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International audience; The high variability and uncertainty introduced into modern electrical distribution systems due to decentralized renewable energy generators requires new solutions for grid management and power quality assurance. One of these possible solutions includes grid integrated energy storage. The appropriate size and placement of decentralized storage is highly dependent on purpose of the battery system and expected operational strategy. However, battery operational strategies are difficult to simulate simultaneously during a sizing and placement planning calculation. The motivation of this paper is to propose an algorithm that is capable of integrating sizing, placement and operational strategies of batteries into an Optimal Power Flow (OPF) distribution grid planning tool. The choice of the OPF approach permits to account for grid constraints which is more adapted for grid-connected storage devices compared to other approaches in the state of the art that are based only on an email balance analysis. This paper presents an alternating current (AC) multi-temporal OPF algorithm that uses a convex relaxation of the power flow equations to guarantee exact and optimal solutions with high algorithmic performance. The algorithm is unique and innovative due to the fact that it combines the simultaneous optimization of placement and sizing of storage devices taking into account load curves, photovoltaic (PV) production profiles, and distribution grid power quality constraints. The choice to invest in battery capacity is highly sensitive to the price of battery systems. The investment in battery systems solely for reducing losses an operational costs was proven not to be cost effective, however when battery systems are allowed to buy and sell electricity based on variable market prices they become cost effective. The assumptions used for this study shows that current battery system prices are too high to be cost effective even when allowing battery system market participation.

International audience; The detailed modeling of distribution grids is expected to be critical to understand the current functionality limits and necessary retrofits to satisfy integration of massive amounts of distributed generation, energy storage devices and the electric consumption demand of the future. Due to the highly dimensional non-convex characteristics of the power flow equations, convex relaxations have been used to ensure an efficient calculation time. However, these relaxations have been proven to be inexact during periods of high RES injection. In this paper additional linear constraints were introduced in the power flow formulation to guaranty an exact relaxation. This convex relaxation is then applied within a multi-temporal algorithm in order to evaluate the benefits of storage grid integration. The case study of a French medium voltage feeder is studied to evaluate the maximum capacity of the grid to host RES sources and the advantages of storage systems in reducing curtailment of RES.

It is well-known that decision-making processes benefit from the inclusion of uncertainty. Such optimization problems typically extend over a control horizon and could span multiple locations or regions. In addition to uncertainty, these optimization problems require as input a trajectory of scalar values that exhibits the correct spatial and temporal dependencies. Probabilistic forecasts quantify the uncertainty by means of quantiles, predictive distributions or ensembles for a forecast horizon and a site or a region separately, and therefore generally lack spatial and temporal dependencies. One solution is to use a copula to model the spatial or temporal dependencies, which, in combination with the probabilistic forecasts, can be used to issue correlated trajectory forecasts. However, there is currently no benchmark model available to compare multivariate probabilistic solar forecasts with. This paper proposes a multivariate probabilistic ensemble (MuPEn) benchmark model and shows that it generalizes the complete-history persistence ensemble (CH-PeEn) to the multivariate case. The proposed benchmark model requires a forecast issue time and a forecast horizon to construct a multivariate empirical distribution of historical clear-sky index measurements from which a multivariate ensemble forecast can be sampled. Similar to CH-PeEn, the proposed benchmark model generates forecasts that are generally calibrated and consistent in terms of energy score and variogram score.

International audience; The benefit of enriching solid–electrolyte interface with fluorine atoms through the use of fluorinated additives into the electrolyte composition has recently gained popularity for anode materials used in secondary lithium-ion batteries. Another strategy is to provide these fluorine atoms via surface fluorination of the electrode material, particularly for multiwalled carbon nanotube (MWCNT)/SnO2-based composites where fluorination must act selectively on SnO2. Our study presents two methods of surface fluorination applied on MWCNT/SnO2, one using F2(g) and the other XeF2(s). These fluorinating agents are known for their different particle penetration depths. An ultrathin and very dense fluorinated layer achieved by the action of F2(g) allows to form a very stable interface leading to gravimetric capacities of 789 mA h g–1 after 50 cycles. A thin and porous fluorinated layer made by the action of XeF2(s) favors the formation of a new Sn-based fluorinated phase, never reported in the literature, which also stabilizes capacities over 50 cycles. In any case, the value of adding fluorine atoms to the surface of the electrode material to improve cycle stability is demonstrated.

