| 1. |
- Bekele, Getachew, et al.
(författare)
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Wind energy potential assessment at four typical locations in Ethiopia
- 2009
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Ingår i: Applied Energy. - : Elsevier BV. - 0306-2619 .- 1872-9118. ; 86:3, s. 388-396
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Tidskriftsartikel (refereegranskat)abstract
- The wind energy potential at four different sites in Ethiopia - Addis Ababa (09:02N, 38:42E), Mekele (13:33N, 39:30E), Nazret (08:32N, 39:22E), and Debrezeit (8:44N, 39:02E) - has been investigated by compiling data from different sources and analyzing it using a software tool. The results relating to wind energy potential are given in terms of the monthly average wind speed, wind speed probability density function (PDF), wind speed cumulative density function (CDF), and wind speed duration curve (DC) for all four selected sites. in brief, for measurements taken at a height of 10 m, the results show that for three of the four locations the wind energy potential is reasonable, with average wind speeds of approximately 4 m/s. For the fourth site. the mean wind speed is less than 3 m/s. This study is the first stage in a longer project and will be followed by an analysis of solar energy potential and finally the design of a hybrid standalone electric energy supply system that includes a wind turbine, PV, diesel generator and battery.
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| 2. |
- Börjesson, Pål
(författare)
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Good or bad bioethanol from a greenhouse gas perspective - What determines this?
- 2009
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Ingår i: Applied Energy. - : Elsevier BV. - 1872-9118 .- 0306-2619. ; 86:5, s. 589-594
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Tidskriftsartikel (refereegranskat)abstract
- The purpose of this study is to describe how the greenhouse gas (GHG) benefits of ethanol from agricultural crops depend on local conditions and calculation methods. The focus is mainly on the fuels used in the ethanol process and biogenic GHG from the soils cultivated. To ensure that "good" ethanol is produced, with reference to GHG benefits, the following demands must be met: (i) ethanol plants should use biomass and not fossil fuels, (ii) cultivation of annual feedstock crops should be avoided on land rich in carbon (above and below ground), such as peat soils used as permanent grassland, etc., (iii) by-products should be utilised efficiently in order to maximise their energy and GHG benefits and (iv) nitrous oxide emissions should be kept to a minimum by means of efficient fertilisation strategies, and the commercial nitrogen fertiliser utilised should be produced in plants which have nitrous oxide gas cleaning. Several of the current ethanol production systems worldwide fullfill the majority of these demands, whereas some production systems do not. Thus, the findings in this paper helps identifying current "good" systems, how today's "fairly good" systems could be improved, and which inherent "bad" systems that we should avoid. (C) 2008 Elsevier Ltd. All rights reserved.
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| 3. |
- Difs, Kristina, et al.
(författare)
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Increased use of district heating in industrial processes - Impacts on heat load duration
- 2009
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Ingår i: Applied Energy. - : Elsevier BV. - 0306-2619 .- 1872-9118. ; 86:11, s. 2327-2334
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Tidskriftsartikel (refereegranskat)abstract
- Current knowledge of the potential for an increased use of industrial district heating (DH) due to conversions of industrial processes to DH is limited. In this paper, a Method for Heat Load Analysis (MeHLA) for exploring industrial DH conversions has been developed. This method can be a helpful tool for analyzing the impact different industrial processes have on the local DH system, when processes that utilize electricity and other fuels, convert to utilizing DH instead. Heat loads for different types of industries and processes are analyzed according to characteristics such as temperature levels and time dependency. MeHLA has been used to analyze 34 Swedish industries and the method demonstrates how conversion of industrial processes to DH can result in heat load duration curves that are less outdoor temperature-dependent and more evenly distributed over the year. An evenly distributed heat load curve can result in increased annual operating time for base load DH plants such as cogeneration plants, leading to increased electricity generation. In addition to the positive effects for the DH load duration curve, the conversions to DH can also lead to an 11% reduction in the use of electricity, a 40% reduction in the use of fossil fuels and a total energy end-use saving of 6% in the industries. Converting the industrial processes to DH will also lead to a potential reduction of the global carbon dioxide emissions by 112,000 tonnes per year.
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| 4. |
- Eriksson, Marcus, 1974, et al.
