To support further technology development and to promote the growth of a renewable biofuels industry that will satisfy the stated expectations of anticipated energy needs, it is essential that energy production systems provide a net energy gain over the course of their lifetime. As a means to provide accurate analysis to the value of alternative energy systems this paper provides a mechanism to evaluate energy systems in terms of energy generation ratios that is in terms of existing analysis techniques utilized in existing energy generation areas, such as the oil industry. This paper also proposes techniques that help perform this net energy analysis in terms of the specific economy considering the infrastructure investment.

The aim of this thesis is to take a broad conceptual overview of the global energy system and investigate what the aims of sustainability might entail for such a system. The work presented uses a biophysical economic approach in that the dynamics of the global economy are investigated using the tool box of the physical sciences, including the laws of thermodynamics and the methods of energy analysis. Modern society currently uses approximately 500 exajoules (EJ = 10^18 J) of total primary energy supply (TPES) each year. This energy consumption has been increasing at roughly 2% per year for the past two hundred years. TPES is currently dominated by three non-renewable energy sources: coal, oil and gas which, together with energy from nuclear fission of uranium, make up around 85% of the energy market. Consumption of finite resources at a continuously growing rate is not sustainable in the long-term. A trend in policy direction is to seek a transition to renewable sources of energy. This thesis seeks to explore two questions: are the technical potentials of renewable energy sources enough to supply the current and/or projected demand for energy and what would be the effect on the physical resource economy of a transition to an energy supply system run entirely on renewable energy sources? The Global Energy Model using a Biophysical Approach (GEMBA) methodology developed here is compared and contrasted with other approaches that are used to study the global energy-economy system, including the standard neoclassical economic approach used in such models as MESSAGE and MARKAL. A number of meta-analyses have been conducted in support of the GEMBA model. These include: meta-analysis of historic energy production from all energy sources; meta-analysis of global energy resources for all energy sources; meta-analysis of energy-return-on-investment (EROI) for all energy sources. The GEMBA methodology uses a systems dynamic modelling approach utilising stocks and flows, feedback loops and time delays to capture the behaviour of the global energy-economy system. The system is decomposed into elements with simple behaviour that is known through energy analysis. The interaction of these elements is captured mathematically and run numerically via the systems dynamics software package, VenSim. Calibration of the model has been achieved using historic energy production data from 1800 to 2005. The core of the GEMBA methodology constitutes the description of a dynamic EROI function over the whole production cycle of an energy resource from initial development, through maturation to decline in production, in the case of non-renewable resources, or to the technical potential in the case of renewable resources. Using the GEMBA methodology, the global energy-economy system is identified as a self-regulating system. The self-regulating behaviour acts to constrain the amount of total primary energy supply that the system can produce under a renewable-only regime. A number of analyses are conducted to test the sensitivity of the system to such changes as: an increase of the technical potential of renewable resources; technological breakthroughs which would significantly increase the EROI of renewable resources; a decrease in the capital intensity of renewable resources and; an increase in the energy intensity of the economy, A statistical analysis reflecting the wide range of values of both the estimates of EROI and technical potentials of renewable energy sources has also been undertaken using a Monte Carlo approach. The results from the modelling suggest that not all levels of energy demand projected by the WEA can be supplied by an energy system running solely on renewable energy. The Monte Carlo analyses suggest that reduction in total energy yield over current (2010) levels might occur with a 20-30% possibility. The middle and high growth scenarios from the WEA are greater than 95% of all scenarios modelled, hence seem unlikely to be sustained by an energy system running solely on renewable energy. This finding has implications for the future direction of both engineering and technology research as well as for energy policy. These implications are discussed.

