Las Cruces Pomegranate Farm Commission

By Don Salamon

For Dr. Abtahi for Intro to Solar Engineering

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Abstract Pomegranate is a citrus fruit that does well in arid environments, a study was commissioned to

determine the feasibility of planting crops in Las Cruces, New Mexico in 1500 hectares of land.

Additionally, the irrigation system was required to be solar powered.

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Table of Contents

Title page 1

Abstract 2

Table of Contents 3

Introduction 4

Fruit 5

Climate 6

Water 7

Irrigation 9

Pumping System 12

Solar Solution 14

Conclusion 16

References 17

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Introduction The scope of this commission is to determine the appropriate size of a photovoltaic (PV) solar

power system to power pump that will be used to irrigate 1500 hectares of pomegranate trees and to

determine the number of trees that the land is capable of supporting. The location of the farm is roughly

20 miles northwest Las Cruces, New Mexico which offers a dry climate suited for the for the trees to grow.

The water requirements for the tree change as the lifecycle transitions from a seed to a fully grown tree,

as such great care was taken to account for these fluctuations, and a system was designed that could be

flexible in meeting those demands.

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Figure 1: Rough approximation of the location of the farm. Courtesy Google Maps

Fruit 1. The recommended number of pomegranate trees for this farm, references on your research should be provided.

Pomegranate is typically cultivated only in India, the Middle East and the Mediterranean. It is a

shrub or small tree growing from 6 to 10 feet, and is very long lived. Pomegranate grows well under semi-

arid conditions and can be grown up to an altitude of 500 m. above m.s.l.. It thrives well under hot, dry

summer and cold winter provided irrigation facilities are available. The tree requires hot and dry climates

during fruit development and ripening. The pomegranate tree is deciduous in areas of low winter

temperature and an evergreen or partially deciduous in tropical and sub-tropical conditions. It can tolerate

frost to a considerable extent in dormant stage, but is injured at temperature below - 11.0 C. Well drained,

sandy loan to deep loamy or alluvial soils is suitable for cultivation.(Ref 1)

It is recommended that Pomegranate plants

have a spacing of 5 x 5 meter or 15 square feet.

Adding a 1 meter path between each row that

makes each trees approximate footprint 30m2 or

323 ft2. Some farmers have spaced them as close

as 2.5 x 4.5 m for higher yield. However this

method is more prone to disease spread. (Ref 1)

Given the spacing discussed above the

approximate number of trees that can be fit on

1,500 hectares (or 162E6 ft2) of land is roughly

500,000 trees. This is approximated in Figure 2.

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Figure 2: Layout with 323 ft2 footprint for each tree, the actual quarter acre size will be 16284 ft2, this includes roads for heavy machinery. The white lines indicate the 3 foot path for access, and the black lines indicate drip irrigation routing.

Climate Pomegranates can grow at elevations up to roughly 5900 ft which is far higher than the site which

is approximately at 4,000 ft. Pomegranates grows good in USDA 7-10 hardiness zones, and this portion

of north west New Mexico is roughly 8

hardiness. (Ref 3)

Thus, this area selected should provide

a good area to grow. Figures 3 and 4 show

the frosting period and the hardiness zone the

farm would be located in. Pomegranates grow

best in fertile, deep, loam soil that is rich with

humus – this type of soil is good for many

types of fruit trees. The difference between

pomegranates and many other fruit trees is

the wide range of soils in which the

pomegranate will grow. From heavy clay,

black earth, lime rich soils, dry rocky

hillsides to sandy soil, the pomegranate

will grow. The pH tolerance is wide,

from 4.5 – 8.2 (from moderately acid to

moderately alkaline) although the best growth is in the pH range of 5.5 to 7.2. Production is less on highly

sandy soils unless a fertilizer program is followed. Heavy clay soils tend to lighten fruit color but if the fruit

is for home use this should not be a problem. The pomegranate is considered a salt-tolerant plant, but

accumulation of salts in excess of 0.5% is harmful (this is way above what the average gardener will find.)

(Ref 5)

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Figure 4: Hardiness level

Figure 3: Last Frost

Water 2. Using USGS or other sources, determine an estimate for the water table and best practices of water pumping in that

region. Online research with references should be provided.

