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How to Connect 2 100 Watt Solar Panels - Everything You Need to Know

By SSK Admin December 26, 2021

How to Connect 2 100 Watt Solar Panels

Connecting two 100 watt solar panels is an effective and simple way to increase the power output of your off-grid solar installation.

Solar panels, like batteries, have negative and positive terminals. How these terminals are used to connect solar panels determines whether the connection is in series or parallel.

Before teaching you how to connect two 100 watt solar panels in series and parallel, we will tell you about the difference between these circuits.

We will cover the equipment needed to install and connect 100-watt solar panels. You will also find out more about the uses of series and parallel circuits, along with their advantages and disadvantages.

How to Connect 2 100 Watt Solar Panels

Series and Parallel: What does it mean?

Why does it matter if your circuit is in series or parallel? How your solar panels are wired directly impacts your system’s performance. It also plays a role in which inverter to use.

Ultimately, you want to wire your solar installation to give you a better return investment and the best possible savings. This is when knowing how to install 100-watt solar panel arrays becomes crucial.

Series

A series connection is created by connecting the positive terminal of one solar panel to the negative terminal of another solar panel. Connecting two or more panels like this creates a PV source circuit.

A circuit in series has only a single path for current to flow along. A series circuit is a continuous, closed-loop where all the circuit’s current has to flow through all of the circuit’s loads.

This is why your entire series circuit would stop working when a single panel is affected. Christmas lights are a great example of a series connection: when one bulb breaks, the entire string stops working.

When panels are connected in series, the voltage of the panels adds up, but the amperage stays the same.

Parallel

A parallel connection is created by connecting the positive terminal of one panel to the positive terminal of another panel and connecting the negative terminals of the two panels.

The positive wires are connected to the positive connector in the combiner box; the negative wires are connected to the negative connector in the combiner box. Multiple panels wired this way are called a PV output circuit.

There are multiple paths for the current to travel along in a parallel circuit. When one panel in a parallel circuit is defective, the current will ignore the broken path and keep moving along other paths.

Parallel connections are used for household electrical wiring. That is why you can turn your TV off, but your lights will stay on.

When panels are connected in parallel the amperage increases, but the voltage stays the same. As the amperage increases, the thickness of your wires will increase too.

Make sure you are clued up on what gauge wire for 100-watt solar panel installations would work best.

How to Connect 2 100w Solar Panels

Series-Parallel

Series-parallel circuits are not simple series or simple parallel circuits – they combine both elements.

Two or more components in a series-parallel circuit may be connected in series to form one “group” of series components. There may be two or more “groups” of series components. These “groups” can be connected in parallel to each other.

If one component in a series “group” fails, the other components in that series “group” also fail. But, the other “groups” of series components will keep working, because they form part of the larger parallel system.

How to Connect Solar Panels in Series

Assembling a series circuit is quite simple and no additional equipment is needed. When you wire solar panels in series, you only need a single wire to connect the panels.

To set up your panels in series you must connect the positive terminal of the first solar panel to the negative terminal of your second solar panel. 

The wire runs from the negative terminal of one panel and is connected to the positive terminal of the next panel – this creates a string circuit.

You would be left with one free positive terminal and one free negative terminal. These need to be connected to either the input of the inverter or the input of the charge controller.

How do you know where to connect it? Off-grid solar systems and grid-tied systems with a battery backup need to be connected to the charge controller.

Grid-tied solar systems without a battery backup need to be connected to the inverter. 

Power Output of Solar Panels in Series

When two solar panels are wired in series, the voltage of the panels adds up, but the amperage remains the same.

Connect 2 100 Watt Solar Panels

How to Connect Solar Panels in Parallel

Wiring your solar panels in parallel is a bit more complicated since you need more than a single wire.

To wire two solar panels in parallel you join the positive terminals of both panels together, and you join the negative terminals of both panels together. 

All the negative terminals need to be connected to each other, and all the positive terminals need to be connected to each other.

In smaller systems, you can accomplish this in different ways, but a branch connector is usually used. Y-shaped branch connectors have two inputs for positive (that changes to one), and two inputs for negative (that changes to one).

You will be left with one common negative terminal and one common positive terminal. This needs to be connected either to your charge controller or your inverter.

How do you know where to connect it? Connect it to the charge controller if you have an off-grid system, or a grid-tied system with a battery backup.

Connect it to the inverter if you have a grid-tied system without a battery backup.

When installing a parallel circuit, you or your installer would need to install a combiner box. Combiner boxes transfer the combined output of multiple panels’ strings to an inverter

Afterward, the charge controller can be installed.

Power Output of Solar Panels in Parallel

When solar panels are connected in parallel the amperage will increase, but the voltage will stay the same.

If you have two 100 watt 12V solar panels and a 12V battery bank, your system needs to be parallel to keep the voltage the same.

Apparatus and Equipment You May Need

When you install solar panels and connect them either in series or parallel, there are some apparatuses that you may need.

Make sure to check your 100-watt solar panel specifications to make sure these devices are compatible.

Solar Charge Controller

Solar charge controllers regulate the flow of current, charge batteries, and run electrical loads. They manage the flow of current between batteries and solar panels for optimal power output.

You may be wondering: What size charge controller do I need for a 100-watt solar panel? A 10-amp charge controller would be suitable for a 100W solar panel with a 12V battery bank.

Maximum Power Point Tracking (MPPT) charge controllers are used in series circuits, while Pulse Width Modulation (PWM) charge controllers are used in parallel.

Connecting two 100w Solar Panels

Inverter

Inverters convert the current flowing from your battery from direct current (DC) into alternating current (AC).

But what size inverter do I need for a 100-watt solar panel?  A 12V 200 Watt inverter would be suitable.

Batteries

Batteries store excess electricity. Without batteries, for your solar installation, you may find yourself without power on cloudy days or during the night.

What size battery for a 100-watt solar panel would be suitable? You would need a 100 Ah 12V battery for a 100-watt solar panel.

When Are Series and Parallel Circuits Used?

Series

Series circuits are rarely found in common household electrical wiring. Usually, Christmas lights and landscape luminaries use series connections.

Power strips and single ground-fault circuit interrupter (GFCI) receptacles which are found in electrical circuits also utilize series connections

Parallel

Parallel circuits are much more common than series circuits. Standard household circuits (120V) are parallel circuits.

Your household branch circuit that runs your lights, appliances, and outlets is a parallel circuit.

Advantages and Disadvantages of Series and Parallel Circuits

Parallel 

Pros

  • One defective branch of a parallel circuit will not affect the other branches or stop the flow of current in the system.
  • Appliances can be connected and disconnected without affecting the entire circuit.
  • The voltage remains constant across the entire circuit.
  • Constant voltage means that all the components function at the same capacity, regardless of the addition or removal of components. (i.e. light bulbs have the same brightness.)
  • Parallel circuits are safe and reliable.

Cons

  •  It is difficult to transport energy over long distances with parallel circuits due to high amperage.
  • Parallel circuits are more expensive to build than series connections.
  • Parallel circuits require additional equipment and more wiring.
  • You cannot increase the voltage of a parallel circuit without decreasing the circuit’s resistance.

Series

Pros

  • Series circuits act as current regulators.
  •  Series circuits cost less than parallel circuits to build.
  • The voltage of the solar system increases.
  •  It is easier to transfer energy over long distances with series circuits.

Cons

  •  If one component fails, the entire circuit fails.
  •  If more components are added the resistance decreases.
  •  Less current flows through each component when resistance decreases. (i.e. bulbs burn less bright)

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