CARBON SAVINGS FROM RENEWABLE ENERGY
There is confusion in Government documents over
the carbon savings which will be realised if the 10 per cent target
for electricity from renewable energy sources is met. Table 1,
below, shows the various estimates in recent DETR and DTI consultation
documents. The latest estimates are only one-third of the initial
It is vital that these savings are accurately
quantified, as it will affect the value of any carbon credits
traded in the future. As the carbon savings ascribed to renewable
sources now seem to be extremely low, any monetary credits derived
from renewable energy sources in the UK may have an artificially
CARBON SAVINGS FROM RENEWABLESPUBLISHED
|DETR:UK climate change programme: consultation paper, October 1998
||5.4 ||"in addition to those expected to be realised from NFFO arrangements already in train"
|DTI: New and renewable energy, March 99
||3.5 to 5.4 ||"above that from existing programmes"
|DTI: New and renewable energy: conclusions, January 2000
||2.6 to 3.0 ||"an additional 2.6 to 3 MtC"
|DETR : Climate change: UK programme. ||2.5
As the reference date for carbon emissions under the Kyoto
protocol is 1990, it makes sense to refer all data to this starting
point. The first DETR consultation paper did so and suggested
that the "arrangements already in train" would account
for 2 million tonnes of carbon (MtC). So the total savings from
the 10 per cent renewable target would be (5.4+2), i.e. 7.4 MtC.
In the latest DETR document that this has been scaled down to
2.5 MtC, without any explanation.
The emissions of greenhouse gases saved by switching electricity
generation to renewables depend on which fossil fuel is displaced.
In the day-to-day running of the UK power system it is coal plant
which is taken off load when additional "base load"
plant such as nuclear or renewables start to generate. All the
nuclear and most of the gas plant has baseload status, and so
their operation is unaffected by the introduction of renewables.
This point is clearly demonstrated in data published by The National
Grid Company which describes the make-up of plant on the system
at various times.
The nuclear and CCGT plant operates continuously throughout the
day and the output of the coal plant is changed to meet changes
In the medium-term, there is another issue to consider: whether
the introduction of new renewable plant will inhibit the construction
of new gas plant or force the closure of nuclear plant. Both scenarios
are highly unlikely. The nuclear closure programme has already
been announced and the closures are likely to be delayed rather
than brought forward. It is also extremely unlikely that construction
of any gas plant will be delayed, as the government found it necessary
to introduce the stricter consent regime (just lifted). It
follows that the introduction of any new plant, including renewables
will accelerate the closure of old coal plant. This reasoning
is reflected in the latest DTI estimates of emissions from power
A report to the House of Commons Energy Committee in 1988
used similar reasoning.
The CEGB suggested carbon dioxide savings from renewables would
lie between 867 and 1000g/kWh by 2005. The corresponding emissions
per unit of electricity, based on the average plant mix, were
620g/kWh. The important point is that emissions based on the average
plant mix were not used to derive the savings attributable to
renewables. A 1994 DTI fact sheet used similar reasoning. Emission
savings elsewhere in Europe (and in America) are calculated in
the same way, unless oil, rather than coal, is the displaced fuel.
A 10 per cent contribution from renewable energy to electricity
supplies corresponds to 38 TWh/yr in 2010, given the expected
rise of electricity consumption. As the UK's large Hydro plant
was operating in 1990 (the baseline year for carbon emissions),
its output must be subtracted. Average output over the last nine
years has been 4.5 TWh, so 10 per cent of renewables will save
emissions corresponding to (38-4.5) = 33.5 TWh of electricity
Each kWh of renewable energy displaces electricity generated
by coal-fired plant and the corresponding emissions are 862
grams of CO2, or 235 grams of carbon. So the carbon
savings associated with 10 per cent of renewable energy are simply
33.5 TWh multiplied by the savings per unit, which gives about
7.9 million tons of carbon (MtC). The figure in a recent House
of Lords report is
slightly lower at 7.6 MtC, but these estimates are broadly consistent
with the figure of 7.4 MtC in the first DETR document.
THE DTI AND
The Government response to the House of Lords Report
did not seek to justify the DTI figures on carbon savings, but
simply argued "it is a complex subject in which there are
no definitive answers". It did, however, reiterate that the
upper bound of carbon savings for 10 per cent RE (above savings
from 5 per cent RE) was 5.4 MtC. As recently as December 1999,
therefore, there was still implicit confirmation that the upper
bound was still 7.4 MtC of savings, relative to 1990 levels.
The DTI/DETR position does not appear to be explained further.
The supporting analysis
to the DTI Renewable Energy consultation document of 1999 proposed
three scenarios for assessing the range of carbon savings:
"Renewables displace combined cycle gas turbines;"
"Renewables displace modern coal plant";
"Renewables displace the current generating
The analysis suggested that the first scenario was unlikely
in practice, but did not comment on the scenarios further. Nor
were the underlying calculations of the carbon savings provided.
An additional anomaly appeared in the Draft Climate Change document,
which suggests nuclear saves 12 to 24 MtC per year. This is inconsistent
with the renewable savings, as it suggests carbon savings from
nuclearper unit of electricitymay be over three
times those of renewables. It is difficult to envisage a technical
basis for this difference.
All the available evidence (including information from government
sources) points to the carbon savings from delivering the 10 per
cent renewable energy target being in the range 7.4 to 7.9 MtC/yr.
The latest DETR figures (which comes with no proper explanation
or qualifications) of 2.5 MtC/yr are far too low.
24 January 2001
National Grid Company plc. 1999 Seven Year Statement. Back
DTI, 2000. Energy projections for the UK. Energy Paper 68. Back
House of Commons Energy Committee, 1988. Energy Policy and the
Greenhouse Effect. Memorandum submitted by the CEGB. Back
This figure has been derived from National Power's Environmental
Performance Review for 1999. It is a weighted average, taking
data from all the coal plant. Back
House of Lords: Select Committee on the European Communities,
1999. Electricity from Renewables. HL78-1. Back
House of Lords: Select Committee on the European Communities.
Electricity from Renewables: further documents. HL Paper 18, December
New and renewable energy: Prospects for the 21st century; supporting