Solar water pumping for college project

SystemSystem Posts: 2,511 admin
Hi all,

I stumbled across this forum while researching for information on solar water supply for my college project. Somebody might be able to give, or point me in the right direction for some backround and helpfull information on the topic.

Project Overview:
This project will use a solar panel to gather energy from the sun and store the energy in a bank of supercapacitors. When the voltage on the capacitors reaches a desired level the energy will be dumped into a water pump which will pump the water up to a storage tank.

I'm reseaching solar water pumping at the minute, and looking for both basic and detailed backround information, describing typical applications, listing the advantages and disadvantages of these systems, and detailed designs.

I'm thinking my project will be based around pumping of well or rain water, but information on all solar water pumping is helpfull.

If anyone has any links that covers the above topics in detail, it would be very much appreciated.



  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Solar water pumping for college project

    Hello and welcome!
    Hope we can be of some help.

    First off, there's the question of how much water, how fast, and what pressure, and what lift.
    Water is bloody heavy stuff and takes a lot of power to move. More lift (100 foot deep well as opposed to 20 foot) needs more power. More rate (20 GPM as opposed to 10) needs more power. More pressure (50 psi instead of 40) needs more power. More volume (100 gallons a day rather than 30) needs more power.

    Until you know what you're trying to accomplish with the water pumping you can't determine any specifications for the pump and the power to run it.

    Our host NAWS has a whole section on DC pumps, including some that run directly from a solar panel (no battery required). Take a look at some of the specs on those:

    Not sure why you want to charge super caps and then dump to a pump, but perhaps that is the project. Usually you'd fill the reservoir using a direct panel-to-pump set up; it runs when it can and fills the reservoir, which mediates the supply to whatever the point-of-use is.
  • BB.BB. Super Moderators, Administrators Posts: 33,143 admin
    Re: Solar water pumping for college project

    Also, instead of super caps, normally a form of linear current booster is used instead. This better matches the output curves of the solar panel to the input power curves of the motor.

    Or, use a variable frequency drive, vfd, to slow the pump down when there is not enough power from the sun.

    Power storage and turning the pump on and off, combined with the need to over come the momentum of the pump and the water in the pipe seems to be a big loss of power unless you have a whole bunch of super caps--have their own aging issues.

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • WindsunWindsun Solar Expert Posts: 1,164 ✭✭
    Re: Solar water pumping for college project

    I don't understand the purpose of the caps. :confused:
  • System2System2 Posts: 6,290 admin
    Re: Solar water pumping for college project

    Thanks everyone for the help and advice.
    The project won't be the best method or must suitable way of pumping water through solar, but that's not the project. I suppose i should of said intermittent water supply would have being a better description.

    I have the components, dc pump and all materials that i will need.

    What i'm looking for is backround information, interesting articles, projects, designs that will help give me information and get a better understanding of solar water pumping.

    Pumping rain water for what ever use might be a practical application of the project? We get alot of rain in Ireland!!!

    Thanks again for the help.

    Edit: I'm also looking for info on DC Pumps compared to AC pumps, advantages and disadvantages. What type of application are DC pumps better suited and why. Any other important info on DC pumps that might be Usefull.

    Windsun wrote: »
    I don't understand the purpose of the caps. :confused:
    Not sure why you want to charge super caps and then dump to a pump, but perhaps that is the project.

    ^^^ Exactly.

    The main part of the project is to build a circuit and program a micro chip using flowcode to utilise the caps to dump the stored energy to the pump.

    It's not RE im studying, It's an automation and control project.

  • BB.BB. Super Moderators, Administrators Posts: 33,143 admin
    Re: Solar water pumping for college project

    With modern electronics, the whole AC / DC motor thing is blurring...

    You can look at the input power requirements as the AC/DC definition, and there are systems that can take either AC or DC then massage the power into that required to run the motor (Grundos and Sun pumps, I assume, use a VFD--Variable Frequency Drive).

    Or you can look at brushed vs single phase or poly phase motors.

    Brushed are the simplest DC motors, but last only hundreds or a couple thousand hours before new brushes (at a minimum) are needed.

    And there are induction motors that, internally, are some version of poly phase motors that are either wired to use 3 phase power, or (typically) use capacitors to create the rotating fields. Although, a VFD is sometimes used.

    And there are AC motors with permanent magnets. This (IIRC) can save ~20% of the power normally used by induction motors to create the rotor magnetic field. However, it usually uses a VFD (a close relative to servo/stepping motors) to control the rotating field.

    The more practical use for your project (at least it seems to me) is a two pump system. One pump to move water from the well to a cistern. A second pump to pressurize the domestic water for sinks/shower, etc.

    The well to cistern is typically setup as an opportunity pumping system. When there is sun/energy available, the pump is on until the large cistern is filled. This can be a large pump that is run once a week, or a small pump that is running many hours per day. The small pump is nice for off-grid systems as it keeps the motor/electronics/power source/power storage (if any) small. However, the large pump pump motors are typically much less costly.

    The large pump model works well with generators (large amount of power and limited run time). The small pump model works well with solar panels (smaller amounts of power available for hours per day).

    The domestic pressure system uses stored power (battery or super cap???) based on demand by the residence. Typically a smaller pump sized for 2-10 GPM at moderate pressure. This usually works well as the power needs are not very large.

    A normal off-grid system would be designed to (ideally) provide stored power for ~3 days of no sun. And would accept power from an alternative source (generator) to account for a week+ or poor weather. For a small system, it should be charged in a cost effective manner with a smaller generator (900 to 1,600 watt genset at ~50% rated power) for efficient fuel use and to allow the genset to warm up properly.

    Which then begs the issue of separate pump power vs the rest of the battery based power for a cabin.


    PS: There is one other use of solar powered pumps--Small pumps used for resurculators in radiant heating and solar thermal domestic water heaters (circulate water/anti-freeze to roof mounted thermal collection panels).
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Solar water pumping for college project

    In terms of comparing AC and DC pumps ...

    AC pumps are more readily available and are a better value in terms of capacity for $.
    On the down side they have high start-up currents and only work at full Voltage; you can't feed an induction motor 1/2V and get it to run at all.

    DC pumps are pricier and not available at every hardware store. Nor are they going to meet the capacity specs of a big ol' AC centrifugal pump.
    On the up side they are more electrically efficient, as there's not a lot of energy lost to power factor or the AC pumps' typical over-capacity. Depending on the exact unit, you can run them at lower Voltage and get a trade-off with capacity. There's no need for an inverter (which consumes significant power) in an off-grid application, although for running from the utility you'd need a DC power supply and that would use energy.

    Otherwise it comes back to the original issue of how much water you're trying to pump from here to where and at what rate. It's hard to compare pumps in generalized terms, as they have quite different features specific to the intended function.

    I don't know about using super caps, but I can tell you that any DC motor will have an upper Voltage limit which must be observed. So the outflow from the capacitors would have to be regulated so as not to exceed that value. As the Voltage falls off from that point there should be no trouble. But you could also design the circuit to regulate the drain from the caps to a fix Voltage over time, rather than a sliding one. The obvious difference being the sliding scale will give marginally more efficiency and possibly pump more water over-all, again depending on the application.
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