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DIY Solar Energy Water

HP Size Pumps with Solar Panels

Concept Statement

Centrifugal pumps running on normal AC power supply are very common, fairly efficient and most importantly they are locally available from wide range of manufacturers. Their use and operation is more or less hasslefree, they are easily serviceable at nearby workshops and pricewise also they are affordable. These points are specifically important in comparison to a classical solar pump system that is available in market these days, and which potentially uses a BLDC 3 phase DC motor/pump with permanent magnets and all stainless steel body.

These standard AC pumps are available in 0.5 HP to 10s of HP of power rating, able to run on single phase (220V) or three phase (415V) AC power supply and available in formats like monoblock pumpset, openwell submersible and borewell submersible pumps.

Monoblock Pump
Openwell Submersible Pump
Borewell Submersible Pump, motor and pump shown separated from each other.

This article discusses the use of such standard AC pumps using Solar Panels as the source of electricity.

Since solar panels generate DC voltage, it is important to have some mechanism or device to convert the DC electricity from the panels to AC power so that the pump can run on it.

A standard AC motor consumes large amounts of current during startup for a few seconds, this current can be 2 to 6 times of the normal operating current at full load. On the other hand solar panels are a current limited source of power i.e. the current output available from a given solar panel is limited by the size of panel. This means that the solar panels which would be sized and selected to meet the current requirements of the pump at normal operating load are not going to be able to start the pump in normal or traditional manner. Some kind of soft start approach is needed.

Also based on sunlight available over the day time, the output voltage, current and power from solar panels is going to vary, this needs to be maximized by making the pump run at various voltage and/or AC frequency. The standard AC motor which is expected to operate at 50 Hz power supply, can actually be made to run over a range of supply frequency (35 to 55 Hz) without any significant side effects. In this range of frequency, the output power of the motor varies almost linearly and this inherent feature can be used to match the solar panel output with the pump-motor power requirements.

All the above leads to a solution which has to be based on some sort of electronics to support following features.

  1. DC to AC conversion
  2. Soft start or gradually increasing voltage during startup
  3. Output voltage and frequency modulation to optimize the power generation from the solar panels.

For 1 and 2 above there already exists a robust industrial device called Variable Frequency Drive (VFD). VFDs are often used in various industries to control the load and/or speed of standard AC motors which drive the heavy plant and machinery.

Most VFDs allow AC (single or three phase) or DC power supply as input and generate three phase AC power as output.

VFD – Variable Frequency Drive

Internally the input AC power supply is first rectified to DC, that is what makes VFD suitable to run with Solar Panels. Then a microcontroller based circuitry drives a set of power transistors (IGBT or MOSFETs) to achieve DC to AC conversion with a SPWM (sinusoidal pulse width modulation) technique.

The output power is a sine wave with a configurable mains frequency (10 to 60 Hz as an example) but laden with spikes or chopped waveform with a carrier frequency of a few kilo-Hz. This is acceptable for standard AC motors, or rather the carrier frequency used in commercially available VFDs is optimized to keep the motors healthy and not to generate any ill-effects, especially high frequency harmonics.

Output Wavefrom from a VFD

The same waveform as explained and shown above, is generated in all the three phases of the output, but appropriately phase shifted by 120 degrees from each other. That makes a nice power source for a three phase AC motor.

During startup the VFD outputs a lower frequency of say 10 Hz and correspondingly lower pulse width (effectively a reduced AC voltage at the output). It is then gradually increased over a period of 5 to 15 seconds to normal operating frequency of 50 Hz. That is how a soft start is implemented.

VFDs have a simple and basic keypad with start, stop, menu buttons. Keypad permits setting of various configurable parameters, and also displays the operating status/errors if any.

Connectivity with external controlls is also provided, which allows dynamically setting the output frequency and voltage, external start and stop commands etc.

A fewer brands of VFDs have started manufacturing VFDs with additional features as below.

  1. Customized phaseshift of 90/110 degrees (instead of 120) between the three output phases, to emulate the 3 wire power supply of a single phase capacitor run motor.
  2. Changes to output frequency at runtime based on an inbuilt MPPT (maximum power point tracking) algorithm, essential for solar panels.

Test Results

With the concept explained so far as above, we have carried out a few real life tests using a VFD and borewell submersible pump.

