| 1. |
- Gehlin, S E A, et al.
(författare)
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Influence on thermal response test by groundwater flow in vertical fractures in hard rock
- 2003
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Ingår i: Renewable Energy. - 0960-1481 .- 1879-0682. ; 28:14, s. 2221-2238
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Tidskriftsartikel (refereegranskat)abstract
- In this paper different approaches to groundwater flow and its effect in the vicinity of a borehole ground heat exchanger are discussed. The common assumption that groundwater flow in hard rock may be modelled as a homogeneous flow in a medium with an effective porosity is confronted and models for heat transfer due to groundwater flow in fractures and fracture zones are presented especially from a thermal response test point of view. The results indicate that groundwater flow in fractures even at relatively low specific flow rates may cause significantly enhanced heat transfer, although a continuum approach with the same basic assumptions would suggest otherwise. (C) 2003 Elsevier Science Ltd. All rights reserved.
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| 2. |
- Gehlin, S E A, et al.
(författare)
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The influence of the thermosiphon effect on the thermal response test
- 2003
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Ingår i: Renewable Energy. - 0960-1481 .- 1879-0682. ; 28:14, s. 2239-2254
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Tidskriftsartikel (refereegranskat)abstract
- The issue of natural and forced groundwater movements, and its effect on the performance of ground heat exchangers is of great importance for the design and sizing of borehole thermal energy systems (BTESs). In Scandinavia groundwater filled boreholes in hard rock are commonly used. In such boreholes one or more intersecting fractures provide a path for groundwater flow between the borehole and the surrounding rock. An enhanced heat transport then occurs due to the induced convective water flow, driven by the volumetric expansion of heated water. Warm groundwater leaves through fractures in the upper part of the borehole while groundwater of ambient temperature enters the borehole through fractures at larger depths. This temperature driven flow is referred to as thermosiphon, and may cause considerable increase in the heat transport from groundwater filled boreholes. The thermosiphon effect is connected to thermal response tests, where the effective ground thermal conductivity is enhanced by this convective transport. Strong thermosiphon effects have frequently been observed in field measurements. The character of this effect is similar to that of artesian flow through boreholes. (C) 2003 Elsevier Science Ltd. All rights reserved.
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| 3. |
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| 4. |
- Granqvist, C. G., et al.
(författare)
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Progress in Smart Windows Research: Improved Electrochromic W Oxide Films and Transparent Ti-Ce Oxide Counter Electrodes
- 1996
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Ingår i: Renewable energy. - : Elsevier BV. - 0960-1481 .- 1879-0682. ; 8:1-4, s. 97-106
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Tidskriftsartikel (refereegranskat)abstract
- We review recent work on sputter deposited W-oxide-based films. Improved electrochemical durability was obtained by electron bombardment during deposition, and enhanced coloration/bleaching dynamics was obtained by fluorination. Spectrally resolved scattering measurements indicated that haze levels ≪ 1 % could be reached. Oblique angle deposition could yield angular selectivity. New results are given for sputtered Ti-Ce oxide films, showing their capacity as counter electrodes in transparent electrochromic devices.
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| 5. |
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| 6. |
- 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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| 7. |
- 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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| 8. |
- 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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| 9. |
- Adsten, Monika, et al.
(författare)
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The influence of climate and location on collector performance
- 2002
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Ingår i: Renewable energy. - 0960-1481 .- 1879-0682. ; 25:4, s. 499-509
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Tidskriftsartikel (refereegranskat)abstract
- The influence of annual climate variations on the performance of solar thermal collectors in the northern part of Europe has been investigated. The annual solar collector energy output has been calculated with the MINSUN simulation program using hourly, measured climatic data for the years 1983–98 for three cities situated in the south (Lund), central (Stockholm) and north (Luleå) of Sweden. A synthetic year created with the Meteonorm weather simulation program was also used in the simulations. Two solar thermal collectors were modelled: a flat plate solar collector and a tubular vacuum collector, both of commercial standard.The thermal energy output is strongly correlated to the annual global irradiation at a horizontal surface. The annual average energy delivered from the flat plate collector was 337 kWh/m2 for Stockholm (337 for Lund and 298 for Luleå), and from the vacuum tube collector 668 kWh/m2 for Stockholm (675 for Lund and 631 for Luleå) at an operating temperature of T=50°C. Maximum deviations from the average value for this 16-year period are around 20% for the flat plate and 15% for the vacuum tube collector, at T=50°C.The relation between global irradiation on a horizontal surface and the annually collected thermal energy at a constant operating temperature could be fitted to a linear equation: qu=aG(0°)+bT, where qu is the energy output from the collector, G(0°) the global irradiation at a horizontal surface, T the average temperature of the collector fluid, and a and b fitting parameters in a double linear regression analysis.
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| 10. |
- 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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