Design Of Small Photovoltaic (PV) Solar-Powered Water Pump .

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Technical Note No. 28PORTLAND, OREGONNaturalResourcesConservationServiceOctober 2010Design of SmallPhotovoltaic (PV)Solar-Powered WaterPump Systems

Design of Small Photovoltaic (PV) Solar-Powered Water Pump SystemsIssued October 2010Cover photo courtesy of Nicholle Kovach, Basin Engineer, USDA NRCS.Trade names mentioned are for specific information and do not constitute aguarantee or warranty of the product by the Department of Agriculture oran endorsement by the Department over other products not mentioned.The U.S. Department of Agriculture (USDA) prohibits discrimination in all itsprograms and activities on the basis of race, color, national origin, age,disability, and where applicable, sex, marital status, familial status, parentalstatus, religion, sexual orientation, genetic information, political beliefs, reprisal, or because all or a part of an individual’s income is derived from anypublic assistance program. (Not all prohibited bases apply to all programs.)Persons with disabilities who require alternative means for communicationof program information (Braille, large print, audiotape, etc.) should contactUSDA’s TARGET Center at (202) 720–2600 (voice and TDD).To file a complaint of discrimination, write to USDA, Director, Office of CivilRights, 1400 Independence Avenue, SW., Washington, DC 20250–9410, orcall (800) 795–3272 (voice) or (202) 720–6382 (TDD). USDA is an equalopportunity provider and employer.Technical Note No. 28, October 2010ii

Design of Small Photovoltaic (PV) Solar-Powered Water Pump SystemsACKNOWLEDGEMENTSThis technical note was written by Teresa D. Morales, Oregon StateDesign Engineer, United States Department of Agriculture (USDA)Natural Resources Conservation Service (NRCS), Portland, Oregon, andJohn Busch, Oregon State Irrigation Engineer, USDA NRCS, Baker City,Oregon.Drawings by Kristi Yasumiishi, Civil Engineering Technician, USDA NRCS,Portland, Oregon.Reviewed by Dave Dishman, Oregon State Engineer, USDA NRCS,Portland, Oregon; Stefanie Aschmann, Leader of Energy TechnologyDevelopment Team, NRCS West National Technology Support Center(WNTSC), Portland, Oregon; Peter Robinson, Water ManagementEngineer, NRCS WNTSC, Portland, Oregon; Clarence Prestwich,Irrigation Engineer, NRCS WNTSC, Portland, Oregon; Kip Yasumiishi,Civil Engineer, NRCS WNTSC, Portland, Oregon; Kelly Albers, BasinEngineer, USDA NRCS, Tangent, Oregon; Ginny Cairo, Basin Engineer,USDA NRCS, Roseburg, Oregon; Bill Cronin, Basin Engineer, USDA NRCS,Medford, Oregon; Kevin Shaw, Basin Engineer, USDA NRCS, Baker City,Oregon.Edited by Erin McDuff, Administrative Assistant, USDA NRCS, Portland,Oregon.Technical Note No. 28, October 2010iii

Design of Small Photovoltaic (PV) Solar-Powered Water Pump SystemsPREFACEThe intent of this technical publication is to provide general guidance onthe design of small solar-powered water pump systems for use withlivestock operations or irrigation systems. This document provides areview of the basic elements of electricity, a description of the differentcomponents of solar-powered water pump systems, important planningconsiderations, and general guidance on designing a solar-poweredwater pump system. This publication also provides design examples fortypical design scenarios and standard drawings for use by the reader.However, this technical note is not intended to be used as a standalonedocument. Instead, users are encouraged to consult the NRCS NationalEngineering Manual (NEH 210) on hydraulics and irrigation engineeringfor additional assistance in the design of water delivery systems.All sources used in the development of this technical note are providedin the References section at the back of the document.Technical Note No. 28, October 2010iv

