| 1. |
- Abedi, Hamidreza, 1979
(författare)
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Assessment of flow characteristics over complex terrain covered by the heterogeneous forest at slightly varying mean flow directions: (A case study of a Swedish wind farm)
- 2023
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Ingår i: Renewable Energy. - : Elsevier BV. - 0960-1481 .- 1879-0682. ; 202, s. 537-553
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Tidskriftsartikel (refereegranskat)abstract
- The impact of heterogeneous forest canopies and complex terrain on the horizontal distortion of the inflow is studied. Large-Eddy Simulation (LES) of the neutral Atmospheric Boundary Layer (ABL) flow is performed for a wind farm in Sweden for three cases associated with three different wind directions at the range of the static yaw misalignment (≃±6∘) where the yaw control system is not activated. The ground topography and forest properties for the numerical modeling are extracted from the Airborne Laser Scanning (ALS) 3D data. The wind turbines within the wind farm are introduced using the actuator disk model. To focus on the airflow deflection only by the complex terrain and vegetation, the study is limited to upstream wind turbines without any wake interaction. The predicted mean wind speed and turbulence intensity for the upstream wind turbines are compared against the nacelle-mounted anemometers taken from the wind farm's turbine SCADA data. To quantify the additional load and moments induced at the rotor blades by the horizontal misalignment of the incoming flow, aero-structural simulation of the upstream wind turbines in the wind farm for all three cases is performed. The results show that the horizontal distortion of the inflow over the rotor swept area is usually kept below the range of static yaw misalignment (≃6∘) for the majority of the upstream wind turbines for all three cases. However, the impact of a large vertical shear exponent leading to misinterpretation of the results must be taken into consideration. Furthermore, the load imbalance of the rotor due to the vertical wind shear has the least direct contribution to the yaw moment. However, for a mean vertical shear exponent larger than α=0.25, contrary to expectation, a positive mean yaw moment under the positive-yawed inflow may be observed.
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| 2. |
- Abedi, Hamidreza, 1979, et al.
(författare)
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Numerical modelling of neutral atmospheric boundary layer flow through heterogeneous forest canopies in complex terrain (a case study of a Swedish wind farm)
- 2021
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Ingår i: Renewable Energy. - : Elsevier BV. - 0960-1481 .- 1879-0682. ; 180, s. 806-828
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Tidskriftsartikel (refereegranskat)abstract
- This paper exposes the risk of generalization of wind conditions from a single met-mast measurement to be representative of the actual flow field in a wind farm situated in complex terrain. As a case study, Large-Eddy Simulation (LES) of the neutral Atmospheric Boundary Layer (ABL) flow for a mid-western Sweden wind farm is performed. The site-specific complex topography and the forest properties like the Plant Area Density and the tree heights are extracted from the Airborne Laser Scanning (ALS) 3D data, thus the forest is heterogeneous. To emphasize the impact of the local topography and surface roughness on the wind field, the wind turbines are not included in the numerical simulations. The predicted wind speeds using LES are compared to wind speed from the nacelle-mounted anemometers taken from the wind farm's turbine SCADA data, focusing on the wake-free turbines. A sufficient degree of match is observed, supporting the accuracy of the numerical simulations. The results show that inflow variables i.e., mean wind speed, shear exponent and turbulence intensity vary at each wind turbine location justifying the need for turbine-specific assessment of the wind resource in a wind farm located in forested complex terrain. The inter-turbine (between turbines in the wind farm) differences in wind resource is quantified in terms of the difference in turbine-specific structural and mechanical loads by running wind turbine mechanical simulations using the extracting the wind fields predicted by the LES. The results show that not only inter-turbine loads varying significantly in the wind farm, but the turbine loads also differ significantly if a homogeneous assumption is made for the forest. Most importantly, it was found that the homogeneous forest assumption predicted a higher turbulence intensity compared to a heterogeneous forest resulting.
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| 3. |
- Adom, Philip Kofi, et al.
