Articoli scientifici

The modernization, efficiency, and decarbonization of the energy supply systems are among the new challenges to be faced in the coming decades to achieve the targets and objectives dictated by European strategic policies. Despite the countless benefits related to renewable energy sources (RES) integration, this brings key challenges to the power system, such as the risk of imbalance between energy generation and demand, sudden changes in flows in transmission lines with a need for expensive and time-consuming upgrades, and the withdrawal of conventional generation systems with consequent demands for new solutions and innovation to support grid services. A potential solution to limit the huge intermittence and fluctuation in power generation from RES is Concentrated Solar Power (CSP) technology integrated with thermal energy storage. The aim of this paper is to discuss the potential benefits related to the use of CSP technology by presenting innovative industrial solutions developed in the Italian SOLARGRID Project, namely the hybridization of CSP–PV systems and the solar thermo-electric system developed by MAGALDI, the parabolic trough collector of Eni, and the new linear Fresnel reflector configuration of IDEA S.r.l. These plant and component solutions are developed for improving the technical performance of CSP technology and reducing the levelized cost of electricity, thereby fostering an effective and massive deployment and encouraging the creation of new business models.

In recent decades, the fight against climate change and the commitment to reduce greenhouse gases have shed a light on the production of energy from renewable sources, in particular those derived from solar energy. This has required the involvement of all stakeholders (producers, but also energy operators, authorities, distributors, and final consumers) which has led to the outline of a new scenario characterized by more efficient technologies, dedicated strategies and business models, and the research of alternatives solutions. Within solar technology, great attention has been given in recent years to concentrating solar power (CSP) technologies, both from research studies and technological development sides. This paper provides a theoretical framework based on a CSP literature review to define the state of the art and to identify research gaps and future research steps related to this technology. The work is based on an innovative bibliometric study to explore technical fields related to CSP, providing both a comprehensive framework with reference to the state of the art of the technology investigated, and a detailed analysis on CSP commercial applications, making the review a very useful tool for stakeholders and decision makers The results of the analysis: (1) help to clarify the technological advances of CSP, the strengths and weaknesses of the current technologies used (parabolic and tower systems are the most widespread), and indications of the prospects for dish systems; (2) identify an alternative to the economic problem that represents an obstacle to the diffusion of CSP, for example, by identifying the ability to couple it with thermal storage as a valid method to increase the flexibility of the system and reduce costs; (3) suggested hybrids, both with renewable and non-renewable technologies, identifying strengths and weaknesses for all the proposed proposals; (4) show that it is possible to identify new ongoing research such as that related to hydrogen production. This paper represents the first part of a larger research study developed within the SOLARGRID Project, which promotes and supports the development of innovative solutions for systems and components for CSP and concentrated photovoltaics (CPV) technologies, with the aim to enhance their energetic performances and economic competitiveness in applications for the distributed generation of both electric and thermal energy frameworks. The main findings of our study highlight that, though there is an increasing number of papers on the topic of CSP, several issues remain neglected.

The integration of a CSP tower system with a PV solar field, sharing a thermal energy storage, is modeled and discussed. The tower system uses a new-design solid particle fluidized bed receiver integrated with a thermal storage, where hot particles are directly collected to store daily energy for overnight production of electricity. The PV solar field is aimed to supply the daily energy demand; when there is a surplus of PV energy production, the electric energy is converted to heat and accumulated in the thermal storage too. The integration of the two energy systems is modeled, building efficiency functions for all the sub-components of the integrated plant (heliostat field, receiver, storage, power block, PV field). Yearly simulations are performed for two different locations, Spain and Australia, obtaining that a system with a peak power of 10 MWe CSP + 15 MWe PV can supply—with a limited curtailment—a fraction of more than 60% (respectively, 62% and 68%) of a realistic electric load with a peak demand around 10 MW, to be compared with the 45/47% of the same load obtained adopting a PV-only system with the same overall peak power. In the integrated system, PV directly supplies 40/41% of the load, the remaining 23/28% being produced by the power block (mainly fed by the CSP).

