pumping with PVs and using AC submercible pumps

[klapeto]

My friend needs 5m3 per day and I have calculated he needs around 500W of solar
panels to do the job of rising this water volume 60m up hill.

He already has two standard submersible AC pumps working at 1500W and 7.7A
195V at full load and having a 11A current at start up of total 2250W
instantaneous power (I measured this with a clump and so this value is a RMS value
and probably not the peak amps).

He has decided to keep these pumps and just replace the diesel generator he uses to
pump with PVs.

I will need to find an inverter with MPPT in order to connect the 12V modules
and get 230V AC at the output in order to run the pump which will be turned on
manually.

The question is, does anybody know if this system can function?
Where I can find such an inverter and what specs does it need to have?
Will the pump function well when it will be partially powered by the solar generator?
Will this affect the total life of the pump?

Any help will be appreciated!

klapeto

[damian]

The short answer is that it will work.  The long answer is that unless the pump has some kind of soft start you will want to have surge capacity in the inverter to match the starting surge of the pump.  The pump will be fine if the inverter can supply full voltage through the starting surge and pump life will not be affected.  Where are you?  What type of pump is it?  Is 60m the total lift or is there a lift out of a well in addition to that?


Best,

Damian 

[klapeto]

The application is in Greece not very close I suppose!

60 meters is the total lift.

I don't know the trade mark of the pump, but these are the specs.

P 1850W-1,75 HP-2800 RPM-50 HZ-230 VOLT-8,5 A-HM 82-10
l/min 5-100  -μf 35  -vc 450 -Hmax 84m

Do you know any inverters for the job?

Thanks for the reply,
klapeto

[hydrosun]

All the inverters with MPPt that I know of are for grid intertie. They need higher than 12 volt dc input and won't work without  connection to the grid.
 All the solar direct pumps usually are special varible speed dc motors. Some examples are the SQF style from grundfos and dc pumps using LCB (linear current booster) converters. there have been other discussions doing that on this site.
 The only way I know to run standard AC pumps is to use the solar panels (perhaps through a mppt controller) to charge a battery bank and then use a large enough inverter to convert to the correct voltage. If you closely match the pump usage with solar input the battery bank wouldn't need to be too large. You could use a voltage controlled relay to only supply power to the pump when the batteries are close to full and automatically shut off if the voltage goes low when too much power is being taken from the batteries.

You may find that the dedicated solar pumps are more efficient than the standard  pumps so that less solar is need. That  may help offset the added cost of new pumps without using batteries.
Chris

[Ungrounded Lightning Rod]

I'd contact Gould's Pumps and see if they have a controller for the job.

[klapeto]

Thanks for your replies.

I have contacted Gould's Pumps but no reply.

I have looked into the application further and found out that I will need to use batteries and an inverter with a soft starter or pump rpm control.

Suppose that I use a 2kW inverter with the 1.8kW pump. The inverter along with the soft starter can provide the amps needed to start the pump.

In order for the battery bank to be small, pumping will occur when there is enough power from the sun.

The question is if I use 500Wp of solar panel (which I have calculated provide enough energy in a summer day to pump the amount of water needed up hill, but for a DC pump system) will they be able to work in the AC pump system?

The modules will provide 500W and the pump will ask from the inverter 1.8kW, which will probably mean that the inverter will get the rest from the batteries.

SO... either I need a huge battery bank or I need to increase the Wp of the PV modules to match the pump maximum power.

Any thoughts on the issue?

[oztules]

I can see what your trying to do..... and I have sad news...... not usefully practical.
You have an induction single phase motor. It's peak current will be 3-4 times run current. So you need a decent inverter to start it reliably.

It also means constant speed ( will follow frequency not voltage) so you cant turn it down ... all or nothing.
This means as you say batteries, which loses a lot of efficiency. It is a KWH game you need to put the KWH into the batteries first, then pump for 1/4 of that time, and charge again. (remember chemical losses). Even full solar while running will only delay the discharge cycle by 1/3rd.

Even if you could slow the motor (variable freq drive?) the chances are that they use a stacked rotor design, rather than a helical design (better but not as popular for some reason).

If this is down a well, where you can't use a surface pump, then you really need this:


 http://www.ebay.com.au/itm/500W-48V-S-S-SOLAR-BORE-PUMP-SYSTEM-2-YR-WARRANTY-/190548812134?pt=AU_Pumps&hash=item2c5d982166 

No batteries, helical pump ( virtually full pressure at any rpm... well almost... not like a stacked rotor) mppt built in for only a grand.

Trying to save by  making use of the current pumps will cost lots more (batteries and controllers and 30% less efficient).

