Another solar pumping question

[Mrburns]

Hey there,

I would like to use solar power to pump around 10.000 L of water/day from a well into a reservoir that I could use for gravity fed irrigation via a drip system. Please give me your thoughts on this, I would like to know if it's doable. I'm a newbie so please bare with me if I ask something outrageous

The pump would sit in the well at around 27 feet, the top of the reservoir would be at 12 feet from the ground level. I'm thinking of using a SCS 18-45 1/2 HP Submersible Pump. The specs on the pump:

At 45 volts DC the peak efficiency point is 18 GPM at 45 feet of head..
Max Current: 8.5 Amps
Max Power: 380 Watts

My question is:

Is it possible to run this pump directly from solar panels with an LCB? Would 2 x 250W panels wired in series do the job?

Thank you in advance for your responses!

[Mrburns]

Forgot to say, my insolation is 5.3

[Mike90250]

Don't know what SCS 18-45 pump is.

But a 1/2 hp brushed DC motor is going to be an electrically noisy thing. I'd contact the motor mfg and ask them if direct off PV is acceptable. I don't know if a LCB will be able to handle that power.

[Mrburns]

Thank you for your reply Mike!

It's a 1/2 HP brushless DC submersible pump from SunPumps, found the full specs for it, they say it was specifically made for solar powered water delivery in
remote locations and they have an MPPT controller that goes with it, so I guess I'm good to go then

Could you please give me an advice on what kind of panel configuration I should use with it to get the 45v needed?

Thank you kindly

[Mike90250]

At 45 volts DC the peak efficiency point is 18 GPM at 45 feet of head..
Max Current: 8.5 Amps
Max Power: 380 Watts

Well, considering PV arrays produce about 80% of nameplate, you need to harvest about 400w @ 45V. That puts the array size at about 500W of PV to get the best pumping with these limited specs. PV configuration is unknown, what is max voltage to the pump and stuff ???

As I pump water for irrigation myself, you count the water pressure at the bottom of the tank, will that be enough to run your irrigation ? What happens on a cloudy day with no pumping? Do you have enough storage, or will you miss a cycle ?

[Mrburns]

All I can see in their specs is:

Voltage Range: 30 to 45 VDC

I suppose 45V is the max voltage then? In that case 2 x 250W panels in series would be enough?

As I pump water for irrigation myself, you count the water pressure at the bottom of the tank, will that be enough to run your irrigation ?

This was going to be my next question The reservoir I would use would be a 10.000L plastic tank, the bottom of it would be sitting at about 5 feet off the ground (I could put it higher if I need to). I would need to drip feed 1500 bushes at around 6.5L/plant. The plants are spread out on 1.2 acres. Do you think gravity would do the job or would I need a booster pump to increase the pressure?

What happens on a cloudy day with no pumping? Do you have enough storage, or will you miss a cycle ?

Thank you for pointing this out, I think I'm making the mistake of undersizing my system. I think I should go with the next level up, the 1 HP brushless pump (it's almost the same price anyways) and use 2 x 10.000 L tanks. What is your suggestion?

Thank you

[Mike90250]

...... What is your suggestion?

Got none, not enough info about the plants, drippers, tube sizes, number of circuits, filter losses, line run lengths and what pressure is needed for the drippers. At this point, all I can do is ask questions.

Drippers usually need 15-30 psi to work reliably. Line lengths reduce pressure, lots of drippers reduce pressure.

Example, I have 60PSI in a 2" main line. about 300 trees. They are on 6 different circuits, controlled by a 6 station timer. Only one is on at at time. each valve feeds a manifold that has 3, 100' lengths of 1/2" dripline. When running, the filter lowers pressure to about 30 PSI at the drippers, as it clogs, pressure drops. You have to calculate all that stuff before buying a single thing.

I suppose 45V is the max voltage then? In that case 2 x 250W panels in series would be enough?

NO. As the pump loads the panels, their voltage drops, so you need a series combo of panels to :
a) stay below the death voltage of the pump ( Voc of panels)
and a parallel combo of panels to provide enough amps for it to run, with your 1/2 hp pump, it needs 500w of panels, if you figure for 40V, then you need 12.5amps Then you look that up on the pump curve (for 40V) and see if you meet your flow and head requirements.

[Mrburns]

Thank you for your reply, your time and your patience Mike and Inetdog, I really appreciate it guys!

First of all I'd like to apologise for the half ass data that I was providing, I just didn't wanted to be that guy, that shows up out of nowhere onto the forums and right away demands others to do the work for him and design his system. After reading your replies though, I realized that I can't expect help without all the detailed info either, so here it is:

Land surface: 1.2 acres
Number of trees: 1500
50 rows of 30 trees/row
Tree distance from each other: 4.5' x 7.5'
Lenght of each row/dripline (0.86" diameter): 135'
2 drippers/tree @ 14 psi
Lenght of 3" main line: 375'
Each tree needs between 6-8 L of water/day
The well: 6" wide, water level at 18'

Currently using a gas powered centrifugal pump, pumping clear water from 27' into the main line (there is a filter on it, don't know it's specs of the top of my head). 1500 trees x 8L= 12,000 L is being pumped through the drippers in about 3 hrs. Flow control valves are opened half way.

Hope I didn't miss anything..

