Types Of Photovoltaic Storage Systems

Off-grid Photovoltaic Power Generation Systems
Off-grid photovoltaic (PV) power generation systems operate independently of the power grid and are used in 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 bank, and loads. When there is sunlight, the photovoltaic array converts solar energy into electricity, which is then used to power the loads and charge the battery bank via the solar-controlled inverter. When there is no sunlight, the battery bank supplies AC loads through the inverter.

Off-grid PV power generation systems are specifically designed for areas without a power grid or areas prone to power outages. They meet a rigid demand, relying on a "storage-as-you-go" or "storage-before-use" operating mode, providing much-needed power. For households in areas without a power grid or prone to power outages, off-grid systems are highly practical. The cost per kilowatt-hour for off-grid PV electricity is approximately 1.0-1.5 yuan, significantly higher than grid-connected systems, but more economical and environmentally friendly than the 1.5-2.0 yuan per kilowatt-hour of a fuel-powered generator.

Off-grid Energy Storage Systems

Off-grid photovoltaic (PV) power generation systems are widely used in applications with frequent power outages, where PV power generation is for self-consumption with no surplus capacity to be fed into the grid, where self-consumption electricity prices are significantly higher than grid-connected prices, and where peak electricity prices are significantly higher than off-peak prices.

The system consists of a PV array composed of solar cell modules, an integrated solar inverter/converter, a battery bank, and loads. When there is sunlight, the PV array converts solar energy into electrical energy, which is then used to power the loads and charge the battery bank via the solar inverter/converter. When there is no sunlight, the battery bank powers the solar inverter/converter, which then supplies power to the AC loads.

Compared to grid-connected power generation systems, off-grid systems add a charge/discharge controller and batteries, increasing system costs by approximately 30%, but offering a wider range of applications. First, it can be set to output rated power during peak electricity prices, reducing electricity costs. Second, it can charge during off-peak hours and discharge during peak hours, profiting from the peak-valley price difference. Third, when the grid experiences a power outage, the photovoltaic system continues to operate as a backup power source; the inverter can switch to off-grid mode, and the photovoltaic system and batteries can supply power to the load through the inverter.

Grid-connected Photovoltaic Energy Storage System

A grid-connected photovoltaic power generation system can store excess generated electricity, increasing the self-consumption ratio. It is applicable in situations where self-consumption cannot cover surplus grid connection, where self-consumption electricity prices are much higher than grid connection prices, and where peak electricity prices are much higher than off-peak prices. The system consists of a photovoltaic array composed of solar cell modules, a solar controller, battery banks, a grid-connected inverter, a current detection device, and a load. When the solar power is less than the load power, the system is powered by both solar energy and the grid. When the solar power exceeds the load power, part of the solar energy supplies power to the load, and the rest is stored through the controller.

In some countries and regions, where a photovoltaic (PV) system was previously installed but subsidies were later phased out, a grid-connected energy storage system can be installed to enable complete self-consumption of PV power. Grid-connected energy storage devices are compatible with inverters from various manufacturers, requiring no modifications to the existing system. When a current sensor detects current flowing into the grid, the grid-connected energy storage device starts working, storing excess energy in the battery. If the battery is fully charged, it can also turn on an electric water heater. At night, when household load increases, the battery can be controlled to supply power to the load via the inverter.

Microgrid Energy Storage System: A microgrid system consists of a solar array, grid-connected inverter, PCS bidirectional converter, smart transfer switch, battery bank, generator, and loads. When there is sunlight, the PV array converts solar energy into electrical energy, which is then used to power the loads via the inverter and simultaneously charge the battery bank via the PCS bidirectional converter. When there is no sunlight, the battery supplies power to the loads via the PCS bidirectional converter.

Microgrids can fully and effectively leverage the potential of distributed clean energy, reducing disadvantages such as small capacity, unstable power generation, and low reliability of independent power supply, ensuring the safe operation of the power grid, and serving as a beneficial supplement to the main power grid. Microgrids can promote the upgrading and transformation of traditional industries, playing a significant role from both economic and environmental perspectives. Experts say that microgrids are flexible in application, ranging in scale from kilowatts to tens of megawatts, and can be developed for everything from large factories and mines, hospitals and schools to small buildings.