The open bin packing problem (OBPP) is a new variant of the well-known bin packing problem. In the OBPP, items are packed into bins so that the total content before the last item in each bin is strictly less than the bin capacity. The objective is to minimize the number of bins used. The applications of the OBPP can be found in the subway station systems in Hong Kong and Taipei and the scheduling in manufacturing industries. We show that the OBPP is NP-hard and propose two heuristic algorithms instead of solving the problem to optimality. We propose two offline algorithms in which the information of the items is known in advance. First, we consider the First Fit Decreasing (FFD) which is a good approximation algorithm for the bin packing problem. We prove that its asymptotic worst-case performance ratio is no more than 3/2. We observe that its performance for the OBPP is worse than that of the BPP. Consequently, we modify it by adding the algorithm that the set of largest items is the set of last items in each bin. Then, we propose the Modified First Fit Decreasing (MFFD) as an alternative and prove that its asymptotic worst-case performance ratio is no more than 91/80. We conduct empirical tests to show their average-case performance. The results show that in general, the FFD and MFFD algorithms use no more than 33% and 1% of the number of bins than that of optimal packing, respectively. In addition, the MFFD is asymptotically optimal when the sizes of items are (0,1) uniformly distributed. / Ph. D.

When procuring a solar PV park in Sweden there are many stakeholders involved. As of today, the metric called performance ratio (PR) is often used to guarantee the park’s performance. Nonetheless, comprehending and evaluating PR can be challenging due to its inherent complexity. This study highlights favorable and unfavorable aspects of using PR as a performance metric in solar park procurements in Sweden. The study analyzes the correlation between PR, yield, and revenue, indicating a weak correlation between PR and yield. Findings show that lower values of PR often correspond to a higher yield, this suggests that PR is not a reliable metric for assessing the performance of a solar park. In addition, it may lead to negative implications for stakeholders involved in both procurement and operation of a solar park Relying solely on PR can potentially result in financial losses.  Furthermore, a sensitivity analysis was conducted with a focus on inverter loss and DC/AC ratio. Results illustrate that PR and inverter loss are strongly correlated for a park with a high DC/AC ratio, and they have a weaker correlation for a park with low a DC/AC ratio. This is due to increased inverter loss resulting from clipping losses in the system. The study suggests that a desirable DC/AC ratio of 1,15 maximizes yield and profit. In conclusion, while PR exhibits lower variation and can entail lower risk for Engineering, Procurement and Construction (EPC) companies, it is not always a reliable metric for assessing park performance. The weak correlation between PR and yield, as well as revenue, has implications for developers and investors. The study suggests that a lower DC/AC ratio may reduce the risk for EPCs guaranteeing PR, but decisions based solely on PR may not guarantee the highest revenue for investors and developers. / När en solcellspark upphandlas är flera olika intressenter involverade. I dagsläget används ett prestandamått som kallas performance ratio (PR) för att garantera parkens prestanda. Däremot är PR ett svårt mått att förstå och förutse på grund av dess komplexitet. Den här studien belyser gynnsamma samt ogynnsamma aspekter av att använda PR som ett prestandamått i upphandlingar av solparker i Sverige. Studien analyserar sambandet mellan PR, yield (normaliserad produktion), normaliserad yield och intäkter. Studien visar på ett svagt samband mellan PR och yield. Resultaten visar att lägre värden av PR ofta korrelerar med högre yield, vilket antyder att PR inte är ett tillförlitligt mått för att bedöma en solparks prestanda. Dessutom kan det bli konsekvenser för intressenter som är involverade i både upphandling och drift av en solpark. Att enbart förlita sig på PR kan potentiellt leda till ekonomiska förluster. Vidare genomfördes en känslighetsanalys med fokus på växelriktarförluster och DC/AC förhållandet. Resultaten visar att PR och växelriktarförluster har en stark korrelation för en park med högt DC/AC-förhållande, medan de har en svagare korrelation för en park med lågt DC/AC-förhållande. Detta beror på ökade växelriktarförluster till följd av clipping loss i systemet. Studien föreslår att ett önskvärt DC/AC-förhållande på 1,15 maximerar yield och vinst. Sammanfattningsvis, normaliserad yield bedömdes inte vara ett bra alternativ för PR och yield i upphandlingar. Studien visar att medan PR uppvisar lägre variation och kan innebära lägre risk för EPC-företag, är det inte alltid ett tillförlitligt mått för att bedöma en parks prestanda. Det svaga sambandet mellan PR och yield, liksom intäkter, får konsekvenser för utvecklare och investerare. Studien föreslår att ett lägre DC/AC-förhållande kan minska risken för EPC-företag som garanterar PR, men beslut som enbart baseras på PR kan inte garantera högsta intäkter för investerare och utvecklare.

