# A Complete and High-Resolution Estimate of Sardinia's Rootrop Photovoltaic Potential
## 3 Methodology
### Estimation of Economic Potential  
An initial estimation of the economic potential is obtained by calculating the levelized cost of electricity (LCOE), which expresses the ratio of the costs incurred for the installation of a photovoltaic system to the energy produced by the system itself over the period of operation. Therefore, it indicates how much it would cost to produce 1 kWh with a 1 kWp photovoltaic system. When the LCOE value is lower than the cost of a kWh purchased from the grid, the investment is remunerative. We calculated the LCOE coefficient as follows [36; 48]:  
\[\text{LCOE}=\frac{\text{CAPEX}+\sum_{n=1}^{N}(\text{OPEX}_{n}-\text{TD}_{n})(1+ r)^{-n}}{\sum_{n=1}^{N}E_{\text{kWp},n}^{Y}(1+r)^{-n}} \tag{14}\]  
\[E_{\text{kWp}}^{Y}=E_{\text{pv}}\cdot A/\eta_{n}=5.5\cdot E_{\text{pv}} \tag{15}\]  
where \(\text{CAPEX}=2000\,\text{\text{\text  
Figure 9b shows how much energy could be produced per resident per year after the installation of photovoltaic modules on suitable rooftops. Depending on the municipality in Sardinia, the technical potential varied from 215 to 265 kWh/m\({}^{2}\)/year, and from 10 to 60 MWh/individual/year. The per capita potential depends on two main factors: the presence of apartment buildings, which are widespread in larger cities, lowering the amount of rooftop area per individual; the presence of vacation houses in tourist areas, which are unused for most of the year, and whose owners are rarely among the residents, increasing the available surface per capita. Compared to the total value, which is strongly related to the extension of the municipality's territory and the number of residents, the photovoltaic potential expressed per m\({}^{2}\) is more indicative of the potential of each individual area. Figure 10a shows the annual average global horizontal irradiance per m\({}^{2}\), as estimated by PVGIS. The map is similar to Figure 4b, but instead of the 0.05\({}^{\circ}\) sectors determined by the PVGIS-SARAH2 database, the GHI values are distributed over the individual territories (from 1600 to close to 1800 kWh/m\({}^{2}\)/year) The reduction in irradiance on the rooftops due to the shading, inclination, and orientation of the panels leads to the map in Figure 10b, which shows the actual irradiance received per m\({}^{2}\) on the plane of the arrays. For some municipalities, the change is drastic, possibly justified by the fortunate exposure of most buildings to the sun. The towns that receive lower irradiance are either in mountainous locations (for which the average irradiance is lower than that for locations on the plains) or are located in deep valleys, situations that greatly reduce the irradiance received when the Sun is not yet high in the sky. The map of the photovoltaic potential in Figure 10c is qualitatively very similar to the previous one; in fact, the (small) differences between one municipality and another are explained by the equally small differences in temperature and wind speed. Lastly, Figure 10d depicts the average levelized cost of electricity in Sardinia for all municipalities ranging from 14 to 21 EuroCent per kWh. Should the cost of energy remain high as it has been, installing photovoltaic systems in the vast majority of the buildings might be worthwhile, and the energy surplus can be sold to other regions. Figure 9: (**a**) Total yearly photovoltaic potential and (**b**) average yearly photovoltaic potential per resident for the municipalities in Sardinia. The estimated annual photovoltaic potential for the island of Sardinia as a whole, equal to 22 TWh, is obtained by computing the energy production from photovoltaic modules distributed over a surface area larger than 92 km\({}^{2}\) (on a total rooftop area of almost 130 km\({}^{2}\)). This equates to an average annual production of 238.92 kWh per m\({}^{2}\), or 1314 kWh produced annually for each kWp installed, using the technology chosen as an example. Figure 11 shows the dependence of annual photovoltaic potential, per m\({}^{2}\), on rooftop orientation and tilt.