One of the main challenges facing the commercialization of parabolic solar systems is their high initial cost, which is not competitive with the low cost, ease of operation, and reliability of photovoltaic technology. However, one potential solution to maximize their energy producibility and improve their economic profitability is to hybridize the power conversion unit. By enabling reliable power generation and reducing reliance on the availability of solar thermal energy, hybridization can be a valid solution to improve the efficiency and practicality of parabolic dish solar systems. This study aims to assess the energy performance of two hybrid parabolic dish systems: the dish-Stirling system located at the University of Palermo, and the dish-Micro Gas Turbine system located at ENEA Casaccia. Different scenarios were examined by varying the installation site and operational strategy, as well as exploring hybridization solutions of the solar source with conventional fossil fuel or renewable ones. The findings suggest that hybridizing parabolic dish systems with conventional fuels or renewable energies greatly enhances their performance, increasing operational hours and maximizing energy producibility.

Concentrated Solar Power (CSP) plants use mirrors to reflect and concentrate sunlight onto a receiver, to heat a fluid and store thermal energy, at high temperature and energy density, to produce dispatchable heat and/or electricity. The secondary mirror is a critical component in the optical system of certain Solar Power Tower plants (SPT), as it redirects the concentrated sunlight from the primary mirror onto the receiver, which can be arranged at ground level. In this study, we propose a design optimisation for the secondary mirror of a CSP plant. The design optimisation method consists of two steps. The first step involves the use of the finite element simulation software Abaqus 2022 to analyse the structural performance of the secondary mirror under thermal loads and wind. The second step consists of the use of simulation results to identify the combination of design parameters and best performances, with respect to both design constraints and structural safety. This is carried out by developing an algorithm that selects those configurations which satisfy the constraints by using safety coefficients. The proposed optimisation method is applied to the design of a potential configuration of a secondary mirror for the beam-down of the CSP Magaldi STEM® technology, although the methodology can be extended to other components of CSP plants, such as primary mirrors and receivers, to further enhance the structural performance of these systems.

An attractive candidate to reduce dependence on fossil fuels and replace them by renewable sources is represented by concentrated solar power (CSP) technology, whose wide deployment is still hindered by its high investment costs. In CSP linear collector plants, a key component with high technological content may be identified in receiver tubes, that are traversed by heat transfer fluid and located on focal line on which solar radiation is concentrated by mirrors. The proposed work aims at developing spectrally selective coatings for receiver tubes able to overcome state-of-the-art technological limitation in terms of both vacuum encapsulation and maximum operative temperature, currently limited at 550°C for molten salts CSP plants. To this aim, a multilayer structure was designed and developed for coating a receiver tube to be employed in open-air environment at temperature of 600°C. The multilayer coating is based on tungsten chromium titanium infrared reflector and includes a solar absorber layer developed with two alternative methods of reactive sputtering and thermal oxidation respectively, finally covered by antireflective and barrier bi-layer of aluminum oxide and silica. Thermal stability was demonstrated of the new developed coatings, since only small variations were measured of the optical parameters after more than 2000 h of aging in open air conditions at temperature of 600°C (on average less than 5%), with final measured solar absorptance αs of 73% and 87% and thermal emissivity εth at 600°C of 18% and 27% for aged multilayer structures including the absorber layer obtained through thermal oxidation and sputtering process, respectively. These results pave the way for further improvement in terms of both optical performance and operative temperature increase, allowing to enhance efficiency and lower costs, thus contributing to ease to deployment of CSP technology.

