Designing Solar Water Pumping Systems for Livestock
Contents
1. S TATE Circular 670 UDA ELSIS Thomas Jenkins INTRODUCTION In many parts of the world including New Mexico NM water and energy availability are growing con cerns In areas where connection to an electric utility is not available the primary technologies for water ac cess surface sources or pumping have remained fairly constant for decades As demands for higher quantities and quality of water lower costs improved reliability and environmental concerns have increased many live stock and agricultural producers are investigating an al ternative technology for remote water pumping direct coupled solar photovoltaic PV powered systems Since the process to design and implement such a sys tem may be a challenging task New Mexico State Uni versity s Engineering NM program initiated a project to provide the Cooperative Extension Service CES with a demonstration module an interactive design spread sheet and literature related to solar water pumping to better inform NM water users about the benefits and methodology of implementing this technology Avail able through NMSU multimedia and the CES statewide Extension agent network these tools serve to educate interested constituencies primarily farmers and ranch ers in using solar energy to pump water This publication provides a general discussion of how to design a photovoltaic powered solar water pumping system for livestock A companion publication Circu2. Total Vertical Lift water level draw down elevation Eq 2 Pumps may be submersed in a well as deep as neces sary to ensure reliable water supply taking into account drawn down levels seasonal variations and recharge rates The water level variable in Equation 2 is mea sured from the water surface to the level of the water in the source not the depth location of the pump Placing the pump lower in the well increasing its submergence will NOT cause it to work harder or to pump less water nor will it increase stress or wear on the pump However there are reasons to NOT set the pump too close to the bottom of the well 1 A deep setting will increase cost length and weight of pipe and cable 2 A setting near the bottom may increase the chance of sand or sediment being drawn into the pump and damaging the pump mechanism The pump must move the water from the well to an elevation but it must also overcome friction losses in the system These losses depend on the type of pipe its roughness total length of pipe including any horizontal runs flow rate speed of the water in the pipe fittings and joints and pipe diameter These friction losses which are expressed in equivalent lengths of vertical pipe distance are added to the static head to yield an equiva lent TDH i e what equivalent height would the pump need to move water given these values To determine friction losses in pipe you should enter in the Tota
3. hundredth due to fittings losses The total length of pipe is 150 well water depth 80 distance from well to storage tank Table 3 Examples of Equivalent Length in Pipe Diameter L d of Sample Pipe Fittings Pipe Fitting L d inches Globe valve fully open 275 Gate valve fully open 9 90 standard elbow 30 Swing check valve 135 Standard tee flow through branch 60 8 distance from surface discharge to tank 238 ft From the HL calculation Equation 3 100 ft of 0 75 in pipe at 4 gpm has a pressure drop of 4 9 ft 100 ft of tube which yields 4 9 x 238 100 11 74 ft The water must be lifted 150 8 158 ft static head therefore TDH Equation 5 is 158 11 74 14 6 184 ft Hydraulic Workload Oftentimes we may work in units other than gallons and feet One U S gallon is equal to about 0 0037854 cubic meters while 1 foot of distance is equal to about 0 3048 meters If we convert TDH from feet to me ters and the daily water volume from gallons to cubic meters then we can calculate something called the hydraulic workload Equation 6 which is an excellent indication of the power that will be required to meet the designed system constraints Hydraulic Workload mf Daily Water Volume m x TDH m Eq 6 If the hydraulic workload is less than 1 500 m then the project is a good candidate for solar PV If it is be tween 1 500 and 2 000 m it will be borderline If the hydraulic workload is grea
