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FCs don't operate via the carnot cycle so in theory can be 90+% efficient in electricity generation. in practice, 35-50% electrical efficiency is possible (alt
by jgamman 12y ago
FCs don't operate via the carnot cycle so in theory can be 90+% efficient in electricity generation. in practice, 35-50% electrical efficiency is possible (although this isn't a ceiling, just a current tech benchmark). coal fired is 25-30% and gas fired 30-40% ish - i think the carnot efficiency maxes out somwhere 40-50% so no matter what you do (and we've been doing this for 100 years now) you aren't going to get 60+% electrical efficiency from burning stuff to drive a turbine. the FC remainder is thermal and in the situation of a combined heat and power unit, this is very useful as a lot of energy is just used for space heating - why waste high grade electrons if you've got some waste heat kicking around anyway. from the users perspective, 50% electrical and 50% thermal is getting close to an ideal 'efficiency' for actual use. i used to work on these systems in the late 90s and there's nothing new here. the dream of having a complicated steam reforming unit coupled to a Faraday device that is expected to run like a fridge with zero user maintenance for 3-5 years at a time is tremendously difficult.
- hatbert 12y ago> FCs don't operate via the carnot cycle so in theory can be 90+% efficient in electricity generation. Sorry, this is wrong. FCs are not heat engines, so the thermodynamic limitations of heat engines are not relevant to fuel cells. That said, thermodynamic limitations do set an upper bound on the efficiency of fuel cells. For hydrogen fuel cells, the theoretical upper bound is 83% [1]. That's for just the process of turning hydrogen into electricity, and that does not include the process for producing hydrogen in the first place. "90+%" efficiency is strictly impossible in theory or practice. > i think the carnot efficiency maxes out somwhere 40-50% so no matter what you do (and we've been doing this for 100 years now) It must be noted that 50% thermal efficiency is a practical upper bound for a real electrical power plant, not a theoretical one. Some combined-cycle gas turbines do exceed 50% efficiency under some operating conditions. [1] http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/electrol.html http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/electrol.h...