At present different PV inverter companies have different technical routes for PV string inverters.
Single-phase PV string inverters that power rating under 10kW and three-phase PV string inverters that under 15kW generally are equipped with two MPPTs,and each MPPT can be connected with one or two strings;
Commercial and Industrial PV string inverters that power range from 10kWto 100kW generally use2~10 MPPTs,and each MPPT can be connected with 2~4 strings.
Normally large utilities choose PV string inverters that power from 180kW to 250kW which have1~15 MPPTs,and each MPPT can be connected with 2~12 strings.
The number of MPPT has a certain impact on the power generation of the system, From the perspective of solving the loss of power, the fewer strings behind the MPPT,the lower energy loss because of each MPPT loop runs independently, and the string configuration is would be more flexible.
With regards to the stability and efficiency, the more strings connected to one MPPT would be better. Because the more MPPTs may bring the higher cost, more energy loss and worse reliability of the whole system.
The most common failure of PV systems is the DC side failure.
The common failure modes of the fuse are over-current,aging,and over-temperature .
Over current broken is a protective process that occurs when overload,short circuit,etc; aging broken refers to a faulty that occurs without over current due to its own aging and reduced current interception capacity during long-term work;
The current of the fuse has a great relationship with the temperature.If the fuse works at a high temperature, the current interception capability will decrease,and the possibility of faulty broken is relatively high.
One MPPT connects 1or2 strings,even if one of the strings is short-circuited,the current will not exceed 15% of the total current, So there is no need to configure a fuse.But if an MPPT is configured with N(N≥3) strings, anyone of the strings is short-circuited,this string will withstand(N- 1)*short-circuit current,so,need to configure a fuse.
The principle is as follows: When an MPPT is configured with N(N≥3)strings,the short circuit will increase.
As shown in figure 2 above, an MPPT is connected to three strings,namely S1,S2 and S3. When a short-circuit to ground occurs somewhere in S3,it can be seen from the figure 2 that the negative current of S3 does not flow to the grounding point through the fuse,and the negative current of S1 and S2 flows to the grounding point through the common point and the fuse of S3. The total current of the fuse is twice time of its rated current and the fuse will break. Therefore, an MPPT that connects more than 2 stings needs to be equipped with a fuse.
According to different landform,application scenarios and solar panel shading conditions, Growatt provide different solutions with different MPPT numbers to reduce the TCO(Total Cost of Ownership),boost the economic benefits for customers.
- For the solar plant deployed on hillsides or rooftop with complex terrain have problems of inconsistent orientation and partial occlusion, we should choose the PV inverter configured multiple MPPTs,which could reduce the power loss because of solar panel mismatch issue. Then an inverter with 2 string inputs for each MPPT would be a better choice, no fuse design, accurate fault location,and easier maintenance.
Growatt new generation MAX100K- 150KTL3-XLV/MV series PV inverters with 10MPPTs and each MPPT has 2 strings,it would be your best choice.
This new series of products also have created many “highest” in the market: the highest power density and the highest power rating of single unit for C&I inverters,the highest string current up to 16A.Furthermore, with the high efficiency, integrate the online IV curve scanning, PID function, AFCI protection and PLC communication optional, all of these could help customers to achieve the highest returns of solar investment.
2. For the solar plant which the terrain and rooftop is not very complicated, we recommend to choose the PV inverter with fewer MPPTs and each MPPT could configure multiple strings, which can take into account PV panels power loss and high efficiency,the design is also more flexible. Growatt MAC 50-60KTL3-XLV/MV series PV inverter that with 3 MPPTs and each MPPT has 4 strings,its the hot-sale products in emerging countries such as south east Asia, Latin American etc.