4. life cycle economics place them at the forefront of choices for supplying water to livestock or agriculture The technology for solar water pumping is exceeding all expectations and will con tinue to be a viable choice for more and more users as its capabilities reliability and versatility increase while costs decrease The spreadsheet documentation and demonstration modules provide you with terminologies knowledge and skill sets that can be the foundation for informed choices relating to alternative water pumping systems For additional information contact your county Cooperative Extension agent or NMSU Thomas Jenkins has been a professor in NMSU3 Department of Engineering Technology and Surveying Engineering since 1990 He previously worked for many years in both private and public sectors as a computer scientist and engineer Professor Jenkins lead the effort to develop the College of Engineering Renewable Energy Technology minor and helped es tablish the NMSU student organi zation Engineers Without Borders ACKNOWLEDGMENTS The author wishes to express extreme gratitude for the assistance of the following College of Engineering and Engineering NM http engr nmsu edu index shtml NMSU Cooperative Extension Service http extension nmsu edu New Mexico Space Grant Consortium http www nmspacegrant com Southwest Technology Development Institute http www nmsu edu tdi Department of Engine
5. may increase water requirements by 2 5 times Pfost et al 2007 Common values of required gallons per day per ani mal in New Mexico can be found in the Daily Water Requirement spreadsheet tab or in Table 2 but you have the option to change these default values depending on your unique situation The water demand should be estimated for the highest demand period typically sum mer and anticipated growth during the design cycle at least 10 years In windy hot dry areas you should also take into account evaporation losses associated with open storage methods Once the total gallons day animal figure is calculated and any extra water requirements are entered values are summed to yield the total daily water requirement in gallons day A multiplier may be added that can provide an extra water cushion offset evaporation losses or refill the storage tank Household water use demand is variable and depends on climate usages and other factors but is typically around 75 gallons person day for drinking cooking and bathing Irrigation water demand depends on local condi tions season crops methods of delivery and evapotrans piration Agriculture watering is usually greater in sum mer seasons when solar radiation is at its highest Storage Tank Capacity Depending on climate and usage storage tank capacity should equal 3 to 10 days of water use For domestic use in a cloudy climate 10 days may be necessary while 10 PV m
6. produced by solar panels can be used for cathode protection to aerate a dugout or to power an electric fence S De rating takes into account temperature and soiling effects on the modules Circular 670 The estimated total daily water pumped gallons day on a full sunny day can be found by Equation 11 Modules x Module Volts x Module Amps x Daily nee x 60 x Pump Efficiency day hr x Module derating factor 0 1885 x TDH Eq 11 Final Design Specifications The Design Specification spreadsheet tab summarizes the design values obtained through the use of the spread sheet and lists the key components and materials for this scenario s direct coupled solar water pumping sys tem The description and quantities for specific items are obtained from calculations or specified by you The cost for each itemized component is calculated by mul tiplying the quantity of each item by a representative retail price but prices will of course vary over time The necessary length of UF wire is roughly determined by the length of pipe plus an extra 25 The market price for the UF wire is for 250 ft rolls Pipe is assumed to be PVC and the price is calculated by dividing the total length of needed pipe by 10 PVC pipe is typically sold in 10 ft lengths and multiplying by its market price The grand total of the entire system not including the well labor storage etc is calculated by adding up all the itemized totals This w
7. characteristics such as water depth draw down levels and recharge rates seasonal variations discharge elevation from earth s surface to water dis Circular 670 e Environmental issues e Manually operated e Accessibility issues e Required periodic maintenance and replacement e Moderate to high initial cost e Fuel costs and storage transportation charge point total feet of pipe nominal diameter of the pipe valves and elbows etc e Storage systems catch tanks concrete or plastic storage tanks etc to ensure the daily water require ment is available during low light conditions e Costs capital operation and maintenance labor life cycle etc In addition these factors should be considered e Who will install and maintain the system e Security although ideal for remote locations sys tems may be vulnerable to theft and vandalism e Environmental benefits including low noise Basic Operation With no moving parts the PV panel takes energy from sunlight and generates DC electricity which is then di rected through a controller to the pump motor in what is termed a direct coupled system Figure 2 The pump motor combination hereafter referred to as the pump moves water from the source through a pipe to a discharge point commonly a storage tank that feeds a trough drinker e Page 3 Photovoltaic Panels Water Source Storage Tank Figure 2 Direct coupled solar pumping syste
