Application of Photovoltaic PV panels for electricity production has rapidly increased in recent years in Sweden after launching a capital subsidy for PV panel installations in 2009. Kungsbacka municipality’s housing company equipped two groups of buildings in Fjärås with PV systems to generate electricity. The newly built residential buildings are connected to a DC-microgrid, whereas the existing buildings have been equipped with a single PV system. This project conducts a cradle to gate life cycle assessment (LCA) for this DC-microgrid energy system. The main purpose of this project is to determine which parts and processes of the DC-microgrid contribute to highest environmental impact throughout their lifespan from cradle to gate stages. Moreover, this study explores the energy payback time (EPBT) and the cumulative energy demand (CED) for the DC-microgrid. Additionally, this study performs two comparative LCA. First the DC-microgrid is being compared with PV system to determine which system has higher environment impacts, and secondly, the DC-microgrid is being compared with the average electricity mix in Sweden in terms of contribution to environmental impacts. The LCA follows the ISO 14040 framework and the baseline method is applied in order to assess 11 environmental impact categories. Two different functional units are adopted in this study. One is based on installed kilowatt peak (kWp) capacity by which environmental impacts of the PV system are compared with the DC-microgrid system. The other functional unit for this study is 1 kWh of delivered electricity to residential buildings produced by the DC-microgrid system. This functional unit is used exclusively for a stand-alone analysis of the DC-microgrid system in order to make it comparable with other microgrid systems or other systems with different energy sources, such as hydro, wind or nuclear. The results of the stand-alone LCA analysis of the DC-microgrid show that the battery has high contribution in human toxicity and terrestrial ecotoxicity whereas the energy hub system (Ehub) is the main contributor to eutrophication, abiotic depletion, fresh water aquatic ecotoxicity and marineaquatic ecotoxicity. The monocrystalline PV panel has the highest impact on global warming and abiotic depletion (fossil fuel). In addition, the EPBT for the DC-microgrid system is approximately 3.7 years. This means that one can get energy free of cost for an estimated time of 26.5 years if the lifetime of the system is assumed to be 30 years. The CED results show that monocrystalline PV production is an intense energy process which requires more non-renewable energy than all remaining parts of the DC-microgrid. The comparison of the DC-microgrid with the PV system reveals that the DC-microgrid has a higher environmental impact almost in all impact categories. This is mainly due to batteries and inverters which have a clear effect on the result. The CED analysis results illustrate that the multicrystalline PV panel production from the PV system is the most energy demanding process in both categories of renewable and non-renewable energy source. Moreover, the analysis illustrates that the DC-microgrid has still higher environmental impacts in all impact categories compared to the average electricity mix in Sweden. This is due to the electricity production in Sweden relies on hydropower and nuclear power with around 83 % of the total electricity production in the year 2017 which causes a lower environmental burden. Although the DC microgrid system shows a higher environmental impact compared to PV system, it is still a proper option to generate electricity since DC-microgrid system allows to achieve some indirect advantages such as energy saving due to an increase in own usage rate and self-sufficiency rate compared to the PV system. It should be noted that the end-of-life procedures becomes very important especially when crediting back for the recycling of materials. The collection and recycling of the PV panels