No description available.

No description available.

To limit the ongoing climate change and to meet the UN target for an increased temperature of maximum 2 degrees, governments worldwide strive for sustainable and fossil free power generation. Hence, Photovoltaic Solar Cells (PVs) are of great interest. The potential from sun is infinite; the annual solar radiation corresponds to 6.000 times the human energy demand (IEA, 2011). In Sweden, the power generation from sun is 0.6 ‰ (Swedenergy, 2016). It is a very small, but strongly growing, share. In the municipality of Kristianstad, south of Sweden, the vision of power generation from sun is clear: by 2040, 5 % of the electricity consumption in the area is to come from PVs (Kristianstad kommun, 2016). Along with an increased interest from subscribers, more grid connected PVs are to be expected. An increased share of grid-connected PVs, influences the power grid. The power quality must comply with legal requirements and maintain a certain voltage. This might be a problem in rural power grids where the distances are far; the grid is getting weaker and the voltage deviation grows. Never the less, the law requires the concession holder to compensate the subscriber in relation to the decreased losses in the grid. With power generation closer to the subscriber, the distances are shorter and the grid losses is decreased. Mellersta Skånes Kraft (MSK) is a power distribution company located in Scania, south of Sweden. In the feeding 6 kV grid, a major part of the conductors are over-head lines, meaning a lot of interruptions caused by stormy weather and fallen trees. Hence, MSK is planning for isolated conductors to decrease the number of interruptions.  At present, MSK have a few, sporadically placed, grid connected PVs and the power generation of today, regarding power quality, is not a problem. However, MSK sees an increased interest in PVs and more power generation the next few years are to be expected. The question is, how several grid-connected PVs will impact the power grid. In this dissertation, the rural low voltage grid of Duckarp, Kristianstad municipality, has been studied. The grid is connected to the very last transformer in a radial grid. Two cases have been modulated: one with existing PVs of today, and one with PVs at all subscribers connected to the transformer T-640, Duckarp. As the feeding 6 kV grid is to be rebuilt, the study included the choice of cable cross section area in the 6 kV grid as well. The study included grid strength, voltage deviation, load in cables and transformer, and grid losses including compensation to subscriber.   The study shows, that with present PVs and with the condition that a tap changing transformer is used, the grid is strong and capable of keeping the voltage required. Due to voltage deviation, more grid connected PVs make the grid weaker and require higher cable cross section areas on the feeding 6 kV grid. The load is not a problem, but still there is a risk of a high proportion of harmonics in the neutral and in the transformer. This, due to the low voltage grid being located in the weakest part of the grid. The reduced losses, due to local power generation, corresponds to a compensation to subscriber of 0.02 SEK/kWh. Building strong power grids is expensive and alternative solutions, so-called smart grids, are of interest; Line Voltage Regulator (LVR), reactive power generation in the inverter, battery storage, or load regulations to mention some. But when there is an ongoing reconstruction of the grid, as in the case studied, it is appropriate to build a strong power grid to meet a future expansion of grid-connected PVs.

