Help required to design off grid system

syedbukhari

Hello,

I am from Pakistan.I am new in solar field. In Pakistan there is a energy crisis but fortunately it is rich with solar radiations. In summer there is sun shine for about 12-14 hr a day and in the winter about 8- 10 hr a day. Kindly guide me i want to install a solar system of 1000 watt at my house, 4000 watt at my fuel station and 6000 watt a my agri form for irrigation purposes. Here is the data of my solar panel that i bought from the market.

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

Kindly guide me about the arrangement of the arrays (parallel,series), size of charger controller, size of inverter and the battery bank for 10 hr back up time for each system.
For home the average load is 700 watt hr
For the fuel station average load is 2800 watt hr but there is a problem in this load. We are using three submersible motors for fuelling and each motor takes 17 Amp at its starts up and settles down at 5 Amp . Kindly guide how can i design solar system for this complex system.
For the agri purpose we are using 5 hp AC motor. We do no need back up time in this system. Kindly guide for this system also and also inform can we use DC motor to reduce the cost of the system.
220 volt used in Pakistan.
I contact with you because in Pakistan in our area electritions are using just hit and trail method for the system designing. I wants someone guide me so that i can save my cost. Waiting for positive response

Cariboocoot

Re: Help required to design off grid system

Welcome to the forum.

It would appear you have a fair understanding in what's involved with a solar electric power system. They all start with the load demands. For clarity's sake I suggest we divide your inquiry into three parts, as you are talking about three separate systems.

You list your home demand as "700 Watt hours". A Watt hour is a very specific unit of total energy, and is not the same as averaging 700 Watts per hour. By North American standards, 700 Watt hours would be small even in an off-grid application. I'm only asking to make sure we're talking about the right amount of power that needs to be supplied. If it is an average of 700 Watts per hour over 24 hours that would be a much bigger quantity: 16.8 kW hours, which would be typical for a house here (in fact about what mine uses).

The other important thing to know is what the maximum demand will be. If there are no loads bigger than 1000 Watts, that would lead to one size inverter and system Voltage. If there are, then you have to have enough capacity to meet that demand even if it is only for a few minutes or seconds.

After that the process goes like this:
Maximum power demand in Watts tells you how big an inverter you need.
Daily Watt hours consumption tells you how big a battery bank you need (Voltage and Amp hour capacity).
The battery bank and local sun conditions determine what you need for solar panels and charge controller to recharge it.

Let's look at a sample system based on 700 Watt hours and very small (under 1kW) loads:
First, the inverter needs to be 220 VAC. Morningstar makes a 300 Watt 220 VAC inverter and Exeltech has quite a wide range of inverters that can meet the requirements (various Wattages and system Voltages). Much of this choice will depend on availability to you.
700 Watt hours is fairly small and can be done on a 12 Volt system. 700 Watts / 12 Volts = 58 Amp hours. That is how much you'd need to supply. To get that without over-discharging the battery bank it needs to be at least twice that size. Rough 120 Amp hours @ 12 Volts (or more). 25% DOD is usually best for long-life, but that needs to be weighed against costs. Again, local availability is going to come in to play here.
Once the battery is sized you can see how much solar you'd need to recharge it. As a design rule-of-thumb if you target a 10% maximum charge rate current the rest falls into line. For the above 120 Amp hour 12 Volt battery you'd be looking at 12 Amps peak current @ 12 VDC (minimum Voltage) or 144 Watts. Now panels don't actually average their output ratings, so a 144 Watt panel would not do. With the heat factor you probably need to account for 75% efficiency, so that is a 192 Watt panel. You need to "round up" that number to the nearest available size, just to be sure. Then you need a charge controller capable of handling the 12 Amps; it should be somewhat larger than that. 15 to 20 Amp would be fine.

That is the basics of off-grid system design. I've left out a lot about calculating losses in wires, sizing circuit protection, and including inverter load.