(författare)
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Energy poverty, development outcomes, and transition to green energy
- 2021
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Ingår i: Renewable Energy. - : Elsevier BV. - 0960-1481 .- 1879-0682. ; 178, s. 1337-1352
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Tidskriftsartikel (refereegranskat)abstract
- There is a close connection between energy and development outcomes. Therefore, energy constraints could adversely influence development outcomes. Consequently, building resilience to energy constraints could be one effective channel to improve development outcomes. This study analyses the effect of energy poverty, while considering the influence of green energy transition, on several development outcomes. Our approach delineates the short and long run dynamics of the net effects of energy poverty and renewable energy transition on development outcomes. First, as a direct effect, we find that energy poverty (renewable energy) has a negative (positive) effect on income, education, life expectancy, employment and mobile phone subscription and a positive (negative) effect on poverty, income inequality, sanitation risk and risk of drinking unsafe water. Conditioning the effect of energy poverty on renewable energy, we find that the transition to green energy partially compensates the adverse effects of energy poverty on the various development outcomes considered in this study. Further, we find that, for several of the development outcomes, the risk of inflated energy cost associated with renewable energy transitions in the short-term is likely to neutralise in the long run, except for income poverty and environmental risk factors. We discuss the policy implications.
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| 4. |
- Afzali Gorouh, Hossein, et al.
(författare)
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Thermal modelling and experimental evaluation of a novel concentrating photovoltaic thermal collector (CPVT) with parabolic concentrator
- 2022
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Ingår i: Renewable energy. - : Elsevier. - 0960-1481 .- 1879-0682. ; 181, s. 535-553
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Tidskriftsartikel (refereegranskat)abstract
- In the present study, a zero-dimensional thermal model has been developed to analyze a novel low concentration photovoltaic-thermal (CPVT) collector. The model has been developed by driving heat transfer and energy balance equations for each part of the collector and then solving all the equations simultaneously. Moreover, a Monte-Carlo ray-tracing software has been used for optical stimulations of the parabolic trough solar collector. The novel CPVT collector has been experimentally tested at Gävle University (Sweden) and the model has been validated against the experimental results. The primary energy saving equivalent to the thermal-electrical power cogeneration of the CPVT collector has been determined. The effect of glass cover removal, heat transfer fluid (HTF) inlet temperature and mass flow rate on the collector performance has been investigated. The optimum HTF mass flow rates of the collector for maximum electrical yield and overall primary energy saving were determined under specified operating conditions by considering the pump consumption. The effect of mean fluid temperature on the thermal and electrical efficiencies has been studied and the characteristic equation of the thermal efficiency has been obtained. The thermal and electrical peak efficiencies of the collector have been found to be 69.6% and 6.1%, respectively.
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| 5. |
- Agar, David, et al.
(författare)
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Pelleting torrefied biomass at pilot-scale – Quality and implications for co-firing
- 2021
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Ingår i: Renewable Energy. - : Elsevier BV. - 0960-1481. ; 178, s. 766-774
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Tidskriftsartikel (refereegranskat)abstract
- The co-firing of solid biofuels in coal plants is an attractive and fast-track means of cutting emissions but its potential is linked to biomass densification. For torrefied materials this topic is under-represented in literature. This pilot-scale (121–203 kg h−1) pelleting study generated detailed knowledge on the densification of torrefied biomass compared to untreated biomass. Four feedstock with high supply availability (beech, poplar, wheat straw and corn cob) were studied in their untreated and torrefied forms. Systematic methods were used to produce 180 batches of 8 mm dia. pellets using press channel length (PCL) and moisture content (MC) ranges of 30–60 mm and 7.3–16.6% (wet basis) respectively. Analysis showed that moderate degrees of torrefaction (250–280 °C, 20–75 min) strongly affected pelleting behaviour. The highest quality black pellets had a mechanical durability and bulk density range of 87.5–98.7% and 662–697 kg m−3 respectively. Pelleting energy using torrefied feedstock varied from −15 to +53 kWh t−1 from untreated with increases in production fines. Optimal pelleting MC and PCL were reduced significantly for torrefied feedstock and pellet quality was characterised by a decrease in mechanical durability and an increase in bulk density. Energy densities of 11.9–13.2 GJ m−3 (as received) were obtained.
