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How to Connect Diode to Solar Panel

By Benjamin Strusnik August 12, 2022

 After installing your 200-watt flexible solar panel, you’ve noticed a current flowing back into your batteries even when fully charged. What could be the problem? It might be that you have installed your solar panel without a blocking diode.

A diode is an electronic component that only allows current to flow in one direction. It’s like a one-way valve for electricity in your solar panel wiring. When current flows through a diode in the forward direction, it acts like a closed switch and conducts current. However, when the current tries to flow backward through the diode, it acts like an open switch and does not conduct current.

In this article, we show you how to connect a diode to your solar panel so you can prevent the current from flowing back into your batteries.

can you connect diode to solar panel

What Is a Diode?

Before we look at connecting a diode to a solar panel, we need to understand what a diode is. In short, a diode is a semiconductor device with two terminals that only allow current to flow in one direction. This unidirectional current flow allows diodes to be used in solar power applications.

Diodes are essential for solar power systems because they prevent what's called "reverse bias." Reverse bias is when the voltage of the solar panel is higher than the voltage of the battery, which can happen when the sun isn't shining on the solar panel.  When this happens, the current flows backward through the diode and into the solar panel, which can damage it.

To prevent reverse bias from happening, you need to connect a diode between the solar panel and the battery. This way, when the voltage of the solar panel is higher than the voltage of the battery, the current will flow through the diode and into the battery, instead of flowing back into the solar panel.

How a Diode Works

To understand how diodes work, we need to understand how semiconductors work. A semiconductor is a material that can conduct electricity under some circumstances and insulate electricity under others.

The two main types of semiconductors are n-type semiconductors and p-type semiconductors. N-type semiconductors are made of materials with extra electrons, while p-type semiconductors are made of materials with extra "holes." Holes are spaces where electrons should be but aren't.

Each type of semiconductor is made from different material. The junction between the n-type and p-type material is called the "p-n junction."

how you can connect diode to solar panel

When no voltage is applied to the diode, the extra electrons in the n-type material and the extra holes in the p-type material cancel each other out, and no current flows through the diode.

However, when you apply a current to the diode, the electrons and holes are forced apart, and the current starts flowing through the diode. The direction of the current is determined by the polarity of the voltage.

If you apply a positive voltage to the n-type material and a negative voltage to the p-type material, the current will flow from the n-type material to the p-type material. 

If you apply a negative voltage to the n-type material and a positive voltage to the p-type material, the current flows from the p-type material to the n-type material. This is called "reverse bias," and it's what we want to prevent in solar power applications.

Benefits of Diodes

Prevent Unidirectional Flow of Current

This is the most basic and important function of diodes. By ensuring current flows in only one direction, they prevent damage to solar panels and other electronic equipment.

Reduce Power Losses

Diodes reduce power losses. When there's no sun, the diode prevents the current from flowing backward through the solar panel and into the battery. This way, the power that's stored in the battery isn’t wasted.

connect diode to solar panel

Protect Against Reverse Polarity

Diodes also protect against reverse polarity. This is a situation where the positive and negative wires are connected to the wrong terminals. This leads to a reverse current flow, which can damage the solar panel. When a diode is connected, it only allows the current to flow in the right direction, preventing any damage. 

However, you need to understand how to wire solar panels to charge batteries to avoid this situation in the first place.

Improve Efficiency

Diodes also improve the efficiency of your solar power system. By allowing the current to bypass the shaded areas of the solar panel, diodes help you get more power from your solar panels. This is because instead of losing the power that would've been wasted in the shaded areas, the diode will allow it to flow through itself. 

Factors to Consider When Choosing a Diode

Reverse Voltage (Vr)

When you want to connect solar panels to a house, one of the most important factors to consider is the reverse voltage of the diode. 

Reverse voltage is the maximum voltage that can be applied to the diode in the reverse direction. If you exceed the reverse voltage, the diode will be damaged. For example, if you're using a 12-volt solar panel to charge a 12-volt battery, you'll need a diode with a reverse voltage of 24 volts. 

