• Energy Research

Abstract Fossil fuels are used as the primary energy source in most countries, negatively contributing to the environmental impact. Even though various technologies exist to exploit solar thermal energy in low-carbon processes, the use of solar thermal energy in the industry sector is currently minimal. The main obstacles are modeling an optimal integration and identifying its energy potential, economic feasibility and environmental benefits. The novelty of this study is the modeling of an integration of solar heat for an industrial process located in a topographically complex territory such as the Alps using the software Dymola – Dassault Systems®. The methodology proposed is structured in several steps: (I) industrial process characterization; (II) collection of local hourly data for radiation and climatic temperature; (III) study of the position of sun and components of incident angle; (IV) comparison among three solar technologies (CPC, LFR, PTC), in terms of efficiency, IAM and heat production; (V) focus on PTC: sizing of HTF, mass flow rate, HEX; (VI) focus on PTC: dynamic modeling with Dymola – Dassault Systems® (HTF temperature, solar heat, solar fraction); (VII) economic and environmental impact. In this paper, the case study of a pasta factory called “Felicetti”, located in the north-east of the Italian Alps, has been considered in order to investigate and evaluate the possibility of supplying solar heat for the drying process. The days of a week in June, exhibiting variable DNI, are used to demonstrate the dynamics and robust integration of the solar heat in the industrial process of pasta drying. The dynamic modelling results show that the PTC solar field can guarantee 23% of weekly energy coverage saving about 4.7 CO 2 / week . The economic analysis shows a pay-back time up to 9 years and a reduction of CO 2 emissions up to 99 t/year.

Abstract Fossil fuels are used as the primary energy source in most countries, negatively contributing to the environmental impact. Even though various technologies exist to exploit solar thermal energy in low-carbon processes, the use of solar thermal energy in the industry sector is currently minimal. The main obstacles are modeling an optimal integration and identifying its energy potential, economic feasibility and environmental benefits. The novelty of this study is the modeling of an integration of solar heat for an industrial process located in a topographically complex territory such as the Alps using the software Dymola – Dassault Systems®. The methodology proposed is structured in several steps: (I) industrial process characterization; (II) collection of local hourly data for radiation and climatic temperature; (III) study of the position of sun and components of incident angle; (IV) comparison among three solar technologies (CPC, LFR, PTC), in terms of efficiency, IAM and heat production; (V) focus on PTC: sizing of HTF, mass flow rate, HEX; (VI) focus on PTC: dynamic modeling with Dymola – Dassault Systems® (HTF temperature, solar heat, solar fraction); (VII) economic and environmental impact. In this paper, the case study of a pasta factory called “Felicetti”, located in the north-east of the Italian Alps, has been considered in order to investigate and evaluate the possibility of supplying solar heat for the drying process. The days of a week in June, exhibiting variable DNI, are used to demonstrate the dynamics and robust integration of the solar heat in the industrial process of pasta drying. The dynamic modelling results show that the PTC solar field can guarantee 23% of weekly energy coverage saving about 4.7 CO 2 / week . The economic analysis shows a pay-back time up to 9 years and a reduction of CO 2 emissions up to 99 t/year.

Shallow geothermal energy has the potential to play a crucial role in future renewable district heating and cooling networks. However, to size, model and design such systems, an accurate underground survey campaign is necessary, providing on-site geological, hydrogeological and thermophysical parameters. This is particularly true in geologically complex environments such as mountain ones. This paper presents a real case study located at the Madonna Bianca neighborhood in the city of Trento (North Italy, in an alpine valley), where a comprehensive geological survey campaign has been conducted by using traditional and innovative techniques, in order to size a low temperature district heating with integrated ground source heat pumps, also evaluating its thermal effects on the underground by using a 3D hydro-thermal finite element modeling (FEM). Relevant scientific novelty is included in the multi-scale and multi-method geological surveys, coupling: on-site coring, surface and downhole geophysics, laboratory petrophysical analyses, on-site thermal response tests (TRTs) by standard device and by novel hybrid optical fiber. The proposed framework is replicable and supports not only the correct plant dimensioning but also the evaluation of energy-efficiency and energy-sustainability over time.

Shallow geothermal energy has the potential to play a crucial role in future renewable district heating and cooling networks. However, to size, model and design such systems, an accurate underground survey campaign is necessary, providing on-site geological, hydrogeological and thermophysical parameters. This is particularly true in geologically complex environments such as mountain ones. This paper presents a real case study located at the Madonna Bianca neighborhood in the city of Trento (North Italy, in an alpine valley), where a comprehensive geological survey campaign has been conducted by using traditional and innovative techniques, in order to size a low temperature district heating with integrated ground source heat pumps, also evaluating its thermal effects on the underground by using a 3D hydro-thermal finite element modeling (FEM). Relevant scientific novelty is included in the multi-scale and multi-method geological surveys, coupling: on-site coring, surface and downhole geophysics, laboratory petrophysical analyses, on-site thermal response tests (TRTs) by standard device and by novel hybrid optical fiber. The proposed framework is replicable and supports not only the correct plant dimensioning but also the evaluation of energy-efficiency and energy-sustainability over time.

