Generally speaking, the electricity generated by photovoltaic systems is prioritized for use by loads. When the photovoltaic power generation exceeds the load's electricity consumption, there will be reverse electricity flowing into the grid, known as "reverse current". The power grid has strict regulations on the grid connection of photovoltaic power generation, and unauthorized reverse power grid connection will face relevant penalties. Meanwhile, for photovoltaic projects that do not require internet access, anti backflow protection is the key to achieving self-sufficiency in green energy.
So what is anti backflow? What is its working principle and solution?
1. What is backflow prevention?
In a photovoltaic system, the output of DC electricity from photovoltaic modules is converted into AC electricity by an inverter for use by the load; When the power generation of the photovoltaic system is greater than the load power, due to the inability of the load to fully absorb the electricity generated by the photovoltaic, the excess electricity will flow into the grid in the opposite direction, resulting in "reverse flow". A photovoltaic system with anti backflow function can timely reduce the output power of the inverter when the power generation exceeds the load power, in order to reduce the overall power generation of the system, ensure that the electricity generated by the photovoltaic is only used by the load, and avoid excess electricity flowing into the grid.
2. Why is it necessary to install anti backflow measures?
Generally speaking, there are several reasons why it is necessary to install anti backflow:
① Power grid policy restrictions. Due to policies and the carrying capacity of the power grid, some regions are not allowed to connect to the grid. Unauthorized reverse power grid connection will face relevant penalties;
② Grid connected power limit. The power grid has strict restrictions on grid connected power. If the excess electricity is injected directly without control, it will have an impact on the power grid;
③ The principle of self use and not connecting surplus electricity to the internet. The photovoltaic power generation system needs to ensure that the generated electricity is preferentially supplied to local loads. If local loads cannot be consumed, anti backflow devices must be used to prevent excess electricity from flowing back to the grid.
3. Working principle of anti backflow
In practical applications, the real-time power, current magnitude, and direction of the line are obtained by installing an anti backflow meter and CT transformer on the incoming line bus of the household. When a current is detected flowing into the grid (reverse current), the anti backflow meter transmits the reverse power data to the inverter through RS485 communication. The inverter responds in seconds after receiving the command, reducing the output power of the inverter and keeping the current flowing from the photovoltaic power station to the grid close to 0, thereby achieving anti backflow and not sending excess electricity to the grid.
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Single Phase/Split Phase/Three Phase Inverter to meet different using environment, with IP65/IP66 Protection Level
4. Anti backflow solution
Always pay attention to the technical application of inverters in photovoltaic projects, and combine different equipment such as photovoltaic inverters, anti backflow meters, and anti backflow boxes to form anti backflow solutions suitable for different scenarios.
(1) Solution for Single phase Anti backflow System
Equipment required: photovoltaic grid connected inverter, anti backflow meter, communication line between meter and inverter. This scheme is suitable for only household photovoltaic scenarios.
(2) Solution for single machine three-phase anti backflow system
For household low-power grid connected inverters, a DC anti backflow meter can be directly used. The AC output terminal of the inverter is directly connected to the meter and then connected to the grid connection point to achieve anti backflow; For high-power grid connected inverters, it is necessary to detect the current on the grid connected bus through CT transformers, proportionally reduce the current through transformers, and connect it to anti backflow meters to achieve current and power measurement at the grid connection point.
(3) Multi machine anti backflow system solution
Multiple inverters are connected in series through communication interfaces to data collectors, suitable for multi machine mode, with more powerful functions and larger capacity.
Summary
The anti backflow solution can effectively meet the policy requirements of "grid connection without feedback" in certain regions. In addition, anti backflow can optimize economy, improve energy utilization efficiency, and adapt to technological development and policy changes while ensuring stable operation of the power grid and enhancing system safety.