## 2 Materials and Methods
### PV Plant  
The design of a PV plant is site-dependent. Numerous factors including site location, spatial constraints, grid connectivity, energy demand, and the availability of solar energy are crucial considerations. Hence, the available area for the installation of photovoltaic panels was identified on the suspended roof of the Olympic Stadium in Rome. The roof structure of the stadium was realized between 1988 and 1990 in view of the 1990 FIFA World Cup. This roof stands as a pioneering example of a spoke wheel roof structural system [36]. The cable roofing system primarily comprises a radial distribution of cable trusses, a polycentric inner tension cable ring, and an outer anchorage system consisting of a space-framed, reticular, polycentric ring [36]. The total surface area of the suspended roof is equal to 42,000 m\({}^{2}\), while the available horizontal area for the installation of photovoltaic modules diminishes to 23,016 m\({}^{2}\).  
The simulated plant is composed of polycrystalline silicon PV modules. The tilt and azimuth parameters are constrained by the geometry and the orientation of the building. Each PV module within every physical segment is inclined at an angle of 5\({}^{\circ}\) to align with the suspended roof's inclination (Figure 4).  
Figure 4: Design of the photovoltaic plant integrated into the roofing.  
The solar panels are supported by spiraled steel girders and cover every inch of the roof. The entire roof is divided into eight zones based on different exposures to north (N), east (E), south (S), west (W), northeast (NE), southeast (SE), southwest (SW), and northwest (NW) (Figure 5).  
Table 1 reports the estimated PV module area for the eight sectors depending on sun exposure. An average efficiency of a typical PV module of 20% is used, and the overall system loss is quantified at 14.08%. The value of the DC-to-AC ratio input is 1.1. The annual AC degradation rate is equal to 0.5%. The rated capacity of the solar energy system, expressed in kilowatts-peak (kWp), signifies the maximum power it can generate under standard test conditions [37]. This capacity has been calculated on the SAM PV Watts-Battery tool for integrated systems using the following equation:  
\[\text{Rated Capacity (kWp) = Energy System Efficiency \(\times\) Solar Irradiance \(\times\) Total PV Area Installed} \tag{1}\]  
The PV plant yields a total peak power of 4432 kW. We simulated a ground-breaking battery energy storage system (BESS) connected to the PV plant. The BESS was sized based on the criterion that its energy capacity should adequately cover the light load during a football match ([PERSON] et al., 2021) [38]. To do that, we analyzed a battery energy storage system similar to JC ArenA in Amsterdam [24]. The BESS had a capacity of 2.8 MWh and a power of 3 MW, and it was made from 2 nd-life electric car batteries. When its rated capacity falls below 80%, its performance diminishes to a level insufficient for powering a vehicle. Reuse can provide the most value in markets where there is battery demand for stationary  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Sector Exposure** & **Surface (m2)** & **Power (kWp)** \\ \hline North & 2440.408 & 470.21 \\ Northeast & 1956.269 & 376.92 \\ East & 4902.105 & 944.52 \\ Southeast & 2097.41 & 404.12 \\ South & 2791.29 & 537.82 \\ Southwest & 2052.466 & 394.46 \\ West & 5259.295 & 1012.35 \\ Northeast & 1517.074 & 292.30 \\ \hline Total & 23,016.32 & 4432.67 \\ \hline \hline \end{tabular}
\end{table}
Table 1: PV plant sectors surface according to the exposure.  
Figure 5: Google Earth image of stadium showing proposed layout of PV plant.  
energy storage applications, as in this case study [38]. The PV system can export surplus energy to the utility grid, thereby prompting the design of a grid-connected system.