CONTENTS1.Design of Small Photovoltaic (PV) Solar-Powered Water Pump SystemsINTRODUCTION . 11.01.12.ELECTRICITY BASICS .2THE PHOTOELECTRIC EFFECT .2SOLAR RADIATION, SOLAR IRRADIANCE, AND SOLAR INSOLATION . 32.02.13.SEASONAL AND LATITUDE VARIATION .5CLOUD COVER .5PHOTOVOLTAIC (PV) PANELS . 63.03.13.24.0PV PANEL ELECTRICAL CHARACTERISTICS .6PV PANEL ORIENTATION AND TRACKING .7ENVIRONMENTAL FACTORS .8STRUCTURE AND FOUNDATION CONSIDERATIONS . 84.04.14.24.3STRUCTURAL SUPPORTS FOR PV PANELS.8MOUNTING POSTS .8EMBEDMENT CONSIDERATIONS FOR MOUNTING POSTS.9CORROSION PROTECTION.95.0ELECTRICAL CONTROLLERS . 106.0SOLAR-POWERED PUMPS . 116.06.17.DESIGN PROCESS . 147.07.17.27.37.47.57.67.77.87.97.107.118.PUMP SELECTION AND SYSTEM DESIGN .11SOLAR-POWERED PUMP CHARACTERISTICS .13STEP 1 – WATER REQUIREMENT .14STEP 2 – WATER SOURCE .14STEP 3 – SYSTEM LAYOUT .15STEP 4 – WATER STORAGE .17STEP 5 – SOLAR INSOLATION AND PV PANEL LOCATION.17STEP 6 – DESIGN FLOW RATE FOR THE PUMP .17STEP 7 – TOTAL DYNAMIC HEAD (TDH) FOR THE PUMP .18STEP 8 – PUMP SELECTION AND ASSOCIATED POWER REQUIREMENT .18STEP 9 – PV PANEL SELECTION AND ARRAY LAYOUT .18STEP 10 – PV ARRAY MOUNTING AND FOUNDATION REQUIREMENTS.18STEP 11 – WATER FLOW RATES AND DELIVERY POINT PRESSURE .19STEP 12 – SUMMARY DESCRIPTION OF THE SYSTEM.19ADDITIONAL CONSIDERATIONS . 19Technical Note No. 28, October 2010v

Design of Small Photovoltaic (PV) Solar-Powered Water Pump SystemsAPPENDIXESAPPENDIX A:REFERENCES . 20APPENDIX B:ADDITIONAL RESOURCES . 21APPENDIX C:DESIGN EXAMPLES . 22DESIGN EXAMPLE 1:DESIGN EXAMPLE 2:SOLAR-POWERED WATER PUMP SYSTEM USING SURFACE WATER (A STREAM) AS A WATER SOURCE .22SOLAR-POWERED WATER PUMP SYSTEM USING SUBSURFACE WATER (A WELL) AS A WATER SOURCE .28APPENDIX D:SOLAR INSOLATION VALUES FOR OREGON . 36APPENDIX E:NREL APPROACH TO DETERMINING SOLAR INSOLATION VALUES . 46APPENDIX F:STANDARD DRAWINGS. 50APPENDIX G:FRICTION HEAD LOSS FOR SCHEDULE 40 PVC PLASTIC PIPE . 56APPENDIX H:SAMPLE WELL LOG . 57APPENDIX I:OREGON DEPARTMENT OF FISH AND WILDLIFE FISH SCREENING CRITERIA . 58APPENDIX J:SOLAR PANEL WIRING . 60APPENDIX K:GLOSSARY OF SOLAR-POWERED WATER PUMP TERMS . 61LIST OF FIGURESFIGURE 1 – A TYPICAL SOLAR-POWERED WATER PUMP SYSTEM, WHICH INCLUDES A SOLAR ARRAY, CONTROLLER, PUMP, AND STORAGETANK. (SOURCE: “THE MONTANA AGSOLAR PROJECT – EXPANDING THE AGRICULTURAL USES OF SOLAR ENERGY IN MONTANA.”) 1FIGURE 2 – THE PHOTOELECTRIC EFFECT AND SUBSEQUENT ELECTRON MOTION. (IMAGE INSPIRED BY .3FIGURE 3 – SOLAR IRRADIANCE AND PEAK SUN HOURS. .4FIGURE 4 – EXAMPLE SUMMER AND WINTER SUN ELEVATION AND ANGLE. (SOURCE: “RENEWABLE ENERGY PRIMER-SOLAR.”) .5FIGURE 5 – SOLAR CELL, PV SOLAR PANEL, AND PV PANEL ARRAY. (SOURCE: “GUIDE TO SOLAR POWERED WATER .6FIGURE 6 – SOLAR PANEL TILT ANGLES: WINTER TILT WITH MORE ANGLE FROM HORIZONTAL [LEFT] AND SUMMER TILT WITH LESS.8FIGURE 7 – PV SOLAR ARRAY WITH STORAGE TANK AND STOCK. .11FIGURE 8 – TYPICAL SURFACE INSTALLATION WITH PERTINENT PARAMETERS. .12FIGURE 9 – TYPICAL WELL INSTALLATION WITH PERTINENT PARAMETERS.12FIGURE 10 – EXAMPLE SOLAR-POWERED PUMP PERFORMANCE CURVES FOR A POSITIVE DISPLACEMENT PUMP.13FIGURE 11 – EXAMPLE SOLAR-POWERED PUMP PERFORMANCE CURVES FOR A CENTRIFUGAL PUMP. .13FIGURE 12 – A PLAN OF AN EXAMPLE WATERING SYSTEM WITH A STORAGE TANK AND PV ARRAY. .16FIGURE 13 – ELEMENTS OF A TYPICAL INSTALLATION SUPPLIED BY A SURFACE WATER SOURCE. .16Technical Note No. 28, October 2010vi

