In the European Union, there is a driver for a change in the electricity system. The trend is to make the system more environmental friendly and improve the markets functionality. This driver often refers to the development towards a smart grid. In order to accelerate innovation in smart grid and technology application, pilot projects need to be deployed. This master thesis has been done as a part of the Stockholm Royal Seaport urban development project that is a pilot project for smart grid on distribution grid level. The aim of this report is to apply market concept and identify regulatory bottlenecks for smart grid. This report has applied market concept and identified several bottlenecks for two aspects of smart grid. The aspects are integration of distributed energy resources in medium and low voltage level and a changing customer behavior. A changing customer behavior contains both demand response and the implementation of electric vehicles. A state-of-art review on feasible solutions that improve the competition and demand side management of electricity market in smart grid and provide incentives to implement smart grid functions has been performed. The emphasis in the market aspect is on how that new actors like aggregators will enter the market and how the dynamic price can reach consumers. The emphasis in the regulatory aspect is on how regulations promote the application of smart grid supporting technologies for both the DSO and the network users. A case study has been performed for EU countries with a deeper look at Sweden. The case study investigates how far that the current regulations have reached on the way to smart grids. A state-of-art review on conclusion papers of pilot projects has been carried out. However, many pilot projects are still ongoing and not included in the review. The result shows there is still a lack of regulatory incentive to promote smart grid development and supporting market structures. Bottlenecks identified for smart grid services in the Swedish electricity market and regulation are related to four areas. These are the metering system, dynamic consumer price, active distributed units with the possibility to provide services to the system and incentives to the DSO to use new smart grid solutions in the work to enable fast and efficient connection of distributed generation. / Stockholm royal seaport project

Combined Cycle power plants have recently become a serious alternative for standard coal- and oil-fired power plants because of their high thermal efficiency, environmentally friendly operation, and short time to construct. The combined cycle plant is an integration of the gas turbine and the steam turbine, combining many of the advantages of both thermodynamic cycles using a single fuel. By recovering the heat energy in the gas turbine exhaust and using it to generate steam, the combined cycle leverages the conversion of the fuel energy at a very high efficiency. The heat recovery steam generator forms the backbone of combined cycle plants, providing the link between the gas turbine and the steam turbine. The design of HRSG has historically largely been completed using thermodynamic principles related to the steam path, without much regard to the gas-side of the system. An effort has been made using resources at both UK and Vogt Power International to use computational fluid dynamics (CFD) analysis of the gas-side flow path of the HRSG as an integral tool in the design process. This thesis focuses on how CFD analysis can be used to assess the impact of the gas-side flow on the HRSG performance and identify design modifications to improve the performance. An effort is also made to explore the software capabilities to make the simulation an efficient and accurate.

Η παρούσα διπλωματική εργασία πραγματεύεται το σχεδιασμό ενός Φωτοβολταϊκού Συστήματος, και τη σύνδεση αυτού στο δίκτυο διανομής. Η εργασία αυτή εκπονήθηκε στο Εργαστήριο Παραγωγής, Μεταφοράς, Διανομής και Χρησιμοποίησης Ηλεκτρικής Ενέργειας του Τμήματος Ηλεκτρολόγων Μηχανικών και Τεχνολογίας Υπολογιστών της Πολυτεχνικής Σχολής του Πανεπιστημίου Πατρών. Σκοπός, πέρα από την εγκατάσταση του εξοπλισμού, είναι η μελέτη του συστήματος που σχεδιάστηκε ώστε να λειτουργεί με 3 διαφορετικούς τρόπους: α) Μονοφασικό Σύστημα συνδεδεμένο στο δίκτυο διανομής, β) Τριφασικό Σύστημα συνδεδεμένο στο δίκτυο διανομής και γ) Μονοφασικό αυτόνομο Σύστημα. Αρχικά, γίνεται μια εκτενής αναφορά στις Ανανεώσιμες Πηγές Ενέργειας και περιγράφεται η κατάσταση στην Ελλάδα σχετικά με αυτές. Στη συνέχεια παρουσιάζονται τα χαρακτηριστικά μεγέθη της ηλιακής ακτινοβολίας, καθώς επίσης και ο τρόπος με τον οποίο καθορίζεται ο βέλτιστος τρόπος τοποθέτησης των φωτοβολταϊκών πλαισίων. Επιπλέον, εξηγείται ο τρόπος λειτουργίας των φωτοβολταϊκών κυττάρων και αναφέρονται οι διάφορες τεχνολογίες των φωτοβολταϊκών κυττάρων που έχουν αναπτυχθεί μέχρι σήμερα. Συνεχίζοντας, παρατίθενται τα στοιχεία ενός συνδεδεμένου στο δίκτυο φωτοβολταϊκού συστήματος και οι