8. e No fuel costs e Federal and state tax incentives e Remote applications e Proven technology with pool of expertise and experience e Lower initial costs e Only works when wind conditions are adequate e Winds are seasonal e Some operating costs and higher repair maintenance costs e Labor intensive e Difficult to find parts and special tools needed e Low flow rates e Extended time to meet required storage e High winds may damage windmill Fossil fuels diesel e Higher flow rate e Often no need for storage e Proven technology with large pool of expertise e Easy to install a user defined scenario For the sake of organization and ease of use the spreadsheet follows the design approach outlined in this publication A companion publication Circular 671 Designing Solar Water Pumping Systems for Livestock User Manual http aces nmsu edu pubs _circulars CR671 PDF cov ers the step by step instructions for using the Excel spreadsheet to design a solar water pump system SOLAR WATER PUMPING SYSTEMS In order to design and successfully implement solar water pumping systems you need an understanding of several concepts as well as information specific to how you will use your system This includes e Daily water requirements and usage drinking ir rigation etc Requirements for high volumes or flow rates may limit applications e Available sunlight which depends on location Low levels of sun may limit PV e Well
9. en windmill pump jacks with portable photovoltaic PV systems For pumping water from underground aquifers via wells access to existing AC electric connections closer than one half kilometer or 0 3 mi is again the best op tion In remote locations though PV water pumping systems represent a very attractive long term cost effec tive alternative to hauling water diesel pumps and even traditional windmills for drinking water and many ir rigation applications drip trickle hose basin and some channel irrigation although typically not for very high flow rates such as might be used in flood irrigation The abundant and varied benefits of PV systems make them attractive in many situations A solar pumping system involves calculations and concepts that may make it difficult to determine a design if one is unfamiliar with the technology and ter minologies With this in mind NMSU developed the following tools to aid and educate a potential user 1 Two portable demonstration devices that illustrate the concepts and major system components for a solar pumping system Each module is portable and therefore available for displays and presentations 2 Literature and educational multimedia materials related to PV water pumping systems http www youtube com playlist list PL89870B418A514D27 Figure 1 Windmills are still a common source of power for off the grid water pumping systems including comparisons between three mai
10. er losses and costs Modules are sized as DC power watts W and come in all sizes from a few watts to over 250 W Rated power is determined by the output voltage and current under standard sun intensity A module rated at 50 W may have an operating voltage up to 17 4 volts V and a maximum current of 3 11 amps A Modules can be wired in series to increase output voltages and in parallel to increase current while also increasing total power If sunlight changes clouds output current will fall and thus power will fall at a relative level e g if sunlight is halved current and power will be halved while volt age remains about the same PV modules are sized and configured series parallel combinations to power the second major component of the system the pump Pumps Pumps move water from wells or surface sources It is important to analyze the system properly in order to make it as efficient and economical as possible while 5 Batteries are expensive must be replaced every few years and require periodic maintenance while the useful life of storage tanks may be decades p P ry y quire p g y PV panels may produce up to 80 of their maximum output power on partly cloudy days and even on extremely overcast days can still produce about 25 of their maximum 7 Asa rule of thumb PV panels are faced due south and at a tilted angle equal to the location s latitude This may be fixed or variable depending on seasonal condi tio
