Do you know the three types of photovoltaic energy storage systems?

Depending on the application scenario, solar photovoltaic energy storage systems are categorized into four types: off-grid photovoltaic power generation systems, off-grid photovoltaic energy storage systems, grid-connected photovoltaic energy storage systems, and microgrid photovoltaic energy storage systems.

1. Off-grid Photovoltaic Power Generation Systems

Off-grid photovoltaic power generation systems operate independently of the power grid and are suitable for applications such as remote mountainous areas, areas without electricity, islands, communication base stations, and streetlights. The system consists of a photovoltaic array, a solar controller, an inverter, a battery pack, and a load. In the presence of sunlight, the photovoltaic array converts solar energy into electricity, which is then supplied to the load through a solar controller-inverter unit and simultaneously charges the battery pack. In the absence of sunlight, the battery supplies power to the AC load through the inverter.

Off-grid photovoltaic power generation systems are specifically designed for use in areas without a power grid or where power outages are frequent. These systems are a critical requirement. Independent of the power grid, off-grid systems rely on a "storage-and-use" or "storage-before-use" model, providing timely assistance. Off-grid systems are highly practical for households in areas without access to a power grid or experiencing frequent power outages. Currently, the cost of off-grid photovoltaic power generation is approximately 1.0-1.5 yuan per kilowatt-hour, significantly higher than a grid-connected system, but more economical and environmentally friendly than a fuel-powered generator, which costs 1.5-2.0 yuan per kilowatt-hour.

2. Grid-connected Photovoltaic Energy Storage System

Grid-connected photovoltaic power generation systems with energy storage can store excess power and increase the proportion of self-generated electricity consumed. They are suitable for applications where self-generated electricity cannot be fed into the grid, where the self-use electricity price is significantly higher than the grid price, and where the peak electricity price is significantly higher than the normal electricity price. The system consists of a photovoltaic array composed of solar panels, a solar controller, a battery pack, a grid-connected inverter, a current sensing device, and a load. When solar power is less than the load power, the system is powered by both solar energy and the grid. When solar power is greater than the load power, some of the solar energy is used to power the load, while some is stored by a controller.

In some countries and regions, where a photovoltaic system was previously installed and subsidies for photovoltaic power were subsequently eliminated, a grid-connected energy storage system can be installed to achieve full self-use of the photovoltaic power. Grid-connected energy storage devices are compatible with inverters from various manufacturers, allowing the existing system to remain unchanged. When the current sensor detects current flowing to the grid, the grid-connected energy storage device activates, storing excess energy in the battery. If the battery is fully charged, it can also power the electric water heater. At night, when household load increases, the battery can be controlled to supply power to the load through the inverter.

3 Microgrid Energy Storage System

A microgrid energy storage system consists of a solar array, a grid-connected inverter, a PCS bidirectional converter, an intelligent transfer switch, a battery bank, a generator, and loads. When the sun is shining, the photovoltaic array converts solar energy into electricity, which is then used to power the load via an inverter and simultaneously charges the battery bank via a PCS bidirectional converter. In the absence of sunlight, the battery bank powers the load via the PCS bidirectional converter.

Microgrids can fully and effectively leverage the potential of distributed clean energy, mitigate disadvantages such as small capacity, unstable power generation, and low reliability of independent power supplies, ensure the safe operation of the power grid, and serve as a valuable complement to larger power grids. Microgrids can promote the upgrading of traditional industries and play a significant role from an economic and environmental perspective. Experts say that microgrids are flexible in application and can range in scale from several kilowatts to tens of megawatts. They can be deployed in enterprises as large as factories, mines, hospitals, and schools, or as small as individual buildings.