What Is a Plug-In Hybrid (PHEV) and How Does It Work?

Electric vehicle advocates may envision a future where EVs dominate the roadways, delighting in their near-silent operation and lack of tailpipe emissions. But today, that future remains distant. A shortage of charging infrastructure and high vehicle prices still hinder mainstream EV adoption, but there is an alternative that bridges the worlds of gasoline and electric: the plug-in hybrid.

Pairing a gas engine with electric motors and a rechargeable battery pack, the plug-in hybrid, or PHEV, offers a taste of EV benefits with the assurance of backup power to seamlessly take over when the battery runs out.

What does PHEV mean?

A plug-in hybrid electric vehicle (PHEV) is just what it sounds like: a hybrid that you can plug in to recharge the battery pack that powers the vehicle's onboard electric motor. Like a regular hybrid, a PHEV can replenish its battery pack through regenerative braking (converting heat energy into battery charging) and by using the gas engine as a kind of generator. But unlike a regular hybrid, a PHEV can also top up its battery by plugging into the grid.

PHEV batteries are larger than a regular hybrid's, allowing a PHEV to travel several miles solely on electric power. Distances vary, but most PHEVs can typically travel 20-40 miles on a full charge. Many offer modes that can force the car to drive in EV operation, or else preserve electric energy for different stages of the drive. You might prefer to drive your local streets in EV mode and have the gas engine take over on the freeway. And of course, the big draw: The gas engine takes over when the battery runs out.

How do PHEVs charge?

PHEVs charge like many other EVs. They can use a Level 1 or Level 2 charger, the former being familiar as the three-prong household outlet. This is the slowest method, typically delivering about 5 miles of range per hour of charging. But even this is feasible for many buyers, allowing an overnight charge to top up most batteries. Level 2 is the faster way, and this is as simple as plugging into a 240-volt outlet like you might find in the garage to power a dryer. Level 2 charging can refill a PHEV's battery in one to two hours.

Many PHEV or EV owners take it a step further and install a dedicated wall charger, with the same kind of plug and a box similar to what you'll find at charging stations at malls, hotels, restaurants and shopping centers.

You won't see PHEVs queueing up for Tesla's Supercharger or other DC fast-charging stations anytime soon, however. The chargers on board most PHEVs, and their relatively small battery packs, simply can't handle the level of current, though this technology is evolving.

Why would I want a PHEV?

The appeal of a fully electric EV (or BEV — battery electric vehicle) is clear. They offer a chance to end your relationship with gas stations. They're also somewhat intoxicating to drive, with their instant surge of electric power, free of the lag you'll get with a gas engine, no matter how good. BEVs are also eerily quiet, so much so that creating fake motorized sounds both inside and outside the car is now a big component of EV development.

But EVs still can't go far enough for some buyers. Most are limited to 250-300 miles, which might be fine for a regular suburban commute but not for longer adventures or the road trip rite-of-passage. Many buyers still express anxiety about running out of juice. Enter the plug-in hybrid.

The primary appeal of PHEVs compared to standard gas-electric hybrids is the ability to travel for longer distances solely on electric power, and some ability to choose when those miles are used. This offers the best of both worlds: electric efficiency for the short daily drives and the backup gas engine for trips farther afield.

Does the math work?

The best of both worlds. A no-brainer, right? Not exactly. Spend anytime researching plug-in hybrids and you'll notice a common theme: They're all pretty expensive, at least relative to their hybrid and non-hybrid counterparts. A PHEV is often several thousand dollars more than the regular model it's based on and raises a question: What's the real cost savings?

Looking at one of today's most popular PHEVs, the Toyota RAV4 Prime, we'll see that it costs about $11,700 more than the RAV4 Hybrid and nearly $15,000 more than the non-hybrid RAV4.

If we plug some numbers into a calculator (WalletBurst has a good one here) — miles driven per year, average gas prices, estimated miles per gallon for our PHEV and a comparable non-PHEV model, and sticker price — we'll learn that the RAV4 Prime will save us about $630 a year in fuel costs compared to the RAV4 Hybrid. At that rate, it'll take us more than 18 years to recoup the difference. If we compare it to the non-hybrid RAV4, it'll only take us 15 years.

And that's before we even factor in the cost of electricity to recharge the Prime. While we can take some measures to reduce our hit with a home solar installation, for example (we might even get money back from our local utility), electricity will probably still cost us something.

So what's the point of a PHEV?

Following our scenario to the end, the odds of us keeping our RAV4 Prime for 15-18 years are near zero. The odds of the battery pack remaining in good enough condition to still deliver a few dozen electric miles is only slightly better. Lithium-ion batteries generally lose 1% to 2% of range per year, and after nearly two decades, our Prime battery would be near the end of its useful capacity. The 2024 RAV4 Prime is rated for up to 42 miles of electric range. The battery wouldn't be useless, of course. It could still continue to operate as a normal hybrid battery, feeding the electric motor in tandem with the gas engine. We just wouldn't see many more purely electric miles from it.

So in the cold, hard light of financial reality, why would we still want a PHEV?

• Convenience
  

  Even with modest annual fuel savings, a PHEV can deliver the convenience of rarely needing to stop at the gas station. If we charge at home and can also charge at work, we could make our daily commute on electric power alone, even on the freeway. Keeping to reasonable speeds of 65-70 mph will avoid waking the gas engine, as will any sudden stabs of the accelerator. With this pattern, we might see our dentist more often than the gas station.

  We'll leave you to decide which is the bigger hassle: plugging in at each end of the journey or waiting for a pump to open at the cheapest gas station in town.



• Extra power
  

  We've already accepted that we're not really saving any money with the PHEV premium, but we can get something else from our plug-in: performance.

  Hybrids and performance aren't typically uttered in the same breath until you get to higher-end sports hybrids like the Porsche Panamera or BMW 530e. But a plug-in powertrain often delivers a much-needed boost to otherwise anemic hybrid systems, especially with more low-end torque, quicker acceleration, and even better handling thanks to a lower center of gravity from the underfloor-mounted battery pack.

  The RAV4 Prime, for example, is almost 2 seconds quicker to 60 mph (5.9 seconds in Edmunds' testing) than its regular hybrid counterpart and 3 seconds quicker than the non-hybrid RAV4. The Prime's combined gas-electric 302 hp gives it the kind of thrust lacking in the other versions, enough that we think it's the best of the RAV4 lineup. Anyone who remembers the V6-powered RAV4 will find the Prime a worthy substitute.

  The same can be said for the Kia Sorento PHEV and its additional 261 hp, compared to the standard hybrid's 227 hp and regular base-trim Sorento at 191 hp. With a strong belt of rechargeable electric power, plug-in hybrids are often good performance surrogates for more pedestrian models.

Are PHEVs the answer?

Given their elevated prices, plug-in hybrids won't make everyone's list. But for buyers interested in soft-launching their EV ownership ambitions with internal combustion peace of mind, PHEVs make a good compromise. Wait long enough, however, and PHEVs may ultimately be a temporary measure. Steady advancements in solid-state battery technology — a more stable and higher-capacity battery than today's current crop of lithium-ion batteries — are expected to help EVs travel much farther than their current limitations. Range estimates of 500 miles or more, roughly double today's EV average, may go a long way to easing range anxiety for hopeful EV owners. Steady advances in charging infrastructure may help seal the deal for many.

So while PHEVs may eventually fade into an automotive footnote, today they still represent a great way to test the EV waters without getting soaked.