Developing countries confront the challenge of generating more electricity to meet demands in a sustainable manner. According to the World Bank’s 2015 Global Tracking Framework, roughly 15% of world population (or 1.1 billion people) lack access to electricity, and many more rely on poor quality electricity supplies. In September 2015, the United Nations General Assembly adopted Agenda 2030 comprised of a set of 17 Sustainable Development Goals (SDGs) and defined by 169 targets. “Ensuring access to affordable, reliable, sustainable and modern energy for all by 2030” is the seventh goal (SDG7). While energy access refers to more than electricity, it is the central focus of this work. Models addressing electrification and access typically need large volumes of reliable energy-related data and information, which in most developing countries have been limited or not available. This paucity of information has decelerated energy planning in the developing World. That situation has fundamentally changed with increasing availability and application of Geographic Information Systems (GIS). GIS layers can provide location specific energy-related information that has not been previously accessible. The focus of this thesis lies on integrating a simple electricity supply model into GIS. In so doing a novel open source spatial electrification tool is developed. It estimates power capacity needs and associated investment (and other) costs for achieving universal access to electricity in developing countries. The dissertation includes a cover essay and six appended papers presenting quantitative methods on coupling selected aspects of GIS and energy systems. It strives to answer three key research questions.  The first research question is: What is the spatially explicit renewable energy potential that can be technically and economically exploited? This information is currently either missing or scattered in developing countries. The provision of low cost, locally available energy can provide a significant opportunity to empower a better standard of living. The first paper presents a GIS based approach to assess the onshore technical wind energy potential on the African continent by applying socioeconomic and geographic restrictions regarding the localization of wind farms and state of the art wind data analysis. The second paper builds on this knowledge and moves one step further by assessing the economic potential and providing cost indicators to assess the viability of wind power (this time in India). The third paper maps the economic wind power potential in Africa based on the methodologies developed in the two preceding papers. Not only wind power but most energy resources have a spatial nature and their availability is linked to geography. Evaluating these other energy sources (solar, hydro etc.) are included and analysed in Papers IV-VI. The second research question is: what is the least-cost set of technologies needed to meet different levels of electricity use accounting for different geographies? Increasing access to electricity effectively requires, inter alia, strategies and programmes that address and account for the geographical, infrastructural and socioeconomic characteristics of a country or region. Paper IV introduces a GIS based methodology to inform electrification planning. It builds on the previous work by taking into account the techno-economic wind, and other resource mapping. This methodology is applied in Nigeria in order to determine the least cost technology mix considering the country’s infrastructure and resource availability on a spatial basis. Paper V utilizes this method and in so doing demonstrates the importance of geospatial calculations in energy access planning. It highlights differences in investment estimates between alternate scenarios with regards to energy demand and technology deployment. Paper VI enhances this methodology and applies it to every square kilometre of Sub-Saharan Africa. The method is subsequently implemented in an Open Source Spatial Electrification Tool (OnSSET) to facilitate education, repeatability and further research. Finally, the third question is: Are there gains to be had by linking geographically explicit analysis with typical (non-spatially explicit) long term energy systems models? The work shows that not only do long-term systems models influence geospatially optimal technology deployment. But vice versa, their output influences long term systems models’ investment profile.  That is because the geospatial disaggregation allows for a better determination of grid versus off-grid connections, and in turn power demand on the national grid. This thesis demonstrates that energy system models should take into consideration the geographic dimension of energy-related parameters, as these play a fundamental role in determining the optimal energy system of a region. / <p>QC 20170524</p>

Power generation with steam as the working fluid has been proven technology in many developed countries around the world. The advantages in using this technology include its ability to use a wide range of fuel and using the cheapest material (water) as a working fluid. This means that if this technology is invested in it can boost the levels of power generation especially in developing countries where only the minority of the population has access to electricity. Currently there is no power plant in Uganda which uses steam technology despite Uganda being endowed with vast sources of fuel ranging from solar, biomass, geothermal and the recently discovered oil in the Albertan region. Blessed by nature, Uganda has a lot of potential to generate power using steam technologies which power when generated can boost the economic development of the country. Due to a low technology level in the country in areas of power generation, there are few commercial steam power plants which are mainly owned by sugar manufacturers and some of them generate power which is supplied to the National grid. There are however accessible demonstration steam power plants in the engineering faculties at both Makerere and Kyambogo Universities. However, the one at Makerere University is malfunctioned and one can only make a study of the performance of these power plants using the plant at Kyambogo University. This study can help the researcher understand the exact challenges of steam power plants, the performance and how to improve efficiency of performance. / <p>Utbildningsprogram i samarbete med KTH</p>