You are fortunate to have so much daylight, but you should know that not all of it will be usable unless the panels can be re-aimed periodically through the day to keep them inline with the sun. Also the resulting higher temperatures will diminish the power available from the panels.

To design based on the panels you mentioned would be a different thing entirely. They are capable of charging a 24 Volt system "as is" or in combination with an MPPT controller 12 Volt, and in multiples 48 Volt.

Now how much did you understand and what did you not understand? We'll try to make it clearer.

syedbukhari

Re: Help required to design off grid system

Cariboocoot wrote: »

Welcome to the forum.

The other important thing to know is what the maximum demand will be. If there are no loads bigger than 1000 Watts, that would lead to one size inverter and system Voltage. If there are, then you have to have enough capacity to meet that demand even if it is only for a few minutes or seconds.

First of all thank you very much for responding positively. As i said before i am new in solar but i will try my best to understand your instructions. We uses 4 fans that consumes 100 watt/each, their working time is 16 hr a day and 6 bulbs that consumes 20 watt/each and their working time is 8 hr a day. This is our total load for home and we do not use any appliance that consumes load over 150 watt. We can use practically sun rays for 7 hours in summer but in summer temperature ranges from 35 to 50 degree centigrade and in winter we can use sun rays for 5 hr, temp. ranges from 5 to 20 centigrade. We need a backup of 6- 8 hr. For heavy loads we will use grid utility or generator. Kindly suggest accordingly.

Cariboocoot

Re: Help required to design off grid system

syedbukhari wrote: »

First of all thank you very much for responding positively. As i said before i am new in solar but i will try my best to understand your instructions. We uses 4 fans that consumes 100 watt/each, their working time is 16 hr a day and 6 bulbs that consumes 20 watt/each and their working time is 8 hr a day. This is our total load for home and we do not use any appliance that consumes load over 150 watt. We can use practically sun rays for 7 hours in summer but in summer temperature ranges from 35 to 50 degree centigrade and in winter we can use sun rays for 5 hr, temp. ranges from 5 to 20 centigrade. We need a backup of 6- 8 hr. For heavy loads we will use grid utility or generator. Kindly suggest accordingly.

Okay, this works out to be quite a bit different from 700 Watt hours:
Four fans @ 100 Watts each is 400 Watts. Run for 16 hours is (400 * 16) 6400 Watt hours.
Six bulbs @ 20 Watts each is 120 Watts. Run for 8 hours is (120 * 8 ) 960 Watt hours.
Total daily consumption based on those numbers: 7360 Watt hours. That's about 10 times different from the first numbers.

With everything on at once you would need to supply 520 Watts. So the inverter needs to be at least that large. Considering the capacity demand, you would be best off getting a 48 Volt system. 24 Volt could also work, but 12 Volt is not a good idea as the battery bank would be difficult to manage. Small inverters do not come in 48 Volt versions.

You may want to consider having multiple small systems. It means more inverters and charge controllers, but adds redundant capacity in case one of the systems fails. Again availability and budget (money) will be factors.

Can you tell us the frequency of your AC supply there? Is it 60 Hertz or 50 Hertz?

I can already see several different ways to go with this.

syedbukhari

Re: Help required to design off grid system

Can you tell us the frequency of your AC supply there? Is it 60 Hertz or 50 He
I can already see several different ways to go with this.[/QUOTE]

AC supply in Pakistan is 50 hertz

Cariboocoot

Re: Help required to design off grid system

Okay; that makes a difference in inverter choices. Technically this would be the European/World/International "standard" of 230 VAC @ 50 Hertz.

Possible choices:
Four separate 12 Volt systems of approximately 2kW storage capacity (around 450 Amp hours) each. One MS 300 Watt 220 VAC 50 Hz inverter per system. One 45 to 60 Amp charge controller and around 700 Watt array per system.

One Exeltech 1100 Watt 24 Volt inverter (for 230 VAC 50 Hz output) with about 700 to 800 Amp hours of 24 Volt battery. Outback FM80 charge controller and 2560 Watt array. Could also use the Outback FX2024ET inverter with this instead of the Exeltech. The Outback has a built-in charger for charging off a generator; the Exeltech (and Morningstar) doesn't.

