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Percorrer I. Componente Universitária por Objetivos de Desenvolvimento Sustentável (ODS) "07:Energias Renováveis e Acessíveis"
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- Alterações de estrutura nos mercados: o exemplo do petróleoPublication . Agostinho, Luís; Viegas, Cristina; Morais, HenriqueA importância dos combustíveis fósseis na oferta mundial de energia e a relação entre as suas flutuações e os fenómenos geoeconómicos e geopolíticos, tornam aliciante analisar as forças maiores por detrás do comportamento, amiúde inesperado, do preço do petróleo. É objetivo deste trabalho estudar os acontecimentos socioeconómicos contemporâneos a alterações de estrutura no preço do petróleo, que com elas possam indiciar relações de causalidade. Neste estudo é utilizada a metodologia de Bai & Perron para a deteção de alterações de estrutura. A amostra consiste em observações dos preços de fecho de contratos de futuros negociados nos EUA, West Texas Intermediate, correspondentes a várias maturidades. Três pontos são por nós identificados como essenciais sobre a formação do preço do petróleo. Em primeiro lugar, observa-se o impacto significativo de fatores macroeconómicos, especialmente os mais relacionados com a procura, como principais impulsionadores de alterações de estrutura nos mercados de petróleo. Também é assinalada a influência da OPEP na determinação dos preços, realçando o seu papel proeminente no panorama global do petróleo, embora com menor impacto nas alterações de estrutura identificadas. Por fim, a pesquisa sugere que, num contexto mais amplo, eventos geopolíticos tendem, por norma, a não desencadear alterações estruturais significativas no mercado do petróleo.
- Application of floquet theory and improvement of electron current flow control in a 1D Fe-Cu molecular chainPublication . Nikolic, Violeta; Mariano, JoséAbstract: In this study is investigated the application of Floquet theory to a one- -dimensional (1D) Fe–Cu molecular chain under periodic driving. It was demonstrated that orbital hybridization induces resonant behavior in the low-frequency regime, highlighting the potential of this system for energy-efficient and robust device applications. For the first time, a Floquet electronic friction framework – incorporating the influence of periodic driving on electron transfer – is applied to a 1D Fe–Cu molecular chain in the presence of strong light–matter interaction (LMI). Electron transport properties are analyzed, revealing the existence of an optimal driving frequency that maximizes the electric current. Two mechanisms for enhancing charge transport in the strong LMI regime are identified: a) hybridization-induced resonances and b) photon-assisted transport processes. In this work is combined Floquet band structure analysis with open-system transport modeling in a 1D Fe–Cu motif, revealing the impact of hybridization and periodic driving, on the enhancement of electron transport via photon- -assisted resonances – an approach that bridges quasi-energy spectra and dissipative transport in a single theoretical framework. These findings provide new insights into driven low-dimensional transition-metal systems and may support the development of Fe–Cu-based materials for electrochemical applications.
- Application of solar HVAC system in residential buildings for winter conditions in mediterranean climatePublication . Conceição, Eusébio; Gomes, João; Conceição, Margarida; Conceição, Maria Inês; Lúcio, Maria Manuela Jacinto do Rosário; Awbi, HazimThe design of thermal strategies applied in buildings based on the use of renewable energies can play an important role in the development of a built environment that is better adapted to the climate. This paper is focused on the application of a renewable solar energy system coupled with a Heating, Ventilation and Air-Conditioned (HVAC) system to promote occupants’ thermal comfort (TC) and indoor air quality (IAQ) in buildings during heating season. In the building thermal design, a building thermal dynamic model is used to calculate the temperatures of the opaque and transparent building surfaces, the temperature of the water supply ducts, the TC level and the IAQ level, among other variables. The TC conditions of the occupants were evaluated using the Predicted Mean Vote index, commonly used in the literature in similar studies. IAQ was assessed by the usual carbon dioxide concentration in environments where most of the pollution is of human origin. The numerical study was carried out in a virtual residential building consisting of two floors and seven compartments. The building is occupied at night and at midday. Two cases were studied, considering, respectively, the non-use and use of the solar HVAC system. The solar HVAC system consists of solar water collectors, installed above the roof area, and thermo-convector heat exchangers, installed inside each occupied space. The results show that the application of this solar HVAC system in a Mediterranean-type climate is able to guarantee, during occupancy, acceptable TC levels in three compartments and near acceptable TC levels in one compartment. Regarding IAQ, acceptable level can be achieved throughout the day.