The huge environmental awareness emerging last years by reason of global warming and greenhouse effect, on one hand, and the need of finding other sources of energy production and conversion due to the declining of fossil resources and the increasing cost of this kind of energy resource, on the other hand, both have led position renewable energies as a powerful alternative on the energy production and conversion. PV-systems have emerged at an exponential rate in recent year as the main candidate and a satisfactory possibility with respect to environmental and economic sustainability. Nowadays, the large volume on photovoltaic market is currently dominated by four types of solar cells, divided by the semiconductor material used to absorb light and convert the energy into electricity: (1) crystalline silicon (monocrystalline and polycrystalline), (2) amorphous silicon, (3) CIGS and (4) cadmium telluride; and among them, monocrystalline silicon and CIGS technologies are installed on the building 45 of the University of Gävle, at the south face of the laboratory. In this context and with the motivation to contribute knowledge on PV field, a comparison between single crystal solar technology and thin film CIGS technology has carried out through f ratio and performance ratio procedures in order to perform an assessment of the energy conversion of each one under field conditions. A logger monitors the power conversion from the PV modules since June 2014 while two pyranometers monitor global and diffuse solar radiation since March 2016. It must take into account that only clear sunny days have been considered during a period from 8:00 to 14:00 in order to avoid shadows effect on the PV systems. The results come to conclude that single crystal silicon modules present a better behavior with respect to energy conversion under no shadows effect conditions by two reason: (1) f ratio, relationship of PV conversion per kW (PV yield) between CIGS and single crystal silicon, is about 87.25% with some variations along a day due to ambient temperature, cell temperature and incidence angle; (2) PV module's performance ratio of monocrystalline silicon modules is higher than thin film CIGS ones during a sunny day about 87.56% and 76.38%, respectively; and they are consistent with usual performance ratio values between 80% and 90% since 2010 onwards. In light of the outcome and in order to confirm these conclusions, it intends to launch a project with the objective of evaluating the data collected and compare the performance of the module after a year of measurements outdoors by the PV module's performance ratio procedure. Along the same lines, the next step of the University of Gävle will be to launch a project with the objective of evaluating the potential to be self-sufficient.