So the cost of gas is around here is $1.6/L, probably going to see $2 soon. I am wondering if there is a way to go solar. I know it can't be done in one stage (like it's the case with gas or diesel powered pumps), that's why I was speculating if I could use a solar powered submersible brushless DC pump (1/2 or 1 HP) to pump it into a (couple) huge tank(s) and then drip it out of there during the day. It would be nice to have a gravity fed system, but the more I read about it, it seems that I would need to use a solar powered booster pump as well..

I know it would be a big investment all at once, but in a span of 20-30 years it could be worthed with the insane gas prices that we have. Is this possible?

Thank you in advance!

[Mrburns]

Hi again!

So I followed up a bit on the pressure loss factors that you recommended Mike, I found a good free online calculator (not sure if I'm allowed to post the link) that takes in account also T-connectors, reducers, elbows, valves etc. Considering that I would like to have a flowrate of 24 gpm, these are the calculations I came up with:

flowrate in the 2" mainline: 24 gpm
pressure loss on 750' of 2" mainline (with 50 T connectors) = 4.4 psi,

flowrate in the 0.75" driplines: 0.48 gpm each (x 50 rows = 24 gpm)
pressure loss on each 135' of 0.75" dripline = 0.04 psi (I'm not sure if I need to multiply this by the 50 lines that I have?)

2" - 150 mesh filter loss = 6 psi (according to the sellers webpage, which seems really low comparing to the 30 PSI you mentioned)

Total loss on the lines and filter 10.44 PSI x 2.31 = 24.11 feet of head
Pressure needed for the drippers 15 PSI x 2.31 = 34.65 feet of head
Water being pumped from 27' + 3' where the dripline would sit = 30 feet

So my total dynamic head (TDH) would be then 88.76 feet of head? So I need to look for a pump that can pump 24 gpm at around 100-120 ft of head, just to be on the safe side? Is this correct?

[Mike90250]

........So my total dynamic head (TDH) would be then 88.76 feet of head? So I need to look for a pump that can pump 24 gpm at around 100-120 ft of head, just to be on the safe side? Is this correct?

If you do, then you may need a pressure regulator - the connections in the drip system & the drippers have a max recommended pressure. Ypi dpn;t want to exceed that.

Filter - catalogs gives loss when it's clean. more loss when it's half dirty. A well should be pretty clean.

Well, can it sustain the flow ? (I guess so, it's doing it now.)

[SunEagle]

If you do, then you may need a pressure regulator - the connections in the drip system & the drippers have a max recommended pressure. Ypi dpn;t want to exceed that.

Filter - catalogs gives loss when it's clean. more loss when it's half dirty. A well should be pretty clean.

Well, can it sustain the flow ? (I guess so, it's doing it now.)

Surprising that even a city water supply has too high a pressure for most drip systems.

I not only have to use throttle back on the faucet flow but need an inline pressure reducer. The one I use has a screen to keep out trash from plugging the drip heads but needs to be cleaned every once in a while due to my hard water crystal build up.

[Mrburns]

Where would one put a pressure regulator, right after the filter on the mainline or one on each individual dripline? Could the pressure regulator be left out if I would hook up more mainline and driplines until all the extra pressure is "used up"? I mean there is more trees to water.

I was looking at the Grundfos Sqflex submersible and the Grundfos CRI surface pumps, acording to the graphs they would both be suitable for my needs. Which one do you guys think would be better to have, the submersible one or a surface pump? Would a surface pump last longer than the submersible one? Maybe also easier to service being more accessible on the surface?

[Mike90250]

First, you must make sure your filter can take the normal line pressure, and if it is sitting in the sun getting hot and soft. Not all filters are rated for high pressures. Make sure your filter can handle the volume of debris for several days before it clogs up. I have to scrub some of my finer filters every 3 weeks. Sometimes, using a pressure gauge on either side of the filter is a good idea for a new system.

Adding more lines to reduce the pressure works fine, until something fails, and then it's a mess. Believe me, about 2 hours ago, I finished fixing a blown out T in 3/4 poly, that had been fine for 4 years. Then last night, I lost 4,000 from my tank when the T blew. A 50 PSI T on a 70 PSI line. Works till it breaks.

If your water is from a well, you need a submersible pump. You can only "suck" water up about 20 feet, before you hit it's vapor pressure in vacuum.

[Mrburns]

Thank you for all the good info Mike! It seems like the Grundfos 25 SQF-7 would be a good candidate for my needs. In the user manual it says that I need to supply it with 120-300 V DC for optimum performance and I would need 1400 W in panels. My question is how would I achieve this voltage range using let's say 250 W panels? How many panels would I need and how would I connect them (how many of them in series and how many parallel)?

[cjb80]

What is the flow rate of the emitters and how many emitters are you going to be using at once? Typically people break up their watering into zones and use an irrigation timer. This information, including the distance to the watering size and elevation will give you the information required to size the pump.

Pressure regulators are usually installed right at the valve for the zone at the highest point in the block. Some pressure will be gained after the pressure regulator due to elevation changes (lower) but 25 PSI gives you about 100 feet of 'fall' before you run into problems with too high of pressure. Typically a 25 PSI pressure regulator is used because the pressure compensating (PC) drip emitters range from 20-60 psi (convert to BARs as necessary).

I have Gundfos and SunPumps pumps and they're both pretty good products. My SunPumps pump runs panel direct and it is 3HP with about 2800watts of solar panels. My vineyard blocks are about 1500' feet away and about 70' up in elevation via 2" PVC pipe. I can water two acres at a time which is about 25 GPM. If you call SunPumps up and talk to an engineer they will ask you all of the questions in my first paragraph and then come up with a solar panel and pump configuration that will reach your goals.