Why is the power generation on my inverter different from that on the meter?

Household photovoltaic power stations mainly utilize idle resources on existing household buildings, such as roofs, wall facades, balconies, courtyards, etc., to install and use distributed photovoltaic power generation systems.

The installed photovoltaic power station not only generates subsidies for electricity, but also provides free electricity for your own use, and unused electricity can be sold to the State Grid. In the past, you spent money on electricity, but now you can make money by selling electricity, with a rate of return of over 10%!

At present, photovoltaic power stations have entered thousands of households, bringing income to the people who installed them. However, when the electricity generated by the household photovoltaic power station is sold to the state grid, many households who installed it ask a question: Why are the inverter and the meter different? Generally speaking, the inverter count is higher than the meter count. Why is this?

1. Errors in the inverter and meter measurement

We inquired about this issue with experienced electricians and inverter manufacturers, and the answer we received was this: Although the inverter can measure electrical work, its purpose is not to accurately reflect the power generation, but to monitor the working status of the power station. Therefore, the metering part is not strictly designed according to the national measurement standards, and its circuit is much simpler, so the error is larger.

The measurement of electric energy meters also has errors. Single-phase or three-phase meters will have accuracy levels marked on the nameplate, such as 0.2S, 0.5S, 1.0S, 2.0S, etc., and errors within ±0.2%, ±0.5%, ±1.0%, and ±2.0% are allowed. The accuracy level of the electric meters commonly used by residents is 1.0S, so there is an error of ±1%. Therefore, it is normal to have errors.

2. Differences in measurement methods lead to

The electric energy meter displays active power, while the inverter displays the apparent power of the system. The difference between the two is cosφ, which is the power factor, which is generally around 0.8.

3. Other factors

One is the irregular output waveform. Generally, electrical appliances are designed according to pulse digital signals, but the working waveform of our photovoltaic power station is through the inverter, which realizes the conversion from DC to AC. However, there is still a certain gap between its waveform and the regular sine waveform, so there is an error in the measurement. The second is the sampling method at the same point. According to the installation requirements: the sampling of the inverter should be closer to the front, closer to the component array; the meter should be closer to the grid connection point, so according to the calculation formula of work: W=UIT.

It can be seen that the voltage and current will definitely change in different ways at different sampling points, which will also lead to different calculation results. The third is the difference in working environment. The uncertainty of the inverter temperature, the inverter and meter calibration coefficient, the material thickness and length of the cable, the contact loss of the terminal, etc. will affect the accuracy of the power measurement.

To sum up, it is normal for there to be errors in the measurement between the inverter and the electricity meter, but don’t get hung up on it. Trust the electricity meter and take the meter installed by the State Grid as the standard.

The use of solar energy to generate electricity has become a trend. Rooftop distributed photovoltaic power generation is favored by people because of its advantages of energy saving, environmental protection, electricity cost saving, and stable income. It is reported that users can not only use photovoltaic power for their own use, but also sell the unused electricity to the power grid company for profit. At the same time, users can also enjoy the photovoltaic power generation subsidy given by the state. If you are interested, install it quickly!