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Gebremedhin, Alemayehu
Publications (10 of 21) Show all publications
Tveit, T.-M., Savola, T., Gebremedhin, A. & Fogelholm , C.-J. (2009). Multi-period MINLP model for optimising operation and structural changes to CHP plants in district heating networks with long-term thermal storage. ENERGY CONVERSION AND MANAGEMENT, 50(3), 639-647
Open this publication in new window or tab >>Multi-period MINLP model for optimising operation and structural changes to CHP plants in district heating networks with long-term thermal storage
2009 (English)In: ENERGY CONVERSION AND MANAGEMENT, ISSN 0196-8904 , Vol. 50, no 3, p. 639-647Article in journal (Refereed) Published
Abstract [en]

By using thermal storages it is possible to decouple the generation of power and heat, and it can also lead to an reduction in investments, as the storage can be used to cover the peak load periods. This work presents a MINLP model that can be used for analysing new investments and the long-term operation of CHP plants in a district heating network with long-term thermal storage. The model presented in this work includes the non-linear off-design behaviour of the CHP plants as well as a generic mathematical model of the thermal storage, without the need to fix temperatures and pressure. The model is formulated in such a way that it is suitable for deterministic MINLP solvers. The model is non-convex, and subsequently global optimality cannot be guaranteed with local solvers. In order to reduce the chance of obtaining a poor local optimum compared to the global optimum, the model should be solved many times with the initial values varying randomly. It is possible to extract a lot of results from the model, for instance total annual profit, the optimal selection of process options, mass flow through the plant, and generated power from each plant. The formulation of the model makes it suitable for deterministic MINLP solvers.

Keywords
Long-term thermal storage, District heating, Combined heat and power, Multi-period MINLP model
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-17287 (URN)10.1016/j.enconman.2008.10.010 (DOI)
Available from: 2009-03-16 Created: 2009-03-16 Last updated: 2009-03-16
Karlsson, M., Gebremedhin, A., Klugman, S., Henning, D. & Moshfegh , B. (2009). Regional energy system optimization - Potential for a regional heat market. Applied Energy, 86(4), 441-451
Open this publication in new window or tab >>Regional energy system optimization - Potential for a regional heat market
Show others...
2009 (English)In: Applied Energy, ISSN 0306-2619, E-ISSN 1872-9118, Vol. 86, no 4, p. 441-451Article in journal (Refereed) Published
Abstract [en]

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.

Keywords
District heating, CO2, Heat market, Optimization, Economic evaluation
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-17168 (URN)10.1016/j.apenergy.2008.09.012 (DOI)
Available from: 2009-03-07 Created: 2009-03-07 Last updated: 2017-12-13
Gebremedhin, A., Karlsson, B. & Bjornfot , K. (2009). Sustainable energy system - A case study from Chile. RENEWABLE ENERGY, 34(5), 1241-1244
Open this publication in new window or tab >>Sustainable energy system - A case study from Chile
2009 (English)In: RENEWABLE ENERGY, ISSN 0960-1481 , Vol. 34, no 5, p. 1241-1244Article in journal (Refereed) Published
Abstract [en]

This paper presents some of the results of a power system analysis for Chile. The two major Chilean electric systems are roughly modelled and optimized using a linear programming method with the option to integrate renewable energy sources like wind power, solar power, mini-hydropower and biomass-fired power and also "municipal waste". A total of four different scenarios are outlined: reference system, new production units, gas and coal price variations and a policy measure to encourage power production based on renewable energy. The objective of the scenarios was to illustrate under what conditions integration of the different energy sources in the existing production system is possible. The study shows that even under current conditions, mini-hydro and waste to energy plants are economically viable. Wind power might be interesting alternatives if policy instrument measures are applied. On the other hand, it is hard for the other energy sources to enter the system even when higher price levels of gas and coal are applied. The system is more sensitive to coal price increases than to gas price increases and this mainly encourages CO2 emission reduction.

