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: SubDrive/MonoDrive

Franklin’s SubDrive and MonoDrive systems have both red and green lights.  What do they do?

The green light is the power light.  When green is on steady, it means the unit has electricity and is waiting to run.  Not unlike sitting on the sidelines waiting to play in the big game.  Once the pump and motor are activated, the green light begins to blink.  A blinking green light tells you everything is “good” and your system is running.  When the red light is on, it means the SubDrive or MonoDrive has found something it does not like.  It is like the “check engine” light on your car.  While it may continue to operate, the red light means something is not quite right and your system is calling for help.

How SubDrive and MonoDrive Measure Water Pressure

SubDrive and MonoDrive, Franklin Electric’s constant pressure controllers, cover ratings all the way from ½ to 5 horsepower, but they all use the same component to measure water pressure. We call it the SubDrive/MonoDrive pressure sensor. In this issue of Franklin AID, we’ll give you a better understanding of how this rugged device works. Continue reading