Thesis (D. Tech. (Electrical Engineering)) -- Central University of Technology, Free State, 2014 / For a sustainable and clean electricity production in isolated rural areas, renewable energies appear to be the most suitable and usable supply options. Apart from all being renewable and sustainable, each of the renewable energy sources has its specific characteristics and advantages that make it well suited for specific applications and locations. Solar photovoltaic and wind turbines are well established and are currently the mostly used renewable energy sources for electricity generation in small-scale rural applications. However, for areas in which adequate water resources are available, micro-hydro is the best supply option compared to other renewable resources in terms of cost of energy produced. Apart from being capital-cost-intensive, the other main disadvantages of the renewable energy technologies are their resource-dependent output powers and their strong reliance on weather and climatic conditions. Therefore, they cannot continuously match the fluctuating load energy requirements each and every time. Standalone diesel generators, on the other hand, have low initial capital costs and can generate electricity on demand, but their operation and maintenance costs are very high, especially when they run at partial loads. In order for the renewable sources to respond reliably to the load energy requirements, they can be combined in a hybrid energy system with back-up diesel generator and energy storage systems. The most important feature of such a hybrid system is to generate energy at any time by optimally using all available energy sources. The fact that the renewable resources available at a given site are a function of the season of the year implies that the fraction of the energy provided to the load is not constant. This means that for hybrid systems comprising diesel generator, renewable sources and battery storage in their architecture, the renewable energy fraction and the energy storage capacity are projected to have a significant impact on the diesel generator fuel consumption, depending on the complex interaction between the daily variation of renewable resources and the non-linear load demand. V This was the context on which this research was based, aiming to develop a tool to minimize the daily operation costs of standalone hybrid systems. However, the complexity of this problem is of an extremely high mathematical degree due to the non-linearity of the load demand as well as the non-linearity of the renewable resources profiles. Unlike the algorithms already developed, the objective was to develop a tool that could minimize the diesel generator control variables while maximizing the hydro, wind, solar and battery control variables resulting in saving fuel and operation costs. An innovative and powerful optimization model was then developed capable of efficiently dealing with these types of problems. The hybrid system optimal operation control model has been simulated using fmincon interior-point in MATLAB. Using realistic and actual data for several case studies, the developed model has been successfully used to analyse the complex interaction between the daily non-linear load, the non-linear renewable resources as well as the battery dynamic, and their impact on the hybrid system’s daily operation cost minimization. The model developed, as well as the solver and algorithm used in this work, have low computational requirements for achieving results within a reasonable time, therefore this can be seen as a faster and more accurate optimization tool.

Thesis (MScEng)--University of Stellenbosch, 2002. / ENGLISH ABSTRACT: The cost of powering Antarctic research stations by conventional diesel electric generator systems is high (Steel, 1993). In order to reduce these costs and airborne pollution due to the combustion of fossil fuels, an investigation into renewable energy sources has been conducted, with the focus on wind turbine energy generation. The aim was to see whether a wind turbine is feasible, both technically and economically, for partial energy production at the SANAE IV base. The existing diesel electrical generators will still be used for the base demand, when there is not enough wind or when the energy demand is more than can be produced by the wind turbine. The work accomplished for this study explains and motivates a MSc. (Eng.) thesis on the feasibility of installing wind electricity generators at Antarctica. This evaluation was done for the South African research station SANAE IV in Antarctica. It provides information on the literature consulted to date, the theoretical