Outback FX2348ET inverter. 600 to 700 Amp hours of 48 Volt battery. FM80 charge controller. 4480 Watt array.

Note that these are not "exactly the same capacity" systems. They fall within the ranges for meeting the load demands and storage capacity. The 24 Volt system in the middle runs higher Depth Of Discharge than the other two.

I can't tell you what to buy or design an exact system; I can only show you options so you get some idea what is necessary to meet your needs. The equipment availability and amount you can afford to spend will have a significant affect on your choice.

Never having designed a system for Pakistan before, I'm a bit out of my element. You may be able to make better use of those long sunny days and reduce the size of the array. On the other hand the heat is going to be bad on the panels, batteries, and other equipment (best not to run things at maximum current when there is high ambient temperature).

solar_dave

Re: Help required to design off grid system

Do you really need the off grid component because of reliability of the grid? Grid tie is much more cost effective even if you just clip the peaks off your loads to minimize the grid impact.

syedbukhari

Re: Help required to design off grid system

Cariboocoot wrote: »

One Exeltech 1100 Watt 24 Volt inverter (for 230 VAC 50 Hz output) with about 700 to 800 Amp hours of 24 Volt battery. Outback FM80 charge controller and 2560 Watt array. Could also use the Outback FX2024ET inverter with this instead of the Exeltech. The Outback has a built-in charger for charging off a generator; the Exeltech (and Morningstar) doesn't.

I think this is better for me. Please also guide me in designing of arrays in the light of my panels specifications.
Also guide if i use a system In which the batteries should be charged through sun light in day time and through main grid in the night or in cloudy days. Actually the problem is that there is a break down of electricity after every 1 hr in our area. UPS fails to work in this short fall because they get minimum time to recharge and running cost for generators is very high that's why i wants to use solar panels to charge the batteries in the day time. If i use this type of system for home and for fuel station would it be cost effective or not?
For agri purpose i want to run the only in the day time with zero back up

syedbukhari

Re: Help required to design off grid system

solar_dave wrote: »

Do you really need the off grid component

I just want uninterrupted power supply that should be most cost effective

niel

Re: Help required to design off grid system

just a quick comment to coot's excellent help he's giving you. i think you would still benefit by having an inverter/charger because the grid would still be able to put a great deal of the power back into the batteries, especially during the night. if the grid can't provide all of the charging power needed at times, that is fine as the solar will put the final charge in when loads are light and in the meanwhile easing the burden on the batteries by providing some of the power for the loads in the daytime. win win.

Cariboocoot

Re: Help required to design off grid system

Yes, given that grid is available but unreliable the Outback inverter with the built-in charger is the best choice.

Would you say grid power is available half of the time or less than that? If the grid is at least "50% reliable" you can reduce both the battery bank size and the array size (because part of the time you'd be relying on the grid for power and charging).

So we can look at it like this:
With grid supplying 50% of the power;
24 Volt system, Outback FX2024ET, approximately 650 to 700 Amp hours of 24 Volt battery (discharge up to 50%), around 1100 to 1200 Watts of array, FM60 charge controller. The choice of battery and array size will be heavily dependent on what is available to you there.

With the grid "totally unreliable";
48 Volt system, Outback FX2348ET, approximately 650 to 700 Amp hours of 48 Volt battery (discharge up to 25%), 2400 to 2600 Watts of array, FM80 charge controller.

Note that the 48 Volt system is chosen to eliminate the grid requirement entirely; any grid power would be a "bonus". Also I have picked Outback equipment because of its long-standing reputation for reliability in adverse conditions. These are "sealed" inverters which helps keep bugs and dust out, something that affects us all no matter where in the world. It just helps to be able to avoid those problems as much as possible when you're far from the service center.

