| 1. |
- Abdelshafy, Alaaeldin M., et al.
(författare)
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Optimized energy management strategy for grid connected double storage (pumped storage-battery) system powered by renewable energy resources
- 2020
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Ingår i: Energy. - : PERGAMON-ELSEVIER SCIENCE LTD. - 0360-5442 .- 1873-6785. ; 192
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents a grid-connected double storage system (DSS) consisting of pumped-storage hydropower (PSH) and battery. The system is supplied by photovoltaics and wind turbines. In the proposed hybrid system, batteries absorb excess renewable energy that cannot be stored in PSH and they cover loads that cannot be supplied from the water turbine. To improve the system performance, a novel energy management strategy for the DSS is proposed. The strategy is based on an optimized factor that governs the charging process of the DSS. The problem of the optimal system design is solved by a non-dominated sorting genetic algorithm (NSGA-II). The multi-objective function considers simultaneously the minimal investment cost and minimal CO2 emissions. A comparative study of photovoltaic/wind/pumped-storage hydropower and photovoltaic/wind/double storage system is performed to show the effectiveness of the proposed strategy in terms of system economic and environmental performance. The considered location of the PSH station is on Attaqa Mountain at Suez (Egypt). The results indicate the effectiveness of the proposed energy management strategy for the storage system from economic and environmental perspectives. Coupling the battery with the PSH reduces the electricity cost by 22.2% and results in minimal energy exchange with the national grid (5% of the annual demand). A sensitivity analysis shows the largest variation of the electricity cost with changing the capital cost of the solar and wind generators. Also, it is observed that when the load increases, the optimal size of the system components increases, but it isn't proportional with the demand increase as could be expected. (C) 2019 Elsevier Ltd. All rights reserved.
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| 2. |
- Ahmad, Waqar, et al.
(författare)
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Benzene conversion using a partial combustion approach in a packed bed reactor
- 2022
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Ingår i: Energy. - : Elsevier. - 0360-5442 .- 1873-6785. ; 239:Part C
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Tidskriftsartikel (refereegranskat)abstract
- This study investigates the partial combustion technique for tar conversion using a modified experimental set up comprising a packed bed reactor with bed-inside probe for air supply. Simulated producer gas (SPG) and benzene were selected as a real producer gas alternative and model tar component respectively. The benzene conversion was investigated under different experimental conditions such as reactor temperature (650–900 °C), packed bed height (0–12 cm), residence time (1.2–1.9 s), air fuel ratio (0.2 and 0.3) and SPG composition. The results showed insignificant effect of temperature over benzene conversion while air fuel ratio of 0.3 caused high benzene conversion than at 0.2. Absence of packed bed lead high benzene conversion of 90% to polyaromatic hydrocarbons (PAHs) compared to similar low PAHs free benzene conversion of 32% achieved at both packed heights. In SPG composition effect, H2 and CH4 had a substantial inverse effect on benzene conversion. An increase in H2 concentration from 12 to 24 vol% increased the benzene conversion from 26 to 45% while an increase in CH4 concentration from 7 to 14 vol% reduced the benzene conversion from 28 to 4%. However, other SPG components had insignificant impacts on benzene conversion.
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| 3. |
- Aichmayer, Lukas, et al.
(författare)
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Thermo-mechanical solar receiver design and validation for a micro gas-turbine based solar dish system
- 2020
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Ingår i: Energy. - : Elsevier BV. - 0360-5442 .- 1873-6785. ; 196
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Tidskriftsartikel (refereegranskat)abstract
- This work presents the comprehensive development of a solar receiver for the integration into a micro gas-turbine solar dish system. Special focus is placed on the thermo-mechanical design to ensure the structural integrity of all receiver components for a wide range of operating conditions. For the development, a 3-dimensional coupled multi-physics model is established and is validated using experimental data. Contrary to previous studies, the temperature of the irradiated front surface of the absorber is included in the comprehensive validation process which results in a high level of confidence in the receiver design.Finally, a full-scale solar receiver for the integration into the OMSoP solar dish system is designed and its performance determined for a wide operating range to define its safe operating envelope using the validated model. It is shown that the receiver is capable of operating at 803_C with an efficiency of 82.1% and a pressure drop of 0.3% at the nominal operating point, while at the same time functioning effectively for a wide range of off-design conditions without compromising its structural integrity. At the nominal operating point, the maximum comparison stress of the porous absorber is 5.6 MPa compared to a permissible limit of 7.4 MPa.
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| 4. |
- Alirahmi, Seyed Mojtaba, et al.
