The Solar Blind Spot: How Clean Energy Creates Dirty Power

1. How Solar Inverters Create Harmonics

Every solar panel produces direct current (DC). To feed this into a building’s electrical network or the grid, an inverter converts it to alternating current (AC). This conversion is where the problem begins.

Solar inverters use Pulse Width Modulation (PWM) — rapidly switching semiconductor devices on and off thousands of times per second to synthesise an AC waveform from a DC input. This switching process is inherently imperfect. Each switching event creates small electrical transients that distort the output current, injecting harmonic frequencies (multiples of the fundamental 50/60 Hz) into the network.

The dominant harmonics from PV inverters are the 3rd, 5th, 7th, 11th, and 13th orders. Higher-quality inverters suppress these more effectively, but no inverter eliminates them entirely. Even premium grid-tied inverters produce 3–5% total harmonic distortion (THD) at rated output.

The partial-load problem

This is where solar becomes uniquely challenging. Unlike a motor that runs at a steady load, PV output fluctuates constantly with cloud cover, time of day, and season. At partial output, THD rises sharply — because the harmonic currents remain roughly constant while the fundamental current drops. A system producing clean power at noon can be injecting 10–15% THD by late afternoon.

2. The Impact on Your Electrical Network

Harmonic distortion from PV inverters doesn’t stay at the solar installation. It propagates through the entire electrical network, affecting every piece of connected equipment.

Distributed PV compounds the problem

A single rooftop PV installation might inject modest harmonics. But modern industrial and agricultural operations often deploy PV across multiple buildings, rooftops, and sites. Each inverter injects its own harmonic currents, and these aggregate across the network. The result is a cumulative distortion level far higher than any single source would suggest.

Consequences

3. Why Capacitor Banks Don’t Solve This

Capacitor banks are the most common power factor correction technology in industrial and commercial facilities. They are effective at correcting displacement power factor — the phase shift between voltage and current at the fundamental frequency. But they are fundamentally unable to address harmonic distortion, and in many cases make it worse.

Three reasons capacitor banks fail with PV harmonics

4. The Solution: Active Harmonic Filtering at the Source

The only effective approach to PV harmonic distortion is active harmonic filtering — injecting compensating currents in real time that are precisely out-of-phase with the detected harmonics, cancelling them at the source.

How it works

An active harmonic filter continuously monitors the current waveform on the network. Using high-speed digital signal processing, it identifies every harmonic component — its frequency, amplitude, and phase. It then generates and injects a mirror-image current for each harmonic, cancelling the distortion before it propagates through the network.

Unlike capacitor banks, active filters are current sources, not passive reactive elements. They do not create resonance risk. They adapt dynamically to changing harmonic spectra — essential for PV, where the harmonic profile shifts continuously with irradiance.

Local correction vs centralised correction

This is the critical distinction. Capacitor banks correct at a single centralised point. Active filtering can be deployed locally, at individual distribution boards or PV connection points, addressing distortion where it originates. This means:

5. The HarmoniQ Approach

HarmoniQ deploys a three-component solution that addresses the full spectrum of power quality issues created by PV installations — not just at the meter, but throughout the internal network.

The result

6. Applicable Standards

Power quality in PV-connected networks is governed by internationally recognised standards. HarmoniQ is designed to bring facilities into compliance with all of the following:

Summary

Solar PV is an essential part of the energy transition. But the power electronics required to connect PV to electrical networks create harmonic distortion that degrades power quality, damages equipment, and erodes the financial return on solar investment.

Capacitor banks — the most common mitigation — correct power factor at the meter but leave the internal network exposed. Worse, they risk harmonic resonance that amplifies the problem.

The solution is active harmonic filtering deployed locally, addressing distortion at its source. HarmoniQ’s three-component approach corrects power factor, stabilises voltage, and eliminates harmonics throughout the network — ensuring that solar installations deliver their full intended value.