Rubén Bravo - Academia.edu (original) (raw)

Papers by Rubén Bravo

EngOpt 2018 Proceedings of the 6th International Conference on Engineering Optimization, 2018

The efficient and flexible design of renewable power plants is key to increase competitiveness of... more The efficient and flexible design of renewable power plants is key to increase competitiveness of clean technologies and accomplish climate targets. However, renewable power plants that deliver energy only when the renewable source is available produce large fluctuations and increase cost of integration in the wider electricity system. Optimised design of renewable power plants with energy storage increases reliability and decreases integration cost of sustainable technologies. Here we show a two-stage multi-objective optimisation framework to optimise the design and the operation of power plants that combine two or more generation technologies and energy storage, with the aim of producing firm or dispatchable electricity. With the optimisation framework it is possible to handle different technologies to design a sustainable, cost competitive, flexible and dispatchable power plant. Besides, the post-optimisation analysis handles other key performance indicators and provides detailed...

Energy Conversion and Management, 2021

Abstract The present work proposes integrating a high-temperature thermochemical energy storage c... more Abstract The present work proposes integrating a high-temperature thermochemical energy storage cycle to boost the solar contribution in solar combined cycles. The main feature of the plant is the possibility of storing solar energy at a very high temperature and releasing it on demand to drive the combined cycle in the absence of solar radiation. Based on the reversible calcination-carbonation of CaCO3/CaO, the Calcium-looping process is proposed since it allows power production above 900 °C by using cheap, non-toxic and widely available raw materials (i.e. limestone or dolomite). Based on an air-open and a CO2-closed combined cycle, two potential configurations are modelled and analysed, including designing a 360° solar field with a 200-meter tower. The novel solar combined cycle analyzed in the present work enhances the annual solar share above 50%, whilst the current state-of-the-art technology is below 15%. From actual solar irradiation data and clustering analysis, results show overall plant efficiencies over 45% (considering off-design performance) with a very high dispatchability, which justifies the interest in further developing this novel cycle.

Applied Energy, 2021

The drive to net zero energy requires high renewable penetration but most renewables are either a... more The drive to net zero energy requires high renewable penetration but most renewables are either affordable or dispatchable but not both. Thermochemical energy storage integrated into concentrating solar power plants can enhance dispatchability and solar-to-electricity efficiency. Combining these technologies with lower cost photovoltaic plants exploits synergies related to dispatchability and costs. However, this combination leads to complex interactions between the different power plant components and requires sophisticated design guidelines to simultaneously achieve low costs and high dispatchability. Here, we develop multi-objective optimisations and guidelines for the design of hybrid solar power plants with a calcium-looping thermochemical energy storage system. The applied tools presented focus on the optimisation of the design and operation of hybrid power plants plants with respect to competing technical and financial performance metrics. First, the design optimisation stage evaluates ten design variables and three objectives. Then, the operational optimisation stage, which is nested inside the design stage, finds the best one-year hourly operational strategy for each configuration considered in the first stage. We evaluated three case studies with different solar resource: Seville (Spain), Tonopah (United States), and the Atacama Desert (Chile). The best dispatchable hybrid solar power plant with an Levelised cost of electricity of 123 USD•MWh −1 and a capacity factor of 73% is reached for the Atacama Desert, which has the best solar resource. The optimisation results are used to develop guidelines for the optimal design of dispatchable hybrid solar power plants with CaL based on the given solar resource and required dispatchability. These guidelines provide an initial design for affordable and dispatchable hybrid solar power plants and can enable their widespread deployment.

Energy Conversion and Management, 2020

Energy storage is key to decarbonising the energy sector by reducing intermittency and increasing... more Energy storage is key to decarbonising the energy sector by reducing intermittency and increasing the integration of renewable energy. Thermochemical energy storage (TCES) integrated with concentrated solar and photovoltaic power plants, has the potential to provide dispatchable and competitive energy. Here we develop a multi-objective optimisation framework to find the best operational strategy of a hybrid solar power plant with a TCES system. The model uses a typical meteorological year to optimise one-year hourly operation. The results demonstrate that the integration of a calcium-looping process as TCES in a concentrated solar power plant provides dispatchability and, when hybridised with photovoltaic, enhances its competitiveness with current electricity prices. The low mismatch between supply and demand, even when a fixed commitment is required throughout the year, together with a high overall efficiency, indicates that the integration of calcium-looping in hybrid solar power plants is an opportunity to increase the penetration of solar energy in the power sector. Through the optimisation framework presented, a seasonal energy storage analysis can be developed, although a second optimisation stage is required to improve the sizing of the main components of the system in order to further reduce the energy costs.

