seperate solar power to pump water?

momofgcmmomofgcm Solar Expert Posts: 35
I have a general question.

I have an off grid house with 500W of solar panels. There is also an outside well that is designed to pump water into a high water tower. This will hold water then feed it into the house when needed. There are no plans for a boost pump to get the water into the house at higher pressure.

The question is do the water pumps generally run off their own independent solar panel (directly wired to pump) or are the water pumps powered from the house system of solar panels?

What is the logic of wiring it one way over the other.

I'm totally new to solar water pumping!

Kim

Comments

  • BB.BB. Super Moderators, Administrators Posts: 30,212 admin
    Re: seperate solar power to pump water?

    You can do the pumping either way...

    If you run it off your main off-grid system, you can share your limited solar power between your indoor uses and the pumping system. And you can use an inverter + AC pumps to pump water at any time.

    With a DC pump made to connect directly to solar panels--you have a more expensive solar DC pump, but no inverter and battery bank... That also saves quite a bit of losses too (no battery or inverter losses). Also you save on having to buy replacement batteries every few years. The pump simply runs while the sun is up until your tank is full.

    Your best bet is to do a paper design of both a shared and independent pumping system and compare costs/maintenance/etc. between the two types of systems and see which is most cost effective for you.

    For both systems--you will probably need to figure out how to use a back up generator for power when bad weather hits or if you need extra water at certain times.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • momofgcmmomofgcm Solar Expert Posts: 35
    Re: seperate solar power to pump water?

    This system is designed to run a 200W solar panel directly to a pump. No batteries or inverter.

    I was thinking that the solar panels are collecting energy and it is being wasted if the pump doesn't need to be run. She doesn't use a lot of water. The house design is marginal and it would be nice to get some extra solar from another solar panel.

    I don't have any idea what type of pump is being used or how deep the well is.

    So you're saying there is no particular reason to run wells independantly of a house solar system.

    Interesting.

    Anyone else have ideas?

    Kim
  • icarusicarus Solar Expert Posts: 5,400 ✭✭✭✭
    Re: seperate solar power to pump water?

    If you don't have reason to pump absolutely as much water as possible as many hours of the day as possible, I would keep the system to one set of panels. That way you can manage water pumping to a time when you have excess PV after the batteries are done bulk charging for example.

    We pump water in the afternoon, when the batteries are nearly fully charged, for a net cost of zero. (Unless we need more water in the evening. Another option is to increase the size of the tank so that you only pump when you have an energy surplus, and then you pump as much as you can,, like several days worth.

    Tony
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: seperate solar power to pump water?

    The obvious answer is to connect the pump's solar panel(s) through a charge controller to the house batteries, if this is feasible (Voltages, wire runs, etc.) BUT if you tap the pump panel(s) directly then there will be a drain on available power when the pump needs to run. So it is probably not practical to do this.

    The other option is to alter the whole set-up, so that all panels go to the battery bank and all power comes off there. This may also not be feasible, as the water pump is probably one designed to run directly from a panel rather than a fixed DC source, and/or the resultant wiring may be too long and involve too much drop if reconfigured this way.

    In short, we'd need a lot of details about the existing system in order to come up with a viable solution. The only problem currently is your loss of 'potential harvest' from the pump panel(s) when not actually pumping water. How big a loss this may be depends on how many Watts they are. Usually, though, direct panel-to-pump set-ups run whenever the PV's are putting out power, so it may not be such a problem after all.
  • BB.BB. Super Moderators, Administrators Posts: 30,212 admin
    Re: seperate solar power to pump water?

    Very roughly, for the same amount of pumping, a solar+battery+plus pump+etc. power will cost roughly 2-4x the amount vs a solar panel to pump only connection... So, if pump is using less than ~50% of the panel+pump combination--then connecting the pump to the battery bank and adding more panels to the home off-grid system would be a better deal.

    I.e., if you need a 200 watt solar panel and run the pump for only 1-2 hours per day--then the rest of the power from the 200 watt panel is wasted.

    Then you would be better off placing the 200 watt panel on the battery bank and moving the pump to the battery bank too (all things being equal which they rarely are--solar panel can be integrated into the battery bank/charger system and the pump can be run off the existing battery bank).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • westbranchwestbranch Solar Expert Posts: 5,183 ✭✭✭✭
    Re: seperate solar power to pump water?

    Kim,

    how far from the house to the well? ie battery to pump distance.

    How deep is the well? gauge of wire? to determine line loss

    the answers to these questions will lead you to the optimal solution for utilizing the PV you will have. Also to choosing the type of pump as well as

    HTH

    Eric
     
    KID #51B  4s 140W to 24V 900Ah C&D AGM
    CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM 
    Cotek ST1500W 24V Inverter,OmniCharge 3024,
    2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
    Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
    West Chilcotin, BC, Canada
  • momofgcmmomofgcm Solar Expert Posts: 35
    Re: seperate solar power to pump water?
    westbranch wrote: »
    Kim,

    how far from the house to the well? ie battery to pump distance.

    How deep is the well? gauge of wire? to determine line loss

    the answers to these questions will lead you to the optimal solution for utilizing the PV you will have. Also to choosing the type of pump as well as

    HTH

    Eric

    I agree. However the house is in Africa and the guy buying the items doesn't give details. I was hoping to find from here general considerations to understand the different considerations for water pumping. He says everyone sets up there systems that way. I wanted to see if that were true.

    My hubby and I are both EE's and when the guy buying stuff for the solar systems talks about the system we get red flags. I've been hanging out at this forum to get more understanding of how solar systems work. Makes me want to design them (after lots more training of course)!!

    It sounds like 'design' is needed to install it properly.

    We are having a meeting next week to discuss this info and I needed some input.

    This forum is great!

    Kim

    Kim
  • System2System2 Posts: 6,290 admin
    Re: seperate solar power to pump water?

    Keep us up to date on what you decide to do.
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