and practical work covered, the theoretical investigations, the results obtained and future implementations. Also included in this work was a trip to Antarctica, so that all the relevant data, like wind speeds and wind direction could be measured. Another reason for having done the trip was to do an energy audit for SANAE IV, so that the energy demand for the base could be established. The energy demand of the base varies among other factors, for summer and winter conditions, for day and night conditions, and for population variations. With the information obtained during the trip, the theoretical evaluation of a possible wind turbine system was performed. With the aid of the data from the 6 m wind mast, wind profiles have been established, from which Wei bull distributions were obtained, and the energy output from 5 different wind turbines, in the range between 10 kW and 100 kW, were calculated. The annual energy production of the 100 kW wind turbine is 430 MWh with a capacity factor of 49 %. The annual energy demand of the base amounts to 1153 MWh, thus the wind turbine could contribute up to 30 % of the power needed at the base taking losses, such as availability and maintenance losses, into account. From the automatic weather station of the South African Weather Services, positioned at SANAE IV, wind speed and direction data for the year 2001 was obtained and this data was analyzed. The results show that the winds at SANAE IV are highly directional, coming mostly from an eastern and southeastern direction. This highly directional wind pattern is well suited for wind turbine application. The average wind speed, being measured at 10m height, is 10.8 m/s and the hourly averaged maximum wind speed for the year 2001 is 38.9 mls. From the wind analysis, site survey, cold weather issues and connection to the electricity grid of the base, it becomes evident that the North Wind NWIOO/19 100 kW wind turbine is the best-suited wind turbine for installation at SANAE IV. One of the major advantages of the NW100/19 is that it features a tilt-up tower erecting system that enables the wind turbine to be installed without the use of a crane. The NW100/19 is the only turbine rated at 100 kW, with this feature. From the economic analysis it is evident that a wind turbine, with the complete installation, operation and maintenance costs, features a break even period of 10 years, when installed at SANAE IV. This relatively short breakeven period, considering that the life of the turbine is 30 years, originates from the fact that the average wind speed at the base is about 11 mis, which is relatively high and yields enormous power productions. This wind turbine operates for approximately 80 % during a year, which is very high, making this renewable energy source very attractive as a power-generating source for SANAE IV. The cost per kWh produced by the wind-diesel system is R1.63/kWh, while the cost per kWh produced by the current diesel generators, satisfying the power demand of the base, is R1.94/kWh. Thus the hybrid system can reduce the cost of power produced by almost 20 %, which again demonstrates the attractiveness of using wind power at SANAE IV. From an environmental point of view, the use of wind power at SANAE IV is favorable, since a wind turbine has minimal effects on the environment at Antarctica. The cost of emissions and fuel spills were calculated for SANAE IV. The fuel saving, resulting from the operation of a wind turbine at SANAE IV, converts to a saving in externalities of about R500 000.00 per year, using an evaluation method that was applied to remote Alaskan villages. It can therefore be concluded that the aims of the project have been fully accomplished and that the use of wind power at SANAE IV is indeed a very attractive option, regarding all the criteria mentioned above. When it is being decided that a budget will be provided for a wind turbine installation, the economic analysis has to be refined, due to the uncertainty of the market value of the South African currency. / AFRIKAANSE OPSOMMING: Die koste verbonde aan krag voorsiening vir Antarktiese navorsingstasies deur middel van konvensionele diesel elektriese kragopwekkers is baie hoog (Steel, 1993). Om hierdie kostes en lugbesoedeling weens die verbranding van fossielbrandstowwe te verminder, is 'n ondersoek na hemubare energiebronne gedoen, met die fokus op windturbiene energie opwekking. Die doelwit van die studie was om te sien of 'n windturbiene aanwending vir kragopwekking vir die SANAE IV stasie lewensvatbaar is, gebaseer op tegniese en ekonomiese uitgangspunte. Die bestaande diesel elektriese kragopwekkers sal nog altyd gebruik