Will this be cost effective? I can't say because I have no information on what the costs for you will be there and how that would relate to your grid costs (including the cost of its unreliability). I could give a more specific component list with prices, but that would be based on what is available in the U.S.A. not Pakistan. Things like batteries are very expensive to ship, so you need to find what is the most cost-effective of those available locally. From that the design needs to be adjusted to meet power and recharging needs.

syedbukhari

Re: Help required to design off grid system

Cariboocoot wrote: »

With grid supplying 50% of the power;
24 Volt system, Outback FX2024ET, approximately 650 to 700 Amp hours of 24 Volt battery (discharge up to 50%), around 1100 to 1200 Watts of array, FM60 charge controller. The choice of battery and array size will be heavily dependent on what is available to you there.
.

Yes this model is suitable for me. Thanks for your support. Now kindly help me in developing the three models for home, fuel station and agri in the light of my solar panels

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
Advice about the setting of arrays(serise or parallel), size of inverter,controller and battery bank(home+fuel)station).
Note in case of agri model there is no need of battery and grid supply.It will run only in day time.

Cariboocoot

Re: Help required to design off grid system

syedbukhari wrote: »

Yes this model is suitable for me. Thanks for your support. Now kindly help me in developing the three models for home, fuel station and agri in the light of my solar panels

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
Advice about the setting of arrays(serise or parallel), size of inverter,controller and battery bank(home+fuel)station).
Note in case of agri model there is no need of battery and grid supply.It will run only in day time.

Okay, using those panels let's see how close we can come to the proposed 1100 to 1200 Watt array. It looks like we have to go bigger. For one thing, you should always buy panels in pairs. It makes wiring configurations much simpler. Four 220 Watt panels @ 880 Watts is too small. Six will give you 1320 Watts, which should be plenty for that system size.

Since it is a 24 Volt system, you need the array Vmp to be above the charging Voltage for that size system. This is approximately 30 to 32 Volts, and that is after losses to wiring and heat. Using the Outback FM60 controller (which is an MPPT type) you can get a lot of flexibility with the array design. Two possible methods for six of these panels would be two strings of three, or three strings of two. They will be the same amount of power and output from the controller, but there are advantages to each.

Three strings of two panels: each string would be Vmp 55.2 (2 * 27.6) and the array Imp would be 23.91 (3 * 7.97).
Advantage: better conversion efficiency from 55.2 to 32 Volts.
Disadvantage: each string needs its own fuse or breaker of 10 Amps.

Two strings of three panels: each string would be Vmp 82.8 (3 * 27.6) and the array Imp would be 15.94 (2 * 7.97).
Advantage: higher Voltage overcomes longer wire resistance if necessary (less power loss from Voltage drop). No fuse or breaker required for strings.
Disadvantage: lower conversion efficiency from 82.8 to 32 Volts.

On the whole, the two strings of three panels each would be my choice. Either way you could expect about 40 Amps of charge current, which would support up to 800 Amp hours of battery (at the minimum recommended 5% rate). In terms of AC Watt hours, you could expect approximately 4000 per day (remember that this system design was based on the idea that at least 50% of the power needs would come from the grid).

Does this sound reasonable? Shall we have a look at the fueling station requirements next?

syedbukhari

Re: Help required to design off grid system

Thank you very much. Now I am feeling very relax and very hopfull I will develop a good system by your kind cooperation. But give me some time to digest and understand this system . After understanding this we will proceed to next model.

syedbukhari

Re: Help required to design off grid system

Cariboocoot wrote: »

Two strings of three panels: each string would be Vmp 82.8 (3 * 27.6) and the array Imp would be 15.94 (2 * 7.97).
Advantage: higher Voltage overcomes longer wire resistance if necessary (less power loss from Voltage drop). No fuse or breaker required for strings.
Disadvantage: lower conversion efficiency from 82.8 to 32 Volts.

