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  • 1.
    Ackermann, Thomas
    et al.
    KTH, Superseded Departments.
    Andersson, G.
    Söder, Lennart
    KTH, Superseded Departments.
    Overview of government and market driven programs for the promotion of renewable power generation2001In: Renewable energy, ISSN 0960-1481, E-ISSN 1879-0682, Vol. 22, no 1-3, p. 197-204Article in journal (Refereed)
  • 2.
    Bekele, Getachew
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Palm, Björn
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Solar-wind-based village electrification in Ethiopia: a comparision of technologiesIn: Renewable energy, ISSN 0960-1481, E-ISSN 1879-0682Article in journal (Refereed)
    Abstract [en]

    The aim of this paper is to investigate the possibility of supplying electriclight and potable water from a solar-wind based hybrid system. The main target is a remotely resettled community in Ethiopia out of reach of the electric grid. The wind energy potential of the location has been assessed in a previous article. The solar potential has also been investigated in an accompanying article awaiting publication. Based on the findings of the potential, a feasibility study has been carried out on how to supply electricity to the community, modeled as having 200 families, comprising of approximately 1000 to 1200 people in total. A community school and a health post is also considered for the community. The electric load considered is of both primary and deferrable types consisting of lighting ,water pumps, radio receivers, and some clinical equipment. In theattempt of finding the most economical solution, a system with less energy efficient, and less expensive components have been compared to a more expensive system with the latest, most energy efficient ,technology on both the supply and load sides.

    A system solution on individual basis (solution per house hold) has also been considered and the net present cost (NPC) is compared against the aggregate solution. A software tool, Hybrid Optimization Model for Electric Renewables (HOMER) is used for the analysis. The result of the analysis is a list of feasible power supply systems, sorted according to their net present cost. Furthermore, sensitivity diagrams, showing the influence of wind speeds, PV costs, and diesel prices on the optimum solutions are also provided.

  • 3. Breton, Simon-Philippe
    et al.
    Nilsson, Karl
    Uppsala University Campus Gotland, Wind Energy, Sweden .
    Olivares-Espinosa, Hugo
    Masson, Christian
    Dufresne, Louis
    Ivanell, Stefan
    KTH, School of Engineering Sciences (SCI), Mechanics, Stability, Transition and Control. Uppsala University Campus Gotland, Wind Energy, Sweden .
    Study of the influence of imposed turbulence on the asymptotic wake deficit in a very long line of wind turbines2014In: Renewable energy, ISSN 0960-1481, E-ISSN 1879-0682, Vol. 70, p. 153-163Article in journal (Refereed)
    Abstract [en]

    The influence of imposed turbulence on the development of the flow along a long row of wind turbines is studied, in search for an asymptotic wake deficit state. Calculations are performed using EllipSys3D, a CFD code that solves the Navier-Stokes equations in their incompressible form using a finite volume approach. In this code, the Large-Eddy Simulation technique is used for modeling turbulence, and the wind turbine rotors are represented as actuator discs whose loading is determined through the use of tabulated airfoil data by applying the blade-element method. Ten turbines are located along a row and separated from each other by seven rotor diameters, which is representative of the distance used in today's offshore wind farms. Turbulence is pre-generated with the Mann model, with imposed turbulence intensity levels of 4.5% and 8.9%. The aim with this study is to investigate features of the flow that depend solely on imposed turbulence and the presence of wind turbine rotors. For this reason, the turbines are isolated from their environment, and no effect from the presence of the atmospheric boundary layer is modeled, i.e., a non-sheared inflow is used. Analysis of the characteristics of the flow as a function of the position along the row of turbines is performed in terms of standard deviation of the velocity components, turbulence kinetic energy, mean velocity, and power spectra of the axial velocity fluctuations. The mean power production along the row of turbines is also used as an indicator. Calculations are performed below rated power, where a generator torque controller implemented in EllipSys3D renders it possible for the turbines to adapt to the flow conditions in which they operate. The results obtained for the standard deviation of the velocity components, turbulence kinetic energy, power and mean velocity as functions of downstream distance show that an asymptotic wake state seems close to be reached, in the conditions tested, near the end of the 10 turbine row. Significant changes towards this state are seen to happen faster when imposing turbulence in the domain. Power spectra of the axial velocity fluctuations are shown to provide interesting information about the turbulence in the flow, but are found not to be useful in determining if an asymptotic wake state is reached. (C) 2014 Elsevier Ltd. All rights reserved.

  • 4.
    Fiedler, Frank
    et al.
    Högskolan i Dalarna.
    Nordlander, Svante
    Högskolan i Dalarna.
    Persson, Tomas
    Högskolan i Dalarna.
    Bales, Chris
    Högskolan i Dalarna.
    Thermal performance of combined solar and pellet heating systems2006In: Renewable energy, ISSN 0960-1481, E-ISSN 1879-0682, Renewable energy, Vol. 31, p. 73-88Article in journal (Refereed)
    Abstract [en]

    Various pellet heating systems are marketed in Sweden, some of them in combination with a solar heating system. Several types of pellet heating units are available and can be used for a combined system. This article compares four typical combined solar and pellet heating systems. System 1 and 2 with a pellet stove, system 3 with a store integrated pellet burner and system 4 with a pellet boiler. The often lower efficiency of pellet heaters compared to oil or gas heaters increases the final energy demand. Consequently, heat losses of the various systems have been studied. The systems have been modeled in TRNSYS and simulated with parameters identified from measurements. For almost all systems the flue gas losses are the main heat losses except for system 3 where store heat losses prevail. Relevant are also the heat losses of the burner and the boiler to the ambient. Significant leakage losses are noticed for system 3 and 4. For buildings with an open internal design system I is the most efficient solution. Other buildings should preferably apply system 2 or 3. The right choice of the system depends also on whether the heater is placed inside or outside of the heated area. Unlike the expectations and results from other studies, the operation of the pellet heaters with modulating combustion power is not necessarily improving the performance. A large potential for system optimisation exists for all studied systems, which when applied could alter the relative merits of the different system types

