| 1. |
- Bolund, Björn, et al.
(författare)
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Flywheel energy and power storage systems
- 2007
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Ingår i: Renewable & sustainable energy reviews. - : Elsevier BV. - 1364-0321 .- 1879-0690. ; 11:2, s. 235-258
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Tidskriftsartikel (refereegranskat)abstract
- For ages flywheels have been used to achieve smooth operation of machines. The early models where purely mechanical consisting of only a stone wheel attached to an axle. Nowadays flywheels are complex constructions where energy is stored mechanically and transferred to and from the flywheel by an integrated motor/generator. The stone wheel has been replaced by a steel or composite rotor and magnetic bearings have been introduced. Today flywheels are used as supplementary UPS storage at several industries world over. Future applications span a wide range including electric vehicles, intermediate storage for renewable energy generation and direct grid applications from power quality issues to offering an alternative to strengthening transmission. One of the key issues for viable flywheel construction is a high overall efficiency, hence a reduction of the total losses. By increasing the voltage, current losses are decreased and otherwise necessary transformer steps become redundant. So far flywheels over 10 kV have not been constructed, mainly due to isolation problems associated with high voltage, but also because of limitations in the power electronics. Recent progress in semi-conductor technology enables faster switching and lower costs. The predominant part of prior studies have been directed towards optimising mechanical issues whereas the electro technical part now seem to show great potential for improvement. An overview of flywheel technology and previous projects are presented and moreover a 200 kW flywheel using high voltage technology is simulated.
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| 2. |
- Grabbe, Mårten, et al.
(författare)
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A review of the tidal current energy resource in Norway
- 2009
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Ingår i: Renewable & sustainable energy reviews. - : Elsevier. - 1364-0321 .- 1879-0690. ; 13:8, s. 1898-1909
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Forskningsöversikt (refereegranskat)abstract
- As interest in renewable energy sources is steadily on the rise, tidal current energy is receiving more and more attention from politicans, industrialists, and academics. In this article, the conditions for and potential of tidal currents as an energy resource in Norway are reviewed. There having been a relatively small amount of academic work published in this particular field, closely related topics such as the energy situation in Norway in general, the oceanography of the Norwegian coastline, and numerical models of tidal currents in Norwegian waters are also examined. Two published tidal energy resource assessments are reviewed and compared to a desktop study made specifically for this review based on available data in pilot books. The argument is made that tidal current energy ought to be an important option for Norway in terms of renewable energy.
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| 3. |
- Khatiwada, Dilip, et al.
(författare)
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Net energy balance of molasses based ethanol: The case of Nepal
- 2009
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Ingår i: Renewable & sustainable energy reviews. - : Elsevier's ScienceDirect. - 1364-0321 .- 1879-0690. ; 13:9, s. 2515-2524
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Tidskriftsartikel (refereegranskat)abstract
- This paper evaluates life cycle energy analysis of molasses based ethanol (MOE) in Nepal. Net energy value (NEV), net renewable energy value (NREV) and energy yield ratio are used to evaluate the energy balance of MOE in Nepal. Total energy requirements in sugarcane farming, cane milling and ethanol conversion processes are estimated and energy allocation is made between co-products (molasses and sugar) as per their market prices. The result shows negative NEV (−13.05 MJ/L), positive NREV (18.36 MJ/L) and energy yield ratio (7.47). The higher positive value of NREV and energy yield ratio reveal that a low amount of fossil fuels are required to produce 1 L of MOE. However, negative NEV reveals that the total energy consumption (both fossil and renewables) to produce the ethanol is higher than its final energy content. Nevertheless, the renewable energy contribution amounts to 91.7% of total energy requirements. The effect of the increased price of molasses and reduced energy consumption in the sugarcane milling and ethanol conversion are found to be significant in determining the energy values and yield ratio of MOE. In addition, there are clear measures that can be taken to improve efficiency along the production chain. Finally, energy security, scarcity of hard currency for importing fossil fuels and opportunities for regional development are also strong reasons for considering local renewable energy options in developing countries.
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| 4. |
- Perers, Richard, et al.
(författare)
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Development of synchronous generators for Swedish hydropower : A review
- 2007
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Ingår i: Renewable & sustainable energy reviews. - : Elsevier BV. - 1364-0321 .- 1879-0690. ; 11:5, s. 1008-1017
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Forskningsöversikt (refereegranskat)abstract
- The development of large-scale hydropower in Sweden started around 1900 when the Swedish government considered replacing of steam engine power with power from water falls, especially for utilization in railway operation. The hydropower development extends more than hundred years. Most of the Swedish hydropower was built in 1950s and 1960s. Due to the advancing age of installations, Sweden is facing an extensive refurbishment work in the upcoming decades. A large variety of individual designs exist among hydroelectric generators. The generator design has constantly strived for more compact and cost-effective constructions and this has resulted in a constant increase in the unit size. This paper describes the evolution of hydropower generators in Sweden. The development of assembling, stator insulation, cooling and materials used are described.
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| 5. |
- Pettersson, Fredrik, et al.
