Series vs. parallel hybrids: what are the differences? – Jalopnik

Late last year we reported that Americans can’t get enough of hybrid cars, and that won’t change much before 2025. Green Carsturnover increased by another 36% in the second quarter of the year. Meanwhile, top sellers like the Toyota RAV4 are going hybrid-only by 2026, so further increases wouldn’t be a surprise, especially when you consider the efficiency and performance benefits of a typical hybrid vehicle.

As a reminder, these benefits come from the fact that hybrids can rely on two forms of motivation. Remember that the traditional hybrid adds regenerative braking, an advanced battery pack and one or more electric motors to an internal combustion engine. The vehicle charges the battery by braking, using the engine, or plugging in (depending on the exact type of hybrid) and can then use that stored electricity to power the engine(s). The motors can combine their forces with the engine or, for short distances, drive the vehicle itself.

It’s a technology that most people think dates back to 1901, when Ferdinand Porsche designed an electrified powertrain for the Lohner-Porsche Mixte. To be clear, this was a series hybrid, meaning the gas engine never powered the wheels. It acted as a generator for the electric motors that did that. In other words, the power sources ran in series. It would take another eighty years before the groundbreaking parallel hybrid – which could use both sources simultaneously – would be invented.

Series hybrids haven’t had much impact on the automotive industry. They usually work best when there are not many changes in speed, without constant starting and stopping, as with diesel-electric locomotives. Here the engine can operate at an optimal speed for generating electricity, and not for literally driving a vehicle.

In fact, driving a series hybrid is a lot like driving a pure electric car, right down to the fact that a conventional transmission is not required, which helps reduce costs and weight. The technology is also less complex, as it does not require hardware and software to manage and merge the two streams. Moreover, if the petrol engine no longer works, you can still drive (provided there is electricity in the battery, of course). That said, when a series hybrid car’s battery is full, it’s like driving with a few hundred pounds of unnecessary metal in your frunk.

The result in practice is that there are very few production vehicles with series hybrid systems. An example from the early 21st century is the BMW i3. This funky little EV was available with a two-cylinder gasoline engine that could run on demand to keep the battery charged. According to BMW, it extended the i3’s range from about 90 miles to 186 miles, and you could stop at a gas station to refuel instead of looking for a working EV charging station. That can be a challenge, even though they are being installed in record time.

Although they had to wait for the right kind of computer technology – to handle the complicated process of managing the engine, motor and battery pack, as we mentioned above – parallel hybrid systems have dominated the industry since the Honda Insight came on the market in the late 1990s; 25 years later, 25% of Honda’s sales were hybrids. However, the idea behind the system goes back to a 1982 partnership between GE and VW that led to an early plug-in hybrid concept car.

Just about every hybrid and plug-in hybrid vehicle on the road today features parallel hybrid technology; many may also use a kind of mixed mode, running on gas only, electricity only, or both. For example, a car like the Prius can use parallel hybrid functionality for much of its driving, being motivated by both gas and electricity at the same time. But it can also disconnect the gas engine from the drivetrain and travel a limited distance on electricity alone. In that case, it actually functions as a series hybrid, using only the electricity developed by the engine (and braking) to drive the electric motors.

However, you should keep in mind that series and parallel hybrid technology don’t come into play with mild hybrids, which are seeing a Toyota-inspired controversy over their claims of being hybrids at all. These vehicles use a 48-volt starting system, but their electric motors are not powerful enough to propel the vehicle on their own.