  • 5. Garcilaso, V.
    et al.
    Barrientos, Javier
    KTH.
    Bobadilla, L. F.
    Laguna, O. H.
    Boutonnet, Magali
    KTH.
    Centeno, M. A.
    Odriozola, J. A.
    Promoting effect of CeO2, ZrO2 and Ce/Zr mixed oxides on Co/Γ-Al2O3 catalyst for Fischer-Tropsch synthesis2019In: Renewable energy, ISSN 0960-1481, E-ISSN 1879-0682, Vol. 132, p. 1141-1150Article in journal (Refereed)
    Abstract [en]

    A series of cobalt-based catalysts have been synthesized using as support γ-Al2O3 promoted by ceria/zirconia mixed oxides with a variable Ce/Zr molar ratio. The obtained catalysts demonstrated oxide promotion results in the protection of the major textural properties, especially for Zr-rich solids. Reducibility of cobalt species was enhanced by the presence of mixed oxides. The chemical composition of the oxide promoter influenced not only physicochemical properties of final catalysts but also determined their performance during the reaction. In this sense, Zr-rich systems presented a superior catalytic performance both in total conversion and in selectivity towards long chain hydrocarbons. The observed Zr-promotion effect could be explained by two significant contributions: firstly, the partial inhibition of Co–Al spinel compound formation by the presence of Zr-rich phases which enhances the availability of Co actives site and secondly, Zr-associate acidic sites promote higher hydrocarbons selectivity.

  • 6.
    Gómez, Maria F
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Energy and Climate Studies, ECS.
    Téllez, A.
    Silveira, Semida
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Energy and Climate Studies, ECS.
    Exploring the effect of subsidies on small-scale renewable energy solutions in the Brazilian Amazon2015In: Renewable energy, ISSN 0960-1481, E-ISSN 1879-0682, Vol. 83, p. 1200-1214Article in journal (Refereed)
    Abstract [en]

    The Brazilian government aims at universal electricity access. The national rural electrification initiative has provided electricity services to more than 14 million people since 2003, mainly through grid extension. However, the initiative has not been able to reach remote areas in the Amazon, thus requiring a review of conditions for small scale off-grid power generation projects. As a result, new rules established under the national rural electrification program address the design and implementation of off-grid power generation projects with an installed capacity up to 100kW. The objective of this paper is to explore the effects of the new set of rules on the levelized cost of electricity for different power generation solutions in the Amazon. Our study shows that the new rules may be beneficial to isolated communities, as they reduce the levelized cost of electricity, favor renewable energy technologies and may contribute to reduce CO2 emissions. In addition, the new rules may help engage new actors to provide rural electrification of the Amazon region. To fully take advantage of the current scheme, action at local level is required to define the most appropriate model for small-scale power generation projects and establish synergies between concessionaires and local energy providers.

  • 7. Holmberg, Henrik
    et al.
    Acuna, José
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Naess, Erling
    Sonju, Otto K.
    Thermal evaluation of coaxial deep borehole heat exchangers2016In: Renewable energy, ISSN 0960-1481, E-ISSN 1879-0682, Vol. 97, p. 65-76Article in journal (Refereed)
    Abstract [en]

    This paper presents a performance study of deep borehole heat exchangers. The coaxial borehole heat exchanger (BHE) has been selected because for the present conditions it has a better performance than the conventional U-tube BHE. A numerical model has been developed to study the coaxial BHE. The model predictions are compared to detailed distributed temperature measurements obtained during a thermal response test. The model is found to accurately predict the behavior of a coaxial BHE. The influence of the flow direction of the mass flow is studied for BHE5 in the range 200 m-500 m. A parametric performance study is then carried out for the coaxial case with different borehole depths, flow rates and collector properties. The results clearly show a significant increase in the system performance with depth. In addition, it is shown that with increasing borehole depth, the heat load that can be sustained by the BHE is significantly increased. An overall performance chart for coaxial BHEs for the depths of 300-1000 m is presented. The chart can be used as a guide when sizing deep BHE installations.

  • 8.
    Horgan, Chris
    et al.
    Department of Civil and Environmental Engineering, University College Cork, Ireland .
    Leahy, Paul
    Department of Civil and Environmental Engineering, University College Cork, Ireland .
    Ni Nuallain, Nora Aine
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Using Energy Payback Time to Optimise Onshore and Offshore Wind Turbine Foundations2013In: Renewable energy, ISSN 0960-1481, E-ISSN 1879-0682, Vol. 53, p. 287-298Article in journal (Refereed)
  • 9.
    Karakaya, Emrah
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Industrial Economics and Management (Dept.), Sustainability and Industrial Dynamics. Universidad Politecnica de Madrid, Spain.
    Nuur, Cali
    KTH, School of Industrial Engineering and Management (ITM), Industrial Economics and Management (Dept.), Sustainability and Industrial Dynamics.
    Hidalgo, Antonio
    Universidad Politecnica de Madrid, Spain.
    Business model challenge: Lessons from a local solar company2016In: Renewable energy, ISSN 0960-1481, E-ISSN 1879-0682, Vol. 85, p. 1026-1035Article in journal (Refereed)
    Abstract [en]

