Distributed home photovoltaic typical design

The distributed household PV introduced in this paper refers to the project of 10kW or less, installed on the roof of the home, connected to the grid through 220V or 380V. Most of them use the self-sufficient balance to access the Internet, and the maximum installed capacity is 25% of the capacity of the upper-level transformer.

1. Choose the appropriate installation site: the roof of the home generally adopts the tile structure and the cement structure. When the installer sells the photovoltaic or receives the application from the user, it is necessary to go to the site for inspection, because not every roof is suitable for installing photovoltaic. First of all, it is necessary to determine whether the load capacity of the roof can meet the requirements. The load capacity of the solar power station equipment for the roof is greater than 30kg/m2. Generally, the cement structure houses built in the past 5 years can meet the requirements, and the brick structure with more than 10 years Houses should be carefully examined; secondly, there are no shadows around them, even small shadows can affect power generation, such as water heaters, utility poles, tall trees, etc. It will be dirty and affect the amount of electricity generated. Finally, it depends on the orientation of the roof and the angle of inclination. The component is facing south and has the highest power generation at the optimal tilt angle. If it faces north, it will lose a lot of power. In the case of encountering unsuitable for photovoltaic installation, it is necessary to decisively refuse to meet the need to influence the amount of power generation and the owner to seek truth from facts, so as to avoid subsequent disputes.

2. Choosing the right PV module : The PV module has three technical routes of polysilicon , monocrystalline silicon and thin film. Various technologies have advantages and disadvantages. Under the same conditions, the efficiency of the photovoltaic system is only related to the nominal power of the component. It is not directly related to the efficiency of components. The component technology is mature. The quality of component manufacturers in domestic first- and second-line brands is relatively reliable. Customers need to choose to purchase from reliable channels. The photovoltaic module has 60 batteries and 72 batteries. The distributed photovoltaic is generally small in scale and difficult to install. Therefore, it is recommended to use 60 battery components, which are small in size and light in installation.

According to the law of the market, each year there will be a power component shipment is particularly large, the industry is called mainstream components, the efficiency of components is increasing every year, 2017 is polycrystalline 265W, single crystal 275W, this model price The highest, it is relatively easy to buy, by 2018 is expected to be polycrystalline 270W, single crystal 280W cost-effective.

3. Choose the appropriate bracket: According to the roof condition, you can choose aluminum bracket, C-shaped steel, stainless steel and other brackets, and consider the factors such as photovoltaic bracket strength, system cost, roof area utilization and other factors. In the case of ensuring that the power generation of the system is not significantly reduced (less than 1%), the tilt angle of the PV array is reduced as much as possible to reduce the wind receiving surface, thereby increasing the strength of the bracket, reducing the cost of the bracket, and increasing the utilization of the limited area. . Leakage is a problem that needs to be paid attention to during the installation of photovoltaic power stations. The waterproof work is done well, and the photovoltaic power station is safe. The photovoltaic support is mounted on the roof to support the components and is connected to the roof. Its design adopts the top-top method, which does not perforate and damage the original waterproof of the roof; the pre-fabricated components of the briquetting block do not need to be cast on site, which can avoid the hard destruction of the waterproof layer of the roof by the installation of the solar bracket.

4. Photovoltaic array parallel design: In the distributed photovoltaic power generation system , the solar cell module circuits are connected in series to form a series branch. The series connection is used to raise the DC voltage to the inverter voltage input range. It should ensure that the solar cell module does not exceed the inverter voltage input range under various solar irradiance and various ambient temperature conditions.

The working voltage is about the rated working voltage of the inverter, and the efficiency is the highest. The single-phase 220V inverter, the inverter input rated voltage is 360V, the three-phase 380V inverter, and the inverter input rated voltage is 650V. Such as 3kW inverter, with 260W components, working voltage 30.5V, with 12 working voltage 366V, power is 3.12kW is the best. The 10KW inverter is equipped with 260W components, 40 components, 20 strings each, the voltage is 610V, and the total power is 10.4kW.

5. Cable selection: In domestic photovoltaic systems, copper cables are recommended. Because the PV module connector of the PV module , the output terminal of the PV inverter , and the terminal block of the grid switch are made of copper core, if the aluminum wire is used, the copper and aluminum are directly connected, a chemical battery is formed, that is, electrochemical corrosion. This will cause poor contact between copper and aluminum and increase the contact resistance. When there is current, it will increase the temperature of the joint, and the temperature rise will accelerate the corrosion of the joint, increase the contact resistance, and cause a vicious cycle until it burns. The output waterproof connector of the inverter has a wire diameter designed according to the copper wire. If an aluminum wire is used, a larger one is required. For example, 30KW inverter, the design output uses 10 square copper wire, the aluminum wire needs 16 square, the cable area increases, and the waterproof terminal area is limited, it may not be able to accommodate, some installers will remove the waterproof terminal Or damage, this will cause the terminal block protection is not strict, easy to enter the water, the insulation is not good. Also choose a multi-strand BVR soft copper wire, do not use BV hard copper wire, because the hard copper wire and the terminal are easy to contact badly, there is stress in the corner, easy to cause the screw to loose, poor contact.

6. Common domestic photovoltaic system design: common household photovoltaic system, single phase is generally 3kW to 8kW, three-phase is generally 4-10kW, when conditions permit, it is recommended to use three-phase grid connection, because under the same conditions, Three-phase grid-connected investment is less than single-phase grid-connected, and the power generation is high. For example, 10kW system, single-phase grid-connected requires 2 inverters, DC input 4 strings, 8 DC cables, and AC requires 2 switches, three As long as one inverter, one DC input, two strings, four DC cables, one switch is required for AC. Third, compared with single-phase current, the loss is less efficient; 380V grid-connected has less impact on the grid and will not stop due to the increase of grid voltage.

3kW home photovoltaic design

The plan requires about 30m2 of roof area, 12 blocks of 265Wp PV modules, and a total power of 3.18KWp. The system adopts a 3KW photovoltaic inverter, which is connected to the original indoor household distribution box of the 220V line, and then connected to the owner's indoor low-voltage distribution network via the 220V line, and then can be sent to the city grid.

The maximum DC voltage of the inverter (maximum array open circuit voltage) is 550V, the maximum power voltage tracking range is 70~550V, and the number of MPPT channels is 1 channel/1. Each solar cell module has a rated operating voltage of 30.8V, an open circuit voltage of 38.3V, and a series connection of 12 solar cells in series under rated conditions of ambient temperature of 25±2°C and solar irradiance of 1000W/m2. The working voltage is 369.6V, and the open circuit voltage is 459.6V, which is within the allowable input range of the inverter to ensure normal operation.

When the operating conditions change, the maximum power point operating voltage of the solar cell module string is 12×30.8×(0.35%×35+1)=415V when the average extreme ambient temperature is −10°C, which satisfies the maximum full load MPPT point of 550V. Input voltage requirement; when the extreme maximum ambient temperature is 42 °C, the operating voltage of the solar module is 12×31.2×(-0.35%×17+1)=352.1V, which satisfies the input voltage requirement of the minimum MPPT point of 70V.

System Configuration

Common domestic photovoltaic system configuration:

4.2kW ​​electrical system diagram

5.0kW electrical system diagram

6.0kW electrical system diagram

8.0kW electrical system diagram

10.0kW electrical system diagram