First contact with photovoltaic friends, will have this a question, photovoltaic electricity, how to ensure that priority to the user's load, rather than photovoltaic electricity sent to the grid, the load from the grid to take electricity. Because the PV electricity sold to the grid price is cheap, only about 0.4 yuan / degree, while the grid sold to the user's price is more expensive, generally to 0.6-1.1 yuan / degree or so.
A: From the circuit principle, the current is flowing from the high voltage to the low voltage, at the same moment, the direction of the current is unique, that is to say, the current cannot both flow out and in at the same point. We take the customer side of the meter as the node, at the same time, the current has only one direction, either the PV current to the grid, or the grid current to the load. So there is no situation where PV electricity is sent to the grid at the same moment and the load takes electricity from the grid.
Q: Why PV power can be used in priority?
A: PV power is a power source, it can output electricity, and can only output electricity, while the grid is a special power source, it can provide electricity to the load, but also as a load to receive electricity, according to the current are from the high voltage place to the low voltage place this principle, when the PV power, from the load, the voltage of the grid-connected inverter is always a little higher than the voltage of the grid, so the load priority to use PV power, only when the power of PV is less than the load power, the voltage of the grid will drop, the grid will supply power to the load.
Distributed photovoltaic, self-generation, surplus online, generally need to install two meters, the inverter out of a meter to record photovoltaic power generation, the user side of the parallel network installed a two-way meter, used to record the photovoltaic to the grid power delivery and users to buy electricity from the grid.
Because the PV inverter voltage is higher than the grid voltage, according to the circuit principle, the current is flowing from the high voltage place to the low voltage place, so as long as the PV can generate electricity, it will definitely be sent to the load side first.
Note things: PV grid-connected points should be installed on the inside of the customer's meter, near the load side. The grid is equivalent to an infinite power supply, PV power generation accounts for very little, so no matter how PV power generation changes, the grid can always remain stable.