    Solar photovoltaic systems are considered vital renewable energy sources for mitigating climate change and reducing dependency on fossil fuels. However, in some countries, the diffusion rate of photovoltaic systems is decreasing. A case in point is Germany, the country with the highest installed capacity of photovoltaic systems. Given the new conditions in the German market, the diffusion rate continuously declined in both 2012 and 2013. Whether the diffusion rate will again take off is not known. While the recent literature has pointed out that local solar companies have a vital driving role in diffusion, not many studies have yet discussed the business models and challenges such local companies may have. Through an extensive case study, this paper explores the business model of a local solar company in a town of 43,000 habitants in Southern Germany. The case of this company tells about an important business model challenge. Overcoming such challenges may not only let the company survive but also drive the diffusion of solar photovoltaic systems in the region. The results include implications for both industrial actors and policymakers.

  • 10.
    Khatiwada, Dilip
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Energy and Climate Studies, ECS. International Institute for Applied Systems Analysis (IIASA), Austria.
    Leduc, Sylvain
    Ecosystems Services & Management (ESM) program, International Institute for Applied Systems Analysis (IIASA), Austria.
    Silveira, Semida
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Energy and Climate Studies, ECS.
    McCallum, Ian
    Ecosystems Services & Management (ESM) program, International Institute for Applied Systems Analysis (IIASA), Austria.
    Optimizing ethanol and bioelectricity production in sugarcane biorefineries in Brazil2016In: Renewable energy, ISSN 0960-1481, E-ISSN 1879-0682, Vol. 85, p. 371-386Article in journal (Refereed)
    Abstract [en]

    In sugarcane biorefineries, the lignocellulosic portion of the sugarcane biomass (i.e. bagasse and cane trash) can be used as fuel for electricity production and/or feedstock for second generation (2G) ethanol. This study presents a techno-economic analysis of upgraded sugarcane biorefineries in Brazil, aiming at utilizing surplus bagasse and cane trash for electricity and/or ethanol production. The study investigates the trade-off on sugarcane biomass use for energy production: bioelectricity versus 2G ethanol production. The BeWhere mixed integer and spatially explicit model is used for evaluating the choice of technological options. Different scenarios are developed to find the optimal utilization of sugarcane biomass. The study finds that energy prices, type of electricity substituted, biofuel support and carbon tax, investment costs, and conversion efficiencies are the major factors influencing the technological choice. At the existing market and technological conditions applied in the upgraded biorefineries, 300 PJ y-1 2G ethanol could be optimally produced and exported to the EU, which corresponds to 2.5% of total transport fuel demand in the EU. This study provides a methodological framework on how to optimize the alternative use of agricultural residues and industrial co-products for energy production in agro-industries considering biomass supply chains, the pattern of domestic energy demand, and biofuel trade.

  • 11.
    Lazzarotto, Alberto
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Technology.
    A methodology for the calculation of response functions for geothermal fields with arbitrarily oriented boreholes: Part 12016In: Renewable energy, ISSN 0960-1481, E-ISSN 1879-0682, Vol. 86, p. 1380-1393Article in journal (Refereed)
    Abstract [en]

    This article is part of a two paper series presenting a development in the methodology for the calculation of response functions for geothermal fields with arbitrarly oriented boreholes. In the method utilized, boreholes are represented as sets of stacked line sources and the borehole temperatures are calculated by means of a superposition procedure. This particular paper is focused on the efficient computation of the building block of this approach, which is the non dimensional mean temperature response g~(t) along a finite line due to a step heat injection along a second finite line, where the lines are arbitrarily oriented. The speed in computing this function is critical for the applicability of the method. The solution proposed to achieve the required performance is a hybrid approach involving analytical, numerical and implementation aspects: an analytical procedure to simplify the expression of g~(t) was developed, the resulting problem was solved with a tailored numerical method, and the algorithm was implemented using a high-performing programming language. Each of these aspects showed to have a great impact from a performance perspective. The performance achieved in the calculation of g~(t) enables the integration of this method within the scheme utilized for g-functions calculation.

  • 12.
    Lazzarotto, Alberto
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Technology.
    A network-based methodology for the simulation of borehole heat storage systems2014In: Renewable energy, ISSN 0960-1481, E-ISSN 1879-0682, Vol. 62, p. 265-275Article in journal (Refereed)
    Abstract [en]

    The optimization of strategies to operate borehole thermal energy storage systems can play an important role for the exploitation of this technology. Available tools utilized for the design of borehole fields don't consider these aspects in the calculation. For this reason a network-based methodology which gives a sufficient level of detail to describe different system operation strategies has been developed. In particular, the method allows to calculate how the heat is distributed among the borehole heat exchangers in the field according to the way the brine is supplied to the borehole heat storage system. This enables to test the same borehole field configuration pattern for different piping arrangement. An example of application where a simultaneous need of heating and cooling is met by extracting and injecting heat in different region of the ground storage is considered to illustrate the potential of the method.