International audience; This paper presents an optimization model for Home Energy Management Systems from an aggregator’s standpoint. The aggregator manages a set of resources such as PV, electrochemical batteries and thermal energy storage by means of electric water heaters. Resources are managed in order to participate in the day-ahead energy and local flexibility markets, also considering grid constraint support at the Point of Common Coupling. The resulting model is a Mixed-Integer Linear Programming problem in which the objective is to minimize day-ahead operation costs for the aggregator while complying with energy commitments in the day-ahead market and local flexibility requests. Three sources of uncertainty are considered: energy prices, PV production and load. Adjustable Robust Optimization is used to find a robust counterpart of the problem for including uncertainty. The results obtained show that using robust optimization allows strategic bidding to capture uncertainties while complying with obligations in the wholesale and local market. Data from a real-life energy community with 25 households is used to validate the proposed robust bidding methodology.

International audience; This study proposes a novel sepiolite-based Aquivion electrolyte membrane which could be operated at low relative humidity. In the study, it was discovered that the functionalization of sepiolite with fluorinated groups (i.e., -C7F15), named SEP-F, helps its dispersion in the composite membrane, compared with the use of natural sepiolite. The Aquivion/SEP-F composite membrane showed increased water uptake, thermo-mechanical and chemical stability as well as proton conductivity and decreased swelling compared with commercially available Nafion HP and pristine Aquivion. Their behavior in single cell MEA testing conditions was also assessed. Aquivion/SEP-F composite membrane can be an interesting alternative for low relative humidity operation of PEMFC (proton exchange membrane fuel cell).

International audience; Dynamic Line Rating is a technology devised to modify an overhead line's current-carrying capacity based on weather observation. The benefits of this modification may include reduced congestion costs, an increased renewable energy penetration rate, and improved network reliability. DLR is already well developed, but few papers in the literature investigate DLR day-ahead forecasting. The latter is central to DLR development since many of the decisions related to grid management are taken at least on a day-ahead basis. In this paper, two problems related to DLR forecasts are dealt with: how to achieve precise, reliable calculations of day-ahead forecasts of overhead line ampacity and how to define a methodology to calculate safe rating values using these forecasts. On the first point, four machine-learning algorithms were evaluated, identifying the best approach for this problem and quantifying the potential performance. On the second point, the developed methodology was tested and compared to the current static line rating approach.

International audience; Real-time current-carrying capacity of overhead conductors is extremely variable due to its dependence on weather conditions, resulting in the use of traditionally conservative static ratings. This paper proposes a methodology for exploiting the latent current-carrying capacity of overhead transmission lines taking into account line ampacity forecasts, power flow simulations and the network operator's risk aversion. The procedure can be described as follows: Firstly, probabilistic forecasts for the current rating of transmission lines are generated, paying particular attention to the reliability of the lower part of the distribution. Secondly, a cost benefit analysis is carried out by solving a bilevel stochastic problem that takes into account the reduction in generation costs resulting from a higher power transfer capacity and the increased use of reserves caused by forecast errors. The risk appetite of the network operator is considered in order to accept or penalize high-risk situations, depending on whether the network operator can be described as risk neutral or risk averse.

