How Does a Solar Pump Inverter Work?

A long time ago if you wanted to run a water pump without using power from the grid you had to use a diesel engine, a generator or a windmill. These options have some downsides, like the cost of fuel, complicated machinery or having to rely on the right wind conditions.. Then solar power came along and changed everything.

The problem is, you cannot just connect a pump motor directly to panels. This is because the panels produce a kind of electricity that varies all the time with the sunlight and most pump motors need a supply of electricity to work.

A solar pump inverter solves these problems at the time. It changes the electricity from the panels into a steady supply that the pump can use. It also keeps track of the power point of the panels so every bit of electricity reaches the motor no matter how the sun is shining or how cloudy it is.

The result is a pumping system that does not cost anything to run, does not need any maintenance, does not need to be connected to the grid and works better when the sun is shining. Which is usually when we need water the most. This article explains how solar pump inverters work, what makes them different from devices and how to choose the right one for your needs.

What a Solar Pump Inverter Does Differently

A standard device that changes the frequency of electricity converts grid power into a kind of electricity inside then changes it back into a controlled frequency to run a motor at different speeds. All without being connected to the grid or a battery.

When the sun is shining brightly the pump runs fast. When it is cloudy the inverter reduces the motor speed to match the power rather than stopping or tripping. At dawn and dusk when the panel output is low the inverter. Stop the pump smoothly at the lowest power level rather than trying to start it at full power.

This is very different from using a device to connect a solar array to a pump. A standard device expects an input voltage but the output of a solar array is always changing with the sunlight, temperature and other factors. A solar pump inverter is designed to work with the range of electricity that a solar array produces.

MPPT: The Technology That Makes Solar Pumping Practical

Maximum Power Point Tracking is the core technology that makes a pump inverter work. It is what makes solar pumping practical.

A solar panel does not produce a voltage. Its output. Current change together in a way that depends on the sunlight and temperature. At any given moment there is a combination of voltage and current that produces the most electricity. If you operate above that point the current drops faster than the voltage rises reducing the power. If you operate below it the voltage drops away. The maximum power point changes all the time as the sunlight changes.

An MPPT algorithm measures the panel arrays output voltage and current calculates the power being produced, makes an adjustment to the operating point and checks if the power increased or decreased. It does this times per second, always looking for the operating point that delivers the most power. In terms a well-implemented MPPT algorithm gets 20 to 30 percent more electricity from a solar array compared to operating at a fixed voltage. Which is the difference between a pump that runs well and one that does not move enough water.

Solar pump inverters use MPPT algorithms that are designed for the input voltage range and fast changes in sunlight that come with solar arrays. The speed of the algorithm matters: an algorithm that takes many seconds to find the new maximum power point after a cloud passes loses a lot of electricity during every weather event. A fast algorithm stays close to the power even when the sunlight is changing quickly.

How the Inverter Manages the Motor Under Variable Solar Input

The challenge a solar pump inverter faces is running a motor that expects a voltage and frequency from a power source that changes all the time. The inverters control system handles this with a combination of voltage-to-frequency ratio maintenance, starting and minimum power thresholds.

The inverter uses the principle that an AC induction motors magnetic flux. And therefore its torque. Is determined by the ratio of the applied voltage to the applied frequency.

At sunrise the panel output builds up gradually from zero. The inverter monitors the input power. Start the motor only when there is enough power to get it turning without too much current. This soft-start behavior prevents the repeated failed start attempts that would happen if the inverter tried to start the motor at voltage before the panels could support it. It also extends the life of the pump and motor by eliminating the shock of full-voltage starting that would happen every morning.

Every pump has a speed below which it stops producing useful water flow. The inverter is configured with a minimum frequency threshold below which it stops the motor entirely rather than running it at a speed that does not move any water and wastes the little panel power that is available. When the sunlight recovers, the inverter restarts automatically.

Where Are Solar Pump Inverters Used?

Solar pump inverters are used in places where water needs to be moved but there is no grid power. This happens more often than you might think.

Agricultural Irrigation

Farmers use solar pump inverters a lot. They use them to run irrigation systems for their fields, crops and greenhouses. The system works during the day when the sun is shining. This is also when the plants need water the most. You don’t need a grid connection. You don’t need diesel fuel.

Livestock and Ranch Water Supply

Ranches and grazing lands use pump inverters. They use them to supply water to animals. A storage tank fills up during the day. The animals drink from it as needed. This works well in areas. There is no grid connection. It is hard to check on a generator every day.

Domestic and Community Water Supply

People in areas and small communities use solar pump inverters. They use them to pump water from wells or boreholes. The water goes into storage tanks for use. It is a solution. Grid power is not always reliable. Sometimes it is not available at all.

Aquaculture

Fish farms use pump inverters. They use them to run water circulation and aeration systems. This reduces electricity costs. It keeps the water healthy during the day. The fish need oxygen.

Desert Management and Greening

Solar pump inverters are used in desert greening projects. They are used to move water to remote and arid areas. There is no grid infrastructure nearby. Solar pumping is often the option.