Equipment used is listed below

  1. FRECON Make Solar VFD, model number FR150T – 2S – 2.2B -H, this accepts single phase AC input or DC input and gives out 3 phase 220 VAC. Has configuration settings to connect a single phase motor across the three U V W output terminals, and also has a MPPT algorithm in-built into it. It is not a Make In India brand but has ample presence of local dealer network in India. Build wise seems a good robust build.
  2. Kirloskar make borewell submersible pump model Jalaraj KP4-1009 with 10 stages impeller, single phase 1 HP, 220VAC oil filled motor.
  3. An unbranded borewell submersible pump, 10 stages, 0.5 HP 220VAC water filled motor, purchased from local market.
  4. Energy Meter Secure Make, single phase 220VAC 30 Amps, 3200 pulses for 1 KWH unit consumption.
  5. Power was taken from normal household AC supply
  6. Water flow and pressure measurement was carried out using conventional simple techniques.

Normal AC power supply was connected to the input of VFD

Output terminals of the VFD were connected to the pump as given in the user guide of the VFD, i.e. U>>Y, V>>R, W>>B

Two different voltage settings were used for testing at 100% and 80% of normal using F00.16 configuration of VFD.

Valve in the delivery line was kept open in such a way as to be near the operating point to get 2.5 to 3.5 bar pressure and around 1800 LPH flow.

Below are few images and videos related to the tests carried out.

Short Video of the Trial Run, shows the simple setup, pump, energymeter and VFD
Frecon VFD
connection diagram
Pressure Gauge
Unbranded 0.5 HP pump, This turned out to be actually a 1 HP pump with much less efficiency than the Kirloskar Pump
Output from VFD visually seen using light bulbs. VFD was configured for a single Phase Motor. This is typical to the FRECON Solar VFD model that they have provided a configuration setting. F08.00 = 2

Important observations

The VFD was tried in two different wiring arrangements.
Two wire output mode: This is as per connection F08.00 = 1, whereby the run capacitor of the motor would be kept in circuit and only two wires of the VFD output were connected to the motor starter. In this case it was seen that the motor draws relatively more current untill it starts rotating and there after settles down to normal operating current. The starting current in this case is not as high as it would be otherwise on normal AC power supply, but still higher than running current. This is expected to be so and likely due to the inadequate capacitance at lower starting frequency.
Three wire output mode: This is as per connection F08.00 = 2, as shown in figure 2.11 In this case the motor draws steadily and gradually increasing current until it stabilizes to the normal running current.
This is a very important and useful aspect of the connection arrangement supported by this VFD since it will help deployment of optimum capacity of solar panels.

Further Work

It is essential to carry out similar tests with input power taken from suitably selected solar panels at various time of the day.

An online calculator for panel capacity is presented here at the below link. This will be useful to select the panel ratings for a given pump capacity.

https://www.pbodas.in/solarvfd.php

Update 1

On 30-March-2022 this VFD and 1HP single phase pump was installed at a farm site in Murbad.

Total of 1600 Watt Solar Panels are used to drive the VFD which is a mixed set as below.
8 x 100 Watt 18 V in series with
(
( 4 x 100 Watt 46 V in series ) 
x 2 such strings in parallel
)

It was seen that pump delivers 3000 to 3600 LPH water at about 30 feet total head, panel side voltage found to be in the order of 300 to 330 VDC, the VFD appropriately keeps regulating the output frequency from 35 to 50 Hz in order to maximize the solar energy generation from the panels and the VFD output voltage was seen to be in range of 160 to 220 VAC.

Long term trial run is planned and results will be published.

Video of the VFD in operation and solar panels used.
Water flow from the pump

Categories
DIY Energy Saving Environment Solar Energy Water

Skid Mounted Mini Pump

For irrigation of small farms where water source is available nearby (either an open well, pond, lake or any such water body) it is possible to use small pumps and operate them on solar panels.

These pumps are easily available at reasonable prices online as well as in local market in most of the cities and small towns accessible to farmers. They are used very commonly in battery operated backpack sprayers used for pesticides.

This post explains some important aspects of this type of pumps for use at small irrigation sites.

Such a pump is run by a DC motor and has a PVC block head where positive displacement of water is achieved by action of miniaturized pistons inside the block.

A pump having single motor is often priced at 550 to 650 INR and delivers upto 3 LPM water and claims to generate pressure of 70 PSI or 5 Bar i.e. upto 50 meters of height.

