1,720,977 research outputs found
Optimal design of PV-based grid-connected hydrogen production systems
Full text linkA cost-optimal design of power-to-hydrogen (PtH) systems is crucial to produce hydrogen at the lowest specific cost. New challenges arise when it comes to ensuring a reliable and cost-effective hydrogen supply in the presence of variable renewable energy sources. In this context, the aim of this analysis is to investigate the optimal design of PV-based grid-connected hydrogen production systems under different scenarios. To this end, an optimisation framework based on the mixed integer linear programming (MILP) technique is developed. Results are presented by employing a set of techno-economic and environmental indicators to provide general guidance on how to optimally size PtH systems, going beyond the analysis of a specific case study. The analysis is applied to Italy and particular attention is paid to exploring the impact of the price of grid electricity. The results indicate that the price of grid electricity strongly affects the optimal design of PtH systems. Specifically, in scenarios with high electricity prices, it is economically convenient to significantly oversize the PV plant and the electrolyser. The optimal PV ratio, representing the ratio between the PV size and the electrolyser size, increases from 1.6 to 2.7 as the electricity price rises from 50 to 300 euro/MWh. Additionally, when electricity prices exceed approximately 120 euro/MWh, the optimal electrolyser size (in terms of hydrogen production under rated conditions) becomes almost three times larger than the average hydrogen demand. By comparing gridconnected and off-grid scenarios, the importance of the electrical grid is also highlighted: even when poorly used, it plays a crucial role in limiting the size of the hydrogen storage. The levelised cost of hydrogen for the optimal PtH configuration falls within the range of 3.5-7 euro/kg (depending on the price of grid electricity) and increases to 8.2 euro/kg when the system operates off-grid. Finally, the hydrogen carbon footprint, quantified as kgCO2,e/kgH2, is also explored. Considering the current price and carbon intensity of grid electricity, t
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
The flexibility of virtual energy storage based on the thermal inertia of buildings in renewable energy communities: A techno-economic analysis and comparison with the electric battery solution
Full text linkThe Renewable Energy Community (REC) concept has been introduced into the European decarbonization guidelines to promote the utilization of Renewable Energy Sources (RES) and to incentivize their self-consumption at the local level. This paper analyzes the flexible use of Heat Pumps (HP) for building heating in an REC context. The Power-to-Heat (P2H) energy conversion process of HP allows the flexibility of the thermal sector to be exploited within the electricity sector: in this way, it is possible to store energy in the form of heat inside the building mass and then use the stored energy to reduce the building heating demand in the hours following the accumulation of energy. This energy storage solution has been defined as building-based Virtual Energy Storage (VES). The flexibility enabled by VES has been used to optimize the self-consumption of an REC. The flexible VES solution was evaluated, from a technical and economic point of view, through a sensitivity analysis on the variation of the RES penetration, and the results were compared with those based on a more traditional centralized electric battery (EB) storage system. The results demonstrated that the VES solution is less flexible than electric batteries. Nevertheless, both flexible solutions (VES and EB) can significantly increase the REC self-consumption: the self-consumed energy increased by between 6% and 44% thanks to the exploitation of the VES flexibility, while the EB flexibility enabled an increase in the self-consumed energy of 19% to 63% according to the scenario analyzed. However, due to the high investment cost of EB, the VES configuration resulted to be the best solution from an economic point of view
Life cycle environmental analysis of a hydrogen-based energy storage system for remote applications
Full text linkEnergy storage systems are required to address the fluctuating behaviour of variable renewable energy sources. The environmental sustainability of energy storage technologies should be carefully assessed, together with their techno-economic feasibility. In this work, an environmental analysis of a renewable hydrogen-based energy storage system has been performed, making use of input parameters made available in the framework of the European REMOTE project. The analysis is applied to the case study of the Froan islands (Norway), which are representative of many other insular microgrid sites in northern Europe. The REMOTE solution is compared with other scenarios based on fossil fuels and submarine connections to the mainland grid. The highest climate impacts are found in the diesel-based configuration (1,090.9 kgCO2eq/MWh), followed by the REMOTE system (148.2 kgCO2eq/MWh) and by the sea cable scenario (113.7 kgCO2eq/MWh). However, the latter is biased by the very low carbon intensity of the Norwegian electricity. A sensitivity analysis is then performed on the length of the sea cable and on the CO2 emission intensity of electricity, showing that local conditions have a strong impact on the results. The REMOTE system is also found to be the most cost-effective solution to provide electricity to the insular community. The in-depth and comparative (with reference to possible alternatives) assessment of the renewable hydrogen-based system aims to provide a comprehensive overview about the effectiveness and sustainability of these innovative solutions as a support for off-grid remote areas
Techno-economic feasibility analysis of Renewable-fed Power-to-Power (P2P) systems for small French islands
No full textIn this paper, the feasibility analysis of H2 and Battery based Power-to-Power (P2P) systems are presented from a techno-economic perspective. For this study, 21 small islands of France based in Europe are selected, being naturally endowed with renewable energy sources (RES) of solar and wind. For each island, three distinct energy storage options, i.e., hydrogen storage, battery storage and hydrogen + battery combined storage are discussed and explored. Optimum sizing of RES and P2P systems are achieved through employing particle swarm optimization (PSO) algorithm, keeping Levelized Cost of Energy (LCOE) as an objective function. The hydrogen and battery storage combination with an average LCOE value of 420Euro/MWh was found to be the most suitable option for all 21 reference islands. The associated Net Present Cost (NPC) was EUR564,388,050 which was lower than that for the other two storage options. The hybrid storage selection necessitated installation of 41 MW of photovoltaic (PV) modules and 122MW of wind turbines at these islands. The required storage capacity comprised of 7700MWh of hydrogen and 7MWh of battery storage combined with the auxiliaries. A considerable emphasis is also laid on highlighting the annual reduction of greenhouse gases (GHGs) and other air pollutants through the adoption of the proposed RES-P2P integrated systems. The annual carbon dioxide equivalent measure (CO2,e) of all islands was computed to be around 99507.52tons. It was revealed that more than 99 thousand tons of CO2 emissions can be prevented by avoiding consumption of more than 34 million liters of diesel per year
