Household photovoltaic energy storage system is one of the important forms of distributed new energy. Home type energy storage system is mainly by putting the excess power generated by solar panels into the battery pack for storage, which is convenient for the family to take at any time. In daytime, when the sunlight is normal, the solar PV modules produce more energy and the batteries can store it to ensure electricity at night or on its another cloudy or rainy day.
It is also because the battery can optimize the use of electricity, it can ensure the effective operation of the whole home-based pure that system. It is mainly composed of photovoltaic power generation system, energy storage system, photovoltaic inverter, charge and discharge controller and other parts.
1 Photovoltaic Inverter
PV inverter is the connection device between PV array and grid, which can convert the DC power generated by PV array into AC power, and usually has some special functions, such as maximum power point tracking and islanding effect protection. PV inverters can be divided into three categories according to the output load: off-grid, grid-connected and off/grid-tied.
Off-grid inverters operate independently, and the output is directly connected to the equipment used; grid-connected inverters connect to the grid and supply power to the load through the grid; off-grid inverters can change their working mode according to the output load.
Photovoltaic inverters can also be divided into three categories according to the differences in the connection of panels: centralized, string and modular. Centralized inverters with power ranging from 50 to 630kW are mostly grid-connected high-power inverters used in large-scale power generation systems; string inverters with power ranging from 1 to 50kW are used in distributed grids and are mainly for home use; modular inverters are constructed by connecting a single PV module to a single micro-inverter with power ranging from 50 to 500W, which can convert DC power from a single PV module to AC power.
2 Photovoltaic Power Generation System
A structure similar to a diode PN junction exists in each photovoltaic cell, and when sunlight shines, voltage is generated at both ends of the structure, so the photovoltaic cell can generate electricity. Due to the small power generation of photovoltaic cells alone, in order to meet the actual use of demand, a number of photovoltaic cells can be formed into photovoltaic arrays, connected in series and parallel, the most commonly used photovoltaic cells are silicon-based solar cells.
Home photovoltaic power generation system is mainly divided into two types: off-grid photovoltaic power generation system and grid-connected photovoltaic power generation system.
2.1 Off-grid photovoltaic power generation system
Off-grid photovoltaic power generation system can also be called independent photovoltaic power generation system, its biggest characteristic is not connected to the grid, independent operation. After the photovoltaic power is generated by the inverter, it can directly supply power to the household AC load.
2.2 On-grid photovoltaic power generation system
A typical grid-connected PV power generation system structure is shown in Figure 1, which mainly consists of PV arrays, PV inverters and other grid-connected links. The power generated by the PV array must be processed by the inverter and filter before it is fed into the grid. At the same time, in order to ensure that the PV array always works at the maximum output power, the maximum power point tracking (MPPT) control of the power conversion link is required. In addition, inverter control is required to make the inverter output current in phase with the grid and to minimize the output of harmonics.
3 Energy Storage System
The power generation capacity of photovoltaic systems is extremely sensitive to weather and is characterized by volatility and randomness. In order to ensure the quality and reliability of the system's electrical energy, it needs to be paired with an energy storage system. In addition, the energy storage system can be used as a backup for the power generation system to achieve uninterrupted power supply. The current mainstream energy storage methods are electrochemical energy storage, supercapacitor energy storage, flywheel energy storage, etc.
The most used PV energy storage is electrochemical energy storage, such as lead-acid batteries, lithium batteries, etc. Most of the batteries used in photovoltaic systems are lead-acid batteries, compared with lithium batteries have the advantages of high specific energy, high energy storage efficiency, long cycle life and so on.
Applications of energy storage system.
1.Remote villages, villas, grassland herders, desert residents where electricity is scarce
2.War, earthquake, tsunami, typhoon, flood, mudslide and other disaster areas
3.Hospitals, schools, banks, farms, communication base stations, ports, docks
4.Building construction, industrial and commercial areas
5.Remote tribes, islands, checkpoints, border posts
6.Forests, highways, railroads, airports, tourist attractions
7.Parking lots, gas stations, electric vehicle charging stations
8.Areas with unstable grid voltage
9.Places where there is a price difference between peak and low hours of electricity consumption
Operation mode:
There are four main operation modes of PV household energy storage system: First, PV is first stored during the day when it generates electricity, and then released at night when users need it; Second, it 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; Third, if you can't sell electricity online, you can install an anti-backflow system, when the PV power is greater than the load power, you can store the excess electricity to avoid waste;
Fourth, when grid blackout, PV can continue to generate electricity, the inverter switches to off-grid working mode, the system continues to work as a backup power, PV and battery can supply power to the load through the inverter.
DC Coupling and AC Coupling
Currently, there are two main topologies: DC Coupling and AC Coupling.
DC Coupling: The DC power from the PV module is stored in the battery bank through the controller, and the grid can also charge the battery through the bi-directional DC-AC converter. The point of convergence of the energy is at the DC battery side.
