A blackout is defined as the loss of electric power for a given period in a particular area. With increasing dependence on reliable electric power, the social and economic ramifications of blackouts are dire, negatively impacting the productivity, safety, and security of communities. To reduce blackout occurrence, power system planners incorporate redundancy and advanced controls to the grid to make it more adaptable to disturbances. However, adding redundant transmission lines is not only expensive, it is suboptimal in some contexts. While it is unattainable to have no blackout, it is possible and necessary to implement measures that minimize the likelihood and scale of these outages. This work proposes a solution that uses a microgrid with advanced energy storage and solar PV to mitigate blackouts in Kigali, the capital of Rwanda. A description and steady state analysis of major weaknesses in the Rwandan electric grid is presented. A microgrid application capable of islanding from the system is simulated in the steady state and shown to strengthen the system and decrease the likelihood of blackouts in Kigali. The composition of the microgrid is then designed, simulated, and optimized for technical and financial feasibility using the HOMER model. A microgrid that uses energy storage and solar PV is shown to not only be feasible, but also competitive with current costs of electricity in Rwanda. For comparison, different combinations that include diesel generation are also simulated. / Master of Science

DC nano-grid system shows promising prospect and enjoys some advantages over AC micro-grid system. It enables easier integration of multiple renewable energy sources with multiple loads. Photovoltaic (PV) is essentially a typical renewable source that serves as main power source in DC nano-grid system. Traditional PV system includes centralized PV system, string PV system and micro-converter PV system. More recently, smart converter PV system has been introduced and shown great improvement in aspects of power generation achieved by distributed Maximum Power Point Tracking (MPPT). It is also advantageous over micro-converter PV system due to lower cost and flexibility. Detailed case study demonstrates that power generation efficiency can be easily compromised because of mismatch between different panels in centralized and string PV systems. In smart converter PV system, this problem can be solved due to distributed MPPT for each individual panel. The smart converter system has a very wide voltage range within which all panels can generate maximum power. The location and the width of this range are subject to change under different mismatch conditions. A second stage converter is needed to locate the array MPPT range. However, there is instability problem when doing second stage MPPT with traditional methods. Modified methods based on conductance control and resistance control are analyzed and compared. Both methods can solve the MPPT instability problem. However, in terms of steady state performance, resistance control MPPT is more promising in terms of higher utilization ratio and faster tracking speed. It is because both methods are of inherited variable operating point step size with constant conductance or resistance perturbation step size. However, the operating point change decreases with resistance perturbation but increases with conductance perturbation otherwise. Therefore, resistance control MPPT is chosen as a good candidate. Both simulation and experimental results verifies the concept. / Master of Science

This master thesis was performed for the consulting firm WSP in collaboration with the think tank Besmå. The main aim of the thesis was to examine if photovoltaic/thermal solar systems (PV/T-systems) is suitable for single family houses in Sweden and if it can be a more viable option than photovoltaic systems based on economical and energy performance aspects. The thesis also examines if the owner of a single family house with existing solar panels can benefit from installing an intercooler and a heat-exchanging system that could add the untapped heat of the panels to the house’s heating system. This would decrease the solar panel temperature, thus increasing their efficiency and electricity production. It also examines the possibility of PV/T-systems playing a role in fulfilling the increased energy performance regulations placed upon contractors today, by reducing the primary energy number (primärenergitalet). To achieve these objectives the heat demand of a typical house in Sweden was simulated in VIP Energy based on a real house in Gothenburg which has a photovoltaic system. A modell for electricity production of a solar cell which included the temperature dependency was created in Matlab and a modell of a PV/T-system was created in Simulink. From these models and real data from the existing house and energy system, total production of heat and electricity was acquired. The results showed that the intercooler can enhance the solar cell performance but a life cycle cost analysis found that it was not a neconomically viable option due to its excess cost. It also showed that the PV/T system can be a suitable choice for single family houses in Sweden under certain conditions, mainly depending on uncertain price points. It did enhance the total energy performance of the house in comparison to solar cells but was only economically viable (from a life cycle perspective and not initial cost) when the main heating system consists of an electric heater. Surprisingly, it was also found that smaller PV/T-systems of 5 square meters of module area can yield a better life cycle cost than solar cells, even when the main heating system is a heat pump. Lastly, it was found that a PV/T-system can act as a viable option when building real estate as a method of lowering the primary energy number, assuming a stable and economically competitive price point and that investing in large scale systems leads to a lower price per produced unit of energy and unit of area of modules.

