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Hypothetical Farm Irrigation. How impossible is this?
#1
So my father in-law is a farmer. He irrigates his field via a 20hp continues pump (220v 49.4amp this doesntd equal 20hp but it's what the faceplate says). 

He was impressed with my efforts for a diy solar / powerwall and asked me what would it take to run his pump. I asked him how often he would want to run it and he said anywhere between 8-24 hrs a day. 

So because I like challenges I tried to crunch the numbers. I wanted y'all's insight to the potential obstacles with this hypothetical system. 

Run time: 8hrs
Power Consumption: 220v @ 49.4A = 10.868kw/hr x 8hr = 86.944 kwh 

Powerbank: 104kwh storage. W/ 20% extra capacity. 

Solar Panels: 18.969kw system with 5.5 sun hours.

Run time: 24hrs
Power consumption: 260.83kwh
Powerbank: 312.99kwh
Solar Panel: 56.91kw system

Inverter: ? I found a few 20-60kw 48v to 220v inverter /mppt combo units but I'm not at all familiar with equipment of this size. 




Has anyone attempted something of this size? 
And what are the potential problems that could arise from a system of this size.
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#2
You're going to need a MASSIVE bank for that. I would try for more than 20% extra capacity to cover degradation over time, packs out of balance at the lower end unless all brand new cells, and not charging fully to 4.2V to make them last longer.

I was going to suggest the AIMS 12kW could handle that beast of a pump but it's max electric motor start rating is only 12hp. I'm not sure what to do about the inverter... That's going to be the hard to find/expensive part I think.
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#3
It's a 3 phase motor, that's why it's 50A. Honestly he doesn't need the off-grid capability so there's no reason why he should go off-grid. If he wants to offset the costs, then a field of solar panels grid-tied should suffice. Otherwise it gets expensive. So the question is does he really need to go off-grid and how much is he willing to spend?
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#4
Huuuuge power consumption. I agree with Mike on the massive bank.

Another thing to consider is, instead of spending >$1000 on an inverter, you could switch over to a 48V DC motor for around the same price. Not sure how the pump head is attached in your setup, as that makes a difference.
If the pump head is just shaft driven and not part of the housing of the motor, you could just replace the motor with a DC version. If the pump head actually "is" part of the motor housing, then you'd have to replace both parts, which makes things a bit tougher.
However, you could sell your existing pump/motor to help offset the new one.

The advantages of this is that you'd have a lot less losses across the board. DC motors run more efficient and usually have more torque than AC counterparts. This is partly due that some have permanent magnets instead of an excited set of coils to run the motor.
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#5
+1 That is a massive power draw!
You might be better off considering a system that is specialized for motor drive - no battery storage.
You would need a very large solar array & the right type of solar-to-motor control box (they do exist).
Obviously this could only run when the sun's reasonably up.

There's no way it would be worth the effort to do batteries for this with 18650's, you'd have to go to large prismatic format cells
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#6
For 3 phase pumps, the best way to run large capacity from DC is with a variable speed drive and feed the DC directly into the DC HV bus in the drive inverter unit. Far cheaper inverter cost per kW and designed for running pumps...

For cost saving, cheapest option is just 10kW of solar with grid tied inverters as this will cover some of the pump load with the biggest return on investment.

Next option is to just over size the solar array to 15kW and allow the excess to grid or another use. The excess capacity will only be an excess generation level for about 1-2 hours in the day...

Next option, increase solar to 20-30kW for a small battery pack approach (<20kW) to level out the cloud cover impact from the solar. Use LTO cells and cycle them 2-5 times per day (discharge when cloud passing over). Grid tied inverters 3(or 6) x 2kW GTIL one per phase. Solar charge controllers for 1/2 to 2/3 of the solar, leave the rest grid tied..
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#7
I think you should also measure the amperage/power of the pump when it is running.  The Nameplate on the pump is the maximum continous power the pump can output and not burn up or get damaged, but the pump is probably not drawing its max power continously.  It depends on how the whole pump control system is set up.  Anyway I would be very surprised if the motor is drawing near it's max load continously.

-Ryan
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