## 4 Discussion  
### Recalculated Euro Efficiency from Measured Equatorial Data  
To determine whether \(\eta_{EURO}\) is suitable for an inverter installed in the Equatorial region, its value was recalculated using the irradiance profile of the region. The one year irradiance profile from the weather station was loaded into the PVAS and the output was used to drive the inverter. The module temperature (\(T_{m}\)) was held constant at 25 \({}^{\circ}\)C. By measuring the output power (\(P_{ac}\)) and input power (\(P_{dc}\)), the efficiency of the inverter (\(\eta_{meas}\)) was obtained. For the SB3000 HF inverter, since the number of logged data that it produced was 593 (this is not necessarily the same for all inverters), the number of \(P_{dc}\)/\(P_{dc\_rated}\) values and level of operation are the same. Correspondingly,  
\[\eta_{\rm WT}=\frac{1T_{1}}{T_{WT}}\eta_{1/593}+\frac{2T_{2}}{T_{WT}}\eta_{2/ 593}+\frac{3T_{3}}{T_{WT}}\eta_{3/593}+\ldots+\frac{593T_{593}}{T_{WT}}\eta_{59 3/593}. \tag{9}\]  
To emulate the original \(\eta_{EURO}\) equation, the \(P_{dc}\)/\(P_{dc\_rated}\) values were grouped into six levels of operation. Thus, the 593 logged data were grouped into six ranges [13]. Taking the SB3000 HF inverter as an example, these boundaries for the \(P_{dc}\)/\(P_{dc\_rated}\) are summarized in Table 2. The six level of operation were 5%, 10%, 20%, 30%, 50%, and 100%. Note that, the 5% level has \(P_{dc}\)/\(P_{dc\_rated}\) ranged from 0 to 7.5%; the 10% level has a \(P_{dc}\)/\(P_{dc\_rated}\) ranged from 7.5 to 15% and so on. These ranges were adopted \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Parameter** & **Unit** & **SB700 LF** & **SB3000 HF** & **K4200 TL** & **K7900 TL** \\ \hline \multirow{3}{*}{**Inverter Technology**} & \multicolumn{2}{c}{**Low**} & \multicolumn{2}{c}{**High**} & \multirow{3}{*}{**Transformerless**} & \multirow{3}{*}{**Transformerless**} \\  & & **Frequency** & & & \\  & **Transformer** & & & & \\ \hline Rated dc power (\(P_{dc\_rated}\)) & W & 780 & 3150 & 4200 & 7900 \\ Rated dc voltage & V & 250 & 700 & 800 & 800 \\ MPPT voltage range & V & 119–200 & 210–560 & 350–600 & 350–600 \\ Rated input current & A & 7.0 & 15.0 & 11.5 & 19.7 \\ Rated ac power & W & 700 & 3000 & 4000 & 6650 \\ Nominal ac voltage & V & 230 & 220–240 & 22–240 & 220–240 \\ Frequency & Hz & 50 & 50 H & 50 H & 50 \\ Maximum efficiency (\(\eta_{\rm max}\)) & \% & 93.0 & 96.3 & 96.5 & 96.7 \\ Euro efficiency (\(\eta_{EURO}\)) & \% & 92.0 & 95.4 & 95.9 & 96.2 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: The electrical properties of the tested PV inverters. Figure 8: Actual PV inverter test set-up. to be consistent with the original \(\eta_{EURO}\) formula. Similarly, the weightage for each corresponding level was adopted from the \(\eta_{EURO}\). They were 0.03, 0.06, 0.13, 0.10, 0.48, and 0.20, respectively. Furthermore, for every level of operation, an average conversion efficiency (\(\eta_{meas\_ave}\)) was computed. It was the average measured efficiency of each logged data in that particular range. The weighted efficiency was the sum of multiplication of the \(\eta_{mass\_ave}\) and weightage, as shown in Table 3. Hence, the general form of weighted efficiency for the six level of operation can be written as  
\[\eta_{\text{WT}}=\frac{1T_{1}}{T_{WT}}\eta_{1/6}+\frac{2T_{2}}{T_{WT}}\eta_{2/ 6}+\frac{3T_{3}}{T_{WT}}\eta_{3/6}+\ldots+\frac{6T_{6}}{T_{WT}}\eta_{6/6}. \tag{10}\]  
The \(\eta_{EURO\_real}\) was the recalculated \(\eta_{EURO}\) when the inverter was operated under the Equatorial condition. Since the (same) \(\eta_{EURO}\) weightage was used for \(\eta_{EURO\_real}\) computation, a certain amount of difference to the former was expected. From Table 4, it can be seen that the \(\eta_{EURO\_real}\) was lower (between 0.27% and 2.06%), depending on the inverter technology and size. This observation suggests that if an inverter with a \(\eta_{EURO}\) datasheet was operated in the Equatorial climate, its energy yield would be lower than the computed value (using \(\eta_{EURO}\)).