word vir kragopwekking, as daar nie genoeg wind is nie, of as die energievraag hoer is as wat kan verskafword deur die wind turbine. Die werk wat vir hierdie studie voltooi is belig en motiveer 'n MSc(Ing) tesis oor die lewensvatbaarheid vir installering van 'n windelektriese kragopwekker op Antarktika. Hierdie evaluasie is gedoen vir die Suid Afrikanse navorsingstasie, SANAE IV, op Antarktika. Dit behels informasie oor die literatuur verwerk tot dusver, die teoretiese en praktiese werk gedoen, die teoretiese ondersoeke, die resultate verkry en toekomstige verwesenlikings. Werk ook ingesluit was 'n expedisie na Antarktika toe, sodat al die relevante data, soos wind spoed en rigtings gemeet kon word. Nog 'n rede om die expedisie te doen was om energie data van SANAE IV te meet, sodat die energieverbruik van die basis bevestig kon word. Die energieverbruik van die basis varieer ten opsigte van somer en winter kondisies, van dag en nag variasies en inwonergetalle. Met die informasie verkry gedurende die expedisie kon 'n evaluasie gedoen word vir 'n moontlike windturbiene stelsel op Antarktika. Met die hulp van 'n 6tn wind toring kon wind profiele gekry word, waarvandaan Weibull verdelings bereken is en die kragopwekking van 5 verskillende windturbienes bereken is, wat wissel van 10 kW tot 100 kW. Die jaarlikse energieopwekking vir die 100 kW wind turbine is 430 MWh met 'n kapasiteitsfaktoor van 49 %. Die jaarlikse energieaanvraag van die stasie is 1153 MWh. Dus kan die wind turbine ongeveer 30 % van die jaarlikse energieaanvraag dek, as verliese soos beskikbaarheids- en instandhoudingsverliese III berekening gebring word. Wind spoed en rigting data vir die jaar 2001 is verkry van die outomatiese weerstasie van die Suid Afrikaanse Weer Diens, wat geposisioneer is by die SANAE IV stasie, en hierdie data is geanaliseer. Die resultate verkry bewys die direksionele stabiliteit van die winde by SANAE IV, waarvandaan die meeste winde uit die oostlike en suidoostlike rigting kom. Hierdie hoogs gekosentreede winde is baie goed geskik vir windturbiene aanwending. Die gemiddelde wind spoed, wat gemeet is op 'n hoogte van 10 m is 10.8 m/s en die uurlike gemiddelde maksimum wind spoed vir die jaar 2001 is 38.9 m/s. Van die wind analise, terrein analise, koue weer informasie en koppeling van die wind turbine by die bestaande elektrisiteits netwerk word bevestig dat die North Wind NW100119 100 kW windturbiene die geskikste windturbiene vir installasie en werking by SANAE IV is. Een van die grootste voordele van die NW100/19 windturbiene is dat dit 'n selfoprigdende meganisme het, wat sonder die hulp van 'n kraan werk. Die NW100/19 is die enigste windturbiene in sy klas, wat so 'n funksie het. Van die ekonomiese analise kan afgelei-word, dat 'n wind turbine met volledige installasie, werking en diens kostes, 'n kapitale terugbetalings periode van 10 jaar het, as dit by SANAE IV geinstalleer word. Hierdie tydperk is relatief kort, as gekyk word na die ontwerp leeftyd van 30 jaar van die NW100/19 wind turbine. Die rede vir die kort terugbetalings periode is afkomstig van die hoe gemiddelde wind spoed by SANAE IV, wat enorme kragopwekking tot gevolgtrekking het. Dit kan ook gesien word aan die hoe werkingsure van die turbine wat 6942 uur per jaar is. Dus wek die turbine vir omtrent 80 % van die jaar krag op, wat beinvloed dat 'n wind turbine opsie vir SANAE IV baie aantreklik is. Die koste per kWh krag opgewek vir die wind-diesel sisteem is R1.63/kWh, terwyl die koste per kWh krag opgewek vir die huidige diesel generator opstelling R1.941kWh is. Dus kan 'n kostebesparing van tot 20% van die energie onkostes verkry word, wat weer eens beklemtoon, dat die wind-diesel sisteem baie aantreklik vir kragopwekking by SANAE IV is. Vanaf 'n omgewingsoogpunt gesien het die gebruik van 'n wind turbine stelsel by die SANAE IV stasie net weglaatbaar klein invloede op die omgewing in vergelyking met die lugbesoedeling van die diesel kragopwekkers. As die koste verbonde aan lugbesoedeling en brandstof lekkasie besoedeling bereken word kan die wind turbine stelsel omtrent R500000.00 per jaar aan besoedeling onkostes spaar. Die getalle vir besoedelings onkostes is gebaseer op die evaluasie van besoedeling vir afgelee Amerikanse dorpies (Isherwood et al., 1999). Dit kan dus afgelei word vanaf die bogenoemde bevindings, dat die doelwitte van die tesis bereik is en dat wind krag opwekking by SANAE IV inderdaad 'n baie aantreklike moontlikheid is. Wanneer 'n begroting beskikbaar gestel word vir 'n windturbiene stelsel vir SANAE IV, moet die ekonomiese analise geoptimeer word weens die onsekerheid van die markwaaarde van die Suid Afrikaanse Rand.