I recently built a solar pumping system for over 70m head >60 lts/min... over 38000lts/day in summer (easy).... but we were pumping from a dam, and so used a helical pump driven by a standard 3hp DC motor with a modified curtis golf cart controller(260A @ 36v.... no batteries )

It. works very well, but we didn't have to draw the water up more than 12 feet..... then up pushed it another 200 feet up and a few kilometers away.

If your pumping from a dam, then this could be a way to go for you too.... but helical pumps are expensive things (our pump was a standard AGP520 Mono... $1800 just for that....  ( we can belt drive it from a diesel next to the electric motor ( swap belts) and pull easily over 120 l/min into 80m head.... it is a big pump).

Single phase induction motors work very well and simply on the mains.......any where else they become a problem with surge and the all or nothing speed thing. You cant reasonably back them off when the sun fades out.... even if you had 2000w solar. Three phase you could do much more easily.



................oztules

[Phil Timmons]

Oz -- I suppose they could throw a small VFD in there?

[oztules]

Phill, It is always a possibility..... but when using fixed speed pumps (induction motors, it seems they tend towards 2 pole single phase motors..... but they drive a stacked centrifugal rotor array to get the required pressure... may be 8 (or more) tiny rotors all adding their differential to get the high pressure.... if you slow the rpm down, you may just spin the rotors but push no meaningful water up the pressure gradient. This is less of a problem with smaller heads.

When they use variable pump speeds, they need to push a piston (fixed displacement.... wind pump?), or use helical pumps.  (for well pumping into high heads)

These can be slowed right down, and still deliver the same(Ish) head. In our case, by 50 rpm, it cant overcome a 100 psi head..... but after that, it runs all the way up to 1000rpm.... the volume changes )L/m), but the pressure  is easily over the 100 psi mark from 50 rpm onwards.... equivalent to dark cloud on our setup. Overcast it will still pump water up the 200' hill. So for these styles of pump, mppt and a stepper motor, or brush motor is ideal. VFD will require a decent, far more stable input source than a brushed DC motor or brushless DC motor and fancy controller.


.......oztules

[Ungrounded Lightning Rod]

The reason I mentioned Goulds Pumps is that I have one of their systems.  It has a pump with a three-phase motor and a controller that soft-starts it and adjusts its speed to maintain the setpoint pressure at virtually any flow.  The pressure tank is smaller than a soccer ball - just to smooth things out a tad while the controller gets things started and/or adjusted when the flow starts, stops, or changes.

This particular controller runs from 240VAC (and has a lot of sensing for various line and wiring faults in the "brains" of the device.)  But I was looking at their web site a couple years ago and saw a bunch of soft-start controllers.  And I think I saw one that was intended for use with a bare (no battery) solar panel, self-starting when sun was adequate and maximizing flow.  So perhaps they have a controller that can do this trick with the pump you already have down the well, or a total system to do just what you want.

(I was looking at their site because my house construction contractor, a decade or so back, apparently got an early model of the device, which had inadequate RF filtering, from a dealer who was supposed to scrap it instead of selling it.  It wiped out my AM reception whenever the pump ran.  Goulds replaced the pump and controller for free (and dropped the dealer).  The new one has a couple points on the AM dial where you can just barely detect it.  But while looking into the issue I browsed their site, which has a lot of interesting stuff.)

[prasadbodas2000]

to minimize the sizes of battery and inverter, I always wonder if it is a better option - to use a smaller capacity pump (AC/DC either) which will almost run when there is sun and use all what the panels can produce almost right away.
Now will this be technically feasible from the perspective of easily available pumps of this head-power range and how much will that cost?

[whythehecknot]

Just a personal testimony here, so I hope it helps, and I am by no means any kind of expert. But we here on the ranch have pumped our water for better than 13 years with an off grid sure flow pump, 800ish dollars US brand new. We now have two of these working, one on a 20,000 gallon rain water tank and the other in a very mineral rich and dirty well. The ranch has a dual water system, well water for toiletts garden etc. and rain water for everything else. The first pump we ran continuous for ten years on solar @12 VOLTS. THE SOLAR WAS A SINGLE 55 WATT PANEL and a controller. It was able to pump what I guessed to be around 500 gallons a day, not sure how that compares to 5m3 but the output of this pump can be doubled by using 24 volt. I know  that the manufacturer says to rebuild these about every three years depending on the usage, which we finally did with the pump in the well, and the cost of the rebuilt was like 200 US. I now have the well pump hooked up to my house batts and can pump 24-7 if I wanted to. These pumps are super efficient and can pump all night on a single deep cycle battery. The rain water tank is on the single solar panel now and the controller. I would recommend these little pumps to anyone that doesnt need allot of water and has a meager budget.
  Just my opinion but maybe you could talk your partner into buying one of these and save a ton of hassle. 

[DanG]

Five cubic meters of water is equal to 1320~ gallons.