(författare)
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An innovative four-objective dragonfly-inspired optimization algorithm for an efficient, green, and cost-effective waste heat recovery from SOFC
- 2023
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Ingår i: Energy. - : Elsevier BV. - 0360-5442 .- 1873-6785. ; 263
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Tidskriftsartikel (refereegranskat)abstract
- This work proposes a novel yet practical dragonfly optimization algorithm that addresses four competing ob-jectives simultaneously. The proposed algorithm is applied to a hybrid system driven by the solid oxide fuel cell (SOFC) integrated with waste heat recovery units. A function-fitting neural network is developed to combine the thermodynamic model of the system with the dragonfly algorithm to mitigate the calculation time. According to the optimization outcomes, the optimum parameters create significantly more power and have a greater exergy efficiency and reduced product costs and CO2 emissions compared to the design condition. The sensitivity analysis reveals that while the turbine inlet temperatures of power cycles are ineffective, the fuel utilization factor and the current density significantly impact performance indicators. The scatter distribution indicates that the fuel cell temperature and steam-to-carbon ratio should be kept at their lowest bound. The Sankey graph shows that the fuel cell and afterburner are the main sources of irreversibility. According to the chord diagram, the SOFC unit with a cost rate of 13.2 $/h accounts for more than 29% of the overall cost. Finally, under ideal conditions, the flue gas condensation process produces an additional 94.22 kW of power and 760,056 L/day of drinkable water.
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| 5. |
- Arnaudo, Monica, et al.
(författare)
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Techno-economic analysis of demand side flexibility to enable the integration of distributed heat pumps within a Swedish neighborhood
- 2020
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Ingår i: Energy. - : Elsevier. - 0360-5442 .- 1873-6785. ; 195
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Tidskriftsartikel (refereegranskat)abstract
- The energy infrastructure in Stockholm faces an imminent problem caused by the saturation of the electricity distribution grid capacity. Given promising economic savings, a few city neighborhoods have decided to switch from district heating to domestic heat pumps. Thus, technical concerns arise. This study aims at proposing demand side management solutions to unlock the integration of distributed heat pumps. A techno-economic analysis is presented to assess the potential of using the buildings’ thermal mass as energy storage. By means of co-simulation, the electricity grid and the buildings are coupled through a feedback control. The grid capacity is monitored to avoid overloadings. The indoor temperature is controlled in order to serve as thermal energy storage. It is found that, given the grid's capacity limits, the infrastructure should still be partly connected to the district heating (around 7% of the heat demand). This dependency decreases of around 1% when the buildings’ thermal mass is used as thermal storage, with a range of ±0.5 °C. On a heat pump level, the disconnections decrease up to 50%, depending on the buildings’ thermal mass capacity. Thus better techno-economic (about −2% on the levelized cost) and environmental (about −1% on the CO2 emissions) performances are unlocked.
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| 6. |
- Arnaudo, Monica, et al.
(författare)
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Waste heat recovery in low temperature networks versus domesticheat pumps - A techno-economic and environmental analysis
- 2021
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Ingår i: Energy. - : Elsevier BV. - 0360-5442 .- 1873-6785. ; 219
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Tidskriftsartikel (refereegranskat)abstract
- The planning of energy infrastructures in new districts often follows the practice adopted for the rest of the city. In Stockholm, district heating is a common solution for multi-apartment neighborhoods. Recently, because of an average clean electricity mix, heat pumps have gained interest. However, European studies suggest to limit the reliance on electrification to avoid an extreme demand increase. Thus, an effort is required to improve the environmental impact of alternative options. This study proposes waste heat recovery in low temperature networks as a promising solution. By means of a techno-economic and environmental analysis, this option is compared to domestic heat pumps. A new approach is proposed to combine a district level perspective with simulation tools able to capture sector-coupling interactions. Scenarios, for a real neighborhood, assess waste heat recovery potential and electricity grid loading status. Results show that a waste heat recovery capacity equal to 10% of the peak load can reduce fossil fuel use of 40%. Local grid limitations are shown to be a bottleneck for the feasibility of domestic heat pumps. Their heat generation cost is 28% higher than for district heating. The carbon footprint is strongly dependent on the emission factor of the electricity mix (+11%/-24%).
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| 7. |
- Averfalk, Helge, 1988-, et al.
(författare)
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Economic benefits of fourth generation district heating
- 2020
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Ingår i: Energy. - London, UK : Elsevier. - 0360-5442 .- 1873-6785. ; 193
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Tidskriftsartikel (refereegranskat)abstract
- The main impetus for lower distribution temperatures in district heating systems is the lower heat supply costs obtained by these lower temperatures. In this paper, the differences in heat supply costs for two different temperature levels have been estimated for various future heat supply options. The estimations were obtained by modelling a district heating system characterised by typical climate conditions for Central Europe. High sensitivity to lower supply costs from lower temperatures was found for geothermal heat, industrial excess heat, and heat pumps, whereas low cost sensitivity was estimated for combined heat and power plants using waste or biomass. Lower heat distribution loss constitutes a minor component of the total cost reductions. The current use of high heat distribution temperatures was identified as an important barrier for the transition to renewable and recycled heat supply in district heating systems. Hence, lower distribution temperatures would facilitate this required transition because lower distribution temperatures provide higher profitability for these renewable and recycled heat sources. © 2019 The Authors. Published by Elsevier Ltd.
