NEWS



22

2022

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11

Why do loads prioritize the use of photovoltaics

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Spontaneous self-consumption, surplus grid refers to the electricity generated by photovoltaics, which is preferentially used for the load, the load is not exhausted, and then sent to the grid. Friends who contact photovoltaics will have many questions: how can the electricity generated by photovoltaics be guaranteed to be prioritized for the load, instead of the electricity generated by photovoltaics entering the grid, and the load takes electricity from the grid? What basis can be used to say that the electricity used by the load is photovoltaic, not the electricity sent by the grid? Will frequent switching between photovoltaic power generation and utility power affect inverters or equipment?

1. At the same time, the current has only one direction.

According to the circuit principle, the current flows from a place with a high voltage to a place with a low voltage, and at the same moment, the direction of the current is unique, that is, the current cannot flow out at the same time at the same point, nor can it flow in at the same time. At the same moment, we take the user-side meter as a node, and the current has only one direction, either the photovoltaic current to the grid, or the current of the grid to the load. Therefore, there is no situation where the photovoltaic is fed into the grid at the same time and the load draws electricity from the grid.

2. Why can photovoltaic power generation be used preferred?

PV power generation is a kind of power supply, it can output electrical energy, and can only output electric energy, and the grid is a special power supply, it can provide electrical energy for the load, but also as a load to receive electric energy, according to the principle that the current is flowing from a high voltage to a place with low voltage, when PV power generation, from the load point of view, the voltage of the grid-connected inverter is always a little higher than the voltage of the grid, so the load preferentially uses PV power generation, only when the power of PV is less than the load power, the voltage at the grid-tied point will decrease, The grid will supply power to the load. Distributed photovoltaic, spontaneous self-consumption, surplus on the Internet, generally to install two meters, inverter out to install a meter, record PV power generation, user side and network to install a two-way meter, user side and network to install a two-way meter, users buy electricity.

In grid-tied feed systems, commercial power supplies are mainly used to build the voltage/frequency/phase of the grid. The grid-connected inverter does not output the voltage, but tracks the phase and waveform of the grid, 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 high voltage to low voltage, so as long as the photovoltaic energy can generate electricity, it will be sent to the load first.

In terms of load, the load consumes current, which is obtained from a current source away from itself. Take the roof system, the grid-connected inverter is after the mains transformer, of course, the grid-connected inverter feeds and is used first.

3. PV and mains frequent switching,

Will it affect the inverter or equipment?

Because the light is unstable, for a long time, the power of solar photovoltaic power generation is also unstable, so the electricity used for the load, sometimes can be photovoltaic power, sometimes can be mains power, sometimes can be photovoltaic power and mains power supply at the same time, in fact, this is on the surface. Theoretically, the electricity used by the user is the electricity of the grid, because the inverter has a function that converts the electricity emitted by the components into exactly the same electricity as the grid, with the same voltage, the same frequency, the same phase. This switching process does not actually exist.

4. How can users distinguish the electricity in use?

Solar PV or power grid?

From the perspective of power quality, users simply cannot tell where the electricity they use comes from. In fact, there is no need to distinguish what kind of electricity is used. As shown in the figure below, the network is installed in the substation room, and the network is installed with two-way meters. The current has two directions, which can measure the electricity generated by the photovoltaic, how much the load is used, and how much the Internet output is. However, plant 1-3, the current has only one direction, and it is not possible to measure which plant photovoltaic uses how much electricity and how much electricity the grid uses.