Key Technical Indicators Determining the Quality of Solar Inverters

What makes a high-quality solar inverter? We have previously shared detailed information on all solar inverter parameters. But what are the main technical indicators of solar inverters? These indicators determine the overall quality and performance of the inverter.

Below, ADNLITE shares the key technical indicators of solar inverters.

Stability of Output Voltage

In off-grid systems, the output voltage of inverters can vary significantly due to the charging and discharging characteristics of batteries. For example, a standard 12V battery can have a voltage range between 10.8V and 14.4V.

A qualified inverter should maintain a steady-state output voltage variation within 5% of the rated value. During load transitions, the output voltage error should not exceed ±10% of the rated value.

Output Voltage Waveform Distortion

Pure sine wave inverters should have a maximum waveform distortion of no more than 5%. High harmonic currents from the inverter can cause additional losses, such as eddy currents, in inductive loads. If the waveform distortion is too high, it can negatively impact the safety and efficiency of electrical devices, significantly affecting the system’s operational performance.

The total harmonic distortion (THD) of the voltage on the low-voltage side caused by the inverter should not exceed 3%. Odd harmonic voltage distortion should not exceed 2.1%, and even harmonic voltage distortion should not exceed 1.2%.

It is essential to provide a third-party laboratory harmonic test report or an on-site harmonic test report of similar string inverters to demonstrate the inverter’s superior output power quality.

Rated Output Frequency

HUAWEI-Soar-INVERTER

For appliances like washing machines and refrigerators, the optimal operating frequency is 50Hz. Deviations from this frequency can cause these devices to overheat, reducing the operational efficiency and lifespan of the solar power system. Therefore, the output frequency of the inverter should be stable, typically at the mains frequency of 50Hz, with an error margin of within 1% under normal working conditions.

Load Power Factor

The load power factor indicates the inverter’s ability to handle inductive or capacitive loads. For a sine wave inverter, the load power factor typically ranges from 0.7 to 0.9, with a nominal value of 0.9. Given a fixed load power:

  • If the inverter’s power factor is low, the required rated power of the inverter needs to be higher. This not only increases equipment costs but also reduces the overall efficiency of the solar power system.

The inverter should be capable of reporting the current status of the inverter’s output power setting (both percentage and absolute values), power change rate setting, and power factor setting.

Grid Adaptability

1. Voltage Adaptability

  • Inverters must pass the certification tests for the local grid’s voltage range. They should operate normally within the grid line voltage range of 380-440V.

The operating regulations for photovoltaic power stations within different grid connection voltage ranges are shown in Table 3.

Table 3: Voltage Range Operating Regulations

Grid Connection VoltageMaximum Disconnection Time
U < 0.5UN0.1 seconds
0.5UN ≤ U < 0.85UN2.0 seconds
0.85UN ≤ U ≤ 1.1UNContinuous operation
1.1UN < U < 1.35UN2.0 seconds
1.35UN ≤ U0.05 seconds

2. Frequency Adaptability
Inverters should have excellent adaptability to grid frequency, with a default frequency range that complies with local standards. They must pass site or laboratory frequency disturbance tests. The frequency range requirements for photovoltaic power stations are shown in Table 4.

Table 4: Frequency Range Operating Requirements
Frequency RangeOperating Requirements
< 48 HzDetermined by the minimum allowable frequency of the PV inverter or grid requirements
48 Hz ≤ f < 49.5 HzThe PV power station should be able to operate for at least 10 minutes each time the frequency drops below 49.5 Hz
49.5 Hz ≤ f ≤ 50.2 HzContinuous operation
50.2 Hz < f ≤ 50.5 HzThe PV power station should be able to operate continuously for 2 minutes each time the frequency exceeds 50.2 Hz, and be capable of stopping power transmission to the grid within 0.2 seconds. The actual operating time is determined by the power dispatch department. PV power stations that are offline are not allowed to reconnect to the grid during this time.
> 50.5 HzThe PV power station should stop power transmission to the grid within 0.2 seconds, and offline PV power stations are not allowed to reconnect to the grid.

Key Components of Grid-Tied Photovoltaic Inverters

Growatt

Below we list the key components. We recommend using high-quality, well-known brands for these components to ensure reliability and performance.

  1. DC Input EMI Filter
  2. AC Output EMI Filter
  3. Leakage Monitoring and Protection System
  4. DC Input Switch
  5. AC Output Relay
  6. DC Input Branch Set Photovoltaic Connectors
    • Rated voltage to ground: ≥ DC 1000V
    • Impulse voltage: ≥ 6kV
    • Rated current: ≥ 30A
    • Operating temperature range: ≥ -30℃ to 85℃
    • Maximum operating temperature: ≥ 105℃
    • Contact resistance: ≤ 1mΩ
    • Flame retardant rating: ≥ UL94-V0
    • UV, ozone, and moisture resistant with protection rating of at least IP67 when mated
  7. DC Input Surge Protector
    • Should protect against both positive and negative pole-to-ground and between positive and negative poles
    • Nominal discharge current (positive/negative pole-to-ground): ≥ 10kA
    • Maximum discharge current (positive/negative pole-to-ground): ≥ 20kA
    • Response time: ≤ 25ns
    • Operating temperature range: ≥ -40℃ to +80℃
  8. AC Output Surge Protector
    • Nominal discharge current: ≥ 10kA
    • Maximum discharge current: ≥ 20kA
    • Response time: ≤ 25ns
    • Operating temperature range: ≥ -30℃ to +80℃
  9. DC Bus Support Capacitor
    • Metal film capacitors (if present): Operating temperature range: ≥ -30℃ to +85℃
    • Electrolytic capacitors (if present): Operating temperature range: ≥ -30℃ to +105℃
  10. IGBT, MOSFET
    • Considering the reliability of power plant operation, SiC devices are not allowed for IGBT, MOSFET, and other power electronic devices in the inverter.
  11. Current Sensor
  12. DC Input Branch Fuse
    • For inverters with three or more strings per MPPT, use reputable brand gPV type photovoltaic fuses to ensure quick isolation of fault points during DC side backfeed current faults.
  13. External Cooling Fan
    • Effective protection rating: ≥ IP65
    • Minimum insulation heat resistance grade: ≥ B grade
  14. AC Output Reactor
  15. AC Filter Capacitor
    • Metal film capacitors (if present): Operating temperature range: ≥ -30℃ to +85℃
    • Electrolytic capacitors (if present): Operating temperature range: ≥ -30℃ to +105℃
  16. AC Filter Reactor

Call to Action

ADNLITE represents renowned inverter brands such as Growatt and DEYE. Contact ADNLITE today for free proposals on solar street lights and solar power systems at competitive prices. Let us help you power your future efficiently and sustainably!