  • 13.
    Lazzarotto, Alberto
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Technology.
    Björk, Folke
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Technology.
    A methodology for the calculation of response functions for geothermal fields with arbitrarily oriented boreholes: Part 22016In: Renewable energy, ISSN 0960-1481, E-ISSN 1879-0682, Vol. 86, no 01, p. 1353-1361Article in journal (Refereed)
    Abstract [en]

    In the modeling of shallow geothermal systems, the accurate representation of the borehole field configuration is important for a proper estimation of the long term thermal behavior of borehole field systems. Modeling tools based on the so-called g-functions method, utilized for the design of borehole fields, assume that boreholes are vertical. This is a limitation since this condition might not apply in a real installation. This paper is focused on the calculation of g-functions of borehole fields featuring non-vertical boreholes. The strategy utilized consists in representing the boreholes as stacked finite line sources. The temperature along these finite lines, can be calculated by superposition of the effects of each linear heat source in the field. This modeling technique allows to approximate uneven heat distribution among the boreholes and along the axis of each individual borehole. This is a required feature for the calculation of g-functions according to Eskilson's boundary conditions. The test cases presented show that the method yields results that are compatible with the expected physical behavior of the system, and similar to previous results by Eskilson. The computational performance achieved indicates that the method proposed could be potentially utilized during the design phase of these systems.

  • 14. Leijon, Mats
    et al.
    Skoglund, Annika
    KTH, School of Industrial Engineering and Management (ITM), Industrial Economics and Management (Dept.).
    Waters, Rafael
    Rehn, Alf
    Lindahl, Marcus
    On the physics of power, energy and economics of renewable electric energy sources - Part I2010In: Renewable energy, ISSN 0960-1481, E-ISSN 1879-0682, Vol. 35, no 8, p. 1729-1734Article in journal (Refereed)
    Abstract [en]

    Environmental concerns have increasingly led to the installation of Renewable Energy Technologies (RETs) despite the fact that they are recognized as expensive. Innovative efforts within the area are beset with difficulties [1], and they are at risk of producing misdirected or insignificant improvements in terms of the cost effectiveness of total energy conversion systems. This paper investigates how RETs can be evaluated, in terms of economy and engineering solutions, by studying the fundamental physics of renewable energy sources and how it matches with the RETs. This match is described by the "Degree of Utilization". The findings indicate that new innovations should focus on the possible number of full loading hours. RETs that are correctly matched to their energy source generate a higher amount of electric energy and have a higher potential of becoming more competitive. In cases where this aspect has been ignored, leading to relatively small degrees of utilization, it can be understood as an engineering mismatch between installed power, converted energy, and the fundamental physics of the renewable energy sources. Since there is a strong and possibly biased support for so-called mature RETs and already existing solutions, a clarification of how fundamental physical laws affect the cost of investments and payback of investments is needed. The present paper is part I out of II and it focuses on the difference between power and energy and the physics of different energy sources and their utilization. (C) 2009 Elsevier Ltd. All rights reserved.

  • 15. Leutz, R.
    et al.
    Ackermann, Thomas
    KTH, Superseded Departments, Energy Technology.
    Akisawa, A.
    Kashiwagi, T.
    Solar radiation for sorption cooling in Australiasia2001In: Renewable energy, ISSN 0960-1481, E-ISSN 1879-0682, Vol. 22, no 1-3, p. 395-402Article in journal (Refereed)
  • 16. Link, Siim
    et al.
    Arvelakis, Stelios
    Paist, Aadu
    Liliedahl, Truls
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology.
    Rosén, Christer
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology.
    Effect of leaching pretreatment on the gasification of wine and vine (residue) biomass2018In: Renewable energy, ISSN 0960-1481, E-ISSN 1879-0682, Vol. 115, p. 1-5Article in journal (Refereed)
    Abstract [en]

    Utilization of biomass residues for energetic purposes increases the share of renewables in the total energy balance. Gasification is one of the thermochemical processes that converts solid biomass to valuable gaseous products. Prior to the gasification process, biomass material could be treated to improve the quality or composition of the product gas. Our focus is on fluidized bed gasification of untreated vine and pretreated vine residue and pretreated wine residue. Natural and artificial leaching were used as pretreatment methods. Our results showed that CO and H-2 content in the product gas are higher in leached (16.9 and 10.0% respectively) vine residue than in untreated material (14.5 and 7.7% respectively). The naturally leached wine residue was found to have the highest CO content (18.1%) and relatively high H2 content (9.7%) in the product gas, but lower CH4 (1.0%) and CO2 content (5.6%). The results of tar measurements indicated that the leaching pre-treatment lowers the tar content in the evolved product gas, e.g. by 36% in the case of vine residues. As a result, the controlled leaching pretreatment is recommended as an effective way of upgrading the composition of agricultural biomass.

  • 17.
    Mentis, Dimitrios
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Energy Systems Analysis.
    Siyal, Shahid Hussain
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Energy Systems Analysis.
    Korkovelos, Alexandros
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Energy Systems Analysis.
    Howells, Mark
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Energy Systems Analysis.
    A geospatial assessment of the techno-economic wind power potential in India using geographical restrictions2016In: Renewable energy, ISSN 0960-1481, E-ISSN 1879-0682, Vol. 97, p. 77-88Article in journal (Refereed)
    Abstract [en]

    India is a privileged country in terms of wind resource regime. However, most of it remains untapped at the same time as ca 240 million people lack access to electricity in the country (19% of the total population). This calls for a thorough estimation of the amount of wind energy that could be technically and economically seized to assess the potential penetration of wind power into the country's energy system. The utilization of wind energy is associated with a plethora of localization criteria and thus it should be systematically addressed by spatial assessments to guarantee its harmonization with socio-economic systems, infrastructure and ecosystems. This study focuses on onshore wind power and strives to provide with estimates of techno economic potential based on state of the art wind power technology. Socio-economic, geographical and technical criteria regarding the localization of wind farms are outlined and implemented through a detailed a Geographic Information Systems (GIS) analysis. The levelized cost of wind generated electricity is then calculated geospatially. According to this assessment there are several states that signify high yearly wind energy yield, such as Rajasthan, Andhra Pradesh and Gujarat, whilst Goa and other states indicate the least or negligible wind power potential. The levelized cost of generating electricity ranges between 57 and 100 USD/MWh, which places wind power in a competitive position in the Indian electricity market.