Micro- generation is the small-scale and localised provision of heat or electricity. Micro-generators have the potential to reduce greenhouse-gas emissions and enhance energy security by providing heat or electricity from either renewable sources, or via the more efficient use of fossil fuels. But this potential is often unquantified or unclear, and hence quantitative information is required concerning both the energetic performance of micro-generators and their ability to provide net reductions in carbon emissions. <br /> In the context of household energy provision in the UK, thermodynamic and related carbon analyses of three micro-generation technologies have been carried out. These studies contribute to the research of the SUPERGEN ‘Highly Distributed Power Systems’ Consortium, which has been addressing a broad range of issues regarding micro-generation. The technologies analysed here are a grid-tied micro-wind turbine (rotor diameter 1.7m, rated power 600 W at 12 m/s), a grid-tied solar photovoltaic array (15 m2, 2.1 kWp mono-crystalline silicon), and a solar hot-water system (2.8 m2 flat-plate collector, direct-feed system). Annual energy outputs were estimated and contextualised against the demands of representative UK households. The overall energy-resource and carbon savings provided by the micro-generators were assessed on the basis that they (partially) displace the established supply systems. Savings were then compared with the energy-resource and carbon ‘debts’ of the micro-generators to determine their net performance. <br /> The displaced energy or carbon payback periods of the micro-generators were estimated to be well within their estimated lifetimes: a maximum 2.5 years for the SHW system, 3.1 years for the micro-wind turbine installed in an ‘open’ environment, and 7.4 years for the solar PV system. After payback, net energy-resource and carbon savings accrue. This thesis thus demonstrates that, given appropriate UK installations, all three micro-generators can reduce carbon emissions and enhance energy security by reducing use of, and dependence upon, fossil fuels.

Installed photovoltaic nameplate power have been growing rapidly around the worldin the last few years. But how much energy is returned to society (i.e. net energy) by this technology, and which factors contribute the most to the amount of energy returned? The objective of this thesis was to examine the importance of certain inputs and outputs along the solar panel production chain and their effect on the energy return on (energy) investment (EROI) for crystalline wafer-based photovoltaics. A process-chain model was built using publicly available life-cycle inventory (LCI) datasets. This model has been kept simple in order to ensure transparency. Univariate sensitivity analysis for processes and multivariate case studies was then applied to the model. The results show that photovoltaic EROI values are very sensitive to assumptions regarding location and efficiency. The ability of solar panels to deliver net energy in northern regions of the earth is questionable. Solar cell wafer thickness have a large impact on EROI, with thinner wafers requiring less silicon material. Finding an alternative route for production of solar-grade silicon is also found to be of great importance, as is introduction of kerf loss recycling. Equal system sizes have been found to yield an primary EROI between approximately 5.5-19 depending on location and assumptions. This indicates that a generalized absolute EROI for photovoltaics may be of little use for decision-makers. Using the net energy cliff concept in relation to primary EROI found in this thesis shows that primary EROI rarely decreases to less than the threshold of 8:1 in univariate cases. Crystalline photovoltaics under similar system boundaries as those in the thesis model does not necessarily constrain economic growth on an energetic basis.

O etanol está consolidado como combustível para movimentação de veículos leves no Brasil e, nos últimos 40 anos, apenas a cultura de cana-de-açúcar tem sido explorada comercialmente para a produção deste combustível. Por outro lado, o desenvolvimento agrícola vem proporcionando safras recordes de grãos nas últimas décadas. A produção de milho se destaca pelo aumento da produtividade, podendo ser semeado como cultura principal ou como cultura de inverno em rotação com a soja. O sorgo, por sua vez, pode atuar como um substituto do milho, apresentando maior rusticidade e tolerância à seca. Dada essa conjuntura, usinas de etanol do Mato Grosso se associaram a produtores de milho e sorgo para incluir novas matéria-primas no processo de produção de combustíveis, compartilhando