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Home of Light and Storage | Typical design of a 10kW household energy storage system
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Home of Light and Storage | Typical design of a 10kW household energy storage system
In developed countries such as Europe and the United States, PV is cheap to go online, but the price of electricity for residential use is high, and in some places it is not available online, and PV power generation and load electricity consumption are not at the same time (power generation in the daytime, electricity consumption mainly in the evening), which turns into a low price to sell electricity and a high price to buy electricity. There are also some less developed areas where the grid is less stable and the price of electricity is high. These places are better suited to a household energy storage power generation system if PV is installed.
The installation of energy storage not only stabilises the voltage, but also allows electricity to be used after a grid outage.
There are four main modes of operation for PV household energy storage systems:
I. First stored during the day when the PV is generating electricity, and then released at night when the user needs it;
ii. Can be charged at the valley of the electricity price and discharged at the peak, using the difference between peak and valley prices to achieve maximum income;
iii. If the electricity cannot be sold online, an anti-backflow system can be installed to store the excess power when the PV power is greater than the load power to avoid waste;
iv. When the power grid blackout, PV can still continue to generate electricity, the inverter switches to off-grid working mode, the system continues to work as a backup power supply, PV and battery can supply power to the load through the inverter.
Comparison of technical routes for household energy storage systems
Household and energy storage systems, including solar modules, controllers, inverters, batteries, loads and other equipment, many technical routes, according to the way the energy pool, there are currently mainly DC coupling "DC Coupling" and AC coupling "AC Coupling "DC Coupling" and "AC Coupling" are the two main topologies.
DC Coupling: The DC electricity emitted from the PV modules is stored, via the controller, in the battery bank, and the grid can also be charged to the battery via a bi-directional DC-AC converter. The point of convergence of the energy is at the DC battery end. AC coupling: The DC power from the PV modules is transformed into AC power through the inverter and is fed directly to the load or to the grid, which can also charge the batteries through a bi-directional DC-AC converter. The point of convergence of the energy is at the AC end.
Both DC and AC coupling are currently mature solutions, each with its own advantages and disadvantages, and depending on the application, the most suitable solution is chosen. In terms of cost, the DC-coupled solution is a little less expensive than the AC-coupled solution. For example, in an already installed PV system, if an energy storage system needs to be added, it is better to use AC coupling, as long as the battery and bi-directional converter are added, without affecting the original PV system, and the design of the energy storage system is in principle not directly related to the PV system, and can be determined according to demand. If it is a newly installed and off-grid system, PV, battery and inverter have to be designed according to the user's load power and power consumption, and it is more suitable to use a DC coupling system. If the user has more load during the day and less at night, it is better to use AC coupling, as the PV module can supply power directly to the load through the grid-connected inverter, and the efficiency can reach more than 96%. If the user has less load during the day and more at night, and the PV power needs to be stored during the day and used at night, DC coupling is better, as the PV modules store the power in the battery through the controller, and the efficiency can reach more than 95%.
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