Submitted by Fabio Sobreira Campos da Costa (fabio.sobreira@ufpe.br) on 2016-07-20T15:19:24Z No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) ANÁLISE OPERACIONAL DE UM SISTEMA FOTOVOLTAICO COM ALTA CONCENTRAÇÃO DE 10 kWp INTERLIGADO À REDE.pdf: 7127801 bytes, checksum: 39d3f0fe3404be063b56673557bb9d3d (MD5) / Made available in DSpace on 2016-07-20T15:19:24Z (GMT). No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) ANÁLISE OPERACIONAL DE UM SISTEMA FOTOVOLTAICO COM ALTA CONCENTRAÇÃO DE 10 kWp INTERLIGADO À REDE.pdf: 7127801 bytes, checksum: 39d3f0fe3404be063b56673557bb9d3d (MD5) Previous issue date: 2015-08-13 / CNPq / No presente estudo foi avaliado o comportamento da eficiência na geração de energia, desempenho e influência sobre os parâmetros de operação da rede elétrica de um Sistema Fotovoltaico de Alta Concentração (HCPV- High Concentrating Photovoltaics) interligado à rede em condições reais de operação. O sistema foi instalado no Departamento de Energia Nuclear (DEN) da UFPE. Os ensaios experimentais, realizados com medições do recurso solar incidente no local de instalação, permitiram estabelecer o comportamento da energia gerada em condições instantâneas, médias diárias e mensais. O sistema HCPV foi comparado com um sistema convencional de Silício policristalino (Si-P), de capacidade similar, operando nas mesmas condições meteorológicas durante o mesmo período. Ao longo do período de análise verificou-se que devido ao alto índice de nebulosidade, o recurso solar em Recife não promove condições vantajosas para o aproveitamento da elevada eficiência de conversão do sistema HCPV, em média 22%, chegando a níveis de 26%. Quando comparado com o sistema Si-P, embora o sistema HCPV apresente uma eficiência maior, o mesmo gerou, em Recife, 22% a menos de energia que o sistema Si-P, devido à capacidade do Si-P de aproveitar a irradiância global, em média 40% maior que a direta normal vista pelo sistema HCPV. Para realizar uma comparação entre o desempenho e a energia gerada pelos dois sistemas foi utilizado o índice de desempenho (PR - Performance Ratio) e o fator de capacidade. Uma simulação com base nos resultados experimentais, comparando os dois sistemas, foi realizada para as cidades de Petrolina (PE), São Martinho (RS) e Barra (BA). Verificou-se que o sistema HCPV é capaz de gerar 9% a mais de energia em Petrolina que o Si-P. Os valores obtidos para São Martinho e Barra foram 22% e 32% superiores, respectivamente. Os resultados mostram que o sistema HCPV pode vir a ser viável para as localidades, com elevados níveis de irradiância direta. Foi possível verificar que devido à pequena potência instalada do sistema HCPV (10 kWp) - comparada ao nível de consumo de energia do DEN - não houve influência apreciável sobre os parâmetros de operação da rede elétrica. / This work presents an analysis of the power generation, efficiency’s behavior, performance and influence on the electrical grid of a High Concentrating Photovoltaic system (HCPV) connected to the grid operating under real conditions. The system was installed at Nuclear Energy Department (DEN) - UFPE. The experimental tests, with measurements of the solar radiation resources at the installation site, allowed establishing the behavior of generated energy in instantaneous conditions, daily and monthly averages. The HCPV system was compared with a conventional polysilicon (Si-P) system, similarly capacity, operating under the same weather conditions over the same period. Along the analysis period, it was found that due to the high amount of cloud cover, the solar resource in Recife does not promote favorable conditions to take advantage of the high conversion efficiency of the HCPV system, with average of 22%, reaching levels of 26%. When compared with the Si-P system, although the HCPV presents higher efficiency, it has generated, in Recife, 22% less energy than the Si-P system due to the ability of the Si-P to take advantage of the global irradiance, in average 40% higher than the direct normal irradiance “view” by the HCPV system. Making a comparison of the performance and of the energy generated by the two systems we used the performance ratio (PR - Performance Ratio) and capacity factor. A simulation based on the experimental results, comparing the systems, was held for the cities of Petrolina (PE), St. Martin (RS) and Barra (BA). It was found that the HCPV system is capable to generate 9% more energy in Petrolina than the Si-P. The values obtained for St. Martin and Barra were 22% and 32% larger, respectively. The results show that the HCPV system could be viable for locations with high levels of direct irradiance. The analysis of the behavior of the HCPV system connected to electrical grid shows that due to the small installed capacity of HCPV system (10kWp) - compared to the level of the Nuclear Energy Department power consumption - no appreciable influence on the operating parameters of the electric grid could be detected.