Can i use 48 volt system to minimise the voltage losses instead of 24 volt system?
Please also guide can i use 5 panels to design the array instead of 6 panels?

vtmaps

Re: Help required to design off grid system

syedbukhari wrote: »

Can i use 48 volt system to minimise the voltage losses instead of 24 volt system?

certainly. You will also have a better controller efficiency going from Vmp of 82.8 to 48 volt nominal than from 82.8 to 24 volt nominal.

syedbukhari wrote: »

Please also guide can i use 5 panels to design the array instead of 6 panels?

No. As Caraboocoot mentioned, buy an even number of panels. You can't make two strings of 3 panels with only 5 panels.
--vtMaps

niel

Re: Help required to design off grid system

syedbukhari wrote: »

Can i use 48 volt system to minimise the voltage losses instead of 24 volt system?
Please also guide can i use 5 panels to design the array instead of 6 panels?

for the 1st question i am assuming you are talking about the battery voltage and upping the battery voltage will lower the current requirements to the load(s) (usually an inverter as the load at 24v or greater battery voltage) and will therefore lower v drop losses enough that one may even be able to use smaller gauge wire. upping the battery voltage will also slightly improve the efficiency on the controller will a smaller conversion span so a 48v battery arrangement may be a good idea.

for the 2nd question the answer is simply no. this applies to either 24v or 48v battery arrangements as that would entail 2 uneven strings of pvs each presenting a different vmp to a single controller. if you run 2 separate controllers you can run the different strings, but that's a larger expense than adding another pv.

if you were to put the 5 pvs in series this would present a high vmp and voc that only a few mppt controllers can handle and the midnite classic 200 would be cheaper than the xantrex. the drawback here is that the next pv expansion would consist of another 5 of the same pvs.

the conclusion would be to have strings of 3 as the best overall avenue to pursue for a 48v battery bank voltage meaning all additional pv strings will consist of 3. you are starting with 6 so you can make it 9 or 12 pvs as 15 would exceed the controller rating of a 60a mppt cc (you indicated you wanted fm60) unless one has an 80a mppt cc and you can go 15 pvs. 5 strings of 3 in series.

ps- i better add here that in a pv expansion it may be necessary to expand the capacity of the battery bank too. if so one should do it within a year or so if the batteries aren't cycled deeply or abused. if one goes to a 48v batery voltage then one has to add the same multiples of batteries to come up with an identical battery string to parallel with the first one. usually 48v battery banks are more expensive to do as it is easier to get 24v from placing batteries in series than 48v which is twice as many batteries to come up with for an expansion.

syedbukhari

Re: Help required to design off grid system

niel wrote: »

.

for the 2nd question the answer is simply no. this applies to either 24v or 48v battery arrangements as that would entail 2 uneven strings of pvs each presenting a different vmp to a single controller. if you run 2 separate controllers you can run the different strings, but that's a larger expense than adding another pv.

Can i use 5 panels in grid tie system without batteries or in a system where there is no need of batteries.

niel

Re: Help required to design off grid system

i thought this was to be for off grid? if grid tied you will need an inverter made for this application and their voltage requirements are usually higher yet, but if you find one capable of operating with the supplied voltage of those pvs, then the answer is yes.

i should also mention there are the type of inverters made for small wattages meant to mount at the pvs. this also means more inverters.
http://www.solar-electric.com/enmigrsy.html

syedbukhari

Re: Help required to design off grid system

niel wrote: »

i thought this was to be for off grid? if grid tied you will need an inverter made for this application and their voltage requirements are usually higher yet, but if you find one capable of operating with the supplied voltage of those pvs, then the answer is yes.

i should also mention there are the type of inverters made for small wattages meant to mount at the pvs. this also means more inverters.
http://www.solar-electric.com/enmigrsy.html

Thank you very much for your information.
I think that i am now in a position to start discussing my second model for fuel station, please also help me in this matter as well.
In my fuel station model i wants to run three submersible motors, at least two will run parallel and the third one will be in standby. The motor takes 17 amp at its start up for 3-4 seconds and settles down at 4-5 amp. Along with these motors i also wants to use 3 ceiling fans@100 watt each, three tube lights @50 watt each.