uma mesma unidade industrial, denominada Usina Integrada ou Usina Flex. No contexto atual, o desenvolvimento de novas tecnologias e setores produtivos exige a consideração de suas potenciais implicações energéticas e ambientais. A Avaliação de Ciclo de Vida (ACV) é uma ferramenta da gestão ambiental usada para avaliar impactos ambientais potenciais associados a produtos, processos e serviço. Sua principal característica é se prestar a essa avaliação de forma sistêmica, levando em conta todas as etapas do seu ciclo de vida. O objetivo deste trabalho foi avaliar e comparar os desempenhos ambiental e energético da produção de etanol a partir dos ativos agrícolas cana-de-açúcar, milho e sorgo, no contexto de usina autônoma integrada, segundo a abordagem do ciclo de vida. Para tanto, estudos de ACV foram conduzidos para cada um dos três produtos, seguindo as diretrizes das normas ABNT NBR ISO 14.040:2009 e ABNT NBR ISO 14.044:2009. Para a análise ambiental aplicou-se o método de Avaliação de Impacto do Ciclo de Vida (AICV) ReCiPe midpoint e, para a análise energética, o método Demanda de Energia Cumulativa foi utilizado, seguido pelo cálculo dos Índices de Retorno Energético sobre o Investimento (EROI) para cada combustível. A unidade funcional dos estudos foi 1 m³ de etanol hidratado e o sistema de produto incluiu a produção de insumos, produção da matéria-prima agrícola, produção de etanol, cogeração e etapas de transporte. Os resultados da análise ambiental demonstraram que o etanol de cana-de-açúcar apresenta melhor desempenho do que o etanol de milho e de sorgo em um número maior de categorias de impacto. As análises energéticas demonstraram que o uso de cavaco de madeira na etapa de cogeração dos processos de produção de etanol de milho e sorgo traduziu-se em ganhos energéticos, mas o etanol de cana-de-açúcar ainda apresenta um desempenho melhor por utilizar o bagaço para cogeração. Em termos de EROI, o etanol de cana-de-açúcar disponibilizou 9,77 unidades de energia para cada unidade consumida, o etanol de milho disponibilizou 2,68 e o etanol de sorgo disponibilizou 3,10. / Ethanol is consolidated as fuel to drive light vehicles in Brazil, but for the past 40 years, only the cultivation of sugarcane has been commercially exploited for the production of this fuel. On the other hand, agricultural development has provided high yields of grain in recent decades. Corn production is distinguished by increased productivity, and can be sown as main crop or as a winter crop in rotation with soybeans. Sorghum, in turn, has a higher roughness and tolerance to drought and can act as a substitute for corn. Given this situation, ethanol plants in Mato Grosso were associated with corn and sorghum producers to include new raw materials in the fuel production process, sharing the same plant, called Integrated Plant or Plant Flex. However, the development of new technology and production sectors requires consideration of its potential energy and environmental implications. The Life Cycle Assessment (LCA) is management tool used to evaluate potential environmental impacts associated with products, processes and services. Its main feature is to provide such an assessment in a systematic way, taking into account all stages of their life cycle. The objective of this study was to evaluate and compare the environmental and energy performance of ethanol production from sugarcane, corn and sorghum in the context of integrated autonomous plant, according to the life cycle approach. For that, LCA studies were conducted for each of the three products, following the guidelines of the standards ISO 14040: 2009 and ISO 14044: 2009. For environmental analysis the method of Life Cycle Impact Assessment (LCIA) Recipe midpoint was applied and for energy analysis Cumulative Energy Demand method was used, followed by the estimate of the Energy Return On Investment (EROI) for each fuel. The functional unit of the studies was 1 m³ of hydrous ethanol and the product system includes the production inputs, production of agricultural raw material, production of ethanol, cogeneration and transport stages. The results of the environmental analysis showed that the ethanol sugarcane performs better than the ethanol maize and sorghum in a greater number of impact categories. Energy analyzes have shown that the use of wood chips in cogeneration stage of corn ethanol production processes and sorghum has resulted in energy savings, but the ethanol sugarcane still performs better by using bagasse for cogeneration. In terms of EROI, the sugarcane ethanol provided 9.77 units of energy for every unit consumed, corn ethanol provided 2.68 and sorghum ethanol provided 3.10.