Pump with twin motor is also available and priced at 1000 INR, delivers 5 to 6 LPM of water at similar pressure.

Next two images show a single motor and dual or twin motor pump.

The DC Motor used is a DC motor with brushes and follows a standard specification named as 775 motor, some details can be found here.

https://somanytech.com/what-is-775-motor/

The motor can be operated over a wide range of DC supply voltage (6 to 36VDC) but the pump manufacturers normally mark the pump for operation in range of 12 to 14.5 VDC only.

We have installed such pumps at a couple of sites and safely connected to solar panels of 12VDC nominal (or 18VDC MPPT voltage). The motor of the pump nicely works with the electricity generated by solar panel during the daytime. As the intensity of sunlight changes throughout the day, the output flow of water varies and is acceptable for the irrigation purposes.

Inlet and outlet of the pump is however a non-standard (or at least not easily available) tubing size. Most suppliers provide a PVC/HDPE tube with threaded PVC nut to attach to the pump outlet nozzle, but the connectors with standard pipe sizes (say 0.5 or 1 inch nominal bore pipe) are difficult to find.

We have used a typical nozzle connection seen in pictures and created a simple skid mounted assembly of this type of pumps, eiether one pump on the skid or 2 on the skid as per the requirements.

With 2 pumps on the skid it is seen that 150 to 200 watt panels are adequate for operation throughout the day. For single pump a panel of 75 to 100 watt is appropriate.

Next few images explain the mounting approach we have used and is only a suggestion. Any suitable alternative can be followed that meets the needs and materials availability at the installation site.

Single Pump Skid

Dual Pump Skid

Front view of the pump skid with inlet and outlet pipes on left side.

Seen from top at an angle / 3-D view.

Left Side View

Rear View

Right Side View

Top View

Important Instructions

  • Pump and motor must never be submerged in water and water must not get into the motor.
  • DC power supply polarity needs to be correctly followed. Green wires to be connected to negative terminal of the battery or solar panels, and red wire to positive terminal.
  • DC supply voltage must never exceed 18 volts.
  • In no case, AC supply / mains supply shall be applied to the motor, it is hazardous besides the fact that it will permanently damage the motor.
  • Testing of pump without water by supplying DC power for a second or say two seconds is ok, but must not run the motor for longer duration without water.
  • At the inlet pipe a suitable filter in form of nylon mesh is highly recommended. The internal piston mechanism of the pump is too small to get clogged by smallest of the particles.
  • This type of pump can generally start from dry run and can self prime in a few seconds, but if it does not do so, please do not run it dry for long time. Instead open the nozzles and check if any clogging or blockages. Try to pull water from outlet nozzle or pipe by sucking the air.
  • The pump can lift water from upto 5-6 feet on the suction side, however it is better to keep the suction pipe length as small as possible.
  • It is recommended to install a footvalve at end of the suction pipe submerged inside the water, it is best to attach a filter mesh around the footvalve.
  • Make sure that the pump skid is mounted on a sturdy platform or base. Alternatively pump can be suspeneded firmly inside an openwell clearly above the water level.
  • Use solar panels of 12VDC nominal voltage only, any higher voltage panels if connected to the pump will damage the same. It is better to first check the nameplate on the backside of the solar panel before connecting for the first time. The nameplate should read 12VDC nominal and/or 17-18 VDC MPPT or maximum power voltage.
  • Single pump skid is suitable to operate with 75 to 100 Watt panel and dual pump skid with 150 to 200 Watts. Excessively higher wattage of the solar panels must be avoided.
  • This type of pump is supposed to be used for intermittent duty only however through our experimentation in actual sites, we find that using the pump every day for 3 to 5 hours is fine.
  • Connect the outlet pipe with suitable coupling or union with the delivery pipe to be arranged at the site to suit the distance of the final delivery location away from the water source.
  • Ensure that the inlet and outlet pipe connections do not lead to forces on the pipes or the skid.
  • If in doubt please reach out to us through email or phone.
Demonstration of 3 pumps at a site in murbad

Thank You.

Categories
Water

Suranga – A fantastic source of water

https://www.youtube.com/watch?v=yglADx4DFlE

This is about manmade cisterns / small tunnels in laterite hillocks. The seepage of rainwater makes them a great source of water round the year.