In recent decades, European countries have adopted new “sustainable” development models, able to match the growing request of energy with social, economic, and environmental aspects. In this framework, the role of the Distribution System Operator (DSO) totally changes, with novel responsibilities with respect to the large-scale use of renewable energy sources (RESs) expected at the distribution level. The work investigates the management of conflicts between DSOs and microgrids (MGs), recognized in the literature as an important open research issue. The authors proposed a new procedure that aims to regulate the rate of energy flow provided by DSO to MGs, considering the different microgrid priorities as parameters able to influence the DSO's decisions. The strategy is based on a proportional fair allocation control adopted by DSO to balance its own technical and economic interests, with the need to guarantee the good operation of the grid, in presence of the new market actors. Although in literature it is possible to find similar decision support models, to the best of our knowledge, this paper is the first to apply this approach to the combined DSO/Microgrids scenario. The effectiveness of the proposed methodology is assessed through the analysis of a case study consisting of three MGs, grid-connected, which exchanged energy with the DSO and between them to guarantee their own internal energy balance.

Concentrated Solar Power plants are energy systems aimed at the production of electric and thermal energy. The Life Cycle Analysis of these energy systems is a trending topic in current research as many studies appeared in the scientific literature recently. However, the end of life of these plants is generally not deeply analyzed in those papers. Therefore, the focus of this work is the definition of several scenarios differing for the recycling level of various materials to provide a careful environmental evaluation of the end-of-life phase. The results show that, while Climate Change is slightly affected by the waste treatment scenario, other indicators such as Minerals and metals depletion can change drastically as a function of the recycling rates. Particularly, the recycling of silver turns out to be extremely important to mitigate the environmental burdens of the system.

Linear Fresnel collectors are good candidates to lower the use of fossil fuels in the built environment and in the industry, due to their compact nature and adaptability. In addition, the technology shows large margins for improvement, in terms of efficiency capital and operational expenditures. The present study presents a new atmospheric double tube absorber, which fully explores non-imaging optics design. An existing LFR system with a second stage concentrator consisting of an evacuated tube with an associated secondary parabolic reflector, is compared with a novel model adopting the same LFR primary field but a new second stage concentrator, which achieves a much wider acceptance angle. It is shown that, beyond a better performance, the novel proposed solution provides simpler maintenance, as in cleaning and parts’ replacement, and a reduced cost, as it includes cheaper standard components. The study was conducted in ray-tracing environment with the Tonatiuh++ software, which is able to directly implement non-imaging optics configurations via analytic equations. The present study is centred on the optical performance of the collector. The quantitative comparison demonstrates that the annual yield of the novel model is increased at least by 8.3% while the cost per metre of the receiver is decreased by 45%.

In this study, the energy scenario in China was analyzed by retracing the trend of exponential population growth, gross domestic product (GDP), and electricity production and consumption. A forecast up to 2050 was made based on the history and forecasts of other field studies. It was possible to deduce data on pollutants in terms of CO2 equivalent (CO2-eq) emitted over time if there were no changes in the way energy was produced. Moreover, different scenarios were hypothesized for the use of pumped hydroelectricity storage plants, namely 4.5%, 6%, 8%, 11%, and 14% (percentage of electricity compared to requirements in 2050), to balance variable renewable energy sources and avoid curtailment, thereby reducing the use of energy produced by coal-fired plants. For this implementation, direct and indirect costs and benefits were considered, with interesting results obtained from an economic standpoint and very positive results from environmental, social, and territorial perspectives.

