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What is a home photovoltaic energy storage system?

Household energy storage is usually used in conjunction with household photovoltaics, and the installed capacity has ushered in rapid growth. A home energy storage system, also known as a battery energy storage system, its core is a rechargeable energy storage battery, usually based on lithium-ion or lead-acid batteries, controlled by a computer, charging and discharging under the coordination of other intelligent hardware and software cycles.

Home energy storage systems can usually be combined with distributed photovoltaic power generation to form a home solar storage system. From the user’s point of view, the household solar storage system can reduce the electricity bill while eliminating the adverse impact of power outages on normal life; from the perspective of the grid side, household energy storage devices that support unified scheduling can alleviate the power shortage during peak hours and provide The grid provides frequency correction.

Incremental market and stock market

The different coupling methods of photovoltaic and energy storage systems, are divided into DC coupling systems and AC coupling systems, which are suitable for the incremental market of newly installed photovoltaic systems and the stock market of installed photovoltaic systems respectively. The incremental market space is larger and will be the main driving force for future market growth:

A. Incremental market (new installation of photovoltaic + energy storage systems in target households): DC-coupled products are generally used. The DC-coupled energy storage system includes a battery system and a hybrid inverter, and the hybrid inverter has the functions of a photovoltaic grid-connected inverter and an energy storage converter.

The advantage of DC coupling is that both photovoltaic and energy storage batteries are converted through hybrid inverters, and no additional installation of photovoltaic grid-connected inverters is required. The system integration is higher, installation and after-sales service are more convenient, and it is convenient for intelligent monitoring. and control. Some households that have already installed photovoltaic systems choose to remove the original photovoltaic grid-connected inverters and install new hybrid inverters.

B. In the stock market (the target family has installed photovoltaics and added energy storage systems), AC-coupled products are generally used. It only needs to install batteries and energy storage converters without affecting the original photovoltaic system, and the design of the energy storage system is not directly related to the photovoltaic system in principle and can be determined according to demand.

The advantage of AC coupling is high safety: in the AC coupling mode, the energy is collected at the AC end, which can be directly provided to the load or sent to the grid, or directly charged to the battery through a bidirectional converter, and low-voltage PV and low-voltage batteries can be selected, to eliminate the risk of DC high voltage in the energy storage system.

On-grid system and off-grid system

According to whether the system is connected to the grid, the home energy storage system can be divided into a grid-connected system and an off-grid system. The core difference lies in whether it is connected to the grid. At present, most regions use a grid-connected and off-grid integrated system.

A. Grid-connected systems, photovoltaic and energy storage systems can be connected to the grid, and electricity can be purchased from the grid when the photovoltaic or battery power is insufficient. It is suitable for areas with a stable power system and relatively low electricity prices.

B. The off-grid system is suitable for areas such as deserts and islands without a grid or areas where the grid is unstable and requires self-use. Use an off-grid energy storage converter, usually with a diesel generator interface, to supplement power at night when the battery power supply is insufficient.

C. On-grid and off-grid all-in-one machine, which has the function of switching between on-grid and off-grid or integrates the on-grid and off-grid modes in one machine, and can complete the switch to off-grid mode during a power outage, suitable for areas with unstable power systems and frequent power outages.

The core hardware equipment of the home energy storage system includes batteries and converters. According to the degree of product integration, there are mainly two modes: integrated machine and split machine. The current market is dominated by split machines, but integrated machines are the development trend of the high-end market…

High voltage battery and low voltage battery

According to the voltage level of the battery pack, it can be divided into high-voltage batteries and low-voltage batteries. The industry is showing a trend of switching to high-voltage batteries. The main purpose is to improve efficiency and simplify system design, but at the same time have higher requirements for battery consistency and BMS management capabilities.

High-voltage batteries usually have a battery pack voltage above 48V, and multiple cells can be connected in series to achieve high voltage at the battery pack level. In terms of efficiency, with batteries of the same capacity, the battery current of the high-voltage energy storage system is smaller, which has less interference with the system, and the efficiency of the high-voltage energy storage system is higher; in terms of system design, the circuit topology of the high-voltage hybrid inverter is simpler, smaller size, lighter weight and more reliable.

However, high-voltage batteries are composed of multiple batteries connected in series and parallel. The higher the voltage, the more batteries are connected in series, and the higher the requirements for the consistency of the batteries. At the same time, it needs to cooperate with an efficient BMS management system, otherwise, it is prone to failure.

