Help required to design off grid system

syedbukhari · June 2012

Re: Help required to design off grid system

BB. wrote: »

Are you sure about 500 GPM (US gallons per minute?). That is a LARGE pump (also depends on how deep the water level is in the well)... A typical "home sized" off grid pump is probably somewhere in the 5-20 GPM range.

Also, besides depth to water (well, etc.), there is a question of how much water pressure you will need... If dumping in irrigation channels, you do not need much pressure. If using some sort of drip/sprinkler irrigation, that additional pressure also adds to the power consumption of the pump.

Grundfos pumps are very good quality with flexible power input (AC/DC, lower to higher voltages, batteries, generators, solar panels). Look here for some documents on system design (and tables of water flow vs water/pressure). But, at least here, these are not big pumps (around 1 HP or so).

-Bill

Yes you are right 500 GPM is high flow rate. In Pakistan some people are using 5 HP mono block pump for irrigation. Its flow rate is 200-250 GPM. Some people are using diesel/electric pumps for higher capacities.
In our area the deep well bore depth is 30 meters and water suction head is 10 meters. The mode of irrigation is through channels.I wants to use this 5 HP mono block.

syedbukhari · June 2012

Re: Help required to design off grid system

Cariboocoot wrote: »

500 GPM you will not get from a single solar-powered submersible pump. This is why you need to know the total volume of water to be used for irrigation, rather than a flow rate. The trick is to have the pump fill up a reservoir over time, and then release the water from the reservoir as needed.

The depth you are pumping from makes a difference too: the deeper the water has to come from, the slower the pump will run (fewer GPM).

But yes there are pumps that can run directly from solar panels; no batteries, no inverter.

Two examples from the same company to explain the operational differences:
Grundfos 60 SQF-3 up to 85 GPM from 45 feet using 1400 Watts of panel.
Grundfos 6 SQF-3 up to 6 GPM from 820 feet using 1400 Watts of panel.

You trade lift (depth to water) for flow rate.

Depending on the well design you can have multiple pumps pulling from the same well so long as the well's recovery capacity is not exceeded. If you are expecting 500 GPM I'd say the well has a very good recovery capacity. I'll hazard a guess that since you were expecting that flow rate the system now uses something like a 10 HP 3-phase AC pump or one powered by a diesel engine (such are typical for agricultural applications). For switching to solar, you have to be able to change the way the water is pumped and used as building a system capable of supplying the amount of power required by these big pumps is not really practical. You would be looking at 10kW+ of array, massive battery bank, multiple charge controllers, and a difficult to set up 3-phase inverter system.

But if you can switch to pumping over time and controlling the release of the water rather than flooding massively all at once then solar can be used for this application.

Yes you are right 500 GPM is high flow rate. In Pakistan some people are using 5 HP mono block pump for irrigation. Its flow rate is 200-250 GPM. Some people are using diesel/electric pumps for higher capacities.
In our area the deep well bore depth is 30 meters and water suction head is 10 meters. The mode of irrigation is through channels.I wants to use this 5 HP mono block.
This is a single phase pump. It normally takes 3 hr to irrigate 1 acre in summer. It will irrigate 2-3 acre on daily basis and i have to irrigate only 12 acres. Kindly advice about its size of array, controller and inverter. Can i use it directly through controller with out the inverter?
I wants to run this only in day time.

Cariboocoot · June 2012

Re: Help required to design off grid system

Solar is not a good choice for that situation. It can be done, but the two solutions to the problem are either a really big solar electric system or a complete redesign of the irrigation system.

Some of the daunting numbers:
5 HP on single phase AC is 3730 Watts. The start-up demand could be over 18 kW. It will certainly be over 10 kW.
For off-grid that would involve stacking multiple (about four) inverters to handle the start. The battery bank would also have to be very large to handle the initial power demand, and then be sized to handle the total run time. Likely you'd be looking at 2000 or more Amp hours @ 48 Volts. From that the array can be sized and it will be very large indeed. In fact there would be two or more arrays due to the need for multiple charge controllers to handle the current involved. All together there would be roughly 12 kW of panel.

It is probably not worth doing this as the expense of such a large system would buy a lot of fuel even in Pakistan.

The other choice is as I mentioned before, with "opportunity" pumping of the water to an above-ground reservoir and gravity distribution from there. That would require more than one pump, as it sounds like a lot of water is needed daily. Pumping from 30 metres (about 100 feet) is not to difficult, but we still don't know the daily volume.

