A Visual Guide to Off-Grid Solar Power System Wiring Design

July 13, 2023

With solar panels accounting for 54% of all new electricity generation capacity, you are still not immune to emergencies and power outages unless you rely on an off-grid solar power system.

Speaking of which, understanding all the ins and outs of an independent solar power system lies in understanding its solar wiring diagram. Today, we are going to explain the solar wiring diagram in detail.

Popular Myths About Solar Panels Busted 5

Off-Grid Solar System Diagram: How It Works

How does the most popular autonomous solar power plant (ASP) work?

A solar power plant is not physically connected to the electricity grid that supplies energy to homes, working due to the photoelectric effect:

  • When the weather is sunny, the batteries are recharged, and the stored energy is redirected to provide heating, lighting, alarms, or refrigeration. On cloudy days, a solar power plant can be combined with a diesel or gasoline generator.

ASP Operation Step-by-Step

Step 1 – Solar Energy Is Absorbed by the Solar Panel

The solar panel absorbs light, converting it into electrical energy and thereby generating direct current (DC). When choosing solar panels for your home, you will be faced with the choice between polycrystalline and monocrystalline.

Polycrystalline solar panels are made of silicon crystallized into multilayer structures. Monocrystalline panels are made of high-purity solid silicon. They have a high energy conversion factor into electric current.

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Source: Shutterstock

Step 2 – The Charge Controller Distributes the Current

The energy generated by the solar panels is sent through the wires to the charge controller like MPPT, which optimizes the voltage and determines system parameters that can increase power.

From the controller, the current goes in two ways: to the devices that consume direct current and the battery to charge it.

Step 3 – Battery Operation

The controller manages the charging modes of the batteries and prevents them from overcharging. The batteries store excess energy for use in cloudy weather or at night.

Step 4 – The Inverter Converts DC to AC

An inverter converts direct current DC to alternating current AC since most electrical devices and systems run on AC power.

Use a stand-alone inverter to ensure optimal power distribution outside the centralized grid and compatibility with energy storage systems. Likewise, make sure the inverter’s capacity exceeds your energy needs to increase the inverter’s durability.

Buying an inverter with a charge control function can save you a lot of money.

Step 5 – System Monitoring and Protection

From the inverter, current is supplied to the junction box, which supplies energy to the entire house. Adding additional sources of electric current will complicate the solar panel diagram, but it will also make the power supply to the house more efficient.

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Important Decisions to Make While Wiring an Off-Grid Solar System

When installing solar panels by yourself, electrical wiring is a crucial element, ensuring the efficient transfer of the energy generated by the power plant to the power supply system of the house.

It is not for nothing that we have told you about the stages of the ASP operation and the main equipment that will be useful in the process. The choice of each tool and the actual work with it requires the coordination of certain decisions related to the wiring of solar panels.

Here is what you may have to set up an off-grid solar panel system:

  1. Estimate energy needs during daytime and nighttime
  2. Calculate the required solar power
  3. Select equipment and design a solar panel wiring diagram
  4. Develop an electricity distribution scheme
  5. Determine the optimal location of the solar panels and the wiring route

Remember that when working with electricity, it is recommended to contact specialists, especially if you have no experience in electrical engineering or do not want to lose the warranty for your solar equipment.

Solar Panel Wiring in a Solar System

The wiring performs a key mission—transporting a continuous flow of solar energy to power the devices. Properly designed wiring guarantees maximum system output and resistance to external influences.

Connecting Solar Panels To House Wiring

In the field of solar energy, wiring solar panels in series and in parallel is equally popular, whereas combined series-parallel wiring is quite rare.

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Source: Shutterstock

Let’s examine the connection options in more detail.

In Series

The positive output of one panel is connected to the negative output of another to increase the voltage while maintaining a constant current (I1 = I2 = I3; U = U1 + U2 + U3). The disadvantage is that a malfunctioning panel can disrupt the entire system.

In Parallel

All positive outputs of the solar panels are connected together, and all negative outputs are connected together. Ensuring stable voltage and increasing the total current of the system (I = I1 + I2 + I3; U1 = U2 = U3), such wiring is suitable for generating more energy at low voltage. The failure of one panel does not stop the system.


Groups of PV panels are connected in series, and each group is connected in parallel. This method combines the advantages of the previous two, providing optimal voltage and current values depending on the specific requirements of the system.

When choosing the optimal connection option, you must consider your system’s requirements and the equipment’s technical parameters.

Choosing Solar Panel Wires

Solar panels generate electricity that needs to be transmitted to another location using solar wires and various connectors. The wires, enclosed in a special sheath, form a single cable.

Insulated wires are used in PV solar panels to protect the system from weather conditions and short circuits and to maintain pole identification. Locate the wires as far away as possible from ventilation compartments that could damage them.