Keywords
Power system, Modelling, Optimisation, Renewable energy, Policy instruments
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-17135 (URN)10.1016/j.renene.2008.10.005 (DOI)
Available from: 2009-03-07 Created: 2009-03-07 Last updated: 2009-03-07
Henning, D. & Gebremedhin, A. (2008). Future biofuel utilisation for small-scale heating and large-scale heat, electricity and automotive fuel production. In: World Bioenergy 2008. Taking you from Know-how to Show-how,2008.
Open this publication in new window or tab >>Future biofuel utilisation for small-scale heating and large-scale heat, electricity and automotive fuel production
2008 (English)In: World Bioenergy 2008. Taking you from Know-how to Show-how,2008, 2008Conference paper, Published paper (Refereed)
Abstract [en]

     

National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-42571 (URN)66139 (Local ID)66139 (Archive number)66139 (OAI)
Available from: 2009-10-10 Created: 2009-10-10
Zinko, H., Gebremedhin, A. & Klasson, J. (2008). Reduction of CO2 emissions in district heating areas. In: 10th World Renewable Energy Congress WRECX,2008 (pp. 2675-2680).
Open this publication in new window or tab >>Reduction of CO2 emissions in district heating areas
2008 (English)In: 10th World Renewable Energy Congress WRECX,2008, 2008, p. 2675-2680Conference paper, Published paper (Refereed)
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-43016 (URN)70779 (Local ID)70779 (Archive number)70779 (OAI)
Available from: 2009-10-10 Created: 2009-10-10
Danestig, M., Gebremedhin, A. & Karlsson, B. (2007). Stockholm CHP potential: opportunity for CO2 reductions?. Energy Policy, 35(9), 4650-4660
Open this publication in new window or tab >>Stockholm CHP potential: opportunity for CO2 reductions?
2007 (English)In: Energy Policy, ISSN 0301-4215, E-ISSN 1873-6777, Vol. 35, no 9, p. 4650-4660 Article in journal (Refereed) Published
Abstract [en]

The potential for combined heat and power (CHP) generation in Stockholm is large and a total heat demand of about 10 TWh/year can be met in a renewed large district heating system. This model of the Stockholm district heating system shows that CHP generation can increase from 8% in 2004 to 15.5% of the total electricity generation in Sweden. Increased electricity costs in recent years have awakened an interest to invest in new electricity generation. Since renewable alternatives are favoured by green certificates, bio-fuelled CHP is most profitable at low electricity prices. Since heat demand in the district heating network sets the limit for possible electricity generation, a CHP alternative with a high electricity to heat ratio will be more profitable at when electricity prices are high. The efficient energy use in CHP has the potential to contribute to reductions in carbon dioxide emissions in Europe, when they are required and the European electricity market is working perfectly. The potential in Stockholm exceeds Sweden's undertakings under the Kyoto protocol and national reduction goals.

Place, publisher, year, edition, pages
Elsevier, 2007
Keywords
District heating, CHP, CO2
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-17211 (URN)10.1016/j.enpol.2007.03.024 (DOI)
Available from: 2009-03-11 Created: 2009-03-11 Last updated: 2017-12-13Bibliographically approved
Gebremedhin, A., Henning, D. & Palm, J. (2006). Energianalys Vingåker. Eskilstuna: Energimyndighetens förlag
Open this publication in new window or tab >>Energianalys Vingåker
2006 (Swedish)Report (Other academic)
Place, publisher, year, edition, pages
Eskilstuna: Energimyndighetens förlag, 2006
Series
ER / Energimyndigheten ; 7
Keywords
energi, fjärrvärme, monopol, konkurs, kommun, energianalys, industri, Vingåker
National Category
Social Sciences Interdisciplinary Other Social Sciences not elsewhere specified
Identifiers
urn:nbn:se:liu:diva-33627 (URN)19662 (Local ID)19662 (Archive number)19662 (OAI)
Available from: 2009-10-09 Created: 2009-10-09 Last updated: 2018-01-13
Henning, D., Trygg, L. & Gebremedhin, A. (2006). Enhanced biofuel utilisation in Swedish industries, buildings and district heating. In: the World Bioenergy 2006 Conference and exhibition on Biomass for Energy, Jönköping, Sweden, 30 may – 1 June: (pp. 198-203).
Open this publication in new window or tab >>Enhanced biofuel utilisation in Swedish industries, buildings and district heating
2006 (English)In: the World Bioenergy 2006 Conference and exhibition on Biomass for Energy, Jönköping, Sweden, 30 may – 1 June, 2006, p. 198-203Conference paper, Published paper (Refereed)
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-14159 (URN)
Available from: 2006-11-27 Created: 2006-11-27 Last updated: 2009-05-18
Henning, D., Danestig, M., Holmgren, K. & Gebremedhin, A. (2006). Modelling the impact of policy instruments on district heating operations: experiences from Sweden. In: 10th International Symposium on District Heating and Cooling, Hanover, Germany: .
Open this publication in new window or tab >>Modelling the impact of policy instruments on district heating operations: experiences from Sweden
2006 (English)In: 10th International Symposium on District Heating and Cooling, Hanover, Germany, 2006Conference paper, Published paper (Refereed)
Abstract [en]