New and old data on screw expanders operating with 2-phase mixtures in the admission line has been combined to enable the first public correlation of adiabatic expansion efficiency as a function of entry vapour fraction. Although not yet perfected, these findings have enabled an entirely new approach to the design and optimisation of Organic Rankine Cycles, ORCs. By allowing a continuous variation of vapour fraction at expander entry optima for thermal efficiency, second law efficiency and cost efficiency can be found. Consequently one can also find maxima for power output in the same dimension. This research describes a means of adapting cycle characteristics to various heat sources by varying expander inlet conditions from pure liquid expansion, through mixed fluid and saturated gas expansion, to superheated gas. Thermodynamic analysis and comparison of the above optimisations were a challenge. As most terms of merit for power cycles have been developed for high temperature applications they are often simplified by assuming infinite heat sinks. In many cases they also require specific assumptions on e.g. pinch temperatures, saturation conditions, critical temperatures etc, making accurate systematic comparison between cycles difficult. As low temperature power cycles are more sensitive to the ‘finiteness’ of source and sink than those operating with high temperatures, a substantial need arises for an investigation on which term of merit to use. Along with an investigation on terms of merit, the definition of high level reversible reference also needed revision. Second law efficiency, in the form of exergy efficiency, turned out to be impractical and of little use. A numerical approach, based on a combination of first and second law, was developed. A theory and method for the above is described. Eventually low temperature power cycle test data was compiled systematically. Despite differences in fluid, cycle, temperature levels and power levels the data correlated well enough to allow for a generalised, rough correlation on which thermal efficiency to expect as a function of utilization of source and sink availability. The correlation on thermal efficiency was used to create a graphical method to pre-estimate key economic factors for low temperature site potential in a very simple manner. A major consequence from the findings of this thesis is the reduced dependency on unique choices of process fluid to match heat source characteristics. This development significantly simplifies industrial standardisation, and thereby potentially improves cost efficiency of commercial ORC power generators.

Dammen i en vattenkraftsanläggning används för att avleda vatten till kraftverkets turbiner och för att möjliggöra lagring och reglering av energi. Vid stora flöden i älven, eller när vattnet av någon anledning inte kan passera genom de energiproducerande delarna, måste det avbördas från magasinet. Detta görs med utskov. I de flesta fall i Sverige är utskoven placerade nära ytan, men ibland finns även bottenutskov. Det är vanligt att dessa användes vid anläggningens byggnation för att avleda vatten, och varit avställda sedan dess. Detta arbete syftade att undersöka möjligheten att driftsätta bottenutskov i anläggningar där de är monterade men inte bruk, för att höja dammsäkerheten. I rapportens första del finns en sammanställning av de problem som teoretiskt kan uppstå vid brukandet av bottenutskov, baserat på litteratur samt på erfarenheter i branschen. Den andra delen av rapporten beskriver resultatet från en fallstudie av en specifik anläggning, Båtfors kraftstation. Här har beräkningar gjorts, med handräkningsmetoder samt med datorsimuleringar för att undersöka anläggningens bottenutskov utifrån identifierade teoretiska möjligheter och problem. Ett antal teoretiska problem med bottenutskov har identifierats, däribland: erosion, kavitation, luftmedrivning, drivgods samt problem vid stängning av bottenutskovsluckorna. För Båtfors kraftstation skattades den nuvarande avbördningskapaciteten med handräkningsmetoder till cirka 900 m3/s vid magasinets dämningsgräns (DG), vilket överensstämmer med anläggningens dokumentation. För vardera av de två bottenutskoven beräknades avbördningskapaciteten vid full lucköppning (2,4 m) till cirka 225 m3/s. De handräknade och simulerade värdena jämfördes för olika lucköppningar, där en viss skillnad (cirka 30–40 %) noterades. Inget simuleringsresultat kunde erhållas för full lucköppning som följd av konvergensproblem. Luftrörelsen i Båtfors båttenutskov undersöktes genom simulering. För små lucköppningar, 0,4 och 0,8 m, kunde luft tillföras från utskovskulvertens nedströmssida vilket inte är möjligt när luckan öppnas 1,2 m. Om detta riskerar att ställa till med problem beror på om tillräcklig luftning kan ske genom öppningar i utskovets tak. Risken för kavitation i Båtfors undersöktes genom att jämföra utskovets lägsta tryck i simuleringen med mättnadstrycket för vatten vid 20 °C. Det fastställdes från detta att kavitation ej bör förekomma i denna anläggning, vilket överensstämmer med litteratur. Som slutsats dras att bottenutskov inte är problemfria, men även att stora möjligheter finns. Dessa utskov kan användas för att öka anläggningens avbördningskapacitet och regleramplitud, som nödutskov och för att möjliggöra avsänkning av anläggningens magasin. Det sistnämnda kan dessutom inte åstadkommas på annat sätt. / The dam in a hydroelectric power station serves to divert water to the station’s turbines, and to allow for energy storage and power balancing. When the flow in the river is high or when the energy producing parts of the facility are inoperative, water needs to be discharged from the reservoir. This is done with outlets. In Sweden, most outlets are near the surface, but in some cases bottom outlets are used. Commonly, these outlets were used during the construction of the dam to divert water and have been unused since then. The purpose of this project was to investigate the possibility to recommission bottom outlets in hydropower dams where they are existent but not in use, to increase dam safety. The first part of the report contains a summary of theoretical problems with bottom outlets, based on industry experiences and literature. The second part presents the results of a case study of a specific facility, Båtfors hydroelectric power station. Calculations have been made, both by hand and with computational fluid dynamics, to identify possibilities and problems. Several theoretical problems have been identified, including: erosion, cavitation, insufficient aeration, debris, and problems with closing the outlet gates. The current discharge capacity for Båtfors power station was estimated by hand to slightly over 900 m3/s at the normal reservoir water level, which is consistent with the documentation of the facility. For each of the two bottom outlets, the discharge capacity was calculated to around 225 m3/s with the gate fully open (2.4 m). The values calculated by hand were compared to simulated ones for different gate openings and a certain difference (around 30–40 %) was noted. No simulation results could be obtained with the gate fully opened due to convergence issues. The movement of air in the bottom outlets of Båtfors were studied by simulations. When the gate was opened to a small degree, 0.4 and 0.8 m, air could be supplied from the downstream opening of the outlet conduit which was impossible when the gate was opened 1.2 m. This may cause problems if sufficient aeration cannot be achieved through openings in the outlet ceiling. The risk of cavitation in Båtfors was investigated by comparing the simulated minimum pressure in the outlet with the saturation pressure of water at 20 °C. It was determined that cavitation likely won’t be an issue at this facility, which conforms with literature. It was concluded that several issues can occur when using bottom outlets, but also that several opportunities exist. These outlets can be used to increase the discharge capacity and drawdown range of the facility, as emergency outlets, and to enable lowering of the reservoir water level. The lattermost can furthermore not be achieved by other means.