  • 18.
    Mentis, Dimitris
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Energy Systems Analysis.
    Hermann, Sebastian
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Energy Systems Analysis.
    Howells, Mark I.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Energy Systems Analysis.
    Welsch, Manuel
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Energy Systems Analysis.
    Siyal, Shahid Hussain
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Energy Systems Analysis.
    Assessing the technical wind energy potential in Africa a GIS-based approach2015In: Renewable energy, ISSN 0960-1481, E-ISSN 1879-0682, Vol. 83, p. 110-125Article in journal (Refereed)
    Abstract [en]

    Nowadays, Africa faces the challenge of generating more electricity to meet existing and future demand in a sustainable way. Africa is a privileged continent in terms of wind resource regime. However, very little of this has been utilized. It is thus essential to identify and define the amount of wind energy that could be technically exploited on the continent. The utilization of wind energy is associated with a myriad of localization criteria and thus it should be systematically addressed by spatial assessments to guarantee its harmonization with socio-economic systems, infrastructure and ecosystems. This study focuses on onshore wind power on the African continent and strives to provide estimates of theoretical, geographical and technical potential based on state of the art wind power technology. Maps of wind power potential at 80m, which is the hub height of a modern wind turbine will be derived via statistical distribution of wind speed data and implementation of wind power curves. Screening criteria regarding the localization of wind farms and related to socio-economic and geographic constraints are outlined and implemented through a thorough GIS analysis. The results of this work are presented and compared with similar approaches and significant conclusions are drawn. Based on the analysis there are some countries that signify high yearly wind energy yield, such as South Africa, Sudan, Algeria, Egypt, Libya, Nigeria, Mauritania, Tunisia and Morocco, whilst Equatorial Guinea, Gabon, Central African Republic, Burundi, Liberia, Benin and Togo indicate the least wind power potential.

  • 19.
    Mohan, Gowtham
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology. American University of Ras Al Khaimah, United Arab Emirates.
    Kumar, N. T. Uday
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology. American University of Ras Al Khaimah,United Arab Emirates.
    Pokhrel, Manoj Kumar
    Martin, Andrew
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
    Experimental investigation of a novel solar thermal polygeneration plant in United Arab Emirates2016In: Renewable energy, ISSN 0960-1481, E-ISSN 1879-0682, Vol. 91, p. 361-373Article in journal (Refereed)
    Abstract [en]

    The demands for space air conditioning and clean drinking water are relatively high in Middle East North African (MENA) countries. A sustainable and innovative approach to meet these demands along with the production of domestic hot water is experimentally investigated in this paper. A novel solar thermal poly-generation (STP) pilot plant is designed and developed for production of chilled water for air conditioning using absorption chiller, clean drinking water with membrane distillation units and domestic hot water by heat recovery. The STP system is developed with a flexibility to operate in four different modes: (i) solar cooling mode (ii) cogeneration of drinking water and domestic hot water (iii) cogeneration of cooling and desalination (iv) trigeneration. Operational flexibility allows consumers to utilize the available energy based on seasonal requirements. Performance of STP system is analyzed during summer months in RAKRIC research facility. Energy flows in STP pilot plant during peak load operations are analyzed for all four modes. STP system with trigeneration mode utilizes 23% more useful energy compared to solar cooling mode, which improves overall efficiency of the plant. Economic benefits of STP with trigeneration mode are evaluated with fuel cost inflation rate of 10%. STP plant has potential payback period of 9.08 years and net cumulative savings of $454,000 based on economic evaluation.

  • 20.
    MosayebNezhad, M.
    et al.
    Politecn Torino, Dept Energy, Turin, Italy..
    Mehr, A. S.
    Univ Bonab, Dept Mech Engn, Bonab, Iran..
    Lanzini, A.
    Politecn Torino, Dept Energy, Turin, Italy..
    Misul, D.
    Politecn Torino, Dept Energy, Turin, Italy..
    Santarelli, Massimo
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
    Technology review and thermodynamic performance study of a biogas-fed micro humid air turbine2019In: Renewable energy, ISSN 0960-1481, E-ISSN 1879-0682, Vol. 140, p. 407-418Article, review/survey (Refereed)
    Abstract [en]

    Biogas is a proven and valuable energy source today for the combined production of heat and electricity (CHP). One of the most reliable and efficient technologies for the CHP application using biogas is represented by microturbine (MT). This prime mover not only shows a very flexible behavior towards change in the fuel composition, but it also sticks out for its reliability, small size, and low weight. Moreover, micro humid air turbine (mHAT) cycle, which is still under development, provides a relatively simple and inexpensive solution to increasing the power output of the microturbines. In this paper, the thermodynamic model of a novel CHP system based on a 500 kW micro humid air turbine (mHAT) in a wastewater treatment plant (WWTP) is presented and discussed. Furthermore, some considerations regarding an appropriate biogas treatment system and heat recovery module are discussed. The results presented in this paper show how the proposed biogas-fed plant can achieve an electrical efficiency of 46.6% together with a CHP efficiency of 81.2%. The impact of integration with WWTPs is beneficial where both biogas and required water for inlet air humidification are available.

