction with existing geological and drilling data, we classified the main lithologies and faults based on their resistivity characteristics. Overall, the mineralized carbonatite reflects high to moderately high resistivity. The mineralized carbonatite dips overall from north to south, with a maximum extension depth not exceeding 1.5 km, and its range of occurrence is controlled by nearly east–west-striking faults distributed along the bounding line between the roof and floor rocks. The Main and Eastern mines are connected at depth, but the morphology and position of the ore bodies have significantly changed due to multiple phases of tectonic activity. The electrical structure does not reveal any obvious syncline structures, further refuting the traditional view that the Bayan syncline controls ore formation. Full article

An assessment of the thermal refurbishment of an outpatient medical center in a tropical location, such as the City of San Francisco de Campeche, was presented with the aim to diminish its energy consumption. A year-long energy audit of the facility was conducted to formulate and validate a numerical simulation model while scrutinizing enhancement strategies. The examined improvement alternatives encompass passive adjustments to the roof (utilizing insulating materials, applying reflective coatings, and installing a green roof), modifications to active systems incorporating inverter technology, and alterations to the walls via reflective paint. The outcomes of the simulated enhancement scenarios were assessed utilizing energy, environmental, and economic metrics: key performance index (KPI), equivalent CO₂ emission index (CEI), and net savings (NS). These results were subsequently juxtaposed against TOPSIS decision-making algorithms to ascertain the alternative that optimally balances the three options. It was identified that using reflective paint on the roof provides the best energy benefits and contributes to mitigating emissions from electricity use. Furthermore, combining this passive technology with the integration of inverter air conditioning systems offers the best economic return at the end of 15 years. For its part, the TOPSIS method indicated that by prioritizing the financial aspect, the reflective coating on the roof combined with inverter air conditioning is enough. However, adding a wall with insulating paint brings environmental and energy benefits. The results of this work serve as a starting point for the analysis of other post-occupied buildings in the region and others under tropical climatic conditions. Full article