BB. · June 2012

Re: Help required to design off grid system

5 HP solar powered pumping... Not impossible--But I would first focus on finding a VFD (variable frequency drive) type controller that can connect from a (large--on the order of 6+ kW array) and power a three phase pump motor directly (these controllers are certainly available inside a 1 HP Grundfos pump).

I found one once--but the company seemed to have disappeared a few years ago.

A I can find on this subject are press releases (here is one) that "talk" about projects--But nothing on who would supply a DC input VFD controller for somebody to connect to their well pump...

I would try contacting a couple of the folks in the above press release and see if they have sources available for your region (and let us know what you find).

Also, I would try contacting VFD distributors (like this one in Texas) and see if they can help research. (don't know anything about the vendors I am linking to).

There has to be somebody making these some where (probably China if you have any contacts over there).

-Bill

syedbukhari · June 2012

Re: Help required to design off grid system

As we were discussing about tube well model i calculated the values for 4HP motor, the observation are as following
It took 45 amp at its start up @ 220 volts and settle down at 15 amp during its running and kindly also guide about inverter surge value
For example
120% surge value for 10 sec
What does it mean?
Dear BB i am also waiting for your updates about VFD

Cariboocoot · June 2012

Re: Help required to design off grid system

"120% surge for 10 sec" means the inverter can handle 120% of its rated maximum load for 10 seconds. That's not much.

Your 45 Amps @ 220 Volts is a whopping 9.9 kW start-up demand. To get that you either need several inverters "stacked" to run concurrently, or else a very large one like the Xantrex XW6048 or Outback Radian GS8048. They can both handle 12 kW surge for about 5 seconds and the outback can sustain 9 kW for up to 30 seconds.

It would require a very large battery bank to withstand this draw, and to maintain the 15 Amps running (3.3 kW) for any period of time (so far you haven't said how long the pump needs to run for). Adding a VFD will help with the first problem (the surge demand) but not with the run time issue.

BB. · June 2012

Re: Help required to design off grid system

I am very sorry Seyd, I do not have anything more to add about VFDs... I would be doing the same as you, searching the web and making local phone calls. Given that you are 1/2 a world away (or I am 1/2 a world away from you;)), whatever I find locally may not be available in your region.

As we were discussing about tube well model i calculated the values for 4HP motor, the observation are as following
It took 45 amp at its start up @ 220 volts and settle down at 15 amp during its running and kindly also guide about inverter surge value
For example
120% surge value for 10 sec
What does it mean?

Induction motors tend to be around 3-5x running current.

For surge, AC inverters are typically rated in Watts, but it is really Volt*Amps.

For AC Power, the equation is:

Power = Volts * Amps * Cosine of (current vs voltage) = Volts * Amps * PF (power factor)

So, when you have an AC induction motor, the Cosine of the "phase angle" or PF is around ~0.67 or so (loading and other factors affect power factor). So while your power requirement may be:

Power = V*A*PF = 15 amps * 220 VAC * ~0.67 = 2,211 watts (guess/example, need to measure accurately)

The actual VA rating (for wiring, generator, inverter, etc.) is:

VA = 220 VAC * 15 Amps = 3,300 VA

So, the inverter would have to be rated at >3,300 VA (or watts where PF=1.0), just to run the pump.

Starting the pump is ~45 amps, so the VA rating for starting load:

45 Amps * 220 VAC = 9,900 VA

Ideally, you would be looking at 10 kW (really 10 kVA) surge/starting load rated inverter to start the pump... You may get away with a smaller inverter to start the pump, but that will take knowledge from your vendor.

Many "good inverters" are rated to support ~2x rated output for short surges (i.e., 2x 3.3 kVA = 6.6 kVA rated inverter).

Another issue, at least in the US, most motors that size would be three phase units, not single phase. And so you would be looking at either a three phase inverter (usually 3 inverters wired as 3 phase units) or a large single phase inverter powering an appropriate single to three phase VFD controller.

At least as I understand the issues.

-Bill

BB. · June 2012

Re: Help required to design off grid system

I should also add--That 15 amps @ 220 volts is pretty low for a loaded single phase 4 HP motor. Are you looking at a 3 phase motor current rating?

-Bill

Cariboocoot · June 2012

Re: Help required to design off grid system

BB. wrote: »

I should also add--That 15 amps @ 220 volts is pretty low for a loaded single phase 4 HP motor. Are you looking at a 3 phase motor current rating?

-Bill

15 Amps * 220 Volts is 3300 Watts / 746 = 4.4 HP. Not that far off the mark, depending on how "loaded" it really is.

westbranch · June 2012

Re: Help required to design off grid system

too bad there is no 'reverse action transfer switch', so you start the pump on grid and run it on PV/batteries

syedbukhari · June 2012

Re: Help required to design off grid system

BB. wrote: »

I should also add--That 15 amps @ 220 volts is pretty low for a loaded single phase 4 HP motor. Are you looking at a 3 phase motor current rating?