Cariboocoot

Re: Help required to design off grid system

syedbukhari wrote: »

Thank you very much for your information.
I think that i am now in a position to start discussing my second model for fuel station, please also help me in this matter as well.
In my fuel station model i wants to run three submersible motors, at least two will run parallel and the third one will be in standby. The motor takes 17 amp at its start up for 3-4 seconds and settles down at 4-5 amp. Along with these motors i also wants to use 3 ceiling fans@100 watt each, three tube lights @50 watt each.

Okay, on to system #2.

17 Amps @ 230 VAC is quite a lot of Watts: 3740. If there is a chance that both pumps may turn on at the same time that would need to be doubled. Some might say you can rely on the surge rating of an inverter to handle this, but manufacturers frequently do no give a time span on their surge ratings and so the inverter may not be able to maintain the higher current long enough to start the pump. The running current is not a problem, even with both pumps at once.

Ceiling fans total 300 Watts. Tube lights total 150 Watts. Not difficult to supply. All together the maximum for starting one pump and running the lights & fans is 4200 Watts. In such a case a 4kW inverter could be used. But if both pumps start at the same time ...

The missing information now is: how long will the pumps, lights, and fans be running for? Obviously the pumps will turn on and off as needed, but you do need to have some sort of time frame in mind in order to size the battery bank large enough to handle demand.

Also, this fueling station will have the unreliable grid available to it? Can you count on 50% of power coming from that as with the house?

All these things enter in to coming up with some sort of plan to meet the power needs.

syedbukhari

Re: Help required to design off grid system

Cariboocoot wrote: »

Okay, on to system #2.

The missing information now is: how long will the pumps, lights, and fans be running for? Obviously the pumps will turn on and off as needed, but you do need to have some sort of time frame in mind in order to size the battery bank large enough to handle demand.

My average sale for high speed diesel is 4000 ltrs/day. Flow rate of the pump is 50 ltrs./mint. By viewing this the total working minutes are 80-100 mints/day. Same is the case with the other gasoline pump but its average sale is 3000 ltrs/day. We assumes in designing that the working hour for each pump is 150-180 mints/day. Also consider, as you mentioned the pumps turn on and off as needed. In case of gasoline pump this factor is very dominant.

Cariboocoot wrote: »

Also, this fueling station will have the unreliable grid available to it? Can you count on 50% of power coming from that as with the house?

All these things enter in to coming up with some sort of plan to meet the power needs.

In this case 40 % from grid and 60 % from solar

Cariboocoot

Re: Help required to design off grid system

Then in terms of run time you're looking at two pumps, each approximately 1150 Watts for up to 3 hours apiece. That's 3450 Watt hours per pump, or 6900 Watt hours total for the pumps. Definitely a 48 Volt system here, in order to store the capacity required and to better meet the start-up demand.

Plus you've got 450 Watts of fan and lights. For how long? 12 hours perhaps? That would be another 5400 Watt hours.

This is a lot of power to supply: over 12 kW hours. On 48 Volts that's 256 Amp hours used, or a minimal 512 Amp hour battery bank. In this instance it may be very important to use two separate systems, one for each pump and part of the fan/light load. That way if one of them fails you can switch the wiring to run the needed pump off the other system. And you are looking at at least 1664 Watts of array, even with the grid contribution. Using the same 220 Watt panels you would have eight for 1760 Watts, assuming you can get batteries close enough to the required capacity.

Please note that these are rough estimates. Part of the calculations is based on being able to use minimal battery size (up to 50% DOD) and minimal array size (5% peak charge current) due to the availability of at least some grid capacity. If the grid is too unreliable the battery bank & array will not do to supply the full needs.

mike95490

Re: Help required to design off grid system

Skip solar, use a small diesel genset and battery charger to top off the batteries, if the grid failure lasts longer than the batteries. I'm thinking XW-6048 with integral .9PF charger, transfer relays, good surge capacity....