at their end-of-life should be considered for future work as soon as reliable data are available. / Användningen av solpaneler har de senaste åren kommit att öka markant i Sverige. Ökningen beror på det statliga bidraget för installation av solceller som lanserades 2009. Kungsbacka kommun installerade solcellssystem i två olika typer av byggnader, ny och äldre befintlig byggnad. Den nya byggnaden anslöts till direkt mikronät (DC-mikcrogrid) och den äldre byggnaden utrustades med solcellssystem. Detta projekt utför en ’från vaggan till porten’ livscykelanalys (LCA) för energisystemet direkt mikronät. Syftet är i huvudsak att fastställa vilka delar och processer av det direkta mikronätet som bidrar till störst miljöpåverkan genom dess livslängd, det vill säga från vaggan till porten. Vidare undersöker studien återbetalningstiden (Energy PayBack Time, EPBT) och den ackumulerade energianvändningen (Cumulative Energy Demand, CED) för det direkta mikronätet. Studien utför två komparativa LCA varpå det direkta mikronätet först jämförs med solcellssystemet i syfte att fastställa vilket av systemen har större miljöpåverkan. Studien ämnar också jämföra det direkta mikronätet med den genomsnittliga energimixen i Sverige, också avseende miljöpåverkan. LCA metoden följer ISO 14040-ramverket. Studien är baserad på två funktionella enheter vilka består av installerad kilowatt peak (kWp) kapacitet vilken används för att jämföra solcellssystemet och det direkta mikromåttet. Den andra funktionella enheten är 1 kWh levererad elektricitet till bostäder som producerats genom det direkta mikronätet. Denna funktionella enhet används för en ’stand-alone’ analys av det direkta mikronätet i syfte att göra det jämförbart med andra mikrosystem eller system med olika energikällor så som vatten-, vind- och kärnkraft. Resultaten från ‘stand-alone’ livscykelanalysen av det direkta mikronätet visar på att batteriet har en större effekt på mänsklig toxicitet terrestrisk ekotoxicitet, varpå systemet för energihubb bidrar främst till övergödning, abiotisk utarmning, vattenlevande ekotoxicitet och havslevande ekotoxicitet. Monokristallin solpanel har större påverkan på global uppvärmning och övergödning (fossilabränslen). I övrigt är EPBT för det direkta mikronätet cirka 3,7 år vilket innebär att energin beräknas kostnadsfri i cirka 26,5 år, givet att det kan antas att systemets livslängd är 30 år. CED-resultat visar på att microkristallin solpanel är en intensiv energiprocess som kräver mer icke-förnybar energi jämfört med resterande delar av det direkta mikronätet. Jämförelsen mellan det direkta mikronätet och solcellssystemet visar på att det direkta mikronätet har större miljöpåverkan i de flesta kategorier. Detta beror i huvudsak på batterier och växelriktare som har tydlig effekt på resultatet. Av resultatet från CED-analysen framgår att produktion av multikristallin solpanel av solcellssystemet är det mest energikrävande processen i båda kategorierna för förnybar och icke-förnybar energikälla. Vidare framgår av analysen att det direkta mikronätet har en större miljöpåverkan i alla kategorier, jämfört med påverkan från genomsnittet av energimixen i Sverige. Detta beror på att elproduktionen i Sverige mestadels består av vatten- och kärnkraft som tillsammans 2017 utgjorde 83 procent av den totala energiproduktionen. Denna produktion orsakaren mindre miljöbelastning. Trots att det direkta mikronätet påvisar en högre miljöpåverkan än solcellssystemet, är det fortfarande ett alternativ till att generera elektricitet eftersom det direkta mikronätet bidrar till indirekta fördelar såsom energibesparing. Energibesparingen i det direkta mikronnätet sker således genom ökad användning av den egenproducerade energin samt självförsörjning. Det ska vidare tilläggas att ’end-of-life’ procedurerna blir viktiga i synnerhet när de återvunna materialet återanvänds. Vidare bör solpaneler återanvändas vid ’end-of-life’ vilket bör finnas i åtanke för vidarestudier och i samband med att data tillgängliggörs.

