## 7 Key Performance Indices  
In this section, the economic and energetic feasibility of the proposed investment are justified with the calculation of specific Key Performance Indices (KPIs). Specifically:  
* Investment payback period: This index is calculated as the ratio of the total set-up cost of the overall proposed project (2,676,700 \(\upxi\)) over the expecting annual monetary saving (229,973 \(\upxi\)) (VAT is not included in either of \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Energy Resource**} & \multicolumn{2}{c}{**Existing Operation State**} & \multicolumn{2}{c}{**Proposed Operation State**} & \multicolumn{2}{c}{**Annual Monetary**} \\ \cline{2-6}  & **Quantity** & **Cost (\(\upxi\))** & **Quantity** & **Cost (\(\upxi\))** & **Saving (\(\upxi\))** \\ \hline Electricity (kWh) & 1,889,198 & 241,389 & 119,475 & 15,257 & 226,132 \\ Diesel oil (L) & 16,500 & 13,200 & 0 & 0 & 13,200 \\ Biomass (tn) & 0 & 0 & 31.197 & 9359 & \(-\)9359 \\ Totals: & 254,589 & & 88,396 & & 229,973 \\ \hline \hline \end{tabular}
\end{table} 
Table 10: Reduction on the energy resources annual procurement cost, due to the proposed energy upgrade measures. \begin{table}
\begin{tabular}{c c c} \hline \hline
**No** & **Cost Component** & **Subtotal (\(\upxi\))** \\ \hline
1 & Photovoltaic station & 750,000 \\
2 & Lighting system upgrade & 400,000 \\
3 & BEMS & 150,000 \\
4 & Biomass heater & 45,000 \\
5 & Solar collectors and thermal tanks & 200,000 \\
6 & Geothermal system & 600,000 \\
7 & Openings replacement & 120,000 \\  & Subtotal & 2,265,000 \\
8 & Contractor’s fee 18\% & 407,700 \\  & Total & 2,672,700 \\ \hline \hline \end{tabular}
\end{table} 
Table 9: Set-up cost comprehensive analysis of the overall examined project. the above amounts). The ratio of the above two amounts gives the payback period equal to 11.6 years. By assuming a discount rate of 3%, the discounted payback period is calculated at 15.5 years. * Annual primary energy saving percentage:  
The existing primary energy specific consumption equals to 429.54 kWh/m\({}^{2}\) of effective covered area. The new primary energy specific consumption equals to 74.51 kWh/m\({}^{2}\). The above values imply percentage reduction of the annual primary energy consumption equal to 82.65%. * R.E.S. penetration:  
The annual percentage penetration of the introduced R.E.S. technologies will be calculated on the common basis of the primary energy annual consumption and the primary energy annual production from the involved R.E.S. technologies in the proposed operation state. Primary energy production from R.E.S. technologies in the proposed operation comes from:  
* the annual electricity production of 932,711 kWh from the PV station, corresponding to 2,704,862 kWh of primary energy;
* the annual thermal energy production from 31.197 tn of biomass pellets, corresponding to 180,691 kWh of primary energy;
* the thermal energy production from the solar collectors. The primary energy that corresponds to the thermal energy produced by the solar collectors will be calculated on the basis of the avoided primary energy consumption for the same thermal energy production at the existing operation state. The solar collectors will substitute thermal energy production from diesel oil and electricity in the Stadium's existing operation. The scope of the analysis below is the primary energy estimation that corresponds to the consumed amounts of diesel oil and electricity for the production of the same thermal energy with the solar collectors' production in the proposed operation. Specifically:  
* The total final thermal energy consumption for the production of hot water was calculated 261,015 kWh (Section 4.2.1). The solar collectors' contribution to this thermal energy production was calculated at 169,700 kWh (Table 4, Section 4.2.3). * The annual diesel oil consumption (16,500 L) implies annual thermal energy production equal to 128,550 kWh, corresponding to 186,059 kWh of primary energy (Table 4, Section 4.2.3).