Solar Energy, 2018

Hybrid solar power plants which combine concentrated solar power (CSP) and photovoltaic (PV) syst... more Hybrid solar power plants which combine concentrated solar power (CSP) and photovoltaic (PV) systems with thermal energy storage (TES) have the potential to provide cost competitive and dispatchable renewable energy. The integration of energy storage gives dispatchability to the variable renewable generation while the combination of different generation technologies can reduce the costs. However, the design of reliable and cost competitive hybrid solar power plants requires the careful balancing of trade-offs between financial and technical performance. This is made more complicated by the dependence on a larger number of parameters compared to conventional plants and due to the integration of TES which requires that the operational profile is optimised for every design. This contribution presents a two-stage, multi-objective optimisation framework which combines multi-objective linear programming methods for the operational optimisation with multi-objective genetic algorithms for the design optimisation. The operational optimisation which is performed for every design point needs to be performed with linear programming methods. Here an automated scalarisation method is developed for the linear programming method which enables the multi-objective optimisation of the operational profile. This enables the evaluation of the trade-offs between financial and technical performance in both the design and operational optimisation, which is required to design reliable and cost competitive sustainable energy systems. The two-stage multi-objective optimisation is applied to analyse and improve the design of the hybrid solar power plant Atacama-1. It is demonstrated that balancing the trade-off between financial and technical performance is key to increase the competitiveness of solar energy and that it is possible to simultaneously increase dispatchability and decrease the levelised cost of energy. This shows that the operational and design optimisations have to be directly linked in order to exploit the synergies of hybrid systems. Thus the optimisation framework presented in this study can improve the decision making in the design of hybrid solar power plants.

Energy Procedia, 2018

Concentrated solar power (CSP) and photovoltaics (PV) systems integrated with energy storage have... more Concentrated solar power (CSP) and photovoltaics (PV) systems integrated with energy storage have large potential to provide cost-competitive and baseload renewable energy. On the one hand, CSP with thermal energy storage (TES) is an affordable and dispatchable option. On the other hand, Electrical Energy Storage (EES) gives dispatchability to PV systems but at high costs due to current prices of EES systems, however an extreme reduction in EES costs is expected. Therefore, there could be a tipping point at which PV + EES becomes the best technology to provide dispatchable power. Here, we explore different scenarios, representing snapshots of technology investment costs according to published projections, in order to identify the dominant technology in a hybrid solar power plant that provides sustainable and dispatchable energy by 2050. The study uses our two-stage multi-objective optimisation framework, in order to optimise the design and operation of a hybrid power plant with energy storage. We found that nowadays CSP with TES is the most affordable technology, but a shift to PV with EES is expected mainly due to the large reduction in the cost of both PV and EES systems. Thus, the presented optimisation analysis can improve the strategies for the design of an effective and economic pathway to decarbonise the power sector.

Journal of Pediatric Gastroenterology and Nutrition, 2001

Background: Helicobacter pylori infection of the gastric mucosa in humans is usually acquired ear... more Background: Helicobacter pylori infection of the gastric mucosa in humans is usually acquired early in life. The chronic inflammation that ensues involves the increased production of inflammatory cytokines. Published data on production of these mediators by gastric mucosa of H. pylori-infected children are few. Methods: Seventy-nine children, aged 5 to 18 years, referred for upper gastrointestinal endoscopy to four separate hospitals in Chile, were studied. The concentrations of interleukin (IL)-1␤, IL-6, IL-8, and tumor necrosis factor ␣ were measured in homogenates of gastric mucosal biopsy specimens. Cytokine expression was confirmed by reverse transcription polymerase chain reaction. These data were correlated with the patients' clinical, histologic and sociodemographic status. Results: Patient rate of colonization by H. pylori was inversely correlated with socioeconomic status (P < 0.005) and positively correlated with age (P < 0.0025). In gastric mucosa, concentrations of IL-1␤, IL-8, and tumor necrosis factor ␣ were all significantly higher in H. pylori-positive patients than in H. pylori-negative patients and in patients who had histologic gastritis than in those with normal gastric mucosa. In patients with peptic ulcer disease, only IL-1␤ and IL-8 concentrations were significantly elevated when compared with those of patients without ulcers. Interleukin-6 concentrations were comparable among the different groups analyzed. Conclusions: This study suggests that increased gastric mucosal production of the proinflammatory cytokines IL-1␤ and IL-8 is probably involved in H. pylori-associated gastric damage in children and may be crucial in determining the different clinical outcomes. JPGN 33:127-132. 2001.

