A Claverton Group Think Tank Member Discusses the Real Efficiency of a CCGT

“55% efficient CCGTs” (David Olivier)

 – no such thing.  The headline efficiencies cited now are 58% but they
deliberately play a marketing trick in pretending that the latent heat
of vaporisation in the wettish steam within the OCGT exhaust that is
finally vented to atmosphere after passing through the heat exchanger is
somehow doing useful “work”.

In terms of a real efficiency in terms of real MWh out of the power
station as electricity as a proportion of the energy content within the
source fuel at its delivered temperature, the correct figure is an ideal
efficiency of 52% but the industry for the purpose of its “spark spread”
calculations works to a figure of 49.13% for a real best of breed new
CCGT at high but not pure base-load figure.  Most of the reason that is
not 58% is not the fact that it is not operating at pure base load, is
the marketing trick I mentioned also known as the LHV/HHV trick.

Pure base load,  so start up amortised over infinitely long period of
max flat out running, in nice cold weather without gusting, you’d get
52%.

People used to use 48% real efficiency (NB some of the earliest CCGTs
like Roosecote and Teesside were well below that, I think more like 44%
real) which (48%) you will find is implicit in the rule-of-thumb in
circulation about 8 years ago that you take the gas price in p/th and
divide by 1.43 to “net back” to a leccy cost in £/MWh (ignoring cost of
carbon).

If you don’t believe me, just google “49.13% ccgt” – it is the new
industry reference efficiency for a new CCGT in good nick, and was
updated from 48% some 4 years back.

Incidentally a friend of mine happened to tag on as an extra visitor to
a visit that was primarily by by the Shadow Climate Change Committee
(CCC) before it was properly constituted, to a certain CCGT to the East
of London where the manager giving the talk proudly cited 56%
efficiency.  My friend piped up “you’re playing the LHV/HHV trick, your
real efficiency is more like 50%” and he said “all right, it’s a fair
cop, most people don’t know that”.

However if you account for the energy used in the liquefaction train in
particular, and take account of the fuel route, it’s way worse. To put
it another way, the CO2 from a CCGT in splendid isolation is 360 grammes
of CO2 per kWh, for a CCGT running on North Sea gas it is 440 (there is
up to 8% CO2 co-associated with the methane and upon separation, the oil
and gas firms lazily vent the purified CO2 to the atmosphere !! – and
there is energy used in the purification of the gas, its compression
onto the NTS and along the NTS in its transmission by what used to be
OCGT compressors, RB211’s, now they are being electrified), but for
CCGTs running on LNG the all-up figure is a whopping 50% higher at 660 g
CO2 per kWh, and for CCGTs running on gas that ultimately comes from
Russia by pipe (8% methane leakage within the Russian gas grid) it’s 690
g CO2 per kWh.  Those data are on the friends of the earth website as
well as having been disemminated by DGTREN and ultimately come from the
CONCAWE and other studies.  Find more at www.fuellers.co.uk – energy
review response. Now you can notionally speak of a CCGT efficiency in
relation to the SOURCE methane in Q’atar of only 30% or so….
rubbish !!!!  NB UK authorities ignore this and mandate the use of the
440 figure for CCGTs for ETS Carbon accounting purposes.  Just like they
ignore the CO2 equivalence altitude multiplier (of x3) for aviation,
after all we wouldn’t want the UK’s effective real CO2 contribution to
not be grossly understated, would be ?

Paul

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