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Water pump on solar  RSS feed

 
Angela Aragon
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I need to be able to run a 120v, 92w, 0.85A submersible water pump on solar 24/7 for an aquaponics system. I am 12.8 degrees north of the equator. The sun is intense here for 5+ hours during the dry season; the wet season is more overcast.

Could someone give me an idea of how many panels and batteries I would need?
 
frank li
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Sure, if you have the nearest weather station information on historical insolation, im sure plenty of of will bench-race and rag chew it up with you.

Mainly, how long are strings of overcast days and what is the result if the pump were to stop for a day, do you use or intend to use a generator and what is your budget. Is the system for the sole purpose of aquaponics or can you use it as base power onsite.

4 days of autonomy would be somewhere around 800ah of lead acid at 24v. You would not need this size and expense on the battery side depending on details of intended use, generator incorporation, and especially need to know the site solar resource.

Its speculation, but you will need to supply the inverter with 2,800 watt hours every day in a combination of storage and pv module source power. For simple operation about 1000 watts pv will cover the day....its only part of the story based on 4 average peak sun hours daily...again speculation, so more data will get your numbers, it could be less, it could be more.

 
Angela Aragon
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Could you explain what historical isolation means? I want to be sure what I am looking for.
 
Eric Bee
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Personally I wouldn't get too fussed about insolation -- how much sun you get. What matters for this application is that you have sufficient battery power for the pump and sufficient solar capacity to re-charge the batteries. Obviously the more sun you get, the smaller the panel you can use.

Since you just want an idea: Without doing any of the math I'd guesstimate you likely need something like a 80-100 ampere hour deep cycle battery with perhaps a 40 watt panel. Take that with a grain of salt and also double check the actual current used by the pump. It may not be 0.85A continuous. Also, you will need an inverter (rated for > 1 amp for that pump) to get from 12 volts DC to 120. If you can find a pump that is 12 volts to begin with it will be cheaper and more efficient. That said, I have one solar doo-hicky that has run on a VERY cheap inverter designed to be used in a car for years without a hitch.
 
frank li
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Angela,
Insolation data, meaning in my use, how much sun falls on a flat surface seasonaly and over the year and for the usual 30 years or some lengthy period that is reliable enough to use as a tool to design with, especially if any significant cost is involved.

Its important.

Your pump may not actually use 93w, your battery storage temps could be extreme, your load could be critical, your actual solar horizon could be whacked by a mountain or daily heavy rain. The 92w is easy to work with and was the information given, along with "need to run".

Using 92 watts and assuming full capacity is a good way to add a layer of derating to a project like aquaponics, where it is common to require 24/7 operation as a critical load.

I hope eric is kidding, and if its a poke, i did speculate a little far...
But you gave a reasonable load scenario and 100ah at 12v and 40 watts pv could never run your pump, even with 24 hour solar noon. He is correct though that the actual measured load, especially as a constant one, is the right tree to climb.

This prioritizes the question, how much water? 24/7. The next important questions would be how critical and, how much sun?

In some cases a PV-battery based systems can be sized for bridging very few days.

There are great dc pumps and small inverters depending on what you have invested in and built on already. High efficiency, reliability and capability costs money and knowing everything about a project and its site is the best thing to be armed with when applying money and effort to a project, especially one that you may depend on.


 
Eric Bee
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Actually Frank I wasn't responding to your post and it was not at all meant as a dig. Simply trying to offer some practical advice to help move a project forward. Most people simply aren't going to do these kinds of calculations just to run a water pump, even if they understand what it all means, which isn't that common.

That is not at all to say that insolation isn't important or that one could not save some trouble and possibly expense by doing the math first. You are undoubtedly much more knowledgable than I in this regard -- I am focused on the practical "get it done" side.

So now that I go back and read the bottom part of your post I have no idea where you get the 1000 watts PV. For a ~100w load, even with an inverter? Even without doing any math or using one of those online calculators that flies in the face of my own experience, which is entirely at the small end with oddball parts and for projects such as Angela's. Also, central to my assumption is that that is peak rather than continuous load -- water pumps always draw way more on start up, but if its running continuously you can count on a fraction of that.