  • 21.
    Nguyen, Van Dang
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Computational Science and Technology (CST).
    Jansson, Johan
    KTH, School of Electrical Engineering and Computer Science (EECS), Computational Science and Technology (CST).
    Goude, Anders
    Uppsala University, Uppsala, Sweden.
    Hoffman, Johan
    KTH, School of Electrical Engineering and Computer Science (EECS), Computational Science and Technology (CST).
    Direct Finite Element Simulation of the Turbulent Flow Past a Vertical Axis Wind Turbine2019In: Renewable energy, ISSN 0960-1481, E-ISSN 1879-0682, Vol. 135, p. 238-247Article in journal (Refereed)
    Abstract [en]

    There is today a significant interest in harvesting renewable energy, specifically wind energy, in offshore and urban environments. Vertical axis wind turbines get increasing attention since they are able to capture the wind from any direction. They are relatively easy to install and to transport, cheaper to build and maintain, and quite safe for humans and birds. Detailed computer simulations of the fluid dynamics of wind turbines provide an enhanced understanding of the technology and may guide design improvements. In this paper, we simulate the turbulent flow past a vertical axis wind turbine for a range of rotation angles in parked and rotating conditions. We propose the method of Direct Finite Element Simulation in a rotating ALE framework, abbreviated as DFS-ALE. The simulation results are validated against experimental data in the form of force measurements. We find that the simulation results are stable with respect to mesh refinement and that we capture well the general shape of the variation of force measurements over the rotation angles.

  • 22.
    Obydenkova, Svetlana
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
    Pearce, J. M.
    Technical viability of mobile solar photovoltaic systems for indigenous nomadic communities in northern latitudes2016In: Renewable energy, ISSN 0960-1481, E-ISSN 1879-0682, Vol. 89, p. 253-267Article in journal (Refereed)
    Abstract [en]

    This study assesses the viability of photovoltaic (PV) technology in northern latitudes as a part of energy supply system for remote nomadic camps of indigenous communities involved in reindeer husbandry. Two boundary locations were analyzed: southern Yakutia, Russia, 56°41’N; and the northernmost area in Norway, Finnmark, 68°51’N. Sixteen scenarios were simulated based on energy consumption, light sources and electric load schedules. The results show that PV-based systems are beneficial under a variety of economic conditions and fuel prices when compared to systems solely fuel-based. Incandescent lights, which are currently common for such settlements, should be replaced with LED lighting to enable easier PV system portability by reindeer sled. For areas with significant numbers of minimal solar flux days partial load scheduling is necessary for economically viable systems. The simulations showed that the specific weight of the system (excluding support structure) measured as the system total weight to the number of camp residents ratio can be reduced by a factor of two for optimized loads to 5.8 kg/person for a low energy-intensive camps and 11.0 kg/person for a high energy intensive camps.

  • 23.
    Olauson, Jon
    KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems.
    ERA5: The new champion of wind power modelling?2018In: Renewable energy, ISSN 0960-1481, E-ISSN 1879-0682, Vol. 126, p. 322-331Article in journal (Refereed)
    Abstract [en]

    Output from meteorological reanalyses are used extensively in both academia and industry for modelling wind power. Recently, the first batch of the new ERA5 reanalysis was released. The main purpose of this paper is to compare the performance of ERA5 and MERRA-2 (a commonly used reanalysis today) in terms of modelling i) the aggregated wind generation in five different countries and ii) the generation for 1051 individual wind turbines in Sweden. The modelled wind power generation was compared to measurements. In conclusion, ERA5 performs better than MERRA-2 in all analysed aspects; correlations are higher, mean absolute and root mean square errors are in average around 20% lower and distributions of both hourly data and changes in hourly data are more similar to those for measurements. It is also shown that the uncertainty related to long-term correction (using one year of measurements and reanalysis data to predict the energy production during the remaining 1e5 years) is 20% lower for ERA5. In fact, using one year sample data and ERA5 gives slightly more accurate estimates than using two years of sample data and MERRA-2. Additionally, a new metric for quantifying the system size and dispersion of wind farms is proposed.

  • 24. Palomino Cuya, D. G.
    et al.
    Brandimarte, Luigia
    , Institute for Water Education, Westvest 7, PO Box 3015, 2601 DA Delft, Netherlands.
    Popescu, I.
    Alterach, J.
    Peviani, M.
    A GIS-based assessment of maximum potential hydropower production in La Plata basin under global changes2013In: Renewable energy, ISSN 0960-1481, E-ISSN 1879-0682, Vol. 50, p. 103-114Article in journal (Refereed)
    Abstract [en]

    Population growth, economic development, urbanization, changes in hydrological regimes and land use are the main drivers affecting allocation and exploitation of water resources. The pressure exerted by these global changes on the five countries -Argentina, Bolivia, Brazil, Paraguay and Uruguay- located in La Plata Basin over the last decades has raised the need for assessing trends in future electricity demand and energy production in the basin.The aim of this research is to assess whether (and when) shortage and vulnerabilities in terms of hydropower generation are to be expected in La Plata basin in the next decades. The methodology proposed has focused on two aspects to reach the objectives: 1) assessment of hydropower production and electricity demand in the basin over the last twenty years (1987-2008), in order to establish growing trends for the next thirty years; 2) computation of maximum potential hydropower using the newly developed Arc-GIS based tool VAPIDRO-ASTE. The assessment and calculation have been applied to La Plata River and its main tributaries: Paranaiba, Grande River, Tiete, Paranapanema, Iguaçu, Uruguay, Negro River, Paraguay and Paraná. The first outcomes of this research show that La Plata Basin has high hydropower potential. About 40% of the hydropower potential is already used to produce and supply energy. Out of the remaining 60% potential, about 25% could hardly be exploited because of environmental issues or low cost/benefit ratio. Thus, the estimated residual potential hydropower is about 35% of the maximum potential hydropower calculated.