The building sector is responsible for a significant part of global energy consumption and greenhouse gas emission. Nowadays, there is a growing interest in the so-called super-insulating materials, particularly Aerogels. The present work examines the performance of novel aerogel blankets obtained thanks to an innovative ambient drying process. Based on these aerogel blankets, two thermal insulation systems are developed: one as external thermal insulation composite system (ETICS) and another one as internal thermal insulation multi-layer system (ITI). The objectives of the current work are to assess the performance of the core material (aerogel blanket) as well as the two developed systems. At a material (core layer) scale, thermal, hydric, and mechanical performance characterizations are carried out. At a system level, in-situ hygrothermal, acoustic, and fire performance characterizations are carried out in real scale test cells. Hygrothermal characterization revealed that the thermal conductivity of the studied blanket is about 0.0165 W/(m.K) in ambient and dry conditions but can increase by up to 40% in a very humid environment (RH > 90%). The integration of the aerogel blanket panels into an interior insulating system, tested in a test-cell located in south of France, show great thermal performance. The U value of the wall decreased from 0.63 W/(m2.K) to 0.33 W/(m2.K)after retrofitting. The in-situ hygrothermal results showed that the external insulation system protects the wall against the moisture risks. For the internally insulated wall, the relative humidity remains lower than 85% even when high moisture generation is present inside the test cell. Concerning the thermal performance, the envelope's thermal transmittance is reduced by more than 80% after applying the insulation systems. The ITI system was tested in-situ to airborne sound insulation (facade), reporting significant acoustic improvement in acoustic insulation: +7 dB, equal to a noise reduction to one quarter compared to the base wall without insulation. The fire test of the ETICS proceeded without any material ignition, while the fire behavior of the internal insulation system depends significantly on the adhesion stability between all single components.

International audience; In the prospect of a large scale deployment of Renewable Energy for electricity production, plasmas will definitively be a major option to get tuneable, high temperature enthalpy sources without direct CO2 emissions. This paper focuses on the direct decomposition of methane for the simultaneous synthesis of hydrogen and high value-added carbon black. After a review of gas phase carbon particle nucleation and growth physico-chemical phenomena, a new original model for the plasma decomposition of methane is presented. The model solves a reactive turbulent flow in a 3D geometry. The nucleation is based on a detailed reaction mechanism and the particle growth is handled by a sectional method. This model opens the way towards a better understanding of carbon particles gas phase nucleation and growth and consequently to a fine control of high value-added carbon black grades.

International audience; New hybrid organic-inorganic benzoxazine aerogel blankets for space applications have been synthesized and studied. Aerogel blankets were produced using a one-pot synthesis method with a PET unwoven fibrous network core, resorcinol, formaldehyde and a silica source (APTES with MTES or MTMS as silica co-precursors). Modifying the composition of the sol significantly impacts the physical characteristics of the resulting material such as texture (density and porosity), hydrophilicity, and thermal conductivity. The apparent density of the materials decreases when the percentage of solid in the sol (%solid) decreases and the molar ratio nMTES/nAPTES increases. Within the density range studied, apparent density and effective thermal conductivities are inversely proportional. By replacing a part of APTES by MTES or MTMS the density of the aerogels decreases notably whilst maintaining the level of thermal conductivity. This replacement is detrimental to water adsorption which increases for most conditions studied. When MTMS is used as silica co-precursor instead of MTES no significant differences in water adsorption and thermal conductivity were found. Using the RF-APTES-MTES chemical system we were able to obtain a 3%solid flexible hybrid blanket with both low apparent density (0.04 g cm−3) and relatively low effective thermal conductivity (0.027 W m−1 K−1 in room conditions). A proof of concept with large panels of this material was done by evaluating them as prototype materials composed of encapsulated aerogel blanket in vacuum and low pressure atmosphere. The blankets show a combination of key characteristics representing the right mix for thermal insulation in space applications operating in non-vacuum environments.

International audience; In the life cycle assessment (LCA) context, global sensitivity analysis (GSA) has been identified by several authors as a relevant practice to enhance the understanding of the model's structure and ensure reliability and credibility of the LCA results. GSA allows establishing a ranking among the input parameters, according to their influence on the variability of the output. Such feature is of high interest in particular when aiming at defining parameterized LCA models. When performing a GSA, the description of the variability of each input parameter may affect the results. This aspect is critical when studying new products or emerging technologies, where data regarding the model inputs are very uncertain and may cause misleading GSA outcomes, such as inappropriate input rankings. A systematic assessment of this sensitivity issue is now proposed. We develop a methodology to analyze the sensitivity of the GSA results (i.e. the stability of the ranking of the inputs) with respect to the description of such inputs of the model (i.e. the definition of their inherent variability). With this research, we aim at enriching the debate on the application of GSA to LCAs affected by high uncertainties. We illustrate its application with a case study, aiming at the elaboration of a simple model expressing the life cycle greenhouse gas emissions of enhanced geothermal systems (EGS) as a function of few key parameters. Our methodology allows identifying the key inputs of the LCA model, taking into account the uncertainty related to their description.

