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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.
- 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.
- 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.
- Exploring the relationship between clean energy indices and oil prices: a ten-day window approachPublication . Dias, Rui; Galvão, Rosa; Cruz, Sandra P.; Irfan, Mohammad; Teixeira, Nuno; Gonçalves, SidalinaThis paper aims to assess the comovements between clean energy indices, namely the Clean Energy Fuels (CLNE), Nasdaq Clean Edge Green Energy (CELS), S&P Global Clean Energy (SPGTCLEN), TISDALE Clean Energy (TCEC.CN), Wilderhill (ECO), West Texas Intermediate (WTI) stock indices, over the period from 1 January 2018 to 23 November 2023. We used 10-day windows to analyse the duration and nature of the shocks. Granger causality tests revealed that 20 of the 30 possible pairs showed significant movements, with the WTI influencing all the clean energy indices, highlighting its global importance. CELS also showed a robust influence on all pairs, while SPGTCLEN had a significant but less far-reaching influence. The CLNE and ECO indices showed limited influences, suggesting the potential for diversification, the TCEC.CN proved to be independent and a determining factor for portfolio diversification. The Impulse Response Functions (IRF) confirmed significant movements between CELS, SPGTCLEN and WTI, reflecting the market's response to policies and adjustments in expectations. Fluctuations in oil prices substantially affect clean energy indices, highlighting the interconnectedness and volatility of these markets. In conclusion, these results indicate that despite the growth of clean energy, the sector is still influenced by fluctuations in the fossil fuel market.
- From home energy management systems to energy communities: methods and dataPublication . Ruano, Antonio; Ruano, MariaThis paper introduces the HEMStoEC database, which contains data recorded in the course of two research projects, NILMforIHEM, and HEMS2IEA, for more than three years. To be manageable, the dataset is divided in months, from January 2020 until February 2023. It consists in: (a) consumption electric data for four houses in a neighbourhood situated in the south of Portugal, (b) weather data for that location, (c) photovoltaic and battery data, (d) inside climate data, and (e) operation of several electric devices in one of the four houses. Raw data, sampled at 1 sec and 1 minute are available from the different sensing devices, as well as synchronous data, with a common sampling interval of 5 minutes are available. Gaps existing within the data, as well as periods where interpolation was used, are available for each month of data.
- Gravitational waves from two scalar fields unifying the dark sector with inflationPublication . Luongo, Orlando; Mengoni, Tommaso; Sá, PauloWe investigate the gravitational-wave background predicted by a two-scalar-field cosmological model that aims to unify primordial inflation with the dark sector, namely late-time dark energy and dark matter, in a single and self-consistent theoretical framework. The model is constructed from an action inspired by several extensions of general relativity and string-inspired scenarios and features a non-minimal interaction between the two scalar fields, while both remain minimally coupled to gravity. In this context, we derive the gravitational-wave energy spectrum over wavelengths ranging from today’s Hubble horizon to those at the end of inflation. We employ the continuous Bogoliubov coefficient formalism, originally introduced to describe particle creation in an expanding Universe, in analogy to the well-established mechanism of gravitational particle production and, in particular, generalized to gravitons. Using this method, which enables an accurate description of graviton creation across all cosmological epochs, we find that inflation provides the dominant gravitational-wave contribution, while subdominant features arise at the inflation-radiation, radiation-matter, and matter-dark energy transitions, i.e., epochs naturally encoded inside our scalar field picture. The resulting energy density spectrum is thus compared with the sensitivity curves of the planned nextgeneration ground- and space-based gravitational-wave observatories. The comparison identifies frequency bands where the predicted signal could be probed, providing those windows associated with potentially detectable signals, bounded by our analyses. Consequences of our recipe are thus compared with numerical outcomes and the corresponding physical properties discussed in detail.
- HVAC systems applied in university buildings with control based on PMV and aPMV indexesPublication . Conceição, Eusébio; Sousa, António F. M.; Gomes, João; Ruano, AntonioIn this work, HVAC (Heating, Ventilation and Air Conditioning) systems applied in university buildings with control based on PMV (Predicted Mean Vote) and aPMV (adaptive Predicted Mean Vote) indexes are discussed. The building’s thermal behavior with complex topology, in transient thermal conditions, for summer and winter conditions is simulated by software. The university building is divided into 124 spaces, on two levels with an area of 5931 m2 , and is composed of 201 transparent surfaces and 1740 opaque surfaces. There are 86 compartments equipped with HVAC systems. The simulation considers the actual occupation and ventilation cycles, the external environmental variables, the internal HVAC system and the occupants’ and building’s characteristics. In this work, a new HVAC control system, designed to simultaneously obtain better occupants’ thermal comfort levels according to category C of ISO 7730 with less energy consumption, is presented. This new HVAC system with aPMV index control is numerically implemented, and its performance is compared with the performance of the same HVAC system with the usual PMV index control. Both HVAC control systems turn on only when the PMV index or the aPMV index reaches values below −0.7, in winter conditions, and when the PMV index or the aPMV index reaches values above +0.7, in summer conditions. In accordance with the results obtained, the HVAC system guarantees negative PMV and aPMV indexes in winter conditions and positive PMV and aPMV indexes in summer conditions. The energy consumption level is higher in winter conditions than in summer conditions for compartments with shading, and it is lower in winter conditions than in summer conditions for compartments exposed to direct solar radiation. The consumption level is higher using the PMV control than with the aPMV control. Air temperature, in accordance with Portuguese standards, is higher than 20 ◦C in winter conditions and lower than 27 ◦C in summer conditions. In Mediterranean climates, the HVAC systems with aPMV control provide better occupants’ thermal comfort levels and less energy consumption than the HVAC system with PMV control.
- Interdependence and spillovers between big oil companies and regional and global energy equity marketsPublication . Hanif, Waqas; Hernandez, Jose Arreola; Kang, Sang Hoon; Boako, Gideon; Yoon, Seong-MinWe examine spillovers and nonlinear dependence dynamics between big oil supermajors and regional and global energy equity markets. We derive our empirical results by fitting a directional spillover index, a conditional value-at-risk (CoVaR) method, and time-varying parameter copulas. Spillover index results indicate that big oil supermajors most largely spillover to the EU energy equity sector than to the US energy equity sector. A big oil supermajor British Petroleum (BP) consistently exerts some of the largest spillovers across regional and global energy markets. The CoVaR analysis reveals that on the downside, shocks from Royal Dutch Shell A most largely spillover to the US energy equity sector, while Royal Dutch Shell B does it on the upside. On the downside, Chevron most largely spillovers shocks to the EU energy equity sector, while BP does it on the upside. ExxonMobil most largely spillovers downside shocks to the world energy equity sector, while Royal Dutch Shell B does it on the upside. The Copula results show an asymmetric dependence between major oil companies and the US energy equity sector. The relationship between big oil companies and the EU energy equity sector is characterised by symmetric dependence dynamics.