# Cost-Benefit Analysis of Small-Scale Rooftop PV Systems: The Case of Dragotin, Croatia
## 3 Results and Discussion  
The average daily data of insolation and electricity production were calculated for each month of the year using Solargis Prospect [24]. Global tilted irradiation is 1549 kWh/m\({}^{2}\) per year and total photovoltaic power output is 4559 kWh per year. Average load values are approximately the same for each month due to routine household activities that are the same almost every day. Even differences in electricity consumption on Sundays and other days of the week can be ignored. Only in September, there are additional seasonal activities that affect electricity consumption and that are taken into account. Figure 9 and Table 6 show the production and load at the average daily level for January for 24 h.  
Analogously, data can be obtained on an average daily basis for all 12 months of the year. Below are graphical representations of data for the months of July and the month of September (Figures 10 and 11) as characteristic months. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Time** & **Production Wh** & **Load** & **From Grid** & **Injection to** \\
**h** & & **Wh** & **Wh** & **Grid Wh** \\ \hline  
Total & 5856.26 & 10,947.14 & 6271.39 & 1180.51 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Energy production and load at the average daily level for January. Figure 9: Load and energy production at the average daily level for January. Based on the calculated data for all months of the year and taking into account the duration of the higher and lower tariff, summary data can be obtained for all months (Table 7) and the whole year (Table 8). Electricity meters register energy delivered to the grid and energy taken from the grid. The amount of electricity taken from the grid or delivered to the grid is calculated for each hour as the difference between load and electricity production. The values of daily energy generated by photovoltaic installation, daily energy imported and exported to the network (assuming current net metering), self-sufficiency (SS), and own consumption (SC) can be defined using Table 7 and Figure 7. \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline \multirow{2}{*}{**Month**} & \multirow{2}{*}{**Load kWh**} & \multirow{2}{*}{**Production**} & \multicolumn{3}{c}{**From Grid kWh**} & \multirow{2}{*}{**To Grid**} & \multirow{2}{*}{**Consumption**} & \multirow{2}{*}{**SC \%**} & \multirow{2}{*}{**SS \%**} \\  & & \multicolumn{2}{c}{**kWh**} & & **Higher** & **Lower** & & & **kWh** \\  & & & **Tariff** & **Tariff** & & & & **from PV kWh** \\ \hline January & 339.36 & 181.54 & 159.71 & 34.70 & 36.60 & 144.95 & 79.8 & 42.7 \\ February & 306.52 & 239.36 & 111.04 & 31.34 & 75.23 & 164.14 & 68.6 & 53.5 \\ March & 339.36 & 392.85 & 69.68 & 34.67 & 157.84 & 235.01 & 59.8 & 69.3 \\ April & 328.41 & 459.29 & 36.88 & 32.12 & 199.87 & 259.42 & 56.5 & 79.0 \\ May & 339.36 & 512.62 & 34.79 & 22.49 & 230.53 & 282.09 & 55.0 & 83.1 \\ June & 328.41 & 520.16 & 28.42 & 20.36 & 240.53 & 279.63 & 53.8 & 85.1 \\ July & 339.36 & 548.42 & 28.48 & 22.40 & 259.94 & 288.48 & 52.6 & 85.0 \\ August & 339.36 & 540.11 & 33.51 & 25.67 & 259.93 & 280.18 & 51.9 & 82.6 \\ September & 544.41 & 417.55 & 128.15 & 115.69 & 116.98 & 300.57 & 72.0 & 55.2 \\ October & 339.36 & 359.30 & 86.56 & 32.03 & 138.54 & 220.77 & 61.4 & 65.1 \\ November & 328.41 & 224.57 & 130.64 & 33.58 & 60.38 & 164.20 & 73.1 & 50.0 \\ December & 339.36 & 163.32 & 169.30 & 34.70 & 27.96 & 135.36 & 82.9 & 39.9 \\ Total & 4211.70 & 4559.11 & 1017.16 & 439.75 & 1804.32 & 2754.79 & 60.4 & 65.4 \\ \hline \hline \end{tabular}
\end{table} 
Table 7: Average monthly values of energy. Figure 11: Load and energy production at the average daily level for September. Figure 10: Load and energy production at the average daily level for July. The traditional definition of self-consumption says that photovoltaic energy is consumed instantly or within 15 min.