We separate fact from fiction about hybrid-electric vehicles and how they are powered. Here’s how hybrid-electric vehicles employ electricity and other forms of energy to drive the vehicle and how much electricity can contribute overall.
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As hybrid-electric vehicles continue to outpace battery-only vehicles in popularity in the American market, the discourse over which technology is “better” is heating up. Before we proceed, I will reveal that my personal view is that there now exists a wide range of fantastic green powertrain options from which to choose, and I’m glad that the American consumer still has the luxury of making that choice. My background as an engineer shaped my brain to think that one should use the best technology available for the application. If you disagree, this story may still offer you some value since it will dispel some widely repeated falsehoods, myths to use a different term, related to hybrid-electric vehicles. Specifically the myth that hybrid-electric vehicles "only run on fossil fuels."
A Primer On Hybrid-Electric Vehicles
Hybrid-electric vehicles, let’s call them HEVs for the rest of the story to save my hands from blistering on the keyboard, are presently being chosen at a greater take rate than battery-only EVs in the American market. Consumers choose HEVs for more than one reason. And that’s because, like all types of vehicles, Vehicles with HEV powertrains come in a wide variety of styles and price points.
In this story, we are focused on HEVs that do NOT plug in to pull energy into their onboard battery packs. The classic example of a hybrid-electric vehicle has long been the Toyota Prius. Today, the RAV4 Hybrid, Toyota Corolla Cross Hybrid, Toyota Highlander Hybrid, Toyota Venza (Hybrid), and many other models from other brands outsell the Prius by many multiples. There are numerous reasons for that. Chief among them is that the global market for automobiles has shifted to more practical and versatile crossover SUVs as the default family and commuting vehicle. That preference is true here in America more than in any other market.
HEVs, regardless of their body style, can offer 30% to 50% better energy efficiency than similar vehicles in their price and size segment, which lack the benefit of hybrid-electric technology. They also reduce greenhouse gasses by roughly the same percentages. This is why HEVs are considered “green vehicles” and have been termed such for over three decades. If reducing your fossil fuel use and lowering your carbon footprint is important to you, choosing a HEV instead of a vehicle with a traditional powertrain is a wise way to achieve that goal. Let’s remember all vehicles come with a carbon debt, even battery-only EVs. The goal is reduction since the elimination of carbon production from transportation is impossible.
Correcting a Myth - Hybrid-electric Vehicles Operate On Electricity as Well As Liquid Fuels
A commonly repeated misconception is that since hybrid-electric vehicles don’t plug in, they only power themselves with fossil fuels (gasoline). This is wrong in two ways: one major and one minor.
First, HEVs employ electric motors to use electricity to propel the vehicle and assist in propelling it. Electricity is generated by the same motors, acting as generators, when the vehicle brakes, slows, or sometimes coasts downhill. The way the electricity is generated is the same as in power plants and also in the same way that battery-only vehicles gain some of their electricity.
A magnet is spun inside a coil of wire, and a current is generated. The video above is outstanding if you need a primer on the physics. That current flows to a battery for storage. Next, that energy is pulled out of the battery by the vehicle, and its electric motor, or motors plural, help propel the vehicle. In many popular HEVs, the vehicle can drive solely using this electricity without the liquid fuel motor being used at all. This is only possible in certain scenarios. For example, the Toyota Venza (hybrid) in my own household fleet can be turned to “on” in the morning, drive out of the garage, up our steep driveway, and turn onto the street without the gasoline engine running. The electricity being used to power the electric motors in the powertrain was generated by braking and was stored in the high-voltage battery. HEVs can also drive in parking lots and in heavy traffic using only electricity, and they do this routinely.
HEVs can also contribute to the total power used to propel the vehicle in other ways. Notably, their electric motors can assist the vehicle’s engine to provide ancillary thrust while the engine operates at a low fuel usage state. Also, the hybrid-electric system can enable the engine to operate in ways that traditional engines cannot. For example, the engine can be off while the vehicle coasts on the highway during slight downhill sections.
How Much Do Hybrid-Electric Powertrains Contribute To A Vehicle’s Total Power Usage?
We spoke to Ben Geller, PhD, a member of the powertrain division of Toyota, to get some answers on how much electric power HEVs offer up when operated. Dr. Geller’s powertrain specialty is hybrid controls, which is why we wanted his input. The upshot of our conversation was that regenerative braking adds as much as about 15- 20% of the power to a modern HEV designed for fuel efficiency.
"Regenerative braking is the primary contributor to the efficiency gains that hybrids offer consumers, Said Dr. Geller. “Use of the Atkinson combustion cycle in THS-type powertrains, stopping the liquid fuel engine when the vehicle is idle, and the ability to allow the engine to operate in its most efficient manner also play important roles." Not all of Toyota's hybrid vehicles are able to employ this efficiency gain. That leads us into our next discussion point.
A Spectrum of Hybrid-Electric Vehicles
Dr. Geller asked that I be sure to clarify that there are many types of HEVs and that not all are solely focused on squeezing out the most MPG possible. He illustrated this concept with a chart with traditional vehicles on the left and battery-only vehicles on the far right. Electrification is available across this wide spectrum. Some HEVs, though not from Toyota, are what are termed “mild hybrids.” These hybrids may only help to power the accessories the car’s many systems rely on. MPG is minimally improved, but the cost of this system may be very minimal as well. Next are Single Motor Hybrids, Multi-Motor Hybrids, plug-in hybrid-electric vehicles (which can also vary greatly on their own spectrum), and then eventually, we reach battery-only vehicles and hydrogen fuel cell electric vehicles.