EngOpt 2018 Proceedings of the 6th International Conference on Engineering Optimization, 2018

The efficient and flexible design of renewable power plants is key to increase competitiveness of... more The efficient and flexible design of renewable power plants is key to increase competitiveness of clean technologies and accomplish climate targets. However, renewable power plants that deliver energy only when the renewable source is available produce large fluctuations and increase cost of integration in the wider electricity system. Optimised design of renewable power plants with energy storage increases reliability and decreases integration cost of sustainable technologies. Here we show a two-stage multi-objective optimisation framework to optimise the design and the operation of power plants that combine two or more generation technologies and energy storage, with the aim of producing firm or dispatchable electricity. With the optimisation framework it is possible to handle different technologies to design a sustainable, cost competitive, flexible and dispatchable power plant. Besides, the post-optimisation analysis handles other key performance indicators and provides detailed...

Energy Conversion and Management, 2021

Abstract The present work proposes integrating a high-temperature thermochemical energy storage c... more Abstract The present work proposes integrating a high-temperature thermochemical energy storage cycle to boost the solar contribution in solar combined cycles. The main feature of the plant is the possibility of storing solar energy at a very high temperature and releasing it on demand to drive the combined cycle in the absence of solar radiation. Based on the reversible calcination-carbonation of CaCO3/CaO, the Calcium-looping process is proposed since it allows power production above 900 °C by using cheap, non-toxic and widely available raw materials (i.e. limestone or dolomite). Based on an air-open and a CO2-closed combined cycle, two potential configurations are modelled and analysed, including designing a 360° solar field with a 200-meter tower. The novel solar combined cycle analyzed in the present work enhances the annual solar share above 50%, whilst the current state-of-the-art technology is below 15%. From actual solar irradiation data and clustering analysis, results show overall plant efficiencies over 45% (considering off-design performance) with a very high dispatchability, which justifies the interest in further developing this novel cycle.

Applied Energy, 2021

The drive to net zero energy requires high renewable penetration but most renewables are either a... more The drive to net zero energy requires high renewable penetration but most renewables are either affordable or dispatchable but not both. Thermochemical energy storage integrated into concentrating solar power plants can enhance dispatchability and solar-to-electricity efficiency. Combining these technologies with lower cost photovoltaic plants exploits synergies related to dispatchability and costs. However, this combination leads to complex interactions between the different power plant components and requires sophisticated design guidelines to simultaneously achieve low costs and high dispatchability. Here, we develop multi-objective optimisations and guidelines for the design of hybrid solar power plants with a calcium-looping thermochemical energy storage system. The applied tools presented focus on the optimisation of the design and operation of hybrid power plants plants with respect to competing technical and financial performance metrics. First, the design optimisation stage evaluates ten design variables and three objectives. Then, the operational optimisation stage, which is nested inside the design stage, finds the best one-year hourly operational strategy for each configuration considered in the first stage. We evaluated three case studies with different solar resource: Seville (Spain), Tonopah (United States), and the Atacama Desert (Chile). The best dispatchable hybrid solar power plant with an Levelised cost of electricity of 123 USD•MWh −1 and a capacity factor of 73% is reached for the Atacama Desert, which has the best solar resource. The optimisation results are used to develop guidelines for the optimal design of dispatchable hybrid solar power plants with CaL based on the given solar resource and required dispatchability. These guidelines provide an initial design for affordable and dispatchable hybrid solar power plants and can enable their widespread deployment.

Energy Conversion and Management, 2020

Energy storage is key to decarbonising the energy sector by reducing intermittency and increasing... more Energy storage is key to decarbonising the energy sector by reducing intermittency and increasing the integration of renewable energy. Thermochemical energy storage (TCES) integrated with concentrated solar and photovoltaic power plants, has the potential to provide dispatchable and competitive energy. Here we develop a multi-objective optimisation framework to find the best operational strategy of a hybrid solar power plant with a TCES system. The model uses a typical meteorological year to optimise one-year hourly operation. The results demonstrate that the integration of a calcium-looping process as TCES in a concentrated solar power plant provides dispatchability and, when hybridised with photovoltaic, enhances its competitiveness with current electricity prices. The low mismatch between supply and demand, even when a fixed commitment is required throughout the year, together with a high overall efficiency, indicates that the integration of calcium-looping in hybrid solar power plants is an opportunity to increase the penetration of solar energy in the power sector. Through the optimisation framework presented, a seasonal energy storage analysis can be developed, although a second optimisation stage is required to improve the sizing of the main components of the system in order to further reduce the energy costs.

