Eco-Tips 16 Jun 2020

Hydrogen Cars? There's an Efficiency Problem

If only we could all drive hydrogen fuel cell cars, right? Electric vehicles have improved greatly, but hydrogen cars could match gasoline or diesel vehicles in range and quick-fueling ability. Best of all, they emit nothing except water vapor and warm air.

Well, there’s a problem. Several problems, actually, but technological advances could fix most of the issues within a few years. The big problem, though, is built-in inefficiency compared to electric cars.

Hydrogen fuel cell cars actually are electric cars; they power their electric motors with energy from a fuel cell instead of a battery. A fuel cell mixes hydrogen (from a tank in the vehicle) with oxygen from the air. The resulting reaction produces electrical energy, plus water and heat.

Several manufacturers are experimenting with hydrogen fuel cell vehicles. Toyota introduced the hydrogen-powered Mirai in 2014 and plans a next-generation version later this year. (The photo at the top of this post shows a Toyota hydrogen concept vehicle on display in Tokyo.)

However, Tom Baxter, a senior lecturer in chemical engineering at the University of Aberdeen in Scotland, explains in an article at The Conversation why he thinks hydrogen cars are “a flawed concept.”

Electricity from Hydrogen

Here, he says, are the steps required for a clean-energy hydrogen fuel cell vehicle:

  1. Use electricity from a clean, renewable source such as a wind turbine or solar panel to generate hydrogen from water through electrolysis; that’s about 75% energy-efficient. (There are also less-green ways to generate hydrogen.)
  2. Compress and chill the hydrogen, and transport it to a filling station where drivers can buy it; that’s about 90% efficient.
  3. Convert the hydrogen back into electricity in the vehicle’s fuel cell; that’s about 60% efficient.
  4. Power the car’s motor with the electricity; that’s about 95% efficient.

Altogether, only about 38% of the original electricity gets used to power the vehicle. Baxter provided this chart showing the “energy vector transition,” starting with a theoretical 100 watts of clean, renewable energy:

Chart courtesy Tom Baxter/The Conversation

Electricity from Batteries

A conventional electric car powered by batteries avoids the electricity-to-hydrogen-to-electricity conversion process:

  1. Use electricity from a clean, renewable source such as a wind turbine or solar panel and send it through the electric grid to the car; transmission is about 95% efficient.
  2. Charge/discharge a lithium-ion battery; that’s about 90% efficient.
  3. Power the car’s motor with the electricity; that’s about 95% efficient.

Here’s Baxter’s chart for battery-powered electric vehicles:

Chart courtesy Tom Baxter/The Conversation

“I struggle to see how hydrogen can compete with electric vehicles,” Baxter said.

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