O etanol está consolidado como combustível para movimentação de veículos leves no Brasil e, nos últimos 40 anos, apenas a cultura de cana-de-açúcar tem sido explorada comercialmente para a produção deste combustível. Por outro lado, o desenvolvimento agrícola vem proporcionando safras recordes de grãos nas últimas décadas. A produção de milho se destaca pelo aumento da produtividade, podendo ser semeado como cultura principal ou como cultura de inverno em rotação com a soja. O sorgo, por sua vez, pode atuar como um substituto do milho, apresentando maior rusticidade e tolerância à seca. Dada essa conjuntura, usinas de etanol do Mato Grosso se associaram a produtores de milho e sorgo para incluir novas matéria-primas no processo de produção de combustíveis, compartilhando uma mesma unidade industrial, denominada Usina Integrada ou Usina Flex. No contexto atual, o desenvolvimento de novas tecnologias e setores produtivos exige a consideração de suas potenciais implicações energéticas e ambientais. A Avaliação de Ciclo de Vida (ACV) é uma ferramenta da gestão ambiental usada para avaliar impactos ambientais potenciais associados a produtos, processos e serviço. Sua principal característica é se prestar a essa avaliação de forma sistêmica, levando em conta todas as etapas do seu ciclo de vida. O objetivo deste trabalho foi avaliar e comparar os desempenhos ambiental e energético da produção de etanol a partir dos ativos agrícolas cana-de-açúcar, milho e sorgo, no contexto de usina autônoma integrada, segundo a abordagem do ciclo de vida. Para tanto, estudos de ACV foram conduzidos para cada um dos três produtos, seguindo as diretrizes das normas ABNT NBR ISO 14.040:2009 e ABNT NBR ISO 14.044:2009. Para a análise ambiental aplicou-se o método de Avaliação de Impacto do Ciclo de Vida (AICV) ReCiPe midpoint e, para a análise energética, o método Demanda de Energia Cumulativa foi utilizado, seguido pelo cálculo dos Índices de Retorno Energético sobre o Investimento (EROI) para cada combustível. A unidade funcional dos estudos foi 1 m³ de etanol hidratado e o sistema de produto incluiu a produção de insumos, produção da matéria-prima agrícola, produção de etanol, cogeração e etapas de transporte. Os resultados da análise ambiental demonstraram que o etanol de cana-de-açúcar apresenta melhor desempenho do que o etanol de milho e de sorgo em um número maior de categorias de impacto. As análises energéticas demonstraram que o uso de cavaco de madeira na etapa de cogeração dos processos de produção de etanol de milho e sorgo traduziu-se em ganhos energéticos, mas o etanol de cana-de-açúcar ainda apresenta um desempenho melhor por utilizar o bagaço para cogeração. Em termos de EROI, o etanol de cana-de-açúcar disponibilizou 9,77 unidades de energia para cada unidade consumida, o etanol de milho disponibilizou 2,68 e o etanol de sorgo disponibilizou 3,10. / Ethanol is consolidated as fuel to drive light vehicles in Brazil, but for the past 40 years, only the cultivation of sugarcane has been commercially exploited for the production of this fuel. On the other hand, agricultural development has provided high yields of grain in recent decades. Corn production is distinguished by increased productivity, and can be sown as main crop or as a winter crop in rotation with soybeans. Sorghum, in turn, has a higher roughness and tolerance to drought and can act as a substitute for corn. Given this situation, ethanol plants in Mato Grosso were associated with corn and sorghum producers to include new raw materials in the fuel production process, sharing the same plant, called Integrated Plant or Plant Flex. However, the development of new technology and production sectors requires consideration of its potential energy and environmental implications. The Life Cycle Assessment (LCA) is management tool used to evaluate potential environmental impacts associated with products, processes and services. Its main feature is to provide such an assessment in a systematic way, taking into account all stages of their life cycle. The objective of this study was to evaluate and compare the environmental and energy performance of ethanol production from sugarcane, corn and sorghum in the context of integrated autonomous plant, according to the life cycle approach. For that, LCA studies were conducted for each of the three products, following the guidelines of the standards ISO 14040: 2009 and ISO 14044: 2009. For environmental analysis the method of Life Cycle Impact Assessment (LCIA) Recipe midpoint was applied and for energy analysis Cumulative Energy Demand method was used, followed by the estimate of the Energy Return On Investment (EROI) for each fuel. The functional unit of the studies was 1 m³ of hydrous ethanol and the product system includes the production inputs, production of agricultural raw material, production of ethanol, cogeneration and transport stages. The results of the environmental analysis showed that the ethanol sugarcane performs better than the ethanol maize and sorghum in a greater number of impact categories. Energy analyzes have shown that the use of wood chips in cogeneration stage of corn ethanol production processes and sorghum has resulted in energy savings, but the ethanol sugarcane still performs better by using bagasse for cogeneration. In terms of EROI, the sugarcane ethanol provided 9.77 units of energy for every unit consumed, corn ethanol provided 2.68 and sorghum ethanol provided 3.10.