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| 6. |
- Ahlström, Johan, 1990, et al.
(författare)
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The role of biomass gasification in the future flexible power system – BECCS or CCU?
- 2022
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Ingår i: Renewable Energy. - : Elsevier BV. - 0960-1481 .- 1879-0682. ; 190, s. 596-605
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Tidskriftsartikel (refereegranskat)abstract
- In this work we study if biomass gasification for production of advanced biofuels can also play a role in managing variability in the electricity system. The idea is a CCU/power-to-gas concept to enhance methane production from biomass gasification. The suggested process is flexible in that CO2 not used for methane production can be stored through a BECCS concept that implies negative GHG emissions. For this purpose, rigorous models of three different gasification process configurations were simplified through surrogate modeling and integrated into a dynamic optimization model of regional electricity systems. The results show the diverse advantages of flexible operation between CCU and BECCS and that it is economically beneficial for the system to invest in gasification at the investigated levels of CO2 charge. The gasification option also provides value for low-priced electricity and thus stimulate increased investments in renewable electricity generation, which indicates the importance of considering geographical diversities in the assessment and highlights the importance of studying this type of concept with a time-resolved model. It is clear that the BECCS option is the most used, however, the limited quantities of CO2 used for the CCU option has a large impact on the investments made in the electricity system.
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| 7. |
- Alinejad, T., et al.
(författare)
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Thermo-environomic assessment of an integrated greenhouse with an adjustable solar photovoltaic blind system
- 2020
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Ingår i: Renewable energy. - : Elsevier Ltd. - 0960-1481 .- 1879-0682. ; 156, s. 1-13
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Tidskriftsartikel (refereegranskat)abstract
- Optimum energy consumption and renewable energy utilization reduce environmental impacts and are cost-effective. They are the key aspects of achieving sustainable energy management, such as in the agricultural industry. The contribution of the horticultural section in the global energy demand is approximately 2%, and among its various sections, greenhouses are one of the main systems in modern agriculture that have a great share on energy consumption. In this study, a rose greenhouse is examined and modeled in EnergyPlus as a greenhouse reference (GR). Validation of the developed greenhouse model is carried out with a site experimental measurement. Using the GR as the basic model, 14 various configurations of greenhouses have been assessed by considering a solar photovoltaic blind system (SPBS) in checkerboard arrays 1 m above the greenhouse roof. These modified greenhouses called solar-blind greenhouses (SBGs) have different shading rates and SPBS sizes. To perform a Thermo-environomic assessment, the effects of various parameters, including temperature, relative humidity, natural gas consumption, electricity consumption, and carbon dioxide (CO2) emission reduction, are studied. Results indicate that covering 19.2% of the roof, with no significant change in the illumination level on the plant canopy, will annually reduce natural gas consumption, electricity demand, and CO2 emission by 3.57%, 45.5%, and 30.56 kg/m2, respectively. Moreover, with the SPBS, the annual electricity production is approximated at 42.7 kWh/m2. © 2020 Elsevier Ltd
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| 8. |
- Antonopoulou, Io, 1989-, et al.
