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Sökning: L773:1996 1073

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  • Rinio, Markus, 1967- (författare)
  • PVcheck—A Software to Check Your Photovoltaic System
  • 2021
  • Ingår i: Energies. - : MDPI. - 1996-1073 .- 1996-1073. ; 14:20, s. 6757-6757
  • Tidskriftsartikel (refereegranskat)abstract
    • Having a photovoltaic (PV) system raises the question of whether it runs as expected.Measuring its energy yield takes a long time and the result still contains uncertainties from varyingweather conditions and possible shading of the modules. Here, a free software PVcheck to measurethe peak power of the system is announced, using the power data of a single sunny day. The softwareloads a data file of the generated power as a function of time from this day. This data file is providedby typical inverters. The software then simulates this power curve using known parameters like angleand location of the PV system. The assumed peak power of the simulation can then be adjusted sothat the simulated curve matches the measured one. The software runs under Microsoft Windows™and makes use of the free library pvlib python. The simulation can be refined by importing weatherdata like temperature, wind speed, and insolation. Furthermore, curves describing the nominalmodule efficiency as a function of the illumination intensity as well as the power-dependent inverterefficiency can be included in the simulation. First results reveal a good agreement of the simulationwith experimental data. The software can be used to detect strong problems in PV systems afterinstallation and to monitor their long-time operation.
  • Akinbomi, Julius, et al. (författare)
  • Evaluation of Fermentative Hydrogen Production from Single and Mixed Fruit Wastes
  • 2015
  • Ingår i: Energies. - : MDPI AG. - 1996-1073 .- 1996-1073. ; 8:5, s. 4253-4272
  • Tidskriftsartikel (refereegranskat)abstract
    • The economic viability of employing dark fermentative hydrogen from wholefruit wastes as a green alternative to fossil fuels is limited by low hydrogen yield due to theinhibitory effect of some metabolites in the fermentation medium. In exploring means ofincreasing hydrogen production from fruit wastes, including orange, apple, banana, grapeand melon, the present study assessed the hydrogen production potential of singly-fermentedfruits as compared to the fermentation of mixed fruits. The fruit feedstock was subjected tovarying hydraulic retention times (HRTs) in a continuous fermentation process at 55 °C for47 days. The weight distributions of the first, second and third fruit mixtures were 70%,50% and 20% orange share, respectively, while the residual weight was shared equally bythe other fruits. The results indicated that there was an improvement in cumulativehydrogen yield from all of the feedstock when the HRT was five days. Based on the resultsobtained, apple as a single fruit and a fruit mixture with 20% orange share have the mostimproved cumulative hydrogen yields of 504 (29.5% of theoretical yield) and 513 mL/gvolatile solid (VS) (30% of theoretical yield ), respectively, when compared to other fruits.
  • Andersson, Joakim (författare)
  • Application of Liquid Hydrogen Carriers in Hydrogen Steelmaking
  • 2021
  • Ingår i: Energies. - : MDPI AG. - 1996-1073 .- 1996-1073. ; 14:5, s. 1392-
  • Tidskriftsartikel (refereegranskat)abstract
    • Steelmaking is responsible for approximately one third of total industrial carbon dioxide (CO2) emissions. Hydrogen (H2) direct reduction (H-DR) may be a feasible route towards the decarbonization of primary steelmaking if H2 is produced via electrolysis using fossil-free electricity. However, electrolysis is an electricity-intensive process. Therefore, it is preferable that H2 is predominantly produced during times of low electricity prices, which is enabled by the storage of H2. This work compares the integration of H2 storage in four liquid carriers, methanol (MeOH), formic acid (FA), ammonia (NH3) and perhydro-dibenzyltoluene (H18-DBT), in H-DR processes. In contrast to conventional H2 storage methods, these carriers allow for H2 storage in liquid form at moderate overpressures, reducing the storage capacity cost. The main downside to liquid H2 carriers is that thermochemical processes are necessary for both the storage and release processes, often with significant investment and operational costs. The carriers are compared using thermodynamic and economic data to estimate operational and capital costs in the H-DR context considering process integration options. It is concluded that the use of MeOH is promising compared to the other considered carriers. For large storage volumes, MeOH-based H2 storage may also be an attractive option to the underground storage of compressed H2. The other considered liquid H2 carriers suffer from large thermodynamic barriers for hydrogenation (FA) or dehydrogenation (NH3, H18-DBT) and higher investment costs. However, for the use of MeOH in an H-DR process to be practically feasible, questions regarding process flexibility and the optimal sourcing of CO2 and heat must be answered
  • Arnaudo, Monica, et al. (författare)
  • Vehicle-to-grid for peak shaving to unlock the integration of distributed heat pumps in a swedish neighborhood
  • 2020
  • Ingår i: Energies. - : MDPI AG. - 1996-1073 .- 1996-1073. ; 13:7
  • Tidskriftsartikel (refereegranskat)abstract
    • The city of Stockholm is close to hitting the capacity limits of its power grid. As an additional challenge, electricity has been identified as a key resource to help the city to meet its environmental targets. This has pushed citizens to prefer power-based technologies, like heat pumps and electric vehicles, thus endangering the stability of the grid. The focus of this paper is on the district of Hammarby Sjöstad. Here, plans are set to switch from district heating to heat pumps. A previous study verified that this choice will cause overloadings on the electricity distribution grid. The present paper tackles this problem by proposing a new energy storage option. By considering the increasing share of electric vehicles, the potential of using the electricity stored in their batteries to support the grid is explored through technical performance simulations. The objective was to enable a bi-directional flow and use the electric vehicles' (EVs)' discharging to shave the peak demand caused by the heat pumps. It was found that this solution can eliminate overloadings up to 50%, with a 100% EV penetration. To overcome the mismatch between the availability of EVs and the overloadings' occurrence, the minimum state of charge for discharging should be lower than 70%. © 2020 by the authors.
