What is a REEV? How Range-Extended Electric Vehicles work, and why they matter.

The EV revolution promises to transform global mobility. However, at least half the world’s vehicles will still feature an engine in 2040. The reason why boils down to basic restrictions linked to geography, infrastructure, cost, and existing long-life vehicles already on the road.

This is where Range-Extended Electric Vehicles (REEVs) step in - a technology that enables pure-electric mobility while retaining the flexibility associated with engine-powered vehicles.

What is a REEV?

A REEV is an electric vehicle whose wheels are driven by electric motors, just like a Battery Electric Vehicle (BEV). The difference between a BEV and a REEV lies in how range is managed.

Instead of just relying on a larger battery pack to boost range, a REEV uses a small, optimized internal combustion engine that acts only as a generator. When battery charge drops below a certain level, the engine produces electricity to maintain charge and extend driving range.

This makes REEVs distinct from BEVs and traditional hybrids. Unlike the latter, a REEV’s engine has no mechanical connection to the wheels at all.

Electric vehicles can use range extenders to overcome challenges relating to geography and infrastructure access

Read more about why automakers should hybridize their BEVs.

How a REEV works

At first glance, a REEV is indistinguishable from a typical BEV. Its battery and electric drive operates exactly like a typical BEV, with it even being chargeable at home or at a public charging station. This means that it offers zero tailpipe emissions for most day-to-day journeys.

The difference comes through the inclusion of a small engine connected to an electrical generator. If it has been fuelled up, then the REEV’s engine will automatically turn on when the battery’s charge drops below a certain threshold. This will top up the battery, adding hundreds of kilometers of extra range to the vehicle. Since 10kg of gasoline contains as much energy as 600kg of fully-charged battery, this allows drivers to significantly boost their vehicle’s range.

Because the REEV’s engine is never connected to the wheels, it runs only within its most efficient operating window. As a result, a REEV is extremely effective in using its fuel energy and converting it into mileage, resulting in lower emissions and reduced noise and vibration.

Range extenders, such as the HORSE C15, are designed to transform EVs into REEVs

Read more about why Germany's new EV subsidy policy gets it right.

Why REEVs matter

Electric vehicle adoption remains strongest in dense, urban regions where charging infrastructure is easiest to deploy. But much of the world is rural, with long distances, limited grid capacity, and diverse mobility needs. REEVs allow a best-of-both-worlds solution: pure electric mobility for longer trips, with extra range for longer-distance travel.

For many regions and applications, BEVs alone are not in a position to cater to their mobility needs - whether it be because of flexibility, affordability, or infrastructure constraints. By combining electric driving with extremely efficient reserve range, REEVs provide a scalable bridge between today’s realities and the future of a fully decarbonized mobility system.

At Horse Powertrain, we see REEVs as a vital part of the future mobility ecosystem. This is why we are leading the industry in developing integrated REEV powertrain solutions like our HORSE C15 system - an ultra-compact engine-generator unit that enables OEMs to use their existing BEV platforms as the foundations for REEV models. By widening product line-ups and addressing varied regional needs, the HORSE C15 offers a practical solution for markets that are not yet ready for full electrification.

To learn about our products, read more here: spotlight solutions.