(författare)
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Single cell oil and ethanol production by the oleaginous yeast Trichosporon fermentans utilizing dried sweet sorghum stalks
- 2020
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Ingår i: Renewable energy. - : Elsevier. - 0960-1481 .- 1879-0682. ; 146, s. 1609-1617
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Tidskriftsartikel (refereegranskat)abstract
- The ability of the oleaginous yeast Trichosporon fermentans to efficiently produce lipids when cultivated in dried sweet sorghum was evaluated. First, lipid production was evaluated in synthetic media mimicking the composition of sweet sorghum stalks and optimized based on the nitrogen source and C: N ratio. Under optimum conditions, the lipid production reached 3.66 g/L with 21.91% w/w lipid content by using a mixture of sucrose, glucose and fructose and peptone at C: N ratio 160. Cultivation on pre-saccharified sweet sorghum stalks offered 1.97 g/L, while it was found that sweet sorghum stalks can support yeast growth and lipid production without the need for external nitrogen source addition. At an attempt to increase the carbon source concentration for optimizing lipid production, the Crabtree effect was observed in T. fermentans. To this end, the yeast was evaluated for its potential to produce ethanol under anaerobic conditions in synthetic media and sweet sorghum. The ethanol concentration at 100 g/L glucose was 40.31 g/L, while utilizing sweet sorghum by adding a distinct saccharification step and external nitrogen source offered ethanol concentration equal to 23.5 g/L. To the authors’ knowledge, this is the first time that the Crabtree effect is observed in T. fermentans.
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| 9. |
- Aqachmar, Z., et al.
(författare)
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Electrification of Africa through CPV installations in small-scale industrial applications : Energetic, economic, and environmental analysis
- 2022
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Ingår i: Renewable energy. - : Elsevier Ltd. - 0960-1481 .- 1879-0682. ; 197, s. 723-746
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Tidskriftsartikel (refereegranskat)abstract
- This paper aims to evaluate the energetic, economic, and environmental performances of small-scale concentrated photovoltaics (CPV) power systems under 107 African climatic and financial zones with different energy mixes. The proposed concept focuses on small-scale installations for small- or medium-scale industrial premises as such devices are involved in the international strategy about micro-grids. Yearly average electric productions, capacity factors, economic and environmental considerations, and sensitivity were all analysed. The mathematical methodology for calculating the power of a concentrated triple-junction solar cell, the annual energy conversion of a CPV plant, the costs, and the CO2 mitigation were assessed. The parametric study shows that the capacity factor becomes highest for a cell area of 5.5 cm2 or if the concentration ratio reaches the value of 2400. Furthermore, LCOE is lowest for Errachidia in Morocco with 15.88 c$/kWh followed by Fada in Chad with 16.82 c$/kWh, while it is highest in Wad Hajm in Sudan as 5.23 × 1016 c$/kWh. Moreover, South Africa allows the highest reduction of indirect CO2 emissions. Furthermore, energy produced is greatest in Errachidia in Morocco (606.27 GWh), Tiaret in Tunisia (601.11 GWh), and Upington in South Africa (598.11 GWh). Results are shown on innovative GIS maps of Africa. © 2022 Elsevier Ltd
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| 10. |
- Aragon-Briceno, Christian, et al.
(författare)
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Integration of hydrothermal carbonization treatment for water and energy recovery from organic fraction of municipal solid waste digestate
- 2022
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Ingår i: Renewable energy. - : Elsevier BV. - 0960-1481 .- 1879-0682. ; 184, s. 577-591
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Tidskriftsartikel (refereegranskat)abstract
- Anaerobic digestion is an efficient way of using a wet fraction of municipal solid waste (MSW) for energy purposes as it can produce biogas. The moisture content of the digestate after application of mechanical dewatering is still high, and the amount of heat needed for drying is significant. Hydrothermal carbonization (HTC) is a process that can potentially offer great benefits by improved mechanical dewatering and valorization of the digestate into a better quality solid fuel. This study focuses on the determination of the optimum HTC process conditions to recover water from the MSW digestate. Different process conditions as temperature (180, 200, and 230 °C) and residence time (30, 60, and 120 min) were tested. Furthermore, a mass and energy balance was carried out and a process model in Aspen Plus was built. Results showed that HTC treatment increased the water recovery (40–48%) during the dewatering process compared with the original feedstock (18%). The process model showed a positive energy balance of 110 kWh per ton of MSW digestate treated with an electrical efficiency of 23.9%.
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