Backing up, here is the approach I advocate for most situations: Especially if cost is an issue and/or you are reclaiming parts, calculations really aren't necessary once you have a ballpark. Angela is not building a whole house array here. Find the panel(s) you can find and add more as necessary. Find the battery or batteries you can find and add more as necessary. If you have a Kill-a-watt or similar (ie ameter) you can determine the actual load of the pump. But it's not like there is much harm, again -especially- if you are recycling, to experimentation. We could spend all day calculating and never build anything, in which case how much did we even learn?
 
Angela Aragon
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OK. Here is some background. Our farm is in San Ramon, Matagalpa, Nicaragua. As I said, we are 12.8° N of the equator. I am not sure if I can find 30-year data for our location. It might be available for Managua and areas south, where there are solar arrays, but we are north and in the mountains.

Nicaragua currently produces most of its electricity from renewables, so this is not a desire to be environmentally responsible. And electricity is not expensive. My average monthly bill is about $8 US.

My primary concern is that almost daily the service will stop for a couple of seconds, then return for a second or two, then go off again, then come back on. After 2-5 switches, it stabilizes. This obviously is being done by the electric company for some reason, as it is fairly predictable (either occurring early afternoon or early evening. I am worried that this on/off behavior will burn out my pump.

I originally spoke to a guy here about setting up a backup system with solar in case of power outages. He recommended that, rather than go the expense of solar, that I should instead simply us the power grid to charge the backup batteries. This made sense to me, particularly because the cost of electricity is low. However, I am very concerned about the on/off behavior and what it will do to my pump.

If the pump were a computer, I would by a back ups, but my pump uses a lot more amps. So, that is it: my reason for considering solar.
 
Eric Bee
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Ah, Angela, that is very helpful. Personally I'd forget about solar for now -- it strikes me as more complicated than you need.

You are very correct that you will kill your pump in no time with frequent stops and starts. You can buy devices which will buffer power failures and wait a certain time before re-activating power to the pump. But your power requirements are really quite modest. Looking at the UPS (Uniterruptable Power Supply) I have sitting right here I'm using 27% of it's capacity at 162 watts. Since the pump will be running on UPS continuously you likely will be just fine. And my UPS has a display showing remaining run time, capacity used, etc. Mine was $99 from Amazon and has a 900W load rating -- once you verify the load of the pump you can very likely down-size from there. To me, for the money this may be the simplest and easiest option -- even if the power is out for several minutes the UPS will keep your pump running. If it goes out longer and the UPS can't keep up, the pump will simply shut off and have time to cool before being restarted. This is what I would do, I believe. 
 
frank li
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http://www.samlexamerica.com/products/ProductDetail.aspx?pid=562

http://www.rvautoparts.com/Samlex-Automatic-Transfer-Switch-STS-30_p_765.html?gclid=CIX1j4mAi9ACFYMCaQodjt4FcQ

There are all kinds of solutions if you want a smooth functioning backup for typical power availability issues in the south. Ups systems are plug and play , be sure of the battery capacity, they typically have small 7-10ah batteries, which may work if you only need a few moments of power, a couple times per day. The whole story comes out eventualy!

The AE series inverter has an automatic transfer switch and a battery charger function. This inverter and a couple stout batteries from a local supplier makes a great, proven combo that would likely support a critical loads panes at your farm for lighting, communications and your aquaponics, possibly domestic water and ceiling fans too. It will automatically transfer back and forth between grid source and inverter source and keep your battery maintained. It has a heavy duty charger. Like a ups, but with gusto and customizable storage.

If you do monitor your usage (Kill-A-Watt meter IS nice, not sure what power form you get there.), then you will have a number for storage requirements during outages, as long as you can approximate them.
 
Angela Aragon
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Thanks guys for all of your help. I have one more question. How do I determine the "load" of my pump? I have it here next to me. It is an ActiveAqua submersible water pump, model #AAPW1000, voltage = 120v; Frequency = 60Hz; Power = 92W; current = 0.85A; Qmax = 1110gph; Hmax = 12.13ft.

That is it. There is no information about the pump's load. If this is important, it seems like it would be the responsible thing for the company to include it.

Is the load the amount of power required to start the pump?
 
Eric Bee
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That's a little pump. It probably really does draw 99 watts. That's the power it uses. For comparison your typical laptop is 40-60 watts and of course your typical CFL light bulb is around 10-15 watts. It doesn't say if that's startup or continuous but with pumps this small it's probably about the same. With big well pumps the draw on start can be huge, but you don't need to worry about that.