γενικές αρχές σχεδίασής του. Έπειτα, παρουσιάζεται η μελέτη, ο τρόπος λειτουργίας και ο εξοπλισμός του συστήματος που εγκαταστάθηκε στο Εργαστήριο, και καταγράφονται οι μετρήσεις που ελήφθησαν και τα σχετικά διαγράμματα για μονοφασική και τριφασική συνδεδεμένη στο δίκτυο λειτουργία. Τέλος, γίνεται αναφορά στις δυσκολίες που αντιμετωπίστηκαν κατά την εκπόνηση της διπλωματικής εργασίας. / The Scope of this thesis is the design of a Photovoltaic System, and its connection to the distribution grid. The project was conducted at the Power Systems Laboratory in the Department of Electrical and Computer Engineering of the School of Engineering at the University of Patras. An additional aim of the thesis is the study of the commissioned system, designed to operate in three different functions: a) Single-phase system connected to the distribution grid, b) Three-phase system connected to the distribution grid, and c) Stand-alone Single-phase system. The opening chapter of this study contains a detailed presentation of the existing Renewable Energy Sources, followed by a description of the current situation in Greece. In the next chapter, the variables concerning solar irradiance are analyzed, and the optimal principles of mounting photovoltaic modules are extrapolated. Furthermore, the photovoltaic phenomenon and the electrical behavior of photovoltaic cells is explained, and the photovoltaic technology employed today is concisely mentioned. Also, the components of a photovoltaic system are presented, and the categories and general design principles are covered in detail. Moreover, the study, mode of operation and components of the commissioned system are presented, along with the measurements and the relevant diagrams concerning the Single-phase and Three-phase, grid-connected operation. In conclusion, there is a description of the difficulties and problems that were encountered during the installation of the components.

Dans le domaine de la distribution d’électricité, l’arrivée progressive de production décentralisée rend certains réseaux de distribution exportateurs de puissance, au point où des investissements sont nécessaires pour permettre l’évacuation de la puissance produite. La progression de l’instrumentation des réseaux permet au distributeur d’obtenir des informations de plus en plus riches sur la production décentralisée et la question d’intégrer celles-ci dans les procédés de planification français se pose. À partir de relevés de production, on vérifie que les situations de référence utilisées pour dimensionner le réseau présentent un risque d’occurrence suffisant pour nécessiter des investissements. Si des solutions offrant de la flexibilité sont utilisées, celles-ci peuvent être intégrées au processus de planification. Une étude technico-économique est nécessaire et des méthodes sont proposées pour estimer les fréquences de forte production et la dispersion possible pour un ou plusieurs producteurs. Des modèles simples de loi jointe sont proposés. Le cas pratique de l’effacement de production est testé sur des réseaux considérés réalistes. À partir des relevés réels et des modèles, l’effacement est comparé à l’option d’investir au niveau du poste source. Des abaques de décision sont tracés permettant une projection rapide du distributeur. Par ailleurs dans une optique d’utilisation de l’effacement pour gérer des contraintes intra-réseau, une méthode de calcul de load flow probabilisé est proposée ; celle-ci permet d’estimer rapidement la quantité d’effacement requise et de réaliser un comparatif économique entre plusieurs options. / In the field of electricity distribution, some grids are more and more frequently exporters due to the gradual arrival of decentralized generation. Some grid investments are required to allow the evacuation of the power generated. As more and more information about decentralized production are available for the DSO, the question of integrating them into the planning processes arises.From data of energy production, it appears that the current situations tested for sizing the grid are likely to be reached on a several years basis. If consumption or production flexibilities are used, these can be integrated into the planning process. A technical and economic study is needed and methods are proposed to estimate the frequencies of high production and possible dispersion for one or more producers. Simple models of joint distribution are proposed.The practical case of curtailing production has been tested on networks with realistic scenarios of producers arrival. From actual data and previous models, curtailment and reinforcement are compared on a technico-economic basis. A abacus is plotted as a simple decision tool for the DSO. The question of using curtailment to defer or avoid intra-grid investment has also been investigated ; a calculation method of probabilistic load flow is proposed; it gives a quick and accurate estimation of the energy to curtail in order to avoid a constraint.

