What is a captive solar power plant, and how does it operate?

Definition of a self-owned solar power plant

A self-owned solar power plant is a solar power generation facility that is constructed, owned, and operated by enterprises, institutions, or individuals themselves, mainly to meet their own electricity demand. Different from the power supply from the public power grid, it is a relatively independent power supply system, and the electricity it generates is mainly supplied to the constructors themselves, such as providing power for factories, schools, data centers, or large residences.

Main components of a self-owned solar power plant and their functions

Solar panels (photovoltaic modules)

These are the core components of a solar power plant, whose function is to convert solar energy into direct current. Solar panels are composed of multiple solar cell units. When sunlight shines on the panels, the semiconductor materials (such as silicon) in the solar cells will absorb photons, generating electron-hole pairs. Under the action of the internal electric field of the cells, the electrons and holes will move to the two poles of the cells respectively, thus forming direct current. For example, the photoelectric conversion efficiency of common monocrystalline silicon solar panels can reach about 15% - 20%, while that of polycrystalline silicon panels is slightly lower, ranging from 13% - 18%.

Inverter

Since the direct current is generated by solar panels and most electrical equipment requires alternating current, the function of the inverter is to convert the direct current into alternating current. It uses complex electronic circuits and techniques such as pulse width modulation (PWM) to convert the direct current into alternating current that meets the requirements of the power grid or load equipment. For example, in a high-quality inverter, the direct current can be converted into alternating current with a frequency of 50Hz or 60Hz (depending on the power grid standards in different regions) and a stable voltage to meet the demands of various alternating current loads such as motors and lighting equipment.

Charge controller (in some systems)

The charge controller is mainly used to control the charging process of the storage battery (if any) by the solar panels. It can prevent the storage battery from overcharging and overdischarging, protecting the service life of the storage battery. For example, when the storage battery is fully charged, the charge controller will automatically cut off the charging circuit between the solar panels and the storage battery; when the storage battery has a low charge level, the charge controller can control the connection of the load to avoid excessive discharging of the storage battery and ensure that the storage battery can work within a safe charge range.

Storage battery (optional component)

The storage battery is used to store the electricity generated by the solar panels so that it can provide power when there is insufficient sunlight (such as at night or on cloudy days). Common storage batteries include lead-acid batteries and lithium-ion batteries. Lead-acid batteries have a lower cost but a relatively low energy density and a shorter lifespan; lithium-ion batteries have a high energy density and a long lifespan but a higher cost. For example, in some off-grid self-owned solar power plants, the storage battery can store the excess electricity generated by the solar panels during the day and provide power for load equipment such as lighting systems and monitoring equipment at night.

Distribution box and monitoring system

The distribution box is used to distribute electricity, distributing the alternating current output by the inverter to each load branch. At the same time, it can also protect the circuit, such as installing circuit breakers and fuses, to prevent circuit overload and short circuit. The monitoring system is used to monitor the operating status of the solar power plant, including the power generation power of the solar panels, the output voltage and current of the inverter, the charge level of the storage battery (if any), and other parameters. Through the monitoring system, equipment failures and abnormal power generation situations can be detected in time, facilitating maintenance and management.

Operation process of a self-owned solar power plant

Power generation stage

During the day when there is sufficient sunlight, the solar panels absorb solar energy and convert it into direct current. During this process, the output power of the solar panels will be affected by factors such as the intensity, angle, and temperature of sunlight. For example, when the sunlight is direct and intense, the power generation efficiency of the solar panels is high and the output power is large; while on cloudy days or when the sun angle is low, the power generation efficiency and output power will decrease accordingly.

Electricity conversion and storage stage (if there is a storage battery)

The direct current generated by the solar panels first enters the storage battery for storage through the charge controller (if any), or directly enters the inverter to be converted into alternating current. If there is a storage battery, when the storage battery is not fully charged, the charge controller will adjust the charging current according to the charging state of the storage battery and the output power of the solar panels to ensure that the storage battery is charged safely and efficiently. When there is no storage battery or the storage battery is full, the direct current directly enters the inverter for conversion.

Power supply stage

The alternating current converted by the inverter enters the distribution box, and the distribution box distributes the electricity to each branch according to the demand of the load to supply power to various electrical equipment. During this process, the monitoring system will monitor the power generation and power supply situations in real time to ensure the stability and safety of the power supply. If it is a grid-connected self-owned solar power plant, after meeting its own electricity demand, the excess electricity can be fed back to the public power grid; if it is a grid-independent self-owned solar power plant, when the solar power generation is insufficient (such as at night), it is necessary to supplement the power supply through a backup power source (such as a diesel generator).