What is the Difference Between a Solar Inverter and an Energy Storage Inverter?

Introduction

With the development and diversification of charging stations, integrated photovoltaic storage and charging stations are gradually becoming a highlight in the field of new energy. This type of station integrates photovoltaic power generation, energy storage systems and electric vehicle charging stations, achieving efficient use and convenient management of energy. Among them, the inverter is the core component of photovoltaics and energy storage. When it plays the role of photovoltaic inverter and energy storage inverter respectively, what are the differences between the two?

Solar Inverter

The photovoltaic inverter is one of the core components of the photovoltaic system. Its main function is to convert the direct current (DC) generated by the solar panels into alternating current (AC) for use in homes or businesses, or to transmit it to the power grid. The efficiency and performance of the photovoltaic inverter directly affect the power generation efficiency and economic benefits of the entire photovoltaic system.

1. Classification by structure

▷ Centralized inverter: Applicable to large-scale photovoltaic power plants, the DC power of all photovoltaic modules is gathered into one inverter for conversion. The capacity of the centralized inverter is large and it is usually used in large photovoltaic power plants.

▷ String inverter: Suitable for small and medium-sized photovoltaic power stations, multiple photovoltaic modules are connected in series, and multiple inverters are used to invert the output of each string separately. String inverters have low cost and flexible installation and are suitable for distributed photovoltaic systems such as residential and commercial buildings.

▷ Micro-inverter: Each PV module is equipped with a small inverter that can independently convert the DC power of each panel. This method can minimize the power generation loss caused by partial shading or failure, and is suitable for residential PV power generation.

2. Classification by working method

▷ Grid-connected inverter: It sends the AC power generated by the photovoltaic system into the public power grid. It usually needs to meet the standard requirements of the power grid company and is suitable for grid-connected photovoltaic power generation systems.

▷ Off-grid inverter: used in areas without grid connection, it stores electricity through batteries and operates independently.

Energy Storage Inverter

An energy storage inverter, also known as a power storage converter (PCS), is a key device in an energy storage system. Its main function is to control the charging and discharging process of the battery and realize the bidirectional conversion of electric energy. In the power system, energy storage inverter can improve the utilization efficiency of energy, balance supply and demand, and enhance the stability of the power grid.

Energy storage inverters can adapt to different voltage levels, capacity sizes, network topologies and working modes according to different application scenarios. According to the application scenarios, they are divided into four categories: household, industrial and commercial, centralized and energy storage power stations, corresponding to small power (<10KW), medium power (10KW-250KW), high power (250KW-1MW) and ultra-high power (>1MW).

The Difference Between the Two Inverters

1.Working Principle

Photovoltaic inverters mainly achieve optimal utilization of the power output of solar photovoltaic panels through maximum power point tracking technology and DC-AC conversion; while energy storage inverters focus on managing the charging and discharging status of energy storage devices and regulating the power output in energy storage systems.

2.Control Strategy

The power control strategy of photovoltaic inverters mainly focuses on efficiently converting the DC power output by photovoltaic modules into AC power. This process exhibits the characteristics of one-way conversion. Its operating period is mainly limited to daytime, and because its power generation is often significantly affected by weather conditions, it shows a certain degree of instability.

In addition, in a photovoltaic system with anti-reverse flow function, the inverter can also flexibly adjust its output power (MPPT) according to the system power generation situation to achieve power control. In contrast, the power control strategy of the energy storage inverter is more complicated. It needs to achieve bidirectional conversion between DC and AC, which can not only transmit the power in the energy storage device to the power grid, but also draw power from the power grid for storage.

At the same time, there are relatively few restrictions on its operating time periods. When the load is low, the electric energy will be stored in the battery; when the load is peak, the stored electric energy will be released to reduce the pressure on the power grid; when a power grid fails, the energy storage inverter can quickly switch to off-grid mode and continue to provide a stable power supply, thereby ensuring stable control of energy.

3.Performance Indicators

Photovoltaic inverters mainly consider the following indicators:

▷ Efficiency: The efficiency of a photovoltaic inverter refers to its ability to convert direct current into alternating current, so the higher its efficiency, the smaller the power loss of the conversion. Generally speaking, the efficiency of a photovoltaic inverter is required to be above 90%.

▷ Power density: During use, photovoltaic inverters need to meet certain power requirements. Therefore, its power density becomes an important performance indicator, generally required to be 1.5~3.0W/cm².

▷ Protection level: PV inverters should have good environmental adaptability, so their external structure should have corresponding waterproof, dustproof, earthquake-resistant, fireproof and other capabilities. At present, conventional standards require that the protection level of PV inverters should not be less than IP54.

The energy storage inverter has the following performance indicators:

▷ Response speed: The energy storage inverter should have fast and stable response characteristics. When the system load changes, the energy storage inverter should have fast response capabilities.

▷ Conversion efficiency: The energy conversion efficiency of the energy storage inverter should be relatively high to ensure the efficiency of storage and discharge.

▷ Storage energy density: In order to achieve efficient storage function, the storage energy density of the energy storage inverter should be as large as possible.

4.Technical Requirements

Photovoltaic inverters generally focus on factors such as DC/AC conversion efficiency, power density, protection functions, and protection levels; energy storage inverters focus more on factors such as charging and discharging efficiency, on-grid/off-grid switching speed, and storage energy density.

5.Application scenarios

Photovoltaic inverters are mostly used in photovoltaic systems such as balconies, households, and industrial and commercial areas. Their main function is to convert photovoltaic DC power into AC power and transmit it to the power consumption area. In addition, large-scale photovoltaic power stations such as ground-based and centralized ones also need to use photovoltaic inverters to convert the DC power they generate into AC power.

Energy storage inverters are commonly used between energy storage systems and power grids, such as industrial and commercial energy storage power stations, household photovoltaic storage, etc. Energy storage inverters can use energy storage devices such as batteries to achieve energy storage and use through charge and discharge management, meet the power demand at different times in various scenarios, and ensure stable and reliable power supply.