Table of Contents
When you hear people talk about “clean” vs. “dirty” power, it can mean one of two very different things.
Much of the time, “clean” power refers to renewable energy sources like solar and wind power.
“Dirty” power is often used to describe energy generated by burning fossil fuels like coal, oil, and gas.
But that’s not the kind of “clean” vs. “dirty” power we’ll examine here.
Instead, we’ll focus on the quality of electricity that different types of generators produce — and when, why, and how much “dirty power” matters.
Total harmonic distortion (THD) is a crucial part of that equation.
Read on to learn more.
What is Total Harmonic Distortion
Total harmonic distortion (THD) measures the amount of undesirable frequencies in a signal that cause it to deviate from its ideal waveform.
THD is widely used as a metric in audio applications. It measures the deviation from a pure and accurate reproduction of an audio signal, resulting in muddy, harsh, or distorted sound.
Everyone knows what a bad sound system sounds like, but THD is also an essential metric in many other applications, including electrical power.
THD is a widely used specification in:
- Electricity generation and transmission
- Audio
- Telecommunications
- Automotive Electronics
- Medical imaging and devices
Sine waves are the fundamental test signal used to measure THD in each application, although the methods vary.
Pure sine waves are the ideal waveform for alternating current (AC) electricity.
Is Higher or Lower Total Harmonic Distortion Better?
Lower THD is preferable in almost every application — ideally, as close to zero as possible.
Crunchy electric guitar riffs are a notable exception, but you don’t want distortion in your household electricity or generator power.
Low THD means signal integrity and efficiency — precisely what you want 99% of the time.
Why Is Total Harmonic Distortion Important for Electrical Power?
High THD doesn’t directly cause voltage drops or surges, but it does lead to deviations from the pure sine wave waveform ideal for alternating current (AC) power.
Waveform fluctuations in AC (household) electricity can damage or destroy sensitive electronic devices like computers and data storage devices like hard drives.
Traditional fossil fuel generators output AC electricity with a high level of THD, often called dirty power.
In this context, “dirty power” doesn’t refer to the gasoline, diesel, or propane burned to generate electricity…
Instead, it refers to the quality of AC output power.
Using a generator with a high level of THD to power precision electronics — including many household appliances and personal devices — is like playing with fire.
What Is the Acceptable Range of Total Harmonic Distortion for a Generator?
The acceptable range of total harmonic distortion for generators varies widely depending on various factors — most crucially, what are you using your generator to power?
High levels of THD can shorten the lifespan and negatively impact the performance of most electronics, but specific categories of devices and appliances are particularly sensitive to dirty power.
Recommended THD Level for Electronic Devices and Home Appliances
| Device/Appliance | Average Power Draw | Recommended THD Level |
| Laptops/Computers | 50-200 W | < 3% |
| Smartphones/Tablets | 10-20 W | < 3% |
| LCD/LED TVs | 50-200 W | < 3% |
| Audio Equipment (Receivers, Amps) | 50-500 W | < 3% |
| Medical Devices | Variable | < 2% |
| Refrigerator | 200-800 W (Starting) | 3-6% |
| Washing Machine/Dryer | 500-1500 W | 3-6% |
| Microwave Oven | 600-1200 W | 3-6% |
| Air Conditioner | 500-2000 W (Starting) | 3-6% |
| Coffee Maker | 500-1500 W | 3-6% |
| Power Drills | 500-800 W | 3-6% |
| Saws | 1000-1800 W | 3-6% |
| Incandescent Lights | 25-100 W | > 6% |
| LED Lights | 5-20 W | < 5% |
Can You Reduce the THD of a Generator?
Yes, the THD level of generators can be reduced to acceptable levels by processing dirty power and making it clean enough for even the most sensitive electronics.
However, retrofitting a conventional generator to produce clean power is rarely a viable option from a cost/benefit perspective.
It’s more effective and affordable to purchase a generator designed and built with clean AC output as a priority.
Inverters and solar generators are widely available options capable of providing <3% THD.
Let’s take a look at each.
Inverter Generators
Fundamentally, inverter generators produce electricity the same way conventional generators do, by burning fossil fuel with an internal combustion engine and converting mechanical energy to AC electricity using an alternator.
However, instead of directly outputting dirty AC power with high THD, inverter generators use sophisticated circuitry and microprocessors to process the electricity and “clean it up” before output.
