Mazda's Electric Car Gets a Rotary Range Extender

Japanese automaker Mazda added a little Wankel engine to its electric car and it makes for a very interesting plug-in hybrid.

One of the biggest worries about battery electric vehicles (BEVs) is the weight of the batteries and the availability of the minerals that go into them. We recently reported on a study that concluded that "even if the car-centricity of the U.S. transportation system continues, limiting the size of EV batteries alone can cut lithium demand by as much as 42%."

Car manufacturers keep putting in big battery packs to deal with range anxiety, even though 60% of vehicle trips are less than six miles, and people who commute to work average about 20 miles each way. They carry around a lot of battery they don't need most of the time, paying an upfront cost and an operating cost to move all that weight.

Mazda, known for making light and agile cars (I miss my Miata!), has not been a force in the electric car world. Its standard MX30-EV had a 35.5-kilowatt-hour battery and a range of about 100 miles, which is more than Treehugger's Sami Grover gets on his Nissan Leaf but low enough to give people serious range anxiety.

Reviews were negative. Car and Driver noted that it "fell short on the key attributes of a successful EV. The $34,000 crossover returned a mere 100 miles of EPA range and an even more paltry 70 miles on our highway range test, and trudged to 60 mph in a 8.7 seconds."

However, Mazda used to be a major force with rotary engines, sometimes called "Wankel" after its German inventor, Felix Wankel. They had poor thermodynamics but were simple and tiny.

Now Mazda has stuck a little 830cc spinner that pumps out 75 horsepower into the EV. But it doesn't drive the wheels on the MX-30 e-Skyactiv R-EV:

"Mazda chose to use a rotary engine to power the generator system. Levering the unique way in which rotary engines can produce the required output with a small power unit, Mazda developed the new rotary engine to work as a generator and positioned it on the same axle as a high-output motor and a generator in the motor room."

The generator charges the little 17.8 kWh lithium-ion battery pack. On battery alone, the car can travel 53 miles, more than enough for most people's daily travels. But when the weekend comes along and you want to boot it out of town, the rotary fires up and, with its 50-liter (13.2-gallon) gas tank, will take you 400 miles.

It's a conundrum. Hybrid cars have added complexity and cost, carrying around both gas and electric drives. Here, you are carrying around a little engine and a gas tank as a range extender. But when I look at the use case, it makes a lot of sense. In my own family, my wife wouldn't need to fill that tank for 8 months of the year. But come summer, when we want to go 150 miles north, this car would do the job nicely without us carting around a thousand pounds of batteries that we don't use the rest of the year.

This is likely an interim solution. Batteries will likely continue to get lighter, cheaper, and have higher energy densities so that nobody has to worry about this. But right now, pairing a little Wankel with a little battery in a little hatchback makes a lot of sense to me.