根據歐盟2009 年發布之再生能源指令，定義熱泵系統所擷取之大氣熱能、水熱能以及地熱能為再生能源之選項，熱泵技術不受日夜與天候影響，且具安全、有低耗能、低排碳的優點，可應用在空調、暖氣、熱水等設備，備受歐美日本等先進國家重視，也是歐美各國政府極力推廣的項目之一。本研究針對台灣地區家戶住宅所使用小型空氣源熱泵熱水機組，透過環境資源及能源效率的角度，來探討熱泵熱水系統對於台灣住宅部門的適用性。 在研究方法上，針對國內熱泵個案廠商進行系統盤查分析，並且估算使用運轉過程中所需之能源投入，以計算熱水系統在製造過程與運轉使用過程中之環境影響。選擇生命週期評估軟體SimaPro 7.3做為評估工具，使用Eco-Indicator 95、EPS 2000兩種衝擊評估模式，來以生命週期評估探討熱泵熱水系統對環境之影響。並輔以淨能源分析法中能源投資報酬率與能源回收期，以及估算熱泵熱水系統生命週期CO2排放量，來衡量熱泵熱水系統之能源效率是否具有其效益。並進一步針對不同的再生能源發電比例與提升熱泵能源效率比例，探討不同方案的敏感度分析。 根據本研究分析結果顯示，熱泵熱水系統不管從Eco-indicator 95或EPS 2000衝擊評估模式下，運轉使用階段對環境衝擊較大，主要的衝擊項目為重金屬汙染，是因為熱泵熱水系統運轉所使用的電力消耗所致。使用熱泵熱水系統對環境衝擊程度遠較電熱水系統來得小，雖在Eco-indicator 95之衝擊評估模式下，瓦斯熱水系統較熱泵熱水系統環境衝擊程度較小，但以EPS 2000衝擊評估模式下，熱泵熱水系統對環境是最為友善的熱水系統。以淨效益估算熱泵熱水系統源投資報酬（EROI）值為1.45～5.55，能源回收期約為0.22年至2.16年，表示熱泵熱水系統從生命週期的角度來檢視能源效率是具有效益的。由於目前熱泵熱水系統對環境最大的負擔來源是電力的使用，若未來能提高再生能源發電比例、降低臺灣電能含碳濃度，或者提高熱泵能源生產效率，均能降低熱泵熱水系統對環境的負面影響。 / The purpose of this study is to apply life cycle assessment (LCA) and net energy analysis to explore the environmental impacts of the heat pump water heater in Taiwan. In order to achieve this objective, domestic data inventory was gathered from local heat pump industry in Taiwan through questionnaires including input of energy, product output and waste, etc. The SimaPro7.3 program and two impact assessment methods including Eco-Indicator 95, EPS 2000 were utilized to evaluate the environmental impact of the heat pump water heater. Also, we used net energy analysis such as energy return on investment and energy payback time, and estimated the life-cycle CO2 emissions to see whether if the heat pump water heater has its energy efficiency. In addition, the sensitivity analysis was performed by varying renewable energy generation portfolio and the heat pump energy efficiency ratio. Emprical results of two impact assessment methods (Eco-indicator 95 and EPS 2000) show that the main impact on environment of heat pump water heater is from operation phase. When operating the heat pump water heater, it needs to consume electricity which is generated from fossil fuel and caused the environmental impact. Compared with the electric water heater, the environmental impact degree of heat pump water heater is much smaller. In Eco-indicator 95 method, gas water heater has less influence on the environment than heat pump water heater; however, heat pump water heater is the most environment-friendly system in EPS 2000 method. That is because gas is a kind of nonrenewable resource. From the viewpoint of resource stock, gas indeed influence “Depletion of reserves” of environmental impact. By utilizing net energy analysis, the estimated energy return on investment (EROI) of heat pump water heater is 1.45～5.55, and energy payback time is 0.22~2.16 years. It indicates that heat pump water heater has significant benefit from life-cycle perspective. The main impact to environment by heat pump water heater is essentially derived from electricity input. To mitigation this environmental issue, one can reduce environmental impact by increase the proportion of renewable energy generation, and reducing the electricity CO2 emission. Furthermore, improving the energy efficiency of the heat pump would also helpful.