11. erent location combined with a managed rotational grazing plan optimizes animal performance pasture use water quality and wildlife in these zones Buscher mohle and Burns n d Morris and Lynne 2002 While cows may wade out to obtain better water calves tend to only drink from the shore By wading into surface sources cattle pollute the water with their urine and feces and may disturb the water with their wading action Eventually cattle may refuse to drink and they will have to be moved even though local for age is still plentiful Calves require higher quality water and will not fight cows or mud to obtain it Increases of 50 pounds head in weaning weight have been reported when water in sufficient quantity and quality is provided Studies have shown that when given a choice cattle drank from a water trough 92 of the time rather than from a nearby stream Bartlett n d Research also shows that yearling steer performance increased 23 when supplied with an alternate water source rather than dugouts earthen dams or reservoirs In addition to increased livestock and resource performance by routing the livestock away from riparian zones very large reductions 50 90 in Professor tjenkins nmsu edu Department of Engineering Technology and Surveying Engineering New Mexico State University An excellent source on windmills http aces nmsu edu ces windmill 3 It has been shown that livestock will only travel a limi
12. ering Technology and Surveying Engineering http et nmsu edu LITERATURE CITED Bartlett B n d Watering systems for grazing livestock Online Available from http www msue msu edu objects content_revision download cfm revision_id 557516 workspace_id 213590 Watering 20Systems 20for 20Grazing 20 Livestock pdf Boyle G 2004 Renewable energy Oxford Oxford Uni versity Press Buschermohle M and R Burns n d Solar powered livestock watering systems Online Available from https utextension tennessee edu publications documents pb1640 pdf Foster R and A Ellis 2003 Renewable energy for water pumping applications in rural villages Online NREL SR 500 30361 Available from http www nrel gov docs fy03osti 30361 pdf Foster R M Ghassemi and A Cota 2010 Solar energy Renewable energy and the environment Boca Raton FL Taylor amp Francis Group Masters G M 2004 Renewable and efficient electric power systems Hoboken NJ John Wiley amp Sons Inc Morris M and V Lynne 2002 Solar powered live stock watering system Online Available from http www clemson edu sustainableag IP217_solar_livestock_watering pdf Mott R L 2006 Applied fluid mechanics 6 ed Upper Saddle River NJ Pearson Prentice Hall National Renewable Energy Labs 1997 Electricity when and where you need it From the sun Pho tovoltaics for farms and ranches Online NREL BR 412 21732 Available from http www nrel
13. gov docs gen fy97 21732 pdf NMSU Water Task Force various publications Avail able at http aces nmsu edu ces watertaskforce index html Pfost D J Gerrish M Davis and M Kennedy 2007 Pumps and watering systems for managed beef graz ing Online Available from http extension missouri edu p EQ380 Surber G K Williams and M Manoukian n d Drinking water quality for beef cattle An environ ment friendly amp production management enhance ment technique Online Available from http animalrangeextension montana edu articles natresourc Drinking 20 Water 20Quality 20 for 20Beef 20Cattle pdf Wiles J 2001 Photovoltaic power systems and the Na tional Electrical Code Suggested practices SAND87 0804 Albuquerque NM Sandia National Labora tories Circular 670 Page 10 Circular 670 Page 11 Disclaimer This document is intended for educational purposes only in providing a basic understanding of terminology and concepts of design It is not intended to be used beyond this purpose The authors incorporated good analysis but all situations are different and you should consult a professional in all cases Contents of publications may be freely reproduced for educational purposes All other rights reserved For permission to use publications for other purposes contact pubs nmsu edu or the authors listed on the publication New Mexico State University is an equal opportunity affirmative action e
14. iencies are in the 25 35 range Circular 670 Figure 4 PV modules mounted to trailers can be easily oriented and moved based on water needs Photo from National Renewable Energy Labs 1997 e Space weight and position limitations as well as cost of equipment and installation e Codes and standards including the National Electri cal Code Wiles 2001 The voltage s and power required for the pump and its working efficiency Once each parameter is clearly addressed a pump can be selected Pumps are classified as either positive displacement or kinetic centrifugal and each has advan tages The list of available pumps and manufacturers is very extensive and many will be capable of pumping from a surface source or a well A pump for a well ap plication is most commonly a DC submersible pump with a range of 12 V to more than 36 V but may be much higher for very deep wells or high flow rates The current is typically in the 3 to 5 A range which equates to a rough operating power up to though typically much less around 1 horsepower or 746 W DC pumps use one third to one half the energy of AC pumps and are specifically designed to use solar power efficiently even during low light conditions at reduced voltages without stalling or overheating Solar pumps are low volume pumping an average of 1 to 5 gallons per minute gpm A majority of pumps are positive dis e Page 5 placement pumps centrifugal ty