-Bill

No, the motor is in single phase and i get the reading on full load. At the reading time the flow rate was 300 GMP. The bore depth was 90 feet and water level is 30 feet.

stephendv · June 2012

Re: Help required to design off grid system

Another direct solar manufacturer is Lorentz: http://www.lorentz.de/en/partners/asia__pakistan.html And they have partners in Pakiston who could help you with the system. None of their pumps will give you 500GPM though.

syedbukhari · June 2012

Re: Help required to design off grid system

stephendv wrote: »

Another direct solar manufacturer is Lorentz: http://www.lorentz.de/en/partners/asia__pakistan.html And they have partners in Pakiston who could help you with the system. None of their pumps will give you 500GPM though.

Thank you very much for use full link. But there is contradiction in the information
According to the web site

Solar Pump System PS4000 HR/C

Submersible solar pump, helical rotor and centrifugal type, for flow rates up to 70 m3/h and lifts up to 350 m

and according the actual installation results are as

Location
Bahawalpur

Solar Pump System
1x LORENTZ PS4000 C-SJ8-15
Vertical Lift: 31 m
Flow Rate: 92 m3/day
Cable Length: 40 m
Solar Generator
21x 175 Wp
3.7 kWp

Installation
June 2010

syedbukhari · June 2012

Re: Help required to design off grid system

westbranch wrote: »

too bad there is no 'reverse action transfer switch', so you start the pump on grid and run it on PV/batteries

Yes you are right but i do not have grid facility for this model. I am running my pump on diesel

stephendv · June 2012

Re: Help required to design off grid system

I didn't see the "C" model, and it looks like it could meet your requirements with a 300+ GPM capability. One thing is the flow rate that the pump is capable of, the other is whether there are enough solar panels and enough sun to support that rate. They seem to have some online sizing tools available that could help you select the right amount of PV to support the required flow rate.

syedbukhari · June 2012

Re: Help required to design off grid system

Cariboocoot wrote: »

"120% surge for 10 sec" means the inverter can handle 120% of its rated maximum load for 10 seconds. That's not much.

Your 45 Amps @ 220 Volts is a whopping 9.9 kW start-up demand. To get that you either need several inverters "stacked" to run concurrently, or else a very large one like the Xantrex XW6048 or Outback Radian GS8048. They can both handle 12 kW surge for about 5 seconds and the outback can sustain 9 kW for up to 30 seconds.

It would require a very large battery bank to withstand this draw, and to maintain the 15 Amps running (3.3 kW) for any period of time (so far you haven't said how long the pump needs to run for). Adding a VFD will help with the first problem (the surge demand) but not with the run time issue.

Thanks for suggesting about inverter. I need to run this for about 7-8 hr in summer and 5-6 hr in winter in day time only and requires no back up. Kind suggest battery bank accordingly. Can i use a single battery just for its starts up and then run it directly?

Cariboocoot · June 2012

Re: Help required to design off grid system

syedbukhari wrote: »

Thanks for suggesting about inverter. I need to run this for about 7-8 hr in summer and 5-6 hr in winter in day time only and requires no back up. Kind suggest battery bank accordingly. Can i use a single battery just for its starts up and then run it directly?

No. Battery-based inverters need enough battery capacity to handle the loads for the full time, even though some of the current may be supplied by the panels once the battery is charged. In this case you're looking at 3300+ Watts for up to 8 hours, or over 29 kW hours (AC converted to DC). That is very large capacity for off-grid. You'd be looking at a 48 Volt system and at least 1200 Amp hours, plus two charge controllers each with about 3.8 kW array each. You might be able to shrink this down a bit if you want to rely more on the solar output and occasional recharging with the generator. Perhaps two 3kW arrays and just under 1000 Amp hours @ 48 Volts.

I know these are vague descriptions, but much of the final design will depend on the actual site installation including real operating temperatures, length of wire runs, and what equipment you end up getting. I'm just trying to give you a rough idea of what would be involved to run that 4 HP pump motor as-is from solar.

mike95490 · June 2012

Re: Help required to design off grid system

Beware - Pumps list their flow rate at 0 head, when you add head (lift) the flow drops down. Be sure to see the pump curve for flow at 30 - 50 feet of lift (I'm quite sure the water level will vary in that well) Make sure the level WHILE you are pumping, matches the flow you need. I can't picture what size well pipe is needed to recharge 300gpm - 8" ?

syedbukhari · June 2012

Re: Help required to design off grid system

Cariboocoot wrote: »

No. Battery-based inverters need enough battery capacity to handle the loads for the full time, even though some of the current may be supplied by the panels once the battery is charged. In this case you're looking at 3300+ Watts for up to 8 hours, or over 29 kW hours (AC converted to DC). That is very large capacity for off-grid.