Main Types of Wires

The correct selection and use of wires are important to ensure the efficiency and safety of electrical systems.

Let’s consider the main types of wires for solar panel systems:

  • THHN: Thermally and fire-resistant, with a nylon coating, used in damp locations up to +75℃ or dry locations up to +90℃.
  • THW: Thermally, fire, and moisture-resistant, without an outer coating, used in damp or dry locations up to +75℃.
  • THWN: Thermally and moisture-resistant, with a nylon coating, used in damp locations up to +90℃.
  • TW: Thermally and fire-resistant, without an outer coating, used in indoor wiring up to +60℃.
  • PV: Thermally and moisture-resistant, with a special insulation coating, used in dry and damp locations under extreme weather conditions from -50°C to +70°C.
  • USE-2: Thermally and moisture-resistant, with a special insulation coating, used in dry, warm locations up to +90℃

Determining the solar panel wire size is crucial for the system’s efficiency. Remember, the higher the power of the solar panels and the greater the distance between the panels and the inverter, the thicker the wires should be.

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Source: Shutterstock

Connecting Electricity in an Off-Grid Solar Installation

Once the solar panels are connected to a single network, it’s time to move on to the next steps.

Let’s consider the specifics of connecting electrical wiring at each stage. As an example, let’s take the key average characteristics of the panel: voltage – 37 V; current – 9 A. This means that one panel generates 270-300 W.

1. Connecting the Solar Panel Wiring to the Charge Controller

Taking into account the power of the solar panels and the distance, you need a wire with insulation capable of withstanding the power and voltage. It may be, for example, a UV-resistant PV wire with a thickness that ensures low resistance and an efficient distance transfer of electrical energy.

For wiring connection:

  • Mark the positive and negative poles on the panel.
  • Mark the positive pole with red (1 output) and the negative pole with black (2 outputs) on the wire.
  • Adhere to the correct polarity during connection: connect the positive output of the panel to the positive output of the wire, and the negative to the negative.

To connect the positive and negative outputs, you can use threaded terminals. Avoid over-tightening during connections to prevent damage.

2. Connecting the Charge Controller Wiring to the Battery

The voltage of the charge controller must match the voltage of the battery. Mismatching voltage can damage the battery or lead to inefficient charging.

Observe the correct polarity when connecting the cables from the charge controller to the battery. Label the positive and negative poles and the corresponding terminals on the controller and the battery. Also, place the charge controller where it will be protected from weather and extreme conditions.

AlliedMarketResearch says that the best battery option for solar panels is lithium-ion. Unlike other types of batteries, these are affordable and store energy well in dark or cloudy conditions.

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Source: AlliedMarketResearch

3. Connecting the Wiring from the Battery to the Inverter

In our case, the power of one panel is 333 W, which means you need 400-500 W inverter. After that, you need to choose a copper wire, for example, THHN, the thickness of which can be determined by the AWG table or through the Omni online calculator.

Correctly label the positive and negative poles and connect the battery, taking into account the polarity. We recommend using safe connections, such as MC4 connectors.

Place the battery closer to the inverter. This will reduce energy loss through the wire and facilitate installation.

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Source: Shutterstock

4. Connecting the Wiring from the Inverter to the Junction Box

When choosing a wire, consider the inverter’s power. In our case, the wire is a copper THWN wire.

Connect the inverter to the junction box, observing the correct designations and polarity. Use connections that allow you to securely fasten the wire and ensure electrical contact without the risk of cutting off.

Ensure that the inverter is grounded. Proper grounding will protect you from electrical shock during the wiring process.

Key Findings

By 2030, every 7th American will have a solar system at home, so there’s a fair chance you will need some knowledge of a solar system diagram soon. That said,  if setting up the electrical wiring yourself based on the solar panel setup diagram, remember to ensure the correct connection of components, choose the appropriate type and size of wires, and put your safety before everything else.

Frequently Asked Questions

How should I choose a panel connection option?

If the system voltage requires more than one panel can provide, use a series connection. If you need to increase the total power of the system, use a parallel connection. To optimize both voltage and power, go for the combined option.

How do you choose the right inverter for ASP?

When choosing an inverter, add an extra 20-30% to the total power of the solar panels to ensure efficient operation of the system under various conditions and unforeseen circumstances.

How do you efficiently transport energy from the battery to the inverter?

Use copper wire with the appropriate cross-section for maximum power transport. Correctly size the wire to avoid overheating and efficient power transfer.

Jed Hilton
Jed Hilton

Jed Hilton, our Founder and CEO, has over a decade of experience in the solar industry. His innovative leadership and expertise in solar technologies guide our company's vision and strategy.

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