Thursday, June 6, 2013

Gas, Coal, and Climate Change: Reports

A new report has been released by the Center for Climate and Energy Solutions (successor of the Pew Center on Global Climate Change): Leveraging Natural Gas to Reduce Greenhouse Gas Emissions.  On one blog I follow, John Hanger enthusiastically endorses the report with "two thumbs up."  After noting the strength of the report's section on methane leakage, Hanger states:
The report further points out that gas cuts carbon emissions, when it displaces coal, or oil but does not do so were it to displace nuclear or renewables.
There is a perception in the United States that because wind, solar and natural gas generation have grown over the past years while coal generation has contracted, renewables and natural gas are a tandem replacing coal.

This is not as firm a proposition as it appears.

A new report, originating in Belgium, makes the proposition look particularly suspect: Impact of the German nuclear phase-out on Europe's electricity generation - A Comprehensive Study.  

Skimming the illustrations I was struck by a graphic demonstrating the exceptional peaking depth of lignite based generation (in the graphic, the solid colouring indicates the minimum output when generators are operating, with the shaded area presents the remaining capability - which I refer to as peaking depth).

In Germany they have had to find a way to avoid the shuttering of some of the newest combined cycle gas turbine (CCGT) facilities while:
Germany is building new ultrasupercritical coal plants designed to ramp up and down at 30 MW/minute and 500 MW within 15 minutes and shutting down older, less-efficient, and less-nimble plants In other words, Germany’s new coal fleet is designed to operate in a symbiotic relationship with renewables. In the U.S., the choices are presented as renewables or coal. As in Germany, the better choice is renewables and coal.   - Coal Power
There are other factors at work in both the United States (low natural gas prices) and Europe (the market merit order and high gas prices) - but the idea that natural gas and renewables are characteristically ideal replacements for coal is highly suspect.

Increasingly there is a recognition that renewables may be better matched with new coal-fired generation than any other generating source except for reservoir hydro (as Don Jones has been communicating for some time).  The Centre for Climate and Energy Policy may see a role for natural gas so long as it doesn't displace nuclear and renewables, but that wish isn't impactful.  Gas replacing coal reduces emissions by about the same amount as renewables replacing gas (as they did in Europe during 2012).

Renewables displace any baseload source, and replacing a baseload coal plant with a baseload nuclear plant results in greater reduction in emissions than the renewables/gas strategy.

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