Tato diplomová práce staví na základech položených v rámci semestrální práce se stejným názvem. Na začátku jsou nejprve uvedeny základní vlastnosti slunečního záření nutné k pochopení výpočtu tzv. performance ratio. Dále jsou popsány solární senzory vyvinuty v ReRa Solutions, které byly zdrojem dat. V následné literární rešerši jsou zkoumány alternativy k nespolehlivému Wi-Fi připojení senzoru a za nejvýhodnější řešení je považována LoRa. V praktické části je detailně popsán proces návrhu a vývoje single page aplikace. Tato aplikace umožňuje jak ukládání dat ze senzorů do databáze, tak jejich opětovné čtení a zobrazení zpět uživateli ve srozumitelné podobě. Aplikace těží z využití moderních programovacích jazyků a frameworků (např. Kotlin, Spring, TypeScript, React, Material-UI). Databázový model, který byl navržen na základně skutečného využití, představuje koncept tzv. monitorované oblasti, což přináší široké konfigurační možnosti. Poté byl model přenesen do databáze ve formě programovatelných entit. Komunikace mezi klientem a serverem podporující autentifikaci na základě uživatelských rolí byla implementována přes REST API. Přes grafické rozhraní aplikace je možné konfigurovat prostředí podle uživatelských požadavků a zobrazit interaktivní grafy obsahující senzory naměřená data. Aplikace byla nasazena v Google Cloudu s oddělenou databází.

Firstly, we deal with the verification of normality and other necessary prerequisites needed in this thesis. We also introduce transformations to converse non-normally distributed data to normal and continue with capability analysis. We describe the design of control charts, useful tools to assess process stability. They help us to eliminate assignable causes and leave only chance causes in process. We obtain process in control state. Finally, we introduce both capability and performance ratios for both normal and non-normal data, and analyse some of their properties. At the end of the thesis, we prove acquired knowledge by performing capability analysis of real process.

Neste trabalho são investigados os aspectos da contabilidade das empresas de construção civil relacionados ao esclarecimento dos problemas existentes e os requisitos para que ela seja útil no apoio aos processos de tomadas de decisões. São demonstradas diferentes formas de contabilização para essas empresas e tecidas sobre essas formas de contabilização à luz da teoria contábil. São também feitos comentários críticos a respeito da análise de demonstrações contábeis dessas empresas e apresentados índices complementares aos convencionais, que revelam dois aspectos importantes da contabilidade: a capacidade informativa da contabilidade e a importância das informações evidenciadas em notas explicativas. / This work investigates the aspects of the accounting of bulding construction companies (contractors) related to clarify the existent problems and the requirements to be useful in supportting the decision making processes. Different entries are demonstrated for those companies and discussions are made regarding those different recording in the light of Accounting Theory. Critical comments are also made regarding the analysis of financial statements of those companies and it is presented a complementary unconventional ratios, showing two important aspects of accounting: the informative ability of accounting and the relevance of information disclosed in footnotes.

Grid connected inverter requires accurate and appropriate sizing which depends on the temperature, inverter operating efficiency, performance ratio, annual system yield and solar radiation characteristics. The aim of this study was to design and size for optimum sizing factor for grid connected inverter. The main component to be considered in any photovoltaic grid connected system is the inverter since the output depends on the inverter sizing ratio, therefore optimal sizing factor was designed by considering factors that affects inverter sizing such as temperature, irradiance and the location. Large and small systems of 50 kW and 5 kW respectively were considered to determine grid connected inverter sizing factors for different climates in Kenya, Sweden, and India using PVsyst simulation. Two different inverter brands of SMA and ABB with 20 kW and 25 kW rating for large system and 4.6 kW, 4 kW inverters for small system. PVsyst simulation result showed that different locations with different orientation angles, the optimum sizing varies hence affects the annual performance of the system. Photovoltaic system inverters are sized based on the rated power of the installed system and this can be achieved when the inverter size is either almost matching or not. In this case the study presents the optimal sizing factor for grid connected inverter for Mandera in Kenya, Norrköping in Sweden and Kerala in India. The determination was done through the use of designing, assessing and analyzing of the relationship between the sizing factor with performance ratio, operational efficiency and annual hourly energy yield. The unique weather profile in Kerala and in Mandera favors the adoption of solar energy technology in the location. Solar radiation for one year was used as a baseline input and the result reveals that Mandera receives yearly radiation of 2.1 MWh/m² while Kerala and Norrköping receives 2 MWh/m² and 1.1 MWh/m² respectively. Design simulation using PVsyst tool made it possible for the determination of the optimal sizing factor for the grid connected system. Considerations such as the losses and the variations within the specific location was done and a graph showing the relationship between the sizing factor in relation to the operational inverter efficiency as well as energy yield and performance ratio was later on compared to see the behavior of the sizing factor. The study concludes that operational efficiency, performance ratio and energy yield affects the array optimum sizing ratio. For the three locations, inverters (SMA and ABB) shows different variations because optimal sizing ratio depends on the location and irradiation. The results reveal that Mandera has an optimal grid connected inverter sizing of the range from 1.1 to 1.4 while in Kerala it has from 1.2 to 1.4 and Norrköping has the range from 1.1 to 1.3. Optimal sizing of grid connected inverters depends on the energy yield and the location therefore the inverter mismatch voltage and its rating values have to be considered while determining the optimal sizing factor. The 25 kW inverters in all the locations had better efficiency and sizing factor and this proves that sizing the photovoltaic inverter will give better performance and efficiency.