The area is currently under drought conditions, but this hasn’t severely impacted the aquifer

levels. In the lower Rio Grande Valley near Las Cruces, N. Mex., infiltration of

irrigation water has produced a slightly saline zone (1,000-3,000 milligrams per liter

dissolved solids) that is about 100 to 150 feet thick at the top of the aquifer. A

transition zone of intermediate salinity (500-1,000 milligrams per liter dissolved

solids) that is 50 to 100 feet thick separates the slightly saline zone from the

underlying freshwater zone (300-500 milligrams per liter dissolved solids) that

extends to depths of 1,000 to 1,500 feet. A second transition zone separates the

freshwater zone from the deep saline zone where dissolved-solids concentrations

can exceed 3,000 milligrams per liter. (Ref 4)

Pomegranates trees can withstand drought periods but the fruit suffers and either falls off or is small.

Water requirement for the pomegranate is variable depending on when and how much rainfall occurs. On

average pomegranates need about 45 inches of water per year [via normal irrigation]; this is not an

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Figure 5: For the farm the Total Crop Water Needs will be equal to be at least 15185 acre feet which translates to roughly 4.9E9 gallons of water yearly. (Ref 7)

absolute figure as it again depends when precipitation occurs. If you receive most of your rain in the

spring and early summer, then the need for irrigation is lessened, but some will still be needed if you have

very dry weather in the middle of the summer. (Ref 5)

This well site is also located in the Mesilla Basin of the Rio Grande aquifer system, and have

shown to yield up to 3,000 gallons per minute (Ref 4).

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Figure 6: Drill depths to reach mean water levels.

Irrigation system 3. Your recommendation on the best irrigation method, given the dry climate of Southern New Mexico. The specific

irrigation components should be included and specified

Drip irrigation is a technique used in watering plants that allow for the

conservation of water and fertilizer by allowing water to slowly leak onto the

roots of plants. The average annual water requirement through drip irrigation

is 40 inches. Drip irrigation helps to save 44% on irrigation and 64% when

sugarcane trash mulch is used. It also helps to increase the yield by

30-35%.(Ref 1). However, this number does not account for the initial period

where more water is required. This number sits around 45 inches per year during the early life cycle.

For this climate the best irrigation technique is drip irrigation despite the initial start costs. One

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Figure 8: Typical drip irrigation system. Courtesy of Wikimages.

Figure 9: Breakdown of water requirement in gallons from a site with a comparable climate. (Ref 7)

Figure 7: Drip irrigation

inch of rain falling on 1 acre of ground is equal to about 27,154 gallons and weighs about 113 tons. Thus

the total requirement at 45 inches per plant is at least 4.9E9 gallons per year of water. This is also the

sizing for the maximum amount of water that is consumed by the plant in June, which is the highest

demand. This means that each well will need to supply 845 kilo gallons of water per day. This translates

for a 10 hour day into a pump requirement of 1406 gallons per minute with each tree receiving 0.045 gal/

min. The component breakdown is provided on the Drip Irrigation Table.

One consideration is that the location of the wells could influence each via a cone of depression

effect outlined in Figure 10. Occasionally, two or more wells have developed their cones of influence in

such a way that they interfere with one another. This situation requires that the wells be relatively close

and developed in the same aquifer. There is always a chance this will occur in any intensive development

of the same groundwater reservoir. Simply stated, the cone of influence of one well overlaps the cone of a

neighboring well. A part of the cone of influence that fed one well

must now satisfy another well also. The amount and areal extent of

the interference is directly related to the rate of pumping of each

well. Other factors of no less importance are the spacing between

the wells and the hydrologic characteristics of the groundwater

reservoir furnishing the water to the two wells. (Ref 7)

If more wells are developed in the same area, the chance for

interference increases. The cones of influence of the initial wells

expand and deepen in order to satisfy their pumps with each

development of another well and its subsequent cone of influence.

The cones must always establish a hydraulic gradient just sufficient to supply the amount of water

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Pump (gallons of water)

Total 13500000

Per zone 843750

Per hour 84375

per minute 1406.25

Figure 10: Cone of depression

required by the pumped well. If this water is not available in the area of the initial cone because some

groundwater is diverted into another cone, the initial cone simply enlarges to an outlying area where

sufficient replenishment can be derived. (Ref 7)

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Drip Irrigation System

Component Use Amount

Pump Extracts water 16

Water Filter Cleans water supply 16

Backwash Controller Prevents back flow into well 16

Pressure Control Valve Pressure controller 16

Main line Primary source 6670 feet

Control Valves Flow control 16

Polytubes Branch lines 46592 feet

Polyfittings Makes connections to mainline 448

Emitting devices Irrigates plants 2240

Storage Water for extraneous needs 400 gal/site

Pumping System“Determine the number and the depth of water wells required. Specify the pumping equipment. You may chose large central pumps or smaller localized pumps. State whether you are using submersible pumps, jack pumps, or other type of pumps”