Solar Energy, 2018

Hybrid solar power plants which combine concentrated solar power (CSP) and photovoltaic (PV) syst... more Hybrid solar power plants which combine concentrated solar power (CSP) and photovoltaic (PV) systems with thermal energy storage (TES) have the potential to provide cost competitive and dispatchable renewable energy. The integration of energy storage gives dispatchability to the variable renewable generation while the combination of different generation technologies can reduce the costs. However, the design of reliable and cost competitive hybrid solar power plants requires the careful balancing of trade-offs between financial and technical performance. This is made more complicated by the dependence on a larger number of parameters compared to conventional plants and due to the integration of TES which requires that the operational profile is optimised for every design. This contribution presents a two-stage, multi-objective optimisation framework which combines multi-objective linear programming methods for the operational optimisation with multi-objective genetic algorithms for the design optimisation. The operational optimisation which is performed for every design point needs to be performed with linear programming methods. Here an automated scalarisation method is developed for the linear programming method which enables the multi-objective optimisation of the operational profile. This enables the evaluation of the trade-offs between financial and technical performance in both the design and operational optimisation, which is required to design reliable and cost competitive sustainable energy systems. The two-stage multi-objective optimisation is applied to analyse and improve the design of the hybrid solar power plant Atacama-1. It is demonstrated that balancing the trade-off between financial and technical performance is key to increase the competitiveness of solar energy and that it is possible to simultaneously increase dispatchability and decrease the levelised cost of energy. This shows that the operational and design optimisations have to be directly linked in order to exploit the synergies of hybrid systems. Thus the optimisation framework presented in this study can improve the decision making in the design of hybrid solar power plants.

Energy Procedia, 2018

Concentrated solar power (CSP) and photovoltaics (PV) systems integrated with energy storage have... more Concentrated solar power (CSP) and photovoltaics (PV) systems integrated with energy storage have large potential to provide cost-competitive and baseload renewable energy. On the one hand, CSP with thermal energy storage (TES) is an affordable and dispatchable option. On the other hand, Electrical Energy Storage (EES) gives dispatchability to PV systems but at high costs due to current prices of EES systems, however an extreme reduction in EES costs is expected. Therefore, there could be a tipping point at which PV + EES becomes the best technology to provide dispatchable power. Here, we explore different scenarios, representing snapshots of technology investment costs according to published projections, in order to identify the dominant technology in a hybrid solar power plant that provides sustainable and dispatchable energy by 2050. The study uses our two-stage multi-objective optimisation framework, in order to optimise the design and operation of a hybrid power plant with energy storage. We found that nowadays CSP with TES is the most affordable technology, but a shift to PV with EES is expected mainly due to the large reduction in the cost of both PV and EES systems. Thus, the presented optimisation analysis can improve the strategies for the design of an effective and economic pathway to decarbonise the power sector.

Journal of Pediatric Gastroenterology and Nutrition, 2001

Background: Helicobacter pylori infection of the gastric mucosa in humans is usually acquired ear... more Background: Helicobacter pylori infection of the gastric mucosa in humans is usually acquired early in life. The chronic inflammation that ensues involves the increased production of inflammatory cytokines. Published data on production of these mediators by gastric mucosa of H. pylori-infected children are few. Methods: Seventy-nine children, aged 5 to 18 years, referred for upper gastrointestinal endoscopy to four separate hospitals in Chile, were studied. The concentrations of interleukin (IL)-1␤, IL-6, IL-8, and tumor necrosis factor ␣ were measured in homogenates of gastric mucosal biopsy specimens. Cytokine expression was confirmed by reverse transcription polymerase chain reaction. These data were correlated with the patients' clinical, histologic and sociodemographic status. Results: Patient rate of colonization by H. pylori was inversely correlated with socioeconomic status (P < 0.005) and positively correlated with age (P < 0.0025). In gastric mucosa, concentrations of IL-1␤, IL-8, and tumor necrosis factor ␣ were all significantly higher in H. pylori-positive patients than in H. pylori-negative patients and in patients who had histologic gastritis than in those with normal gastric mucosa. In patients with peptic ulcer disease, only IL-1␤ and IL-8 concentrations were significantly elevated when compared with those of patients without ulcers. Interleukin-6 concentrations were comparable among the different groups analyzed. Conclusions: This study suggests that increased gastric mucosal production of the proinflammatory cytokines IL-1␤ and IL-8 is probably involved in H. pylori-associated gastric damage in children and may be crucial in determining the different clinical outcomes. JPGN 33:127-132. 2001.