Neste trabalho são investigados os aspectos da contabilidade das empresas de construção civil relacionados ao esclarecimento dos problemas existentes e os requisitos para que ela seja útil no apoio aos processos de tomadas de decisões. São demonstradas diferentes formas de contabilização para essas empresas e tecidas sobre essas formas de contabilização à luz da teoria contábil. São também feitos comentários críticos a respeito da análise de demonstrações contábeis dessas empresas e apresentados índices complementares aos convencionais, que revelam dois aspectos importantes da contabilidade: a capacidade informativa da contabilidade e a importância das informações evidenciadas em notas explicativas. / This work investigates the aspects of the accounting of bulding construction companies (contractors) related to clarify the existent problems and the requirements to be useful in supportting the decision making processes. Different entries are demonstrated for those companies and discussions are made regarding those different recording in the light of Accounting Theory. Critical comments are also made regarding the analysis of financial statements of those companies and it is presented a complementary unconventional ratios, showing two important aspects of accounting: the informative ability of accounting and the relevance of information disclosed in footnotes.

DC system and DC microgrids are gaining popularity in recent times. This thesis suggests a method to state the workability of a DC based PV system using the softwares Simulink, PVsyst and HOMER. The aims of this project include suggesting a DC based architecture, finding out the performance ratio and a cost analysis. The advantages of the DC based system, the cost benefits associated with it and its performance will determine its feasibility.   Not many softwares have the functionality to simulate DC based PV systems. PVsyst is considered as one of the most sought-out softwares for the simulation of PV systems. It can simulate a DC based PV system but has a lot of limitations when it comes to the architecture and voltage levels. Due to these factors, the results from softwares Simulink, Homer and PVsyst are used to calculate the performance ratio of the suggested DC system.    The simulation of the DC system involves modelling of a DC-DC converter. DC-DC converters are used in HVDC transmission and are being considered for small scale and medium scale microgrids. The DC-DC boost converter is coupled with a MPPT model in Simulink. P and O algorithm is chosen as the MPPT algorithm as it is simple and widely used. The Simulink model of PV array and MPPT based boost converter provides the power output at the needed voltage level of 350V. The input for the Simulink model is obtained from the results of HOMER. The inputs include solar irradiation data and cell temperature. The same input data is used for the simulations in HOMER and PVsyst. The performance ratio is obtained by combining the power output from Simulink with the other aspects of the system from PVsyst. The performance ratio is done only for the month of January due to the limitations in Simulink. The performance ratio is found out to be 65.5 %.   The cost estimation is done for the distribution and power electronics aspects of the system. It is found out that the cost associated with the conductors will have an impact on the total cost only if the conductors used for distribution is more in length. The cost associated with the power converters will make a difference in total cost only if the system is within the range of 100kW. The study shows the workability of the PV based DC system based on the above mentioned aspects