From the perspective of inverter trends, the demand for hybrid inverters suitable for incremental markets and off-grid inverters that do not need to be connected to the grid has increased.

(1) The newly added photovoltaic distribution and storage power are sufficient, and the demand for hybrid inverters increases. Because the current household energy storage system is mainly based on the incremental market (new distributed photovoltaic user supporting energy storage), the demand for hybrid inverters has increased. The stock market already has photovoltaic grid-connected inverters, so energy storage inverters are selected when incrementally installing energy storage systems, and the incremental market generally combines photovoltaic inverters and energy storage converters into a hybrid inverter device.

Users are more inclined to install energy storage when newly installing photovoltaics, mainly because the uncertainty of overseas household photovoltaic net metering policies has become stronger, the uncertainty of household photovoltaic revenue has increased, and users have the motivation to configure energy storage for self-use. Reduce earnings uncertainty.

(2) The demand for off-grid inverters is driven by markets such as the United States and South Africa. There are frequent natural disasters in the United States, and the risk of power outages is high, and the American grid is relatively fragile and aging. To stabilize the grid, some photovoltaic system power companies do not allow it to connect to the grid. Therefore, it needs to be installed off-grid for self-use and replace the generator. The US market is growing rapidly, and the demand for off-grid energy storage converters suitable for the US market has increased significantly.

From the perspective of terminal product trends, the split type is currently the main type, that is, the battery and inverter system are used together, and the follow-up will gradually develop into an integrated machine.

Regional Market Trends

From the perspective of regional market trends, differences in grid structures and power markets cause slight differences in mainstream products in different regions. The European grid-connected model is the main one, the United States has more grid-connected and off-grid models, and Australia is exploring the virtual power plant model.

(1) There are many grid-connected models in Europe at present. The penetration rate of photovoltaics in the European market is high, and the power grid is relatively stable. The use of grid-connected systems can meet the demand. The energy storage system needs to interact with the grid, so the product inverter needs to be certified for grid connection to meet the requirements of the local grid. Customers can switch modes during grid-connected applications. In normal power generation mode, photovoltaics meet the needs of electrical appliances during the day, and then charge the battery, and automatically switch at night. With the DC output of the battery terminal, the inverter switches to 220V to supply power to the load at home; photovoltaics on rainy days When the power generation is insufficient, an instruction is sent to the grid to purchase electricity from the grid to meet the household load and charge the battery at the same time.

(2) There are many off-grid models in the US market. The laying of the power grid in the United States was concentrated in the last century, and the grid facilities are relatively old, burying hidden dangers for the power grid transportation capacity and load capacity, and the problems of aging equipment and outdated technology are prominent. According to the statistics of the US Department of Energy, 70% of transmission lines and power transformers have been in operation for more than 25 years, and 60% of circuit breakers have been in operation for more than 30 years.

According to IEA statistics, U.S. users experienced an average of 3.2 hours of outage during a major event and 1.5 hours without a major event, for a total of nearly 5 hours. For areas with frequent severe weather, the annual average power interruption can reach more than 10 hours. The on-grid and off-grid all-in-one machine can realize fast on-grid and off-grid mode switching. During a power outage, the battery is used as the power supply. When the battery power is not enough, the battery can only be fully charged the next day. Therefore, the off-grid needs to match diesel engines, photovoltaics, or wind power. Interface.

(3) Australia is exploring the virtual power plant model. Families with photovoltaic energy storage systems installed by multiple households can accept the VPP agreement and accept grid dispatch. Families can sell excess electricity; when there is electricity demand, purchase electricity through this setting, and then connect it to the grid.

China’s product advantages

Most of the products in operation in the world are produced in China. China is a country with vast land and abundant resources and the second-largest economy in the world. Most of the products circulating in the world are produced in China. It has to be admitted that China is a big country of products. No product cannot be made in China, so the industrial chain is also very complete.

Voices of people all over the world

Protecting the earth is the appeal of people all over the world, not just China, every country must vigorously advocate and support the development and use of new energy. In addition, only by developing and utilizing new energy products can we achieve sustainable development, benefit our future generations, save China’s existing resources, and gain a foothold in longer-term development. Everyone has the right to protect the earth, so each of us should contribute a little to protect the earth, save water, save electricity, promote new energy products, start from me, and start from the small things around me.

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