Home photovoltaic energy storage - understand its characteristic and benefits

In recent years, smart home photovoltaic energy storage systems have become increasingly popular. It can provide green electricity to households day and night, and through solar power, there is no need to worry about high electricity prices. 

At the same time, home photovoltaic energy storage can also save electricity costs, and at the same time better ensure the high quality of life of each family. What are the components of such a powerful home photovoltaic energy storage and what does it mainly rely on? What are the classifications of home photovoltaic energy storage? How to choose the right home photovoltaic energy storage? This article intends to answer these questions in detail.

1. What is a home photovoltaic energy storage system

Home photovoltaic power station energy storage system is a system that combines solar photovoltaic conversion systems with energy storage equipment, which can convert solar power generation into energy that can be stored. Such systems allow home users to generate electricity during the day and store excess electricity for use at night or in low-light conditions.

2. Classification of home photovoltaic energy storage

Home photovoltaic energy storage is currently divided into two types, one is grid-connected home photovoltaic energy storage, and the other is off-grid home photovoltaic energy storage.

① Grid-connected home photovoltaic energy storage

It consists of five parts, including: solar array, grid-connected inverter, BMS management system, battery pack, and AC load. The system uses hybrid photovoltaic and energy storage systems. When the utility power is normal, the load is powered by the photovoltaic grid-connected system and the mains power. When power is cut off, it is supplied jointly by the energy storage system and the photovoltaic grid-connected system.

Grid-connected home photovoltaic energy storage is divided into three working modes:

• Photovoltaic provides energy storage, surplus electricity on the Internet. 
• PV provides energy storage and some users use electricity.
• PV only provides partial energy storage.

② Off-grid home photovoltaic energy storage

It is self-contained and has no electrical connection to the grid. Therefore, the whole system does not need a grid-connected inverter, and the photovoltaic inverter can meet the requirements.

Off-grid home photovoltaic energy storage is divided into three working modes:

• photovoltaic provides energy storage and user electricity (sunny days). 
• Energy storage and off grid solar batteries provide power to the user (cloudy days). 
• The energy storage battery provides the user with electricity (evening and rain).

Whether it is a grid-connected home energy storage system or an off-grid home energy storage system, it is inseparable from the inverter, which is like the brain and heart in the system.

3. What is an inverter

The inverter is a typical component in power electronics, which can convert DC energy (battery, battery) into alternating current (generally 220v50HZ sinusoidal or square wave). In layman's terms, an inverter is a device that converts direct current (DC) into alternating current (AC).

It consists of an inverter bridge, control logic, and filter circuitry. Common components are rectifier diodes and thyristors. Almost all household appliances and computers have rectifiers installed in the power supply of electrical appliances, DC to AC, called inverters.

4. Why inverters are so important

AC transmission is more efficient than DC transmission and is widely used in power transmission. Due to cost and technical limitations, it is difficult to reduce the resistance of the transmission lines (such as copper wires) used, so reducing the transmitted current is the only effective method. Turning direct current into alternating current, increasing the voltage of the power grid can reduce the current in the wire, so as to achieve the purpose of saving energy.

Similarly, in the process of home photovoltaic energy storage, the electrical energy generated by the photovoltaic array is DC power, but many loads require AC power. DC power systems have great limitations, they are not easy to convert voltages, and the range of load applications is limited. Except for special electrical loads, inverters are required to convert direct current into alternating current.

The PV inverter is the heart of the solar photovoltaic power generation system, which converts the direct current generated by PV modules into alternating current, which is delivered to the local load or grid. Power electronics with relevant protection functions.

Photovoltaic inverter is mainly composed of power modules, control circuit board, circuit breaker, filter, reactor, transformer, contactor and cabinet, etc., the production process includes electronic parts preprocessing, machine assembly, testing and packaging and other process links. Its development depends on the development of power electronics technology, semiconductor device technology and modern control technology.

5. Classification of home photovoltaic energy storage inverters

Home photovoltaic energy storage inverters can be roughly divided into the following three categories:

① Grid-tied inverter

The grid-connected inverter is a special inverter. In addition to converting direct current into alternating current, the output alternating current can be synchronized with the frequency and phase of the mains. Therefore, the alternating current output can be returned to the mains.

That is, the grid connected inverter has the ability to synchronize with the mains line. This inverter is designed to transmit unused power to the grid without the need for batteries, and can be equipped with MTTP technology in its input circuit.

② Off-grid inverter

Off-grid inverters are typically installed on solar panels, small wind turbine generators, or other DC power sources to convert direct current into alternating current that can be used to power the home, which can use energy from the grid and batteries to power electrical loads. Because it has nothing to do with mains power and does not require any external power supply, it is called off-grid.

Off-grid inverters are initially battery-powered systems to implement regional microgrids. In the case of current input, DC input, fast charging input, high capacity DC output and fast AC output, the off-grid inverter can store energy and convert it to other uses. It uses control logic to adjust input and output situations to ensure optimum efficiency from sources such as inverter battery, solar panels or small wind turbine generators, and optimizes energy quality by using pure sine wave outputs.

