Inverter sizing and selection
The inverter is sized and selected almost completely based upon the power demands of the user outlined in the Load evaluation#AC load evaluation. The size of the PV source does not affect the size of the inverter and the energy storage system is only a concern if its capacity is significantly undersized relative to the size of the inverter as all types of batteries have a maximum amount of discharge current that they can safely supply.
The basic considerations for sizing and selecting an inverter are the following:
- The voltage must match the system voltage.
- The inverter must be able to meet the continuous power demand for all loads that will operate at the same time.
- The inverter must be able to meet the continuous power demand for all loads and the surge power demand for all loads that will operate at the same time.
This process is intended to serve as a guide, but the best option for a particular project will largely depend upon the available inverter sizes, the cost and the particular project. There are a few common cases in which one may choose an different inverter size than is suggested here:
- It make sense to buy an inverter that is smaller than is suggested by this process to keep costs low as the next size of inverter is significantly more expensive or would require the addition of an additional inverter that is stacked or added in parallel. In this case the users that they will have to manage their loads to avoid overloading the inverter. This makes the most sense with large infrequent loads that the users turn on and off. This approach is not recommended for projects that have large loads that may operate automatically - like a well pump or a refrigerator - as they loads are difficult to manage.
- It may make sense to buy an inverter that is larger than is suggested by this process to enable system expansion in the future or new additional loads.
Step 1: Determine the inverter continuous duty rating
• C/20 = Battery AH capacity used for charging/disch. arging rules of thumbs • C/20 = "Average" discharge rate • C/10 = "Heavy" discharge rate • C/8 = "Max continuous load • C/5 = "Short Term" very heavy loads (well pump? for a few minutes at a time) • C/2.5 = "Max Surge" load (few seconds to minute or so)
