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MattEDP

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Reply with quote  #1 
Hi there,

I'm very new to this so would really appreciate some help.  I'm volunteering at a school and we're setting up an aquaponics system and would like to have it running off grid.  It will be a very small setup (a proof of concept for the students) but I'm not sure if we have the necessary equipment.

We currently have one 250W solar panel that we need to power the water pump which must run 24 hours a day.  I'm located at roughly 5 degrees latitude, so we get 12 hours of sunlight every day (assuming no clouds), so I'll need a battery system to run it through the night.

The current pump we have says Max 10 A and Max 1.1 kW (I don't know much about pumps).  Assuming sunny days, will our one panel be sufficient to run tis?  Also, what kind of battery system should I be looking for to power it through the night and cloudy days?

Thanks in advance for your help.

stmbtwle

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Reply with quote  #2 
At first glance, I don't think so. At 1.1 kw that's a big pump.

But to start, what voltage is it?

Another issue is how much does it ACTUALLY draw when running. The 1.1 kw could just be the startup load, and the actual running load should be a lot less. How much less depends on conditions. Is there any you can measure the amps while the pump is pumping?

What city are you near? We need that data for the solar calculator.

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Willie, Tampa Bay
MattEDP

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Reply with quote  #3 
Thanks for your reply.

The pump says 220-240V 50-60Hz, but I have no idea how much it actually draws when running.  It's currently sitting on a table, and I doubt we have the equipment here to measure amps while it's running.

I'm near Accra in Ghana if that helps your calculations.
Rick H Parker

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Reply with quote  #4 
1.1 kW * 24 hours = 26.4 kWh per day.  
26.4 kWh / 0.250 kW * 105.6 hours.  You would need at least 105.6 hours of sunlight per day to keep up with the energy consumption of the pump with a 250W panel ... not going to happen.
105.6 hours / 12 hours = 8.8. 
8.8 * 250 watts = 2200 watts. Your need 2500 - 3000 watts of panels.


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Rick H Parker
Kansas, USA
Electronics Engineering Technologist
Rick H Parker

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Reply with quote  #5 
But to start, what voltage is it?

11000 watts/10A = 110V.

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Rick H Parker
Kansas, USA
Electronics Engineering Technologist
stmbtwle

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Reply with quote  #6 
Your panel in your location will give you about ONE kwh per day, so it's a pretty definitive NO on one panel. If you can install the pump and run it on utility power you can eventually determine how much power it needs in real life, then you can figure out how many panels (and batteries) you'll need to run it for 24 hrs.

Here's the site: http://pvwatts.nrel.gov/pvwatts.php
You'll need to plug in your location (Accra), the size of your array (.25) and the tilt if any. It will give you kwh per month. Divide that by 30.

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Willie, Tampa Bay
Rick H Parker

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Reply with quote  #7 
Your panel in your location will give you about ONE kwh per day, so it's a pretty definitive NO on one panel.

He is in the tropics about 350 miles from the equator. Daylight/Night split stays pretty close to a 1:1 ratio year around.

250w * 12h = 3000Wh = 3kWh. 

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Rick H Parker
Kansas, USA
Electronics Engineering Technologist
MattEDP

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Reply with quote  #8 
So this isn't looking promising to us.

From your calculations, it looks like we'd need at minimum 10 250W panels to keep this pumping running.  Does that take into account the charging of the batteries so it can run through the night?  Just out of curiosity, how many batteries would be needed to run this system when there's no sun?  I know batteries vary considerably, but what would be a rough estimate for number and cost?

I guess we only have a few options then.  Either buy more panels, downsize the pump or hook it up to our grid.
stmbtwle

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Reply with quote  #9 
Depends on what you're trying to do. If you're using it for a water supply, it's very possible that:
A. The pump when running will require less than the rating.
B. The pump will cycle on and off.

Both cases will reduce the power needed, but until you put it into service and measure the actual consumption you simply won't know. The only way to do that is to put it on the grid and meter it. Once you do that and determine the kwh required you can figure out how many panels you need (24 hrs operation plus a good margin). What the pump doesn't use in the daytime will go into the batteries for use at night. You'll need at least enough batteries to run the pump for 18 hrs or so (more is better).

Suppose you determine you need 10 kwh per day. That would be 10 or more panels in your location (say 12 or more).

Batteries are rated by volts and amp hours, and volts x amp hours = watt hours. A 12v, 100 amp hour battery will hold 1200 watt hours or 1.2 kwh. For battery life you can only use about half that, or .6 kwh. For 10 kwh you'll need 10 รท .6 = 17 batteries. Bigger batteries, you'll need fewer batteries, smaller batteries, you'll need more. On top of all that you'll need a charge controller and an inverter.

It won't be cheap, sorry. But FIRST you need to determine your actual power requirement, which will require connection to the grid anyway. I think you might be better served to stop right there.

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Willie, Tampa Bay
Rick H Parker

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Reply with quote  #10 
Does that take into account the charging of the batteries so it can run through the night?

Yes but it does not take into account system inefficiencies and weather and it assumes the pump is drawing it's maximum power 24 hours a day. If you quantify the energy consumption better and it is lower, the quantity and cost of the required equipment will come down also.


I know batteries vary considerably, but what would be a rough estimate for number and cost?

Rough ... I think your looking at around $5000.00 - $7000.00 for enough battery storage to make it through the night reliability at the maximum consumption rate of the pump.

If you can gather up a list of equipment to consider
  1.  With specifications and cost.
  2.  Tell us your location, longitude and latitude, so that I can look up the solar radiation data for your location.
I could model a system that would work and trim the cost.

downsize the pump

Conservation of energy is the smart first step in any energy project. It saves a lot of money in terms of required equipment.

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Rick H Parker
Kansas, USA
Electronics Engineering Technologist
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