abstract: The students of Arizona State University, under the mentorship of Dr George Karady, have been collaborating with Salt River Project (SRP), a major power utility in the state of Arizona, trying to study and optimize a battery-supported grid-tied rooftop Photovoltaic (PV) system, sold by a commercial vendor. SRP believes this system has the potential to satisfy the needs of its customers, who opt for utilizing solar power to partially satisfy their power needs. An important part of this elaborate project is the development of a new load forecasting algorithm and a better control strategy for the optimized utilization of the storage system. The built-in algorithm of this commercial unit uses simple forecasting and battery control strategies. With the recent improvement in Machine Learning (ML) techniques, development of a more sophisticated model of the problem in hand was possible. This research is aimed at achieving the goal by utilizing the appropriate ML techniques to better model the problem, which will essentially result in a better solution. In this research, a set of six unique features are used to model the load forecasting problem and different ML algorithms are simulated on the developed model. A similar approach is taken to solve the PV prediction problem. Finally, a very effective battery control strategy is built (utilizing the results of the load and PV forecasting), with the aim of ensuring a reduction in the amount of energy consumed from the grid during the “on-peak” hours. Apart from the reduction in the energy consumption, this battery control algorithm decelerates the “cycling aging” or the aging of the battery owing to the charge/dis-charges cycles endured by selectively charging/dis-charging the battery based on need. ii The results of this proposed strategy are verified using a hardware implementation (the PV system was coupled with a custom-built load bank and this setup was used to simulate a house). The results pertaining to the performances of the built-in algorithm and the ML algorithm are compared and the economic analysis is performed. The findings of this research have in the process of being published in a reputed journal. / Dissertation/Thesis / Masters Thesis Electrical Engineering 2018

There are a number of factors that influence both the physical and the economical performance of a photovoltaic solar energy (PV) installation. The aim of this project was to develop a simulation and optimization model with which these factors could be analyzed and the PV installation optimized. By supplying the model with meteorological data, electricity consumption data and available building surfaces the model finds the optimum PV installation. The output consists of both physical and economical performance as well as information on how to distribute and install the PV modules on the available building surfaces. The model was validated using annual and hourly measurement data from Swedish PV installations. The validation shows that the model is a reliable tool for simulating the electricity generation from a PV system. In the second part of the project the model was used to evaluate the PV potential at two different hospitals and one health care center within the Uppsala County, Sweden. The model was also used to study the effect of different house orientations on the PV potential in Swedish neighborhoods. The physical and economical PV potentials are high for the hospitals and the health carecenter. This is mainly due to a high electricity demand but also due to a good match between the load profile and the PV electricity generation profile. The study on different neighborhoods shows that for gable roof buildings it might be more favorable to plan the houses so that the roofs face east-west rather than north-south. / Det är många faktorer som påverkar de fysikaliska och ekonomiska resultaten av en planerad solcellsinstallation. Syftet med det här projektet var att utveckla en simulerings- och optimeringsmodell med vars hjälp det skulle gå att analysera dessa frågor och hitta det bästa installationsalternativet i varje enskilt fall. Modellen som togs fram i detta projekt kan både studera ett givet installationsalternativ och räkna ut den mest optimala installationen utifrån de av användaren specificerade målen och begränsningarna. För att kunna göra detta behöver modellen förses med meteorologiska data för den aktuella platsen, elkonsumtionsdata från det aktuella objektet samt mått och orienteringar för de tillgängliga byggnadsytorna. Dessutom behöver användaren ange vissa ekonomiska parametrar såsom exempelvis avbetalningstid, ränta och aktuellt solcellspris. Resultatet från modellen består av både fysikaliska och ekonomiska resultat, exempelvis timvis nettoflöde av elektricitet, avbetalningstid och genomsnittligt elpris från solcellssystemet. I optimeringsresultatet redovisas hur solcellerna bör fördelas och installeras på de olika byggnadsytorna för att ge bäst resultat enligt målspecifikationen. För att validera modellen jämfördes dess simuleringsresultat med årliga och timvisa mätvärden från svenska solcellsanläggningar. Dessutom jämfördes modellens resultat med motsvarande resultat från andra simuleringsverktyg för solceller. Valideringsresultaten visar att modellen är ett pålitligt verktyg för att simulera elgenereringen från solcellsystem med olika moduler, växelriktare och installationssätt. Som ett delresultat vid modellutvecklingen simulerades ett stort antal olika solcellssystempå platta och svagt lutande tak. Utifrån dessa simuleringar utformades ett antal tumregler för hur uppvinklade moduler på platta eller svagt lutande tak skall monteras. Tumreglerna visar vilket avstånd mellan modulraderna och vilken vinkel på modulerna som ger den högsta taktäckningsgarden (största installationen) vid olika övre gränser för de interna skuggningsförlusterna. I projektets andra del användes modellen för att utvärdera solcellspotentialen på Akademiska sjukhuset, Enköpings lasarett och Tierps vårdcentral. Resultaten som levererades till Landstinget i Uppsala län visar att både den tekniska och den ekonomiska solcellspotentialen är stor på dessa enheter. Huvudanledning till den höga potentialen är att elbehovet är väldigt stort på dessa enheter samt att solcellernas elgenereringsprofil stämmer mycket väl överens med när elbehovet är som störst. Modellen användes även för att studera hur olika byggnadsorienteringar påverkar solcellspotentialen i olika tänkbara svenska bostadsområden. De olika resultaten från dessa studier visar att det i många fall är bättre att orientera byggnader med sadeltak så att taken pekar i östlig och västlig riktning snarare än mot syd och nord. Därmed föreslås en översyn avde nu rådande rekommendationerna att optimera huvudorienteringarna av taken mod syd vid detaljplanering av stadsdelar.

