Solar power generation serves as a valuable complement to traditional energy sources. Due to its significant role in environmental protection and economic growth, all developed countries are actively promoting the development of solar energy. Currently, small and medium-sized solar power systems have evolved into a mature industry. There are two primary methods of solar power generation: photovoltaic (PV) power generation and solar thermal power generation. Among these, photovoltaic power stands out for its ease of maintenance and flexibility in power output, making it widely used for medium and small-scale grid-connected systems.
Photovoltaic power generation systems can be connected to the grid in two main ways: centralized and distributed grid connection. Centralized grid connection involves direct transmission of electricity to the main power grid, with the grid managing power distribution to users. This method is one-way and suitable for large-scale solar farms located far from load centers, such as desert-based photovoltaic plants.
On the other hand, decentralized or distributed grid connection allows the generated electricity to be directly supplied to local loads, with any surplus or deficit being managed through the main grid. This type of connection typically enables two-way power exchange and is ideal for smaller systems, especially those integrated into urban buildings.
As the government continues to support residential distributed PV systems, the installed capacity is expected to reach 60GW by 2020, surpassing that of centralized PV plants. More individuals are now getting involved in photovoltaics, but many lack the necessary technical knowledge. Therefore, this article aims to provide a detailed guide on the correct wiring methods for electricity meters when connecting photovoltaic systems to the grid.
Currently, photovoltaic grid-connected electricity meters are divided into three-phase and single-phase types. When the inverter capacity of a PV system is 5kW or less, a single-phase meter is typically used. To better understand this, it's essential to first grasp the differences between three-phase and single-phase electricity.
Three-phase power refers to a system where three alternating currents are generated with equal amplitudes, frequencies, and a 120° phase difference between them. This type of power is commonly used in power grids, including China’s three-phase four-wire system, which consists of three phase lines (U, V, W) and one neutral line. The voltage between phase lines is 380V (line voltage), while the voltage between a phase and the neutral line is 220V (phase voltage). If the load is unbalanced, it can cause a shift in the neutral point, leading to voltage fluctuations.
In contrast, household electricity is single-phase, using only one of the three phase lines along with the neutral line, resulting in 220V. Most household appliances operate on this single-phase system, whether they have two or three prongs. Two-prong sockets are for live and neutral lines, while three-prong sockets include an additional ground line for safety, particularly for metal-cased devices.
Single-phase electricity is essentially part of the larger three-phase system. A three-phase four-wire system can be split into three separate single-phase circuits. Many residential buildings are designed with this in mind, distributing power evenly across the three phases to balance the load and maximize efficiency.
For most home users with systems under 5kW, a single-phase inverter is used, requiring a bidirectional meter for grid connection. These meters are designed to measure both the electricity consumed from the grid and the surplus power fed back. They usually have six terminals: two for incoming lines, two for outgoing lines, and two for pulse outputs.
When installing a bidirectional meter, it’s important to connect the main supply to terminal 1, the neutral line to terminal 4, and the outgoing lines to terminals 6 and 3. A unidirectional meter is also needed on the user side to measure total PV generation. Proper wiring ensures efficient self-consumption and surplus power feeding into the grid.
There are various wiring configurations, including combinations of bidirectional and unidirectional meters, depending on system size and requirements. For three-phase systems, similar principles apply, with specific terminals designated for each phase.
Before installation, it’s crucial to consult a qualified electrician to ensure safety and compliance with local regulations. Additional components like air Switches and leakage protection devices should also be considered to safeguard the electrical system.
By understanding these connections and following proper installation procedures, homeowners can efficiently integrate solar power into their daily energy usage, contributing to a sustainable and cost-effective energy future.
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