Inverter DC Oversizing Guide
Table Of Contents
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Oversizing of SolarEdge Inverters, Technical Note
PV inverters are designed so that generated output power will not exceed the maximum AC power. In many cases, oversizing the inverter, i.e.
having more DC power than the inverter AC power, may increase power output in lower light conditions, thus allowing the installation of a
smaller inverter for a given DC array, or alternately, installation of more DC power for a given inverter. However, too much oversizing of the
inverter may have a negative impact on the total energy produced and on the inverter lifetime. This document provides considerations for
oversizing inverters and presents the maximum allowed DC/AC oversizing of SolarEdge inverters.
Introduction
PV modules do not consistently perform at their nominal output rating. The module output power is affected by the weather, the sun’s
position during the day/different seasons, local site conditions and array orientation. In addition, module output power may decrease due to
aging, soiling and shade.
For an inverter with maximum AC power output (
) connected to a PV array with STC power (
), the inverter is oversized if:
DC/AC oversizing is defined as the ratio between the array STC power and the inverter AC power:
The maximum AC power output of the inverter (
is the rated/nominal maximum power of the inverter
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or the SW limited power set
by the user, whichever is lower.
DC/AC Oversizing Considerations
The main reason to oversize an inverter is to drive it to its full capacity more often. This will maximize power output in low light conditions,
thus allowing the installation of a smaller inverter for a given DC array (or alternately installation of more DC power for a given inverter).
Oversizing the inverter is typically not a requirement, however an experienced PV designer may choose to oversize the inverter in order to
maximize the power production, due to the following:
Actual PV module power vs. module nominal power
Financial considerations
On the other hand, too much oversizing may negatively affect the inverter power production: Inverters are designed to generate output
power up to a maximum AC power that cannot be exceeded, and they limit (clip) the power when the actual produced DC power is higher
than what the inverter can output. This results in loss of energy.
Oversizing the inverter also causes the inverter to operate at high power for longer periods, thus affecting its lifetime. Operating at higher
power also increases inverter heating and may heat its surroundings. Inverters will reduce their peak power generation in case of
overheating.
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Maximum Oversizing of SolarEdge Inverters
Oversizing SolarEdge inverters is allowed and will not harm the power optimizers or the inverters as long as some limits are met:
SolarEdge allows DC/AC oversizing of up to 125%
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.
Oversizing of up to 135% is allowed in geographical places with moderate climate. These are defined as locations where the average yearly
high temperature is below 25°C. See below a detailed list of cold locations.
Maintaining this limit ensures the lifetime of the inverter and is needed for keeping the inverter covered by its warranty. However, the
information in this document is not a recommendation of optimal oversizing. In many cases, you may design with lower sizing to ensure that
the inverter does not clip power. SolarEdge recommends performing proper simulations before oversizing the inverter. You may refer to the
SolarEdge Site Designer application to estimate the generated energy from the installation and the energy that may be lost due to clipping.
There is no minimum power sizing limit of the SolarEdge inverters as long as minimal string length is kept.
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As specified in the inverter datasheet.
2
Refer to the inverter installation manual, (Inverter Power De-rating appendix) for details on how the temperature affects the inverter power generation.
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In all limits, the rated STC power of the modules should be used regardless of module location, tilt or orientation.