International audience; A facile method to synthesize light weight thermally superinsulating composite aerogel is being presented here. A polymethylsilsesquioxane (PMSQ) – cellulose composite aerogel starting from a trifunctional precursor viz. methyltrimethoxysilane (MTMS) and kapok fibers have been synthesized. Kapok fibers have been employed as they have a homogeneous hollow structure and also possess intrinsic low density. A PMSQ-Kapok composite aerogel with a density as low as 0.053 gcm−3 with a thermal conductivity of 0.018 W m−1 K−1 in room conditions has been synthesized. Besides, a flexural strength (at maximum stress) of 108 kPa ± 21 has been obtained through three points bending test. All the composite aerogels are mesoporous as characterized by N2 sorption isotherms and hydrophobic as shown by sessile drop experiments. On comparison with the earlier reported works and with some of the commercially available aerogel composites, the current results seem promising. For demonstrating the real application purpose, thin composite aerogel sheets have also been synthesized which could be easily rolled/bended.

International audience; Cooling demand in the building sector is growing rapidly; thermal energy storage systems using phase change materials (PCM) can be a very useful way to improve the building thermal performance. The right use of PCM in the envelope can minimize peak cooling loads, allow the use of smaller HVAC technical equipment for cooling, and has the capability to keep the indoor temperature within the comfort range due to smaller indoor temperature fluctuations. This article presents an overview of different PCM applications in buildings for reducing cooling loads under different climate conditions, and the factors affecting the successful and the effective use of the PCM. Many drawbacks have been found in PCM applications, mainly the intense impact of summer weather conditions over the PCM performance, which prohibits its complete solidification during night, and thus, limiting its effectiveness during the day. Proposed solutions are reviewed in this article. Finally, a topology diagram is presented to summarize the steps leading to an effective use of PCM in building applications.

International audience; SnO2 nanoparticles were synthetized in three different ways (solvothermal, hydrothermal, sol-gel) and heat-treated under argon at 600 °C to obtain different physico-chemical characteristics (texture, structure and surface chemistry) determined by X-ray powder diffraction (XRD), infrared spectroscopy (FTIR), 119Sn solid state Nuclear Magnetic Resonance (NMR), Electron Spin Resonance (ESR), scanning electron microscopy (SEM) and 77 K nitrogen sorption. When used as electrode material in a lithium ion battery, their electrochemical properties were evaluated by galvanostatic measurements. Among crystallinity, particle size, specific surface area and associated porosity, hydroxyl groups and paramagnetic centers, only the last two parameters appear as determinants of electrochemical performance. Solvothermal and hydrothermal syntheses lead to the presence of certain hydroxyl groups in the oxide whereas sol-gel one prevents their formation but forms paramagnetic species. The hydroxyl groups favour a good coulombic efficiency and an interesting reversibility of the conversion process. Paramagnetic species limit the electrochemical process. Their elimination by a heat-treatment at 1000 °C under argon improves the electrochemical properties. Understanding the key factors to favour SnO2-based materials allows to obtain capacities of about 900 mAh.g−1 over 5 cycles.

International audience; The manual shift of residential wet appliances (dishwashers and washing machines) in French households that have subscribed to a Time of Use (ToU) tariff represents a flexibility potential available already today and at zero-cost. In this paper we quantify, for the first time, this potential by building a national representative synthetic population for France and using a novel bottom-up model. This includes a stochastic occupant behaviour model for predicting the use of the wet appliances and an overlying agent-based model for predicting their manual shifting under a ToU tariff system. The two models are calibrated and validated using empirical data collected over two recent monitoring campaigns, each carried out in more than 100 French households. By using the new model we observe that a 100% penetration rate of the ToU tariff together with an improved (but practically feasible) households’ flexibility could lead, between 19:00 and 20:00, to a mean hourly load reduction of 0.48 GW, which represents around 0.5% of the typical French annual peak load. This flexibility potential, which is today only partially exploited, could be achieved with zero additional costs for new infrastructures, by encouraging eco practices and/or making the ToU tariff more economically attractive for the households.