The environmental awareness has led to many political decisions and initiated laws that regulate the market towards responsible energy usage. The demand of sustainable power has led to an increasing integration of renewable energy sources to the electric grid. Solar power is the 3rd largest renewable power source after wind and bio-power. One of the main reasons to this fast expansion is the German renewable energy act that has motivated households to install PV systems in their houses. This has led to a large amount of producers on the low-voltage network. The small scale producers receive compensation for electricity generated from the PV systems, both when it is used directly in the producer’s home and when it is sold to the grid due to low usage. The systems can be more profitable by storing the energy instead of selling it on the grid. In this way the amount of bought electricity can be reduced. There are concerns regarding the connection of renewable sources to the grid. This project aims to examine the impact from single-phase PV systems on the low-voltage grid. The focus of this bachelor thesis is understanding problems such as harmonic distortion and grid asymmetry. Simulations have been carried out using the software MATLAB in order to study harmonic distortion in the output of a single-phase PV system. Grid asymmetry is examined through calculations and simulations of a worst case scenario in the software NEPLAN. This scenario contains a low voltage grid with a star-star connected transformer, where all PV-systems are connected to the same phase. The simulations in combination with a literature review have provided the conclusion that harmonic distortion caused by the inverter becomes higher when the voltage supply is too low. Integration of battery energy storage systems together with PV systems does not cause additional harmonic distortion. The results also show how single-phase systems contribute to the asymmetry in the grid. When the production from the PV systems is high, and all systems are connected to a certain phase, the current and voltage will also have an impact on the other phases in the worst case scenario.

Πειραματική προσομοίωση μιας εγκατάστασης φωτοβολταϊκών σε στέγη κτιρίου με έμφαση στα σχολικά κτίρια. Βελτίωση της ηλεκτρικής τους απόδοσης με την δημιουργία αεραγωγού για την ψύξη των συλλεκτών και προσθήκη ενδιάμεσου μεταλλικου φύλλου και πτερυγίων βάσης. Εκτίμηση του ηλεκτρικού κέρδους σε πιθανή εγκατάσταση σε σχολική στέγη. / Experimental simulation of PV collectors’ establishment on inclined roofs and application on school buildings (as a paradigm). Study for the improvement of the PV/T collectors’ electrical efficiency by the addition of an air duct with natural air flow. The air duct contains either an internal/interspace thin metal sheet or basal metal fins (metal fins on its base). Effort for the estimation of the electrical energy benefit/gain by such an establishment on a typical school building.

