Definition and Types of Photovoltaic Systems

Definition of Photovoltaic Systems

A household solar photovoltaic (PV) system converts solar energy into electrical energy using solar cell modules and other auxiliary equipment. Generally, PV systems are classified into standalone systems, grid-connected systems, and hybrid systems. Based on application form, scale, and load type, they can be further subdivided into the following six categories: small solar power supply systems, simple DC systems, large solar power supply systems, AC/DC power supply systems, grid-connected systems, and hybrid power supply systems. The working principles and characteristics of each system are explained below.

1. Small Solar Power Supply System

This system features only DC loads with low power consumption, resulting in a simple structure and easy operation. It is primarily used in household systems, civilian DC products, and entertainment equipment. For example, such systems have been widely promoted in western China to power DC lights, addressing household lighting needs in off-grid areas.

2. Simple DC System

This system powers DC loads that have no specific time-of-use requirements, typically operating during daylight hours. It does not include batteries or controllers; instead, solar modules directly supply power to the loads. By eliminating energy storage/release in batteries and energy loss in controllers, it improves energy utilization efficiency.

3. Large Solar Power Supply System

Like the above two systems, it is designed for DC power supply but serves higher-power loads. To ensure stable and reliable power, it requires large-scale PV arrays and battery banks. Common applications include power sources for communication, telemetry, and monitoring equipment, rural centralized power supply, navigational beacons, and streetlights.

4. AC/DC Power Supply System

Unlike the previous three systems, this type powers both AC and DC loads. It incorporates an inverter to convert DC to AC for AC load requirements. Due to higher power consumption, the system scale is typically larger. It is used in communication base stations and PV power plants with both AC and DC loads.

5. Grid-Connected System

The key feature of this system is that DC power from PV arrays is converted by a grid-tied inverter into AC power that meets utility grid standards, then directly fed into the grid. Excess power from the PV array, after supplying on-site AC loads, is exported to the grid. A dedicated grid-tied inverter is required to ensure output voltage, frequency, and other parameters comply with grid specifications.

6. Hybrid Power Supply System

In addition to solar PV arrays, this system integrates a diesel generator as a backup power source. The goal is to leverage the advantages of multiple generation technologies while mitigating their drawbacks. For instance, standalone PV systems offer low maintenance but rely on weather conditions, leading to unstable output; hybrid systems address this by combining solar power with diesel backup.

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