The Most Comprehensive Guide to Grid-Tied Inverter Parameters

It is well-known that inverters are a crucial component of photovoltaic systems.

Understanding inverter parameters is essential for better system design and equipment selection, ensuring the efficient operation and maintenance of solar power systems. Therefore, ADNLITE has meticulously compiled this detailed guide to grid-tied photovoltaic inverter parameters. Additionally, we provide explanations for key parameters to help you gain deeper insights.

Below, we will use the GROWATT MID_15-25KTL3-X as an example.

Detailed Parameters of Grid-Tied Inverters

Growatt inverter specs. Input DC

Model and Naming

Growatt grid-tied inverters are named based on their rated AC output power. For example, the MID_15-25KTL3-X corresponds to a rated AC output power of 15-25KW. The “T” stands for “Three,” indicating it is a three-phase inverter.

Maximum Input Power

This refers to the maximum DC power that the inverter can handle from the solar panel strings, which is the total power of the solar modules. According to the specification sheet, the MID_15-25KTL3-X has a maximum input power of 22.5KW.

ADNLITE advises ensuring that the total input voltage and current of the modules fall within the inverter’s DC input voltage and current range.

Maximum Input Voltage

This is the maximum voltage that can be input into the inverter, meaning the sum of the open-circuit voltages of all panels in a single string should not exceed this value. For the MID_15-25KTL3-X, the maximum input voltage is 1100V.

ADNLITE reminds you to consider the negative temperature coefficient of the open-circuit voltage of the modules in cold weather. As the temperature decreases, the open-circuit voltage of the solar panels increases. Therefore, it’s important to ensure that this increased voltage does not exceed the inverter’s maximum input voltage.

MPPT Voltage Range

A wider MPPT (Maximum Power Point Tracking) voltage range allows for earlier power generation in the morning and extended generation after sunset. When the string’s MPPT voltage falls within the inverter’s MPPT voltage range, the inverter can track the string’s maximum power point. For example, the MID_15-25KTL3-X has an MPPT voltage range of 200V-1000V.

ADNLITE advises that the optimal operating voltage for a three-phase inverter is around 620V, where the inverter’s conversion efficiency is highest. When the string voltage is below the rated voltage (620V), the inverter’s boost circuit activates. This results in some energy loss and reduced efficiency. Therefore, it is recommended that the MPPT voltage of each string be slightly higher than 620V during string configuration.

MPPT Channels and Number of Strings per MPPT Channel

This refers to the number of MPPT channels in the inverter and the number of strings that can be connected to each MPPT channel. Using the diagram below as an example, the inverter has six DC inputs labeled A, B, C, D, E, and F. PV1 and PV2 represent the two MPPT inputs.

The number of strings connected to each MPPT input must be equal. However, the number of strings under different MPPT inputs can vary. This means that A should equal B and C, and D should equal E and F, but A does not need to equal D.

Maximum DC Current

This parameter refers to the maximum current that the inverter allows to pass through. The maximum DC input current is calculated as the maximum input current of a single string multiplied by the number of strings.

An increase in the maximum input current on the DC side of the inverter allows for more flexible configuration of solar modules. For example, the MID_15-25KTL3-X can connect two strings of solar panels to a single MPPT. The maximum input current for a single MPPT of the MID_15-25KTL3-X is 27A. Therefore, the input current for a single string of solar panels is 13.5A. This current level is compatible with the current parameters of some bifacial solar modules.

Inverter AC Output Side Technical Parameters

On grid inverter output specsifications

Rated Output Power

This is the power output of the inverter at the rated voltage and current. It represents the power that can be continuously and stably output over a long period.

Maximum Output Power

Also known as peak power, this is the maximum power value that the inverter can output for a very short period. Since this maximum power can only be maintained briefly, it does not hold significant practical value.

Power Factor

In an AC circuit, the cosine of the phase difference (Φ) between the voltage and current is called the power factor, denoted as cosΦ. The power factor is a crucial aspect for commercial and industrial distributed photovoltaic projects. The higher the power factor, the lower the amount of reactive power wasted at the load end. In other words, a higher power factor indicates better quality and efficiency.

Efficiency

Inverter efficacy

Inverters are essential components in a photovoltaic power station, converting the DC power generated by the solar modules into AC power. During this conversion process, a small portion of energy is lost as heat. The ratio of the AC output power to the DC input power is known as the inverter’s conversion efficiency.