  • Aslanzadeh, Solmaz, et al. (författare)
  • The Effect of Effluent Recirculation in a Semi-Continuous Two-Stage Anaerobic Digestion System
  • 2013
  • Ingår i: Energies. - : M D P I AG. - 1996-1073 .- 1996-1073. ; 6:6, s. 2966-2981
  • Tidskriftsartikel (refereegranskat)abstract
    • The effect of recirculation in increasing organic loading rate (OLR) and decreasing hydraulic retention time (HRT) in a semi-continuous two-stage anaerobic digestion system using stirred tank reactor (CSTR) and an upflow anaerobic sludge bed (UASB) was evaluated. Two-parallel processes were in operation for 100 days, one with recirculation (closed system) and the other without recirculation (open system). For this purpose, two structurally different carbohydrate-based substrates were used; starch and cotton. The digestion of starch and cotton in the closed system resulted in production of 91% and 80% of the theoretical methane yield during the first 60 days. In contrast, in the open system the methane yield was decreased to 82% and 56% of the theoretical value, for starch and cotton, respectively. The OLR could successfully be increased to 4 gVS/L/day for cotton and 10 gVS/L/day for starch. It is concluded that the recirculation supports the microorganisms for effective hydrolysis of polyhydrocarbons in CSTR and to preserve the nutrients in the system at higher OLRs, thereby improving the overall performance and stability of the process.
  • Dyachuk, Eduard, et al. (författare)
  • Measurements of the Aerodynamic Normal Forces on a 12-kW Straight-Bladed Vertical Axis Wind Turbine
  • 2015
  • Ingår i: Energies. - 1996-1073 .- 1996-1073. ; 8:8
  • Tidskriftsartikel (refereegranskat)abstract
    • The knowledge of unsteady forces is necessary when designing vertical axis wind turbines (VAWTs). Measurement data for turbines operating at an open site are still very limited. The data obtained from wind tunnels or towing tanks can be used, but have limited applicability when designing large-scale VAWTs. This study presents experimental data on the normal forces of a 12-kW straight-bladed VAWT operated at an open site north of Uppsala, Sweden. The normal forces are measured with four single-axis load cells. The data are obtained for a wide range of tip speed ratios: from 1.7 to 4.6. The behavior of the normal forces is analyzed. The presented data can be used in validations of aerodynamic models and the mechanical design for VAWTs.
  • El Gohary, Fouad, et al. (författare)
  • Identifying Challenges in Engaging Users to Increase Self-Consumption of Electricity in Microgrids
  • 2021
  • Ingår i: Energies. - : MDPI. - 1996-1073 .- 1996-1073. ; 14:5
  • Tidskriftsartikel (refereegranskat)abstract
    • A microgrid's self-consumption rate reflects its ability to retain its own energy and decrease its reliance on the synchronous grid. This paper investigates the empirical case of a microgrid equipped with photovoltaic (PV) panels and identifies challenges in engaging the microgrid's users to increase their self-consumption. Accordingly, we explored both the physical and social dimensions of the microgrid. The former involved mapping the electricity consumption and production through an exploratory data analysis, and evaluating the associated price signals, while the latter involved the use of design interventions to explore users' perceptions of the system. We highlight the problem of price signal impedance, the need for cost reflective pricing and the challenge in designing and extending internal price models in settings with various actors. We address the limitations of price signals, alongside alternative unidimensional signals, and emphasize the need for an integrated approach to a user engagement strategy as well as the challenges that this approach entails. Our results shed light on the complexity of energy communities such as microgrids, and why their implementation can introduce multidimensional challenges that demand cross-disciplinary approaches.