The primary component used in this process is — you guessed it — an inverter.
An inverter converts the raw AC power to direct current electricity and back to AC again, resulting in a much cleaner final AC output.
High-quality inverter generators can output AC electricity with a THD rating of >3% or less.
Traditional generators output AC electricity with a THD of 5% to 15% or more — making the power far too dirty to operate computers and other precision electronics.
Inverter generators are typically more expensive per kilowatt or kilovolt-amp (kVA) of AC output, mainly because of the additional components required, including:
- Rectifiers
- DC bus (capacitors and filters)
- Electronic control module
- Pulse-width modulation (PWM) inverter
- Output filter
- Throttle and governer (speed control)
However, inverters have many benefits over conventional generators, including:
- Clean, stable AC power with minimal THD
- Better fuel efficiency, especially under light to medium electrical loads, primarily due to engine throttling
- Quieter operation
Learn more about inverter generators vs. generators for home use.
Solar Generators
Unlike conventional and inverter generators, solar generators generate direct current (DC) electricity from sunlight utilizing the photovoltaic effect.
PV modules — like solar panels or shingles — contain and protect photovoltaic cells that harvest photons from visible light.
DC electricity is inherently cleaner at the source than the AC power produced by fossil fuel combustion engines and alternators in conventional generators.
THD is caused by mechanical rotation and electromagnetic induction, the very forces that make electricity generation by combustion engines and alternators possible — technically known as Faraday’s Law.
Solar panels generate DC power directly, with no moving parts, and the output is free of harmonic distortion at the source.
However, solar panels don’t connect directly to your home appliances, power tools, or whatever else you want to run with generator power.
Almost all electronic devices and appliances operate using alternating current, and AC electricity is delivered to your home through power lines and the utility grid.
Grid-connected, off-grid, and hybrid solar power systems all require an inverter to convert DC power to AC electricity.
Total harmonic distortion is introduced in the DC-to-AC conversion process…
How much THD depends on the quality of the inverter components.
Solar generators store DC electricity in a solar battery, meaning the DC power from PV modules is first routed through a charge controller and is only converted to AC by the built-in inverter for output.
Alternating current is created by electronic switching, which inevitably introduces harmonics and distortion.
Inverters can approach 0% THD, but generating AC power without harmonics isn’t physically possible.
Solar power systems with low-quality inverters can output AC power with 3% THD or higher, putting sensitive electronics at risk.
EcoFlow’s solar generators, like DELTA Pro 3 simulate pure sine wave output — as close to zero THD as inverters can get.
That means it can safely operate and prolong the lifespan of even the most sensitive electronics, such as computers, hard drives, and medical devices.
DELTA Pro 3’s industry-leading LFP batteries offer multiple charging methods in addition to solar panels to ensure you’re never without clean, reliable power.
If THD is a concern for you — and you wouldn’t be reading this if it wasn’t — EcoFlow’s solar generators provide the cleanest AC output you can get.
Frequently Asked Questions
Total harmonic distortion (THD) measures how clean or dirty a generator’s AC output is—not in the sense of what fuel it burns but rather the quality of the power output. The higher the THD rating, the more likely the generator is to damage sensitive electronic devices like computers, hard drives, and sophisticated home appliances. A THD level of 3% or less is safe for most devices.
A THD rating under 3% is recommended for many electronic devices, such as desktop computers, audio systems, and LED/LCD televisions. Medical equipment and external data storage devices like hard drives typically recommend less than 2% THD. Most home appliances won’t be harmed by 5% THD. THD is less of a concern for professional power tools and heavy machinery. Construction-site generators often have THD of over 10%.
Final Thoughts
If you’re in the market for “clean” off-grid power, consider a solar generator.
EcoFlow DELTA Pro 3 offers pure sine wave AC output with nearly zero harmonic distortion.
Not only is the AC output clean, but if you recharge the portable power station with solar panels, there are zero carbon emissions and no ongoing fuel costs.
You can even use a conventional generator to charge EcoFlow DELTA Pro 3 and use it to output clean, near-zero THD AC power.
EcoFlow offers a wide variety of pure sine wave uninterruptible power supply (UPS) solutions for off-grid, home office, and whole house backup.
Check out our selection today.