Volumetric absorbers constitute one of the key elements in order to achieve high thermal conversion efficiencies in concentrating solar power plants. Regardless of the working fluid or thermodynamic cycle employed, design trends towards higher absorber output temperatures are widespread, which lead to the general need of components of high solar absorptance, high conduction within the receiver material, high internal convection, low radiative and convective heat losses and high mechanical durability. In this context, the use of advanced manufacturing techniques, such as selective laser melting, has allowed for the fabrication of intricate geometries that are capable of fulfilling the previous requirements. This paper presents a parametric design and analysis of the optical performance of volumetric absorbers of variable porosity conducted by means of detailed numerical ray tracing simulations. Sections of variable macroscopic porosity along the absorber depth were constructed by the fractal growth of single-cell structures. Measures of performance analyzed include optical reflection losses from the absorber front and rear faces, penetration of radiation inside the absorber volume, and radiation absorption as a function of absorber depth. The effects of engineering design parameters such as absorber length and wall thickness, material reflectance and porosity distribution on the optical performance of absorbers are discussed, and general design guidelines are given.

Volumetric absorbers constitute one of the key elements in order to achieve high thermal conversion efficiencies in concentrating solar power plants. Regardless of the working fluid or thermodynamic cycle employed, design trends towards higher absorber output temperatures are widespread, which lead to the general need of components of high solar absorptance, high conduction within the receiver material, high internal convection, low radiative and convective heat losses and high mechanical durability. In this context, the use of advanced manufacturing techniques, such as selective laser melting, has allowed for the fabrication of intricate geometries that are capable of fulfilling the previous requirements. This paper presents a parametric design and analysis of the optical performance of volumetric absorbers of variable porosity conducted by means of detailed numerical ray tracing simulations. Sections of variable macroscopic porosity along the absorber depth were constructed by the fractal growth of single-cell structures. Measures of performance analyzed include optical reflection losses from the absorber front and rear faces, penetration of radiation inside the absorber volume, and radiation absorption as a function of absorber depth. The effects of engineering design parameters such as absorber length and wall thickness, material reflectance and porosity distribution on the optical performance of absorbers are discussed, and general design guidelines are given.

Abstract The development of additive manufacturing techniques is allowing for the design of highly customised components with enhanced functionality in many application sectors. This paper describes the full aerothermal assessment of four novel hierarchically-layered fractal-like volumetric absorbers, designed to be employed in high temperature concentrating solar power applications. Absorbers are built by the lateral repetition of elementary cells on a 2D plane, which are arranged into constituent layers and stacked up following fractal growth patterns. They have been manufactured in stainless steel by selective laser melting. By fine tuning both the geometry of elementary cells and their growth patterns, the absorber porosity distribution can be tailored on a per-layer basis. This leads to optimised aft-shifted radiation absorption profiles and allows for the introduction of intricate convective heat transfer augmentation features. Experimental temperature measurements are presented which demonstrate that these variable porosity absorbers are able to generate and exploit volumetric effects, an advancement with respect to both monolithic honeycombs and isotropic foams. Solar-to-thermal conversion efficiencies, however, are shown to be of the same order as in those other receiver geometries. It is argued that the main reasons for this lie in the use of stainless steel, a material of relatively high reflectivity, and the predominantly low convective heat transfer rates found in the laminar flows established in these components.

Abstract The development of additive manufacturing techniques is allowing for the design of highly customised components with enhanced functionality in many application sectors. This paper describes the full aerothermal assessment of four novel hierarchically-layered fractal-like volumetric absorbers, designed to be employed in high temperature concentrating solar power applications. Absorbers are built by the lateral repetition of elementary cells on a 2D plane, which are arranged into constituent layers and stacked up following fractal growth patterns. They have been manufactured in stainless steel by selective laser melting. By fine tuning both the geometry of elementary cells and their growth patterns, the absorber porosity distribution can be tailored on a per-layer basis. This leads to optimised aft-shifted radiation absorption profiles and allows for the introduction of intricate convective heat transfer augmentation features. Experimental temperature measurements are presented which demonstrate that these variable porosity absorbers are able to generate and exploit volumetric effects, an advancement with respect to both monolithic honeycombs and isotropic foams. Solar-to-thermal conversion efficiencies, however, are shown to be of the same order as in those other receiver geometries. It is argued that the main reasons for this lie in the use of stainless steel, a material of relatively high reflectivity, and the predominantly low convective heat transfer rates found in the laminar flows established in these components.

Graphical abstractDisplay Omitted HighlightsDomain knowledge related to energy systems is incorporated into the algorithms.The proposed technique provides better starting points for the optimization.The adopted state-of-the-art stopping criterion increases computational efficiency.The combined approach produces better energy systems in shorter time. Energy plays a key factor in the advancement of humanity. As energy demands are mostly met by fossil fuels, the world-wide consciousness grows about their negative impact on the environment. Therefore, it becomes necessary to design sustainable energy systems by introducing renewable energies. Because of the intermittent availability of different renewable resources, the designing of a sustainable energy system should find an optimal mix of different resources. However, the optimization of this combination has to deal with a number of possibly contradictory objectives.Multi-objective evolutionary algorithms (MOEA) are widely used to solve this kind of problems. As optimizing an energy system by using a MOEA is computationally costly, it is necessary to solve the problem efficiently. For this purpose, we propose the incorporation of domain knowledge related to energy systems into different phases (i.e., initialization and mutation) of a MOEA run. The proposed approaches are implemented for two widely used MOEAs and evaluated on the Danish Aalborg test problem. The experimental results show that each approach individually achieves significant improvements of the energy systems, which is expressed in better trade-off sets. Moreover, a state-of-the-art stopping criterion is adapted to detect the convergence in order to save computational resources. Finally, all proposed techniques are merged within two MOEAs with the result that our combined approaches yield significantly better results in less time than generic approaches.