- Assessment of cell disruption methods in an integrated multi-product biorefinery for Nannochloropsis Oceanica: from process design to economic analysis.Publication . Cunha, Pedro; Carvalho, Bernardo; Kholany, Mariam; Pereira, Hugo; Varela, JoãoMicroalgae are bioresources with significant potential within a sustainable, circular, bio-economy. However, high production costs have limited the widespread use of algae biomass. This study aimed to develop a multi-product biorefinery for Nannochloropsis oceanica that generates multiple revenue streams from the biomass, thereby enhancing the economic viability of algal production. The effectiveness of cell wall disruption using high-pressure homogenization and enzymatic hydrolysis was evaluated. Enzymatic hydrolysis solubilized nearly half (48.2 ± 1.5%) of the dry cell weight, compared to only 27.3 ± 3.2% with high-pressure homogenization, resulting in more concentrated water-soluble fractions and significantly higher protein extraction yields. Lipid extracts obtained after enzymatic hydrolysis had higher lipid (72.0 ± 5.3% w/w) and eicosapentaenoic acid (28.1 ± 6.9% w/w) contents than those from high-pressure homogenization (38.8 ± 6.1% w/w lipids; 9.1 ± 0.6% w/w eicosapentaenoic acid), despite similar lipid extraction yields (around 30%). Increasing the ethanol volumetric ratio from 58% to 75% v/v significantly improved lipid extraction yields (57.4 ± 3.1%) in the enzymatic hydrolysis-based biorefinery, with even higher yields observed upon scaling up (70.1%). All fractions, including lipid extracts, exhibited a balanced essential amino acid profile that exceeded the WHO/FAO/UNU-recommended values. A preliminary economic analysis indicated that lipid production was more cost-effective when cells were permeabilized by enzymatic hydrolysis than by high-pressure homogenization.
- Asymmetric connectedness among regional green economies, carbon markets, and oil shocksPublication . Hanif, Waqas; El Khoury, Rim; Gubareva, Mariya; Teplova, TamaraThis study investigates spillovers among the US, Europe, and Asia green economies, carbon allowances and oil price shocks in 2010–2023. We segregate oil shocks in demand-, supply-, and risk-driven price movements. The TVP-VAR methodology is applied to model the dynamic interrelationships among the markets. Our static connectedness outcomes highlight a substantial role of the US and European green economy and the demand-driven shocks as emitters of innovations to other markets. It is found that European green economy is the main innovations contributor to global carbon allowances whereas the demand-driven oil shocks dominate in transmitting spillovers to others. We demonstrate that major economic events make connectedness increase. Our asymmetry analysis reveals a heightened susceptibility of the system to negative news, with the impacts of negative spillovers overcoming those of positive ones. The dynamics of spillovers emphasize how crucial it is to take into account both the time and the sign. Our research advances understanding of the complex relationships within the green-carbon-oilshocks system. The results are potentially useful for risk managers and investors, as they allow the creation of effective risk management plans.
- Catalytic transfer hydrogenation reactions of Glycerol Over Zr-Incorporated Zeolite Beta prepared by a mechanochemical approachPublication . Fernandes, Auguste; Ribeiro, M. Filipa; Lourenço, João P.Zr-containing zeolite beta catalysts were prepared by a post-synthesis procedure involving a dealumination followed by a mechanochemical step and tested in the gas-phase conversion of glycerol. The catalytic data indicate that the catalysts are active in the conversion of glycerol, promoting not only the typical dehydration but also its hydrogenolysis without an external source of hydrogen, resulting in the production of significant amounts of ethylene glycol and methanol. Partially frameworkattached (Si─O)2Zr═O species were identified and are suggested to play an important role in the catalytic behavior of these materials.
- A cost-effective solution for predictive maintenance in industrial pumping systemsPublication . Brito, Sergio; Azinheira, Gonçalo; Semião, Jorge; Sousa, NelsonThis paper presents a cost-effective, Internet of Things (IoT)-based solution for predictive maintenance (PdM) in industrial pumping systems. The proposed system integrates custom-built hardware with machine learning (ML) algorithms to monitor and detect anomalies in real-time. The innovation of the system lies in its non-intrusive design, ease of installation, and adaptability to a variety of industrial environments, providing a practical, low-cost alternative to traditional PdM solutions. Detailed discussion is provided on the hardware component selection, which prioritizes affordability without sacrificing performance, as well as the machine learning strategies used for anomaly detection. Preliminary results from laboratory and field testing demonstrate the system’s potential for reducing downtime and maintenance costs, with a focus on extending the application to broader industrial contexts.