Trading optimal wind power in energy and regulation market offers possibil-ities for increasing revenues as well as impacting security of the system in apositive way[33]. The bidding in both energy and regulation markets can bedone through stochastic optimization process of both markets.Stochastic optimization can be possible once the probabilistic forecst is avail-able through ensemble forecast methodology. For stochastic optimization, thepost-processing of the ensembles to generate quantiles that will be used in op-timization can be accomplished by employing different methodology. In thisstudy, we will concentrate on the impact of post-processing of ensembles onthe stochastic optimization.Generation of quantiles needed for stochastic optimization used herein formarket optimization will be the main focus of the investigation. The impactof price ratios between energy and reserve market will be also investigated toanalyse the impact of said ratios on the revenues. Furthermore this analysiswill be performed for both US and Swedish markets.

Die Software alaska ist zunächst ein allgemeines Werkzeug zur Modellierung und Simulation der Dynamik mechanischer/mechatronischer Systeme. alaska wird am Institut ür Mechatronik in Chemnitz entwickelt. Mit dem Erweiterungsmodul alaska/Wind erhält alaska Funktionalitäten die erforderlich sind, um das dynamische Verhalten von Windkraftanlagen (WKA) mit dem Ziel zu simulieren, die resultierenden Belastungen zu ermitteln. Bestandteile von alaska/Wind sind u.a. Komponenten zu Beschreibung der aerodynamischen Umgebungsbedingungen und der Berechnung der daraus resultierenden, an der WKA angreifenden Windkräfte sowie ein Basis-WKA-Simulationsmodell. Inhalt des Vortrages ist es zu zeigen, wie dieses Basis-Simulationsmodell vom Anwender, also vom Entwickler/Hersteller von Windkraftanlagen, an seine spezifischen Anforderungen angepasst wird, wie es in seinen Produktentstehungsprozess eingebunden wird und wie mit dem Einsatz der alaska- Komponente alaska/DC (DistributedComputation) weitestgehend automatisch auf der Basis mehrerer Tausend Simulationsrechnungen Design-treibende Belastungen ermittelt werden.

The wind power development in Greece has been rising the last decade, aiming to exploit the country's excellent wind resources. Though the project developers' experience in the wind energy industry has been expanded, wind power project risks are always present, having the potential to have a major impact on the project outcome. Thereafter, the question generated is “which are those risks, and how can they effectively be addressed?”. This Thesis is aiming to identify those risks, specifically for the Greek wind energy sector, present the results of a quantitative risk analysis, and propose risk response strategies for each of the identified risks. For that purpose, a case-study in S. Euboea region was applied; a typical 8 MW onshore wind farm was designed inside a Wind Priority Area. The risk data were collected by a panel of experts, chosen to identify and quantify the potential risks through the implementation of the Delphi and the Project Risk FMEA (RFMEA) methods. The results showed 21 risks that should be considered when developing a wind power project in Greece, and also presented their response priority ranking, based on each risk's ratings inprobability, impact and detection factors. Afterwards, the risk response strategies, for each risk, were proposed, as those were collected by the experts panel group-interviewing. Through the analysis of the results, it is clarified that the country's economic crisis and the current changes in the political scene have created new and affected the already existing risks of the Greek wind energy sector, bringing the regulatory risk to the top of the critical risks.