Ok what would happen if i use an inverter without battery?

Cariboocoot wrote: »

You'd be looking at a 48 Volt system and at least 1200 Amp hours, plus two charge controllers each with about 3.8 kW array each. You might be able to shrink this down a bit if you want to rely more on the solar output and occasional recharging with the generator. Perhaps two 3kW arrays and just under 1000 Amp hours @ 48 Volts.

If i have to go with this setting then i should buy at least 200 batteries of 200 AMP/H. It is too costly to run a pump.

syedbukhari · June 2012

Re: Help required to design off grid system

mike90045 wrote: »

Beware - Pumps list their flow rate at 0 head, when you add head (lift) the flow drops down. Be sure to see the pump curve for flow at 30 - 50 feet of lift (I'm quite sure the water level will vary in that well) Make sure the level WHILE you are pumping, matches the flow you need. I can't picture what size well pipe is needed to recharge 300gpm - 8" ?

I have seen myself running 4 HP pump on grid supply and it was giving 300 GPM flow. This pump was lifting water from 30 ft depth, well bore depth was 100 ft and discharge pipe size was 5 inch.

BB. · June 2012

Re: Help required to design off grid system

If that is measured current--then you are probably running closer to 3 HP from that pump rather than 4 HP--Which is fine.

Typically, induction motors have a "poor" power factor (0.6-0.7 or so)... Part of the current is "in phase" with the voltage, and is "Watts". The other part is out of phase with current (~0.3-0.4) and "does no work".

Wiring and inverter/transformers/etc. have to be large enough to carry the VA (volts*amps), but the battery bank/solar panels only have to be large enough to carry the Power (Watts=Volts*Amps*Power Factor or Cosine of the phase angle).

You need a power meter that can measure both voltage and current (and their phase relationship) at the same time to accurately measure Power (or a standard utility meter measures power too).

A VFD is sort of like a special purpose Inverter... There is nothing to stop a designer/manufacturer from making a VFD that can accept energy directly from a solar array (and no battery bank--at higher costs to customer).

But "standard" DC to AC inverters are not designed to operation with straight AC panel input power (plus, most 120/230/240 VAC loads do not like variable voltage/variable ffrequency--which is how a Grundfos pump electronics package adjusts the AC load output based on available DC solar input).

-Bill

syedbukhari · September 2012

Re: Help required to design off grid system

Once again i need help from this forum
I have installed 14 panel on my fuel station with the following specification
Rating power at STC(Wp) 220W*
Open circuit voltage(Voc) 34.0V*
Short circuit current(Isc) 8.58A*
Rated voltage(Vm) 27.6V*
Rated current(Im) 7.97A

I used 2 strings of 7 panels by doing this i get 55.4 volts but failed to get desired amp and only getting 20-30 amps. In the beginning days i get up to 40-50 amp after few days it drops up to 25-35 amp. then i checked short circuit current of a panel it was 8.5 it means panel is generating its power rightly. Please guide then what is fault with this system?
I am using 48 volt battery bank
Please also guide can i charge 48 volt battery bank with 48 DC volt ?

Secondly the batteries are showing 1150 gravity and the multi meter showing 12.6 volt why this is so?

westbranch · September 2012

Re: Help required to design off grid system

You may have one or more connections that are loose between the panels and the charge controller.

Have you tightened them all since the installation?

What charge controller are you using?

Your 2 panels in series (55.4 V) is not adequate for a good charge on a 48 volt battery.

niel · September 2012

Re: Help required to design off grid system

you may or may not have a fault in your system. if your batteries have a full charge in them and you don't have a load being drawn the pvs won't be required to deliver their power.

a 48v battery bank is not at 48v, but at a range of voltages around that nominal number. i don't know the type of batteries you employ, but the voltage can approach 60v with around 58v more typical. this varies, but the point is another 48v source is too small to do any charging for the batteries.

syedbukhari · September 2012

Re: Help required to design off grid system

westbranch wrote: »

You may have one or more connections that are loose between the panels and the charge controller.

Have you tightened them all since the installation?

What charge controller are you using?

Your 2 panels in series (55.4 V) is not adequate for a good charge on a 48 volt battery.