For off-grid solar systems, batteries are mandatory, which store energy through batteries. For use at sunset or without electricity. Off-grid inverters also help reduce dependence on the traditional grid, which often leads to outages, blackouts, and energy instability that utilities can't eliminate. Also, an off-grid inverter with a solar charge controller means that the solar inverter has a PWM or MPPT solar controller inside.

Users can connect the PV input to the solar inverter and check the PV status on the solar inverter display, which is convenient for system connection and inspection. Off-grid inverters perform self-testing in backup generators and batteries to ensure complete and stable power quality. It is mainly used to provide electricity for some residential and commercial projects, with low wattage used to power household appliances.

③ Hybrid inverter

For hybrid inverters, there are usually two different meanings. One is an off-grid inverter with a built-in solar charge controller, and the other is an inverter that integrates the grid and the grid. It can be used for both grid-connected and off-grid photovoltaic systems, and its batteries can also be flexibly configured.

6. The main function of home photovoltaic energy storage inverter

● Automatic operation and shutdown functions

Throughout the day, as the angle of the sun increases, the intensity of solar radiation increases, and the photovoltaic system can absorb more solar energy. Once the output power required for the inverter to work is reached, the inverter can start running automatically. When the power output of the photovoltaic system becomes small, and the output of the grid-connected or energy storage inverter is 0 or close to 0, it will stop running and become in standby state.

● Anti-islanding function

In the process of photovoltaic grid-connected power generation, the photovoltaic power generation system and the power system are connected to the grid. When the public power grid is cut off due to abnormalities, if the photovoltaic power generation system cannot stop working in time or disconnect from the power system, it is still in the state of power supply, which is called the islanding effect.

The island effect occurs, which is dangerous for photovoltaic systems as well as the power grid. The grid-connected and energy storage inverters are equipped with anti-islanding protection circuits, which can intelligently detect the voltage, frequency and other information of the power grid to be merged into in real time.

Once it is found that the public power grid is abnormal due to abnormalities, the inverter can disconnect the current of home photovoltaic energy storage in the corresponding time according to different measured values, stop the output, and report the fault.

● Maximum power point tracking control function

The maximum power point tracking control function is the MPPT function, which is the core key technology, which refers to the ability of the inverter to track and find the maximum output power of the component in real time. The output power of the photovoltaic system will be affected by many factors and is in a changing state, and it is impossible to maintain the nominal best output power all the time.

The MPPT function can track the maximum power that the module can output in real time in each time period, and intelligently adjust the voltage (or current) at the working point of the home photovoltaic energy storage to bring it closer to the peak power point, so as to maximize the power generation of the photovoltaic system, thereby ensuring that the system can continue to work efficiently.

● Intelligent string monitoring

On the basis of the original MPPT monitoring, the intelligent string detection function has been realized. Compared with MPPT monitoring, the monitoring of voltage and current is accurate to each branch string, and users can clearly view the real-time operation data of each string.

At present, the energy storage equipment required by users is mainly BMS battery management system, photovoltaic grid-connected inverter, and energy storage inverter. In response to the above household energy storage equipment needs, the following problems may also be of concern to everyone.

7. Precautions for home photovoltaic energy storage inverter installation

• Before installation, we should first check whether the PV inverter is damaged during transportation.
• When choosing an installation site, it should be ensured that there is no interference from other power electronic equipment around.
• Before making an electrical connection, be sure to cover the photovoltaic panels with opaque materials or disconnect the DC side circuit breaker.
• If exposed to sunlight, PV inverter arrays will generate dangerous voltages.
• All installation operations must be done by professional technicians only.
• The cables used in photovoltaic power generation systems must be firmly connected, well insulated and of suitable specifications.
• All electrical installation steps must meet local and national electrical standards.

• PV inverters can only be connected to the grid after obtaining permission from the local power department and all electrical connections are completed by professional technicians.
• Before carrying out any PV inverter repair work, the electrical connection between the inverter and the grid should be disconnected first, and then the DC side electrical connection should be disconnected.
• Wait at least 5 minutes until the internal components are discharged before repairs.
• Any fault that will affect the safety performance of the PV inverter must be eliminated immediately before the inverter can be turned on again.

8. Conclusion

During the day, home photovoltaic energy storage systems absorb solar power generation and automatically store it for nighttime loads. In the event of an unexpected power failure, the system can also automatically switch the backup power supply for the home in time to ensure the normal operation of lighting, electrical appliances and other equipment systems at all times.

During low power consumption hours, the battery pack in the home energy storage system can charge itself. Used when backup power peaks or power outages, except as an emergency power source. Home photovoltaic energy storage can also balance the electricity load, thereby saving household electricity costs.

Smart home photovoltaic energy storage is similar to a micro energy storage power station, and its operation is not affected by the pressure of urban power supply. Home photovoltaic energy storage is environmentally friendly and does not have to pay electricity bills.

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