| 1. |
- Abedi, Hamidreza, 1979, et al.
(författare)
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Assessment of Wind Field Generation Methods on Predicted Wind Turbine Power Production Using a Free Vortex Filament Wake Approach
- 2022
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Ingår i: Journal of Solar Energy Engineering, Transactions of the ASME. - : ASME International. - 1528-8986 .- 0199-6231. ; 144:2
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Tidskriftsartikel (refereegranskat)abstract
- The generated power and thrust of a wind turbine strongly depend on the flow field around the turbine. In the present study, three different inflow methods, i.e., a time series (TS) from large eddy simulation (LES) of atmospheric boundary layer flow field, a synthetic turbulent flow field using the Mann model (MM), and a steady-state mean wind profile with shear, are integrated with the free vortex filament wake method to investigate the effect of wind field generation methods on the wind turbine performance where the impact of the turbine and the trailing wake vortices on the turbulent flow fields is ignored. For this purpose, an in-house vortex lattice free wake (VLFW) code is developed and used to predict the aerodynamic loads on rotor blades. The NREL 5-MW reference wind turbine is used for the VLFW simulations. For a fair assessment of different inflow generation methods on power production of a wind turbine, it is not sufficient that the generated wind fields employed in the TS and MM methods have the same streamwise mean velocity and turbulence intensity at hub height. Instead, the generated inflows must have equivalent power-spectral densities especially at low frequencies since the rotor blades essentially respond to the large-scale fluctuations (macroscopic scales) rather than small-scale fluctuations (microscopic scales). A faster energy decay rate of LES inflow leads to a higher energy content in the TS method at low frequencies (associated with the macroscopic dynamics of the rotor blades). This extra kinetic energy results in a slightly higher mean power production while using the TS method although the inflow conditions at hub height/rotor plane are the same for both the TS and MM methods. Moreover, the impact of simulation time (the length of time integration) on the power production of a wind turbine (exposed to an unsteady inflow) must be taken into account. A short simulation time remarkably affects the mean wind speed over the rotor area for identical turbulent inflows. For Taylor's hypothesis application using a single LES flow field, the results show a significant difference in the mean powers corresponding to the different realizations due to large turbulent fluctuations.
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| 2. |
- Abedi, Hamidreza, 1979, et al.
(författare)
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Enhancement of Free Vortex Filament Method for Aerodynamic Loads on Rotor Blades
- 2017
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Ingår i: Journal of Solar Energy Engineering, Transactions of the ASME. - : ASME International. - 1528-8986 .- 0199-6231. ; 6B
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Tidskriftsartikel (refereegranskat)abstract
- The aerodynamics of a wind turbine is governed by the flow around the rotor, where theprediction of air loads on rotor blades in different operational conditions and its relationto rotor structural dynamics is one of the most important challenges in wind turbine rotorblade design. Because of the unsteady flow field around wind turbine blades, predictionof aerodynamic loads with high level of accuracy is difficult and increases the uncertaintyof load calculations. An in-house vortex lattice free wake (VLFW) code, based on theinviscid, incompressible, and irrotational flow (potential flow), was developed to studythe aerodynamic loads. Since it is based on the potential flow, it cannot be used to predictviscous phenomena such as drag and boundary layer separation. Therefore, it must becoupled to tabulated airfoil data to take the viscosity effects into account. Additionally, adynamic approach must be introduced to modify the aerodynamic coefficients forunsteady operating conditions. This approach, which is called dynamic stall, adjusts thelift, the drag, and the moment coefficients for each blade element on the basis of the two dimensional(2D) static airfoil data together with the correction for separated flow. Twodifferent turbines, NREL and MEXICO, are used in the simulations. Predicted normaland tangential forces using the VLFW method are compared with the blade elementmomentum (BEM) method, the GENUVP code, and the MEXICO wind tunnel measurements. The results show that coupling to the 2D static airfoil data improves the load andpower predictions while employing the dynamic stall model to take the time-varying operating conditions into consideration is crucial.
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| 3. |
- Benini, Ernesto, et al.
(författare)
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Optimal design of horizontal-axis wind turbines using blade-element theory and evolutionary computation
- 2002
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Ingår i: Journal of solar energy engineering. - : ASME International. - 0199-6231 .- 1528-8986. ; 124:4, s. 357-363
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Tidskriftsartikel (refereegranskat)abstract
- This paper describes a multi-objective optimization method for the design of stall-regulated horizontal-axis wind turbines. Two modules are used for this purpose: an aerodynamic model implementing the blade-element theory and a multi-objective evolutionary algorithm. The former provides a sufficiently accurate solution of the flow field around the rotor disc; the latter handles the decision variables of the optimization problem, i.e., the main geometrical parameters of the rotor configuration, and promotes function optimization. The scope of the method is to achieve the best trade-off performance betoveen two objectives: annual energy production per square meter of wind park (to be maximized) and cost of energy (to be minimized). Examples of the best solutions found by the method are described and their performance compared with those of commercial wind turbines
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| 4. |
- Dyachuk, Eduard, et al.
