If photovoltaic panels are installed at home, can the charging pile control board recognize the "priority charging with surplus electricity"?

The home is equipped with photovoltaic panels, and the charging pile control board implements "priority charging with surplus electricity" primarily through communication-based judgment, rather than adding an additional current transformer. The mainstream solution in 2026 is the "inverter→EMS→pile" digital handshake, which is cost-effective, fast-responding, and highly accurate.

1. Why Not Use a Current Transformer

• The current transformer solution requires one unit each at the busbar of the distribution box, the photovoltaic outgoing line, and the charging pile incoming line. Synchronizing the sampling of the three transformers is challenging, with a 100ms time difference leading to a 10% error in power calculation.

• The transformer has a precision of 0.5 grade, but in low-power scenarios (excess photovoltaic power of 500W), the error reaches 25W, making it impossible for the post to determine whether it is "excess power" or "theft.".

• The hardware cost is high, with three current transformers + transmitter + wiring approximately costing 150 yuan, and requires drilling and modifying the distribution box.

2、 Communication judgment scheme (mainstream)

Photovoltaic inverters (Huawei, Sunshine, Goodway) come with RS-485/Modbus interfaces for real-time output:

Current power generation P_pv

• Current grid connected power P_grid (positive value for selling electricity, negative value for buying electricity)

• Available surplus power P_surplus=P_pv - P_load_mame (internal calculation of inverter)

• The energy management system (EMS) or home intelligent gateway reads inverter data and runs simple algorithms:

If P_surplus>7kW, charge the pile at full power

• If 3kW<P_surplus<7kW, dynamically adjust the pile to P_surplus -0.5kW (margin)

• If P_surplus<1kW, the pile will be suspended or the reservation for night valley electricity will be changed

• EMS sends the "Allow Power" command to the charging station control board via RS-485 or WiFi, and the control board executes it directly with a response time of less than 500ms.

3、 Pile end hardware requirements

In 2026, mainstream control boards have reserved dual RS-485 interfaces:

• Connect all the way to the inverter/EMS to receive residual power instructions

• Connect the electricity meter all the way, and the metering and billing do not affect each other

No need for additional transformers, BOM cost increases by 0 yuan (interface reserved), only firmware support for Modbus RTU master station mode is required.

4、 Minimalist solution without EMS

If the user does not have EMS, some control boards support "single RS-485 direct inverter":

• As a Modbus slave, the station reads the inverter register at regular intervals

• Onboard MCU runs lightweight algorithms and autonomously decides charging power

Limitations: No household load data available, possible misjudgment (such as sudden start of air conditioning causing a sudden drop in residual power)

5、 One sentence summary

The priority charging of surplus electricity for vehicles relies on inverter → EMS → pile communication judgment, rather than current transformers. In 2026, the charging pile control board comes standard with dual RS-485, and the firmware supports Modbus for zero cost access. The response time is less than 500ms, and the accuracy is guaranteed by the inverter. Only old photovoltaics without communication interfaces can be replaced with transformer solutions.

The communication charging pile control board produced by Xincheng Technology is of high quality and good price. Welcome to inquire and purchase!