According to research institutions, it is expected that by 2023, over 55% of energy storage systems will be deployed in conjunction with solar power generation facilities. With the expansion and development of the market, its system architecture will become an important consideration for developing solar+energy storage projects.

According to the latest survey report by research firm WoodMackenziePower&Renewables, the application of DC coupled solar energy+energy storage projects on the grid side (FTM) is becoming increasingly common and is likely to dominate the residential market. In addition, although eligibility for the US federal investment tax credit is a factor contributing to the growing share of DC coupled grid side solar+energy storage systems, its share is expected to continue to grow even as the investment tax credit (ITC) gradually decreases in 2021.

This growth is also due to the new changes brought about by the DC coupled system architecture, which has made DC coupled solar+energy storage projects the first to become grid side applications and have received more attention. Typically, the user side (BTM) DC coupling system uses a multi port hybrid inverter related to battery storage systems and solar power generation assets. Although these inverters are suitable for user side (BTM) battery energy storage projects, they are not suitable for grid side (FTM) battery energy storage projects.

The new changes in the DC architecture of the FTM battery energy storage project involve independent DC-DC converters connected to the battery. These new grid side (FTM) DC coupled systems typically have lower interconnection costs than AC coupled systems, as they only rely on a single interconnection point. Interconnection costs will significantly affect the capital expenditure of project developers (depending on the size of the system, interconnection costs can account for 20% to 35% of the system's balanced cost stack).

This single point interconnection in DC coupled systems also enables large-scale solar power generation facilities to store excess power in battery energy storage systems, making it economically feasible, thereby supporting economic and effective time shifting of excess solar energy.

Given the elimination of AC acquisition systems, reduction of system balance requirements, and ease of interconnection, the installation cost of DC coupled systems is currently 3% to 10% lower than that of AC coupled systems, depending on the scale of the solar+energy storage project and the duration of battery discharge.

However, as the system scale increases, the DC system begins to lose its cost advantage. The scale of solar energy+energy storage projects has increased, and the economies of scale achieved through power conversion and other hardware components will not translate into overall system capital expenditure, as solar power generation facilities and battery energy storage systems are beginning to occupy more costs.

The DC coupling system is easily eligible for federal investment tax credits in the United States, and by the end of 2021, the proportion of grid side (FTM) battery energy storage projects will decrease to 10%. However, according to the report, although eligibility for the US federal investment tax credit is a factor contributing to the growing market share of DC coupled grid side solar+energy storage systems, its market share is expected to continue to grow even as the investment tax credit (ITC) gradually decreases in 2021.

Due to the current DC system not allowing batteries to be charged from the grid, AC coupled systems will become the default architecture choice for battery installation systems primarily used for grid support applications.

The user side (BTM) battery energy storage market in the commercial and industrial industries is the only area where DC coupled systems have not grown. WoodMackenzie stated that the department will continue to adopt an AC coupling system and will continue to do so in the short term. Although it has the advantages of easy installation and low system balance requirements, making the DC coupled architecture popular in the residential solar+energy storage market, there are currently some issues with multi port hybrid inverters, such as single point faults, fixed input voltage, and loss of flexibility, which reduce their attractiveness to the non residential market of user side (BTM) battery energy storage systems.

AC coupled systems are also more suitable for future deployment of solar power generation facilities or upgrading of battery energy storage systems, as well as microgrids that require higher reliability and flexibility than DC coupled systems.