(författare)
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Simulating Pitching Blade With Free Vortex Model Coupled With Dynamic Stall Model for Conditions of Straight Bladed Vertical Axis Turbines
- 2015
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Ingår i: Journal of solar energy engineering. - : ASME International. - 0199-6231 .- 1528-8986. ; 137:4
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Tidskriftsartikel (refereegranskat)abstract
- This study is on the straight bladed vertical axis turbines (VATs), which can be utilized for both wind and marine current energy. VATs have the potential of lower installation and maintenance cost. However, complex unsteady fluid mechanics of these turbines imposes significant challenges to the simulation tools. Dynamic stall is one of the phenomena associated with the unsteady conditions, and it is in the focus of the study. The dynamic stall effects are very important for VATs, since they are usually passively controlled through the dynamic stall. A free vortex model is used to calculated unsteady attached flow, while the separated flow is handled by the dynamic stall model. This is compared to the model based solely on the Leishman-Beddoes algorithm. The results are assessed against the measured data on pitching airfoils. A comparison of force coefficients between the simulations and experiments is done at the conditions similar to the conditions of H-rotor type VATs.
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| 5. |
- Gabrielsson, A, et al.
(författare)
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Thermal energy storage in soils at temperatures reaching 90 degrees C
- 2000
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Ingår i: Journal of solar energy engineering. - 0199-6231 .- 1528-8986. ; 122:1
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Tidskriftsartikel (refereegranskat)abstract
- Using soil and groundwater for heat storage offers an opportunity to increase the potential for renewable energy sources. For example, solar heating in combination with high temperature storage, e.g., using ducts in the ground, has the potential of becoming an environment friendly and economically competitive form of heat supply. Technology is developed to reduce ground construction costs and to ensure that adequate attention is paid to the geotechnical potentials and limitations of such systems, in the temperature range between neutral ground temperature up to 90 degreesC. Investigations of real plants and in the laboratory have given valuable knowledge on the thermal effects on clayey soils as well as on the surroundings of high temperature stores in soft clay. The operational function of heat stores, with respect to heat transfer capacity of ground heat exchangers and heat losses, can be predicted with good agreement. For the uppermost part of the temperature range, long term performance, cost verification and thermal endurance of materials involved including the storage medium, is recommended using a full-scale demonstration plant.
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| 6. |
- Guedez, Rafael, 1989-, et al.
(författare)
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A Methodology for Determining Optimum Solar Tower Plant Configurations and Operating Strategies to Maximize Profits Based on Hourly Electricity Market Prices and Tariffs
- 2016
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Ingår i: Journal of solar energy engineering. - : ASME Press. - 0199-6231 .- 1528-8986. ; 138:2
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Tidskriftsartikel (refereegranskat)abstract
- The present study analyzes the influence that market conditions have on determining optimum molten salt solar tower plants with storage that maximizes profits (in terms of plant configuration, sizing, and operation) for a location in South Africa. Three different scenarios based on incentive programs and local wholesale electricity prices are considered. A multi-objective optimization modeling approach was followed, showing the tradeoff curves between minimizing investment and maximizing profits when varying critical size-related parameters (such as nameplate capacity, solar multiple (SM), and storage capacity) together with power-cycle design and operating specifications including dynamic startup curves and different storage dispatchability strategies. Results are shown by means of a comparative analysis between optimal plants found for each scenario, highlighting the value that storage has under the current two-tier tariff scheme and the relevance of designing a suitable policy for technology development. Finally, a final analysis is performed with regard to the indicators used for economic evaluation of power plants, by comparing the differences between optimum designs found when using the levelized cost of electricity (LCoE) solely as performance indicator instead of cash-flows and profit-based indicators, such as the internal rate of return (IRR).
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| 7. |
- Guedez, Rafael, et al.
(författare)
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A Techno-Economic Analysis Of Hybrid Concentrating Solar Power And Solar Photovoltaic Power Plants For Firm Power In Morocco
- 2016
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Ingår i: Journal of solar energy engineering. - : ASME Press. - 0199-6231 .- 1528-8986.
