## 3 Results
### Smart Roof Solutions' Assessment
#### 3.2.3 Solar Energy Technology  
After the analysis of monthly and annual solar radiation on each rooftop (Figure 10), taking into account 570 heated, pitched buildings and roof surface with annual solar radiation higher than 1200 kWh/m\({}^{2}\)/year, the ST collectors and PV modules were dimensioned according to domestic hot water consumption and electrical consumption of residential and nonresidential users. According to the Italian Decree 28/2011, 50% of domestic hot water consumption of residential sector is covered by ST collectors. The percentage reaches 100% in June, while in the winter months (December and January) ST production is able to cover about 7% of the residential consumption (Figure 11a). In addition, there is a GHG emission reduction of 1958 ton/CO\({}_{2}\)/year. The requirements indicate that 50% of consumption must be covered; this dimensioning is appropriate, given that in July hot water can only be used to cover domestic hot water. Figure 9: Solar Reflectance Index (\(SRI\)) (%) values of existing roof at block-of-building scale: (**a**) Before (**b**) and after high-reflectance strategy. The PV panels can be dimensioned in two ways: By covering 100% of consumption in the month of maximum irradiation or by reaching 100% of annual self-consumption, taking into account that the overproduction in the summer months that is fed into the grid will be consumed in winter. In this work, the PV panels were dimensioned according to the National Decree 28/2011 using the footprint area of the buildings (\(A\)), where the installed power is equal to \(A\) divided by a \(K\) coefficient = 50 (Figure 11b). According to the installed power and the annual utilization hours of use (in the Piedmont region are 1130 h), the electricity produced from PV panels was compared to the electrical consumption. Therefore, knowing that a typical Turin family needs about 2000 kWhel/year for electricity supply and, in the district analyzed, the number of families is equal to 10,638 (ISTAT data, 2011), the 13% of the annual residential and nonresidential electrical consumption has been covered with a GHG emission reduction of 1853 ton/CO2/year. Considering only the residential sector, PV production covers the 18% of electricity consumption. In the summer months it covers 38% and in the winter months, 2-3%. Table 6 shows the total roof area, the quota well exposed with no disturbances (15-35%), the quota used for the ST collectors to satisfy the domestic hot water (DHW) consumptions, and the quota for the PV panels, as requested by the standards (1/50 kW/m\({}^{2}\)). Using the maximum energy potential that can be produced from PV panels with the left available roof area, it is possible to cover 82% of residential electrical consumption; with the reverse procedure, an optimal value of \(K\) of about 11 m\({}^{2}\)/kW was calculated. From this analysis, it emerged that to reach the 50% coverage of domestic hot water, heating, and cooling consumption, it is necessary to use not only solar technologies but also other renewable energy technologies, such as the energy taken from the cold source with heat pumps for heating or PV panels for cooling. In fact, in the city, there are few renewable energy sources available, but there are sources that can be exploited in public spaces, such as the PV panels on shelters, micro-power plants (of which in Turin city there are three) and mini-wind on commercial buildings, considering the acoustic impact. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Area**} & \multirow{2}{*}{**Roof**} & **Well Exposed with No** & **ST for** & **PV** & **PV** \\  & & **Disturbances (15–35\%)** & **DHW Energy-Use** & **1/50 kW/m\({}^{2}\)** & **max** \\ \hline m\({}^{2}\) & 172,749 & 101,048 & 4717 & 21,141 & 96,631 \\  & 100\% & 58\% & 2.7\% & 12.2\% & 55.8\% \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Roof area for solar energy production.