I have to think you'd be totally fine even with a very small UPS or similar thing.

Edit: To clarify, you can look at the ratings for UPS units to see how long it would run on battery. E.g. The APC brand model BE350G is rated 5.6 minutes with a 100 watt load which would be quite adequate for the situation you described. and is US$43 on Amazon. I'd imagine units are locally available and you can often find them used -- even a really old one will still have more than enough capacity for you. Of course, it's only about a $100 pump so maybe it's not worth it.
 
frank li
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The best way to determine load is to measure it in watts for the duration you expect to back it up for. If using lead acid you will want to size the battery so that the cycle uses 10%-20% of your capacity in watt-hours.

Knowing the head or height that you are pumping water to with that pump might help if you cannot measure it.

This can be done with a multi-meter or a plug in meter device as a KILL-A-WATT or WATTS UP power meter. These are great because they are inexpensive and accurate enough. They have calculators and elapsed time display for $/watt, accumulated over time and calculated forward, day, month, year. There are other functions that i dont use and models i have not used.

http://m.homedepot.com/p/P3-International-Kill-A-Watt-EZ-Meter-P4460/202196388?cm_mmc=Shopping%7cTHD%7cG%7c0%7cG-VF-PLA-D27E-Electrical%7c&gclid=CL-Jx7PNi9ACFQkPaQodfPIDBA&gclsrc=aw.ds


You could size for 50% or even 80% depth of discharge depending on how long a service life you need the battery to provide. If its cheap, you might just pump and dump till the wheels fall off, but for a serious long term power supply and having an ample budget and desire to operate without interuption, i would do it right, which could possibly be an off the shelf, office type UPS. Even at low wattages, 24/7 operation is a far cry from the intermittent operation you stated.

How much damage does the interuption cause to your cultures?
How long and how often are the grid outages and how long in between?

This is important to know, after running watts. Then, the equipment has to be able to supply it and the charger has to be able to re-charge the battery before the inverter is called enough to cycle the battery completely or you will "pump" it down and sacrifice the materials, effort and time, which may be small change, depending...
 
frank li
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The "load" is stated in watts, as 92w. So 92 multiplied by hours per cycle will yield watt-hours.

The name plate number is small enough and the duration and repetition is short and seldom enough to just go with it, unless there are budget or other reasons. This number multiplied by cycles required daily (or not quite daily, depending on charge/discharge time and storage and charging capacity) plus rough inverter and battery efficiency derating is used to get to where you can start to apply equipment specs to solving outages and the equipment features or lack of features or desired capability or lack of capability may modify the final design, especially where using off the shelf ups systems or other available things like budget or existing equipment.



 
frank li
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Eric, how long do you supply 100w constant for on your odd bits? I think you would enjoy the calculators and they do put a damper on my dreams too sometimes, but...numbers.
 
Eric Bee
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Frank, actually I do use the calculators and am reasonably familiar with the formulas, etc. I am by no means saying they aren't helpful, because they are. You are very right about that.

But you can see what that gets you: dampened dreams. More often than not the numbers inform what I'm doing but if I took them at face value every time what fun would that be?

As for how long a load, I have no idea, but I didn't say it was 100w. I know the battery isn't dead and the unit does what I want. My time doing the math and trying to validate on paper what I can just have validated in the real world... it just isn't worth it when I'm not spending money on parts. And that to me is the point.

Alas, just so you don't think I'm flying by the seat of my pants all the time: the unit I was referring to, which includes a heater to keep water for chickens from freezing, is managed by a microcontroller which seeks to minimize power use -- ie there is a temperature sensor in the water and although it lacks an RTC it can semi-intelligently derive time of day from temperature cycles, so it only powers the heater when it makes sense. If the temp drops at night it won't power because the chickens are asleep unless the temp is so low that it wouldn't be able to melt it in the morning. Stuff like that. The point being in part that I didn't and couldn't know watt hours and don't care as long as spot checks show the battery isn't dead.
 
frank li
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Absolutely. I have plenty of successful projects that never had a calculator involved too. But she did ask, how much and to provide a responsible answer, we look into it, at least to a shallow depth.
 
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