Allt hårdare lagkrav gör att det är svårt att energieffektivisera befintliga byggnader utan att förändra deras utseende. Syftet med examensarbetet är att utreda hur stor energieffektivisering, för tre befintliga småhus uppförda under 1900-talet, som är möjlig att uppnå genom förbättring av byggnadernas klimatskal, det vill säga tak, väggar, golv, fönster och dörrar, utan att förvanska byggnadernas utseende och samtidigt bevara deras kulturhistoriska värden. Arbetet bestod av en förstudie där tre byggnader identifierades, ett undersökningsskede där information om byggnaderna togs fram och ett slutsatsskede där energibesparande åtgärdsförslag togs fram och utvärderades. Byggnader som var goda representanter för sin tid och stil söktes. Byggnader från 1910-talet, 1930-talet och 1970-talet, lokaliserades. Sedan gjordes det fallstudier med intervjuer och inventeringar. För att utreda byggnadens klimatskal utfördes u-värdesberäkningar och energiberäkningar av befintliga byggander och byggnader baserade på föreslagna åtgärdsförslag. Ingen av byggnaderna nådde efter föreslagna åtgärder ner till passivhuskravet 59 kWh/år/m2 Atemp eller BBR-kravet 110 kWh/år/m2 Atemp för en byggnads specifika energianvändning. Den största möjliga energieffektivisering för de tre byggnaderna uppförda under 1900-talet, som är möjlig att uppnå utan att förvanska byggnadernas utseende och samtidigt bevara deras kulturhistoriska värden är 13,0 kWh/år/m2 Atemp, 49,7 kWh/år/m2 Atemp respektive 64,8 kWh/år/m2 Atemp. Slutsatser från arbetet är att byggnader från 1910-tal kan åtgärdas genom att isolera fönstren, sätta dit en extra dörr på insidan av ytterdörren samt tilläggsisolera snedtaket. Byggnader från 1930-tal kan åtgärdas genom att isolera fönstren med en isolerruta på insidan av fönstret och dörrarna med en extra dörr på insidan av ytterdörren. Byggnader från 1970-tal kan åtgärda fönstren genom att byta ut dem till energifönster, ingen åtgärd för golvet men fasaden isoleras utvändigt med vakuumisolering. Byggnaden från 1970-talet klarade sig bäst i jämförelsen eftersom den var i autentiskt skick från början vilket gjorde att förbättringen blev större än för till exempel byggnaden från 1910-talet som redan var ombyggd innan åtgärder föreslogs. / Increasingly stringent legal requirements make it difficult to energy efficiency in existing buildings without changing their appearance. The purpose of the study is to investigate how much energy, for three existing single-family homes built in the 1900s, which is achievable by improving the building envelope, ie, ceilings, walls, floors, windows and doors, without distorting the building's appearance and while maintaining their cultural values. The work consisted of a pilot study where three buildings were identified, a research stage where information about the buildings were developed and an inference stage where energy saving measures proposed were developed and evaluated. Buildings that were good representatives of their time and style sought. Buildings from the 1910s, 1930s and 1970s, was located. Since it was done case studies, interviews and surveys. To investigate the building envelope was conducted U-value calculations and energy calculations of the existing building commitment and buildings based on the proposed policy proposals. None of the buildings reached after the proposed action down to the passive house requirement 59 kWh/year/m2 Atemp or BBR requirement 110 kWh/year/m2 Atemp for a building-specific energy consumption. The maximum possible energy efficiency for the three buildings erected during the 1900s, which is achievable without corrupting the buildings' appearance while preserving their cultural values is 13.0 kWh/year/m2 Atemp, 49.7 kWh/year/m2 Atemp respectively 64.8 kWh/year/m2 Atemp. Conclusions of the work is that buildings from the 1910's can be addressed by isolating the windows, put one extra door on the inside of the front door and additional insulation in sloping roof. Buildings from the 1930s can be addressed by isolating windows with insulating glass on the inside of the windows and doors with an extra door on the inside of the front door. Buildings from the 1970s can fix the windows by changing them into energy windows, no action on the floor but the facade insulated externally with vacuum insulation. The building from the 1970s fared best in the comparison because it was the authentic condition from the beginning, which meant that the improvement was greater than for example the building from the 1910s that was already rebuilt before action was proposed.

