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>> The “dirty electricity” angle is less obvious to me.

A power plant typically gets about 60% of energy from a fossil source. A car does about 30%. So even if the electricity comes from say coal, it's still more efficient than buying gas in a car engine.

Of course, these days, it's likely that a substantial portion (up to 100% in some cases) is not "fossil electricity" but rather comes from solar, wind, hydro etc. Ie "clean" electricity.



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60% efficiency? How do these power plants manage to circumvent the limit set by Carnot efficiency?


They don’t. they capture the waste heat from the gas turbine and use it to make steam to spin another turbine. A gas turbine is ~40% efficient, add in a HRSG to make a combined cycle plant and you can get up to ~60%. You don’t even need a gas turbine to use a HRSG, any exhaust stream with enough heat will work, a boiler plant or similar.

https://en.wikipedia.org/wiki/Heat_recovery_steam_generator

https://en.wikipedia.org/wiki/Combined-cycle_power_plant


Natural gas burns at ~2200 K. Ambient temperature is ~300 K. 1 - 300/2200 = 86% as the Carnot limit?


Coal burns dirtier and and is more Co2 intense than gas though.




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