What Are Centralized and String Inverters in Photovoltaic Systems?

In photovoltaic (PV) power generation, inverters play a crucial role by converting direct current (DC) into alternating current (AC) for grid integration. There are two primary types of inverters: centralized inverters and string inverters. Understanding their characteristics and applications can help you choose the most suitable solution for your PV system.

1. Types of Inverters

1. Centralized Inverters

   • Designed to convert aggregated DC power into AC power.
   • Commonly used in large-scale PV plants, with capacities exceeding 500 kW.

2. String Inverters

   • Convert DC power from individual PV module strings into AC power before aggregation.
   • Typically used in smaller PV systems, with capacities under 100 kW.

2. Centralized Inverters

These are ideal for large-scale PV installations in environments like industrial rooftops, desert power stations, and ground-mounted plants.

Advantages

1. Ease of Maintenance: Centralized management simplifies operational oversight.
2. High Power Density: Compact design with integrated high-capacity components.
3. Safety Features: Equipped with comprehensive protection functions for enhanced system safety.
4. Power Adjustment Capabilities: Includes features like active power factor adjustment and high/low voltage ride-through functionality.

Disadvantages

1. High DC Combiner Box Fault Rate: Failures can disrupt the entire system.
2. Narrow MPPT Voltage Range: Typically between 450-820V, limiting module flexibility and reducing efficiency in low-light conditions.
3. System Noise and Maintenance Complexity: Requires additional ventilation and cooling, leading to higher operational noise and more intricate upkeep.
4. Impact of Module Issues: Centralized tracking makes it impossible to monitor individual module performance, so shading or faults in one module can reduce the system’s overall efficiency.
5. No Redundancy: A fault in the centralized inverter halts the entire system’s operation.

3. String Inverters

String inverters are versatile and suitable for various PV scenarios, from residential rooftops to commercial facilities.

Advantages

1. Modular Design with Individual MPPT: Each string has its own MPPT (Maximum Power Point Tracking) unit, reducing the impact of module shading or performance differences and maximizing energy output.
2. Wide MPPT Voltage Range: Typically 200-1000V, with some models reaching 600-1500V, providing greater flexibility in module configuration and longer operating hours in low-light conditions.
3. Compact and Lightweight: Easier to transport, install, and operate without specialized tools, equipment, or dedicated distribution rooms, saving space and costs.
4. Simplified Connections: Eliminates the need for DC combiner boxes and DC distribution cabinets, reducing construction complexity.
5. Low Self-Consumption and Failure Rates: More reliable with minimal maintenance requirements.

Key Differences at a Glance

Choosing the Right Inverter

Both centralized and string inverters have their advantages and limitations. Your choice depends on factors such as system size, location, budget, and desired efficiency.

• For large-scale projects with consistent sunlight and significant power needs, centralized inverters are a cost-effective choice.
• For small to medium installations or areas with variable shading, string inverters offer better flexibility and higher efficiency.

For expert guidance and high-quality inverters tailored to your PV project, contact Yunfan Power today!