  • Fachrizal, Reza, et al. (författare)
  • Improved Photovoltaic Self-Consumption in Residential Buildings with Distributed and Centralized Smart Charging of Electric Vehicles
  • 2020
  • Ingår i: Energies. - : MDPI. - 1996-1073 .- 1996-1073. ; 13:5
  • Tidskriftsartikel (refereegranskat)abstract
    • The integration of photovoltaic (PV) and electric vehicle (EV) charging in residential buildings has increased in recent years. At high latitudes, both pose new challenges to the residential power systems due to the negative correlation between household load and PV power production and the increase in household peak load by EV charging. EV smart charging schemes can be an option to overcome these challenges. This paper presents a distributed and a centralized EV smart charging scheme for residential buildings based on installed photovoltaic (PV) power output and household electricity consumption. The proposed smart charging schemes are designed to determine the optimal EV charging schedules with the objective to minimize the net load variability or to flatten the net load profile. Minimizing the net load variability implies both increasing the PV self-consumption and reducing the peak loads. The charging scheduling problems are formulated and solved with quadratic programming approaches. The departure and arrival time and the distance covered by vehicles in each trip are specifically modeled based on available statistical data from the Swedish travel survey. The schemes are applied on simulated typical Swedish detached houses without electric heating. Results show that both improved PV self-consumption and peak load reduction are achieved. The aggregation of distributed smart charging in multiple households is conducted, and the results are compared to the smart charging for a single household. On the community level, both results from distributed and centralized charging approaches are compared.
  • Forslund, Johan, 1985-, et al. (författare)
  • Experimental Results of a DC Bus Voltage Level Control for a Load-Controlled Marine Current Energy Converter
  • 2015
  • Ingår i: Energies. - 1996-1073 .- 1996-1073. ; 8:5, s. 4572-4586
  • Tidskriftsartikel (refereegranskat)abstract
    • This paper investigates three load control methods for a  marine current energy converter using a vertical axis current  turbine (VACT) mounted on a permanent magnet synchronous generator  (PMSG). The three cases are; a fixed AC load, a fixed pulse width  modulated (PWM) DC load and DC bus voltage control of a DC  load. Experimental results show that the DC bus voltage control  reduces the variations of rotational speed by a factor of 3.5 at the cost  of slightly increased losses in the generator and transmission lines.  For all three cases, the tip speed ratio   can be kept close to  the expected    . The power coefficient is estimated to be  0.36 at    ; however, for all three cases, the average  extracted power was about  \%. A maximum power point  tracking (MPPT) system, with or without water velocity measurement,  could increase the average extracted power.
  • Gantasala, Sudhakar, et al. (författare)
  • Numerical Investigation of the Aeroelastic Behavior of a Wind Turbine with Iced Blades
  • 2019
  • Ingår i: Energies. - : MDPI. - 1996-1073 .- 1996-1073. ; 12:12
  • Tidskriftsartikel (refereegranskat)abstract
    • Wind turbines installed in cold-climate regions are prone to the risks of ice accumulation which affects their aeroelastic behavior. The studies carried out on this topic so far considered icing in a few sections of the blade, mostly located in the outer part of the blade, and their influence on the loads and power production of the turbine are only analyzed. The knowledge about the influence of icing in different locations of the blade and asymmetrical icing of the blades on loads, power, and vibration behavior of the turbine is still not matured. To improve this knowledge, multiple simulation cases are needed to run with different ice accumulations on the blade considering structural and aerodynamic property changes due to ice. Such simulations can be easily run by automating the ice shape creation on aerofoil sections and two-dimensional (2-D) Computational Fluid Dynamics (CFD) analysis of those sections. The current work proposes such methodology and it is illustrated on the National Renewable Energy Laboratory (NREL) 5 MW baseline wind turbine model. The influence of symmetrical icing in different locations of the blade and asymmetrical icing of the blade assembly is analyzed on the turbine’s dynamic behavior using the aeroelastic computer-aided engineering tool FAST. The outer third of the blade produces about 50% of the turbine’s total power and severe icing in this part of the blade reduces power output and aeroelastic damping of the blade’s flapwise vibration modes. The increase in blade mass due to ice reduces its natural frequencies which can be extracted from the vibration responses of the turbine operating under turbulent wind conditions. Symmetrical icing of the blades reduces loads acting on the turbine components, whereas asymmetrical icing of the blades induces loads and vibrations in the tower, hub, and nacelle assembly at a frequency synchronous to rotational speed of the turbine.
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