International audience; In the recent years, several short-term forecasting models of household electricity demand have been proposed in the literature. This is partly due to emerging smart-grid applications, which require these kinds of forecasts to manage systems such as smart homes, prosumer aggregations, etc., and partly thanks to the availability of data from smart meters, which enable the development of such models. Since most models are academically developed, they often do not address challenges related to their implementation in a real-world environment. In the latter case, several issues arise, related to data quality and availability, which affect the operational performance and robustness of a forecasting system. In this paper, we design a hierarchical forecasting framework based on a total of 5 probabilistic models of varying complexity, after analyzing the respective performance and advantages of the models with an offline dataset. This multi-layered framework is necessary to address the various problematic situations occurring in practice and abide by the requirements for a real-world deployment. The forecasting system is deployed in a real-world case and evaluated here on data from 20 households. Field data, comprising forecasts and measurements, are analyzed for each household. A detailed comparison is drawn between the online and offline performances. Since a notable degradation is observed in the operational environment, we discuss at length the reasons for such an effect. We determine that the exact settings of the training and test periods are marginally responsible, but that the main cause is the intrinsic evolution of the demand time series, which hinders the forecasting performance. This evolution is due to unknown household characteristics that need to be monitored to provide more adaptable models.

International audience; Silica aerogels are excellent thermal insulators, but their brittle nature has prevented widespread application. To overcome these mechanical limitations, silica–biopolymer hybrids are a promising alternative. A one-pot process to monolithic, superinsulating pectin–silica hybrid aerogels is presented. Their structural and physical properties can be tuned by adjusting the gelation pH and pectin concentration. Hybrid aerogels made at pH 1.5 exhibit minimal dust release and vastly improved mechanical properties while remaining excellent thermal insulators. The change in the mechanical properties is directly linked to the observed “neck-free” nanoscale network structure with thicker struts. Such a design is superior to “neck-limited”, classical inorganic aerogels. This new class of materials opens up new perspectives for novel silica–biopolymer nanocomposite aerogels.

International audience; Convex relaxations of the optimal power flow (OPF) problem have received a lot of attention in the recent past. In this work, we focus on a second-order cone (SOC) relaxation applied to an OPF based on a branch flow model of a radial and balanced distribution system. We start by examining various sets of conditions ensuring the exactitude of such a relaxation, which is the main focus of the existing literature. In particular, we observe that these sets always include a requirement on the objective to be a minimization of a function increasing with the branch flow apparent powers. We consider this hypothesis to be at odds with what is to be expected of an active distribution system and demonstrate in specific case studies its counterproductive impact. We continue by introducing an objective function allowing distributed generations and storages (DGS) to take advantage of the benefits they bring to the power system as a whole. As this entails the possibility for the relaxation not to be exact, we describe and prove the theoretical convergence to optimality of an algorithm consisting in adding an increasingly tight linear cut to the SOC relaxation. In order to allow the attainment of a solution satisfying the network constraints in a finite number of steps, we continue by introducing a tailored termination criterion. Afterwards, we investigate the ability of our algorithm to obtain a satisfactory solution on several case studies, spanning various network sizes, number of nodes equipped with DGs and their level of penetration. We then conclude on the benefits brought about by this approach and reflect on its limits and the opportunities for further improvements.

International audience; This paper presents the first passive solar wall providing simultaneously super insulation, heat storage and daylighting to the inner space. The wall’s external layer is composed of a silica aerogels bed for high insulation and solar radiation transmission. The second layer, internal, is composed of glass bricks filled with a eutectic phase change material (PCM) for heat storage and restitution. The whole wall is translucent. The experimentations carried out to characterize thermal and optical properties of the materials used are described. Then results are given for a full scale comparative experimentation on a twin zones building located in the south of France for the solar wall and a standard opaque high thermal capacity wall. Results show the heat losses through the wall are very low while the heat and light gains are high: The U value of the solar wall is 0.59 W m−1 K−1 and 0.72 W m−1 K−1 respectively when the PCM is in liquid and solid state. With the test building in free floating condition, the temperature difference between the outdoor and indoor air provided by the wall is about 9 °C in winter. The wall can provide up to 500 lux to the inner environment, which is sufficient for conference rooms. The tested wall has proven more effective in winter and shoulder season, particularly for cold sunny climates, but may cause overheating in summer.