This well site is also located in the Mesilla Basin of the Rio

Grande aquifer system, and have shown to yield up to 3,000

gallons per minute (Ref 4). This is much larger than the 1400

gallons per minute required, however the cone of depression

caused by one well in one of the 16 farming zones may

disrupt the water table in the other zones. To help to

minimize this each of the 16 pumps should be dug to a depth

of twice the depth to the aquifer itself. Therefore, the

pumping depth will be about 45 feet instead of the normal

22.5 feet recommended. This translates to a minimum 45

foot head requirement on the pump however this will be

much larger due to the coverage needed and the losses associated with the lines and

equipment. Each zone will require 2912 feet of polytubing, along with 417 feet of mainline. This

means multi staging boost pumps will also have to be used to overcome the friction losses

induced. For the primary well pump the requirement

is 1400 rpm with a minimum of 45 feet of head. The

TACO model 2340 Single stage double suction

pump shown in Figure 12 was selected as the

primary pump. Its performance curve is shown in

Figure 13.

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Figure 11: Typical deep well pump

Figure 12: Model 2030 pump

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Figure 13: Pump curve for Model 2030

Solar solution Design a solar PV system to run the pump or pumps with no back-up. The design should include the type and number of panels, the

specification of inverters or pump controllers, and any required electrical components, including a one-line electrical diagram. The

design should also include a general description of the structures supporting the solar panels.

The peak power requirements will be identical for each zone, thus we consider only one zone for

the calculations. The total amount of power to the pump is 17.2 kW at peak. Considering that the pumps

would need to run a maximum of 10 hours per day as calculated the total comes to 172 kWh of energy

required per zone.

In order to satisfy these requirements a total of 16 solar panels at a power rate of 310 watts would

need to be used. This number was determined by using the online calculator located at

www.Wholesalesolar.com

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Figure 14: Solar requirement calculator

16 panels would be placed each along the larger breakout areas of the zones for a total of 64

panels (extra to account for losses). The type of panels that would be used are shown in Figure 16. These

are well suited for the environment, and the majority of hardware (charge controller and batteries) would

be located at the jumpstation Figure 15.

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Figure 16: Solar panel and battery pack type

Figure 15: Pumpstation layout

Due to the nature of the peak sun hours the battery pack is sized to provide 3 days of power at 10

hours of continuous operation, plus a 50% increase for battery standards. Figure 16 shows the type of

panel and battery pack that would be required at each of the 16 pumpstations. The inverter is rated at

20kW to handle the peak demand of 17270 watts of power. The charge controller, Figure 17, is specified

to handle a max of 80 amps, which is slightly lower than the max rated output, however the power is not

expected to reach that high.

The total price of this entire package comes to $31334 per zone, or $501344 total for the farm.

This does not include the support structures for the panels themselves, or the housing station for the

equipment.

The panels would be supported by a normal support structure capable of withstanding wind gusts

of up to 100 miles per hour. The average windspeed in Las Cruces, New Mexico is 18 miles an hour with

a maximum of 51 mph (Ref 9). Figure 18 describes the structures that will be used.

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Figure 17: Charge controller and inverter

Figure 18: Solar panel mock up

ConclusionThe conclusion of the commission is that the farm is feasible given the location and

climate. The solar power requirement and drip irrigation provide for a steep startup cost that

may prove not to incentivize the investors. Dividing the plot into 16 zones independently

powered allows for discrete trouble shooting or control of irrigation if weather causes additional

water accumulation within areas.

These 16 zones each have a pump station with solar power equipment totaling a battery

storage rated at 61 kWh, with 64 panels providing a peak power output of 20.16 kW.

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References1) http://nhb.gov.in/report_files/pomegranate/POMEGRANATE.htm

2) http://shramajeeviimages.com/download/Free_Download/Agriculture/Agri._General/Irrigation/O/

3) http://www.plantmaps.com/88007

4) http://pubs.usgs.gov/ha/ha730/ch_c/C-text4.html

5) http://ucanr.edu/sites/Pomegranates/files/164443.pdf

6) https://www.researchgate.net/publication

264007889_Estimating_the_water_requirement_of_some_fruit_crops_according_to_plant_age_under_dri

p_irrigation_system_in_arid_zone

7) http://www.fao.org/docrep/x0490e/x0490e0a.htm

8) http://www.ngwa.org/fundamentals/hydrology/pages/unconfined-or-water-table-aquifers.aspx

9) http://www.wholesalesolar.com/solar-information/start-here/offgrid-calculator#systemSizeCalc

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