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Bilge Pump + Solar/Wind + Battery = 24 Hour Functioning Water Pump

Discussion in 'Power Electronics' started by moyaanomalous, May 19, 2013.

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  1. moyaanomalous


    May 18, 2013
    I am trying to prove how easy and inexpensive it is to build a sustainable off-grid bilge pump that should work indefinitely through the use of a battery and solar, wind, and/or just about any alternative energy device I can buy.

    Can someone tell me exactly what is needed to keep a 12v 5amp DC pump running 24 hours? I understand a deep cycle battery is optimum for the type of operation I am trying but those batteries run in the thousands and that is not cost effective for the people I trying to help... not even close.

    My father (master electrician) suggested marine batteries to handle the fluctuations in current but those cost too much as well. I think the charging of the battery can be regulated by a voltage regulator and have it shut off if power drops below minimum charging levels. Can anyone point me to a voltage regulator that I can buy for this? Is there anything I am overlooking?

    My father Is busy so getting him to help me can sometimes be stressful. Can someone help me? I am trying to get an idea of what I should purchase.
    Last edited: May 19, 2013
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    Jan 21, 2010
    Let's assume the power input is just solar. (similar calculations apply to the others).

    And let's assume that the pump operates continuously (in practice it shouldn't and you can make adjustments for that too).

    So, the power required to operate the pump is 60W, and over a 24 hour period is 1440 Wh.

    But we don't really want to discharge the batteries more than 50%, so we require 2880 Wh of capacity.

    Let's say that we can have up to three days without significant sun.

    Our storage needs to be around 3 x 2880 = 8640 Wh.

    We need to, on average, put at least as much charge into the batteries as we take out. That's 1440 Wh. But Lead Acid batteries are not overly efficient on recharge, so we probably need to put in about twice that, or 2880 Wh of energy.

    Next, we need to see how much energy we can get from the sun. On way this is measures is in "equivalent hours". This means, if the sun were shining directly perpendicularly to the panels, how many hours of this would be equivalent to what we can get from the sun as is tided in the morning to when it sets in the evening. This varies depending on your latitude, but let's assume it drops to 4 hours in winter..

    So, you have 4 hours to collect 2880 Wh of energy. So, you need 720W of solar panels.

    But remember that we said we had to allow for up to three days without significant sun. We need to be able to put more energy back into the batteries to allow for this. Somewhere between 50% and 100% more capacity might be needed. Let's go for something mid-way and go for 1200W of panels.

    OK, 1200W of panels and 9 kWh of battery storage.

    Now let's look at charging. To do that properly you'll need a MPPT solar regulator. These often include features like detaching the load when the battery voltage falls too.

    If your pump is only on about 10% of the time, you can divide all these figures by 10. But then you'll also want to calculate the maximum run time of the pump should it be required to run continuously.

    There are other things to consider (like aging of panels, power lost in wiring, lower generation at elevated temperatures, etc.) but there's enough slop in most of what I've calculated here that we can ignore them.

    It's also worth considering that in summer, with more hours of daylight available, and probably less days with cloud cover (and maybe less need for the bilge pump) that you're going to be generating many times more power than you need. If you can't use it, you're wasting available energy.
  3. infernalis


    May 8, 2013
    I like the way you explained that Steve.

    As a note to the original poster, I don't know what exactly the situation is that would require this, irrigation???

    Northern Tool has 400 watt wind turbines (an alternator with blades) that produce 12 volts for around $500. Then you need to install them.

    2 choices, and both are expensive.. the tower (with guy wires and foundation) or set utility poles with an auger and mount on top of them.

    A 12 or 24 volt continual duty pump is going to be expensive also.

    No matter what, expect to have a budget of thousands before beginning.

    Good luck.

    CDRIVE Hauling 10' pipe on a Trek Shift3

    May 8, 2012
    This is usually the point where we get a link to a youtube video where a guy is powering his entire house, next door neighbor's too, with a palm sized home brew solar panel. :D

  5. moyaanomalous


    May 18, 2013
    No, I'm sorry. You miss understood, or perhaps I have added an "or" where it should say "and."

    I am aware of the deficiencies that come with having solar. I am also aware of the deficiencies that come with wind. However, in tandem, I believe they should be able to function well enough to keep a pump running indefinitely; if only to keep the battery charged.

    So, not just solar but wind as well. Both mediums would be used to power the pump. If there is another alternative energy device that I am unaware of, then I would be willing to consider this as an option as well.

    Actually, if anyone can think of an alternative to getting a pump working 24/7 then I would be willing to listen. However, it must run completely off of the grid.
    Last edited: May 19, 2013
  6. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    Jan 21, 2010
    The best alternative is to plug the holes in your boat. The bilge pump should only operate intermittently (and preferably with a very low duty cycle) as the level of water in the bilge exceeds some level. If it's operating constantly then if you get a leak which increases the volume of water flowing into the bilge it will rapidly overwhelm the pump and you will go down.

    The same is true if it's a pump in your basement, except the house probably won't sink.

    Combining wind, solar, hydro, etc., is a good thing because there is a higher probability of having at least one available and thus your battery requirements drop (as does the minimum solar panel size).

    If you have a source of energy that is more available (or at least not less available) when your peak energy uses occur, then the system also need not be quite so extravagant. For example, do you have windy winters?

    To plan the system size, you really need to have data on the availability of power from each of the sources throughout the year (solar is comparatively easy for this)
  7. moyaanomalous


    May 18, 2013
    Electrical > Mechanical

    This isn't for a boat but for aquaponics. Constant circulation of water needs to take place, if only intermittently. However, as far as your knowledge of which pump I should use, there are far more people that have used the same pump I am using to circulate water so I do not need help with mechanics.

    What I really need is insight on how I should wire this up and what I should use to ensure that the battery or batteries do not explode or what have you. Recommendations for the proper voltage regulator would be perfect and anything I may be missing.

    A few requirements however...
    • It must be able to supply grid power in the off chance that solar and wind are insufficient.
    • It must run monitor and keep the battery charged.
    • It must use the battery to power the device.

    PS. What do you think of this device?
  8. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    Jan 21, 2010
    OK, aquaponics. That makes a difference.

    Your last post confuses me a little. Do you have grid power or not? Do you want this (1) as a backup for grid power, (2) an alternative to grid power, or (3) to be used in the total absence of grid power.

    If (1) then you only need to provide power during outages, and solar/wind aren't really required, just charge the batteries form the mains (it's a UPS)

    if (2) then you can likewise have a smaller capacity system, and operate from the mains when there are cloudy days.

    if (3) then you need to go the whole hog as above.

    In the (2) and (3) scenario, you may be able to operate your pump intermittently at night or when there is insufficient sun/wind to charge the batteries.

    I know that I can run my NFT hydroponics 1 min on, 1 min off with almost no problems. If I went to the trouble to set up a header tank I could probably run the pump 1 min on, 10 min off.

    Here is a link to some solar chargers. If you're using a wind turbine you may want a regulator which shorts out the output under overload conditions. This will apply a braking effect to the turbine in high wind conditions and help prevent it from over-speeding.
  9. moyaanomalous


    May 18, 2013
    Oh, so you are familiar with aquaponics. Great!

    I prefer option 3 because this is supposed to be offered to the public for free but I realize conditions will not always be perfect so I am opting for option 2. Is there a voltage regulator that could take the DC current from both mediums and manage the system that way? I am trying to make it easy and less expensive for the layman.

    I am using the water basin method that Murray Hallam showed in his "Do It Yourself" Aquaponics video. The water is only pumped after draining from the grow bed.
    Last edited: May 20, 2013
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