| 1. |
- Bernhoff, Hans, et al.
(författare)
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Wave energy resources in sheltered sea areas : A case study of the Baltic Sea
- 2006
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Ingår i: Renewable energy. - : Elsevier BV. - 0960-1481 .- 1879-0682. ; 31:13, s. 2164-2170
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Tidskriftsartikel (refereegranskat)abstract
- Wave energy is a renewable source, which has not yet been exploited to a large extent. So far the main focus of wave energy conversion has been on the large wave energy resources of the great oceans on northern latitudes. However, large portions of the world potential wave energy resources are found in sheltered waters and calmer seas, which often exhibit a milder, but still steady wave climate. Examples are the Baltic Sea, the Mediterranean and the North Sea in Europe, and ocean areas closer to the equator. Many of the various schemes in the past consist of large mechanical structures, often located near the sea surface. In the present work we instead focus on wave power plants consisting of a number of small wave energy converters, forming large arrays. In this context, we look at advantageous arrangements of point absorbers, and discuss the potential of the Baltic Sea as a case study.
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| 2. |
- Boström, Cecilia, et al.
(författare)
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Experimental results of rectification and filtration from an offshore wave energy system
- 2009
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Ingår i: Renewable energy. - : Elsevier BV. - 0960-1481 .- 1879-0682. ; 34:5, s. 1381-1387
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Tidskriftsartikel (refereegranskat)abstract
- The present paper presents results from a wave energy conversion that is based on a direct drive linear generator. The linear generator is placed on the seabed and connected to a buoy via a rope. Thereby, the natural wave motion is transferred to the translator by the buoy motion. When using direct drive generators, voltage and current output will have varying frequency and varying amplitude and the power must be converted before a grid connection. The electrical system is therefore an important part to study in the complete conversion system from wave energy to grid connected power. This paper will bring up the first steps in the conversion: rectification and filtration of the power. Both simulation studies and offshore experiments have been made. The results indicate that this kind of system works in a satisfactory way and a smooth DC power can be achieved with one linear generator.
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| 3. |
- Eriksson, Sandra, et al.
(författare)
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Simulations and experiments on a 12 kW direct driven PM synchronous generator for wind power
- 2008
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Ingår i: Renewable energy. - : Elsevier BV. - 0960-1481 .- 1879-0682. ; 33:4, s. 674-681
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Tidskriftsartikel (refereegranskat)abstract
- A direct driven permanent magnet (PM) synchronous generator has been designed and constructed and results from the first experimental tests are presented. The generator has been designed using the finite element method (FEM) and dynamic simulations have been performed to study the generator. The simulations are performed by using an electromagnetic model, which is described by a combined field and circuit equation model and is solved in a finite element environment. The stator winding of the generator consists of circular cables and the rotor has surface mounted, arched PMs. A complete experimental setup has been constructed consisting of a motor, a frequency converter, a gearbox and electrical loads. Oscilloscopes are used to measure the voltage and the current for each phase. Measurements have been performed for both full load and no load at rated speed. The harmonic content of the voltage is analyzed and compared to results from simulations. Furthermore, the generated electric power has been calculated from knowing the voltage and current and is compared to the simulated power. The agreement between experimental results and results from simulations based on finite element calculations is very high.. especially considering harmonics. Several sources of error are suggested that could cause the small differences between the simulated results and the measured data for the constructed generator.
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| 4. |
- Fiedler, Frank, et al.
(författare)
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Thermal performance of combined solar and pellet heating systems
- 2006
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Ingår i: Renewable energy. - : Elsevier BV. - 0960-1481 .- 1879-0682. ; 31, s. 73-88
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Tidskriftsartikel (refereegranskat)abstract
- 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
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| 5. |
- Göransson, Lisa, 1982, et al.
(författare)
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Dispatch modeling of a regional power generation system - Integrating wind power
- 2009
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Ingår i: Renewable Energy. - : Elsevier BV. - 0960-1481 .- 1879-0682. ; 34:4, s. 1040-1049
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Tidskriftsartikel (refereegranskat)abstract
- A modeling tool has been developed which can be used to analyze interaction between intermittent wind power generation and thermal power plant generation in a regional electricity grid system. The model uses a mixed integer programming (MIP) approach to determine the power plant dispatch strategy which yields the lowest systems costs. In the model, each large thermal plant is described separately, including properties such as start-up time, start-up cost and minimum load level. The model is evaluated using western Denmark as a case study.For western Denmark, it is found that the inclusion of start-up performance (i.e. start-up time and related costs) and minimum load level of the power generating units have a significant impact on the results. It is shown that the inclusion of these aspects influences the analysis of the effect of wind power variations on the production patterns of thermal units in the system. The model demonstrates how the introduction of wind power production and associated variations change the dispatch order of the large thermal power plants in the western Denmark system so that the unit with the lowest running costs no longer has the highest capacity factor. It is shown that this effect only is detected if start-up performance and minimum load level limitations are included in the optimization. it can also be concluded that start-up performance and minimum load level must be taken into account if the total system costs and emissions are not to be underestimated. The simulations show that if these aspects are disregarded, both total costs and total emissions of the power system are underestimated, with 5% in the case of western Denmark. Models such as the one developed in this work can be efficient tools to understand the effects of large-scale wind power integration in a power generation system with base load plants.
