What Is Solar Pumping Inverter

Solar Pumping Inverter controls and regulates the operation of the solar water pump system, converts the DC power emitted by the photovoltaic array into AC power, drives the water pump, and adjusts the output frequency in real time according to the changes in the intensity of sunlight to achieve maximum power point tracking (MPPT).

Photovoltaic water pump inverters is one of the many types of inverters. Its main function is the same as our common grid-connected inverter, which converts photovoltaic DC power into AC power. However, the water pump inverter has made many improvements, saving a lot of cost for the system and expanding the scope of photovoltaic applications.

A photovoltaic water pump inverter is an off-grid inverter that does not rely on the power grid and can work independently with loads. However, conventional off-grid inverters need to be equipped with batteries to work, and lead-acid batteries are expensive, accounting for about 30% of the system cost, and have a short life of only 3-5 years, which affects the investment return of the system. The photovoltaic pumping system does not need to be equipped with batteries. It works as long as there is sunlight. A water tower is built at a high place. When water is needed, water can be taken from the water tower. The inverter itself will also be equipped with a water level switch, which is very convenient and practical. Its function is equivalent to the battery in the off-grid system, but the cost of the water tower is much lower than that of the battery.

The motor is the most difficult load to carry in the off-grid system, because the motor needs a lot of energy to start. The starting power of the conventional motor is about 3 times the rated power, and the water pump motor needs to pump water to a high place. The starting power is about 5 times the rated power. If the conventional off-grid inverter is to carry the water pump motor, it needs to be enlarged 5 times. For example, a 2kW water pump motor requires a 10kW off-grid inverter to drive it. During normal operation, the DC input must also be greater than 2kW for the motor to continue to run. This increases the system cost, and the photovoltaic water pump inverter has added a special algorithm, which generally only increases the power by 20%. For example, a 4kW water pump motor can be started with a 5kW pumping inverter. During operation, the photovoltaic input power does not need 4kW to run continuously, and about 1kW can make the water pump run.

Why does the water pump inverter have such a powerful function?

This starts with the principle of alternating current. Alternating current has three elements: voltage, current and frequency. Under normal circumstances, the frequency is constant at 50Hz. When the motor starts, it rotates 50 times per second. The power changes with the current and voltage, so we usually use voltage and current to calculate the power. But the motor is different. Its power is related to the frequency. The normal rated power is the power at a frequency of 50Hz. When the frequency decreases, the power will also decrease. The rated power of the motor = rated torque × rated speed. As long as the rated torque remains unchanged, the motor can run. In this way, when the frequency and voltage decrease, the rated power decreases in direct proportion to the speed or frequency. The water pump inverter adds a frequency converter function to the inverter, which can change the frequency of the AC output. When starting, the frequency is reduced to exchange speed for power. After the motor starts, the frequency is increased to increase the speed. The frequency can also change with the light, so even a 1kW photovoltaic input can drive a 4kW water pump. Isn't it amazing?

Since the functions of water pump inverters are so powerful, can their application range be expanded? The answer is no. Since the output voltage, current, phase, and frequency of water pump inverters all change with light, they cannot be used in many occasions.

1. Due to technical limitations, water pump inverters cannot be used in parallel. One inverter must be equipped with one motor, so the maximum power will be limited; there is currently no water pump inverter that supports energy storage. DC coupling in some low-temperature areas in winter, the water tower outside will freeze, and the photovoltaic pumping system will also be limited; the water pump inverter cannot be connected to the grid because the grid requires frequency and voltage synchronization.

2. The loads that the water pump inverter can carry are very limited. At present, except for the water pump motor, any load with stable power and requirements on voltage and frequency cannot be carried. For example, the water pump inverter cannot directly carry electric lights, refrigerators, computers, washing machines, and even variable frequency air conditioners. It can only carry pure resistive loads such as water heaters.