Photovoltaic power generation PK--isolated model VS non-isolated model

Photovoltaic grid-connected inverter is the core equipment in solar power generation system. Its main function is to convert the direct current power generated by solar energy into alternating current power with the same frequency and phase as the power grid, and supply electricity to the load equipment connected to the power grid.

The main technical features of photovoltaic grid-connected inverters include maximum power tracking efficiency, tracking response speed, input-output conversion efficiency of the whole machine, operation stability, anti-islanding protection function, total harmonic distortion rate of grid-connected current, full-power stable operating ambient temperature range and maximum power tracking input voltage range. For the end users, the most important thing is the power generation of the photovoltaic system, and the most direct factors affecting the power generation are maximum power tracking efficiency, tracking response speed, whole machine conversion efficiency and component conversion efficiency.

Photovoltaic grid-connected inverters are mainly divided into two categories: one is the isolated model; the other is the non-isolated model. It is generally believed that the non-isolated model must generate more electricity than the isolated model because it omits the isolation link of the intermediate transformer, while ignoring the impact of other factors on the power generation. For this, we conducted a comparative experiment and installed two photovoltaic grid-connected power generation systems. The nominal power of the components is 3 kilowatts. The parameters, installation orientation and lighting environment of the photovoltaic components are exactly the same. The inverters are 3 kilowatts of high-frequency isolation models of Suzhou Zezhong New Energy and 3 kilowatts of non-isolated models of a certain inverter company (a typical representative of non-isolated models). Since the operation in September 2014, the power generation of the two systems has differed by 76 kWh. The system using the isolated inverter of Zezhong New Energy generates 0.51 kWh more electricity per day on average than the system using the non-isolated inverter. In the first two months of our statistics on power generation, this gap was only 0.48 kWh, which shows that the gap in power generation between the two systems is widening.

Through the analysis of the above phenomenon, we draw the following conclusions: At the beginning of system installation, the main factors affecting power generation are the maximum power tracking efficiency, tracking response speed and overall conversion efficiency of the photovoltaic inverter. As the system runs longer, the PID (potential induced degradation) effect in the non-isolated system gradually emerges and the attenuation of the photovoltaic module conversion efficiency caused by this factor gradually increases, resulting in a gradual widening of the power generation gap.

In summary, the use of high-quality isolated photovoltaic grid-connected inverters in photovoltaic power generation systems not only makes the entire system safer and more reliable, but also facilitates installation, saves time and materials, and can extend the service life of photovoltaic modules, bringing maximum benefits to installation users.