- Digital twin modelling for a renewable energy community: a case study of the culatra island’s smart gridPublication . Ogunsola, Idris Olalekan; Santos, Joni; Monteiro, Jânio; Pacheco, AndréThis study develops and tests a Digital Twin (DT) of the Culatra Island’s distribution grid to enable the evaluation of demand side management strategies, in the scope of Renewable Energy Communities. Built in MATLAB/Simulink and structured across five functional layers, the DT integrates real-world data from five photovoltaic (PV) production units, monitored and fixed electrical loads, and realistic network parameters derived from the island’s infrastructure. Three steady-state test scenarios were simulated to assess voltage stability, and power flow under: 1) baseline grid operation without PV generation, 2) distributed PV integration under normal load conditions, and 3) high-demand operation near generationload equilibrium. Results show that PV integration improves voltage regulation and reduces losses through localized energy injection and bidirectional power flow. However, under peak load conditions, the system exhibits significant undervoltage, revealing the need for advanced control strategies and infrastructure reinforcement. Overall, the DT proves to be an effective analytical and decision-support tool for optimising distributed energy systems. This work provides a replicable application-oriented framework for data-driven planning in emerging Renewable Energy Communities and supports Culatra Island’s transition toward full energy self-sufficiency. Unlike prior studies that report generalized benefits of PV integration, this work explicitly identifies voltage instability thresholds under high-demand conditions in a real REC configuration, providing actionable insight into when passive operation becomes insufficient.
- Do investors tend to overreact when investing in clean energy stock indices?Publication . Dias, Rui; Galvão, Rosa; Cruz, Sandra P.; Gonçalves, Sidalina; Irfan, Mohammad; Teixeira, Nuno; Alexandre, Paulo; Palma, Cristina; Almeida, LilianaDue to climate change, investors are increasingly interested in clean energy stocks attracting many investors due to clean energy prospects. This paper analyses investor overreactions to long-term prices in various clean energy stock indices, such as Clean Energy Fuels (CLNE), Global Clean Energy (GCEI), as well as the Dow Jones Industrials (DJI) stock index, over the period from 24 February 2022 to 23 May 2024. The results show that the Global Clean Energy (GCEI) clean energy stock index rejects H0 at the 16-day lag at a significance level of 1%; similarly, the Clean Energy Fuels (CLNE) index rejects the null hypothesis at lags 8, 9, 10, 11 and 12 days, both indices show negative serial autocorrelation, which means that price movements are not entirely random and are influenced by prior price movements. This evidence could mean that investors overreact to the information that reaches the market. On the other hand, the ETF (PWYF) and the Dow Jones Industrial Stock Index (DJI) show that the random walk hypothesis has not been rejected. In other words, these markets show that they are in equilibrium and that the existence of exaggerated reactions on the part of investors is not significant. The answer to the research question was partially accepted, so the Russian invasion of Ukraine in 2022 led to the partial presence of overreactions in these stock indices. In conclusion, investors operating in these markets should exercise caution and consider their risk tolerance before investing. Investors should, therefore, continue to monitor market trends and adjust their investment strategies accordingly.
- Energy transition effects on food security amidst climate change and progress toward sustainable development goalsPublication . Tamasiga, Phemelo; Dzingai, Valentine Munyaradzi; Onyeaka, Helen; Ngameni Tchonkouang, Rose Daphnee; Siyanbola, Kehinde Favour; Genesis, Ulakom; Mudimu, George T.Transitioning to net-zero societies affects how energy is produced and consumed, with consequences for food security. Through a systematic review of 43 peer-reviewed studies that follow the PRISMA protocol, results reveal that renewable energy can enhance agricultural productivity by reducing operational costs, increasing efficiency in irrigation and processing, and providing reliable access to energy. However, challenges exist, including competition for land and water resources between renewable energy projects and food production, high upfront costs of clean energy technologies, limited access to credit facilities, and institutional bottlenecks. To overcome these challenges, recommended policies include offering subsidies and financial incentives to make clean energy more affordable for farmers, as well as providing education and training to support the adoption of sustainable practices. Furthermore, promoting collaboration between the public and private sectors is crucial to stimulate investment in renewable energy infrastructure. Moreover, these policies must be designed for specific national circumstances. High-income or upper-middle-income countries can deploy capital-intensive agrivoltaic and biogas technologies via concessional finance. In contrast, low-income settings should prioritize low-cost, decentralized solar pumps and off-grid dryers to build farmer confidence and trust. Countries with stronger regulatory frameworks and secure land tenure systems are better equipped to support large-scale renewable energy projects. At the same time, regions with weaker governance tend to benefit most from community-owned mini-grids. The mapping of policy options onto economic, institutional, and agro-ecological dimensions provides a nuanced, context-sensitive framework to guide equitable and effective energy transitions in diverse agricultural landscapes.
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