The reverse voltage determines the amount of power that can be dissipated by the diode. If you're working with high voltages, you'll need to choose a diode with a higher reverse voltage. 

connect diode to solar panels

Forward Voltage (Vf)

Forward voltage is the voltage drop across the diode when the current is flowing in the forward direction.

You need a diode with a low forward voltage. This ensures there's minimal power loss when the current is flowing through the diode.

Forward Current (If)

This is the maximum amount of current that can flow through the diode in the forward direction. This is an important factor to consider because you don't want the diode to overheat and fail.

Choose a diode with a forward current that's higher than the current you expect to flow through it. This ensures the diode can handle any potential spikes in current.

Reverse Recovery Time (trr)

Diodes need to recover from a reversed biased state before they can be turned on again. This is known as the reverse recovery time. The shorter the reverse recovery time, the faster the diode can be turned on and off. This is important if you use the diode in a switch mode power supply.

can you connect diode to solar panels

Operating Temperature

Another factor to consider is the operating temperature. This is the temperature range that the diode can be operated in. This temperature is determined by the maximum junction temperature of the diode, which is the highest temperature at which the diode can be operated without damage. 

What Size Diode Do I Need?

For solar applications, you need a 3-8 amp diode. The size you choose depends on several factors, including:

The size of your solar system: The size of your solar system is the primary factor in determining what size diode you need. If you have a large solar system, you will need a larger diode to handle the increased current. Similarly, you will need a smaller diode if you have small solar panel kits.

The amount of current your solar panel produces: The amount of current your solar panel produces is also a factor in determining the size of the diode you need. If your solar panel produces more current, you will need a larger diode to handle the increased current.

how to connect diode to solar panels

The type of solar panel you have: The type of solar panel you have is also a factor in determining the size of the diode you need. If you have a monocrystalline solar panel, you will need a larger diode than if you have a polycrystalline solar panel. This is because monocrystalline solar panels such as 150 Watt 12V Monocrystalline Solar Panel from Shop Solar Kits produce more current than polycrystalline solar panels.

Where Do I Put The Diode For My Solar Panels? 

Make sure you install a blocking diode on each solar panel. This prevents reverse current flow when the sun is not shining on the solar panel.

On the other hand, Bypass diodes are used in parallel-connected solar cell strings to prevent the entire string from shutting down when one or more solar cells are shaded.

We recommend using an ABS project box to house your diodes. This will protect the diodes from the weather and keep them organized.

connecting diode to solar panel

Storage Temperature

The storage temperature of a diode is the temperature range in which it can be stored without degrading its performance. The storage temperature of a diode is typically -40 to +85 degrees Celsius. Make sure you choose a diode with a storage temperature that is appropriate for the environment in which it will be used.

How to Connect a Diode to a Solar Panel

Now that you know the basics of diodes let's take a look at how to connect a diode to a solar panel.

Step One: Install Your Solar Panels

The first thing you need to do is wire solar panels to your house grid. This is a job that requires skills and knowledge. If you're not comfortable doing this, then you should hire a professional to do it for you.

Step Two: Connect the Diodes

When connecting diodes, it's important to ensure the cathode is connected to the positive terminal of the solar panel and the anode is connected to the negative terminal of the solar panel. In case you do the opposite, the current will be blocked, and your solar panel won’t work.

To connect the diodes, you need the following tools:

  • A soldering iron
  • Solder
  • Heat shrink tubing
  • Wire cutters
  • Diodes

First, strip the solar panel's wire by about half an inch. Then, tin the end of the wire with solder. Next, place the diode so that the banded end faces the positive terminal of the solar panel.

Solder the wire to the anode of the diode. Then, slide a piece of heat shrink tubing over the connection and heat it until it shrinks. This provides insulation and prevents the connection from shorting. 