  • 25.
    Ren, Guorui
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems. Harbin Institute of Technology, Harbin, China.
    Liu, J.
    Wan, J.
    Li, F.
    Guo, Y.
    Yu, D.
    The analysis of turbulence intensity based on wind speed data in onshore wind farms2018In: Renewable energy, ISSN 0960-1481, E-ISSN 1879-0682, Vol. 123, p. 756-766Article in journal (Refereed)
    Abstract [en]

    Wind speed turbulence intensity is crucial for wind turbine structure design and aerodynamic loads calculation. In the study, the actual turbulence intensity observations are compared with the Normal Turbulence Model defined by IEC standard. The results show that the Normal Turbulence Model overestimates the turbulence intensity. A new turbulence intensity model is proposed based on the actual observations, which shows better performance than the Normal Turbulence Model. Then the variation pattern of turbulence intensity during a day is analyzed. The turbulence intensity exhibits obvious daily periodicity in two wind farms. Furthermore, the causes of daily periodicity are discussed and verified by the wind speed dataset 3. Finally, an improved time-varying turbulence intensity model is developed according to the daily periodicity.

  • 26.
    Samadi, Afshin
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Shayesteh, Ebrahim
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Eriksson, Robert
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Rawn, Barry
    Söder, Lennart
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Multi-objective coordinated droop-based voltage regulation in distribution grids with PV systems2014In: Renewable energy, ISSN 0960-1481, E-ISSN 1879-0682, Vol. 71, p. 315-323Article in journal (Refereed)
    Abstract [en]

    High penetrations of photovoltaic (PV) systems in distribution grids have caused new challenges such as reverse power flow and voltage rise. Reactive power contribution by PV systems has been proposed by grid codes and literature as one of the remedies for voltage profile violation. Recent German Grid Codes (GGC), for instance, introduce a standard active power dependent reactive power characteristic, Q(P), for inverter-coupled distributed generators. Nevertheless, the GGC recommends a voltage dependent reactive power characteristic Q(V) for the near future, recognizing that the Q(P) characteristic cannot explicitly address voltage limits. This study utilizes the voltage sensitivity matrix and quasi-static analysis in order to develop a coordinated Q(V) characteristic for each PV system along a radial feeder using only the local measurement and drooping technique concepts. The aim of this paper is using a multi-objective design to adjust the parameters of the Q(V) characteristic in the proposed droop-based voltage regulation in order to minimize the reactive power consumption and line losses. On the other hand, it is also possible to adjust the parameters in order to reach equal reactive power sharing among all PV systems. A radial test distribution grid, which consist of five PV systems, is used to calculate power flow and, in turn, the voltage sensitivity matrix. The comparison of results demonstrates that both approaches in the proposed droop-based voltage regulation can successfully regulate the voltage to the steady-state limit. Moreover, it is shown that the profile of reactive power consumption and line losses are considerably reduced by the multi-objective design.

  • 27.
    Sanches Pereira, Alessandro
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology. University of São Paulo, Brazil .
    Lönnqvist, Tomas
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Energy Processes.
    Gómez, Maria F.
    Universidad de La Sabana.
    Teixeira Coelho, Suani
    USP University of São Paulo.
    Tudeschini, Luís G.
    USP University of São Paulo.
    Is natural gas a backup fuel against shortages of biogas or a threat to the Swedish vision of pursuing a vehicle fleet independent of fossil fuels?2015In: Renewable energy, ISSN 0960-1481, E-ISSN 1879-0682, Vol. 83, p. 1187-1199Article in journal (Refereed)
    Abstract [en]

    The objective of this study is to verify whether natural gas is only a backup fuel against shortages of upgraded biogas or a threat to the Swedish vision of pursuing a vehicle fleet independent of fossil fuels. The paper uses Stockholm County as a case study to guide our analysis. The region not only concentrates the largest number of inhabitants in Sweden but also holds alone around 35% of the Swedish fleet of passenger cars using gas as fuel. The region's potential vehicle gas demands are 460 GWh by 2020 and 1202 GWh by 2030. The methodological approach relies on Network Theory to guide the numerical analysis of the vehicle gas supply chain in the region. Our results show that natural gas will keep on being an important resource and playing a vital role within the local vehicle gas supply chain but no longer as a backup fuel against upgraded biogas shortages. In fact, natural gas has become a price regulator responsible for vehicle gas attractiveness, especially for passenger cars in the region. As a result, phasing out natural gas could hamper future developments of biogas supply chain in the country, hindering the achievement of a green fleet.