Outages and power interruptions are a common and unenviable part of power distribution system operations. Growing demands on reliability in distribution systems has opened up for new technological solutions for fault location at MV and LV level in distribution systems, previously reserved for transmission systems. This report compiles and compares available methods for fault location at distribution level and maps the current fault location process at the power distribution company Ellevio, with the aim of reaching a recommendation for a new fault location scheme. The advocated method is an impedance based method motivated by its reliability, applicability and affordability. The performance and implementation procedure is evaluated through a number of case studies where the methods impact on power reliability demonstrated as well as the need for grid analysis before implementation. Fault indicators and fault current, through relay communications, was identified as key factors for a successful implementation of the method.

The electricity generation composition in the South African national grid has changed in recent years from mostly thermal generation to a combination of thermal generation plants and a variety of plants owned and operated by Renewable Energy Independent Power Producers (REIPPs). The need arises to determine whether the existing planning and design guidelines of distribution networks in South Africa are sufficient in terms of equipment specifications and general sizing and rating principles, used during the network planning process, under increasing penetration levels of embedded generation. The correlation between increases in embedded generation penetration levels and voltage variation, unbalance and harmonic emissions are determined by simulating various operating scenarios of varying load and short circuit level for penetration levels of 10%, 25% and 40%. The existing distribution grid planning standard NRS 097 allows for a 25% penetration level where several consumers share one feeder or distribution transformer. Some of the limits contained in the South African power quality standards NRS 048 and the distribution grid planning guidelines NRS 097 are exceeded when penetration levels of grid connected Photovoltaic (PV) generation exceeds certain levels. - Switching embedded generation in or out of service does not cause voltage variations that exceed the planning limit of 3% at the shared feeder. - Voltage unbalance due to embedded generation connected to the same phase does not cause the compatibility limit of 3% to be exceeded. - Current unbalance should be monitored as it is very likely that equipment ratings may be exceeded when the integration of embedded generation is not coordinated. - Voltage harmonic limits of the odd harmonic which are multiples of 3 are exceeded. - Current harmonic planning limits of several harmonics are exceeded for penetration levels of 25%. The criteria and limits contained in the standards and guidelines relating to current unbalance and harmonic currents should be reviewed to ensure that future grids with high penetration levels of embedded generation can withstand the inherent power quality challenges without having an adverse effect on distribution equipment. Distribution transformers can age faster when they are subjected to harmonic currents and voltages exceeding their design parameters [12]. The distribution transformer isolates the Medium Voltage (MV) distribution grid from the 400 V residential grid. The voltage harmonics and voltage unbalance on the Low Voltage (LV) grid therefore do not permeate to the MV grid. Proposed future work includes translating the qualitative suggestions made in this dissertation into quantitative terms that can be included in revisions of the distribution equipment standards and grid planning guidelines. / Dissertation (MEng)--University of Pretoria, 2017. / Electrical, Electronic and Computer Engineering / MEng / Unrestricted

Planning of distribution grids is based on statistically estimating the maximum load that will occur given a certain range of criteria (location, household types, district / electric heating etc.) Charging of electric vehicles is not one of these criteria. However, given the expected `boom' in sales of Chargeable Electric Vehicles (CEVs), and the lengthy planning process of distribution grids (>10 years) the knowledge gap is becoming a more pressing issue. This research has been conducted to investigate if Vattenfall, a Swedish electric utility company with distribution assets in both Sweden and Germany, needs to take action to react to the expected increase in CEVs in the near term. The study has been conducted with Uppsala Municipality as a showcase and 2030 as the time frame. The findings of this study show that Vattenfall should incorporate CEV usage into distribution planning to avoid overload of