Emission allowances aim at reducing carbon dioxide emissions in the European Union. Feed-in tariffs and green certificates increase renewable electricity generation in some countries. Undesired energy carriers, such as fossil fuels, can be taxed to decrease consumption. In Sweden, monetary policy instruments have been used for many years, which has influenced district-heating utilities’ operations and investments.

The energy system optimisation model MODEST may help elucidating the impact of policy instruments on choices of fuels and plants. The model can minimise operation and investment costs for satisfying district heating demand, considering revenues from electricity sales and waste reception. It has been used to analyse heat and electricity production for 50 local Swedish utilities. This paper shows how some plants, systems and policy instruments have been modelled and results from some case studies. It may help analysts who face policy instruments, which probably will have a growing influence on district heating operations.

Policy instruments should reflect external costs and induce behaviour that is beneficial from an overall viewpoint. Swedish fossil-fuel taxes hampered cogeneration during many years. Earlier, fuel input could be freely allocated to output energy forms and wood was often used for heat production and coal for electricity generation to minimise taxes. Now, lower taxes promote fossil cogeneration but green certificates make it more profitable to invest in renewable electricity generation.

Carbon dioxide emission allowances can reduce local emissions due to districtheating and electricity production significantly at current price levels but the impact depends on allowance price. With emission trading, investment in a natural-gas-fired cogeneration plant may be beneficial for some utilities due to high electricity prices in the European electricity market, partly caused by emission allowances.

District-heating demand can enable utilisation of resources that otherwise would be of no value. A landfill ban now increases waste incineration, which may reduce industrial waste heat utilisation and heat disposal from cogeneration plants and thereby decrease electricity production. A tax on incinerated waste may reduce the profitability of investing in waste incineration.

Keywords
Energy policy, taxes, green certificates, emission allowances, CHP
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-14204 (URN)
Available from: 2007-01-04 Created: 2007-01-04 Last updated: 2009-05-18Bibliographically approved
Trygg, L., Gebremedhin, A. & Karlsson, B. G. (2006). Resource-effective systems achieved through changes in energy supply and industrial use: the Volvo Skövde case. Applied Energy, 83(8), 801-818
Open this publication in new window or tab >>Resource-effective systems achieved through changes in energy supply and industrial use: the Volvo Skövde case
2006 (English)In: Applied Energy, ISSN 0306-2619, Vol. 83, no 8, p. 801-818Article in journal (Refereed) Published
Abstract [en]

The result presented in this paper shows that the Volvo plant can decrease its electricity use by 44% by making the use of electricity more efficient and converting from oil and electricity to district heating for hot tap-water, space heating and cooling. The increased demand of district heating makes investing in a new planned CHP and cooperation between the Volvo plant and the local energy utility production cost fall by 46% at current unit electricity price and by 64% when calculating with a European unit electricity price and investment in an optimised CHP system instead of the planned plant. The study furthermore shows that the global emissions of the greenhouse gas carbon-dioxide will be reduced by 350% a year if the two energy-supply measures are taken and the electricity unit prices are at a European level.

Keywords
CHP; Co-operation; Deregulated electricity market; District heating; Electricity price; Emission trading
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-14160 (URN)10.1016/j.apenergy.2005.09.005 (DOI)
Available from: 2006-11-27 Created: 2006-11-27 Last updated: 2009-06-05
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