In this work, tungsten nitrides sputtered at different powers supplied to a W target (300 W, 500W, 700 W) and proposed for solar thermal applications as part of solar absorbers, as active and robust materials for capacity energy storage and as plasma-facing materials were annealed in vacuum at medium-high temperatures (470 _C, 580 _C) and characterized by means of X-ray diffraction (XRD), AFM, micro-Raman, FTIR, UV–VIS—NIR, sheet, surficial energy and wetting angle measurements. From the overall set of analyses, some important modifications and differences between samples after annealing emerged (which will be useful for selecting them for specific applications) and have been correlated to sputtered W metallic clusters’ ability to adsorb, form complexes with and react with the strong N2 triple bond under the various plasma conditions of a reactive sputtering process. In particular, the 300 W film of poor crystalline quality as deposited, after annealing released entrapped nitrogen and retained its W2N structure up to a temperature of 580 _C. Despite there being no phase transition, there was an increase in sheet resistance, which is detrimental because the preservation of metallic character is an important requisite for the proposed applications. The 500Wfilm had a stable crystalline structure and a metallic character unmodified by increasing temperature. The 700W film, whose structure as deposited was almost amorphous, underwent the most severe modification after annealing: crystallizing, disproportioning and giving rise to a composite and porous nature (W + WNx) not ideal for spectrally selective coating applications, but useful for tailoring capacitive energy storage devices, or for catalysts for hydrogen evolution reactions (as an alternative to platinum) in alkaline water electrolysis.

The integration of renewable energy sources into the energy system requires both new investment in network infrastructures, and the introduction of new models of energy management.
In this framework, new structures of collaborations were born: the aggregator is one of them. It involves grouping different players of the power system, acting, however, as a single entity both when  it participates in the electricity markets and sells services to the operator. In this work, a new methodology to determine the optimal revenue of a Unità Virtuali Abilitate Miste (UVAM), which is an  Italian virtual energy unit managed by an aggregator, is proposed. The methodology is articulated in several steps, the core of which is represented by the two models: (1) a cost–benefit analysis  in order to identify the main costs/benefits that impact on the UVAM’ revenues; and (2) a decision-making model based on the sensitive analysis to capture the optimal interaction between users and aggregator. The results show how, on varying the parameter costs depending on the aggregator-users’ strategy, it is possible to obtain different optimal “working-points”. Finally, the analysis identifies two main cost factors that impact on the optimal revenue: the Energy Management Platform and the Communication costs, confirming the importance of these parameters in the general economy of UVAM.

The optimisation of the support structure of heliostats in concentrating solar power plants is a fundamental task aimed at attempting to reduce the high levelised cost of energy (LCOE) of current configurations. In this work, an integrated multi-objective optimisation framework is presented, which relies on the combination of a lean and fast structural model with a genetic algorithm to simultaneously minimise both the overall mass of the support structure and the mean angle of rotation of the mirror surface, which directly affects the optical efficiency of the component. A particular feature of the proposed framework is that it represents an integrated solution, i.e., it allows to simultaneously optimise the main components of the heliostat support structure, i.e., the pedestal, the truss and the back support structure, assuming they are off-the-shelf components easily available on the market. The optimisation problem is set up selecting as design variables (i) the number of elements in the back support structure and (ii) the relevant characteristics of all the components considered, i.e., section shape and dimensions, according to the components commercial datasheets. At each iteration of the optimisation process, the structural model is fed with the current design variables values and, according to some computed aerodynamic loads, it allows evaluating the displacement and rotation of the points of interest within the mirror surface. An aerodynamic model present in the literature based on experimental wind tunnel tests is used to estimate the wind forces acting on the heliostat as a function both of the mirror inclination angle with respect to the ground and of the wind direction with respect to the mirror orientation. In this work, the proposed methodology is demonstrated on a realistic case study and the results commented in detail, highlighting possible future developments and the limitations of the framework.

This paper is a review of the existing Life Cycle Assessment stu­dies of Concentrated Solar Power technologies that are available in literature. These systems are based on the reflection of solar rays on a relatively small surface to produce high temperature heat and high electric power rates. 25 papers, including reviews and research analyses, are summarized. The most relevant literature gap emerging from this review is the lack of inventory primary data, especially for some systems like Solar Dishes and Tower plan­ts. Extending the number of real-world installations analysed using a life cycle analysis would be very important to fill this gap. Moreover, a wider characterization in terms of environmental indicators adopted to describe the eco-profile of these technologies would be important. Indeed, Global Warming Potential is the most common impact category used to describe the results, but it does not account for issues like materials depletion.