power stations in Uppsala by 2030. The ndings shows that 1) we can expect a 'boom' in sales of CEVs in the near future and that 73% of cars in trac in Uppsala may be CEVs by 2030 and 2) that CEV charging is expected to have a signi- cant impact on the distribution grid, with certain power stations in Uppsala seeing a peak load increase of up to 30%. The recommended actions are the following: • Monitor specific areas with a high concentration of cars and low energy consumption per household that already have substations with capacity below the recommended dimensions • Monitor CEV sales to reevaluate current projections on CEV development in Uppsala • Monitor trends of car ownership and evaluate whether this will aect CEV charging behaviour • Reconstruct Velander constants, used for grid planning, to take the CEV load into consideration • Investigate smart charging solutions, to shift the CEV load peak to a different time of the day / Dimensionering av distributionsnat baseras pa att statistiskt uppskatta den maximala lasten som kommer att intraa pa natet, givet olika faktorer (geograskt lage, hushallstyp, fjarrvarme / elvarme etc.). Laddning av elbilar ar inte en av de faktorer som man tar hansyn till. Givet en vantat kraftig okning av laddningsbara bilar, samt den langa planeringshorisonten for distributionsn at (>10 ar), blir dock fragan hur elbilar kommer att paverka elnatet valdigt aktuell. Denna studie har bedrivits for att avgora hur Vattenfall, ett statligt, svenskt elbolag med distributionsnat i Sverige och Tyskland, behover agera for att anpassa sig till den forvantade okningen av elbilar. Den har studien har genomforts som en fallstudie pa Uppsala Kommun med ar 2030 som tidsram. Resultaten fran studien visar att Vattenfall bor ta hansyn till laddning av elbilar vid dimensionering av distributionsnat for att undvika overbelastning pa natstationer i Uppsala ar 2030. Resultaten visar dels att 1) man kan forvanta sig en kraftig okning av forsaljning av laddningsbara fordon inom en snar framtid och uppemot 73 % av alla bilar i trak i Uppsala kommer att vara laddningsbaraar 2030 samt att 2) laddningsbara fordon kommer att ha en signikant paverkan pa distributionsnatet med okningar pa upp till 30 % av maxlasten for vissa natstationer. Foljande atgarder rekommenderas saledes: • Overvaka specika omraden med hog biltathet och lag energianvandning per hushall som ar anslutna till natstationer som ar underdimensionerade • Folj utvecklingen av forsaljning av laddbara fordon for att omvardera genom forda projektioner over laddningsbara bilar i Uppsala • Overvaka trender inom bilagande och utvardera hur detta paverkar laddningsbeteende • Gor om Velanderkonstanter sa att de tar hansyn till lasten fran laddbara fordon vid planering av elnat •  Utvardera smarta laddningslosningar for att ytta last fran elbilsladdning till en annan tidpunkt pa dygnet

Demand response (DR) has been widely documented as a potential solution for severalchallenges the electrical power system is facing, such as the integration of intermittentrenewable electricity generation and maintaining system reliability undera rapid, global electrification. While l ots of r esearch has been done i nto differentmarket designs and tariffing methods, less work is available on the implications ofdemand response on power grid operation, especially for the low voltage side. Thepurpose of this thesis is to estimate the impact of a demand response program on thepower losses in the low-voltage distribution network.The thesis will also contributeto the, currently limited, knowledge base on practical implementation of demandresponse by evaluating the outcome of a real-life DR pilot project. This pilot is partof smart cities development project ’Stockholm Royal Seaport’ (SRS) in the east ofStockholm.The study compared the consumption behaviour of around 400 reference consumerswith a group of 154 DR enabled apartments, that are provided with an hourly varyingelectricity tariff. The goal was to evaluate what percentage of daily consumptionis being shifted from peak to off-peak hours by the active consumers in responseto the price signal, using hourly metering data collected between the 1st of Januaryand the 22nd of March 2017. During this period, grid measurements were also collectedfrom the SRS smart grid and used to estimate the technical power losses inthe low-voltage distribution network. By combining the daily load shift of the DRconsumers and the observed daily power loss fraction in the grid, an estimation wasmade of the impact of the demand response on the grid losses. A simulation modelwas also proposed, and used to simulate the effect of load shift on losses in a givengrid situation.It was found that the DR apartments overall exhibit a load shift of 2.8% of dailyelectricity consumption towards peak hours, and have a lower average load factor(0.57 versus 0.62 for the