Thesis (MScEng)--Stellenbosch University, 2012 / ENGLISH ABSTRACT: A technology that has advanced immeasurably as a result of the necessity for green energy production is the harnessing of wind energy. One of the most important aspects of a wind turbine is its supporting structure. The tower of a wind turbine needs to be sufficiently reliable and structurally sound to ensure that the design life of the wind turbine machine is unaffected. The tower also needs to be of the correct height to ensure that the full potential of energy capture is realised. The supporting structure of a wind turbine constitutes up to as much as 30% of the total costs of a wind turbine. The most common wind turbine supporting structures seen worldwide today are Steel Monopole Towers. The large cost proportion of the tower compels the industry to investigate the most feasible alternative supporting tower structures and thus prompted the research developed in this thesis. In this thesis the focus is on small scale wind turbines (<50kW), more specifically, a 3kW Wind Turbine. The proposed alternative design the support structures of small scale wind turbines to the presently used Steel Monopole tower was a Steel Lattice tower. Both a Steel Lattice and Steel Monopole Tower was designed for a 3kW Wind Turbine using rational design methods determined from pertinent sections of the South African design codes. The Tower designs needed to incorporate the details of the element connections, so as to encompass all of the cost parameters accurately. The foundation design of each of the towers was also required from the point of view of cost analysis completeness, and ended up playing a critical role in the feasibility analysis. To validate the design methods, the two towers were modelled in the finite element package Strand7 and a number of different analyses were performed on the two towers. The analyses included linear static, nonlinear static, natural frequency and harmonic frequency analyses. The towers were assessed for a number of different load case combinations and were examined in terms of stress states, mass participation factors and deflections, to mention a few, for the worst loading combination cases that were encountered. Once a final design was reached for both the Steel Lattice and Steel Monopole Towers, each element from which they were made was assessed from a structural viewpoint to determine manufacturing and construction costs. The cost analysis was conducted by means of asking a number of leading construction companies for unit prices for each of the identified elements to be assessed. The fabrication and construction of each of the Towers was then compared to determine which one was more feasible, in terms of each design aspect considered as well as looking at the complete end product. It was found that the Steel Lattice Tower was more feasible from the points of view of fabrication, and construction, as well as having a far more cost effective foundation. This was a positive conclusion from the perspective of the proposal for a more feasible alternative to the presently used Steel Monopole Towers. The outcome of the research conducted here could certainly prove to be worth considering from a wind farm development perspective, with particular focus on the up and coming Wind Industry developments in South Africa. / AFRIKAANSE OPSOMMING: As gevolg van die noodsaaklikheid vir die produksie van volhoubare energie is ʼn tegnologie wat met rasse skrede vooruitgegaan het die vir die benutting van windenergie. Een van die belangrikste aspekte van 'n windturbine is die ondersteunende struktuur. Die toring van 'n windturbine moet funksioneel en struktureel betroubaar wees om te verseker dat die ontwerpleeftyd van die windturbine masjien nie nadelig beïnvloed word nie. Die toring moet ook die regte hoogte wees om te verseker dat die volle potensiaal van die wind energie in meganiese energie omgesit word. Die koste van die ondersteunende struktuur van 'n windturbine verteenwoordig tot 30% van die totale koste van 'n windturbine. Die mees algemene vorm van ondersteunende strukture vir windturbines wat vandag wêreldwyd teëgekom word, is die van 'n enkel staal buisvormige toring. Die groot koste‐komponent van die toring dwing die industrie om ondersoek in te stel na die mees koste effektiewe prakties uitvoerbare alternatief vir die ondersteunende toring struktuur. Hierdie aspek van die struktuur konseptualisering het gelei tot die navorsing wat in hierdie tesis onderneem is. Die fokus van die navorsing is op klein skaal windturbines (<50kW), en meer spesifiek op 'n 3kW windturbine model. Die alternatiewe ontwerp wat ontwikkel is vir klein skaal wind turbines se ondersteunende structure, is 'n staal vakwerk toring as alternatief vir die staal buisvormige toring. Beide 'n staal vakwerk en staal buisvormige toring vir 'n 3kW wind turbine is ontwerp deur rasionele ontwerp metodes. Die toepaslike gedeeltes van die Suid‐Afrikaanse ontwerp kodes is hiervoor gebruik. Die ontwerp vir die toring moet die besonderhede van die element verbindings in ag neem en die nodige koste parameters moet akkuraat bepaal word. Die ontwerp van die fondament van elke toring is ook noodsaaklik vir die volledigheid van die koste‐ontleding en dit speel ook 'n kritieke rol in die gangbaarheid analise. Om die ontwerp metodes te bevestig, is die twee tipes torings in die eindige element pakket, Strand7, gemodelleer en 'n aantal verskillende ontledings vir die twee torings is uitgevoer. Die ontledings sluit lineêr en nie‐lineêr statiese ontledings asook natuurlike frekwensie en dinamiese ontledings onder harmoniese belastings in. Die torings is vir 'n aantal verskillende lasgevalkombinasies ondersoek en in die spannings toestande, massadeelname faktore en defleksies vir die ergste laskombinasie gevalle wat ondervind is, is geassesseer. Sodra 'n finale ontwerp vir beide die staal vakwerk en staal buisvormige toring voltooi is, is elke element beoordeel uit 'n strukturele en materiaal oogpunt om die kostes