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Comment by alexeldeib | Hacker News Reader

re: waste heat, I've been thinking forever that someone must capture this. I've generally assumed the economics don't work out or no one has cracked it outside of scenarios like regenerative braking. We waste so much energy that we could capture and put back to use.

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Regen braking doesn’t use waste heat. It converts mechanical energy back to electrical.

And in so doing, reduces waste heat due to friction, which is likely what the parent commenter meant.

Some say it doubles the lifespan of brake pads.

> We waste so much energy that we could capture and put back to use.

The biggest current waste of energy is residential heating. We take high quality energy in the form of natural gas and fuel oil and use it to produce low quality heat.

Co-gen systems burn fuel to generate electricity and use the waste heat for heating buildings.

Something like 55-60% of the thermal energy created by burning fossil fuels is currently wasted.

It’s kind of ironic that cars and power plants work hard on getting rid of that energy.

Modern power plants work hard at getting every last bit of that energy before it escapes. Current Combined Cycle plants, that generate steam from the exhaust of a gas turbine, are currently getting over 60% efficiency.

One must be a bit careful there. 60% efficiency based on the LOWER heating value of natural gas. That ignores the heat available from condensing the water of combustion. Coal plants typically use the higher heating value when computing efficiency, which does reflect the latent heat of vaporization of that water.

I know ICE engines use turbochargers to "recapture" the energy. Exhaust can be used to power the intake fan, which can increase air-pressure available to the engine's intake.

Turbocharged engined still need a ton of cooling but yes I think they are more efficient overall .

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