Characteristics of a Grid-Tie Inverter

Inverter manufacturers publish datasheets for the inverters in their product line. While the terminology and content will vary by manufacturer, datasheets generally include the information listed below.

• Rated Output Power: This value will be provided in watts or kilowatts. For some inverters, they may provide an output rating for different output voltages. For instance, if the inverter can be configured for either 240VAC or 208VAC output, the rated power output may be different for each of those configurations.
• Output voltage(s): This value indicates to which utility voltages the inverter can connect. For smaller inverters that are designed for residential use, the output voltage is usually 240VAC. Inverters that target commercial applications are often compatible with 208, 240, 277, and/or 480VAC.
• Peak efficiency: The peak efficiency represents the highest efficiency that the inverter can achieve. Most grid-tie inverters on the market as of this date (July 2009) have peak efficiencies of over 94%, some as high as 96%. The energy lost during inversion is for the most part converted into heat. It's important to note that this means that in order for an inverter to put out the rated amount of power it will need to have a power input that exceeds the output. For example, a 5000W inverter operating at full power at 95% efficiency will consume 5,263W (rated power divided by efficiency). Inverters that are capable of producing power at different AC voltages may have different efficiencies associated with each voltage.
• CEC weighted efficiency: This efficiency is published by the California Energy Commission on its GoSolar website. In contrast to peak efficiency, this value is an average efficiency and is a better representation of the inverter's operating profile. Inverters that are capable of producing power at different AC voltages may have different efficiencies associated with each voltage.^[3]
• Maximum input current: This is the maximum amount of DC current that the inverter will use. If a DC power source, such as a solar array, produces an amount of current that exceeds the maximum input current, that current will not be used by the inverter.
• Maximum output current: The maximum output current is the maximum continuous AC current that the inverter will supply. This value is typically used to determine the minimum current rating of the overcurrent protection devices (e.g., breakers and fuses) and disconnects required for the output circuit. Inverters that are capable of producing power at different AC voltages will have different maximum outputs for each voltage.
• Peak Power Tracking Voltage: This is also a very important value. This represents the DC voltage range in which the inverters' maximum point power tracker will operate. The system designer must configure the strings optimally so that during the majority of the year, the voltage of the strings will be within this range. This can be a difficult task since voltage will fluctuate with changes in temperature.
• Start Voltage: This value is not listed on all inverter datasheets. The value indicates the minimum DC voltage that is required in order for the inverter to turn on and begin operation. This is especially important for solar applications, because the system designer must be sure that there is a sufficient number of solar modules wired in series in each string to produce this voltage. If this value is not provided by the manufacturer, system designers typically use the lower band of the Peak Power Tracking Voltage range as the inverter's minimum voltage.
• NEMA Rating: The NEMA rating indicates the level of protection the device has against water intrusion. Most inverters are NEMA 3R which means it is outdoor rated for most situations.