LIST OF TABLESDesign of Small Photovoltaic (PV) Solar-Powered Water Pump SystemsTABLE 1 – ELECTRICITY FOR NON-ELECTRICAL .2TABLE 2 – SOLAR RADIATION FOR FLAT-PLATE COLLECTORS FACING SOUTH AT A FIXED TILT OF 43 FOR NORTH BEND, OR .4TABLE 3 – EXAMPLE PV SOLAR PANEL ELECTRICAL .6TABLE 4 – TYPICAL WATER USE REQUIREMENTS .14LIST OF EQUATIONSEQUATION 1.2EQUATION 2.2EQUATION 3.18Technical Note No. 28, October 2010vii

1. INTRODUCTIONDesign of Small Photovoltaic (PV) Solar-Powered Water Pump SystemsPhotovoltaic (PV) panels are often used foragricultural operations, especially in remoteareas or where the use of an alternative energysource is desired. In particular, they have beendemonstrated time and time again to reliablyproduce sufficient electricity directly from solarradiation (sunlight) to power livestock andirrigation watering systems.A benefit of using solar energy to poweragricultural water pump systems is thatincreased water requirements for livestock andirrigation tend to coincide with the seasonalincrease of incoming solar energy. Whenproperly designed, these PV systems can alsoresult in significant long-term cost savings and asmaller environmental footprint compared toconventional power systems.The volume of water pumped by a solarpowered system in a given interval depends onthe total amount of solar energy available inthat time period. Specifically, the flow rate ofthe water pumped is determined by both theintensity of the solar energy available and thesize of the PV array used to convert that solarenergy into direct current (DC) electricity.Figure 1 – A typical solar-powered water pump system,which includes a solar array, controller, pump,and storage tank. (Source: “The MontanaAgsolar Project – Expanding the AgriculturalUses of Solar Energy in Montana.”) The principle components in a solar-poweredwater pump system (shown in Figure 1, right)include: The PV array and its support structure,An electrical controller, andAn electric-powered pump.It is important that the components bedesigned as part of an integrated system toensure that all the equipment is compatible andthat the system operates as intended. It istherefore recommended that all componentsbe obtained from a single supplier to ensuretheir compatibility.The following information is required to designa PV-powered pump: The site-specific solar energy available(referred to as “solar insolation”).The volume of water required in a givenperiod of time for livestock or irrigationpurposes, as well as for storage. (Astorage volume equal to a three-daywater requirement is normallyrecommended for livestock operations asa backup for the system’s safety featuresand cloudy days.)The total dynamic head (TDH) for thepump.The quantity and quality of availablewater.The system’s proposed layout andhydraulic criteria.The following sections will first provide anintroduction to the basic concepts involved insolar-powered pump systems, then descriptionsof and design considerations for the previouslymentioned, individual system components.(See Appendix K: Glossary of Solar-PoweredWater Pump Terms for definitions of thetechnical terms and abbreviations used.)Technical Note No. 28, October 2010Page 1