15. ill reflect an approximate cost to construct the system plus the costs of other materi als labor sales taxes shipping etc Federal and state tax incentives may lower the initial costs by up to 40 as of 2012 CONCLUSION Using the spreadsheet allows you to test various design scenarios and demonstrate the design method and ter minology for a direct coupled solar water pumping sys tem It is important to consider the limits of this spread sheet because it is only able to calculate for flow rates up to 4 gpm and TDH values no greater than 230 ft due to the very limited PV and pump selection options within this version In the case of design values outside these limits or for pumps or PV module choices not available within the spreadsheet you should reference alternative performance data provided by other pump or PV manufacturers We hope that later versions of this spreadsheet will address several of these issues Photovoltaic powered water pumping systems are attractive for livestock and agricultural producers with remote water sources and limited access to AC power e Page 9 Even though wind has been in use for decades and will continue to provide effective solutions for water pump ing solar power has made significant steps toward be coming the system of choice for these situations Solar systems low maintenance and simple operation lack of fuel transportation or storage costs environmental friendliness and competitive
16. l Dynamic Head tab of the spreadsheet the 13 All areas of New Mexico meet this limit with values well above 5 kWh m per day New Mexico climate website http climate nmsu edu has good historical solar wind and temperature data 14 Draw down is the level of water that may drop in the well as pumping occurs the well pipe is refilled at a recharge rate The low flow rates of solar systems have less negative impact on draw down Circular 670 e Page 7 type of pipe PVC steel etc total length of the pipe being used and the nominal inside diameter of the pipe The approximate head loss HL caused by friction within the pipe is calculated using the Hazen Williams Empirical formula with assumptions of mediocre water temperature and somewhat turbulent pipe flow The val ue generated is in units of feet of head Mott 2006 Equation 3 illustrates the Hazen Williams formula 1 852 10 472 P Q lt I Eq 3 C182 D487 AL The roughness coefficient variable C within the equa tion depends on the type of pipe but the roughness coef ficient is typically around 140 Q is the flow rate in gpm Dis the nominal inside diameter of the pipe in inches and L is the total length in feet of the pipe for the system Another standard rule of thumb is that friction losses in the pipe are typically 2 5 for a well designed system The friction loss due to fittings must also be calculated The friction losses for pipe fitti
17. lar 671 Designing Solar Water Pumping Systems for Livestock User Manual http aces nmsu edu pubs _circulars CR671 PDF provides step by step instructions for us ing a Microsoft Excel spreadsheet to perform necessary calculations for designing a solar pumping system SURFACE WATER SOURCES AND LIVESTOCK Livestock crops and people often depend upon surface sources of water streams ponds catch tanks etc or wells accessing underground aquifers Because of a vari NM Designing Solar Water Pumping Systems for Livestock Cooperative Extension Service College of Agricultural Consumer and Environmental Sciences ety of benefits and increased regulations in some states it is often desirable to move water from a surface source to a different location elevation or drinker or to pump water from a remotely located well For surface sources a well vegetated riparian zone establishes a buffer that filters and purifies water as it moves across the zone reducing sediment loads sup porting soil stability improving water quality and en hancing wildlife habitat Excessive livestock pressure on surface sources often causes nutrient loading streamside vegetation damage erosion pollution and decreased animal growth and health One approach is to remove or limit access to these areas however often this is the only viable water source for producers Fortunately research shows that in many cases pumping water to a diff
18. m Adapted from The University of Tennessee Extension Figure 3 This direct coupled system is intended to op erate only during the day when sunlight is present thus eliminating the expense and complexity of batteries In a properly designed direct coupled system extra water must often be pumped into a storage tank By providing storage a producer can still provide their daily water re quirements from the storage tank at night or on cloudy days The amount of water pumped depends primarily on the amount of sunlight hitting the PV panels the type of pump and a few other factors The amount of available sunlight is predictable by location but there are always variations in weather e g cloudy days By using a simple direct coupled approach the operation maintenance costs and complexity of the system are greatly reduced Components Solar water pumping systems are composed of two primary components other than the well itself the PV panels or modules and the pump PV Panels PV panels are installed with mounting hardware that allows the panels to be oriented to adjust the tilt of the modules to an optimum angle elevate the modules for security and minimize shading and damage Figure 4 It is critical to minimize shading from structures and vegetation during all watering seasons because even par tial shading can cause significant power loss Locating modules close to the water source also helps minimize pow
