| 1. |
- Ahlborg, Helene, 1980, et al.
(author)
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Drivers and barriers to rural electrification in Tanzania and Mozambique - grid-extension, off-grid, and renewable energy technologies
- 2014
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In: Renewable Energy. - : Elsevier BV. - 0960-1481 .- 1879-0682. ; 61, s. 117-124
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Journal article (peer-reviewed)abstract
- Mozambique and Tanzania are countries with very low rural electrification (RE) rates as only about 5% of the rural population use electricity. Despite efforts to extend the national grid in rural areas, most remote areas will not be reached within the foreseeable future. Off-grid (decentralized) electricity grids are seen as a complement and forerunner to the national grid, making electricity available many years in advance and creating demand and a customer base. Renewable energy sources are plentiful in the region and may be particularly useful for off-grid systems. The countries' power sectors are undergoing interesting changes with potential to speed up the pace of RE. However, there are significant barriers to effective RE by grid-extension and off-grid installations.In this study, the specific drivers and barriers for RE in Mozambique and Tanzania are explored across a spectrum of involved actors. By qualitative methodology, drivers and barriers were first identified through literature survey, then data was collected both in semi-structured interviews carried out with power sector actors from national to local level and in visits to off-grid electricity users in Tanzania and Mozambique during eight weeks in 2010. Findings illustrate generic, country-specific, and renewable-energy-technology-specific drivers and barriers to grid and off-grid rural electrification, as perceived by different power sector actors. Results were validated and discussed with three external specialists. Drivers and barriers strongly relate to the roles of national and local actors in planning and implementation. The main drivers are political ambitions based on expected growth of demand, but bottom-up drivers such as local initiatives by industries or churches also exist. The barriers are related to lack of access to human capital, to difficulties in planning and donor dependency, to low rural markets and little interest from private sector, and to more straightforward technical matters such as difficulties with installing electric equipment in traditional buildings. Although off-grid systems and renewable energy sources are recognized by the actors, specific barriers to these systems are related to young organizations responsible for implementation and to guilt-by-association with dysfunctional diesel-based off-grid systems.
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| 2. |
- Amiri, Shahnaz, et al.
(author)
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Simulation and introduction of a CHP plant in a Swedish biogas system
- 2013
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In: Renewable energy. - Oxford : Elsevier. - 0960-1481 .- 1879-0682. ; 49:SI, s. 242-249
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Journal article (peer-reviewed)abstract
- The objectives of this study are to present a model for biogas production systems to help achieve a more cost-effective system, and to analyse the conditions for connecting combined heat and power (CHP) plants to the biogas system. The European electricity market is assumed to be fully deregulated. The relation between connection of CHP. increased electricity and heat production, electricity prices, and electricity certificate trading is investigated. A cost-minimising linear programming model (MODEST) is used. MODEST has been applied to many energy systems, but this is the first time the model has been used for biogas production. The new model, which is the main result of this work, can be used for operational optimisation and evaluating economic consequences of future changes in the biogas system. The results from the case study and sensitivity analysis show that the model is reliable and can be used for strategic planning. The results show that implementation of a biogas-based CHP plant result in an electricity power production of approximately 39 GW h annually. Reduced system costs provide a profitability of 46 MSEK/year if electricity and heat prices increase by 100% and electricity certificate prices increase by 50%. CO2 emission reductions up to 32,000 ton/year can be achieved if generated electricity displaces coal-fired condensing power.
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| 3. |
- Athanassiadis, Dimitris
(author)
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Sub-national TIMES model for analyzing future regional use of biomass and biofuels in Sweden and France
- 2013
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In: Renewable Energy. - : Elsevier BV. - 0960-1481. ; 60, s. 415-426
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Journal article (peer-reviewed)abstract
- The objective of this study is to improve evaluations of the future use of biomass sources in Sweden and France by representing the high spatial variations of the supply and cost of biomass sources in energy system models, The proposed methodology considers a high spatial disaggregation of biomass supply sources, as well as detailed biomass cost supply curves, and is thereby able to account for spatial differences in heterogeneous land qualities, management strategies, and possible adaptation rates. Integrating the methodology into national or regional energy system models will enhance cost-effective evaluations of biomass sources as well as the development of the bioenergy sector. A TIMES energy system model was used to evaluate bioenergy production potential for France and Sweden based on domestic biomass sources and under the assumption that bioenergy production should not be at the expense of domestic food and forestry supply. Results show that by 2050, the biomass sources considered could provide as much as 250 PJ of bioenergy in Sweden, and 1470 PJ of bioenergy in France. Results further showed that 1st generation biofuels are likely to continue to play a substantial role in the biofuel mix. While 2nd generation biofuel production in Sweden is likely to be low, larger amounts of 2nd generation biofuels could be produced in France. However, the amount and type of 2nd generation biofuel produced in France was found to be highly dependent on the bioenergy demand level. (C) 2013 Elsevier Ltd. All rights reserved.
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| 4. |
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| 5. |
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| 6. |
- Blunden, L. S., et al.
