Manuel L. Nunes

Analysis of energy security and sustainability in future low carbon scenarios for Brazil

This study estimated a series of indicators to assess the energy security of supply and global and local environmental impacts under different mitigation scenarios through 2050 in Brazil, designed with the integrated optimization energy system model MESSAGE‐BRAZIL. The assessment of interactions between environmental impacts and energy security dimensions was complemented through the application of life cycle assessment (LCA) methodology. Overall results imply energy security establishes more synergies than trade‐offs in increasingly stringent mitigation scenarios, especially patent within the sustainability dimension, which increases energy security and provides additional benefits regarding climate change mitigation and air pollution emissions. It is still necessary to extend analysis to other energy sectors in addition to the power supply sector and to promote a better understanding of repercussions of energy scenario expansion in energy security.

Credits trading mechanism for corporate social responsibility: an empirically grounded framework

This paper proposes a framework for assessing credits trading mechanisms for corporate social responsibility (CSR). The motivation to structure this framework derives from contemporary market-based mechanisms of emissions trading (or carbon/credits/offsets) and renewable energy credits (RECs). However, the framework proposed herein moves beyond existing forms of credits trading mechanisms that are primarily focused on reducing the environmental footprint of the ongoing industrial/non-industrial activities. By adopting a comprehensive perspective, the paper emphasises simultaneously social sustainability-related considerations and CSR related activities based on the sale of CSR credits or certificates which bears striking resemblance to the sale of renewable energy credits (RECs) for subsidising the production of renewable energy. This is in direct contrast to emissions trading mechanism in which carbon credits/offsets are purchased by parties who desire to release a corresponding quantity of emissions above the permitted cap. Furthermore, the paper discusses the feasibility of the proposed CSR credits trading mechanism from a broader context of the ongoing climate change crises, political economy and geopolitical circumstances which are known drivers for determining the success of CSR activities by corporation(s) in domestic or overseas locations.

On solving the profit maximization of small cogeneration systems

Cogeneration is a high-efficiency technology that has been adapted to small and micro scale applications. In this work, the development and test of a numerical optimization model is carried out in order to implement an analysis that will lead to the optimal design of a small cogeneration system. The main idea is the integration of technical and economic aspects in the design of decentralized energy production considering the requirements for energy consumption for the building sector. The nonlinear optimization model was solved in MatLab®environment using two local optimization methods: the Box and the SQP method. The optimal solution provided a positive annual worth and disclosed reasonable values for the decision variables of the thermo-economic model. Both methods converged for the same solution, demonstrating the validity of the implemented approach. This study confirmed that the use of numerical optimization models is of utmost importance in the assessment of energy systems sustainability.

Modeling a stirling engine for cogeneration applications

The interest on decentralized power generation technology has been drastically increasing over the last few years. This great interest is due to the necessity of achieving new ways for improving energy efficiency, the national security of energy supply and the reduction of carbon dioxide emissions. Combined heat and power generation (CHP) systems can be a good option to achieve those goals. In Europe and for the building sector, this fact can be translated in the development of low power systems (micro-CHP), designed to fulfill building equivalent loads. These systems will replace the usual boilers that satisfy the dwelling’s heat requirements and, additionally, generate electricity for own consumption or export back to the electricity grid. The most cited technologies in small and micro-scale are Fuel Cells, Internal Combustion Engines, and Stirling Engines. Stirling Engines are gaining some attention due to their advantages: high total efficiency, fuel flexibility, low emissions, low noise/vibration levels and good performance at partial load. Due to these characteristics, Stirling engines seem to be a good alternative for residential energy conversion, and thus, a pathway for more energy-efficient systems that rise to the challenges of increasing market competition. Many studies have been conducted in order to assess Stirling Engines performance, but the integration of technical and economic evaluation for micro-CHP systems applications is an issue that is not focused in literature, and is the final objective of this project.Copyright

Optimal design of micro-turbine cogeneration systems for the portuguese buildings sector

The use of combined heat and power (CHP) systems to produce both electric and thermal energies for medium-size buildings is on the increase, due to their high overall efficiency, high energy prices and political and social awareness. In this paper, an energy-economic study is presented. The main objective is to implement an analysis that will lead to the optimal design of a small cogeneration system, given the thermal power duration curve of a multi-family residential building. A methodology was developed to obtain this curve for a reference B-class building located in the North of Portugal. The CHP unit is based on a micro gas-turbine and includes an Internal Pre-Heater (IPH), typical of these types of small-scale units, and an external Water Heater (WH). A numerical optimization method was applied to solve the thermo-economic model. The mathematical model yields an objective function defined as the maximization of the annual worth of the cogeneration system. A purchase cost equation was used for each major plant component that takes into account size and performance variables. Seven decision variables were selected for the optimization algorithm, including performance of internal gas-turbine components and electrical and thermal powers. The results show that, the revenue from selling electricity to the grid and fuel costs have the greatest impact on the annual worth of the system. The optimal solution for the small CHP is sensitive to fuel price, electricity feed-in-tariff, capital cost and to the thermal load profile of the building. High European energy prices point towards future micro gas-turbines with better electrical efficiencies, achieved via a higher pressure-ratio compressor and turbine inlet temperature.Copyright