International audience; Silica aerogels are highly porous and open-cell materials made of amorphous silica nanoparticles, interconnected in a 3D random network. Silica aerogel-based materials have a great potential as thermal insulation in building thanks to their very low thermal conductivity. However, pure silica aerogels are fragile with low mechanical moduli. Making aerogel composite materials by combining fibers with a pre-gel mixture of a gel precursor or by impregnating a fiber network by such a mixture seems to be a promising way to enhance the mechanical properties of such materials. After drying, the resulting composite is called aerogel blanket. The aerogel blanket is mechanically strengthened, flexible and still has a very low thermal conductivity. Aerogel blankets are usually dried using supercritical process but it is considered as a main drawback for large scale industrialization. The present study uses an innovative micro wave drying. The purpose of this work is to analyze and characterize a handy, light, super-insulating aerogel blanket dried in ambient conditions and see if it could be suitable for building thermal insulation. Two types of blankets have been investigated: the first one with a glass fiber web and the second one with a PET (polyethylene terephthalate) fiber web. Hygro-thermal characterizations were done and show that the aerogel blankets have an excellent thermal conductivity (0.015 W m−1 K−1) and a hydrophobic behavior. The studied aerogel blankets obtained using a new ambient drying process show practically the same characteristics as their counterpart dried with a supercritical process and mark a step forward in the aerogel blanket industrialization.

International audience; Microgrid operations are challenging due to variability in loads and renewable energy generation. Advanced tools capable of taking uncertainty into account are essential to maximize microgrid benefits when operating microgrid owned DERs. This paper proposes a novel optimization model for day-ahead economic dispatch of flexible resources within a microgrid environment, considering uncertainty of PV and loads.This model is conceived to support the microgrid supervisory control layer, providing a security-constrained day-ahead strategy to operate three types of microgrid flexible resources: PV, electric storage and controllable loads. The work presented in this paper introduces a novelty in microgrid operations by presenting a stochastic version of the day ahead scheduling of microgrid DERs to deal with uncertainties associated with PV, load and temperature while considering microgrid network limits and end-user comfort as optimization constraints. An annual analysis quantifies the benefits of to the microgrid-owner of a stochastic formulation over a deterministic one both in terms of ensuring end-user comfort and decreasing operation costs.

International audience; This study aims at examining the energy behaviour of the buildings' multi-layer exterior wall structures. Most of the studies dealing with this issue have considered a continuous operation of the cooling/heating systems. Our objective here is to find the best wall structure and the number and position of insulation layers within exterior walls for continuous heating, intermittent heating, and no heating operation modes for some commonly used construction materials. Furthermore, among the different materials used, a recently patented insulating coating based on the (super)-insulating materials "Silica Aerogels" is being assessed. Results from a one-dimensional heat transfer numerical model in a multi-layer wall structure are compared to on-site measurements of an experimental set-up, having the new aerogel-based coating, under real weather conditions. The numerical model is then used to carry out all the simulations. Several assessment parameters are used: time lag, decrement factor, energy consumption, and thermal comfort index. Results show that for continuous and no heating cases, the best wall from maximum time lag and minimum decrement factor perspective is dividing the insulation layer into two and placing one at the middle of the wall and one at the exterior surface. For intermittently heated spaces, placing the insulation material as one layer at the interior wall surface is the most efficient from an energy consumption perspective. Also, when using the thermal comfort index for the no heating operation mode, the best performance is achieved when placing the insulation at the interior wall surface. For most of the cases studied, the aerogel-based insulating coating shows better performance than other insulating materials.

