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Solar Water Pumping Design Specification Spreadsheet

User Manual

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NMSU Engineering New Mexico Resource Network engr.nmsu.edu/outreach.shtml

NMSU Cooperative Extension Service

extension.nmsu.edu

New Mexico Space Grant Consortium nmspacegrant.com

NMSU Southwest Technology Development Institute

nmsu.edu/~tdi

NMSU Engineering Technology and Surveying Engineering Department et.nmsu.edu

Thomas Jenkins, Professor, NMSU Engineering Technology and Surveying Engineering Department

Copyright © NMSU 2012

Disclaimer: This document is intended for educational purposes only in providing a basic understanding and estimating for design considerations and should not be used beyond this purpose. The authors incorporated engineering analysis but all situations are different and the user should consult a professional in all cases.

APPRECIATION GOES TO THE FOLLOWING SUPPORTERS

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TABLE OF CONTENTS

Overview ................................................................................................................................................................. 1 Step 1: Sketch Out Well Parameters ................................................................................................................... 3 Step 2: Using the Spreadsheet ........................................................................................................................... 4 Step 3: Calculate Solar Insolation ....................................................................................................................... 5 Step 4: Determine the Pump Size ....................................................................................................................... 6 Step 5: Pump Selection ....................................................................................................................................... 8 Step 6: Sizing the Array ...................................................................................................................................... 12 Step 7: Generate Design Specifications ............................................................................................................ 13 Step 8: Printing Design Specifications ............................................................................................................. 14 More Information ................................................................................................................................................ 15

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The purpose of this spreadsheet is to assist you with the basic process of designing a solar

water pumping system and aid in feasibility and implementation decisions. The system is

designed to let you enter values such as location, number and type of animals, other daily

water requirements, depth of well, etc. By allowing you to enter different values, you can

investigate different scenarios before final decisions are made.

Before beginning, read Appendix 1 (Solar Water Pumping in New Mexico) and skim this

user manual to get a basic understanding of the spreadsheet and a general overview of

solar water-pumping. It may also be useful to view a short video on solar pumps at:

http://tinyurl.com/89ulvgr. See more alternative energy videos at: http://engr.nmsu.edu/

outreach.professional.shtml.

There are NO expressed guarantees with this system, nor is it intended to replace professional expertise. It is also important to note that the system is designed around the

use of a small set of submersible DC pumps and a PV modules as a teaching example

ONLY; other pumps and PV modules are available and there are no implied endorsements.

This educational version has theoretical design limit of flow rate less than 4 gpm and does

not exceed a pressure head of 230 feet.

Before starting, it is useful to have an understanding of how the spreadsheet is designed,

calculations used, and the recommendations for proper use. The spreadsheet consists of

eight different sheets or pages that are indexed via tabs at the bottom of each window.

There is a title sheet, six sheets which represent the six main steps in the design

methodology, and a conclusion sheet.

OVERVIEW

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Overview: Continued

Figure 1 shows the Daily Water Requirement sheet and sheet index.

These sheets will be referenced continuously throughout this manual. Looking at Figure 1

again, notice different shaded boxes or cells. There are blue and light purple shaded cells

which are instructions and user notes that should be read when using each sheet. The

green cells are where information can be entered by the user. To enter a value, move the

cursor and click on the cell (green box), then enter your value in that green cell (typically

a number) followed by pressing the “enter” key. The orange cells display intermediate

values that are automatically calculated by the spreadsheet. The yellow cells show the final

calculations on each sheet. These yellow values will be used to generate the final design

specifications.

Figure 1: Different sheets within the spreadsheet.

Active (current) sheet tab

USER NOTE: Some cells have a red triangle in the top right corner

These cells have a “pop-up” note that gives an additional short explanation related to the information of that cell. When the user places the cursor on the cell, this informational note will be displayed. Some input cells are restricted in their allow-able entries. For example, the multiplier cell in Figure 1 will only accept entries between 0-20. If a user enters a value out-side of this range, an error message will be displayed and the user must re-enter a valid value in this cell before continuing.

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Read the accompanying paper1 and skim this manual to get a basic understanding of the

spreadsheet and general overview of solar water-pumping. You should have a fundamental

understanding of water wells. Some experience with computers and spreadsheets is

helpful.

