'The same power station, using different brands of inverters actually generates more than 4% of the difference,' said a person in charge of a power plant in Yunnan. Actually, there are more than one power stations in the country that currently encounter such a situation. What is more surprising is that At present, most inverter manufacturers in China have efficiency of over 98%, and the difference is also a few per cent. Why can the difference in power generation be so great? Are we neglecting other measures that cannot be measured or predicted? Factors? Today we will take you from a technical perspective to reveal this mystery!
"With different inverters, the difference in power generation is 4% or more?"
With doubts and incomprehension, we visited a photovoltaic power station in Yunnan Province, which is a typical Yunnan-Guizhou mountain terrain. The average annual sunshine hours of the power station is 2370h, the annual average total radiation is 6462.9MJ/m2, and the elevation is 2080m~ 2360m. The light resources are abundant. As a key local photovoltaic project, the overall project plan is divided into 7 phases with a total capacity of 200MWp. Today, we focused on the analysis and comparison of the three phases of 40MWp power generation.
Taking the 40MWp project of the third phase of the power plant as an example, from the perspective of the PV array, the project is divided into three sets of power lines. All the arrays in the power collection line are connected to 1.6184 MWp photovoltaic modules. Each array uses a domestic well-known manufacturer 340W single. Crystalline silicon modules, using 20 photovoltaic modules in series per string, are identical in component specifications, parameters and series configuration.
As the core equipment that determines the power generation of photovoltaic power plants, the inverter uses two domestic famous brands of string inverters. A 50kW string inverter of 34 domestic A manufacturers was used; No. 2 collectors and No. 3 collectors had 9 square arrays and 8 square arrays respectively, and both square arrays also used the same old domestic inverters. Thirty-four TS50KTL_PLUS inverters from Tebian Electric.
By comparing and analyzing the measurement data obtained by the independent electricity meters of each collection line, we intercepted the electricity generation data for January and February of 2018. The result was surprising. There are 2 collector wires with different inverters. The difference in electricity generation in the month was as high as 4%. The specific data are as follows:
"Why is there 4% difference in power generation?"
As we all know, photovoltaic power plant is an integrated and integrated system engineering. Under the limited application environment, only the seamless connection and matching between each device can make the performance of each device get the most out of it.
The application of this project is a typical plateau mountainous terrain. There is a problem of installation loss, installation orientation, and loss of power generated by shading. Due to the block between the front row and rear row of the unit, the string itself and the field wiring The voltage difference between the strings and the shadows caused by dust, clouds, and shadows on the site are inevitable problems for photovoltaic power plants, and are also a major 'culprit' for at least 4% of power generation losses.
Once again contrasting the 1-2 months of power generation of a PV project in Yunnan, we found that the biggest difference is that the two sets of inverters are used for each set of power lines. It is reported that the 4-way MPPT string is used by the A manufacturer of the No. 1 power line. Inverters, No. 2 and No. 3 collectors use TBEA's 8 independent MPPT string inverters (8 independent MPPTs and 4 MPPTs are shown below).
From the above figure, we can see that the PV arrays of No. 2 and No. 3 collective wires are connected to the MPPT of each inverter of the single channel separately, while the No. 1 collective wire is the average 2-way set of inverters connected to the MPPT. Visually comparing the obvious findings, if one of the PV arrays is blocked or damaged, the independent MPPT design of No. 2 and No. 3 collector lines using TBEA inverters will only affect the range of the corresponding strings. The 2-way string pair 1 MPPT used by the No. 1 collector line will affect the power generation of the 2-way string.
"The superior advantages of TBEA inverters"
After finding the difference, we analyze the technical characteristics of the TBEA inverter used in this project. The product adopts an 8-channel independent MPPT design to increase the MPPT permeability of each string to 100%, which ensures the complex situation. The system boosts the power generation of the system by more than 4%, and completely eliminates the loss of parallel mismatch between strings. At the same time, each independent MPPT design enables the inverter to have a natural anti-reverse function to ensure the safe and stable operation of the system. The modified DC side adopts precision detection technology, with IV diagnostic function, inverter efficiency increased by 0.2%; rated voltage on the AC side is 540V, and the cable loss on the AC side of the traditional 500V string inverter is reduced by 14.3%. The increase of 0.286%. Combining these data, I think it is not difficult for everyone to understand why the same application environment actually has more than 4% of the power generation gap.
From the perspective of the PV power plant application environment, the application of the ground conditions is increasingly complex, and the shadow of the photovoltaic array is shadowed and inevitably obstructed. The shunted parallel connection caused by shadow shading greatly influences the amount of power generation, causing the components to receive shadows after being shaded and blocked. Illumination and temperature are affected, directly restricting the output characteristics of the component.
From the perspective of the products currently being introduced by external parties, after the introduction of the TS50KTL_PLUS tandem inverter in 2017, due to the outstanding performance of product field applications, the company’s self-confidence in products has been continuously strengthened and innovatively improved, targeting successively the mid-size commercial and industrial roofs. Village-level poverty alleviation and double-sided batteries introduced the TS36KTL_PLUS/TS60KTL_PLUS/TS70KTL_BF/TS75KTL_BF/TS80KTL_PLUS series of cascade inverters. The series of products all have independent MPPT tracking technology, which increases the string MPPT permeability to 100% and is applied in complex ways. The system can at least increase the system power generation by 4% and reduce the parallel mismatch loss to 0.
The 4% power generation loss at the power station is not just a figure, but also reflects the characteristics and technology of the product. Nowadays the 'leader' has continuously forced the photovoltaic industry chain to carry out technological improvement and innovation. The inverter, as the core equipment of the photovoltaic power station, only adapts. Different characteristics of the terrain, a variety of application environments, and high conversion efficiency, and long-term reliable operation can maximize the return on investment, will be the power station was 'stuck' power generation back to the owners, in order to protect the owner's maximum return.
