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.

Hotline FAQ: Pressure Tank for Constant Pressure Systems

Do I still need a pressure tank with a Franklin constant pressure system?

Variable Frequency Drive systems including Franklin’s MonoDrive and SubDrive still use a bladder tank but are typically much smaller than one sized for a standard system.

In a SubDrive or MonoDrive installation the tank’s role is to capture water turbulence, not store water. The MonoDrive and SubDrive systems are designed to hold water pressure to plus or minus one psi of the set point. With a switch this sensitive, any water turbulence around the pressure sensor would cause wider pressure swings. The tank’s job is to capture any wave action in the plumbing coming from the pump side, so the water moving around the pressure sensor is smooth and steady.

The gallons per minute, or gpm rating of the pump, determines the size of the tank needed. The tank’s air pre-charge is also different than a conventional system. Please see your installation manual for complete instructions.

See previous frequently asked questions on our FAQ page.

Hotline FAQ: Constant Pressure Systems

Franklin Electric offers many different constant pressure systems.  What are the differences?

Different models for different horsepowers.

Different horsepowers for different water needs.

MonoDrive is for Franklin 3-wire, 230-volt, single-phase motors, ½, ¾ and 1 hp.
MonoDrive XT is for Franklin 3-wire, 230-volt, single-phase motors, 1 ½ and 2 hp.
SubDrive 2W is for Franklin 2-wire, 230-volt, single-phase motors ½, ¾ and 1 hp.
SubDrive 75, 100, 150 and 300 are for Franklin 230-volt, three-phase motors 1 ½ hp, 2 hp, 3 hp and 5 hp respectively.

MonoDrive: Constant Pressure Available for Single-Phase Systems

 The MonoDrive is the newest member of Franklin Electric’s Constant Pressure family. It is designed to answer the need posed by many home owners and water well contractors for a constant pressure system that can be installed on existing 3-wire single-phase water systems. It is great for homes that have a wide range of flow demand with performance in the ¾ or 1 Hp range, and with MonoDrive there is no need to replace the pump, motor, or the pressure tank that are already in place.

Easy Upgrade For Existing Systems
The CP Water MonoDrive is intended for use with conventional ¾ Hp or 1 Hp pump and motor systems that are currently installed. The existing pump, motor, and pressure tank can be used to keep installation costs low. Simply install the MonoDrive controller in place of the 3-wire control box and replace the pressure switch with the pressure sensor that is provided with the MonoDrive unit. Continue reading

SubDrive 150 Joins Franklin’s CP Water Family


Like the SubDrive 75, the SubDrive 150 controller is a variable-speed system. It continuously monitors the system pressure and adjusts the pump / motor speed to meet the water demand and maintain a constant pressure. You may remember that the SubDrive 75 uses a 3/4 Hp pump coupled to a 1 1/2 Hp motor. In the case of SubDrive 150, it works with a 1 1/2 Hp pump on a 3 Hp motor. The unit’s system performance will be similar or better than a conventional 3 Hp pump of the same flow rating (pump series). And, like SubDrive 75, any brand of off-the-shelf pump can be used. Continue reading

CP Water = Franklin Electric Innovation

Franklin Electric is pleased to announce its latest motor innovation. After extensive laboratory and field-testing, we would like to introduce CP Water.

CP Water is an innovative system that solves what has plagued rural homeowners for years – getting city-like water pressure from their wells. People moving from municipal to private water well systems tend to be unaware of 2 things – the need for a large pressure tank and the inherent pressure cycling present in a conventional water well system. CP Water is a submersible motor system that maintains constant water pressure using a high-speed, variable speed motor and a sophisticated electronic control.

CP Water consists of a specially designed motor and control unit. The concept is really pretty simple. Standard water system motors are single speed. The Franklin CP Water is designed to vary the speed (rpm) of the motor to give you variable Hp from one motor. When you need more water, it runs faster. When you need less water, it runs at a slower speed. Continue reading