Solar Power for Subs: Panel Connections

In this edition of Franklin AID, we continue our series on solar pumping systems, specifically the configuration and wiring of solar panels. Though this step is relatively straightforward, it is a critical one. A system could have all the right panels, but if they are not wired together correctly, the controller/motor won’t receive the voltage and/or current needed to fulfill the system’s water requirements.

Solar panels are DC devices. That is, just like batteries, they produce a direct current. Also just like batteries, they can be wired together to produce the exact combination of voltage and current required. There are two key points to remember when connecting multiple solar panels:

1)     When panels are connected in series, the total voltage delivered is the sum of the voltage produced by each panel. However, the amount of current (amperage) available will only be the current produced by a single panel. This is very similar to what happens when two or more pumps are connected in series. The total head produced will be the sum of the pressures produced by each pump, but the flow produced will remain equal to the flow of one of the single pumps.

2)     When solar panels are connected in parallel, results are flipped. The currents become cumulative, but not the voltages. Once again, this is very similar to connecting two or more pumps in parallel. If the intakes and discharges of two or more pumps are connected, we produce more flow, but the pressure generated will only be the pressure generated by a single pump.

So how are solar panels connected in series and in parallel? Using our pump analogy again, think about connecting two or more pumps in series. The discharge of the first is connected to the intake of the second and so forth. Likewise, to connect two or more solar panels in series, the positive terminal of one solar panel is connected to the negative terminal of the next. The positive connection of the panel can even be thought of as the “output” and the negative terminal as the “input”. This is shown in the diagram below.

panels in series

To wire two or more solar panels in parallel, all of the positive terminals are simply connected together and the all of the negative terminals are connected as seen below.

panels in parallel

To summarize, when panels are connected in series:

  • Total voltage is the sum of each panel in the series
  • Current (Amps) remains the same as a single panel in the series
  • Power (watts) is the sum of each panel in the series (since power = voltage x current, this makes sense) 

When panels are connected in parallel:

  • Voltage remains the same as a single panel in the parallel connection
  • Current (Amps) is the sum of each panel in the parallel connection
  • Wattage is the sum of each panel in the parallel connection

What about a combination of panels in which some are wired in series and others in parallel? The same rules apply, of course. Voltage will add up for those panels that connected in series and current will add up for those panels connected in parallel. In some installations, a combination of connections may be needed to produce the voltage and current required.

The good news is that Franklin Electric’s SolarPAK Selector provides the needed panel array configuration for any given installation. In that segment of the Selector, note that in the first column of the Panel Array Configuration box, the term “String” denotes how many panels should be wired together in series.  The second column indicates how many strings (groups wired in series) should be wired in parallel. Looking at the example we used in the last post, the SolarPAK Selector tells us that we need ten of the panels we have specified and that they need to be configured in one parallel string (one string of ten wired in series).

 Solar Screenshot-frank

Once again, we’ve only provided three pieces of information – location, water requirements, and the panel characteristics supplied by the manufacturer, and Franklin’s Solar Selector has done the rest, even how to connect our panels.

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.

Solar Power for Subs: The Panels

When it comes to solar-powered pumping systems, they all start with the panel. After all, it’s the panel that captures the sunlight needed to run the system.

How it works

Solar-cell2The electricity to run the pump and motor in any solar-powered system resides in the property of certain types of silicon crystals to produce a small amount of DC voltage when exposed 111022-N-OH262-322to light. This is called the photovoltaic effect, and it is often just abbreviated PV. The term photovoltaic or PV system simply refers to a solar system that generates electricity using this property.

When silicon crystals are connected together, they can generate useful amounts of electricity. One unit of these connected crystals is called a solar cell, and dozens of cells are contained in a single solar (photovoltaic) panel.

How to spec a solar panel

Several different variables are associated with solar panels, but for a pumping system, we only need to consider four values: Voc, Vmpp, Impp, and Wmpp.  Voc stands for open circuit voltage and is exactly what the name implies. That is, with no load (zero current being delivered), the array will generate this amount of DC voltage. This is similar to measuring AC voltage from the power company in a conventional water system when the motor is not running.