Use Figure 2 as an example to sketch out the basic parameters of your well. The key

values needed are the discharge elevation in feet, well water level, total length of pipe and

its nominal inside diameter, and fittings like elbows and valves. Units of length are feet.

Water level is defined as the lowest depth of the water in the well including any draw-

down levels and seasonal variations – not the pump set level which is the depth of the

pump below the water level. Elevation is the level above ground to the discharge point.

Total length of pipe is the pipe from the pump to the discharge point (including any

horizontal pipe such as from the well head to the storage tank). There is an example in the

spreadsheet that is color-coded for your convenience.

Once you have sketched out the basic layout of your piping system and have the specified

values described above, you can move onto Step 2: Using the Spreadsheet.

1T. Jenkins et al, “Solar Water Pumping in NM for Livestock and Agriculture”- A Report and Demonstration Project from the NMSU College of Engineering for NMSU Cooperative Extension Service, 2012

STEP 1: Sketch Out Well Parameters

Figure 2: Basic schematic of a pumping system from a well to a storage tank.

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STEP 2: Using the Spreadsheet

Open the spreadsheet and click on the Title Page sheet (the left-most tab at the bottom

of the page). Read the material and view the Internet links. Proceed to the first design

page by clicking on the Daily Water Requirement tab at the bottom of the page. You

should see a view similar to Figure 1. Always make sure you can view all the page con-

tents beginning at the top and read the user notes and instructions.

The purpose of the Daily Water Requirement sheet is to calculate the required amount of

water you need per day based upon the number and type of animals, plus any other water

needs. Keeping in mind that you only enter data into the green boxes, click on each ap-

propriate cell and input the number of each of the animal types you want to water. If you

do not have any of a particular type, just leave that cell blank (or put in 0). If something

is not listed, input the amount of gallons that the item requires per day under the catego-

ry Other Water Requirements. The amount of water for each animal is calculated by mul-

tiplying the quantity of animals (5 horses for example) by the amount of water each ani-

mal needs per day (15 gal/day). The amount of water each animal needs varies due to

animal size, season and location – desert vs. mountain, etc.2 but generally one would use

a worst case value – typically water needs are the highest during summer. This sheet

shows common water requirements for various animals but you may change these default

values by entering new or other values in the green cells at the bottom left of this sheet

under the heading Water requirement for animals. Grey coded cells indicate a recom-

mended range of typical New Mexico values. Using the values in the green cells multiplied

by the number of each animal, the system will calculate a total daily water requirement

for each animal and then will sum all these to get a total daily water requirement which is

displayed in yellow. See Figure 1.

You may also enter a percentage multiplier (0-20 percent) which will add an additional

percentage to the final calculation. This can be used to offset evaporation, refilling a stor-

age tank, or adjusting for anticipated growth in water requirements. The new adjusted

total is also displayed in yellow. Under this is the required water in units of liter/day.

Similarly, you may enter a number of days for storage3. This will only be used to provide a

general size of a storage tank that might be used with the system. It has no other use in

the design. For New Mexico, a normal storage value is three days but may be up to ten.

2The accompanying paper gives info on water needs or you may contact your extension agent for specific values for your location, season, conditions, and animal types. 3Solar (like windmills) often pump extra water into a storage tank to supply water to a drinker at night or during periods of

low light.

Figure 3: Water requirement for animals.

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Click on the Solar Resource sheet. The purpose of this

sheet is to calculate the total daily solar insolation

(sunlight) falling upon the well’s location. Enter the near-

est latitudinal coordinate between the values of 31° and

37°N (the latitudes of New Mexico) in the latitude cell for

your well location. A green highlight will appear on the

map according to the user entered latitude. See example

below for 31° entry.

After this value is entered, you may choose a season (summer, winter, or Yr_Avg) during which time animals may be watering or grazing. It is strongly recommended that you se-lect winter so that the system uses the shortest day of the year or a worst case sunlight value. A summer choice might be appropriate if the user plans to only graze or water live-stock during the summer months while Yr_Avg (a yearly solar average) would be used for spring or fall only times, which is rare.

STEP 3: Calculate Solar Insolation

USER NOTE: This cell, like several others, has a drop down menu associated with it. You can access this menu by clicking on the cell. A note is displayed along with a drop down menu to the right of the cell. When you select items from this menu, the valid entries for this cell are displayed.