(författare)
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The diffusion of renewable electricity in the presence of climate policy and technology learning: The case of Sweden
- 2009
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Ingår i: Renewable & sustainable energy reviews. - : Elsevier BV. - 1364-0321 .- 1879-0690. ; 13:8, s. 2031-2040
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Tidskriftsartikel (refereegranskat)abstract
- The overall objective of this paper is to analyze the impact of climate policy and technology learning on future investments in the Swedish power sector. Methodologically we assess the lifetime engineering costs of different power generation technologies in Sweden, and analyze the impact of carbon pricing on the competitive cost position of these technologies under varying rate-of-return requirements. We also argue that technological learning in the Swedish power sector - not the least in the case of wind power - is strongly related to the presence of international learning and R&D spillovers, and for this reason capacity expansions abroad have important influences of the future cost of power generation in Sweden. The results suggest that renewable power will benefit from existing EU climate policy measures, but overall additional policy instruments (e.g., green certificate schemes) are also needed to stimulate the diffusion of renewable power. Moreover, under a recent European Commission scenario and using estimated learning rates for wind power and the combined cycle gas turbine (CCGT), wind power gains considerable competitive ground due to international technology learning impacts. These latter results are, however, very sensitive to the assumed learning-by-doing rates for wind power and CCGT, respectively.
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| 6. |
- Silveira, Jose Luz, et al.
(författare)
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The benefits of ethanol use for hydrogen production in urban transportation
- 2009
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Ingår i: Renewable & sustainable energy reviews. - : Elsevier BV. - 1364-0321 .- 1879-0690. ; 13:9, s. 2525-2534
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Forskningsöversikt (refereegranskat)abstract
- The purpose of this paper is to describe the benefits of sugar cane ethanol in Brazil, appointing the productivity of this type of fuel based on hectares of plantation, its carbon dioxide cycle and the contribution to reduce the greenhouse effect. In the following step the uses of ethanol for hydrogen production by steam reforming is analyzed and some comparison with natural gas steam reforming is performed. The sugar cane industry in Brazil, in a near future, in the hydrogen era, could be modified according to our purpose, since besides the production of sugar, and ethylic and anhydric alcohol, Brazilian sugar cane industry will also be able to produce biohydrogen. Fuel cells appear like a promising technology for energy generation. Among several technologies in the present, the PEMFC (proton exchange membrane fuel cell) is the most appropriate for vehicles application, because it combines durability, high power density, high efficiency, good response and it works at relatively low temperatures. Besides that it is easy to turn it on and off and it is able to support present vibration in vehicles. A PEMFC's problem is the need of noble catalysts like platinum. Another problem is that CO needs to be in low concentration, requiring a more clean hydrogen to avoid fuel cell deterioration. One part of this paper was developed in Stockholm, where there are some buses within the CUTE (clean urban transport for Europe) project that has been in operation with FC since January 2004. Another part was developed in Guaratingueta, Brazil. Brazil intends to start up a program of FC buses. As conclusion, this paper shows the economical analysis comparing buses moved by fuel cells using hydrogen by different kinds of production. Electrolyze with wind turbine, natural gas steam reforming and ethanol steam reforming.
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| 7. |
- Söderholm, Patrik, et al.
(författare)
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Wind power development in Sweden : global policies and local obstacles
- 2007
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Ingår i: Renewable & sustainable energy reviews. - : Elsevier BV. - 1364-0321 .- 1879-0690. ; 11:3, s. 365-400
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Tidskriftsartikel (refereegranskat)abstract
- Recently, the Swedish government adopted a national planning goal of a yearly wind power generation of 10 TWh by 2015, implying a substantial increase from the current 0.6 TWh level. In this paper, we provide an economic assessment of the potential for future wind power investments in Sweden in close conjunction with an analysis of the legal, attitudinal and policy-related uncertainties that face a wind mill investor. It is shown that the economics of Swedish wind power is negatively affected by: (a) the lack of policy stability; (b) public criticism at the local level; and, in particular, (c) the legal provisions governing the assessment of the environmental impacts of wind mills and the planning procedures for mill location. While national and global energy policies as well as the general public point out wind power as particularly environmentally friendly, most of the objections to its expansion at the local level tend to have environmental origins. The interests of those who object to wind mill installations gain strong legal protection, and the municipal territorial planning monopoly in Sweden implies that it is hard to make national energy policy goals heard at the local implementation stage. Compared to its competitors, wind power is the technology that tends to have the most to loose from the risk and uncertainties created by this investment environment. The paper identifies and discusses a number of ways in which the national policy interests could be strengthened at the local level. We discuss the role of citizen participation, as well as solutions within the realms of the legal system. Moreover, since the diffusion of wind power encounters the most strident legal and attitudinal obstacles where it interferes with competing land uses, a move offshore appears to be an efficient strategy from the perspective of a wind mill investor. A stronger political commitment to wind power expansion in legal provisions as well as in the form of long-run stability in policy instrument implementation will probably be necessary to attain the 2015 policy goal.
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| 8. |
- Gössling, Stefan, et al.
(författare)
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A target group-specific approach to "green" power retailing: students as consumers of renewable energy
- 2005
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Ingår i: Renewable & Sustainable Energy Reviews. - : Elsevier BV. - 1364-0321. ; 9:1, s. 69-83
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Forskningsöversikt (refereegranskat)abstract
- An extensive body of literature exists on the obstacles that have to be overcome in green power retailing. In this article, target group-specific marketing is evaluated as a strategy to increase the share of residential customers of green power. A sample of students in the city of Freiburg, Germany was interviewed in order to assess their awareness of environmental issues, their willingness to change to green power products, and to better understand individual hindrances in changing the power supplier. The analysis shows that students are highly positive towards green power products, but for several reasons difficult to reach in marketing campaigns. Aspects to be considered in addressing this consumer-group include the students' particular expectations towards green products, their living-conditions, price sensitivity, and their perception of the relative effort involved in changing the power provider.
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