(författare)
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Future use of heat pumps in Swedish district heating systems: Short- and long-term impact of policy instruments and planned investments
- 2007
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Ingår i: Applied Energy. - : Elsevier BV. - 1872-9118 .- 0306-2619. ; 84:12, s. 1240-1257
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Tidskriftsartikel (refereegranskat)abstract
- Heat pumps constitute one of the major technologies used in district heating systems in Sweden. Totally about 6 TWh of heat are supplied annually by heat pumps, equivalent to 12% of the heat supplied in district heating systems. New policy instruments that have recently been introduced will change change the conditions for technologies in the district heating systems. It is likely that the incentives for waste incineration and combined heat and power will be improved. This study estimates how different policy instruments, and new investments in waste incineration and combined heat and power, affect heat pumps in Swedish district heating systems. The results indicate that heat pumps are affected in both a short-term and a long-term perspective, and that heat pumps will play a less important role in district heating systems in the future. Depending on the policy instruments applied in the district heating sector, the long-term use is between 18% and 71% lower than current use. In a long-term perspective, it is in the systems which currently use heat pumps during a large part of the year that new investments in waste incineration and combined heat and power can be expected, resulting in a convergence between different district heating systems regarding how much heat is supplied by combined heat and power and waste incineration, and regarding the annual operating hours for heat pumps. (C) 2007 Elsevier Ltd. All rights reserved.
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| 5. |
- Fiedler, Frank, et al.
(författare)
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Carbon monoxide emissions of combined pellet and solar heating systems
- 2009
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Ingår i: Applied Energy. - : Elsevier BV. - 0306-2619 .- 1872-9118. ; 86:2, s. 135-143
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Tidskriftsartikel (refereegranskat)abstract
- Emissions are an important aspect of a pellet heating system. Low harmful emissions, particularly carbon monoxide, are a measure of a well performing system. High carbon monoxide emissions are often caused by unnecessary cycling of the burner and when the average load is below the lowest possible combustion power of the burner. Combining pellet heaters with a solar heating system can significantly reduce cycling of the pellet heater and avoid the inefficient summer operation of the pellet heater. Five combined systems representing the range of typical solutions of this system type and one recently developed system have been studied, modelled and simulated. These systems are compared to a reference system, which is based on a pellet boiler and is not combined with a solar heating system. The aim was to study CO-emissions of the different types of systems and to analyse the potential of CO-emission reduction when the pellet heater is combined with a solar heating systems. Another aim was to compare the yearly CO-emissions obtained from simulations under realistic dynamic conditions with the yearly CO-emissions calculated based on the values that are obtained by the standard test methods. The study was performed with the simulation tool TRNSYS. The parameter used in the study have been identified from lab measurements on existing pellet boilers/stoves and solar heating systems. The results from the simulations show that it is possible to almost halve the CO-emission if the pellet heater is combined with a solar heating system. The results also show that the CO-emission of existing combined solar and pellet heating systems can be drastically reduced if the pellet heater is properly controlled and some basic design rules are observed. This can also be seen when analyzing the results for the new system concept where these rules have been taken into account. Comparing the yearly CO-emissions obtained from the simulations with the yearly CO-emissions calculated based on the standard test methods shows that using the latter give too low CO-values for the whole year. It is also shown that for the existing systems the average emissions under these realistic annual conditions were greater than the limit values of two Eco-labels.
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| 6. |
- Grubbström, Robert W.
(författare)
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An attempt to introduce dynamics into generalised exergy considerations
- 2007
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Ingår i: Applied Energy. - : Elsevier. - 0306-2619 .- 1872-9118. ; 84:7-8, s. 701-718
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Tidskriftsartikel (refereegranskat)abstract
- In previous research, the author developed a general abstract framework for the exergy content of a system of finite objects [Grubbström RW. Towards a generalized exergy concept. In: van Gool W, Bruggink JJC, editors. Energy and time in the economic and physical sciences. Amsterdam: North-Holland, 1985. p. 41-56]. Each such object is characterised by its initial extensive properties and has an inner energy written as a function of these properties. It was shown that if these objects were allowed to interact, there is a maximum amount of work that can be extracted from the system as a whole, and a general formula for this potential was provided. It was also shown that if one of the objects was allowed to be of infinite magnitude initially, taking on the role as an environment having constant intensive properties, then the formula provided took on the same form as the classical expression for exergy. As a side result, the theoretical considerations demonstrated that the second law of thermodynamics could be interpreted as the inner energy function being a (weakly) convex function of its arguments, when these are chosen as the extensive properties. Since exergy considerations are based on the principle that total entropy is conserved when extracting work, these processes would take an infinite time to complete. In the current paper, instead, a differential-equation approach is introduced to describe the interaction in finite time between given finite objects of a system. Differences in intensive properties between the objects provide a force enabling an exchange of energy and matter. An example of such an interaction is heat conduction. The resulting considerations explain how the power extracted from the system will be limited by the processes being required to perform within finite-time constraints. Applying finite-time processes, in which entropy necessarily is generated, leads to formulating a theory for a maximal power output from the system. It is shown that such a theory is possible to develop, and the resulting equilibrium conditions are compared with to those of the exergetic equilibrium. © 2007 Elsevier Ltd. All rights reserved.
