How we calculate the energy efficiency in the PV installation?

As you can see on the attached graph of energy flow in the PV system, solar energy reaching from the sun is relatively large, and maybe more importantly free for everyone. The lowest energy efficiency they have photovoltaic panels and despite their continuous improvement, their efficiency does not exceed 20%. The highest energy efficiency, and also the smallest losses?

In the system have inverters. Here, energy efficiency varies from 95% to 99%.

When calculating the efficiency of the system, one can not forget about the losses on the wires and connection points. The higher the quality of these elements, the lower the losses and the impact of time on the deterioration of parameters.

Total energy efficiency the system is the product of the efficiency of its individual elements and for the installation Individuals range from 16% to 18%.I