Solar photovoltaic energy storage systems and off-grid systems both use solar energy to generate electricity, but they have some key differences:

1. Connectivity:
Photovoltaic energy storage systems are usually connected to the grid and can store excess solar power for use at night or during cloudy weather. This system is a typical distributed energy system that can be exchanged with other power resources through the power grid.
Off-grid systems (also known as isolated systems) are not connected to the grid and rely entirely on solar power and storage of power through energy storage systems. Off-grid systems are often used in remote areas or those places where grid power is unreliable to provide an independent power solution.

2.Power grid support:
Photovoltaic energy storage systems can use the grid to supplement energy needs or provide power to the grid when needed, thereby increasing system flexibility and reliability.
Off-grid systems must operate independently and cannot rely on the grid to provide additional power or receive support from the grid.

3. System design:
Photovoltaic energy storage systems are typically designed to provide backup power when grid power is insufficient and to deliver excess solar power to the grid when needed.
Off-grid systems require more storage capacity and backup energy to handle day and night changes and fluctuations in weather conditions to ensure all energy needs are met.

use:
Photovoltaic energy storage systems are commonly used in cities and towns as part of the power grid to provide residents and businesses with a reliable, clean energy supply.
Off-grid systems are mainly used in remote areas or those places without access to the grid, such as some islands, mountains or desert areas.
In general, photovoltaic energy storage systems and off-grid systems are both solutions for generating electricity from the sun, but they have significant differences in system design, connectivity and purpose.