No description available.

No description available.

On behalf of Halmstads Energi och Miljö (HEM) this paper investigates the possibilities to reduce power peaks in their district heating production through demand side management. The purpose with this paper is to reduce the power peaks with 10 MW and investigate which customers or areas HEM should focus on. In addition, two bottlenecks in the district heating network are analyzed by the effects of demand side management. A theoretical model of demand side management was constructed. The model uses hourly data from production and endeavor to daily average values. The model also included parameters such as storage capacity and manipulated outdoor temperature. The results from demand side management relates to the total daily variations of the district heating system. The demand side management has been applied to a selection of 214 substations and three independent demand side management schemes for the year of 2016, one for each bottleneck and one for the total 214 substations. The choice of substations for demand side management is based on which buildings are connected to them. Criteria for the selection are buildings with high thermal mass, which give high thermal inertia and buildings with high heat demand (large apartment buildings). It is of great interest to investigate how demand side management affects the indoor temperature in selected buildings because limit values cannot be exceeded. The result shows that the power peaks can be reduced by 11.7 MW (mean value) for the whole year excluding the months of spring and summer and for the winter months 13.1 MW (mean value). The reasons why the power peaks can be reduced to a greater extent during the winter months was due to a larger heat demand and heat load variations. Two bottleneck areas applied one theoretic demand side management scheme each where power peaks can be reduced by 0.63 MW(mean value) and 0.7 MW(mean value) excluding spring and summer months and 0.71 and 0.72 only including winter months. The profit from reducing the power peaks for HEM is shorter operating time for the peak heating boilers. The power peaks is later compensated and balanced with renewable bio energy. The simulation from 2016 brings a cost saving to 2.7 million SEK. The profit comprises the cost difference between fossil fuels, natural gas and renewable fuels such as wooden chips. The carbon dioxide reduction during the same period of time was 1671 metric tonne CO2- equivalents.