  • 28.
    Skoglund, Annika
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Industrial Economics and Management (Dept.).
    Leijon, Mats
    Rehn, Alf
    Lindahl, Marcus
    Waters, Rafael
    On the physics of power, energy and economics of renewable electric energy sources - Part II2010In: Renewable energy, ISSN 0960-1481, E-ISSN 1879-0682, Vol. 35, no 8, p. 1735-1740Article in journal (Refereed)
    Abstract [en]

    Renewable Energy Technologies (RETs) are often recognized as less competitive than traditional electric energy conversion systems. Obstacles with renewable electric energy conversion systems are often referred to the intermittency of the energy sources [1] and the relatively high maintenance cost. However, due to an intensified discourse on climate change and its effects, it has from a societal point of view, become more desirable to adopt and install CO2 neutral power plants. Even if this has increased the competitiveness of RETs in a political sense, the new goals for RET installations must also be met with economical viability. We propose that the direction of technical development, as well as the chosen technology in new installations, should not primarily be determined by policies, but by the basic physical properties of the energy source and the associated potential for inexpensive energy production. This potential is the basic entity that drives the payback of the investment of a specific RET power plant. With regard to this, we argue that the total electric energy conversion system must be considered if effective power production is to be achieved, with focus on the possible number of full loading hours and the Degree of Utilization [2]. This will increase the cost efficiency and economical competitiveness of RET investments, and could enhance faster diffusion of new innovations and installations without over-optimistic subsidies. This paper elaborates on the overall problem of the economy of renewable electric energy conversion systems by studying the interface between physics, engineering and economy reported for RET power plants in different scientific publications. The core objective is to show the practical use of the Degree of Utilization and how the concept is crucial for the design and economical optimization disregarding subsidies. The results clearly indicate that the future political regulative frameworks should consider the choice of renewable energy source since this strongly affects the economical output from the RET power plants. (C) 2009 Elsevier Ltd. All rights reserved.

  • 29. Srithar, K.
    et al.
    Rajaseenivasan, T.
    Karthik, N.
    Periyannan, M.
    Mohan, Gowtham
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
    Stand alone triple basin solar desalination system with cover cooling and parabolic dish concentrator2016In: Renewable energy, ISSN 0960-1481, E-ISSN 1879-0682, Vol. 90, p. 157-165Article in journal (Refereed)
    Abstract [en]

    A stand-alone triple basin solar desalination system is experimentally tested and the results are discussed in this paper. This system mainly consists of a triple basin glass solar still (TBSS), cover cooling (CC) arrangement, parabolic dish concentrator (PDC) and photovoltaic (PV) panel. Four triangular hollow fins are attached at the bottom of the upper and middle basin in order to increase the heat transfer rate and place the energy storing materials. The performance of the system is studied by, conventional TBSS system, integrating the TBSS with CC, TBSS with PDC, and TBSS with CC and PDC. Also, each configuration is tested further by using fins without energy storing material, fins filled with river sand, and fins filled with charcoal. The results of the test reveal that, TBSS with charcoal and TBSS with river sand enhance the distillate by 34.2 and 25.6% higher than conventional TBSS distillates. TBSS with cover cooling reduces the glass temperature to about 8 °C compared to the conventional TBSS. The presence of concentrator increases the lower basin water temperature upto 85 °C. The maximum distillate yield of 16.94 kg/m2.day is obtained for TBSS with concentrator, cover cooling and charcoal in fins.

  • 30.
    Woldemariam, Daniel
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
    Kullab, Alaa
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
    Khan, Ershad Ullah
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
    Martin, Andrew
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
    Recovery of ethanol from scrubber-water by district heat-driven membrane distillation: Industrial-scale technoeconomic study2018In: Renewable energy, ISSN 0960-1481, E-ISSN 1879-0682, Vol. 128, no SI, p. 484-494Article in journal (Refereed)
    Abstract [en]

    Membrane distillation (MD) integrated with a district heating network (DHN) to supply the heat demand has been investigated in a bioethanol production plant (BP). The specific application considered here is ethanol recovery from fermentation off-gas (CO2) scrubber water, where the main objective of this study was to develop an air gap MD system that is driven by heat from DHN, thereby offloading the steam-driven distillation column. Experiments conducted on an MD laboratory facility combined with data from the bioethanol industry were used to assess the technological and economic feasibility of this integrated MD-DHN-BP system. Comparisons were also made between the distillation column and MD units regarding heat demand and economic savings. Results of the study showed that MD could be a competitive technology for ethanol recovery given that low-grade heat such as from district heating network or waste heat is accessible.

  • 31. Zhang, Liang
    et al.
    Yu, Zitao
    Fan, Liwu
    Wang, Wujun
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
    Chen, Huan
    Hu, Yacai
    Fan, Jianren
    Ni, Mingjiang
    Cen, Kefa
    An experimental investigation of the heat losses of a U-type solar heat pipe receiver of a parabolic trough collector-based natural circulation steam generation system2013In: Renewable energy, ISSN 0960-1481, E-ISSN 1879-0682, Vol. 57, p. 262-268Article in journal (Refereed)
    Abstract [en]

    The performance of a parabolic trough collector (PTC)-based steam generation system depends significantly on the heat losses of the solar receiver. This paper presents an experimental study of the heat losses of a double glazing vacuum U-type solar receiver mounted in a PTC natural circulation system for generating medium-temperature steam. Field experiments were performed to determine the overall heat losses of the receiver. Effects of wind, vacuum glass tube, radiation, and structural characteristics on the heat losses were analyzed. The thermal efficiency of the receiver was found to be 0.791 and 0.472 in calm and windy days, respectively, at a test temperature of about 100 degrees C, whereas the thermal efficiencies became 0.792 and 0.663, respectively, while taking the receiver element into consideration. The heat losses were increased from 0.183 to 0.255 kW per receiver for the two cases tested. It was shown that neither convection nor radiation heat losses may be negligible in the analysis of such U-type solar receivers.

1 - 31 of 31
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