daarvan te bepaal. Die koste‐analise is baseer op data wat voorsien is deur 'n aantal vooraanstaande konstruksiemaatskappye op 'n prys per eenheid basis vir elk van die geïdentifiseerde elemente wat geassesseer moes word. Die vervaardiging en konstruksie van elke toring is dan vergelyk om te bepaal watter een die mees haalbaar is, in terme van elke toepaslike ontwerpsaspek en deur ook die volledige eindproduk te evalueer. Daar is bevind dat die staal vakwerk toring uit die oogpunt van vervaardiging en konstruksie, asook as gevolg van 'n meer koste‐effektiewe fondament, die voorkeur alternatief verteenwoordig het. Dit was 'n positiewe gevolgtrekking uit die oogpunt van die soeke na 'n ander alternatief as die buisvormige staal torings wat tans algemeen in gebruik is. Die uitkoms van hierdie navorsing verdien oorweging uit ʼn windplaas ontwikkelingsperspektief, met ʼn spesifieke fokus op die opkomende ontwikkelinge in die wind energie industrie in Suid‐Afrika.

<p>During the last two decades, increase in electricity demand and environmental concern resulted in fast growth of power production from renewable sources. Wind power is one of the most efficient alternatives. Due to rapid development of wind turbine technology and increasing size of wind farms, wind power plays a significant part in the power production mix of Germany, Spain, Denmark and some other countries.</p><p>Wind power has to be built in areas with good wind potential. The best conditions for installation of wind power are, thus, in remote areas free of obstacles, and consequently with low population density. The transmission system in such areas might not be dimensioned to accommodate additional large-scale power plants. Insufficient transmission capacity problem, however, would emerge for any type of new generation, planned in similar conditions, although wind power has some special features that should be considered solving this problem.</p><p>In this thesis the four possibilities are considered. One possibility is to revise the methods for calculation of available transmission capacity. Another solution for large-scale integration of wind power in such areas is to reinforce the network. This alternative however may be expensive and time consuming. Since wind power production depends on the wind speed, the wind farm utilization time is only 2000-4000 hours a year, and power production peaks not necessarily occur during periods with insufficient transmission capacity. Therefore wind energy curtailment may be considered as an alternative for large-scale wind power integration. It is also possible to store excess wind energy during the periods with insufficient transmission capacity. Conventional power plants with possibilities of fast production control (e.g. hydro power plants or gas power plants) may also be employed for this purpose.</p><p>There is a lot of research regarding first two measures, therefore, this thesis provides a review and summarized conclusions from the existing work and further concentrates on development of the methods for estimation of wind energy curtailment and evaluation of wind energy storage possibility in hydro reservoirs.</p><p>Methods similar to probabilistic production cost simulation are developed for estimation of wind energy curtailment. The developed methods are applicable to discrete variables (measurements) and also generalized for continuous variables with known distribution.</p><p>For evaluation of wind energy storage possibility the optimization problem is formulated, the objective of this evaluation is to minimize the costs for power production under consideration of the future water value. The developed method allows us to analyze previous years of operation of the power system (e.g. dry, wet and normal year) and evaluate physical possibilities for wind energy storage. The developed methods are than tested for Swedish power system and the results are also summarized in this thesis.</p><p> </p><p> </p><p> </p><p> </p><p> </p><p> </p><p> </p><p> </p><p> </p><p> </p><p> </p><p> </p><p> </p><p> </p><p> </p><p> </p><p> </p><p> </p><p> </p><p> </p><p> </p><p> </p><p> </p> / QC 20100607

A novel probabilistic method has been developed for modelling the operation of energy storage in electricity systems with significant amounts of wind and solar powered generation. This method is based on a spectral analysis of the variations of wind speed and solar irradiance together with profiles of electrical demand. The method has been embodied in two Matlab computer programs: Wind power only: This program models wind power on any time scale from seconds to years, with limited modelling of demand profiles. This program is only capable of modelling stand-alone systems, or systems in which the electrical demand is replaced by a weak grid connection with limited export capacity. 24-hours: This program models wind power, solar PV power and electrical demand, including seasonal and diurnal effects of each. However, this program only models store cycle times (variations within a time scale) of 24 hours. This program is capable of modelling local electrical demand at the same time as a grid connection with import or export capacity and a backup generator. Each of these programs has been validated by comparing its results with those from a time step program, making four Matlab programs in total. All four programs calculate the power flows to and from the store, satisfied demand, unsatisfied demand and curtailed power. The programs also predict the fractions of time that the store spends full, empty, filling or emptying. The results obtained are promising. Probabilistic program results agree well with time step results over a wide range of input data and time scales. The probabilistic method needs further refinement, but can be used to perform initial modelling and feasibility studies for renewable energy systems. The probabilistic method has the advantage that the required input data is less, and the computer run time is reduced, compared to the time step method.

