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Orientador(es)
Resumo(s)
O contínuo aumento do nível de emissões de gases com efeito de estufa e a necessidade
de segurança face a crises energéticas, que provocam a subida dos preços dos
combustíveis, são os principais impulsionadores do esforço de transição energética para
fontes renováveis de energia. Essa transição passa pela massificação na utilização de
tecnologia de produção de energia renovável, que apresenta uma grande variabilidade
na produção, por estar dependente da disponibilidade do sol, água ou vento. Atendendo
a essa variabilidade, a par do incremento de fontes de energia renovável, está também
o armazenamento de energia, que pelo seu papel de conservação de energia, além de
reduzir o desfasamento entre a oferta e procura, melhora o desempenho, fiabilidade e
eficiência dos sistemas energéticos. Isto proporciona a poupança de combustíveis, pela
redução do desperdício de energia, aumentando a rentabilidade do sistema energético
e reduzindo assim o custo de capital.
A presente dissertação, realizada em parceria com a empresa MC, nomeadamente no
Entreposto de Congelados do Pólo Logístico da Maia, visa estudar a eficiência
energética, a viabilidade económica e o impacto na pegada de carbono obtida pela
implementação de um sistema passivo de armazenamento de energia térmica,
utilizando materiais de mudança de fase (PCMs) no interior da câmara de congelados.
Com o objetivo de se determinar a produção de eletricidade da instalação de painéis
fotovoltaicos, efetuou-se uma simulação, utilizando o software PVsyst. Conhecida a
energia produzida pela instalação fotovoltaica, consumida para autoconsumo e
disponível para venda à rede, o diagrama de cargas da instalação e os consumos do
sistema de produção de frio negativo, foi efetuada a ponderação da energia consumida
à rede mensalmente, hora a hora, e aplicada a tarifa tetra-horária correspondente ao
respetivo período, com a finalidade de se conhecer o valor pago anualmente pela
eletricidade consumida na instalação.
Tendo-se definido o cenário base, ou seja, os consumos e custos com eletricidade da
instalação, procedeu-se então à simulação dos diferentes cenários/perfis de carga do
sistema de PCMs, que utilizam o sistema de produção de frio em diferentes momentos
do dia. Os cenários considerados foram: carga noturna, carga diurna e carga combinada.
Para cada um destes cenários foi ponderada a eficiência associada à utilização dos PCMs
e as variações de energia consumida e vendida à rede, considerando diferentes tarifas
de compra e venda de eletricidade. Foram calculados os indicadores financeiros e
pegada de carbono decorrente da variação de eletricidade consumida à rede, para cada
cenário, tendo-se concluído que é possível obter proveitos na utilização de PCMs na câmara de congelados. No cenário de carga noturna o benefício é exclusivamente
financeiro, havendo um incremento na pegada de carbono, devido ao acréscimo de
eletricidade comprada à rede. No cenário de carga combinada verificaram-se benefícios
financeiros e também ambientais, pela redução do consumo de eletricidade à rede,
reduzindo a pegada de carbono. O cenário de carga diurna consegue benefício
ambiental, mas não financeiro, pelo que foi desconsiderado.
Constatou-se que a aplicação dos PCMs possibilitam a diversificação do sistema de
modo a viabilizar apenas a carga noturna ou aproveitar também o excedente FV,
oferecendo assim a possibilidade de absorver e articular alterações de funcionamento
ao longo do tempo, atendendo a flutuações do mercado ou necessidades internas do
Pólo. Verificou-se ainda que permite, até certo ponto, flexibilizar e diversificar os
horários de carga e de consumo de acordo com as condições tarifárias de eletricidade.
Outra conclusão é que bons indicadores económicos podem não corresponder a um
menor consumo energético, que se reflita numa redução da pegada carbónica. Pode ser
mais vantajoso vender eletricidade à rede, em vez de usar para autoconsumo, levando
à compra de eletricidade, na qual o vetor energético é menos sustentável.