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Tidskriftsartikel (refereegranskat)abstract
- The present study evaluates the optimum configurations and operating strategies of hybrid concentrating solar power and solar photovoltaic power plants for minimizing levelized costs of electricity. These configurations were also required to meet specific design objectives as provided by competitive bid tenders, such as power plant size and operating hours, for a suitable location near Midelt, Morocco. A detailed techno-economic model of the hybrid plant was developed at KTH’s in-house optimization tool DYESOPT, which allows power plant evaluation by means of technical and economic performance indicators. Results show that hybrid plants are able to achieve higher capacity factors. It is also confirmed that, under current cost estimates, hybridization enables a lower cost solution for a given high capacity factor objective than what is achievable either with stand-alone concentrating solar power or solar photovoltaic power plants, respectively. The analysis highlights synergies among the technologies and shows the relation and influence between sizing and operation of their critical components. Main challenges for successful hybridization are also raised together with recommendations for addressing them. Lastly, optimum configurations found for different tender conditions are compared and a brief discussion section at the end is introduced to highlight the relevance of adequate policy design and its impact on the work of project developers for proposing the most competitive solutions
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| 8. |
- Guedez, Rafael, et al.
(författare)
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Reducing the Number of Turbine Starts in Concentrating Solar Power Plants through the Integration of Thermal Energy Storage
- 2015
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Ingår i: Journal of solar energy engineering. - : ASME Press. - 0199-6231 .- 1528-8986. ; 137:2
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Tidskriftsartikel (refereegranskat)abstract
- The operation of steam turbine units in solar thermal power plants is very different than in conventional base-load plants. Due to the variability of the solar resource, much higher frequencies of plant start-ups are encountered. This study provides an insight to the influence of thermal energy storage (TES) integration on the typical cycling operation of solar thermal power plants. It is demonstrated that the integration of storage leads to significant reductions in the annual number of turbine starts and is thus beneficial to the turbine lifetime. At the same time, the effects of storage integration on the electricity costs are analyzed to ensure that the designs remain economically competitive. Large storage capacities, can allow the plant to be shifted from a daily starting regime to one where less than 20 plant starts occur annually. Additionally, the concept of equivalent operating hours (EOHs) is used to further analyze the direct impact of storage integration on the maintenance planning of the turbine units.
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| 9. |
- Hallström, Olof
(författare)
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Design Optimization of a Sorption Integrated Sydney Type Vacuum Tube Collector
- 2017
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Ingår i: Journal of solar energy engineering. - : ASME International. - 0199-6231 .- 1528-8986. ; 139:2
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Tidskriftsartikel (refereegranskat)abstract
- In order to reach the targets on emissions set by the European Commission, both new and existing buildings must reduce their fossil fuel inputs. Solar thermal cooling supplying on-site renewable heating and cooling could potentially contribute toward this goal. In this paper, a novel concept for solar thermal cooling providing efficient coproduction of cooling and heating based on sorption integrated vacuum tube collectors is proposed. A prototype collector has been constructed and tested in a solar laboratory based on a method developed specifically for sorption integrated collectors. From the test results, the key performance parameters have been determined and used to calibrate a mathematical model for trnsys environment. System simulation has been conducted to optimize the collector and sorption module configuration by performing a parametric study where different vacuum tube center-center (C-C) distances and sorption module designs are tested for a generic hotel in Ankara, Turkey. The parametric study showed that the heating and cooling output per year can be as high as 1000 kWh/m2 for solar fractions above 50%, and that the output per sorption module compared to the prototype can more than double with an optimized design. Furthermore, cooling conversion efficiencies defined as total cooling output per total solar insolation can be as high as 26% while simultaneously converting 35-40% of the incident solar energy into useful hot water.
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| 10. |
- Laing, D, et al.
(författare)
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Hybrid Dish/Stirling systems: Combustor and heat pipe receiver development
- 2002
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Ingår i: Journal of Solar Energy Engineering. - : ASME International. - 0199-6231 .- 1528-8986. ; 124:2, s. 176-181
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Tidskriftsartikel (refereegranskat)abstract
- A hybrid sodium heat pipe receiver has been developed within the project HYHPIRE, funded 50% by the European Commission. The hybrid receiver was designed for the SBP/LCS 10-kWel dish/Stirling system with the SOLO-161 Stirling engine. Design of the heat pipe receiver and combustion system are described in this paper The system has been tested successfully in all operation modes. Results and experience from the lab tests in combustion-only mode, as well as results from demonstration testing in the dish in solar-only, gas-only, and hybrid mode on the Plataforma Solar de Almeria (PSA) in Spain, are reported.
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