# Solar Hybrid Micro Gas Turbine Based on Turbocharger
## 3 Results  
### Solar-Only MGT-T/C  
This configuration operates solely on solar energy. The compressed air is heated in the receiver by the solar power and then expands through the turbine. The achievable TIT depends solely on the available solar power. Furthermore, the receiver outlet temperature is limited to be equal to the TIT (specified in a particular design). When irradiance is so high that it could drive the receiver outlet temperature above the limit, then the outlet temperature is set to a value equal to the limit, by defocusing an appropriate number of mirrors in the heliostat field. Before presenting results of \begin{table}
\begin{tabular}{c c} \hline \hline
**Component** & **Value** \\ \hline Investment Cost & \\ \hline T/C [USD] & 2000 \\ Burner [USD] & 10,000 \\ Generator [USD] & 50,000 \\ Mirrors [USD/m\({}^{2}\)] & 200 \\ Tower/Receiver [USD/MWh] & 231,000 \\ \hline \multicolumn{3}{c}{Annual Operational Cost} \\ \hline T/C [USD] & 2\% of Inv. Cost \\ Burner [USD] & 2\% of Inv. Cost \\ Generator [USD] & 2\% of Inv. Cost \\ Mirrors [USD/m\({}^{2}\)] & 1.1 \\ Tower/Receiver [USD/MWh] & 11,400 \\ Tower/Receiver [USD/MWhth] & 0.68 \\ Fuel [USD/t] & 465 \\ CO\({}_{2}\) emissions [USD/t] & 5 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Economic data. T/C—turbocharger. performance calculations of this set up, it is useful to comment on some aspects of its operation and control. Considering the use of a variable speed generator and/or power electronics, variable shaft speed is allowable. When irradiation is such that TIT for a given mass flow rate is lower than the desired TIT, shaft speed is reduced, leading to lower mass flow and thus higher receiver temperature (TIT), given the available solar thermal power. The reduction of air mass flow and the augmentation of the TIT have opposing effects on the power output. In order to optimize the engine performance to produce the maximum possible power, the optimum speed value for different receiver thermal input values was determined, and thus the speed schedule was obtained and utilized in the presented work. The installation can be operational when the thermal input leads to turbine power higher than the one needed by the compressor. Thus, there is a minimum thermal input for sustainable operation, at which turbine and compressor powers are equal. For thermal inputs higher than this minimum, net output power is available for electricity generation. Furthermore, this minimum value depends on the ambient conditions. For example, increase of the ambient temperature leads to the augmentation of the minimum value because compressor power demand is increased. In order to determine when this configuration can be operational, the minimum thermal input value is computed considering different ambient conditions. These operation aspects are incorporated in a simulation model of the installation studied and different scenarios for design parameters are considered. The performance of the solar-only configuration is computed for the three values of TIT (400, 600 and 800 \({}^{\circ}\)C) for a different number of mirrors and is depicted in Figure 3 (for the case of TIT = 400 \({}^{\circ}\)C), in terms of produced energy over a year and LEC. For each TIT, yearly produced energy increases with the number of mirrors, while LEC becomes minimum for a particular number. Energy production for the three TITs are shown in Figure 4. For a given number of mirrors, energy output increases significantly as TIT increases. This is a direct consequence of the increase of thermal efficiency shown in Figure 2 and the higher receiver temperature limit, which permits the exploitation of a larger amount of the available solar energy. A given number of mirrors correspond to a certain amount of solar energy captured by the heliostat field. The higher the TIT, the higher the efficiency and the higher the exploitable amount of the solar energy.