Figure 4: Determining the amount of sun at your location.

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Click on the next sheet titled Total Dynamic Head. The purpose of this sheet is to deter-

mine how much the pump must work to pump water from the well, through the total

pipe length and all fittings to a discharge level at a certain speed or flow rate. This value

is used to determine the pump size and PV modules required for this system.

Enter the values (elevation, water level, etc.) that you pre-determined in Step 1, into their

associated green cell boxes within the sheet. Use the color-coded example drawing on the

left side of the spreadsheet as an aid. These values are used to calculate the total vertical

lift of the system plus friction loss due to the pipe and fittings used to transport the water

from the well to the discharge point giving what is called the Total Dynamic Head.

Water level is the lowest depth of water in the well, including any draw-down and season-

al variations. This in not the depth of the pump which is located deeper (submerged under water). Pump level is how far below the water lever the pump is located. This is used to

determine the total pipe length. The total length of pipe includes the entire pipe in the

well, from the surface to the pump, above ground, and horizontal runs.

Next, enter the pipe size4 (inside diameter in inches) and type (PVC, Poly, or Metal)5. Using

the schematic from Step 1 and the spreadsheet example diagram, input the number of

each type of fitting you think you might use in your concept design of the piping system.

These values should be entered as an integer within the column titled Quantity and within

the designated row of the specific fitting specified. If you do not have or plan to use some

of the fittings listed, leave the cells empty or 0.

4It is best to use the smallest feasible pipe diameter. A common mistake is to use too big a pipe . 5PVC is recommended

STEP 4: Determine the Pump Size

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The TDH is calculated and is displayed in units of feet in yellow (with equivalent meters

above and equivalent psi below).

STEP 4: Continued

Figure 5: Figuring the Total Dynamic Head.

USER NOTE: Under the example well diagram on the left (Typical Solar Water Pumping Layout), there is a calculated hy-draulic workload value (see red arrow above). This value can be used to determine if the system designed to this point is a candidate for solar. If the value is less than 1,500, it is a good candidate. If it is between 1,500 and 2,000, it is marginal. If it is greater than 2,000, other pumping options should be considered.

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If the Hydraulic Workload is acceptable for a solar solution, go to the Pump Selection

sheet to determine an acceptable pump, the voltage at which you will run the pump, and

the solar panel wattage needed to power the pump. This is all determined by the two im-

portant parameters: the previously calculated flow rate (Q) and TDH. For this version of

the spreadsheet, having limited choices for pumps, only values less than 4 gpm and 230

feet of TDH are permitted.

You must look at a couple of example pump curve charts to determine the pump voltage

and wattage required. Each pump can operate only at a maximum flow rate for a certain

TDH. Consider the following examples: The SDS-D-128 can pump water up to a maxi-

mum calculated equivalent TDH of 231 feet, but only at flow rates less than1 gpm. If you

run a SDS-D-128 at 15V, it can only pump at a rate of 0.54 gpm (from this depth). If you

run this same pump at 30V, then you could pump at 1.25 gpm at this same TDH. If you

run the pump/motor at 15V and the TDH is 92 feet, you can pump only at a maximum rate of approximately 0.71 gpm.

If the calculated flow rate is about 0.95 gpm and the calculated TDH is about 100 feet,

then several pumps would work at several different operating voltages. You would want

to select a pump that could be run at the lowest pump/motor voltage and require the

lowest Peak Panel Wattage. By using the smallest values, you minimize the size and num-

ber of PV modules, thereby lowering cost.

STEP 5: Pump Selection

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On this sheet, you must look at the different pumps from the small selection SDS-D_128, for example), and find one that can meet the calculated TDH and the required flow rate. When that is determined, you will note the Motor Voltage and the Peak Panel Wattage (W) from that pump’s chart which is below on the sheet and then manually enter these

values into the green cells labeled with these names.

You are aided in this choice by the spreadsheet coloring values in the charts that fit (greater than or equal to) the flow rate and TDH calculations. Finding a pump where both colors are active in the same row will indicate that this pump can operate at the required flow rate and TDH. For example, if the calculated required flow rate is 3.7 gpm and the total dynamic head is 114 feet, or 34.7 meters, the SDS-Q-135 pump would only work at 30V and require 230W of power to operate. See where the green and orange highlighted colors meet in Figure 7.

