Titolo della tesi: The reversible solid oxide cell technology application to the building sector
The energy transition can be achieved recurring to different set of technologies. When it comes to buildings, and especially residential buildings, independently of the possible installable solutions, the objectives are always the same two: energy efficiency and clean energy sources.
This was firmly stated at different times by the European Union initiatives as the concrete direction to be undertaken to achieve a more sustainable future for everyone. In the last years, besides those two concepts, it has been seen recognised hydrogen ascent, with its multiple applications, even in the building sector energy systems.
In this context, it is paramount to combine those three pillars, and from these assumptions this PhD thesis stems.
The first step of the thesis consisted of a detailed review of the current literature, namely the following review was developed:
• Hydrogen can be used to manage intermittent Renewable Energy Sources (RES), especially in systems with high-RES share which are expected to be installed in future buildings. The transition toward smart energy architectures calls for mature, low-cost, low-space solutions bringing attention to unitized items such as the reversible Solid Oxide Cell (rSOC). This device, made of a single unit, can work as a Solid Oxide EleCtrolyzer (SOEC)and as Solid Oxide Fuel Cell (SOFC). with high efficiency, fuel flexibility and producing combined heat. The objective of this chapter is to identify and classify rSOC applications to the building sector as an effective operational solution and to show how much this technology is near to its commercial deployment. Research & Development projects were analysed and discussed for a comprehensive overview of the topic and the foreseen technological advances for the actual integration of the energy systems. Conclusions show an increasing interest in the reversible technology, although it is still at pre industrialisation stage with few real applications in the building sector, of which, the majority is reported, commented on, and compared for the first time
Then, after having identified the current gaps in the literature, specific energy models developed by the candidate to be able to reconstruct building hourly load shapes are presented:
• Hourly energy consumption profiles are of primary interest for measures to apply to the dynamics of the energy system. Indeed, during the planning phase, the required data availability and their quality are essential for a successful scenario projection. As a matter of fact, the resolution of available data is not the requested one, especially in the field of their hourly distribution when the objective function is the production-demand matching for effective renewables integration. To fill this gap, there are several data analysis techniques but most of them require strong statistical skills and the proper size of the original database. Referring to the built environment data, the monthly energy bills are the most common and easy-to-find source of data. The model calibration is carried out together with a sensitivity analysis of on-site solar electricity production. The method gives a predicted result with an average 25% MAPE and a 32% cvRMSE during one year of hourly profile reconstruction when compared with the measured data given by the Distributor System Operator (DSO).
• The problem of accurately representing dynamic behaviour (e.g. electric load profiles) while retaining simple and easy-to-use modelling approaches (i.e. supporting a "human in the loop" approach to data-driven methodologies) is a challenging task, especially when operating conditions are very variable. For these reasons, we used an interpretable (regression-based) technique called Time Of Week Temperature (TOWT) to predict the dynamic electric load profiles before, during, and after the COVID lockdown (for nearly 4 years) of a public office building in Southern Italy, the Procida City Hall. TWOT models perform reasonably well in most conditions, and their application allowed for the detection of changes in energy demand patterns, critical aspects to consider when tuning them, and areas for improvement in the algorithmic formulation and data visualisation, which will be the focus of future research.
Being able to reconstruct building load profiles, it is now possible to model the rSOC characteristics and to appreciate its functioning in real simulated conditions. In doing so, as the first step, the rSOC is simulated in an archetype building, which will be located in different Italian clime zones, to understand how much the external temperatures and solar irradiations can affect the overall results. This specific work is done also considering the latest events that are happening in Ukraine, which are endangering Italian gas supplies.
• The Italian energy system depends mostly on imported fossil fuels, and the actual geopolitics scenario can challenge the once well-established import routes. Nonetheless, renewable energies are mature enough to sustain a transition, enhancing local independence from external resources and decarbonization. Combined with Renewable energy penetration, hydrogen is gaining momentum as a multipurpose energy vector. The Solid Oxide technology, thanks to its reversibility can be seen as a solution to be adopted in this energy transition. Additionally, this research shows how the different climate conditions affect the outputs of the same technology, with a result variation recorded in the order of 4% in closer regions and above 10% from northern to southern conditions considering the selected KPIs: hydrogen production, consumption, and excess, avoided gas and electricity demand, avoided emissions and Self Sufficiency Rate.
In the second step, the attention will be shifted from archetypes to existing buildings, hence the location where a real rSOC will be installed following the activities of the GIFT project (Horizon2020, Geographical Island Flexibility G.A. 824410). In the second step, on different buildings able to host the rSOC is performed a sensibility analysis in terms of energy load shape, storage availability, and renewable production.
• The renewable energy source (RES) penetration in end-use must be strengthened to reach the prefixed decarbonization targets. A penetration obstacle is represented by the Power Grid, designed with an architecture disinclined to RES unpredictability. Nowadays, different solutions are available to integrate these latter issues without affecting the Grid, among these, the reversible Solid Oxide Cell (rSOC) promises high efficiencies and the possibility to control energy fluxes in both production and storage. Not only the technical characteristics are important to decide the energy solution to be adopted, but also studying the building behaviour is fundamental. The simulation results show the rSOC capacity to integrate RES increased from 40% to 62% just according to the different storage capacity and the building’s hourly load curves and seasonal consumptions.
Finally, the attention will be focused on the techno-economical study, done in collaboration with Sylfen, partner in GIFT and rSOC manufacturer, to analyse the rSOC impacts in a building from an environmental, economic and Power grid point of view. In this case, the rSOC functioning will be simulated coupled with a battery storage system, creating the so-called Smart Energy Hub, which is the solution which will be soon commercialised by Sylfen:
• In this study, the deployment of a real reversible Solid Oxide Cell was simulated in different scenarios considering the data recorded in one year in the island of Procida, Italy. Up to date, the use of this technology was mostly relegated to the industrial sector or to prototype tests. While, this research aimed to analyse the functioning of near commercialization technology in civil environments such as hotels, offices and hospitals to understand its feasibility in this new context. It wants to be proved that the advantages of this emerging technology can be exploited as well in the civil environment. Three economic indicators, i.e. Payback Period, Internal Return Rate and Net Present Value were selected to evaluate the simulated scenarios, while, the primary energy saving, the emission reduction and its storage efficacy were studied to evaluate the environmental achievements. To perform the simulations, the MATLAB model ConfigDym built by Sylfen was used. Finally, a sensitivity analysis in terms of economics was carried out. The results show an important decrease in emissions and an energy self-sufficiency increase of at least 29% and 58% respectively, differently the economic analysis returns a payback period currently near to its lifetime, while for the future a three years period is reachable.
Hence, the thesis proves the rSOC potential in the building sector with a literature analysis, and by demonstrating it via case study analysis by means of different models and software. It identified the current gap in the literature and filled part of it with ad-hoc research.