Where is the difference between the inverter screen display power generation and the meter metering power generation?

Now more and more people have installed photovoltaic power stations in their homes. Most families use photovoltaic power stations as a financial tool, and their electricity bills are not earned at all. But often a friend will encounter a problem, why do they see through the inverter screen power generation data and the last received electricity (electricity) will be inconsistent? Or more directly, why see from the inverter and the final meter of electricity generation will be inconsistent?
Today, Xindun will help you from a theoretical point of view to analyze the inverter screen power generation and meter measurement of power generation in the end where the difference is: Difference one reason: measurement accuracy requirement is different.

The photovoltaic inverter can calculate the output of the inverter by sampling the alternating current (Uac, Iac), but its main purpose is to detect the working conditions of the photovoltaic power station, such as voltage, frequency, THDI, etc. The generation measurement is only preliminary measurement, not to accurately measure the output. Therefore, the scheme design and measurement accuracy of the inverter integrated electric energy metering are somewhat different from the national standards for professional electric energy metering tools, so the measurement error will be greater.

Electric energy meter is what we usually say, the purpose of installation is to accurately measure the power generation, so whether in hardware and software design or measurement accuracy must be strictly in accordance with national standards, the real power generation measurement error must be controlled within a certain range. For example, the nameplates of the watt-hour meters currently commonly used by residents will be marked with a precision rating of 1.0S, which means that only a measurement error of (+) 1% is allowed.

That is because of the above explanation, the accuracy requirements are different, will naturally lead to people see the inverter power generation and the actual electricity generation capacity of the meter is not consistent with the situation.

Difference two reasons: measurement method is different.

According to the system experts, the general inverter display is the apparent power of the photovoltaic system, while the meter shows the active power, there is a certain difference between the two.

Active power refers to the part of power (such as heat, light or mechanical energy) that is consumed in an AC circuit and irreversibly converted by a resistive element. The apparent power refers to the total power that an alternating current power supply can provide. It is numerically the product of voltage and current in an alternating current circuit.

In addition, there is also a reactive power in the AC circuit, which refers to the reversible conversion of electrical power due to the presence of reactive elements (pure inductance or pure capacitance) in the AC circuit, which expresses the maximum rate of energy exchange between the AC power source and the magnetic field or electric field.

The apparent power, active power and reactive power form a right-angled triangle, which we call the power triangle, so the relationship is: power is denominated as P active power in kilowatt (kW) and S apparent power in kilovolt-ampere (kVA).
S= (KVA) full power (apparent power); P= (KW) active power; Q= (Kva) reactive power

The above explanations are too obscure, but it\'s simple to say that an ammeter measures active power, while an inverter measures apparent power, and the two can\'t be equally signed, so the end user will see the difference between the display of the inverter screen and the ammeter.

Difference cause three: line loss

According to the photovoltaic system design and installation layout diagram (the following figure), the installation of photovoltaic inverter is closer to the module array, through the inverter AC output, through the AC cable connected to the AC distribution box to the power meter, grid.

Thus, there must be loss in the power transportation process from inverter to photovoltaic meter. The loss may be affected by the thickness and length of cable material, contact loss of terminal and so on. Therefore, there will be differences between the measured data of the inverter and the metering data of the meter.

All of the above, in fact, put together a sentence: from a scientific point of view, there is a difference between the inverter and the meter on the amount of electricity measurement is normal, if the two measurement is consistent, it is accidental.

We do not have to be entangled in the future between the two differences, to a normal point of view, the inverter screen data as a normal work of the photovoltaic system as a feedback, as a reference to real power generation (after all, we can not always look at the meter). At the same time, we must be absolutely convinced that the power metering meters provided by the State Grid are strictly tested, and the State Grid will be in accordance with the accurate meter data for real-time settlement.