The continuous increase in the level of greenhouse gas emissions and the need for security in the face of energy crises, which cause fuel prices to rise, are the main drivers behind the energy transition to renewable energy sources. This transition involves the widespread use of renewable energy production technology, which, however, is highly variable, as it depends on the availability of sun, water or wind. Given this variability, along with the increase in renewable energy sources, there is also energy storage, which, due to its role in energy conservation, not only reduces the gap between supply and demand, but also improves the performance, reliability and efficiency of energy systems. This leads to fuel savings by reducing energy waste, increasing the profitability of the energy system and thus reducing the cost of capital. This dissertation was developed in collaboration with the company MC, at the Maia Logistics Hub, more specifically at the Frozen Food Warehouse, with the aim of studying the energy efficiency, economic viability and impact on the carbon footprint of implementing a passive thermal energy storage system, using phase change materials (PCMs) inside the frozen food chamber. In order to determine the electricity production of the photovoltaic panel installation, a simulation was carried out using the PVsyst software. Once the energy produced by the photovoltaic installation, consumed for self-consumption and available for sale to the grid, the installation's load diagram and the consumption of the negative cold production system were known, the energy consumed from the grid was weighted hour by hour on a monthly basis and the four-hourly tariff corresponding to the respective period was applied in order to find out the amount paid annually for the electricity consumed at the installation. Having defined the base scenario, in other words, the facility's electricity consumption and costs, we then proceeded to simulate the different load scenarios/profiles for the PCM system, which use the cold production system at different times of the day to charge the PCMs. The scenarios considered were: night load, daytime load and combined load. For each of these scenarios, the efficiency associated with the use of PCMs and variations in energy consumed and sold to the grid were weighted. Having said this, the financial indicators and carbon footprint resulting from the variation in electricity consumed by the grid were calculated for each scenario, and it was concluded that it is possible to obtain benefits from the use of PCMs in the frozen food chamber. In the night load scenario, the benefit is exclusively financial, with an increase in the carbon footprint due to the increase in electricity purchased from the grid. In the combined load scenario, there were financial as well as environmental benefits, due to the reduction in electricity consumption from the grid, reducing the carbon footprint. The daytime load scenario achieves an environmental benefit, but not a financial one, so it was, for the purpose of this study, disregarded. It was found that the application of PCMs makes it possible to diversify the system in such a way as to enable only night load or to also take advantage of the PV surplus, thus offering the possibility of absorbing and articulating changes in operation over time, in response to market fluctuations or the internal needs of the Hub. It was also found that it allows, to a certain extent, flexibility and diversification of charging and consumption schedules in accordance with electricity tariff conditions. Another conclusion is that positive economic indicators may not correspond to lower energy consumption, which is reflected in a reduced carbon footprint. It may be more advantageous to sell electricity to the grid instead of using it for self-consumption, leading to the purchase of electricity, in which the energy carrier is less sustainable.
The continuous increase in the level of greenhouse gas emissions and the need for security in the face of energy crises, which cause fuel prices to rise, are the main drivers behind the energy transition to renewable energy sources. This transition involves the widespread use of renewable energy production technology, which, however, is highly variable, as it depends on the availability of sun, water or wind. Given this variability, along with the increase in renewable energy sources, there is also energy storage, which, due to its role in energy conservation, not only reduces the gap between supply and demand, but also improves the performance, reliability and efficiency of energy systems. This leads to fuel savings by reducing energy waste, increasing the profitability of the energy system and thus reducing the cost of capital. This dissertation was developed in collaboration with the company MC, at the Maia Logistics Hub, more specifically at the Frozen Food Warehouse, with the aim of studying the energy efficiency, economic viability and impact on the carbon footprint of implementing a passive thermal energy storage system, using phase change materials (PCMs) inside the frozen food chamber. In order to determine the electricity production of the photovoltaic panel installation, a simulation was carried out using the PVsyst software. Once the energy produced by the photovoltaic installation, consumed for self-consumption and available for sale to the grid, the installation's load diagram and the consumption of the negative cold production system were known, the energy consumed from the grid was weighted hour by hour on a monthly basis and the four-hourly tariff corresponding to the respective period was applied in order to find out the amount paid annually for the electricity consumed at the installation. Having defined the base scenario, in other words, the facility's electricity consumption and costs, we then proceeded to simulate the different load scenarios/profiles for the PCM system, which use the cold production system at different times of the day to charge the PCMs. The scenarios considered were: night load, daytime load and combined load. For each of these scenarios, the efficiency associated with the use of PCMs and variations in energy consumed and sold to the grid were weighted. Having said this, the financial indicators and carbon footprint resulting from the variation in electricity consumed by the grid were calculated for each scenario, and it was concluded that it is possible to obtain benefits from the use of PCMs in the frozen food chamber. In the night load scenario, the benefit is exclusively financial, with an increase in the carbon footprint due to the increase in electricity purchased from the grid. In the combined load scenario, there were financial as well as environmental benefits, due to the reduction in electricity consumption from the grid, reducing the carbon footprint. The daytime load scenario achieves an environmental benefit, but not a financial one, so it was, for the purpose of this study, disregarded. It was found that the application of PCMs makes it possible to diversify the system in such a way as to enable only night load or to also take advantage of the PV surplus, thus offering the possibility of absorbing and articulating changes in operation over time, in response to market fluctuations or the internal needs of the Hub. It was also found that it allows, to a certain extent, flexibility and diversification of charging and consumption schedules in accordance with electricity tariff conditions. Another conclusion is that positive economic indicators may not correspond to lower energy consumption, which is reflected in a reduced carbon footprint. It may be more advantageous to sell electricity to the grid instead of using it for self-consumption, leading to the purchase of electricity, in which the energy carrier is less sustainable.
Descrição
Palavras-chave
Carbon footprint Latent heat Passive thermal energy storage Phase change materials Rational energy use Walk-in freezer