Solar Power for Subs: More Sizing Info

In the last edition of Franklin AID, we demonstrated how to enter information into Franklin Electric’s Solar Selector. We selected Amarillo, Texas as the location and in this fictional example, the end user initially specified 900 gallons per day. However, let’s say that he has since come back and said that he actually needs 9000 gallons per day. No problem, right? We can easily input the new requirement into the Solar Selector.

SolarPAK example updated

Just given that amount of data, the Solar Selector automatically provides a wealth of information, starting with the average amount of useable sunlight that location receives each month. In our Amarillo example, we see that Amarillo receives an average of 5.35 hours of useable sunlight each day over the course of a year. Of course, this value is an average; it doesn’t account for specific weather conditions or real-time trends. But we can also see a monthly average. For example, Amarillo receives 4.65 hours in February and 6.31 hours in July. (Click the image above for a larger view in a new window.)

Although this information is interesting, what we really want to know is which SolarPak system is needed. The Solar Selector figures this out automatically. In this case, the Selector has specified model 25SDSP-3.0HP. Although you actually don’t need to make the translation, this means a 25 GPM unit attached to a 3 horsepower motor.

Below this you can see the monthly performance of the system. For example, in October this installation is projected to be able to deliver 9102 gallons per day, based on the system capability and the average solar hours.

In summary, all we’ve done is provide the location and water requirements. The Solar Selector has done the rest, telling us which SolarPak product is right for this installation.

There’s one more piece of information that the Solar Selector needs: the electrical characteristics of your panel. These values are specified by the panel manufacturer and in this example, the panel manufacturer tells us the each panel delivers 250 watts at its maximum power point (Wmpp), its open-circuit voltage (Voc) is 37, and the voltage at the its maximum power point (Vmpp) is 30. Note that these are for each individual panel. (For an explanation of these terms, see the post Solar Power for Subs: The Panels.) Given this information, the Solar Selector tells us how many panels we need and in what configuration. In this example, we need a total of 10 panels connected in a single parallel string.

There you have it. From three pieces of information – location, water requirements, and panel characteristics – Franklin’s Solar Selector has done all the work to spec our SolarPak and our array. In the next post, we’ll discuss connecting panels in parallel versus connecting them in series.

Solar Power for Subs: Sizing the System

In the third post in our series on solar pumping systems, we’ll start our discussion with sizing a submersible solar pumping system. With today’s web tools, sizing is usually remarkably easy, as most solar manufacturers offer some type of online sizing tool. For our example, we’ll use Franklin Electric’s SolarPak Selector. To find it, go to, which will take you to Franklin’s solar home page.

Solar sizing1

From here, click on “Solar Selector”. You should see the following page:

Solar sizing2

There are three things we need to specify on this page in order to properly size our solar pumping system:

1. Where is the installation located? (This will help determine how much sun is available.)
2. How much water is needed in terms of pressure and volume? (Just like a conventional system.)
3. What are the electrical characteristics of my solar panels?

In the first step, the system calculates how much sun should be available based on the latitude and longitude of the installation. Chances are, you don’t have those numbers handy, but that’s not a problem. Although you can enter the latitude and longitude of the installation directly, an easier way is to select “Look up Your Latitude and Longitude”. With this option, a map will pop up and give you two options: 1) move the crosshairs on the map to the location or 2) simply enter the name of your location in the box at the top of the page and the SolarPak Selector will do the rest. If you do enter the latitude and longitude directly, don’t forget that in the Western Hemisphere, longitude is expressed as a negative number. You also have the option to use the device’s location (iPad, laptop, etc.). As soon as you open the SolarPak Selector page, you should see a pop-up menu that asks for permission to track your physical location, as you can see on the bottom of the screen shot above. If you allow this, your coordinates will automatically load into the SolarPak Selector. Of course, your device should be somewhat close to the installation’s location for this to work properly.

If you choose to use the map to look up your coordinates, you should see this screen:

Solar sizing3

For our example, we’ll use Amarillo, Texas, which we would enter into the box at the top left of the screen.

Solar sizing4

The SolarPak Selector calculates that on average, Amarillo receives 5.35 hours of usable sunlight each day for our solar pumping system.

Solar sizing5

Step 2 (and actually, the order here doesn’t matter) is to specify how much water we need per day and at what total dynamic head. Note that our volume requirement per day can be expressed in cubic meters (m3), gallons, or liters. The drop down box allows you to select your unit of measure. Similarly, Total Dynamic Head can be expressed in meters, feet, or PSI, again specified with the adjacent drop down box.

For our example in Amarillo, we’ll say that on average, we need 900 gallons per day at 200 feet of head. We enter this into the Output Requirements section on the left of the SolarPak Selector page.

Solar sizing5

Once we enter this information, the SolarPak Selector goes to work and provides us with a wealth of information, including which Franklin system is recommended for this installation.

The only input we haven’t covered is solar panels. Simply enter the manufacturer-listed Wmpp, Vmpp, and Voc values (covered in our last post) into the boxes provided in the section called Solar Panel Characteristics. The SolarPak Selector will do the rest, helping you define your array.

That’s all the information the Solar Selector requires to size the system. In our next post, we’ll move on to what information the Solar Selector does with that information.

Generator Sizing for Submersible Motors

Last issue we discussed alternative energy. This time we would like to help eliminate some of the mystery and confusion that occurs when sizing a portable generator. Obviously Y2K has prompted an influx of power loss concerns, but generators have always been used with submersible motors.

Safety First: If you are adding a generator for Y2K or other emergency power needs to your present power supply, you must follow all local, state, and national electrical code requirements. One of the most commonly overlooked safety devices is a TRANSFER SWITCH. A transfer switch is required by the National Electrical Code (NEC) and is used to isolate the utility electrical supply from your generator. If this is not done, your generator can backfeed into the utility lines causing serious injury or death to you, your neighbors, or utility work crews.

In addition, always read and understand the manufacturer’s instructions. Properly ground your generator per manufacturer’s instructions and local electrical codes. Also remember, generators use fuel to operate. Proper ventilation is required for exhaust fumes, and never re-fuel the generator while running. Continue reading