An MILP approach for the optimal design of renewable battery-hydrogen energy systems for off-grid insular communities
Full text linkThe optimal sizing of stand-alone renewable H2-based microgrids requires the load demand to be reliably satisfied by means of local renewable energy supported by a hybrid battery/hydrogen storage unit, while minimizing the system costs. However, this task is challenging because of the high number of components that have to be installed and operated. In this work, an MILP optimization framework has been developed and applied to the off-grid village of Ginostra (on the Stromboli island, Italy), which is a good example of several other insular sites throughout the Mediterranean area. A year-long time horizon was considered to model the seasonal storage, which is necessary for off-grid areas that wish to achieve energy independence by relying on local renewable sources. The degradation costs of batteries and H2-based devices were included in the objective function of the optimization problem, i.e., the annual cost of the system. Efficiency and investment cost curves were considered for the electrolyzer and fuel cell components in order to obtain a more detailed and precise techno-economic estimation. The design optimization was also performed with the inclusion of a general demand response program (DRP) to assess its impact on the sizing results. Moreover, the effectiveness of the proposed MILP-based method was tested by comparing it with a more traditional approach, based on a metaheuristic algorithm for the optimal sizing complemented with ruled-based strategies for the system operation. Thanks to its longer-term storage capability, hydrogen is required for the optimal system configuration in order to reach energy self-sufficiency. Finally, considering the possibility of load deferral, the electricity generation cost can be reduced to an extent that depends on the amount of load that is allowed to participate in the DRP scheme. This cost reduction is mainly due to the decreased capacity of the battery storage system
The role of hydrogen in the optimal design of off-grid hybrid renewable energy systems
Full text linkThe optimal design of off-grid hybrid renewable energy systems (HRESs) is a challenging task, which often involves conflicting goals to be faced. In this work, levelized cost of energy (LCOE) and CO2 emissions have been addressed simultaneously by using the ε-constraint method together with the particle swarm optimization (PSO) algorithm. Cost-emissions Pareto fronts of different HRES configurations were developed to gain greater awareness about the potential of renewable-based energy systems in off-grid applications. Various combinations of the following components were investigated: photovoltaic panels, wind turbines, batteries, hydrogen and diesel generators. The hydrogen-based system comprises an electrolyzer to convert the excess renewable energy into hydrogen, a pressurized tank for H2 storage and a fuel cell for the reconversion of hydrogen into electricity during renewable energy deficits. Electrolyzer and fuel cell devices were modelled by means of part-load performance curves. Size-dependent costs and component lifetimes as a function of the cumulative operational duty were also considered for a more accurate techno-economic assessment. The proposed methodology was applied to the Froan islands (Norway), which were chosen as a reference case study since they are well representative of many other insular microgrid environments in Northern Europe. Results from the sizing simulations revealed that energy storage devices are key components to reduce the dependency on fossil fuels. In particular, the hydrogen storage system is crucial in off-grid areas to enhance the RES penetration and avoid a sharp increase in the cost of energy. Hydrogen, in fact, allows the battery and RES technologies not to be oversized, thanks to its cost-effective long-term storage capability. Concerning the extreme case with no diesel, the cheapest configuration, which includes both batteries and hydrogen, has an LCOE of 0.41 €/kWh. This value is around 35% lower than the LCOE of a system with only batteries as energy storage
Trace contaminants in biogas: Biomass sources, variability and implications for technology applications
Full text linkBiogas represents a renewable and controllable energy source. Although predominantly composed of methane and carbon dioxide, it also contains various trace contaminants that can be detrimental to the technologies used for its conversion. The aim of this work is to comprehensively explore trace contaminants in biogas. The assessment employs a two-level approach: an extensive literature review on biogas trace contaminants, complemented with on-site analyses from real-scale biogas plants to enhance and validate the literature findings. The biogas contaminants – sulphur compounds, siloxanes, halocarbons and aromatic compounds – are quantified and categorised into four distinct groups: landfill gas, agricultural gas, gas derived from the organic fraction of municipal solid waste (OFMSW), and gas from wastewater (WWTP). This study also provides contaminant effects and required thresholds for different biogas conversion technologies, including internal combustion engines, upgrading to biomethane, and innovative solid oxide fuel cells (SOFCs). The two-level analysis reveals significant variability in contaminant levels across different biogas sources, with H2S being the most prevalent contaminant, averaging between 181 (WWTP) and 901 ppm (landfill gas). Other sulphur compounds show the highest average concentration in biogas from OFMSW (98 ppm), followed by agricultural and landfill gases. Siloxanes are typically more abundant in biogas from WWTP (2.55 ppm), while landfill gas exhibits the highest average concentrations of halocarbons and aromatic compounds (6 ppm and 109 ppm, respectively). Moreover, this study highlights the need for in-depth measurements of contaminants for highly sensitive technologies, such as SOFCs, to properly design tailored contaminant removal solutions
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
- …
