Preface 

Energy storage technology can help reduce the abandonment rate of photovoltaic projects and ensure large-scale photovoltaic grid connection. Among the currently mature and commercialized energy storage technologies, electrochemical energy storage is suitable for development in conjunction with photovoltaic projects due to its advantages of not being limited by natural conditions, fast response, and long cycle life.

1、 Photovoltaic system, also known as solar photovoltaic power generation, is a technology that utilizes the photovoltaic effect of semiconductor interfaces to convert light energy into electrical energy. It mainly consists of three parts: solar panels (photovoltaic modules), controllers, and inverters.

Divided by component layout, photovoltaic power stations can be roughly divided into two categories: centralized photovoltaic power stations and distributed photovoltaic power stations.

Centralized photovoltaic power stations are large-scale photovoltaic power stations built in desert and other areas, which are directly connected to the public power grid after power generation and connected to the high-voltage transmission system to supply long-distance loads. Commonly found in Qinghai, Ningxia, Gansu, Xinjiang and other regions.

Distributed photovoltaic power station refers to the construction and operation of power plants on or near the user's site, mainly for self use by the user, with surplus electricity connected to the grid. Utilizing scattered areas such as roofs and carports to construct photovoltaic power stations is common in southern and northern China. Due to being included in the scale indicator management, the development of distributed photovoltaics has encountered difficulties. Later, the policy of "whole county distributed pilot" became a hot topic in the industry.

2、Energy storage system,There are two technologies that can be used for energy storage system access in photovoltaic power plants, namely centralized AC side access and distributed DC side access.

1） The centralized arrangement method on the AC side adopts the centralized arrangement and access method on the AC side. The energy storage battery pack is centrally arranged in the power station booster station/switch station, and the DC power supply is connected to the AC bus of the booster station through inverter boosting. The power exchange between the energy storage system and the power system is subject to dispatch control. The centralized energy storage solution on the communication side requires the configuration of multiple PCS machines to achieve parallel operation, as well as the addition of step-up transformers and distribution equipment.

2）The DC side distributed layout access method is to disperse the energy storage units in each photovoltaic sub array, and each photovoltaic sub array is equipped with a set of energy storage devices, mainly composed of photovoltaic inverters, step-up transformers, DC/DC modules, and energy storage batteries. In distributed energy storage solutions, communication between DC/DC modules and photovoltaic inverters can achieve the smoothing of optical power, but cannot store excess electricity on the AC side. To achieve bidirectional flow of electrical energy, the unidirectional photovoltaic inverter needs to be replaced with a bidirectional PCS.

The distributed layout and access method on the DC side is limited for existing photovoltaic power stations due to limited equipment layout sites, large electrical wiring changes, long power outage and expansion time, and high costs.

The application of electrochemical energy storage systems in photovoltaic projects can ensure the quality and grid connection capability of clean energy, and meet the mandatory energy storage requirements of power grid companies. At the same time, it can solve the problem of abandoned light and reduce resource waste.