Our alarming rate of resource exploitation and its consequences on the environment is fuelling an increase in sustainable energy production around the world. Wind power appears to be a particularly promising energy source relative to its environmental footprint, with the exception of potential negative effects of wind power on birds. Varying results from impact assessments around the world indicate that knowledge of both abiotic and biotic factors, as well as bird behavior and ecology, is required to assess the cumulative impact of any given wind farm on local bird communities. This study aims to assess the cumulative impact of a proposed wind farm on a threatened seabird, the red-throated diver (Gavia stellata), at one of its breeding "hotspots" in Sweden: the Holmöarna islands. Measurements of environmental variables in lakes on Holmöarna are combined with breeding surveys from 2012 to 2015 to assess which environmental variables may be associated with lakes that red-throated divers do or do not breed in, and which variables are correlated with breeding success. These results are combined with a literature review to assess the potential negative effects of the proposed wind farm on the breeding population on Holmöarna. The results show that average breeding success over the survey period was 0.35 fledged young per pair per year. No difference was found in environmental variables between lakes that divers had or had not bred in. Lake area/perimeter ratio and distance to the sea were significantly negatively correlated with breeding success, although distance to the sea was only significant for lakes with at least one successful breeding attempt during the survey period. Based on these correlations, 33 of a total 40 breeding lakes are shown to have relatively high area/perimeter ratios and long distances to the sea, which may pre-dispose divers breeding within them to low breeding success. These lakes are, therefore, identified as being at high-to-moderate risk of increased breeding failure if breeding success is further reduced as a result of external factors, including that of any negative impacts of the proposed wind farm. 31 of the 40 breeding lakes are also within 1 km of the proposed wind turbine sites, which may render red-throated divers breeding within them vulnerable to displacement as a result of wind farm-related disturbance. The literature review highlights the mechanisms that may determine the cumulative impact of the wind farm on red-throated divers in terms of collision mortality, habitat displacement, and barriers to movement. The strong sensitivity of red-throated divers to disturbance is considered to be the most likely driver of any negative effects of the wind farm. In this context, I thus argue the need for a precautionary approach to planning wind power developments in the vicinity of breeding red-throated diver populations.

The objective of this Thesis is to investigate the phenomenon of voltage unbalance on electrical wind power systems. A large part of this work is the literature review of all relative work that has been done so far. This serves first as a guideline to define and measure voltage unbalance and second as a tool to spot open research questions that can inspire future work. A case study is then used to investigate the voltage unbalance at a wind farm in Näsudden, Gotland. Using real-time measurements and a simulation of the power system in MATLAB/Simulink, an evaluation of the propagation of the voltage unbalance from the distribution to the turbine level is carried out. The effect that different transformer connection types have on the propagation is studied through simulations. Many assumptions and simplifications had to be made due to several limiting factors during this work, mainly related to time and data restrictions. The main result shows that when Delta – Wye Grounded and Wye – Wye Grounded transformers are used, the unbalance is halved when it passes to the turbine side. On the other hand, when Wye Grounded – Wye Grounded configuration was used, the unbalance was unaffected. The results also include a comparison of the use of different indices to quantify a voltage unbalance.