STEP 5: continued

Figure 6: Selecting a pump.

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STEP 5: Continued

Figure 7: Pump values—voltage, gpm, TDH.

Using the pump chart, locate a pump model that will meet (or exceed) the requirements

of both flow rate and total dynamic head. Input the selected model name into the green

box next to Pump Choice. Using the pumps chart, find the values for motor voltage and

peak panel wattage of the model specified for the nearest values of the system calculated

flow rate and dynamic head. Enter those values into their respective cells located below

the Pump Choice cell.

Meets the 3.7 gpm value

Watts needed

Meets the 114 foot value

Voltage needed

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If for a particular pump there are multiple cases where both colors are active together, you

should choose the one with the smallest pump voltage (15 V over 30 V) and the smaller

Panel Wattage values. By choosing smaller values, you minimize the number of PV panels

required.

To the left of the pump selection graph, there are some calculated values:

These calculations and assumptions (pump efficiency) are used primarily as a validity check for the required PV power necessary to run the pump. These values should be close to the pump table value that you select from the charts. If not, there is an error in the choice or in the system and values should be rechecked.

STEP 5: Continued

Figure 8: Pump selection values.

DESIGN NOTE: The calculations assume a submersible pump with an efficiency of 35 percent and PV modules with an 85 percent de-rating value for temperature and soiling effects.

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Go to the Array Sizing sheet to determine the amount of modules required in series (called a string) to provide enough energy (wattage) for the pump to operate at the calculated flow rate and TDH, thereby meeting the daily water requirements specified ear-lier. It also calculates the amount of photovoltaic strings that will be needed in parallel, which means parallel rows of modules in series.

You are not required to enter any data within this specific sheet.

In this example, six 50W solar panels (six panels at 50W each = 300W total) are needed to generate the required power to run the pump. There will be three strings of two panels in series (providing the 30V required) and the current to power the pump. This system will generate more energy than required by the pump and therefore, will pump more water than calculated. This, generally, is not an issue especially if pumping to a storage tank with a float switch. (A float system in the storage tank can turn the pump off when the storage tank is full.)

STEP 6: Sizing the Array

DESIGN NOTE: This version only uses 50W Kyocera PV modules but many, many other models and sizes exist.

Figure 9: Determining the Photovoltaic values

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Go to the Design Specifications sheet to summarize and generate design specifications for the direct-coupled solar pumping system scenario. The sheet includes most of the materi-als required, specific descriptions of each, for example size and model names, the quantity of each item or material, an itemized total for each item or material, and an approximate grand total price for the entire system minus labor, well, construction materials, and other minor costs.

You do not have to enter data in this sheet.

Example prices are from 2012 and from a random supplier. No endorsement of this sup-plier is implied and prices always change.

STEP 7: Generate Design Specifications

Figure 10: Final design specifications and representative costs.

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Print out the design specifications sheet and go to the conclusion sheet before closing the spreadsheet.

Upon completion of Step 8, you have gone through the basic step-by-step method to de-sign a direct-coupled solar water pumping system for your specific application. The parts and materials can be purchased through many different suppliers, many of which also provide professional installation and consulting. This is an educational tool and should only be used in that manner.

STEP 8: Printing Design Specifications

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If you need further assistance, you can contact most solar pump manufactures, or the fol-lowing:

Engineering New Mexico Resource Network: engr.nmsu.edu/outreach.shtml

New Mexico State University Cooperative Extension Services: aces.nmsu.edu/county

MORE INFORMATION

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The College of Engineering at New Mexico State University is dedicated to enriching the state’s economic competitiveness through the advancement of innovation, entrepreneurship and employee preparedness required to meet the changing needs of the 21st century.

The Engineering New Mexico Resource Network fosters the delivery of engineering-based programs that fulfill the following objectives:

Delivery of professional development programs to ensure a technically skilled workforce that remains adaptable, innovative and relevant to the needs of the state;

Delivery of technical support and relevant resources to industry, government agencies and non-governmental organizations; and

Delivery of learning programs for K-12 students that support educational attainment in STEM career fields.

ABOUT THE ENGINEERING NEW MEXICO RESOURCE NETWORK

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College of Engineering New Mexico State University Las Cruces, NM 88003-8001

575-646-2913

engr-nm@nmsu.edu engr.nmsu.edu/outreach.shtml