reference group). This could either mean that the pricesignal does not sufficiently manage to change load behaviour, or that the referencegroup was not representative. However, a strong variation in average load shift wasobserved amongst the individual DR apartments, ranging from -16% (shift towardspeak hours) to 7%. Especially the most electricity consuming apartments showedpositive load shifts. No direct influence of the load shift on the level of grid losseswas found. This could be due to a too small amount of DR consumers in the grid orconfounding factors such as variations in power factor and load size. To circumventthis problem, the simulation model was used to calculate loss reductions for severalpossible reference consumer groups and their possible reactions to a price signal. Itwas found that in the SRS project, the potential for loss reductions is limited becausethe reference group are already ’good’ consumers. The maximum loss reductionwould be around 4%. For grids with severe peak consumption however, optimalloss reductions from load shifting up to 25% were found.The key take-away is that, while the technical potential for loss reduction is considerablein grids with strong peak loads, more research is needed to identify incentivesthat effectively manage to make households change their consumption behaviour.More work should also be done to find methods that can correctly evaluate loadshifts. / Efterfrågeflexibilitet (DR) har i stor utsträckning setts som en möjlig lösning för flerautmaningar som elsystemet står inför, till exempel integration av intermittent förnybarelproduktion och för att upprätthålla tillförlitligheten i elsystem under en snabb, globalelektrifiering. Medan mycket forskning har gjorts i olika marknadslösningar ochtariffsystem är mindre arbete tillgängligt om konsekvenserna av efterfrågeflexibilitetpå elnätet, speciellt för lågspänningssidan. Syftet med detta examensarbete är attuppskatta inverkan av ett efterfrågeflexibilitetprogram på förluster ilågspänningsdistributionsnätet. Rapporten kommer också att bidra till den förnärvarande begränsade kunskapsbasen om praktisk genomförande avefterfrågeflexibilitet genom att utvärdera resultatet av ett verkligt DR-pilotprojekt.Denna pilot är en del av ett utvecklingsprojekt för smarta städer "Stockholm RoyalSeaport" (SRS) i östra delen av Stockholm.Studien jämförde konsumtionsbeteendet hos cirka 400 referenskonsumenter med engrupp av 154 DR-aktiverade lägenheter, som är försedda med ett varierande timprisför el. Målet var att utvärdera vilken procentandel av daglig förbrukning de aktivakonsumenterna flyttar från höglasttimmar till låglasttimmar som svar på prissignalen.Studien är baserad på timmätningsdata samlad mellan den 1:a januari och den 22:amars 2017. Under denna period samlades också mätdata från elnätet in och dessa datahar använts för att uppskatta de tekniska förlusterna i lågspänningsdistributionsnätet.Genom att kombinera den dagliga lastförflyttningen av DR konsumenterna och denobserverade dagliga effektförlustfraktionen i nätet gjordes en uppskattning av effektenav efterfrågeflexibilitetet på nätförlusterna. En simuleringsmodell föreslogs också, ochanvändes för att simulera effekten av lastförflyttning på förluster i en given situationför nätet.Det konstaterades att DR-lägenheterna totalt sett uppvisar en lastförflyttning på 2,8 %av det dagliga elförbrukning mot höglasttimmar, och har en lägre genomsnittliglastfaktor (0,57 mot 0,62 för referensgruppen). Detta kan antingen betyda attprissignalen inte lyckas tillräckligt med att ändra förbrukningsbeteende eller attreferensgruppen inte var representativ. En stark variation i genomsnitt lastförflyttninghar emellertid observerats bland de enskilda DR-lägenheterna, från -16 % (flyttningtill höglasttimmar) till 7%. Speciellt de mest elförbrukande lägenheterna visadepositiva lastförflyttningar. Inget direkt inflytande av lastflyttning på nätförlusternahittades. Detta kan bero på en för liten mängd DR-konsumenter i nätet eller andrafaktorer som variationer i effektfaktor och belastningsstorlek. För att kringgå dettaproblem användes simuleringsmodellen för att beräkna förlustreduktioner för fleramöjliga referenskonsumentgrupper och deras eventuella reaktioner på en prissignal.Det konstaterades att potentialen för förlustreduktioner är begränsad i SRS-projekteteftersom referensgruppen är redan "bra" konsumenter. Den maximalaförlustreduktionen skulle vara omkring 4 %. För nät med hög topplast hittadesoptimala förlustreduktioner från lastförflyttning upp till 25 %. Den viktigasteslutsatsen är att medan den tekniska potentialen för förlustreduktion är stor i nät medhög topplast så krävs det mer forskning för att identifiera incitament som effektivtlyckas få hushållen att förändra sitt konsumtionsbeteende. Mer arbete bör också görasför att hitta metoder som korrekt kan utvärdera lastförflyttningar.

