by Alec Shkolnik, co-founder & CEO of LiquidPiston

Months before stepping down as CEO of Toyota, Akio Toyoda zigged at a time when the rest of the automotive industry zagged: he argued for an electrified future powered by both EVs and hybrid electric vehicles (HEVs).

I couldn’t agree more.

New hybrid innovation is just as important as innovation in fully electric vehicles. And if our goal is to reduce carbon footprint or increase energy efficiency, we must view it as a crucial optimization.

We can achieve it by adopting a multi-pronged, multi-dimensional approach that considers factors like propulsion technology, energy sources, energy conversion, and storage options under a hybrid framework.

HEVs Are Vital to Electrification Efforts

I want to start by noting that EVs are a marvel of engineering, resulting from decades of improvements in battery, motor, and control technology. They offer a range of benefits, from emission mitigation (or at least moving emissions away from urban populated areas – more on that later), to improved efficiency via regenerative braking. But there are significant hurdles to widespread EV adoption.

EVs still cost more than conventional ICE vehicles. Despite five decades of steady improvement to EV batteries, liquid fuels still offer more than 30x greater energy density (an EV must carry around 1,200 pounds of battery to replicate the energy of 36 pounds of fuel).

This is, in a word, expensive. And despite increasing economies of scale, the price of batteries actually increased in 2022 by seven percent. We’re also struggling to build enough chargers (as is Europe). To reach the US federal government’s goal of 50 percent zero-emission vehicle sales by 2030, the US needs 1.2 million public and 28 million private EV chargers. Today, there are only around 130,000 public chargers.

And this doesn’t even consider the future demands that will be placed on energy generation. Transportation alone requires almost as much energy (27 quadrillion BTU or “quads,” as of 2021 in the United States) as the entire electric grid can supply (37 quads).

And maybe most strikingly: it takes more than six times the raw materials and minerals to produce an EV compared with a conventional car. This puts an incredible strain on supply, requiring significant energy (50 kWh of energy are required to produce one kWh of battery) and water (500,000 gallons of water to produce each ton of lithium). That comes at a cost—financially and environmentally.

According to a recent Toyota memo, the raw materials in one long-range EV could instead be used to produce six plug-in hybrid vehicles or 90 HEVs. The lifetime carbon reduction of those 90 HEVs is 37 times greater than that of a single EV.

This is why we need HEVs (something Renault and Geely recognize, per the recent launch of Horse, an $8.8-billion joint venture which aims to develop low-emission ICEs and hybrid powertrains for the automotive market). HEVs combine the strengths of EVs (like regenerative braking) and those of conventional ICE vehicles. HEVs help us optimize our carbon emission reductions with the infrastructure and technology we have today.

But to properly harness the power of HEVs…

We Can’t Overlook Innovation for the Internal Combustion Engine

The battery component of hybrid vehicles is getting its fair share of attention. But if we believe in hybrids (and we should), we need to be as focused on the engine as we are on the battery.

If we reduce the weight and volume of the engines in HEVs, that, in turn, reduces the:

• Vehicle’s weight.

• Manufacturing costs.

• Emissions produced.

• The amount of energy required to propel the vehicle.

For example, my startup LiquidPiston has developed a rotary engine that is five times smaller and lighter than a traditional piston engine of similar power. For a hybrid application, decreasing the engine size and weight increases the under-the-hood “budget” for a battery.

But shrinking engines isn’t the only way to rethink them to improve an HEV’s efficiency. We are also building a rotary ICE that burns hydrogen and other low-carbon fuels. As sustainable fuels scale, this type of ICE development will be just as important as ongoing battery innovation to power our net-zero transportation future.

There’s No One-Size-Fits-All – We Need Application-Specific Hybrid Vehicles

Embracing hybrid vehicles as part of decarbonizing transportation means embracing an incredible array of options: series and parallel configurations, engines and batteries of various horsepowers, different battery and fuel types, and so on.

No one option is objectively best for all use cases; instead, the ideal combination is always application-dependent. A vehicle driven mostly on highways (like long-haul trucks) would likely perform best with a parallel hybrid configuration. Passenger cars meant to be driven in cities may do better as a series hybrid.

But the optimal hybrid configuration should always achieve these two objectives:

1. Operate the engine at the peak of its efficiency curve during its most common driving conditions.

2. Operate as efficiently as possible during edge-case driving.

That optimization will be complex, of course: cost, government policy, fuel type, and drive cycles will all impact what constitutes “optimal.” But starting to think about engine innovation together with battery innovation will help us ultimately accelerate the decarbonization of transportation.

To Decarbonize Transportation Quickly, We Must Embrace Hybrid Approaches

I’m not just talking about the engine-battery combinations people may see under the hoods of their Toyota Highlander Hybrids. I’m talking about the energy we draw from, how we convert that energy, how we scale our grid’s capacity and resiliency, and how we make all of this affordable. Maybe that comes from a mix of biofuels and fossil fuels paired with more charging infrastructure and diversified vehicle types and business models (higher tax credits, government incentives, etc.).

But the takeaway here is clear. An ICE that’s designed with a focus on hybrid power system compatibility, optimized thermodynamics for increased fuel efficiency, and multi-fuel capability can play a pivotal role in powering and accelerating our hybrid transportation future.

Alec Shkolnik is co-founder & CEO of LiquidPiston, which is a leading developer of combustion engines and hybrid power solutions that are scalable, compact, and capable of utilizing efficient fossil or renewable fuel. Alec has a PhD from MIT’s Computer Science and Artificial Intelligence Laboratory, where he was an NSF Graduate Research Fellow and a postdoctoral researcher.