EMC Nightmare: When Solar Inverters Become Illegal Transmitters

Solar energy is a powerful ally in the fight against climate change. But hidden beneath the glossy panels on our rooftops lies a growing issue—electromagnetic interference (EMI) caused by improperly filtered solar inverters. This is not just a nuisance for radio operators and neighbors; it can cross into illegality when emissions exceed limits set by national and international standards.

The Root of the Problem

Most residential solar installations place the inverter—responsible for converting the DC power from the panels into usable AC—in the basement or utility room (the kelder in Belgium). Meanwhile, the solar panels are located on the roof. This creates a situation where long, unshielded DC lines must run between the roof and the inverter.

These long DC cables act like antennas. The switching power supplies inside the inverter operate at high frequencies (SMPS: Switched-Mode Power Supplies), often producing hash noise in the HF bands (3 to 30 MHz) if not properly filtered. This noise radiates via the DC cables and pollutes the electromagnetic spectrum.

The Legal Implications

If you can hear this noise at S9+20 on a receiver—even tens of meters away—then the inverter is emitting far above the legal limits. In such cases, the system effectively becomes an illegal unintentional transmitter.

In Belgium, such violations can lead to action by the NCS (Nationale dienst voor de controle op het spectrum). Repeat offenders risk not only fines but also impoundment of the offending inverter.

What Can Be Done?

One of the core challenges is that most solar installers are not trained in electromagnetic compatibility (EMC). Their focus lies on electrical safety, panel placement, and energy efficiency—not radio-frequency interference. As a result, they often unknowingly create setups that act as broadband noise sources. Even when made aware of the problem, many installers lack the technical knowledge or experience to implement effective mitigation strategies, such as correct ferrite placement, differential-mode suppression, or common-mode filtering. This makes education and awareness a critical part of the solution.
Luckily, this is a solvable problem. The key is to properly filter the DC lines between the inverter and the solar panels:

  • DC line filters (specifically designed common-mode and differential-mode chokes)
  • Shielded cabling, if practical
  • Ferrite clamps or beads placed at the inverter end
  • Ensuring proper earthing and bonding

Additionally, inverters must meet EMC Class B compliance for residential environments. Not all cheap or older models do.

Call to Action: Silence the Noise

It’s a myth that solar panels and antennas can’t coexist. In fact, many radio amateurs—including us—have both on the same roof. The key lies in proper filtering and smart installation. With the right measures, solar power and clean reception can go hand in hand without compromise.
If you're a radio amateur or simply someone noticing strange interference on your electronics, consider checking nearby solar installations. You may be the unwilling neighbor of an illegal emitter.

Installers and homeowners: EMC is not optional—it's part of legal operation. When installing or upgrading your solar system:

  • Choose EMC-compliant inverters.
  • Use certified DC EMC filters.
  • Minimize cable length where possible.
  • Work with an installer who understands and respects electromagnetic compatibility.

Let’s harness the sun—without polluting the airwaves.

 

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Written by Joeri Van Dooren, ON6URE – RF, electronics and software engineer, complex platform and antenna designer. Founder of RF.Guru. An expert in active and passive antennas, high-power RF transformers, and custom RF solutions, he has also engineered telecom and broadcast hardware, including set-top boxes, transcoders, and E1/T1 switchboards. His expertise spans high-power RF, embedded systems, digital signal processing, and complex software platforms, driving innovation in both amateur and professional communications industries.