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| 8. |
- Badenes, Borja, et al.
(författare)
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Development of advanced materials guided by numerical simulations to improve performance and cost-efficiency of borehole heat exchangers (BHEs)
- 2020
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Ingår i: Energy. - : Elsevier Ltd. - 0360-5442 .- 1873-6785. ; 201
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Tidskriftsartikel (refereegranskat)abstract
- One promising way to improve the efficiency of borehole heat exchangers (BHEs) in shallow geothermal applications is to enhance the thermal properties of the materials involved in its construction. Early attempts, such as using metal tubes in the 1980s or the utilization of thin–foil hoses, did not succeed in being adopted by the market for diverse reasons (cost, corrosion, fragility, etc…). In parallel, the optimization of pipe size, the use of double-U-tubes, thermally enhanced grout, etc. were able to bring the measure for the BHE efficiency, the borehole thermal resistance, from 0.20 to 0.15 K/(Wm) down to 0.08–0.06 K/(Wm) in the best solutions today. A further improvement cannot be expected without development of new, dedicated materials, combining the versatility of plastic like PE with an increased thermal conductivity that matches the respective properties of the rock and soil. This goal was included in the Strategic Research and Innovation Agenda of the European Technology Platform on Renewable Heating and Cooling in 2013. Within an EU supported project, both BHE pipes and grouting materials have been produced prototypically in small amounts, suitable for the first tests in the intended environment. The present work explains the research pathways envisaged and the resulting sensitivity analysis to highlight the influence of some of the most critical parameters that affect the overall performance of a GSHP system. The results have allowed guiding the real development of more efficient new advanced materials for different scenarios representative of different European regions. Finally the developed materials and their properties are discussed, including a comparative assessment about their compliance with reference material properties as currently seen in the BHE market. © 2020 The Author(s)
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| 9. |
- Balderrama, Sergio, et al.
(författare)
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Surrogate models for rural energy planning : Application to Bolivian lowlands isolated communities
- 2021
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Ingår i: Energy. - : Elsevier BV. - 0360-5442 .- 1873-6785. ; 232
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Tidskriftsartikel (refereegranskat)abstract
- Thanks to their modularity and their capacity to adapt to different contexts, hybrid microgrids are a promising solution to decrease greenhouse gas emissions worldwide. To properly assess their impact in different settings at country or cross-country level, microgrids must be designed for each particular situation, which leads to computationally intractable problems. To tackle this issue, a methodology is proposed to create surrogate models using machine learning techniques and a database of microgrids. The selected regression model is based on Gaussian Processes and allows to drastically decrease the computation time relative to the optimal deployment of the technology. The results indicate that the proposed methodology can accurately predict key optimization variables for the design of the microgrid system. The regression models are especially well suited to estimate the net present cost and the levelized cost of electricity (R-2 = 0.99 and 0.98). Their accuracy is lower when predicting internal system variables such as installed capacities of PV and batteries (R-2 = 0.92 and 0.86). A least-cost path towards 100% electrification coverage for the Bolivian lowlands mid-size communities is finally computed, demonstrating the usability and computational efficiency of the proposed framework.
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| 10. |
- Behi, Mohammadreza, et al.
(författare)
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Experimental and numerical investigation on hydrothermal performance of nanofluids in micro-tubes
- 2020
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Ingår i: Energy. - : Elsevier Ltd. - 0360-5442 .- 1873-6785. ; 193
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Tidskriftsartikel (refereegranskat)abstract
- Nanoscale solid particles suspended in a base liquid are a new class of nano-engineered colloidal suspension, defined with a coined name of nanofluids (NFs). The effect of dispersing nanoparticles (NPs) on the hydraulic and thermal (hydrothermal) performance of the conventional coolants is a matter of importance in many applications. This work experimentally and numerically presents the effect of different parameters, including the concentration and size of the NPs, on two primary parameters, namely heat transfer coefficient and friction factor in a microtube. The numerical modeling of colloidal suspensions was conducted based on single-phase as well as Eulerian-Mixture two-phase approaches and showed a good agreement with experimental results. The numerical results displayed that the suspended NPs remarkably increased the convective heat transfer coefficient as well as friction factor by as much as 42% and 22% (in NP concentration range of 1%–9%, and NP size range of 13–130 nm and Reynolds number of 400) respectively. Besides, two new correlations were developed based on the results obtained from experimentally validated models to predict the hydrothermal response of NFs in the laminar regime. Moreover, correlations were successfully created to predict the Nusselt number and friction factor of nanofluids, with ±8% and ±5% agreement between numerical data and predictions, respectively.
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