19. mployer and educator NMSU and the U S Department of Agriculture cooperating October 2013 Las Cruces NM Circular 670 Page 12
20. n remote water pumping technologies Table 1 used in New Mexico today contrasting two different ways to mount PV modules fixed angle mounting vs single axis tracking systems and a simple cost analysis for each of the three technologies and mounting systems Foster et al 2010 3 A Microsoft Excel spreadsheet to provide an easy and visual educational tool to present concepts behind PV technology and system design methodology available to download at http aces nmsu edu pubs _circulars CR67 1 CRG7 1 xlsx This tool allows the user to fol low the basic step by step design process and offers sample components and simple economic analysis for Tt can cost 10 000 to 30 000 per mile to install electrical power line through rugged terrain Circular 670 Page 2 Table 1 Remote Water Pumping Technologies Comparison Chart Technology Advantages Disadvantages Solar e Renewable sustainable e No fuel costs e Can be portable and remote e Very low operation maintenance costs e Federal and state tax incentives e Acceptable capital costs and low recurring costs e Reliable warranty of 20 years for panels e Relatively easy to install e System is modular and may be modified to fit needs e Variable water delivery depending on sun intensity e Low flow rates e Supplemental storage needed e Extended time to meet required storage e Higher initial costs although costs are trending lower Wind e Renewable sustainable
21. ngs are converted to an equivalent length of pipe in feet and are a function of several variables Losses due to fittings may be significant To determine these losses the spreadsheet lists many common fittings that might be utilized within the design of the system and you should enter the quantity of each fitting used in your system The equivalent friction loss for each fitting type is calculated using Equation 4 Table 3 shows a partial listing of some values used to calculate friction loss due to a fitting Equivalent Length ft pipe diameter x quantity x Lid 12 Eq 4 The equivalent head pipe friction loss values are cal culated for each specific fitting used These are then summed to give a total loss due to fittings Mott 2006 TDH can now be calculated by using Equation 5 Total Dynamic Head ft Static Head H Friction Loss Due to Fittings Eq 5 Example of a TDH Calculation What is the TDH in a well with water depth of 150 ft no draw down and flow rate of 4 gpm The well is 80 ft from the storage tank and the delivery pipe rises 8 ft to discharge into a tank The piping is 0 75 in diameter PVC and there are three 90 elbows one swing type check value and one gate type valve in the pipe Solution From Table 3 the three 90 elbows add the equivalent of 5 625 ft of pipe the check valve 8 4375 ft and the gate valve 0 56 ft giving a total equivalent pipe length head of 14 6 ft rounded to the nearest
22. ns and other factors For example a summer tilt angle would be flatter to capture more sun with tilt angle equal to the latitude angle 15 while a winter tilt angle might be latitude angle 15 In Las Cruces the latitude angle would be 32 tilt a summer tilt of 17 and a winter tilt of 47 Circular 670 Page 4 Figure 3 PV powered pump systems often discharge to a storage tank to provide the daily water requirement even under low light conditions Photo from National Renewable Energy Labs 1997 still meeting the watering requirements Choosing and matching PV modules and pumps to meet the design constraints is vital In designing an efficient system one should minimize the amount of work re quired of the pump which minimizes the amount of energy needed to operate the pump and thus the size and cost of components By understanding these ba sic concepts beforehand the designer will be able to determine the appropriate pump and PV modules for a system In selecting a pump the following parameters should be considered e The required capacity or flow rate how many gal lons per minute or per day are needed e The conditions on the suction side of the pump lots of grit sand or dissolved minerals in the wa ter algae growth etc e Whether the pump will be submersible in a well or pump from a surface source e The total head capability how high can the pump move water Average pump effic
