<![CDATA[Grist - Comment Feed for Coal the culprit in rising emissions intensity]]> Grist Comment Feed en Comment #1 by EcoJane http://www.grist.org/article/coal-the-culprit-in-rising-emissions-intensity/ Wed, 22 Apr 2009 12:51:24 -0700 http://www.grist.org/article/coal-the-culprit-in-rising-emissions-intensity/1 The other issue here is that the first plants to get "turned off" when we use less electricity are the natural gas peakers.  Since natural gas has less CO2 per kWh than coal the CO2 intensity of the mix can go up when we use less electricity even if we aren't using any more coal.  Intensity is an interesting measure, but it doesn't tell the whole story.

]]> The other issue here is that the first plants to get "turned off" when we use less electricity are the natural gas peakers.  Since natural gas has less CO2 per kWh than coal the CO2 intensity of the mix can go up when we use less electricity even if we aren't using any more coal.  Intensity is an interesting measure, but it doesn't tell the whole story.

]]> Comment #2 by garyshu http://www.grist.org/article/coal-the-culprit-in-rising-emissions-intensity/ Thu, 23 Apr 2009 06:15:19 -0700 http://www.grist.org/article/coal-the-culprit-in-rising-emissions-intensity/2 Whoa there, careful with the data interpreations...

RE: "...for at least one individual coal plant, CO2 emissions per megawatt-hour inched up (bottom graph) when the plant was run at 50 percent capacity (top graph). If that’s a common problem, then it might suggest that it would be better to shut one coal plant down entirely, rather than turning several plants down a bit.  The reality might be more complicated, and the economics hard to figure out.."

Hard to figure out?  Not really.  In deregulated markets with each plant bidding in their offer curves (i.e. supply curve, for those of the economics persuasion) to an system operator dispatch, if you have a carbon price, this would adjust the curvature of their bids and the dispatch would take care of the rest.

RE: "One possible interpretation: coal remained much cheaper than natural gas last year, so when electricity demand declined, power producers turned down the gas more than they ramped down coal."

There's a couple of ambiguities here that EcoJane hints.  Coal indeed remained cheaper than gas, but it's electricity from coal and electricity from natural gas we're comparing.  And that's almost always true.  Coal usually doesn't get ramped down - that's why it's baseload.  It needs to stay hot and fired to be efficient.

Finally, looking at one plant is especially bad: sample size of one, anybody?  There could be a number of reasons why its capacity factor turned down and its intensity went up from poor quality coal shipped in to needed maintainence.  How else can you explain that the Amos' coal plant capacity factor went down while the overall share of electricity from coal went up at the same time?

]]> Whoa there, careful with the data interpreations...

RE: "...for at least one individual coal plant, CO2 emissions per megawatt-hour inched up (bottom graph) when the plant was run at 50 percent capacity (top graph). If that’s a common problem, then it might suggest that it would be better to shut one coal plant down entirely, rather than turning several plants down a bit.  The reality might be more complicated, and the economics hard to figure out.."

Hard to figure out?  Not really.  In deregulated markets with each plant bidding in their offer curves (i.e. supply curve, for those of the economics persuasion) to an system operator dispatch, if you have a carbon price, this would adjust the curvature of their bids and the dispatch would take care of the rest.

RE: "One possible interpretation: coal remained much cheaper than natural gas last year, so when electricity demand declined, power producers turned down the gas more than they ramped down coal."

There's a couple of ambiguities here that EcoJane hints.  Coal indeed remained cheaper than gas, but it's electricity from coal and electricity from natural gas we're comparing.  And that's almost always true.  Coal usually doesn't get ramped down - that's why it's baseload.  It needs to stay hot and fired to be efficient.

Finally, looking at one plant is especially bad: sample size of one, anybody?  There could be a number of reasons why its capacity factor turned down and its intensity went up from poor quality coal shipped in to needed maintainence.  How else can you explain that the Amos' coal plant capacity factor went down while the overall share of electricity from coal went up at the same time?

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