# Explain hydrogen fuel cell efficiency to me

**URL:** <https://boards.straightdope.com/t/explain-hydrogen-fuel-cell-efficiency-to-me/815130>\
**Category:** Factual Questions\
**Created:** [May 30, 2018, 2:13pm UTC](https://boards.straightdope.com/t/explain-hydrogen-fuel-cell-efficiency-to-me/815130 "2018-05-30T14:13:50Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![bizerta](https://avatars.discourse-cdn.com/v4/letter/b/3be4f8/32.png) [@bizerta](https://boards.straightdope.com/u/bizerta)\
**Post date:** [May 30, 2018, 2:13pm UTC](https://boards.straightdope.com/t/explain-hydrogen-fuel-cell-efficiency-to-me/815130/1 "2018-05-30T14:13:50Z")

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I don’t quite understand fuel cells, but the net result is energy and water. On source states,

> [@](#):
>
> The energy efficiency of a fuel cell is generally between 40–60%; however, if waste heat is captured in a cogeneration scheme, efficiencies up to 85% can be obtained.

OK. So how much more efficient is this than simply using the H in an internal combustion engine where the output is the same. If more energy is wasted in an internal combustion engine, where does the energy go? More waste heat?

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**Author:** ![engineer\_comp\_geek](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/engineer_comp_geek/32/504_2.png) [@engineer\_comp\_geek](https://boards.straightdope.com/u/engineer_comp_geek)\
**Post date:** [May 30, 2018, 2:23pm UTC](https://boards.straightdope.com/t/explain-hydrogen-fuel-cell-efficiency-to-me/815130/2 "2018-05-30T14:23:29Z")

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An internal combustion engine typically converts somewhere between 25% to 35% or so of the total energy into motion. The rest gets wasted as heat.

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**Author:** ![am77494](https://avatars.discourse-cdn.com/v4/letter/a/d2c977/32.png) [@am77494](https://boards.straightdope.com/u/am77494)\
**Post date:** [May 31, 2018, 6:10am UTC](https://boards.straightdope.com/t/explain-hydrogen-fuel-cell-efficiency-to-me/815130/3 "2018-05-31T06:10:52Z")

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> [@bizerta](#):
>
> I don’t quite understand fuel cells, but the net result is energy and water. On source states, OK. So how much more efficient is this than simply using the H in an internal combustion engine where the output is the same. If more energy is wasted in an internal combustion engine, where does the energy go? More waste heat?

This is a very complicated question and the answer is very nuanced. For example :

1. It takes very little energy to refine oil to gasoline and then transport it to cars. It takes a lot of energy to convert oil into Hydrogen and then transport the resulting hydrogen to cars. So when reporting efficiency from your quote, they are only comparing the efficiency of the hydrogen going into the fuel cell versus the energy out which doesn’t show the whole picture. A better measure is the well to wheel efficiency.

2. Hydrogen in an internal combustion engine could give you much higher efficiency than gasoline. This is simply because Hydrogen burns hotter. However, higher temperatures mean that the Nitrogen in air will also “burn” making NOx emissions. You can overcome this by using pure oxygen mixed with another inert like CO2 but purifying oxygen takes energy and so you introduce a new variable.

3. Fuel cells are old news. They didn’t deliver the promise they made. I know many former fuel cell researchers who work on Oil and Gas now. Sure there are some niche applications but in general fuel cell based energy is about the same as woo.