Unlike AC power from the power company, however, once we start to pull current (amperage) from the array (to drive a motor for example), the amount of voltage produced will start to fall off as the amount of current increases. This is remarkably similar to a pump curve. That is, Voc can be thought of as the shut-off head.

As we move down the pump curve delivering water (GPM), the pressure drops accordingly. At a point about midway on the curve, the pump will deliver its maximum horsepower. In the case of a solar cell, the amount of power being delivered will simply be the voltage multiplied by amperage:

power (in watts) = voltage X amperage

This point where the most power is delivered is denoted by Wmpp, or maximum power point watts. It’s also sometimes called just Pmax or maximum power. The voltage and current at this point are called Vmpp and Impp for maximum power point voltage and maximum power point current, respectively.

All panel manufacturers provide the values Voc, Vmpp, Impp, and Wmpp for each of their panels. For example, in the data sheet excerpt below, Vmpp is 32.1 volts and Impp is 8.42 amps. Notice that when those two are multiplied (32.1 x 8.90), it equals 270 watts.

SolarWorld Sunmodule™ solar panel 270 watt mono black data she

The values above are at standard conditions. Since the amount of energy produced by a solar panel is dependent on the amount of light striking it as well as the ambient temperature, the industry has defined a standard set of conditions to ensure that different panels from different manufacturers can be compared side-by-side. In real-life conditions, the actual values will be somewhat more or less than listed by the manufacturer.

Today, dozens and dozens of companies manufacture solar panels. In most cases, your local distributor can probably make some recommendations.

What’s next?

Although the values above are for a single panel, most solar pumping systems will require more than one. The question then becomes, “for my given water requirements, how many panels do I need?” With today’s web tools, calculating this is quite easy. We’ll cover this topic in the next post of Franklin AID.

Solar Power for Subs: Part 1

solar installHarness the power of the sun; over time, that age-old dream has become a reality. With solar technology, we can use the sun’s energy to do work, to move things and drive machines. Today several manufacturers, including Franklin Electric, offer solar pumping systems that harness the power of the sun to get water from the ground—even where there’s no power grid.

Over the next several weeks, Franklin AID will examine in detail how these systems work, their sizing, their proper application and set-up, and their advantages and disadvantages. By the end of this series, you will have a very complete understanding of where solar pumping fits into your product portfolio, along with how to install one of these systems.

Why Solar?

To begin with, why use a solar pumping system? There are two simple answers: 1) because there’s no power where the water well is located, and 2) because the power is free. But there can be other reasons to use a solar pumping system that may be less obvious. Perhaps power is available where you need water, but it’s unreliable. If that location is remote, the end user may not even be aware when the power is off. Couple that with a critical water supply and the simple reliability of solar pumping can make a strong case for it. A prime example here is open range livestock.

In other cases, there may be power nearby, but the well is several hundred feet away from the power source. The cost of trenching and running copper to the wellhead could often outweigh the cost of a solar pumping system. In other areas, electrical power may available but very expensive. Since the sun shines for free, solar simply makes the economic sense.

Finally, some people want to use greener products as much as possible and nothing fits the bill better than solar. Marketing reasons can even enter the picture. For example, organic farm operations that market themselves as such may want to use solar pumping for irrigation in order to be able to promote this to their customer base. In such cases, electricity from the grid may be readily available.

Why Not Solar?

Of course, solar pumping by definition has a big drawback: it needs the sun to operate.  As a result, pumping systems that are strictly solar can’t deliver water 24 hours a day. But irrigation normally isn’t required 24 days a day, and in other applications, a storage tank or cistern may store more than enough water when the sun is down or the weather doesn’t cooperate.

In a residence or business, however, we do want water to be available under pressure 24 hours per day. So although stand-alone solar pumping systems aren’t likely to completely replace conventional residential systems, that doesn’t mean they can’t be combined with battery-powered systems or traditional grid systems. We’ll cover these options later.

In summary, where solar systems really come into their own are in applications such as livestock watering, irrigation, vineyards, and anywhere a grid power is unreliable or nonexistent. That’s a pretty exciting development for our industry.

