# Concentrating Solar Collectors for a Trigeneration System--A Comparative Study
## 3 Results and Discussion  
### Daily Performance of the Examined Systems  
Firstly, the system performance with the three collectors during a summer day in June is presented. Figure 3 shows the daily variation of the incident angle modifier (IAM) for the three systems. The solar dish had the maximum value which was 100% due to the tracking system in the two-axis. PTC presented a higher incident angle modifier than the LFR during the day which was explained by the existence of two factors in the product of the incident angle modifier in the LFR. Only in the solar noon, the IAM of the PTC and LFR was approximately the same and close to 72%. \begin{table}
\begin{tabular}{c c} \hline
**Parameters** & **Values** \\ \hline Nominal solar direct beam irradiation & 700 W m\({}^{-2}\) \\ Nominal incident sun angle & 30\({}^{\circ}\) \\ Nominal level of the ambient temperature & 25 \({}^{\circ}\)C \\ Operating time during the year & 2500 h \\ Nominal electricity power & 7.72 kW \\ Nominal heating power & 20.14 kW \\ Nominal cooling power & 18.63 kW \\ \hline \end{tabular}
\end{table} 
Table 2: Data of the system in the nominal design point. Figure 3: Daily variation of the incident angle modifier for the three collectors in June. PTC: parabolic trough collector; LFR: Linear Fresnel reflector; DISH: Solar dish. \begin{table}
\begin{tabular}{c c} \hline
**Parameters** & **Values** \\ \hline Parabolic trough collector specific cost & 250 \(\upepsilon\) m\({}^{-2}\) \\ Linear Fresnel reflector specific cost & 200 \(\upepsilon\) m\({}^{-2}\) \\ Solar dish collector specific cost & 300 \(\upepsilon\) m\({}^{-2}\) \\ Organic Rankine cycle specific cost & 3000 \(\upepsilon\) kW\({}_{\mathrm{\mu}}\)\({}^{-1}\) \\ Storage tank specific cost & 1000 \(\upepsilon\) m\({}^{-3}\) \\ Absorption chiller specific cost & 1000 \(\upepsilon\) kW\({}_{\mathrm{cool}}\)\({}^{-1}\) \\ Cooling production cost & 0.067 \(\upepsilon\) kWh\({}^{-1}\) \\ Electricity production cost & 0.2 \(\upepsilon\) kWh\({}^{-1}\) \\ Heating production cost & 0.1 \(\upepsilon\) kWh\({}^{-1}\) \\ Cost for operation and maintenance & 1\% of the C\({}_{0}\) \\ \hline \end{tabular}
\end{table} 
Table 3: Economic input data of the present paper [36; 41]. Figure 4 exhibits the daily variation of the collector thermal efficiency. The LFR had the lowest thermal efficiency among the examined technologies. The PTC presented the highest efficiency in the morning and in the afternoon, while the dish was the most efficient system close to solar noon. Practically, close to solar noon, the tracking system of the parabolic trough collector was not able to eliminate the optical loss due to the solar altitude, something that was possible with the solar dish. The results of the incident angle modifier of Figure 3 validate the previous statement. Figure 5 shows the daily variation of the available solar irradiation on the collector aperture. The quantity took into consideration the unavoidable optical losses due to the non-ideal tracking for the PTC and the LFR. For the dish, the available solar irradiation was practically equal to the solar irradiation due to the two-axis tracking system. So, the highest available solar irradiation was found for the dish with the PTC and the LFR to follow, respectively. At solar noon, the PTC and LFR had the same available solar irradiation because the transversal incident solar angle was zero and so there were the same optical losses in both systems due to the solar position. Figure 6 illustrates the daily variation of the useful heat production. It was found that the LFR had the lowest heat production throughout the day, while the dish was the best case close to the solar noon. The PTC was the most efficient choice during the morning and afternoon hours. It is important to state that this figure gives similar results to Figure 4 because the useful heat production is dependent on the collector thermal efficiency. Figure 4: Daily variation of the collector thermal efficiency for the three collectors in June.