Conversion Efficiency Details

  1. Maximum Conversion Efficiency
    • This refers to the inverter’s peak conversion efficiency at a specific moment. However, in practical use, this figure holds limited value since the inverter cannot continuously operate at a single load point.
  2. European Efficiency & China Efficiency
    • Compared to maximum efficiency, European efficiency is a more relevant metric for evaluating an inverter’s power generation performance. European efficiency calculates the overall efficiency of an inverter based on various DC input power points, reflecting typical European sunlight conditions.
    • With the implementation of China’s Top Runner Program, “China Efficiency” is also becoming increasingly significant in the photovoltaic industry. It takes into account China’s specific sunlight conditions to estimate inverter efficiency.
  3. MPPT Efficiency
    • MPPT (Maximum Power Point Tracking) efficiency measures the inverter’s ability to track the maximum power point of the solar modules over a period. It is the ratio of the DC energy obtained by the inverter from the solar modules to the theoretical energy output if the modules operated at their maximum power point. MPPT efficiency is a critical metric for assessing the overall efficiency of the inverter.

Inverter Protection Functions

Inverter Protection Functions
  1. Insulation Resistance Detection
    • Inverters are equipped with ISO (Insulation Monitoring Device) protection functionality. If the grounding insulation resistance of the solar module array is too low, the inverter will not connect to the grid and will display an ISO error.
  2. Leakage Protection
    • When the inverter is connected to the AC grid and the AC circuit breaker is closed, the inverter will continuously monitor residual current. The inverter detects and monitors both excessive continuous residual current and sudden surges in residual current under any circumstances.
    • The limits are as follows:
      • a) Continuous Residual Current: If the continuous residual current exceeds the following limits, the inverter will disconnect within 0.3 seconds and signal a fault:
        1. For inverters with a rated output of 30kVA or less, the limit is 300mA.
        2. For inverters with a rated output greater than 30kVA, the limit is 10mA per kVA.
      • b) Sudden Surge in Residual Current: If the surge in residual current exceeds the limits listed in the table below, the inverter will disconnect within the specified time.
  3. Temperature Protection
    • Normally, the inverter can output at its rated power when the external ambient temperature is below 45 degrees Celsius. When the ambient temperature exceeds 45 degrees, the inverter will reduce its load and may eventually stop operating to prevent overheating.

These protection functions are crucial for ensuring the safety and reliability of the inverter and the overall photovoltaic system. For more detailed guidance and high-quality solar power system components, contact ADNLITE.

Standard Parameters Of On Grid Inverter

Inverter standard specs.

Size, Weight, and Installation Method

Photovoltaic inverters that are compact, lightweight, and easy to install are highly favored by customers. Smaller size and lighter weight usually mean easier transportation, which reduces the risk of damage during transit. Wall-mounted installation is preferred by customers, as it only requires checking that the wall or mounting point is stable and secure. This installation method also reduces labor and material costs.

Operating Temperature Range

The operating temperature range is a critical technical parameter that reflects the inverter’s ability to withstand both low and high temperatures, which affects its lifespan. An inverter with a wider operating temperature range demonstrates superior performance and durability under extreme temperature conditions.

Protection Rating

Generally, photovoltaic inverters are classified for indoor or outdoor use. Indoor inverters typically have a lower protection rating, such as IP20 or IP23, and require a dedicated inverter room. Outdoor inverters meet higher protection standards, such as IP54 and IP65, and do not need an inverter room.

ADNLITE advises that inverters with an IP65 protection rating can be safely installed outdoors. However, it is recommended to install a cover or place the inverter under an eave to avoid direct sunlight and mitigate various adverse factors. This ensures the protection of the photovoltaic system and maximizes the return on investment over its entire lifecycle.

Cooling Method

There is considerable debate among inverter manufacturers regarding the cooling method. Some believe that fans are unnecessary, while others think all inverters should be equipped with fans. Each viewpoint has its merits.

Fans are prone to wear and tear, which can lead to damage over long-term use, reducing the inverter’s stability and increasing maintenance costs. On the other hand, without fans, the inverter’s ability to dissipate heat may be compromised, particularly in high-temperature environments, affecting its lifespan. Additionally, in specific conditions, it is essential to consider how to protect fan-equipped devices from dust and sand.

Certification and Standards

Inverters must comply with local grid regulations in different countries, posing significant challenges to their adaptability. The more regulations an inverter complies with, the more it demonstrates the manufacturer’s comprehensive capabilities.

Call to Action

ADNLITE has been in the photovoltaic industry for over a decade, producing and providing high-quality solar lights and solar system components. We are authorized dealers for major brands like GROWATT and DEYE. Contact ADNLITE, and we will provide you with free solar system and solar lighting proposals.