Seawater Desalination

Some systems use pump inverters. They use them to drive pumps, in small-scale desalination setups. They convert seawater into freshwater. This happens in island areas. Grid access is limited or does not exist. Solar pump inverters help. They make freshwater for people.

Solar Pump Inverter vs. Standard VFD: The Key Differences

The comparison shows that a standard VFD is not good enough to replace a solar pump inverter in a system that connects panels directly to a pump. A solar pump inverter has features like handling the voltage from the solar panels using the energy from the sun in the best way starting up when it is not very sunny and protecting the pump when it is dry. These features are not available in a VFD. If you try to use a VFD with a solar panel it will probably cause a lot of problems like the system shutting down all the time, not using the energy from the sun very well and reducing the life of the VFD. This is because the circuits that protect the VFD think the varying voltage from the panel is a problem.

Sizing a Solar Pump Inverter: The Things That Matter

Motor Power Rating

The solar pump inverter has to be strong enough to match the power of the pump motor. To do this you have to read the label on the pump motor to find out how much power the solar pump motor uses. The power rating on the label of the pump motor is the power the solar pump motor uses when the solar pump motor is running at full speed. The solar pump motor uses power when the solar pump motor is connected to the electricity supply. You need to use the power the solar pump motor uses when the solar pump motor is connected to the electricity supply to choose the solar pump inverter.

PV Array Sizing

The solar panels need to be big enough to give the pump power to run at full speed when the sun is shining brightly. They also need to give the pump power to run at a slower speed when it is not sunny. A good way to start is to make the solar panel system 1.2 to 1.5 times bigger than the power the inverter can handle.

DC Input Voltage Range

The way solar panels are connected is important. This is called the panel array configuration. This range is important because the voltage from the panels changes with the weather. In the mornings the voltage from the solar panels is higher. On days the voltage from the solar panels is lower. The solar panel manufacturers specifications are used to determine the voltage range. These specifications are adjusted for the temperature range at the installation site.

Total Dynamic Head

The total dynamic head is the pressure that the pump must overcome to deliver water. This includes the height from the water source to the outlet. It also includes the friction losses in the pipes, fittings and check valves. A pump and inverter combination that works well for a well may not work well for a deep well. This is because the motor power needed to lift water increases with the depth of the well.

Agricultural Irrigation

Solar pump inverters are often used for irrigation. This is because they can save farmers money on fuel and maintenance. Fields and orchards that are far from the grid can use solar pump inverters to pump water. The solar pump inverter works well because it produces the power when it is needed the most. This is usually during sunny weather.

Livestock Watering

Solar pump inverters are also used for livestock watering. Remote grazing land and ranches use solar pump inverters to fill troughs from boreholes or surface water sources. The daily water volume needed is predictable and relatively modest. A storage tank can be used to store water for one to three days. This provides continuity during cloudy periods.

Domestic Water Supply

Rural homes and small communities use solar pump inverters to get water. Solar pump inverters are used for this purpose. The solar pump inverter pumps water from wells or boreholes or rivers into storage tanks that are on rooftops or are elevated. These storage tanks are like a buffer between the solar-powered pumping and the fact that people are using water all the time. The solar pump inverter and the storage tank work together to supply water to homes and small communities.

Aquaculture and Fish Farming

Solar pump inverters can be used in aquaculture and fish farming. They can power aeration and water circulation pumps in ponds. This reduces the grid electricity consumption. Saves money.

A solar pump inverter is a type of inverter. It is designed to run a pump motor from a battery-free PV power source. The MPPT algorithm, input voltage handling, soft-start behaviour and dry-run protection are all features that make the solar pump inverter work well.

To size a pump inverter correctly you need to know the motor power, total dynamic head, flow rate requirement, expected daily water volume and solar resource at the site. You need to match these parameters to make sure the system runs reliably with minimal maintenance.

The running cost of a solar pump inverter is effectively zero. There is no fuel cost, no generator servicing cost and no grid electricity bill for pumping. This makes a solar pump inverter an investment for off-grid infrastructure.

Conclusion 

A solar pump inverter is a device made for solar power. It is not a solar inverter that has been adjusted for solar use. This device is designed to handle the challenges of powering a pump motor from solar panels.

The solar pump inverter has features like the MPPT algorithm. This helps get the power from the solar panels. It also handles a range of input voltages. The device starts slowly when the sun is not strong. It also protects the pump from running dry.

These features are necessary. This is because the solar panels do not have a battery to store power. A standard inverter was not made for these conditions.

To choose the solar pump inverter you need to know some things. These include the power of the motor. You also need to know the head and flow rate of the water. The expected daily water volume is also important. You need to know how sunlight the site gets.

If you match these details carefully the system will work well. It will need maintenance for as long as the solar panels last. The cost of running the solar pump inverter is nothing. There is no fuel to buy. You do not need to service a generator. You do not pay an electricity bill for pumping water.

For farms, livestock and homes in places with sunlight a solar pump inverter is a good investment. It is reliable. Does not cost much to run. This makes it easy to invest in, off-grid infrastructure.