Yes I checked all the connections.
I am not using MPPT charger
Please also advise about the difference in voltages and the gravity of the battery

syedbukhari · September 2012

Re: Help required to design off grid system

I am using 12 lead acid flooded batteries of 12 volt and 200 amp
Currently I am using simple charger but now I have ordered for a MPPT charger.
Please guide about the difference in gravity and voltages of the battery.

Photowhit · September 2012

Re: Help required to design off grid system

syedbukhari wrote: »

Once again i need help from this forum
I have installed 14 panel on my fuel station with the following specification
Rating power at STC(Wp) 220W*
Open circuit voltage(Voc) 34.0V*
Short circuit current(Isc) 8.58A*
Rated voltage(Vm) 27.6V*
Rated current(Im) 7.97A

Looks like info from the back of panels, panels are made for MPPT controller. What controller do you have?

syedbukhari wrote: »

I used 2 strings of 7 panels

I hope you mean 7 strings of 2 panels, but that is wrong as well since 2 panels won't reach charging voltage for a 48V battery bank. 7 in series will be 238 VOC very high for all but grid tie hybrid Charge controllers and the Midnite classic 250

syedbukhari wrote: »

by doing this i get 55.4 volts but failed to get desired amp and only getting 20-30 amps. In the beginning days i get up to 40-50 amp after few days it drops up to 25-35 amp.

This sounds like you have 7 strings of 2 so the voltage isn't high enough to charge 48V battery bank.

syedbukhari wrote: »

then i checked short circuit current of a panel it was 8.5 it means panel is generating its power rightly. Please guide then what is fault with this system?

This would be the correct amperage (ISC) for a single panel or series of panels

syedbukhari wrote: »

I am using 48 volt battery bank
Please also guide can i charge 48 volt battery bank with 48 DC volt ?

No you need a higher voltage to charge a 48V battery, your input to charge controller should be around 70 volts (or higher with MPPT) and out put should be above the battery voltage, the hotter the panels get the more the voltage drops from the panels. You likely needed to set some voltage levels into the charge controller. For regular 48 volt flooded battery you could start with 59Volts bulk, 54.8V float, equalize around 61Volts, You can see in strings of 2 your panels don't produce enough voltage. What Charge controller do you have?

syedbukhari wrote: »

Secondly the batteries are showing 1150 gravity and the multi meter showing 12.6 volt why this is so?

Is this across the 48 V bank, or is this for a single 12 volt battery? What batteries are you using and did they come with an information sheet? In the US we typically use higher specific gravity, but some batteries are designed to use lower... Did you do a test when new?

There is a section on Batteries Here.

Photowhit · September 2012

Re: Help required to design off grid system

For the short term, while waiting on your new charge controller, you might check the specs on the current charge controller, you might be able to use 3 in series to charge your batteries in the short term. If they are showing 12.6 volts across the 48V bank, I would do this NOW. Your batteries will die very quickly if you don't get them charged!

I would guess most PWM charge controllers could handle 3 in series, but check your specs! Most PWM don't worry about the VOC but the VMP would be around 83 volts might be a problem for some, but I doubt it. (too high a VOC will kill an MPPT charge controller)

Cariboocoot · September 2012

Re: Help required to design off grid system

syedbukhari wrote: »

I am using 12 lead acid flooded batteries of 12 volt and 200 amp

There's problem #1. Parallel battery strings are notorious for uneven current sharing.

Currently I am using simple charger but now I have ordered for a MPPT charger.

There's problem #2. Your panels' Vmp is 27.6 which is not enough in any configuration to work out properly. Without the MPPt advantage of down-converting higher Voltage to current at the right charging Voltage all you'll get out of the panels is the Imp current. A 48 Volt battery bank actually needs and array Vmp around 70 Volts for proper charging.

Please guide about the difference in gravity and voltages of the battery.

This is a result of problems #1 & #2. Voltage does not equate perfectly to actual SOC.

You need to get those batteries recharged fully and properly as soon as possible or else you'll be needing to replace them.

Photowhit · September 2012

Re: Help required to design off grid system

Cariboocoot wrote: »

You need to get those batteries recharged fully and properly as soon as possible or else you'll be needing to replace them.

Most important thing 'Coot said!

I would risk ruining a cheap PWM charge controller rather than let the batteries sit at 1.15 SG for a week waiting on a MPPT charge controller. To be honest I would hook them up directly and watch them carefully rather than let them sit. In a week you likely will be able to recycle/replace the batteries, if nothing is done.

Is the 12.6 Volts across the bank?

Help required to design off grid system

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