There is no single answer as to how much of the total power a hybrid-electric vehicle uses is from electricity and how much is from liquid fuels. That depends on the design of the vehicle. Some vehicles, the Prius is a perfect example, focus almost exclusively on maximizing the total efficiency of the vehicle. These vehicles may have a high percentage of electric power in the mix. Another vehicle, let’s say a Ford F-150 Hybrid pickup truck, may be designed with an HEV powertrain that is intended primarily to boost torque (towing, plowing, and other uses), and/or provide outlets for electrical appliances to pull power from. While these utility vehicles with hybrid-electric powertrains may not post up the highest possible MPG numbers, the electrification gains are very meaningful when one considers their abilities.
We have already explained how most of the electricity that powers HEVs is generated, but there is a second, less common way. Some hybrids employ solar panels on their roofs that can add electricity to the batteries for propulsion or to be used for cabin cooling. The Hyundai Sonata Hybrid offers a perfect example of just how much energy can be gained by simply adding solar cells to the roof. How much electric range do these panels add? Hyundai says, “2 miles per day.” We flexed our math skills a bit to see how many driven miles the Sonata Hybrid’s solar array could add to the vehicle’s total and came out with roughly 14,000 electric-enabled miles over the vehicle’s lifespan. Of course, the vehicle needs to be parked in a sunny spot every day for this to work, but for many owners, that is their daily parking reality anyway.
The primary reason that liquid fuels are on the outs is that they are mainly derived from “fossil fuels.” The reason that this is bad is the carbon sequestered in the fuel is released back to the atmosphere when the fuel is used for combustion. Carbon is considered to be a negative for the atmosphere since the consensus is that it plays a role in man-made climate change. So, “gasoline is bad.” But not everything we pump into our fuel tanks is “gasoline.”
Here in America, a big percentage of what we use as fuel is ethanol. This liquid fuel has a long list of benefits. It’s high octane, it acts as an oxidizer to reduce pollutants in exhaust, and we can make it. How is it made? More or less the same way we make beer, wine, and hard liquors. We grow a crop, ferment part of that crop, and then we collect the alcohol. It’s hard to argue that growing fuel is not “sustainable.” Particularly since much of the farm acreage in America is used to grow crops we refine into a poison we intentionally ingest to create a state of impairment. While every activity has some carbon footprint, this is a fuel many consider to be low in net carbon. A lot lower in carbon than electricity created from natural gas, as one example.
So, if you use fuel with ethanol, 10% of that liquid fuel is not a fossil fuel and is not carbon-intensive. Here is the EPA’s official page on ethanol as a fuel and oxygenator. The summary includes, “More than 98% of U.S. gasoline contains ethanol…” as well as “(ethanol) reduces air pollution,” and finally, “Ethanol produced from corn demonstrates a positive energy balance.” Vehicles can be designed to run on blends of ethanol as high as 85%. The amount of ethanol in liquid fuel varies, but 10% is common. All of our hybrids are tested with fuel consisting of 10% ethanol. It’s the only liquid fuel available to us.
How Much Of the Propulsion Hybrid-Electric Powertains Provide Is Not From Fossil Fuels?
We’ve explained in this story that there are three main ways that a hybrid-electric vehicle can be propelled other than using fossil fuels. They are:
- Electricity generated by braking, slowing, and coasting (up to around 20%)
- Solar-electric power gained from a rooftop solar array (up to around 5%)
- Liquid fuels that are not fossil fuels (typically 10%, but up to 85% is possible)
As you can see, hybrid-electric vehicles are not powered exclusively by “burning fossil fuels.” In practice, hybrid-electric vehicles employ a significant amount of electric propulsion, and other methods in use right now reduce the amount of fossil fuel used to power the vehicle.
None of these arguments are intended to leave the reader with the impression that hybrid-electric vehicles are the single best solution to everyone’s transportation needs. As I explained in the opening of the story, my personal view is that a variety of powertrain options, many of them green, exists, and that consumers benefit from being able to choose which works best for their specific needs. What message do we hope the reader of this story will take away? That stating hybrid-electric vehicle run solely on fossil fuels is not just factually untrue, but it is commonly used as an argument by those who wish to advocate for a “one size fits all” approach to personal transportation needs.
Bonus Section - The Winter Efficiency & Highway Efficiency Myths vs. Reality
One often repeated myth I’ve observed in online discussions related to hybrid-electric and battery-only vehicles is that “all vehicles see winter efficiency drops.” This has not been my experience testing vehicles weekly for over a decade. Hybrids and conventionally-powered vehicles that I test in winter routinely exceed their EPA-estimated Combined fuel economy ratings. Our personal Venza hybrid was purchased this past winter, and it never had any results lower than the EPA Combined MPG. In fact, like most hybrids we test from all brands, the Venza is presently running above the MPG Combined estimate, and it is most efficient on the highway, not during mixed suburban driving. By contrast, battery-only vehicles I have tested have all seen meaningfully lower efficiency in winter and on the highway than their EPA estimates (expressed in range). Numerous studies mirror my experience with battery-only vehicles in winter and on the highway.
John Goreham is an experienced New England Motor Press Association member and expert vehicle tester. John completed an engineering program with a focus on electric vehicles, followed by two decades of work in high-tech, biopharma, and the automotive supply chain before becoming a news contributor. In addition to his eleven years of work at Torque News, John has published thousands of articles and reviews at American news outlets. He is known for offering unfiltered opinions on vehicle topics. You can connect with John on Linkedin and follow his work at our X channel. Please note that stories carrying John's by-line are never AI-generated, but he does employ Grammarly grammar and punctuation software when proofreading.
Image of Toyota hybrid energy monitor and RAV4 courtesy of Toyota media gallery. Other images by John Goreham.
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