## 3 Results and Discussion  
The following diagram (Figure 2) shows the SGVTC useful heat power in the example of a 3 mm thick glass tube. The results are show depending on the operating conditions, i.e., indicators (Table 5): absorber temperature (V3), ambient temperature (V4) and wind speed (V5). Figure 2: Useful heat power of the SGVTC for different values of absorber temperature, ambient temperature and wind speed (the thickness of the GT is 3 mm). Regardless of the operating conditions, the SGVTC useful heat power is the highest (between 28.63 and 63.866 W) when the absorber is 150 mm wide (upper limit case). As its width decreases, its useful heat power also decreases, so it is the smallest (between 7.28 and 21.09 W) when \(L_{abs}\) = 50 mm (lower limit case). Wind speed, unlike the absorber width, negatively (but not to a greater extent) affects the performance of the analyzed SC. Therefore, the useful heat power curve for \(W\) = 1 m/s is above the useful heat power curve for \(W\) = 3 m/s, and therefore, the \(W\) = 3 m/s useful heat power curve is above the \(W\) = 5 m/s useful heat power curve (Figure 2). The absorber temperature also reduces power. For example, if \(t_{o}\) = 30 \({}^{\circ}\)C, \(L_{abs}\) = 125 mm and \(W\) = 3 m/s, \(Q_{heat}\), in that case, is as follows: 52.56 W (\(t_{abs}\) = 40 \({}^{\circ}\)C), 48.77 W (\(t_{abs}\) = 50 \({}^{\circ}\)C), 44.6 W (\(t_{abs}\) = 60 \({}^{\circ}\)C), 40.03 W (\(t_{abs}\) = 70 \({}^{\circ}\)C), 35.03 W (\(t_{abs}\) = 80 \({}^{\circ}\)C) and 29.58 W (\(t_{abs}\) = 90 \({}^{\circ}\)C). These effects can be mitigated with an increase in ambient air temperature. One more conclusion can be drawn by analyzing Figure 2--for the same temperature and width of the flat absorber plate, with an increase in the ambient temperature, the SGVTC useful heat power increases (example for \(L_{abs}\) = 125 mm and \(t_{abs}\) = 60 \({}^{\circ}\)C): 38.48 W (\(t_{o}\) = 10 \({}^{\circ}\)C), 41.40 W (\(t_{o}\) = 20 \({}^{\circ}\)C), 44.60 W (\(t_{o}\) = 30 \({}^{\circ}\)C), 48.09 W (\(t_{o}\) = 40 \({}^{\circ}\)C). These effects can be explained by the temperature driving force, which depends on the difference \(t_{abs}\)-\(t_{o}\). Namely, with the increase in the temperature difference \(t_{abs}\)-\(t_{o}\), the heat loss in the SGVTC also increases so that the useful heat power decreases. As soon as this difference decreases (between \(t_{ab}\) and \(t_{o}\)), the heat loss decreases and thermal power increases. If the thickness of the glass tubes is increased from 3 to 4 mm, the useful heat power would be reduced between 0.47% (for \(L_{abs}\) = 150) mm and 0.56% (for \(L_{abs}\) = 50 mm). By increasing the thickness of the glass by another 1 mm, i.e., 5 mm, the reduction in useful heat power would be between 0.94% (for \(L_{abs}\) = 150) mm and 1.12% (for \(L_{abs}\) = 50 mm). Analogous to Figure 2, Figure 3 shows the thermal efficiency of SGWTC for the same indicators. The thermal efficiency is highest and lowest in the following two cases (for \(d_{gt}\) = 3 mm): \(\eta\) = 0.68 (\(L_{abs}\) = 150 mm, \(t_{abs}\) = 20 \({}^{\circ}\)C, \(t_{o}\) = 10 \({}^{\circ}\)C and \(W\) = 1 m/s) and \(\eta\) = 0.226 (\(L_{abs}\) = 50 mm, \(t_{abs}\) = 90 \({}^{\circ}\)C, \(t_{o}\) = 10 \({}^{\circ}\)C and \(W\) = 5 m/s). For \(d_{gt}\) = 4 mm (\(\eta_{max}\) = 0.677  
Figure 3: Thermal efficiency of the SGVTC for different values of absorber temperature, ambient temperature and wind speed (the thickness of the GT is 3 mm). and \(d_{gt}\) = 5 mm (\(\eta_{max}\) = 0.675 and \(\eta_{min}\) = 0.221), the results are achieved for the same geometric-operational criteria as in the case of a glass thickness of 3 mm. By comparing the different dimensions of \(L_{abs}\) with each other, the largest gradient of change (for \(\eta\) value) is characteristic for \(L_{abs}\) = 50 mm, while the smallest gradient of change (the gentlest slope of the thermal efficiency curve) is characteristic for \(L_{abs}\) = 150 mm.