23. ounts may be fixed racks or poles or some type of tracking system that follows the sun 1 See your NMSU county Extension agent for more information Contact your county Extension agent for information on estimated evapotranspiration rates for your area y y Circular 670 Page 6 Table 2 Selected Example Amounts of Water Per Day for Various New Mexico Livestock Required amount of water per day Item gallons day Nursing Cow 17 5 Bred Dry Cows and Heifers 14 5 Bulls 19 0 Horses 15 0 Sheep 2 0 Humans 75 0 For drinking cooking bathing etc in sunny climates such as New Mexico 3 days of stor age for livestock watering may be sufficient The storage tank size is calculated by multiplying the days of storage requirement by the daily water requirement and is pro vided as a reference only Solar Resource Once the daily water requirement is calculated the solar resource insolation or total sunlight reaching a spe cific location is determined Sunlight will provide the energy via the PV modules to run the pump and sun light value is determined by the nearest latitudinal coor dinate of the well location between 31 and 37 in New Mexico When you insert this value the spreadsheet determines the solar insolation for winter summer or a yearly average It is recommended to use winter val ues since winter has the least amount of sunlight per day and it is best to design for the worst case scenario Ne
24. pe pumps are also com mon which enables them to maintain their lift capacity all through the solar day at varying speeds that result from changing light conditions A good match between the pump PV array and system parameters is necessary to achieve efficient operation Morris et al 2002 Other components that should be considered within the system are e Mounting system for the PV modules e A controller that allows the pump to start and oper ate under weak sunlight periods cloudy conditions early morning late afternoon e Water level sensor for on off operation if using storage e Direct burial wire UF grounding disconnects and lightning protection e Pipe fittings and other balance of system compo nents a common mistake is to oversize the piping Most PV applications will be pumping at low flow rates 1 5 gpm and these low flow rates will not have sufficient water velocity through a large pipe to keep suspended solids from settling out into the bottom of the piping One half to two inch piping is typically sufficient for most scenarios smaller is cheaper and often more efficient DESIGNING THE SYSTEM A livestock watering well will be used in this example This section will reference the accompanying Excel spreadsheet covered in Circular 671 available to download at http aces nmsu edu pubs _circulars CR671 CR67 1 xlsx Itali cized text e g Daily Water Requirement refers to sheet
25. s in the spreadsheet sheets are accessed using the tabs at the bottom of the spreadsheet window Daily Water Requirement The first step in a design is to determine the total amount of water needed per day Many producers are used to thinking of pumping lots of water in a short time frame with large capacity pumps Solar pumping like windmills will pump water at slower flow rates gpm over a longer time See Foster et al 2010 for a more complete pump and PV discussion To determine Daily Water Requirement using the spreadsheet tool enter the quantity and type of animals cow horse etc you wish to service from this well These entries and Equation 1 are used to calculate total daily water required for each animal type item Gallons of Water Day _ Quantity x required gallons Item of water per day per item Eq 1 Livestock s daily water requirements vary with air temperature the animal s age and size activity distance to water lactation dry matter intake and dry matter moisture content Water needs closely correspond to quantity of feed or forage intake as intake increases the water requirement level will increase However with a moisture content of 70 to 90 lush forage may supply a large amount of required moisture in cooler weather Water consumption is almost directly proportional to the level of milk production and lactating cows there fore need higher amounts of water Air temperatures of 70 to 95 F
26. ted distance to water sources with typical water source spacing of one source per 250 ha to harvest grasslands otherwise there is strong potential for overgrazing close to water supplies To find more resources for your business home or family visit the College of Agricultural Consumer and Environmental Sciences on the World Wide Web at aces nmsu edu streptococci and coliform fecal organisms waterborne diseases foot rot red nose TB mastitis etc nitro gen phosphorous suspended solids and surrounding erosion are realized By pumping water to drinkers ranchers can better utilize pastures get superior animal growth and health and provide higher quality water Pfost et al 2007 Surber et al n d WATER PUMPING BASICS Costs reliability and environmental concerns often influence a producer s choice of surface water pump ing system When producers do not have economical access to grid electric power they generally look to op tions such as ram sling diesel wind Figure 1 or solar powered pumps When these choices are compared solar pump systems are often the best choice due to the operational conditions inherent to New Mexico which allows them to function effectively and economically Foster et al 2010 Solar pumping systems for surface sources or wells can be portable which is appealing because more and more producers want systems that can move among various locations Some users are even powering brok