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| 7. |
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| 8. |
- Jansson, Christer, et al.
(författare)
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Cassava, a potential biofuel crop in (the) People's Republic of China
- 2009
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Ingår i: Applied Energy. - : Elsevier BV. - 0306-2619 .- 1872-9118. ; 86, s. S95-S99
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Tidskriftsartikel (refereegranskat)abstract
- Cassava ranks fifth among crops in global starch production. It is used as staple food in many tropical countries of Africa, Asia and Latin America. In (the) People's Republic of China, although not yet a staple food, cassava is of major economic importance for starch for a large area of southern (the) PRC, especially in the provinces of Guangdong, Guanxi, Yunnan and Hainan. Recently, cassava-derived bioethanol production has been increasing due to its economic benefits compared to other bioethanol-producing crops in the country. We discuss here the possible potentials of cassava for bioethanol production
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| 9. |
- Joelsson, Anna, et al.
(författare)
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District heating and energy efficiency in detached houses of differing size and construction
- 2009
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Ingår i: Applied Energy. - : Elsevier BV. - 0306-2619 .- 1872-9118. ; 86:2, s. 126-134
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Tidskriftsartikel (refereegranskat)abstract
- House envelope measures and conversion of heating systems can reduce primary energy use and CO2 emission in the existing Swedish building stock. We analysed how the size and construction of electrically heated detached houses affect the potential for such measures and the potential for cogenerated district heating. Our starting point was two typical houses built in the 1970s. We altered the floor plans to obtain 6 houses, with heated floor space ranging between 100 and 306 m2. One of the houses was also analysed for three energy standards with differing heat loss rates. CO2 emission, primary energy use and heating cost were estimated after implementing house envelope measures, conversions to other heating systems and changes in the generation of district heat and electricity. The study accounted for primary energy, including energy chains from natural resources to useful heat in the houses. We showed that conversion to district heating based on biomass, together with house envelope measures, reduced the primary energy use by 88% and the CO2 emission by 96%, while reducing the annual societal cost by 7%. The choice of end-use heating system was decisive for the primary energy use, with district heating being the most efficient. Neither house size nor energy standard did significantly change the ranking of the heating systems, either from a primary energy or an economic viewpoint, but did affect the extent of the annual cost reduction after implementing the measures.
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| 10. |
- Karlsson, Magnus, et al.
(författare)
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Regional energy system optimization - Potential for a regional heat market
- 2009
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Ingår i: Applied Energy. - : Elsevier BV. - 0306-2619 .- 1872-9118. ; 86:4, s. 441-451
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Tidskriftsartikel (refereegranskat)abstract
- Energy supply companies and industrial plants are likely to face new situations due to, for example, the introduction of new energy legislation, increased fuel prices and increased environmental awareness. These new prerequisites provide companies with new challenges but also new possibilities from which to benefit. Increased energy efficiency within companies and increased cooperation between different operators are two alternatives to meet the new conditions. A region characterized by a high density of energy-intensive processes is used in this study to find the economic potential of connecting three industrial plants and four energy companies, within three local district heating systems, to a regional heat market, in which different operators provide heat to a joint district heating grid. Also, different investment alternatives are studied. The results show that the economical potential for a heat market amounts to between 5 and 26 million EUR/year with payback times ranging from two to eleven years. However, the investment costs and the net benefit for the total system need to be allotted to the different operators, as they benefit economically to different extents from the introduction of a heat market. It is also shown that the emissions of CO2 from the joint system would decrease compared to separate operation of the systems. However, the valuation of CO2 emissions from electricity production is important as the difference of emitted CO2 between the accounting methods exceeds 650 kton/year for some scenarios.
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