Every year, transient over-voltages hit solar installations around the world, causing millions of dollars in damage. A solar SPD is designed and used to protect against this type of damage. That makes it a vital part of solar power systems, both in terms of safety and in the prevention of costly repairs. Here is more about how an SPD for solar power systems works and what it does.

What is a Surge Protection Device?

The surge protection device definition first: A surge protection device is an electrical device that helps to protect against sudden and excessive voltage surges. Voltage spikes and surges can be caused by a number of things, including lightning strikes, utility grid switching, and faults in the electrical system.

A surge protection device works by diverting or absorbing the excess voltage, thus protecting the equipment connected to the electrical system. SPDs are installed in a variety of settings, including homes, office buildings, and industrial facilities.

Surge protection devices are also commonly used in solar power installations to protect against damage from lightning strikes and other voltage spikes. Talking of the solar system SPD, here is what it is and its working principle.

Solar Surge Protection Device, SPD

Just like any other electrical system, a solar power installation is vulnerable to damage from voltage spikes. A solar SPD is a surge protection device that is specifically designed for use in a solar power system and its components.

Solar surge protection devices essentially divert any excess voltage that is produced by a lightning strike or other voltage spike, protecting the solar installation from damage. There are mainly two kinds of these devices, AC and DC solar SPD.

Solar AC Surge Protection Device

A solar AC surge protection device is connected to the AC side of the solar installation, between the inverter and loads. This type of SPD cannot be used on the DC side of the system as it is only designed to work with AC voltage.

Solar DC Surge Protection Device

A solar DC surge protection device is connected to the DC side of the solar power installation, between the inverter and the array or panels. DC SPD for solar systems works by diverting any excess voltage to the ground, thus protecting the solar panels from damage during an overvoltage by a lightning strike or other overvoltage.

How Does a Solar SPD Work?

Most solar SPDs consist of a metal oxide varistor (MOV). MOVs are devices that can change their resistance in response to changes in voltage. When the voltage is high, the MOVs have a low resistance, allowing them to conduct current. When the voltage is low, the MOVs have a high resistance, preventing them from conducting current.

The image above shows the inside of a typical MOV surge protection device. The resin-covered/insulated metal oxide varistor is seen in the center, with two metal plates on either side. The MOV is connected to the metal plates using braided copper wires. Here is the surge protection device working principle (MOV type).

• Under normal conditions, the voltage across the MOV is low, and the resistance is high. This prevents current from flowing through the MOV.
• When a surge or spike in voltage occurs, the voltage across the MOV increases. This increase in voltage causes the electrical resistance of the MOV to decrease, allowing current to flow through it.
• The current flowing through the MOV creates heat, which is dissipated by the device. Because transient over-voltages only last for a short period of time, the MOV never gets hot enough to be damaged.
• Once the voltage returns to normal, the resistance of the MOV increases, and it goes back to blocking current.

Solar SPDs are conveniently rated to handle specific voltage levels and are usually connected in parallel with the solar system’s equipment. When a voltage spike occurs, the MOVs will divert the excess voltage. This protects the solar installation and its components from damage by preventing the voltage spike from reaching sensitive components.

Solar SPDs are designed to withstand multiple strikes from lightning, meaning that they can provide long-term protection for a solar installation. In addition, SPDs will also provide protection from other types of overvoltage events, such as those caused by utility grid switching.

Where to Install Surge Protectors in a Solar Power System

Let’s now see where to install solar surge protectors in a solar power system. Ideally, an SPD should be installed as close to the equipment as possible to provide the best protection. In most cases, this will be at the inverter. A solar SPD for inverter protection will help to protect the inverter from damage by voltage spikes.

For AC sides of solar systems, the SPD should be installed between the inverter and the loads. For DC sides, the SPD should be installed between the inverter and the array or panels. This will help to protect the equipment from damage by diverting any excess voltage to the ground.

An SPD for solar protection can also be installed at the point of connection between the utility grid and the solar installation. This will help to protect the solar installation from voltage spikes that are caused by the working of the utility grid.

Small-rated solar SPDs, on the other hand, can be installed at the load terminals to provide protection to individual loads. This can be a good option for sensitive loads that are particularly vulnerable to voltage spikes.

Solar SPD Price

The SPD price is a key factor to consider when selecting the right SPD for your needs, as you will need more than a single unit of these devices in your solar power system. Solar SPDs typically range in price from $50 to $300. The surge protection device price will depend on the features and specifications of the SPD.

Basically, the higher the voltage rating and the higher the current rating, the more expensive the SPD will be. However, it is important to select a solar SPD that is rated for the specific voltage and current requirements of your solar installation.

Note that there will usually be a number of different surge protection devices in a solar system installed in a cascading manner. The primary SPD will be installed at the point of connection between the utility grid and the solar installation and between the panels and the inverter.

The secondary SPD will then be installed at the inverter, with smaller rated SPDs installed at the load terminals to provide protection to individual loads. This type of cascading configuration provides the best possible protection for a solar installation by diverting.

Conclusion

Solar SPD devices are vital protection devices for PV power systems. They help to protect the equipment from damage, usually by diverting excess voltage to the ground. When properly used, they can provide long-term protection for a solar installation, since most are modular and easy to replace. These devices are essential to ensure a reliable solar power system. That’s in addition to helping prevent the losses associated with damage by lightning or other voltage spikes.