# A Solar-Thermal-Assisted Adiabatic Compressed Air Energy Storage System and Its Efficiency Analysis
## 4 Results and Discussion
### Typical Operational Conditions
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Parameters** & **Units** & **Values** \\ \hline Ambient pressure & MPa & 0.1 \\ Ambient temperature & \({}^{\circ}\)C & 20 \\ Compression stage & / & 4 \\ Expansion stage & / & 3 \\ Compressor exhaust pressure & MPa & 10 \\ Inlet pressure of air turbine & MPa & 6.9 \\ Inlet temperature of air turbine & \({}^{\circ}\)C & 280 \\ \(\tau_{\text{ch}}\) & h & 4 \\ \(\tau_{\text{dch}}\) & h & 4 \\ Mass flow rate of air-fluid & kg/s & 0.56 \\ Mass flow rate of VP-1 to PTC & kg/s & 0.54 \\ Temperature of hot water & \({}^{\circ}\)C & 80 \\ Temperature of return water & \({}^{\circ}\)C & 30 \\ Adiabatic efficiency of air compressor & \% & 90 \\ Adiabatic efficiency of air turbine & \% & 85 \\ Inlet temperature of cooling water & \({}^{\circ}\)C & 20 \\ Volume of stored air tank & m\({}^{3}\) & 3000 \\ Range of temperature with hot oil tank & \({}^{\circ}\)C & 300-305 \\ Direct normal irradiance & W/m\({}^{2}\) & 841.1 \\ Solar heat storage duration & h & 6 \\ Hot water supplying duration & h & 8 \\ Efficiency of heat collection & \% & 68.18 \\ Solar hours/day & h & 12/173 (22 June) \\ Total effective aperture & m\({}^{2}\) & 99.7 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Basic design parameters of ST-CAES system. To assess the performance of each subsystem, the exergy efficiency, and destruction were calculated from Equations (26) and (27) and Table 2. Figure 3 shows the exergy efficiency of each subsystem. The exergy efficiencies of the STC subsystem were much lower than those of the other subsystems except HEX of TUR, because of the basic STC characteristics. In the STC, absorption energy of the heat medium is supplied by stored Therminol VP-1 in the HOT hot oil tank, and this is greatly affected by the area of mirrors field, mass flow, weather, optical efficiency, and tracking accuracy of PTC [32]. Further, the HEX of TUR enthalpy efficiency is the lowest, due to the high temperature difference between the cold and hot fluids in the discharging process. \begin{table}
\begin{tabular}{c c c c c c c} \hline
**Stream** & **T** (\({}^{\circ}\)**C) & **P (MPa)** & **h (kJ/kg)** & **s (kJ/kg-K)** & **Ex (kJ/kg)** & **m (kg/s)** \\ \hline O1 & 115 & 0.1 & 13.77 & \(-\)2.72 & 14.53 & 0.54 \\ O2 & 115.2 & 0.4 & 14.30 & \(-\)2.72 & 14.90 & 0.54 \\ O3 & 305 & 0.1 & 633.92 & \(-\)1.48 & 273.06 & 0.54 \\ O4 & 300 & 0.2 & 346.60 & \(-\)2.03 & 144.64 & 0.76 \\ O5 & 300 & 0.1 & 624.90 & \(-\)1.50 & 268.91 & 0.76 \\ O6 & 300 & 0.1 & 624.90 & \(-\)1.50 & 268.91 & 0.26 \\ O7 & 102.8 & 0.1 & \(-\)3.36 & \(-\)2.76 & 10.54 & 0.26 \\ O8 & 300 & 0.1 & 624.90 & \(-\)1.50 & 268.91 & 0.25 \\ O9 & 134.3 & 0.1 & 42.11 & \(-\)2.65 & 21.99 & 0.25 \\ O10 & 300 & 0.1 & 624.90 & \(-\)1.50 & 268.91 & 0.25 \\ O11 & 135 & 0.1 & 43.16 & \(-\)2.64 & 22.22 & 0.25 \\ O12 & 123.8 & 0.1 & 26.50 & \(-\)2.69 & 17.87 & 0.76 \\ WA1 & 20 & 0.1 & 84.01 & 0.30 & 0.00 & 0.24 \\ WA2 & 80 & 0.1 & 335.06 & 1.08 & 22.66 & 0.24 \\ WA3 & 20 & 0.1 & 84.01 & 0.30 & 0.00 & 0.31 \\ WA4 & 80 & 0.1 & 335.06 & 1.08 & 22.66 & 0.31 \\ WA5 & 20 & 0.1 & 84.01 & 0.30 & 0.00 & 0.32 \\ WA6 & 80 & 0.1 & 335.06 & 1.08 & 22.66 & 0.32 \\ WA7 & 20 & 0.1 & 84.01 & 0.30 & 0.00 & 0.49 \\ WA8 & 80 & 0.1 & 335.06 & 1.08 & 22.66 & 0.49 \\ WA9 & 80 & 0.1 & 335.06 & 1.08 & 22.66 & 1.36 \\ WA10 & 20 & 0.1 & 84.01 & 0.30 & 0.00 & 1.36 \\ WA11 & 80 & 0.2 & 335.13 & 1.08 & 22.76 & 0.66 \\ WA12 & 30 & 0.2 & 125.91 & 0.434 & 0.27 & 0.66 \\ \hline \end{tabular}
\end{table} 
Table 6: Thermodynamic parameters of water and Therminol VP-1 stream.