AC coupling: The DC power from the PV module is changed to AC power through the inverter, which is given directly to the load or sent to the grid, and the grid can also charge the battery through the bi-directional DC-AC converter. The point of convergence of energy is at the AC end.
DC coupling and AC coupling are both mature solutions, each with its own advantages and disadvantages, and the most suitable solution is chosen according to different applications. In terms of cost, the DC coupling scheme is a little lower than the AC coupling scheme.
If the user has more load during the day and less at night, it is better to use AC coupling, because the PV module can supply power to the load directly 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, the PV power needs to be stored during the day and used at night, it is better to use DC coupling, and the PV module stores the electricity to the battery through the controller, the efficiency can reach more than 95%.
What is meant by building-integrated distributed PV system?
Building-integrated distributed PV system is an important application form of distributed PV system at present, and the technology is progressing rapidly, mainly in the installation method of building-integrated PV and the electrical design of building PV. According to the different installation methods combined with the building can be divided into Building Integrated PV or Building Integrated PV (Building Integrated PV, which is commonly known as BIPV) and Building Attached PV (Building Attached PV, abbreviated as BAPV).
BIPV: Specially designed PV modules are used to replace the original building materials or building components when installed, and the building is integrated into the PV system. If the PV module is removed, the building cannot be used normally. Photovoltaic modules must not only meet the functional requirements of photovoltaic power generation, but must first meet the basic functional requirements of the building, such as strong and durable, thermal insulation, waterproof and moisture-proof, proper strength and stiffness, etc. Commonly available are photovoltaic tiles, photovoltaic curtain walls, photovoltaic canopies, photovoltaic windows and photovoltaic awnings or sunshades.
BAPV: A PV system that uses common PV modules that are installed on the original building and do not replace building materials or building components and are installed directly onto the roof or attached to the wall. Removing the PV modules from this building does not affect the basic function of the original building.
What kind of houses are suitable for installing household distributed PV systems?
At present, domestic building roofs can be divided into sloping roofs and flat roofs according to their shapes. In principle, any form of roof can be installed with PV system, but attention should be paid to the compatibility of system design and house structure and the coordination with the surrounding environment. In addition, the installation of distributed PV systems for households should also pay attention to architectural safety, construction safety and convenience of grid connection, building roof maintainability and other aspects of the problem.
What are the common styles of household distributed photovoltaic systems combined with buildings?
(1) Conventional pitched roof household distributed photovoltaic system
For conventional pitched roof scenario, according to the difference of housing structure in different areas, there are aluminum alloy bracket form and C steel bracket form installed along the roof, the base is fixed under the tile by hook form, which does not affect the original drainage; in addition, for the northern region to uncover the tile inconvenience and local customs and other special circumstances, the overhead bracket form can be used to fix the module, the form does not destroy the original waterproof, and applicable to a variety of tile type.
(2) Conventional flat roof household distributed PV system for conventional flat roof scenario, there are different solutions according to cast-in-place and prefabricated roofing, through a variety of layout options combined form, can cope with different sizes of roof, improve the utilization rate of the roof at the same time, maximize the power generation capacity of photovoltaic power station.
(3) Flat to slope distributed PV system for households with flat roof conventional installation can not solve the problem of flat roof leakage, and for the follow-up to do waterproofing brings difficulties, but also to the roof in winter snow removal brings difficulties and security risks, through the flat to slope transformation effectively reduce the wind and sun, rain and snow corrosion of the roof, reduce the loss of indoor heat. And snow slides along the slope, reducing the workload of snow removal. Flat to slope household distributed photovoltaic system is loved by rural users, and at the same time can form a certain height of storage space, so that the house has a new look and unified style.
(4) PV courtyard, PV sunroom/shed PV courtyard, sunroom/shed and other PV systems not only achieve the purpose of PV power generation and avoid the risk of roof leakage for users, but also provide a place for users to relax.
Benefits of Household PV Energy Storage System
1.Emissions reduction - Reduces pollution and demand from coal and natural gas dependent grids
2.Power outage safety - provide backup power in case of power outage or emergency
3.Cost reduction - save money by using less energy from the grid (can be disregarded for energy-stressed areas in the country)
4. Cost related issues, for foreign countries, their electricity costs can be 10 times higher compared to domestic)
5.Become energy independent - store excess solar energy to reduce grid usage
6.Reduce peak demand - support the grid during peak hours and provide grid stabilization services
Boland Renewable Energy Co.,LTD have rich experience in Household PV Energy Storage System.As an integrated new energy power company, providing you with high quality integrated wind energy , solar energy and energy storage system solutions.Boland is now a subsidiary of CRRC, and is responsible for the overseas expansion of CRRC's wind power & solar power business. We have a relatively complete internal supply chain, service network and excellent product quality and technology.
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