Some Knowledge about Solar Water Pump Inverter

2020-11-23

Solar water pump inverter is one of many categories of inverters. The main function is the same as our common grid-connected inverter, which converts photo voltaic direct current into alternating current. However, many improvements have been made to the water pump inverter, which saves a lot of costs for the system and expands the scope of photovoltaic applications.

The solar pump inverter is an off-grid inverter, which does not depend on the grid and can work independently with the load. However, the conventional off-grid inverter needs to be equipped with a battery to work, and the lead-acid battery is expensive, the cost accounts for about 30% of the system, and the life span is only 3-5 years, which affects the system's investment income. The photovoltaic water pumping system does not need to be equipped with batteries. It works when there is sunlight. Build a water tower at a high place, and when water is needed, water can be taken from the 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 of an off-grid system, but the cost of the water tower is much lower than the battery.

The motor is the most difficult load for off-grid systems because the motor requires a lot of energy to start. The starting power of a conventional motor is about 3 times the rated power, while the pump motor needs to pump water to a high place. The starting power is 5 times the rated power. If the conventional off-grid inverter is equipped with a water pump motor, it needs to be amplified by 5 times. For example, a 2kW water pump motor requires a 10kW off-grid inverter to drive it. In normal operation, the DC input must be greater than 2kW, so the motor can run continuously. This increases the cost of the system, and the solar water pump inverter adds 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 also make the pump run.

Why the water pump inverter can have such a smart function? This should start from the principle of alternating current. Alternating current has three elements: voltage, current and frequency. Under normal circumstances, the frequency is constant at 50 Hz. The motor starts and turns 50 times every second, the power changes with current and voltage, so we generally use voltage and current to calculate power. But the motor is different. Its power is related to frequency. The normal rated power is the power at a frequency of 50Hz. When the frequency drops, the power will also drop. The rated power of the motor = rated torque × rated rotation, as long as the rated torque does not change, the motor can run, so that when the frequency and voltage drop, the rated power decreases in proportion to the speed or frequency. The water pump inverter adds the inverter function to the inverter, which can change the frequency of the AC output. When starting, the frequency is reduced, and the speed is exchanged for power. After the motor is started, the frequency is increased and the speed is increased. The frequency can also change with the light. In this way, even a 1kW photovoltaic input can drive a 4kW water pump to run. Isn't it amazing?