## 4 Results
### Extended Concept  
The extended concept pointed out in Figure 1 provides an additional electrical heating in the low- or in the high- pressure stages, as well as depending, proportionally, on both pressure stages. To identify suitable configurations with low losses in round trip efficiency and high potentials in component \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \(\eta_{0}\) & (\(\overset{\mathcal{Q}}{\boldsymbol{\uptau}}\))\({}_{\boldsymbol{LP-TES,0}}\) & (\(\overset{\mathcal{Q}}{\boldsymbol{\uptau}}\))\({}_{\boldsymbol{HP-TES,0}}\) & \(k\)O\({}_{\text{TES-HTX,0}}\) & \(m_{F,0}\) & \(\Sigma\)P\({}_{\text{Compressor,0}}\) \\ \hline
73.7 [\%] & 66.2 [kWh/m\({}^{3}\)] & 63 [kWh/m\({}^{3}\)] & 3100 [kW/K] & 3450 [t] & 88.2 [MW] \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Central results for the reference concept based on thermal storage efficiencies of 90% with a pressure level in the first stage of \(\text{p}_{\text{LP}}\) = 8.1 bar during compression. Figure 3: Total round trip efficiency and thermal storage density in relation to thermal storage efficiencies. size reduction, simulation studies are performed related to the pressure in the first stage (p\({}_{\rm LP}\)) and the heating power and its distribution (x\({}_{\rm LP,P2H}\)) in the LP and HP ranges, respectively. Here, the LP pressure variations are limited by the maximum compressor outlet temperatures of 350 \({}^{\circ}\)C for both stages, leading to LP compression pressures between 5.3 bar and 12.4 bar and pressure ratios \(\pi\) between 0.7 and 1.5 bar compared to an equal pressure ratio in all stages of p\({}_{\rm LP}\) = 8.1 bar. Additionally, inside the simulation studies with varying electric heating powers, the maximum operational temperature for the HP-TES liquid storage medium of 400 \({}^{\circ}\)C is considered. Due to highly linear behaviors with increasing electrical heating power, P2H-specific results are illustrated. These results--representing the effect of decreasing total round trip efficiencies and the potentials of cost reduction through lower component sizes--are compared directly with those of the reference case (index 0) without an additional electrical heating. Therefore, three potential heating power locations are investigated: the first, with uniform power distribution in both pressure stages (x\({}_{\rm LP,P2H}\) = 50%), the second, only in the low-pressure (x\({}_{\rm LP,P2H}\) = 100%) stage, and the third, only in the high-pressure stage (x\({}_{\rm LP,P2H}\) = 0%). Firstly, the influence on total round trip efficiency is shown in Figure 4 related to the pressure level in the first stage (p\({}_{\rm LP}\)). As illustrated by the thick line representing the reference case without an additional electrical heating, a nearly constant total round trip efficiency of 73.7% is visible, and only negligible effects are observed with varying low pressures. Those effects results from temperature- and pressure-dependent material properties in combination with heat losses inside the safety coolers. Considering the influence of the investigated electrical heat locations, significant effects with varying low pressures are obviously. The results show the lowest reductions in specific total round trip efficiency of \(-\)0.34%/MW\({}_{\rm P2H}\) for the integration location only in the high-pressure stage (x\({}_{\rm LP,P2H}\) = 0%) at low pressures of 5.3 bar and with an opposed behavior of the integration location only in the low-pressure stage (x\({}_{\rm LP,P2H}\) = 100%) at high pressures of 12.4 bar. These characteristics are based on increasing pressure spreads inside the HP and LP turbine during the discharging period, respectively, resulting in a higher exergetic utilization of the electrical heat. In contrast, a different behavior is visible for the integration option in both pressure stages with uniform power distribution (x\({}_{\rm LP,P2H}\) = 50%).