Why Does the Load Give Priority to Photovoltaic Power Generation?
"Spontaneous production and self-use, and the remaining amount on the national grid" refers to the electricity generated by photovoltaics, which is given priority to the load, and the load is not used up before it is sent to the grid. Friends who are new to photovoltaics will have many questions. How can the electricity generated by photovoltaics be guaranteed to be used by the load first, instead of the photovoltaic electricity being fed into the grid and the load taking electricity from the grid? Is there any basis to explain that the electricity used by the load is photovoltaic electricity, not electricity sent from the grid? Will the frequent switching of photovoltaic power generation and mains power affect the inverter or equipment?
1. The current has only one direction at the same time
From the circuit principle, the current flows from the place with high voltage to the place with low voltage. At the same time, the direction of the current is the only one. That is, current cannot both flow out and flow in at the same point at the same time. We take the user-side meter as a node. At the same time, the current has only one direction, either the photovoltaic current goes to the grid, or the grid current goes to the load. Therefore, there is no situation in which photovoltaic power is fed into the grid at the same time, and the load takes power from the grid.
2. Why should photovoltaic power generation be used first?
Photovoltaic power generation is a power source that can output electrical energy and can only output electrical energy. The power grid is a special kind of power source, which can both provide electrical energy to the load and receive electrical energy from the load. According to the principle that current flows from places with high voltage to places with low voltage, when photovoltaic power is generated, the voltage of the grid-connected inverter is always a little higher than the voltage of the grid when viewed from the load. Therefore, the load preferentially uses photovoltaic power generation. Only when the photovoltaic power is less than the load power will the voltage of the grid connection point drop, and the grid will supply power to the load. Distributed photovoltaics, self-consumption, and the surplus are connected to the Internet. Generally, two electricity meters are installed, one is installed from the inverter to record photovoltaic power generation, and a two-way electricity meter is installed at the grid connection point on the user side to record the transmission of electricity from photovoltaics to the grid and the electricity purchased by users from the grid.
In the grid-connected feeder system, the commercial power is mainly used to construct the voltage/frequency/phase of the grid. The grid-connected inverter does not output voltage but tracks the grid phase and waveform, and only outputs current to the grid, because the voltage of the photovoltaic inverter is higher than the grid voltage. According to the circuit principle, the current flows from the place with high voltage to the place with low voltage, so as long as the photovoltaic can generate electricity, it will be sent to the load first.
From the perspective of the load, the load consumes current and obtains the current from the current source closest to itself. Taking the rooftop system as an example, the grid-connected inverters are all after the mains transformer, of course, the grid-connected inverters feed power and are used first.
3. Frequent switching between photovoltaic power generation and commercial power will not affect the inverter or equipment?
Due to the instability of light, the power of photovoltaic power generation is also unstable. Therefore, the electricity used by the load may sometimes be photovoltaic power, sometimes it may be main power, and sometimes it may be the simultaneous supply of photovoltaic power and main power. In fact, this is superficial. Theoretically, the electricity used by the user is the electricity from the grid, because the inverter has a function that can turn the electricity from the components into the same electricity as the grid, with the same voltage, the same frequency, and the same phase. This switching process does not actually exist.