Stay tuned for the next post in this series, where we’ll cover the starting point of all solar pumping systems: the panels.

SubMonitor: What it CAN’T do

In the last few Franklin AID posts, we’ve discussed how SubMonitor protects a 3-phase submersible installation against a wide variety of potentially harmful conditions. It does this by continuously monitoring voltage, current, and a heat sensor in Subtrol-equipped motors.

On the mechanical side, however, there are a few things that SubMonitor just can’t protect against. One of these is water hammer. Water hammer most often occurs when a check valve is not used, has been improperly installed, or leaks. As a result, when the pump stops, the water drains back down through the pump inlet and creates a vacuum in the discharge piping. When the pump restarts, water rushes to fill that vacuum at a high velocity. When it strikes the hardware or stationary water above, it causes a hydraulic shock that can split pipes, break joints, and damage the pump/motor. The picture below shows a thrust bearing that was destroyed by water hammer.

Water Hammer

Another mechanical condition that SubMonitor won’t protect against is radial side loads. The most common cause of side loading is misalignment of the pump and motor. This creates a side which, depending on the how extreme that load is, can cause a rapid failure in the radial motor bearing near the top of the pump.

Radial bearing

Finally, another condition that SubMonitor won’t protect against is upthrust. As the name implies, upthrust occurs when a large volume of water pulls the impellers upward. This carries across the pump coupling/motor shaft assembly and pulls the shaft up with it. This generally occurs at start-up, and the pump and motor are designed to handle this on a momentary basis. However, if the pump is operating on the far right-hand side of the curve for long periods of time, the resulting upthrust can damage the motor and pump.

When looking at these three mechanical failure modes, it may seem obvious that no electronic protection device could guard against these types of failures. These situations underscore the importance of using good installation procedures. Combined with the protection that SubMonitor offers against events that you can’t control, your submersible installation will reliably deliver water for years to come.

SubMonitor: Overheat and Rapid Cycling Protection

In previous posts, we’ve covered the details of how SubMonitor protects a 3-phase installation from high/low voltage and under/overload conditions. This time around, we’ll cover overheat and rapid cycling.

All motors generate heat. In order to ensure proper operation and maximum life, a motor must be able to effectively dissipate the heat it generates. In the case of a submersible motor, that method is the cooling flow of water that is drawn past the motor by the pump above it. If that cooling flow is interrupted for any reason, the motor can overheat and fail.

Franklin Electric submersible 6- and 8-inch motors labeled “Subtrol Equipped” contain a built-in sensor that can detect and report an overheat condition when connected to a SubMonitor. When an overheat condition occurs, the sensor sends a series of continuous electrical pulses up the motor lead and drop cable. SubMonitor recognizes this signal and takes the motor offline to protect it.

No temperature adjustment is required if an overheat condition occurs; the sensor is pre-calibrated, and SubMonitor’s default setting for overheat detection is ON. If SubMonitor detects an overheat condition, it will take the motor offline for 10 minutes and then attempt a restart. If the overheat condition is still present on the restart, SubMonitor will take the motor offline again, repeating the cycle until it reaches a maximum number of attempts.  Both the time-out and restart settings can be adjusted manually. This time-out setting can be adjusted from 5 to 60 minutes in 5 minute increments (default is 10), and the restart setting can be adjusted from 0 to 10 restarts (default is 3).


SubMonitor also protects against rapid cycling conditions that can occur, for example, with chattering contacts. If SubMonitor detects more than 10 starts in 10 seconds, it will take the motor offline one minute. After that minute has elapsed, it will attempt to restart the motor 3 more times before requiring a manual reset. This setting is also adjustable, but the default parameter generally covers the vast majority of installations.


Even though SubMonitor protects against many of the circumstances that can harm a submersible motor, there are certain damaging conditions to which SubMonitor does not apply. We’ll cover those in our next post.

Note: Even if a motor does not contain a Subtrol heat sensor, SubMonitor will still protect it from high/low voltage, under/overload, and rapid cycling conditions.