Discerning the factors explaining the change in energy efficiency

Due to the high rates of energy consumption and its impact on environment over the last decades, policy decision-makers are increasingly recognising the need to take actions that allow to address problems associated with the deployment of non-renewable resources and climate changes. One field of action has been the promotion of measures that contribute to improve energy efficiency of countries. The purpose of this study is to identify the main factors explaining changes in energy efficiency applying the multiplicative Log Mean Divisia Index decomposition method for a set of countries (Portugal, UK, Brazil and China) with different socio-economic background and energy mix. The results show that overall energy efficiency trends display different patterns between countries and the same happens within each country from a sectoral perspective. Major drivers of improvements of overall energy efficiency were the intensity effect and the affluence effect, whereas the driver that hampered those improvements was the energy consumption per capita. Some policy implications derived from the results achieved are: policy decision-makers should support measures that promote the adoption of energy-saving technologies resulting from new technological developments; policy measures should be directed to raise awareness of end-users regarding energy efficiency and energy conservation efforts; policy measures promoting economic growth through the development (or expansion) of sectors of activity that consume less energy can also be implemented; finally, policy instruments may also be used to reduce the costs of implementing energy efficiency and energy-saving measures to households and firms.

Energy sector: A cross-country resource and impact decoupling analysis

Traditionally energy consumption and economic growth have been closely related, in an unsustainable manner. However, common concerns with energy security and climate change has led developed and emerging countries to promote resource and impact decoupling to achieve energy sustainability. This paper presents a cross-country comparison of decoupling trends in order to assess the impact of economic growth on energy consumption and on energy-related CO2 emissions, between 1990 and 2013. Results show a greater decoupling dynamic between energy and carbon emissions as environmental pressures from GDP PPP than population as a driving force. Therefore policy-makers should take into consideration not only technical but also behavioural features to attain effective energy decoupling, regarding resource and impact aspects.

Maximum Profit of a Cogeneration System Based on Stirling Thermodynamic Cycle

Stirling engine technologies have been applied to cogeneration systems mainly for residential applications. The performance of Stirling engines has been evaluated considering different operational conditions, which include the electrical and thermal production, working fluid pressure, components geometrical sizing and others. Thermal-economic evaluation represents an effective tool to optimize a power plant with this type of technology. This study presents a mathematical model that encloses the physical variable equations able to simulate the thermodynamic transformations of the cycle, and a set of equations that define the purchase cost of the main plant components. The paper presents a numerical study faithfully simulating a micro-cogeneration unit based on an alpha type Stirling Engine. The simulations were performed through a Mat Lab code able to disclose the best economic output for the best combination of decision variables. Stirling engine performance is affected by geometrical and operational parameters optimization is required in order to obtain the best performance. Results show that the implemented mathematical model reached an optimal solution disclosing a positive profit for the best physical configuration of the system. Also, the cost estimation based on sizing and quality parameters shows a good correlation with the capital investment costs of commercial models.

Numerical Study of Regenerator Configuration in the Design of a Stirling Engine

The sustainable development involves the rational use of energy, by satisfying energy demands without compromising the safety of future supply. The use of renewable energy sources together with combined heat and power systems is currently considered a priority in Europe. The market trends are evolving to decentralized energy conversion with the increasing replacement of boilers and other conventional systems by small and micro-scale cogeneration units, able to produce the same amounts of useful energies. Micro scale cogeneration systems have been developed as ideal solutions to meet the energy needs for the building sector. These technologies, which include the Stirling engines, allow the production of high quality electricity and heat, efficiently and close to the final point of use. Stirling engines seem to be a good alternative for residential energy conversion. The main objective of this paper is to study alternative configurations for the regenerator of an alpha Stirling engine and evaluate the overall performance of the system. Numerical simulations were performed via a MatLab® code that includes the thermodynamic cycle analysis accounting for the effects of non-ideal heat exchangers and pumping losses. Based on a previously developed costing methodology, the investment purchase cost for each configuration is also estimated. Results showed that, for mean pressure values above 30 bar, the Stirling engine efficiency is higher for a regenerator with a wired mesh matrix rather than with a wrapped foil matrix. This is due both to better heat transfer and to lower pumping losses with the wired mesh configuration. The capital cost of the system was calculated and showed that the heater and the engine bulk are the most expensive components.Copyright

Exergy Efficiency Optimization for Gas Turbine Based Cogeneration Systems

The authors would like to express their acknowledgments for the support given by the Portuguese F01mdation for Science and Technology (FCT) through the PhD grant SFRH/BD/62287/2009. This work was financed by National Funds-Portuguese Foundation for Science and Technology, under Strategic Project and PEst-OE/EME/UI0252/2011 and also the PEst-C/EME/UI4077/2011.