Photovoltaic (PV) materials and devices convert sunlight into electrical energy, by connecting smaller PV cells together to form larger units known as modules or panels which are then used to form arrays.  The arrays can then be connected to the electrical grid to form a complete PV system.  PV systems might also include mounting structures that point panels toward the Sun, along with the components that take the dc produced by modules and convert it to the ac electricity used to power all of the appliances in a home (see the United States Department of Energy website for more information on PV systems).

Of relevance to amateur radio operators, is the fact that residential solar is on the rise.  According to the Solar Energy Industries Association (SEIA), in 2021, residential solar installations exceeded 4 GWdc and more than 500,000 systems (see the SEIA Solar Market Insight Report).

This rise in residential solar has also brought to light an increase in RFI cases reported to the ARRL due to the various design technologies used to convert and condition the electricity produced by the panels.  It should be noted that the PV cells themselves do not create RFI — they are basically large diodes — it is the power conversion process which changes the solar energy from dc to ac, and the associated componenets and wiring of the systems that has the potential to create RFI.  

RFI has been experienced by hams who have installed systems on their own homes, and by hams whose neighbors have installed systems in their homes. ARRL Lab staff have noted there are at least three basic mechanisms by which residential PV arrays can generate RFI. Some or all may be present in a given array, depending on the manufacturer’s system architecture.  More information can be found on typical system architecture on the EnergySage website, but the architecture generally includes some combination of PV panels, string inverters, power optimizers, and microinverters.  RFI mechanisms can include the following:

• RFI from inverters. These devices are responsible for switching the high voltage dc from the array to 60 Hz phase-synchronous ac, meaning ac power in-phase with the utility ac waveform. One or more inverters may be incorporated in a given array, depending on its size. Typically, RFI from these devices is radiated by the dc wiring to the PV panels with an 18 kHz to 60 kHz fundamental switching frequency. Harmonics can extend well into the HF bands and lower VHF bands.
• RFI from power optimizers. Power optimizers might be installed at every PV panel, or there may be a single power optimizer for several PV panels, depending on the component manufacturer and system size. Under full sunlight, power optimizers can have fundamental operating frequencies ranging from 39 kHz to 200 kHz.  As with inverters, there may be harmonics extending through HF and into the lower VHF bands.  It should also be noted that when power optimizers are in the “off” or non-power generating mode, the PV array is disconnected from the ac wiring but may still generate RFI as there is still some part of the device powered by the sunlight.  RFI may be reduced significantly but it can still be noticeable.
• Data collection and system control devices. These devices may be stand-alone or integral to other components in the PV system. They also have the least potential to cause widespread RFI, and typically only the operator of the PV array might be subjected to RFI from these components. Typical communications channels observed thus far include 60 kHz to 74 kHz and 1.8 MHz. 

So what should you do if you have RFI from a PV system?  In ARRL's experience, it's generally good to start with your installer (if it's your system), or by letting your neighbor know that you have an RFI issue, provided you are comfortable approaching them.  It's all about trying to open a dialogue with them, and getting the RFI resolved.  Once vendors are aware of an issue, they usually start by isolating and testing to ensure the RFI issue an amateur might be experiencing is actually being caused by the vendor’s system.  This can be as simple as shutting down the solar installation briefly to ensure the RFI goes away at the amateur’s station. Once the vendor performs the diagnostic tests and identifies the RFI as coming from their system, solutions employed by vendors might include component changes or enhancements, addition of ferrite chokes, or modifying wiring to include twisted-pair wiring harnesses. 

Vendors of these systems, from local installers to component manufacturers such as SolarEdge, Enphase and Generac, have all been cooperative in working with hams and the ARRL to work through RFI issues related to solar installations.  If there is any sign that the installer or your neighbor (as the operator of the system) does not understand the issue, feel free to contact our RFI Engineer -- ARRL has developed effective working relationships with solar vendors, so we can usually help.