And when the tanks run out, you don't need the pump anymore

Cariboocoot

Re: Help required to design off grid system

mike90045 wrote: »

Skip solar, use a small diesel genset and battery charger to top off the batteries, if the grid failure lasts longer than the batteries. I'm thinking XW-6048 with integral .9PF charger, transfer relays, good surge capacity....

And when the tanks run out, you don't need the pump anymore

Except that fuel prices in Pakistan may be incredibly high; perhaps even higher than Vancouver, BC! Spending your inventory to sell your inventory is not a good practice, and since the grid can only be relied on 40% of the time the gen would be doing most of the recharge work. The OP has said he has a gen set for emergencies, and I rather imagine he'd like to avoid using it. Solar is a good long-term solution to the problem. As he also said they have abundant sunshine.

Nor would I choose a Xantrex product for this application. First of all you'd be buying GT capability which probably could not be used (an extra $1,000). There's no point in trying to sell back to a utility that is down 60% of the time. Second, does the XW come in a 230 VAC 50 Hz configuration? Probably. I don't know because I stay away from Xantrex due to reason #3: their reliability and functionality is not that good (look at all the problems reported on this forum for getting the things to work right) and their customer support is frankly terrible. Can you imagine the nightmare of trying to get them to respond to inquiries from halfway around the world? They don't even answer you if you live in North America!

syedbukhari

Re: Help required to design off grid system

Cariboocoot wrote: »

Except that fuel prices in Pakistan may be incredibly high; perhaps even higher than Vancouver, BC! Spending your inventory to sell your inventory is not a good practice, and since the grid can only be relied on 40% of the time the gen would be doing most of the recharge work. The OP has said he has a gen set for emergencies, and I rather imagine he'd like to avoid using it. Solar is a good long-term solution to the problem. As he also said they have abundant sunshine.

!

Yes you are right, fuel prices are very high in Pakistan and also the electricity prices as well. Yes i have a gen set but its running and maintenance cost is very high, on the other hand the installation cost of solar is high but it is long term solution and we have abundant source of sun shine. I physically saw a deep tube well pump running at its full load on solar for 6 hr every full sunny day. I think solar is the best solution for our Pakistani people.

westbranch

Re: Help required to design off grid system

As you will learn, there is a steep learning curve with solar, yet well worth the effort. However from what I see so far you need to think about which of the 3 proposals you can start with to 'work out the kinks' as we say. I would lean towards the Agri application as it appears to be the simplest, no batteries (probably) and just a pump to power during the day, then proceed to the Gas station as you already have a backup generator there then to the house as those loads are the most UN-predictable (other people using power than yourself) .

HTH

Cariboocoot

Re: Help required to design off grid system

Like Westbranch said, the third system is probably the easiest. So let's have a look at it.

You need to know how many litres or gallons of water is needed per day.

Typically a direct solar-powered pump will run at whatever rate and time the available sunlight can supply. This will fill a reservoir above ground and preferably in a location that would allow gravity feed of the irrigation system (otherwise distribution pumping is necessary and that requires additional energy). The well(s)' recovery rate has to be taken into account also, so that the pump does not take the well dry.

Some examples of direct-from-solar pumps can be found here: http://www.solar-electric.com/sodcwapu.html

A tip from someone who has worked in agriculture and dry climates: it works best to irrigate in the evening, otherwise much of the water will be evaporated away by the heat before the plants get a chance at it.

syedbukhari

Re: Help required to design off grid system

Cariboocoot, please advice i wants a DC submersible pump that out put 500 GPM.

Also guide about the arrangement of the arrays and confirm can i run DC pump without inverter and batteries by using only controller?

BB.

Re: Help required to design off grid system

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

Cariboocoot

Re: Help required to design off grid system

syedbukhari wrote: »

Cariboocoot, please advice i wants a DC submersible pump that out put 500 GPM.

Also guide about the arrangement of the arrays and confirm can i run DC pump without inverter and batteries by using only controller?

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.