International audience; Thermal bridges are weak areas of the building envelope in which they can significantly increase the energy load of houses. In this study, we tackle the thermal bridges resulting from windows offset from exterior walls. First, we present an innovative insulating coating which can be used to limit thermal bridge effects. Second, we compute the cooling/heating load coming from the windows offset thermal bridges of a typical French house before and after adding the insulating coating. Third, we compare the time lag and decrement factor when the 2D heat transfer effects of the thermal bridge are taken into consideration. The methodology is to incorporate 2D heat transfer into a whole building energy simulation program. This is done through co-simulation between a 2D heat transfer model developed in MATLAB and the building energy simulation software EnergyPlus using the software BCVTB. This latter enables us to link the two programs and allow them to exchange data at each simulation time step. Results showed that the windows offset thermal bridges energy load percentage of the total house load constitutes around 2-8% depending whether exterior walls have interior insulation or not. Applying 1 cm and 2 cm of the coating on these thermal bridges reduces the windows offset energy load by about 24-50%. Concerning time lag and decrement factor, we obtain high values for decrement factor and low values for the time lag for wall positions near the thermal bridge. Applying the coating decreases, significantly, the decrement factor and increases the time lag.

International audience; A 3-phase AC plasma torch has been developed and aims at overcoming some limits of the classical DC torches in terms of efficiency, cost and reliability. However, the arc behavior in 3-phase plasma torch remains poorly explored. This paper is dedicated to the high speed video camera at 100,000 frames per second and electrical signal analyses of arcs behavior in a 3-phase AC arc plasma torch. First, a reference case at 150 A, in nitrogen as working gas, has been deeply analyzed. Afterwards, a parametric study based on current and inter-electrode gap has been carried out. Results show that only one arc can exist at a given time and arcs rotate by switching from a pair of electrodes to another one, following the maximal electrical gap potential. However, a particular "abnormal" arc behavior was sometimes observed. Indeed, the arc motion within the inter-electrode gap increases the heat exchange and stabilizes the 3-phase discharge whereas the system is unbalanced when the arc is in the periphery. The analysis highlights that the arc motion is strongly influenced by the electrode jet velocity and repulsive Lorentz forces. The parametric study shows that the current increases both jet velocity and arc discharge stability. Elsewhere, the increase of the inter-electrode gap can also stabilizes the electrical 3-phase arc discharge. Furthermore, the correlation between arc motion and current waveform is highlighted. This work is likely to open the way toward a better understanding of 3-phase discharges in the perspective of their further optimization.

International audience; The increasing concentration of wind farms in some parts of the world calls for a new descriptive framework of power fluctuation that can summarize spatio-temporal characteristics of the wind power production process. In the mean time, this high number of measurement devices has great potential for informing or alerting about upcoming front or phase errors. In this paper, we shed light on the spatio-temporal characteristics of wind power forecast errors. We justify and use two strategies for obtaining the main direction and the speed of propagation. The first of these relies on an analysis of the local maxima of the correlation structure, and the second builds upon a planar wave modeling. The connection is made with meteorological parameters. Our analysis is presented so as to be easily reproducible in other cases.

International audience; Three-dimensional Fe-N-C aerogel catalysts for the oxygen reduction reaction (ORR) are prepared with resorcinol–formaldehyde–melamine and iron precursor using one-pot sol-gel process followed by supercritical drying and heat treatment in nitrogen (N2) and then ammonia (NH3) atmospheres. We studied the effect of the synthesis conditions (Fe precursor and Fe content) of organic aerogel and the heat treatment parameters (including temperature and duration) under N2/NH3 atmosphere on the structural properties and ORR catalytic activities of the resulting Fe-N-C aerogel catalysts. The Fe-N-C aerogel catalysts were characterized by X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, and N2-adsorption/desorption, and the ORR activities were studied by the rotating disk electrode method. It was found that the pore structure, the chemical composition, and ultimately the ORR performance were largely affected by the nature of iron precursor, iron content, and the conditions of heat treatment. The catalysts using Iron (III) acetylacetonate as Fe precursor incorporated with 3 wt% of Fe followed by the HT at 800 °C for 1 h under N2 and then 950 °C under NH3 for 30 min showed the highest content of active site (Fe-Nx) and largest mesopore volume, resulting in an enhanced catalytic activity and mass-transport property.

International audience; Electricity systems around the world are decarbonizing, driven by reductions in the cost of renewable energy and encouraged by supportive regulatory policy. Electricity market designs are increasingly being tested to ensure that the bulk power system can deliver reliable, cost-effective energy to all consumers.