abstract: Infant mortality rate of field deployed photovoltaic (PV) modules may be expected to be higher than that estimated by standard qualification tests. The reason for increased failure rates may be attributed to the high system voltages. High voltages (HV) in grid connected modules induce additional stress factors that cause new degradation mechanisms. These new degradation mechanisms are not recognized by qualification stress tests. To study and model the effect of high system voltages, recently, potential induced degradation (PID) test method has been introduced. Using PID studies, it has been reported that high voltage failure rates are essentially due to increased leakage currents from active semiconducting layer to the grounded module frame, through encapsulant and/or glass. This project involved designing and commissioning of a new PID test bed at Photovoltaic Reliability Laboratory (PRL) of Arizona State University (ASU) to study the mechanisms of HV induced degradation. In this study, PID stress tests have been performed on accelerated stress modules, in addition to fresh modules of crystalline silicon technology. Accelerated stressing includes thermal cycling (TC200 cycles) and damp heat (1000 hours) tests as per IEC 61215. Failure rates in field deployed modules that are exposed to long term weather conditions are better simulated by conducting HV tests on prior accelerated stress tested modules. The PID testing was performed in 3 phases on a set of 5 mono crystalline silicon modules. In Phase-I of PID test, a positive bias of +600 V was applied, between shorted leads and frame of each module, on 3 modules with conducting carbon coating on glass superstrate. The 3 module set was comprised of: 1 fresh control, TC200 and DH1000. The PID test was conducted in an environmental chamber by stressing the modules at 85°C, for 35 hours with an intermittent evaluation for Arrhenius effects. In the Phase-II, a negative bias of -600 V was applied on a set of 3 modules in the chamber as defined above. The 3 module set in phase-II was comprised of: control module from phase-I, TC200 and DH1000. In the Phase-III, the same set of 3 modules which were used in the phase-II again subjected to +600 V bias to observe the recovery of lost power during the Phase-II. Electrical performance, infrared (IR) and electroluminescence (EL) were done prior and post PID testing. It was observed that high voltage positive bias in the first phase resulted in little/no power loss, high voltage negative bias in the second phase caused significant power loss and the high voltage positive bias in the third phase resulted in major recovery of lost power. / Dissertation/Thesis / M.S. Engineering 2011

During the recent years the popularity of solar power have increased tremendously. With the increased interest in solar power comes a development of more efficient and different types of technology to harvest the sun rays. Monofacial panels have been on the market for a long time and have rather developed simulation models. The bifacial technology on the other hand have been researched for years but just recently found its way to the market. Simulation models for the bifacial panels are continuously being developed and they are a key aspect to increase the knowledge about the bifacial technology. Most of the research that has been conducted until today is mainly about the bifacial gain, not about the bifacial simulation models.The purpose of this thesis was to evaluate and validate simulation models of bifacial solar panels in PVsyst with comparisons to measured data from six different bifacial installations in Sweden. The installations had different system configurations and varied in: tilt, azimuth, pitch, elevation, number of rows and albedo. Furthermore, the installation configuration parameters were analyzed to see how they affect the bifacial system and what an optimal configuration would be for a bifacial installation in Sweden.The results show that the main difficulties for an accurate simulation model is to determine the proper input data. The irradiance and albedo proved to be the most difficult parameters to determine. The irradiance was accurate looking at yearly level but already during monthly distribution the error is taking effect. One of the reasons for the errors is the difficulties to determine the diffuse irradiance fraction of the light, especially during cloudy days. The albedo was found to have a linear dependency on the yield, which meant that it is possible that the inaccuracy of the model are solely dependent on albedo.For tilted installations without optimizers the yearly error of the simulation ranged between -5,2% to +3,9% where the lower limit value is suspected to be caused by a wrong albedo value. For a tilted installation with optimizers the error was +9,1%. This could be caused by two reasons; the optimizers are even more dependent on the irradiance or that the software exaggerates the benefits of optimizers. The simulations of vertical installations had an error between -5,4% to -3% and are more accurate than the tilted simulations.Different parameters effect on the specific yield were studied using a simplified simulation model and stepwise change of each parameter. The results were that four of the six studied parameters have no characteristic change on each other and the optimal conditions was to maximize the pitch, elevation and albedo and minimize the number of rows. The remaining two parameters tilt and azimuth showed a dependence on the other parameters, where the optimal azimuth only was affected by tilt while the optimum tilt was affected by all the other parameters. This revelation lead to the conclusion that tilt is the most suitable parameter for optimization of installations because of its dependence on ambient conditions. The optimum tilt was found for the studied cases and in five of the six cases it would have an increased specific yield if the tilt was optimized. Note that for four of those five would lead to an increase of less than 0,5% while for the fifth an increase by 14,2%.