Repeat this process for the cathode of the diode. Make sure you connect the cathode to the negative terminal of the solar panel. Use your wire cutters to cut off any excess wire.

connecting diode to solar panels

Step Three: Test Your Diodes

Once you have installed diodes, you must test them to ensure they are operational. This is a critical step before connecting your diodes to your solar panel, as it will ensure that they are working properly and will not cause any damage to your system.

To test your diodes, you will need a multimeter. Set your multimeter to the diode testing function and touch the probes to the anode and cathode of the diode. If the diode works properly, you should see a reading of around 0.45 volts.

If you do not see a reading, or if the reading is significantly different, this indicates that the diode is not working properly and should be checked or replaced.

Diode Installation Best Practices

diode to solar panel connection

Use Ohm's Law (V=IR)

Ohm's law states that the voltage across a circuit is equal to its current multiplied by the resistance. This law is important when installing diodes because you need to ensure that the voltage drop across the diode (Vf) is less than the voltage of your solar panel (Vp).

If the voltage drop across the diode is greater than the voltage of your solar panel, the current will be limited, and your solar panel won’t work as efficiently.

Use a Heat Sink

A heat sink dissipates the heat generated by the diode. Even though it isn’t required, it’s still a good idea to use one. This prolongs the life of your diode.

There are many different types of heat sinks available on the market, so make sure you choose one that's appropriate for your application.

Don't Forget the Bypass Diode

Most people will install the blocking diode and forget about the bypass diode. A bypass diode is just as important as a blocking diode.

Bypass diodes prevent reverse current flow when there’s partial shading on the solar panel. Without a bypass diode, the reverse current will flow through the shaded part of the solar panel and cause it to overheat.

The bypass diode is connected in parallel with the solar panel. This means that the anode of the diode is connected to the positive terminal of the solar panel, and the cathode is connected to the negative.

how you should connect diode to solar panel

Ensure Proper Ventilation

When installing diodes, it's important to ensure that there’s proper ventilation. Diodes generate heat, and if they're not properly ventilated, they can overheat and fail.

Ventilation can be achieved by using heat sinks or by installing the diodes in a well-ventilated area. If you aren’t sure how to properly ventilate the diodes, you should consult a professional.

Types of Diodes

There are two main types of diodes, but only two are effective for solar applications:

Bypass Diode

This is the most common type of diode used in solar power systems. It's a single diode that's connected in parallel with the solar panel.

A bypass diode prevents "hot spots" in the solar panel. Hot spots are solar panel areas that can get damaged if the current flows backward through them. They’re also used to improve the efficiency of the solar power system.

When the solar panel is partially shaded, the bypass diode allows the current to bypass the shaded area and flow through the diode instead.

Blocking Diode

A blocking diode is connected in series with the solar panel. It prevents the current from flowing backward through the solar panel when there's no sun. Whether you have wired solar panels in series or parallel, this diode can be placed at the end of the last solar panel in the system.

diode to solar panel installation

How to Connect a Diode to a Solar Panel FAQs

Below are some frequently asked questions about diodes.

Does a Diode Come with Your Charge Controller?

Diodes are not included with your charge controller. They are separate components that should be purchased separately.

Do I Need A Diode If I Have a Charge Controller?

You need to purchase a diode even if you have a charge controller to prevent reverse-current flow. A charger controller is a great way to regulate the current flowing from your solar panel to your battery. However, it does not block reverse current flow. This is the job of the diode.

Final Thoughts

Installing a diode in your solar panel is a great way to ensure your solar panel works properly and efficiently. By following the steps above, you can be sure that you’re choosing the right diode for your solar panel and installing it correctly.

how to install diode to solar panel

However, you need to know that this process requires equipment, skills, and knowledge the average person does not have. If you aren’t comfortable doing this yourself, we recommend you hire a professional to do it for you. This not only ensures the job is done correctly but also saves you time and money in the long run.

An expert also knows other things, such as how to connect solar panels to a battery bank charge controller inverter; so they can give you more tips on how to get the most out of your solar system. 

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