## 2 Review of PV Inverter Efficiency
### Types of Inverter Weighted Efficiency
If the world map of Koppen-Geiger Climatic Classification System (KGCCS) shown in Figure 3 is referred to, Izmir and Sacramento (where the data for \(\eta_{CEC}\) is collected) actually share the same climatic condition. It is labeled as \"Csa\", which is characterized by a mild temperate climate as well as a dry and hot summer [18]. \[\eta_{IZM}=0.04\cdot\eta_{10\%}+0.12\cdot\eta_{30\%}+0.21\cdot\eta_{50\%}+0. 53\cdot\eta_{70\%} \tag{6}\]  
The first localized weighted inverter efficiency from India is the Chennai Efficiency (\(\eta_{CHE}\)) [19]. Chennai is a city located in the Southeast of India. Under the KGCCS, the climate is marked as \"Aw: tropical, with dry winter\". The \(\eta_{CHE}\) was based on the data gathered in 2010-2013 of a working 155 kW PV system. However, these procedures did not comply with the IEC 61683 [6; 7; 8], in which the efficiency must be derived using the PV array simulator that is fed by the local irradiance profile at a fixed temperature of 25 \({}^{\circ}\)C. In this case, both of the irradiance and temperature varies. Furthermore, the irradiance was measured horizontally (not in-plane), which did not comply with IEC 61724 [20; 21]. The developed equation for \(\eta_{CHE}\) is  
\[\eta_{CHE}=0.03\cdot\eta_{10\%}+0.08\cdot\eta_{20\%}+0.22\cdot\eta_{40\%}+0. 21\cdot\eta_{65\%}+0.24\cdot\eta_{80\%}+0.17\cdot\eta_{95\%}+0.05\cdot\eta_ {100\%} \tag{7}\]  
Another Indian weighted efficiency is the Kanpur Efficiency (\(\eta_{KAN}\)) [22]. As the name suggests, the \(\eta_{KAN}\) is derived using the irradiance collected at the Indian Institute of Technology, Kanpur, in Northern India. Under the KGCCS, the climate is marked as \"Cwa: mild temperate, with a dry winter and hot summer\". Unfortunately, as with the case of the Chennai efficiency, the \(\eta_{KAN}\) is not derived using the PV simulator as required by IEC 61683. As a replacement, the real data of a 40 kW PV system is used. Moreover, it is not based on a yearly data as suggested by reference [20] and reference [21]. Instead the irradiance data is a sample of two sunny days (23 January 2014 and 17  
Figure 3: World map of the Koppen-Geiger climate classification system [18]. February 2014) is used. Hence, it is not surprising that one of the significant features of \(\eta_{KAN}\) is the large weightage (0.84) given for level of operation of 100% (0.84), i.e.,  
\[\eta_{KAN}=0.01\cdot\eta_{5\%}+0.01\cdot\eta_{10\%}+0.03\cdot\eta_{20\%}+0.03 \cdot\eta_{30\%}+0.08\cdot\eta_{50\%}+0.84\cdot\eta_{100\%} \tag{8}\]  
In conclusion, it can be deduced that of among existing weighted efficiencies, only the \(\eta_{CEC}\) and \(\eta_{IZM}\) were formed according to the required standards [6; 7; 8; 20; 21]. However, the \(\eta_{IZM}\) can be deemed as being redundant since both \(\eta_{IZM}\) and \(\eta_{CEC}\) actually represent the same climatic profile. Even though this profile is shared by many countries situated in the Mediterranean, the \(\eta_{CEC}\) is not popular, except in North America. Despite the inadequacies of \(\eta_{EURO}\) (with regards to the compliance of standards) it is still the most common standard in the rest of the world. This is mainly due to similarities in the voltage and frequency settings, which favor the \(\eta_{EURO}\). Furthermore, \(\eta_{EURO}\) was introduced much earlier than other weighted efficiency formula, and has remained as the standard bearer ever since.