Comet-ME Solar Magnetic Plunger Pump (SMPP)

November 2022


Comet-ME’s Solar Magnetic Plunger Piston Pump (SMPP) is a first-of-its-kind, double-action, submersible borehole plunger pump designed for shallow aquifer pumping, that can deliver 20-30 cubic meters a day, enough to irrigate up to 1 hectare per day or for daily domestic usage for a small community.

The SMPP offers a game-changing water-pumping solution for off-grid smallholder farmers in the Global South. Developed by Comet-ME over the past five years, the SMPP is in advanced stages of alpha-site testing, showing impressive performance levels.

The SMPP’s innovative design takes the ancient and proven plunger pump technology and transforms it into a high-flow, robust, simple, and reliable solar pump that outdoes existing solar pumps on the market in efficiency, serviceability, operation in a high-sediment environment, and of lowest cost of ownership. The unique mechanical design (US Patent No. 10753355 (B2)) of the SMPP allows for dual action pumping that fits into 4” borehole diameter.

This document provides an overview of existing piston and plunger pumping technologies and outlines the SMPP’s technological innovativeness and competitive edge in the field.

Plunger and Piston Pumps – An Overview

Piston and plunger pumps are positive displacement pumps known to be robust and immune to solid and sand particles in the pumped fluid. They are used in various applications such as water, oil, and sewage pumping, or high-pressure water pumps for industrial applications.

The basic design of the plunger pump includes a piston that moves inside a cylinder to create a progressive change in the volume, an inlet non-return valve, and an outlet non-return valve. When the piston retracts, fluid enters the cylinder through the inlet valve. When the piston moves forward into the cylinder volume, the pressure increases inside the cylinder and the fluid is forced through the outlet valve. A plunger pump differs from a piston pump in that the seals are stationary and are not part of the piston assembly. In both cases, the pump’s mover is driven by a mechanical arrangement.

Plunger and piston pumps

Crank-shaft motor driving plunger and piston pumps

The most common mechanical arrangement for driving the plunger or piston is a crank shaft that translates a spinning motor motion into a linear motion. The crank shaft is connected to a rod that drives the piston.

Crank shaft driving a plunger pump
This type of design is common in the old windmills that pump water and in oil pump-jacks. Such pumps are still operating in many parts of the world and are considered exceptionally reliable.

However, this type of mechanism has several disadvantages:

  • The mechanical gear translating the circular motion into a linear motion has limited efficiency, adds extra cost to the system, and has a limited lifetime cycle
  • All of the gear designs that are used in these pumps must translate the circular motion of the motor or the wind vanes into a linear motion with a speed profile of a sine. This means that the piston or the plunger cannot maintain a fixed speed along the stroke, resulting in lower flow rate.
  • Flow rate is generally low as the rod design makes it impractical to apply a double action pumping mechanism in a small diameter borehole.
Among other modern solutions is the axial piston pump, which consists of a large number of pistons with a complicated gear. Usually, these pumps have low pumped volume per revolution and need to operate at high RPM to reach a high flow rate. These pumps are mainly used for high-pressure applications such as reverse osmosis and are not designed for submersed borehole applications.

Dual action piston and plunger pumps

Turning the simple piston or plunger pump design into a dual action pump that delivers water in both stroke directions allows the doubling of flow rate with the same power.

Dual Action pump design with two inlet and two outlet ports.

In this design, there is an inlet port at the top and at the bottom ends of the stroke. Water is discharged from both the top and bottom outlet valves of the pump. The flow paths from each side of the piston then merge and continue towards the top of the pump where it exits into the riser pipe.

The major problem with existing dual-action plunger or piston pumps designs is that they are not sufficiently compact to allow the pump to fit into a 4” borehole without sacrificing flow rate. This is one of the main technological challenges we have addressed in the development of the SMPP.

The Solar Magnetic Plunger Pump (SMPP)

The SMPP is a high-end submersible solar magnetic plunger pump developed for off-grid rural communities and smallholder farmers for irrigation and domestic purposes. To meet the needs in the field, the SMPP was designed with the following specifications:
  • High-flow, robust, simple, and reliable 
  • Modular assembly with few subassemblies. No special tools or accurate alignment are necessary for assembly and disassembly, allowing for easy field servicing of the pump.
  • Compatible with different solar array combinations, from 300-900Wp depending on the pump head and water capacity requirements. No batteries required.
  • Pump can operate with high level of sand and sediments in the water with high reliability for very long period of time.
  • Integrated Maximum Power Point Tracker (MPPT) that optimally harvests available solar power
  • High efficiency throughout full range of pump head 
  • Ability to operate at low solar power (at lower pump flow rate) to reach higher daily flow capacity
  • Less than half the cost of comparable products
  • Length: 120 cm. Weight: ~15Kg.
  • Can fit into a 4” borehole, the most common borehole size for shallow aquifer pumping

Dual action mechanical design

The innovative mechanical design of the SMPP allows for double-action pump flow inside small boreholes and can be scaled up and down. The design is protected by our granted patent application, both for the US patent office and worldwide through the PCT.
Animation of water flow inside the plunger pump

When the plunger moves to the right, water fills the pumping chamber through the left inlet check valve. At the same time, pressure is built in the pumping chamber to the right, and water flows out through the outlet check valve on the right-hand side of the pump. The water flows inside the pump cover to the outlet port on the left-hand side of the pump. When the plunger moves to the left, water fills the right side of the pump and is pumped out of the left side of the pump. The flow of water cools the motor.

