Maximizing Efficiency with Solar Pump Curves

It’s important to understand customer needs so you can provide the right solar pump.

By Lana McGee Straub, RL

The big freeze that Texas suffered through this past winter demonstrated the importance of energy diversity both on and off the power grid.

Solar pumps are one method that gives water well owners a new way of powering their pumps without depending on a traditional power grid. So, understanding a solar pump curve is an essential role for groundwater professionals in helping to find the right pump for their customer’s application.

It is important to understand how to pick the correct pump for a job, and a pump curve can help you do just that as they are the graphical representation of the performance of a pump.

“A pump’s size—its flow, the pressure it generates, and the horsepower needed—is determined on a number of different factors,” says Tom Drew, a technical sales manager with Grundfos Americas Corp. in Waco, Texas.

“The proper flow and head pressure will determine the horsepower needed by the motor. The interaction between your flow rate and head pressure plays a vital role in proper pump sizing and efficiency.”

A QH-curve for a solar pump measures the flow and head to help determine the dimensions of a pump.

Matching Pump and Need

Many pump manufacturers offer training on how to read and understand pump curves. Grundfos offers a free course on its Ecademy website. The course helps viewers understand the importance of pump curves and how they help groundwater professionals choose the right size and type of pump to meet the customer’s needs.

In the course, the viewer learns valuable information about what each curve measures in a pump curve. The QH-curve measures the pump head at the specified flow. The ŋ-curve measures the pump’s efficiency. The P2-curve measures the relationship between a pump’s power consumption and flow. The NPSH value stands for net positive suction head and denotes the minimum absolute pressure that must be present at the suction side of a pump to avoid cavitation.

Cavitation occurs when there are rapid changes in flow and air bubbles are created. As a pump professional, you must know that cavitation problems can damage the impellers on the pump and significantly reduce the lifespan of the pump.

You should use all four pump curves to obtain the best values for sizing your pumps. Each curve gives a specific value that helps the end user understand what the pump is doing under certain circumstances.

Here are why all four curves are important and bear repeating:

  1. In a QH-curve, which measures the flow and head, you can see that a low flow results in a high head and a high flow results in a low head. Once you have identified the requirements for your application, the flow (Q) and head (H) will help you determine the overall dimensions of the pump.
  2. An ŋ-curve highlights a pump’s efficiency. The total efficiency is the ratio between hydraulic power and supplied power. It is worth noting the efficiency is always below 100%, as the supplied power is always larger than the hydraulic power due to losses in motor and pump components.
  3. A P2-curve measures the relationship between a pump’s power consumption and flow. The pump’s power consumption determines the size of the electrical installations which must supply the pump with energy.
  4. Net Positive Suction Head (NPSH) describes conditions related to damaging cavitation. It must be known for the largest flow and temperature within the operating range.

Understanding your pumping application is an important step in sizing the pump. This information can be obtained by talking to the customer about their goals for the water well and matching those goals to the amount of output the well is providing.

To properly size the pump, Drew recommends these questions be answered:

  1. How much water volume is required for the application?
  2. How much pressure is needed for the application?
  3. What is the water level in the well?
  4. How far does the water have to travel after it leaves the well and is there any elevation?

Once these questions are answered, you will have a better idea of the inputs needed for the pump curve to establish the best efficiency to maximize the life of the well and the pump while fulfilling the customer’s end-use goals.

Measuring Efficiency

Efficiency is one of the most important aspects of pump sizing and can vary greatly in solar pumps. According to the Grundfos training: “The efficiency depends on the pump’s duty point, underlining the importance of selecting a pump that fits the flow requirements to ensure that it is always working in the most efficient flow area.”

Since solar power is not constant or controlled by a grid, maintaining constant power is an important part of building the solar system. The efficiency of your solar system will affect the efficiency of your pumping system. A pump curve helps you determine how to set up your solar system that will power the pump off the grid.

“Because solar pumps are based on wattage used,” Drew says, “the curve helps the installer determine not only the pump’s model or size to provide the correct GPM and pressure, but also how much wattage will be needed.”

The solar pumping curve not only tells you the efficiency of the pump, but it is also a key component in choosing the size and arrangement of your solar panels. Therefore, to properly size a solar pump, you must understand solar arrays and panels and how they generate electricity off the grid.

Learning Panels

The website, www.Solar.com, is helpful as it offers a Solar Learning Center that has a breadth of knowledge on solar panels and their many applications.

As Water Well Journal stated in its May 2021 article “Saving Water for the Future,” significant research is being conducted by several agricultural interest groups to improve the performance of solar panels for water conservation applications.

Solar panels have evolved since the 1970s. In fact, their efficiency has improved at a rate of about 0.5% annually since 2010 due to improvements in panel material components, reflectance efficiency, and thermodynamic efficiency.

Reflectance efficiency and thermodynamic efficiency are key components to creating an array that converts the most electricity at a constant rate, helping it to mimic a power grid.

To be efficient, solar panels should absorb the sun and not overheat. On Solar.com, it explains the importance of reflectance efficiency as the glass panel’s ability to absorb the maximum amount of the sun’s rays with a minimal amount of reflection.

To achieve this, anti-reflective coatings are placed on the glass to maximize absorption and minimize reflection. Thermodynamic efficiency—the height at which the sun’s energy can be converted to electricity—is currently at 86%. To increase efficiency, solar panels are grouped in a multiple panel arrangement of multi-junction or tandem solar cells. This configuration allows for more absorption and less overheating, which increases the ability to create electricity.

Solar.com reported the five manufacturers with the highest efficiency ratings in residential solar panels as of 2020 are Sunpower, LG, REC Group, Solaria, and Panasonic.

But if you do not want to create a system from scratch, you can contact specialty distributors. For example, Solar Power & Pump Co. LLC in Elk City, Oklahoma, is a supplier that has been focused on providing solar-powered water pumping systems since 1998. The parent distributor company for SunRotor brand solar pump products, it provides ready-made assemblies designed with groundwater professionals in mind.

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Research shows solar pumps are becoming a popular method for pump applications off grid. Currently, the government is offering a 26% tax credit for solar installations, making a solar pump an even better option for your customers.

While sizing and choosing solar pumps and solar systems may seem intimidating, it does not have to be. There are tools out there for you to learn with and experts ready to answer your questions so you can find the right solar pump for your customer’s needs.

</em>Tooling Up<em>
Need to learn a little more about using solar power and pump applications? Check out these sources to tool up for your next solar project:

Find Out About Hybrid Solar Pumps
Click here to read a Water Well Journal article on hybrid solar pumps. Titled “Seeing the Light,” the article from the August 2018 issue discusses details on hybrid solar pumps and how to troubleshoot them.

Lana McGee Straub, RL, has written for WWJ for more than 15 years and reported for several national publications, including the Washington Post and NPR. She has an MLS in oil, gas, and energy law from the University of Oklahoma College of Law and is a ROW agent. She has worked in the groundwater industry for more than 20 years as the operations manager for Straub Corp. in Stanton, Texas.