27. ter than 2 000 m you may need to consider other options Pump and Flow Rate The flow rate gpm is the volume of water that is pumped in a set time period and is determined via Equation 7 Total Daily Water Requirement Total Daily Solar min Insolation x 60 hr In the Pump Selection tab of the spreadsheet you are shown the calculated Q and TDH Using these two key values you must manually choose a specific pump from an initial limited selection that will be capable of pumping water at the necessary Q and TDH Once a pump is selected we determine at what voltage this pump will operate 12 V 30 V etc and how much Flow Rate Q Eq 7 Circular 670 Page 8 power watts is required to run this pump assuming standard pump efficiency n 35 This is the power that de rated PV modules must supply to operate the pump Pump power can often be looked up in pump tables but it can a lso be determined by Equation 8 Pump Power W 0 1885 x TDH x Q n Eq 8 PV Determination The Array Sizing spreadsheet tab involves the automatic sizing of the PV array given the calculated and manu ally selected pump parameters The first calculation performed is to determine the number of PV modules in series a string Each PV module has an operat ing output current and voltage Connecting modules in series increases the total voltage to match or exceed the required pump motor voltage determined earlier Eq
28. uation 9 illustrates this while Equation 10 describes how the PV strings may be connected in parallel to increase total current and thus total power to match or exceed the required pump s power also determined earlier Voltage multiplied by current determines total power provided by the PV array in watts or converted to horsepower HP NOTE It is possible that there will only need to be a single module or modules only in se ries and not in parallel In Equation 9 the 17 4 V value represents the opera tional voltage for our PV module Modules in Series Pumps Motor Voltage Eq 9 rounded to higher integer 174V In Equation 10 the 3 11 A represents the PV panel s rated current at standard operating conditions and the 0 80 value represents the de rating factor Number of PV Strings Pumps Peak Panel Wattage in Parallel integer Modules in Series x 174V Eq 10 x 3 11A x 0 80 NOTE These values are for a pre selected example PV module If other size PV modules are selected then the values must be changed to reflect those modules voltage and current Because we round up the number of strings and par allel combinations to whole numbers the total amount of energy and therefore water pumped will be greater than our daily requirements on any full sunny day This is typically not an issue when float switches are incorpo rated into storage systems which will stop the pumping when the tank is full Excess power
29. vertheless you can choose to use the summer insola tion value if you plan to water a summer only pasture A good rule of thumb is that the solar resource must be greater than 3 0 kWh m per day 3 000 watt hours per square meter of area in one day for choosing a solar option Pumping Requirements Total dynamic head TDH is the total equivalent vertical distance that the pump must move the water or the pressure the pump must overcome to move the water to a certain height Water pressure is expressed in pounds per square inch psi and is defined as the force caused by the weight of water in a column of a certain height also known as head Head is a term relating feet of water in a column that exerts a certain pressure for example a column of water 10 ft high would exert 10 ft of head or 4 3 psi pressure Knowing head you can determine pressure and vice versa Head is impor tant to determine how hard the pump must work to move water from the source to a discharge point i e to overcome the equivalent pressure of that water Static head is a major part of TDH and refers to the total vertical lift distance from the water level in the well to the discharge level Static head is composed of the water depth in the well at its lowest seasonal and draw down levels plus the elevation from the water surface to the discharge point Entering these values static head is calculated by Equation 2 Static Head ft or
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