The awareness of the problems with fossil energy sources have increased the past decades. To decrease the effects of the fossil fuels on the climate and the environment, the use of intermittent energy sources such as solar- and wind power are increasing. Intermittent generation creates instability in the power grid, which cause fluctuations in the voltage and the frequency of the power grid. To be able to handle these fluctuations, regulating capacity such as for example pumped storage or batteries are needed. This thesis has investigated how the placement and the power capacity of a battery energy storage system affects the possibility for frequency and voltage regulation in a weak distribution grid. The investigation was made in MATLAB Simulink by creating a weak radial distribution grid with a high penetration of solar power. The distribution grid had variable loads with different power consumption at each bus, creating instability in the distribution grid. The optimal placement of a battery energy storage system is firstly at the largest load and secondly as far away from the other power generation units as possible. A battery storage with a power capacity that can handle all consumption is optimal. It is possible to have a smaller power capacity if the grid is stable enough to withstand the appearing fluctuation of frequency or voltage. The frequency variations are more dependent on the power capacity and the voltage variations are more dependent on the placement of the battery energy storage system. ISSN:

Dans le contexte de la transition énergétique, il existe des inconnues liées à la fonctionnalité du réseau électrique futur avec l’augmentation de la consommation et l’introduction de nouvelles formes de production. L’adaptation du système actuel est inévitable, néanmoins, les solutions efficaces sont difficiles à définir. Les stratégies actuelles de la planification du réseau de distribution ne répondent pas précisément aux problématiques des nouvelles productions décentralisées, le changement du profil de la consommation, l’automation du réseau de distribution avec de nouvelles stratégies de gestion du réseau ainsi que la déréglementation du marché de l’électricité. De plus, la visibilité et la contrôlabilité du réseau de distribution est limité, l’implémentation d’une gestion active optimale n’est pas à présent une réalité. L’évaluation du réseau intelligent est critique pour comparer aux solutions traditionnelles.L’objectif principal de cette thèse est d’explorer les barrières technico-économiques pour l’intégration massive des énergies renouvelables sur le réseau de distribution. Cette thèse explore plusieurs solutions au travers d’algorithmes d’optimisation de type flux de puissance qui utilisent des relaxations convexes. Pour le cas du réseau électrique basse tension, des systèmes triphasés déséquilibrés sont considérés. Pour analyser les incertitudes associées avec la génération et la demande, des algorithmes stochastiques sont abordés. Ces outils sont utilisés pour i) l’optimisation de l’emplacement et le dimensionnement des batteries, ii) l’optimisation des stratégies de gestion de la demande, iii) l’évaluation des stratégies d’opération de flexibilité du réseau centralisé et aussi décentralisé et iv) étudier l’impact de différents scénarios de pénétration des énergies renouvelables sur les réseaux existants. / In the context of the energy transition, there are many unknowns related to the required capabilities of future electric distribution systems to meet the growing electric load and new forms of electric production. The transformation of current electric distribution systems is inevitable, however, the most cost-effective investments are difficult to evaluate. Current electric distribution grid planning strategies are inadequate to take into account the accommodation of massive decentralized production, increased electric load with higher volatility, automation of distribution grids and unbundling of electricity markets. Due to a lack of observability and controllability in the distribution grid, the feasibility of optimal power flow management is not currently a reality. The quantification of smart distribution grids is critical to evaluate the added benefit of this solution in comparison to infrastructure upgrades.The primary objective of my PhD is to explore the techno-economical barriers of massive renewable energy integration into the distribution grid. This thesis will explore different solutions through convex relaxations of optimal power flow analysis. For the low voltage distribution grid case, three-phase unbalanced power flow analysis is considered. In order to consider realistically the uncertainties related to renewable generation and demand, stochastic optimal power flow (OPF) algorithms are proposed. These tools are used among others to i) optimize placement and sizing of grid connected storage, ii) optimize demand response strategies, iii) study different operation strategies for storage devices including centralized and decentralized ones and iv) study the impact of different renewable energy integration scenarios into real-world distribution grids.