The efficiency of the inverter drives the efficiency of a solar panel system because inverters convert Direct Current (DC) (as produced by the solar panels), into Alternating Current (AC) (as used by the electric grid). This leads many to wonder what effect over-sizing or under-sizing an inverter will have on overall system efficiency. This entry sheds some light on this issue, hopefully helping you to make better decisions with regard to your current or future photovoltaic installation.
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Similar to any other component in the solar power system, the inverter has an optimal operational window within which it performs at its most efficient point. With respect to the graph above, where the red-line represents an average inverter efficiency and the green arrow suggests the size of power output from your solar panels, the grey box becomes the operational window of the inverter based on the input from the solar panel and the predetermined inverter efficiency.
Under-sizing your inverter
Using the graph above as an example, under-sizing your inverter will mean that the maximum performance of your system will be dictated by the size of your inverter and regardless of how big the output of your solar panels is, the output will be cut-off by the inverter. On the other hand, if the inverter is sized with the ‘average power received on-site’ then some money can be saved by choosing a smaller inverter (‘average power received’ being a calculation based on meteorological data and estimated solar panel efficiency at those conditions). However, under-sizing your inverter can also lead to overheating and shorter life-span of the components in the system.
Over-sizing your inverter
When over-sizing your inverter, the efficiency of the system (as seen in the example graph) depends on what your average point of operation is (which in turn is based on the size of your solar panels). Thankfully, most inverters have been designed for this. This means that when the inverters were designed, the inverter companies predicted that a natural choice would be to oversize the inverters and, as seen in the graph above, in this case this means it is in the optimal operation range between 85-95% efficiency. Furthermore, if you do decide to add more panels to your existing installation the most you’ll loose is 10-15% of total system efficiency.
Written by Prateek Chourdia
MEngSc – Photovoltaics and Solar Energy, UNSW
Solar Energy Analyst
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