In some areas without electricity, it is more economical and environmentally friendly to install photovoltaic off-grid energy storage systems than to use oil generators to generate electricity. Compared with the grid-connected system, the off-grid system is more complicated, and it is necessary to consider the user’s load, electricity consumption, and local weather conditions, especially the diversified load conditions, such as inductive loads such as water pumps and resistive loads such as electric furnaces. , there are single-phase and three-phase. For off-grid photovoltaic systems larger than 10kW, single-unit or multi-unit parallel connection can be used, but each has its own advantages and disadvantages.
This blog mainly introduces the design method of medium and high power off-grid system built with multiple off-grid inverters.
Growatt off-grid SPF5000TL HVM (integrated control and inverter) model supports up to 6 units in parallel, and can build photovoltaic off-grid systems within 30kW. It can form both a single-phase system of 30kW and a three-phase system of 30kW.
Considering that the three-phase load is not necessarily balanced, when six inverters form a three-phase system, there are various configuration methods, such as 222, 321, 411, etc., which can meet the needs of users in different scenarios. The following table shows the actual load and power consumption of a user.
This system is special, there are two types of single-phase load and three-phase load, and the three-phase load is unbalanced. According to the distribution of the load, we first carry out the inverter selection design. The total load power of the system is 24kW. The user said that not all loads will run at the same time, and the maximum power is about 20kW. Therefore, the design adopts 6 sets of 5kW single-phase off-grid Inverter, A-phase uses 3 units totaling 15kW, B-phase uses 2 units totaling 10kW, and C-phase uses 1 unit totaling 5kW, forming a 30kW three-phase unbalanced off-grid system.
Single-phase inverter output has two lines: phase line and neutral line. The neutral lines of 6 inverters are all connected together, the phase lines of 3 inverters are connected to phase A, and the phase lines of 2 inverters are connected to phase A. The line is connected to phase B, and the phase line of one inverter is connected to phase C.
Multiple inverters are connected in parallel, and each inverter needs to be connected to a communication line. The three inverters in phase A are connected together, and the two inverters in phase B are connected together. After connecting the cables, connect the battery. , turn off the output circuit breaker, set the inverter phase on the panel, SPF5000 enters the setting item 23, 3 units of phase A are set to 3P1, 2 units of phase B are set to 3P2, and 1 unit of phase C is set to 3P2. For 3P3, the setting is completed and it can be run.
After selecting the inverter, we calculate the component consumption. The system needs an average of 80 kWh of electricity per day, and the local peak sunshine hour data is an average of 3.5 hours per day. The efficiency of the off-grid system is lower than that of the grid-connected system, about 0.7, so it is calculated as 80 /(3.5*0.7), about 32kW of photovoltaic modules are needed, 120 modules of 280W are used in the design, each inverter has 20 pieces, and the power is 5.6kW. The modules are connected to the inverter in 10 series and 2 parallel. Power 33.6kW.
Then calculate the battery capacity. It is understood that most of the time the user uses electricity during the day, about 50 degrees, and when there is no sun at night, the electricity consumption is about 30 degrees. The customer requires as few batteries as possible to meet the basic requirements, so the design uses 12V250AH There are 16 lead-carbon batteries with a total capacity of 48 degrees, a depth of discharge of 0.7, and a usable power of 33.6 degrees, which basically meets the needs of customers.
Compared with a 30kW medium-power off-grid inverter, the use of multiple low-power single-phase parallel inverters makes wiring and debugging more complicated, but the price is cheaper and the flexibility is high. Even if there are one or two inverters Damaged, the system can continue to run, is a good choice.