1.0 Electricity BasicsDesign of Small Photovoltaic (PV) Solar-Powered Water Pump SystemsAmperage refers to the movement or flow ofelectrons (i.e. the electrical current) throughthe system. It is measured in units of Amps (A).Table 1 – Electricity for Non-ElectricalEngineersElectricity in a WireWater in a PipeAmpQ(flow of electrons)(flow rate of water)VoltsPressure(energy potential)(energy potential)Watts (power)Hydraulic/Water Power Amps x Volts Q x PressureResistanceFriction Minor LossesHigh Voltage, SmallHigh Pressure, SmallWire High Amps, High Pipe High Velocity,Resistive losses, HeatHigh Friction Losses,and FiresBlown PipeVoltage multiplied by amperage is the powerproduced. It is measured in units of watts (Pw),as shown in Equation 1:loss is also influenced by the wire material: agood conductor, such as copper, has a lowresistance and will result in less energy loss.It is important to be familiar with fundamentalelectrical concepts, such as energy, voltage,amperage, and resistance, before you begin todesign a solar-powered water pump system.Voltage is the electrical potential (i.e. thepressure) in the solar-powered system. It ismeasured in units of Volts (V).Watts Volts x AmpsEquation 1Electrical energy is the amount of powergenerated over a period of time. Energy istypically measured in kilowatt-hours (kWh).Lastly, resistance is a measure of a material’sresistance to the flow of electrons across it. It ismeasured in Ohms (Ω).A good analogy to help describe the flow ofelectrons in a wire is the flow of water througha pressurized line. In order to illustrate thisanalogy, Table 1 (right) compares the flow ofelectricity through a circuit with the flow ofwater through a pipe.As with water flowing through a pipe, resistance(friction, in the case of water) in the electricalline results in an energy loss in the system. It isinfluenced by the length, size, and type of wireconductor. Specifically, resistance isproportional to the length of the wire andinversely proportional to the cross-sectionalarea of the wire. In other words, the longer thewire, the greater the loss and the larger thewire diameter, the less the loss. The energyAnother effective way to reduce electricallosses in a system is to decrease the currentflow. Power losses in an electrical circuit areproportional to the square of the current, asshown in Equation 2:Power Loss Current2 x ResistanceEquation 2Consequently, as indicated in Equations 1 and 2,increasing the voltage while reducing thecurrent will result in the same powertransmission, but with less power loss.Therefore, higher voltage pumps tend to bemore efficient than lower voltage pumps,assuming all other properties are similar.1.1 The Photoelectric EffectPV systems harness the sun’s energy byconverting it into electricity via thephotoelectric effect. This occurs whenincoming photons interact with a conductivesurface, such as a silicon cell or metal film, andelectrons in the material become excited andjump from one conductive layer to the other, asshown in Figure 2, on the following page.Technical Note No. 28, October 2010Page 2

Design of Small Photovoltaic (PV) Solar-Powered Water Pump SystemsFigure 2 – The photoelectric effect and subsequent electron motion. (Image inspired byMerriam-Webster, 2006.)In this figure, the excitation of electrons andtheir movement from the p-layer to the n-layerresults in a voltage differential across th

components of solar- powered water pump systems, important planning considerations, and general guidance on designing a solar-powered water pump system. This publication also provides design examples for typical design scenarios and standard drawings for use by the reader. However, this technical note is not intended to be used as a standalone

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