(author)
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Tidal current power for Indonesia? An initial resource estimation for the Alas Strait
- 2013
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In: Renewable energy. - : Elsevier BV. - 0960-1481 .- 1879-0682. ; 49:0, s. 137-142
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Journal article (peer-reviewed)abstract
- Indonesia – with its many narrow straits and significant tidal range – might be expected to have considerable potential for tidal current power generation. A particularly promising site is the Alas Strait, with shallow depth, high tidal current velocity and location far from major shipping lanes. In this study, a hydrodynamic numerical model of the Alas Strait was run and validated against some tidal current velocity measurements. The results of the model were then used to estimate the practically exploitable energy resources in the strait, using a development of a method used in previous resource estimations. In this method, the incident velocity on each row of an array was extracted from the model and then attenuated based on the direction of the flow and the number of rows deep into the array. In this way, the effects of practical array shape can be simulated without the need to include computationally expensive parameterization of turbines in the model. Two scenarios were considered, with and without a maximum depth limitation of 40 m. The first scenario gave an estimate of the practically exploitable annual energy yield from the Alas Strait of 330 GW h with the second scenario nearly double at 640 GW h.
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| 7. |
- Breton, Simon-Philippe, et al.
(author)
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Study of the influence of imposed turbulence on the asymptotic wake deficit in a very long line of wind turbines
- 2014
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In: Renewable energy. - : Elsevier BV. - 0960-1481 .- 1879-0682. ; 70, s. 153-163
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Journal article (peer-reviewed)abstract
- 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.
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| 8. |
- Bülow, Fredrik, et al.
(author)
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No-load core loss prediction of PM generator at low electrical frequency
- 2012
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In: Renewable energy. - : Elsevier BV. - 0960-1481 .- 1879-0682. ; 43, s. 389-392
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Journal article (peer-reviewed)abstract
- A method for measurement of frequency dependent electromagnetic core loss of a permanent magnet generator is presented. Core loss of a PM generator is measured at electrical frequencies ranging from 4 to 14 Hz. Core loss in the same interval is simulated using the finite element method and frequency domain loss separation. The specific loss is both extrapolated from specific loss at 50 Hz and measured directly at 4, 8, 12 and 16 Hz. Core loss simulations based on extrapolated specific loss are 38–53% smaller than measured loss. Core loss simulations based on specific loss measured at 4, 8, 12 and 16 Hz are 19–23% smaller than measured loss.
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| 9. |
- Bååth, Lars, 1948-
(author)
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Noise Spectra from Wind Turbines
- 2013
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In: Renewable energy. - Oxford : Pergamon Press. - 0960-1481 .- 1879-0682. ; 57, s. 512-519
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Journal article (peer-reviewed)abstract
- This paper presents observations of audio noise in frequency range 20e20 000 Hz from wind turbines. The observations were performed around the theoretically calculated 40 dBA noise perimeter around the wind turbine farm at Oxhult, Sweden. This paper describes a newly designed and constructed a field qualified data acquisition system to measure spectra and total noise level of sound from wind turbines. The system has been calibrated at SP Borås. It is shown that it has a flat frequency response and is linear with amplitude and time.The total noise level (as integrated 20e20 000 Hz) is shown to be below 35 dBA (below the reference background noise at 36 dBA) at a 10 m altitude wind speed of 4e5 m/s. The measurements were made along the theoretical 40 dBA border at 8 m/s.It is concluded that the theoretical 40 dBA border seems reasonable calculated if the manufacturer specifications are used to extrapolate the sound level to correspond to 8 m/s at 10 m. Our data indicate that a simple sound propagation model is sufficient since the sound level is more affected by the nearby environment than the large scale forest structure. Also, the large scale forestry structure is bound to change with time and the error bars of measurements on total sound level are about 1 dBA, which is larger than any fine tuning with a more sophisticated model. More care should be taken to model the reflections from walls and other obstacles close to the microphones.The distribution of the spectral noise level around the turbine farm suggests that the noise originates from individual wind turbines closest to the measurement location rather than from the wind turbine farm as a whole. The spectra show narrow band spectral line features which do not contribute signifi-cantly to the total noise at this level. The narrow band features are only detectable at very long inte-gration time and at 1 Hz spectral resolution. The spectral features are typical to originate from mechanical noise.The spectral acquisition method described in this paper can be used as a field qualified system for sound measurements in forest areas. The high spectral resolution is a viable remote diagnostic method for mechanical faults in the turbine machinery. Future work will concentrate on these two areas.
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| 10. |
- Castellucci, Valeria, et al.
(author)
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Tidal effect compensation system for point absorbing wave energy converters
- 2013
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In: Renewable energy. - : Elsevier BV. - 0960-1481 .- 1879-0682. ; 51, s. 247-254
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Journal article (peer-reviewed)abstract
- Recent studies show that there is a correlation between water level and energy absorption values for the studied wave energy converters: the absorption decreases when the water levels deviate from average. The situation appears during tides when the water level changes significantly. The main objective of the paper is to present a first attempt to increase the energy absorption during tides by designing and realizing a small-scale model of a point absorber equipped with a device that is able to adjust the length of the rope connected to the generator. The adjustment is achieved by a screw that moves upwards in the presence of low tides and downwards in the presence of high tides. Numerical results as well as experimental tests suggest that the solution adopted to minimize the tidal effect on the power generation shows potential for further development.
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