Microgrid can provide stable, clean, and sustainable electricity supply for remote places since it can operate on renewable energy sources and work isolated from the utility grid. This thesis evaluates the life cycle greenhouse gas (GHG) emissions of the microgrid system which is located at the ‘North-five Islands’ of Changshan archipelago in China. The existing electricity generation technologies of the microgrid system are wind turbine, PV system and diesel generators with the capacity of 2 MW, 300 kW and 2046 kW, respectively. The total demand of electricity (362.2 GWh) will be supplied by the wind turbine, PV system and diesel generators with 32.03%, 2.36% and 65.62%, respectively, if the microgrid system is required to supply the electricity demand for the ‘North-five Islands’ area alone under the islanded mode during 20 years lifespan. The thesis uses the Life Cycle Assessment (LCA) to evaluate the life cycle GHG emissions of the microgrid system. The life cycle stages of this study include: raw material extraction, manufacturing, transportation and operation. In order to assess the environmental benefits of the microgrid system, three electricity supply options – ‘microgrid electricity supply option’, ‘grid extension electricity supply option’, and ‘conventional fossil diesel generators electricity supply option’ are designed to evaluate the life cycle GHG emissions for supplying 20 years electricity demand (362.2 GWh) of the ‘Northfive Islands’. The results show that the life cycle GHG emissions of the ‘microgrid electricity supply option’ are 223.19 million kgCO2eq. Compared to the ‘grid extension electricity supply option’ and ‘conventional fossil diesel generators electricity supply option’, the net savings of the GHG emissions are 70.56 and 112.18 million kgCO2eq, respectively. It mainly results from the differences of the electricity supply methods of the three electricity supply options. For the ‘microgrid electricity supply option’ itself, the operation stage takes the most responsibility of the life cycle GHG emissions with 97.6%. The raw material extraction, manufacturing and transportation stages account for 1.93%, 0.44% and 0.026%, respectively. For the system components of the microgrid system, the wind turbine, PV system, diesel generators, energy storage system, and cables account for 0.34%, 0.18%, 97.75%, 0.60%, and 1.12%, respectively, of the microgrid system’s life cycle GHG emissions. The thesis conducts the sensitivity analysis of diesel burn rate efficiency (L/kWh) of the microgrid system’s diesel generators due to a large quantity (60.84 million L) of diesel consumption by the diesel generators during 20 years operation time. According to the results of the sensitivity analysis, the diesel burn rate efficiency can directly impact the diesel consumption of the diesel generators, and consequently has a significant impact on the life cycle GHG emissions of the ‘North-five Islands’ microgrid system. Since the diesel burn rate efficiency represents the amount of diesel consumption, this results highlight the significance of any factors that affect the diesel consumption (e.g. quantity of diesel, temperature, altitude, etc.), in affecting the life cycle GHG emissions of the ‘North-five Islands’ microgrid system. In addition, the thesis performers the sensitivity analysis of renewable energy (wind and solar energy in specific) fraction of the studied microgrid system because of the huge potential of available renewable energy (63.65 MW of wind turbines) nearby the microgrid system. The results of the sensitivity analysis show that the life cycle GHG emissions of the microgrid system decrease linearly with the increase of wind and solar energy fraction. Particularly, the life cycle GHG emissions of the microgrid system decrease 1.46% (3.26 million kgCO2eq) and 1.37% (3.05 million kgCO2eq) with an increase of 1% in wind and solar energy, respectively.

For effective operation of microgrid systems (MGSs), it is important to understand the major types of power grid failures and how to deal with them. Detecting the fault, locating it, and isolating the faulty line are important to avoid damaging components and interrupting the service for customers. This will also improve the reliability and protection level of the system during fault conditions. Among the most successful protection methods to limit fault currents in power systems is the fault current limiter (FCL). The FCL improves the reliability of the system, voltage stability, and the fault current reduction. However, limited researches consider its applications inMGSs. The location and impedance size of the FCL play a major role in limiting fault currents in the system. Several studies concluded that installing FCLs near all generators, transformers, or loads in the system enhanced the performance of the system during fault conditions. However, increasing the number of FCLs in the system leads to an increase in cost. This dissertation proposes several effective approaches to specify the optimal locations and impedance values of the required number of installed FCLs in a grid-connected MGS. These FCLs improve the reliability and the protection level of the system by limiting fault currents during fault conditions. The goal is to reduce the required number of installed FCLs in the system. These installed FCLs must be able to reduce fault currents under the interrupting ratings of circuit breakers in the system. This goal will lead to lower the cost of installed protection devices in the system. In order to achieve this goal, this dissertation presents a novel fault management approach, sensitivity analysis, and an optimization model to find the optimal solutions. The study of this dissertation is meant to be used during the planning stage of power distribution system design. The results of this dissertation prove the robustness of the proposed approaches. This enhances the system’s performance while minimizing the required number of installed FCLs. Their sizes limit fault currents within safe ranges. Thus, the FCL significantly improves the reliability and protection scheme of the grid-connected MGS.