A short video of the pump may be seen here.

The Solar Magnetic Plunger Pump is designed for up to 60 meters of head with flow rates of up to 45 LPM (at all pump heads, depending on input solar power).

Cross-section of the plunger pump model
Photo of the pump assembly without the cover
The modular design of the pump allows for easy assembly and maintenance. Most of the parts of the pump are made from plastic, allowing for low-cost plastic injection mold production.

Check valves (non-return valves)

The check valves of the double action plunger pump are a key component of the system. The basic requirements of the check valves are:

  • >5 years of operation without service
  • Quick and efficient response
  • Immune to sand, sediments, and biological matter in the water
  • Allows for large flow rate with minimal losses.
  • Compact design that can be accommodated in very small space
  • We have not found an off-the-shelf solution that meets all the above requirements and therefore we had developed our own valves. Valves were tested by a third party and approved. The valves are operating in our pump models for more than three years. And a continuous improvement plan brought it to a very high-performance level meeting all the above requirements.
The design of the check valve is patent pending. Following is an image of the check valve assembly.
SMPP Check valve

Core technology: 3-phase tubular linear BLDC motor

At the heart of the SMPP is a 3-phase advanced tubular linear BLDC motor, directly driving a plunger in a dual action mode. This core technology, designed and built in-house by Comet-ME over the past five years, can be used to power a family of pumps with higher flow rates or higher heads, as well as applications in other fields, expanding product portfolio at limited investment.

The tubular linear BLDC motor driving the plunger makes the SMPP very efficient and reliable, with only one moving part (the plunger itself) directly pushing the water up to the surface. No mechanical gears or crank shafts are required. Moreover, the relatively slow speed of the plunger reduces the wear that is common for high revolution speed centrifugal or helical pumps, making the pump exceptionally reliable even in the presence of sediments or sand in the water.

The SMPP’s 3-phase tubular linear BLDC motor is cooled by the stream of water inside the pump and is designed for more than 1 KW of input power. The magnets and the pole pieces are encapsulated inside a thin sealed stainless steel wall tube to allow for minimal magnetic air gap between the plunger and the iron core of the motor. The motor can produce > 600N of thrust force at less than 900W input power and it can be scaled up. Furthermore, the motor is designed to have minimal magnetic cogging forces, which increases efficiency during stroke direction change of the plunger.

Motion control

The pump motion controller is designed to provide an optimal speed profile of the plunger to maximize the flow rate under all solar conditions. Because plunger pumps can produce a flow in a single stroke (contrary to centrifugal pumps that must reach high revolution speed before they may push water up), the SMPP pumps water at a usable rate under low solar radiation conditions.

The pump motion controller is embedded in the pump and has a communication line to the monitoring system positioned on the surface. All the controller parameters may be set and controlled. F/W of the controller may be upgraded through the communication line.

The motion controller sets the speed of the mover and thus the flow rate, according to the available solar power level to maximize the harvested solar power under all solar conditions.

The pump motion controller calculates the water flow by monitoring the progressive volume that the plunger creates during the stroke motion and provides accurate flow rate readings that may be used for different payment methods including Pay As You Go (PAYG). It also includes:

  • Smart dry-well and over-heating protection
  • Automatic switch that stops pump operation when the water tank is full
  • Automatic start and stop of the pump with sunrise/sunset

Online monitoring system

The pump includes a dedicated monitoring system that transmits all pump parameters live to the net via mobile communication. Monitoring the pump’s performance is especially important in remote rural locations, where remote tracking of the pump’s health facilitates scheduling of service routines. The monitoring system will support PAYG infrastructure, provide relevant data from the pump such as flow rate, solar power, soil moisture, temperature, and pump events (dry well, motor overheating, daily consumption, full water tank etc.). The monitoring system provides the SMPP with the following advantages:
  • Support proactive maintenance and service of the pump
  • Allow for financing services for end-users
  • Data collected from the various sensors will be valuable for various stakeholders along the value chain (financers, agri-businesses, policymakers)

Pump Performance

The pump’s performance was evaluated for a long time through our monitoring system. Following are a few curves that show the flow vs. power at given head and the daily operation of the pump. The flow vs. power curve measurement was carried out during the day, where different solar power levels were recorded.

Future Applications

Surface pump

The robust design of the SMPP and immunity to sand and sediment content in the water easily lends itself to adaptation to a compact surface pump design.

Double action diaphragm pump

The SMPP design can be applied to a double action diaphragm pump design, for cases where there is a need to isolate the fluid chamber from the driving mechanism.

Dosing pump

The accurate positioning and velocities control of the pump mover is translated into a precise measurement of the pumped fluid. This may be applied to the dosing pump applications.

Grid tie pump models

The pump can be connected fairly easily to the grid instead of the PV connection. A simple DC power supply is required.


Noam Dotan, Comet-ME Technical Manager
Elad Orian, Comet-ME General Manager

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