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| 6. |
- Henfridsson, Urban, et al.
(författare)
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Wave energy potential in the Baltic Sea and the Danish part of the North Sea, with reflections on the Skagerrak
- 2007
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Ingår i: Renewable energy. - : Elsevier BV. - 0960-1481 .- 1879-0682. ; 32:12, s. 2069-2084
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Tidskriftsartikel (refereegranskat)abstract
- Wave power, along with renewable energy-generating sources like tides and streams, is underestimated considering its advantageous physical properties and predictability. This paper examines possible examples of wave power installations in the Baltic Sea and the Danish part of the North Sea. Hindcasting data is used allowing estimations of wave energy generated and results show promising areas in the North Sea, but also several parts of the Baltic Sea are of interest. The study is based upon linear generator technique, placed on the seabed using point-absorbers arranged in arrays of up to several thousand units. The study aims at showing the physical possibilities of wave energy, including economical feasibility and environmental advantages of wave energy even in moderate wave climates. With discussion from two examples in the Baltic Sea, one in the Danish North Sea and a new pilot study site in the Swedish part of Skagerrak, this study show feasible illustrations of wave energy takeouts. Project examples vary in size due to distance to grid, grid voltage, and may thus be economically feasible. Examples also show considerations in societal and nature conservation matters, including aspects such as industrial and military interests, archaeological or marine reserves and local geology. The authors conclude that wave energy electric conversion is an option that needs more attention and which has several advantages compared to conventional renewable sources. Sound engineering, in combination with producer, consumer and broad societal perspective is advised for a sustainable development of wave energy conversion.
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| 7. |
- Leijon, Mats, et al.
(författare)
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An electrical approach to wave energy conversion
- 2006
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Ingår i: Renewable energy. - : Elsevier BV. - 0960-1481 .- 1879-0682. ; :31, s. 1309-1319
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Tidskriftsartikel (refereegranskat)abstract
- Motions in nature, for example ocean waves, can play a significant role in tomorrow's electricity production, but the constructions require adaptations to its media. Engineers planning hydropower plants have always taken natural conditions, such as fall height, speed of flow, and geometry, as basic design parameters and constraints in the design. The present paper describes a novel approach for electric power conversion of the vast ocean wave energy. The suggested linear electric energy converter is adapted to the natural wave motion using straightforward technology. Extensive simulations of the wave energy concept are presented, along with results from the experimental setup of a multisided permanent magnet linear generator. The prototype is designed through systematic electromagnetic field calculations. The experimental results are used for the verification of measurements in the design process of future full-scale direct wave energy converters. The present paper, describes the energy conversion concept from a system perspective, and also discusses the economical and some environmental considerations for the project.
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| 8. |
- Lundh, Magdalena, 1979-, et al.
(författare)
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Swedish solar heated residentialarea with seasonal storage in rock : Initial evaluation
- 2008
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Ingår i: Renewable energy. - : Elsevier BV. - 0960-1481 .- 1879-0682. ; 33:4, s. 703-711
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Tidskriftsartikel (refereegranskat)abstract
- A partly solar heated building area comprising 50 residential units has been built in Anneberg, Sweden. The system includes low-temperature space heating with seasonal ground storage of solar heat. Heating is supplied by 2400 m(2) solar collectors and individual electrical heaters for supplementary heating. The ground storage comprises about 60,000 m(3) of crystalline rock with 100 boreholes drilled to 65 m depth and fitted with double U-pipes. The collectors will have favourable working conditions but the store is rather small, the estimated heat loss from the beat store is about 40% of stored solar heat and the average solar fraction is estimated to 70% after 3-5 years of operation. An initial evaluation after 2 years of operation shows that, although problems have occurred and several parts seem to work less efficient than expected, the overall system idea works as intended.
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| 9. |
- Martins, Marcia, 1966, et al.
(författare)
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Validation of fixed speed wind turbine dynamic models with measured data
- 2007
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Ingår i: Renewable Energy. - : Elsevier BV. - 0960-1481 .- 1879-0682. ; 32:8, s. 1301-1316
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Tidskriftsartikel (refereegranskat)abstract
- Power system dynamics studies involving fixed-speed wind turbines normally use a wind turbine model consisting of two lumped masses, an elastic coupling and a induction generator model which neglects stator transients. However, validations of this model with measured data are rarely reported in the literature. This paper validates the model using a recorded case obtained in a fixed speed, stall regulated 180 kW wind turbine through a voltage dip. The work analyses the performance of the reduced order induction generator model which neglects stator transients, compared to the detailed induction generator model. It also includes a study of the convenience of representing mechanical damping in the drive train, and an evaluation of the single mass mechanical model.
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| 10. |
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