Carbon Intensity of Balancing Actions

The carbon intensity of balancing actions measures the difference between the carbon intensity of the combined Final Physical Notice (FPN) of machines in the Balancing Mechanism (BM) and the equivalent profile with balancing actions applied.<br/>

Publicly Available 
 
1 
Authors: Fraser MacMillan 
Issue: April 2021 
Introduction 
The carbon intensity of balancing actions 
measures the difference between the carbon 
intensity of the combined Final Physical Notice 
(FPN) of machines in the Balancing Mechanism 
(BM) and the equivalent profile with balancing 
actions applied. 
This report details the methodology behind the 
calculating the carbon intensity estimates. For 
more information about the Carbon Intensity visit 
here [1]. 
 
What is and is not included 
The metric looks specifically at dispatchable 
machines in the BM. It uses the Bid Offer 
Acceptance (BOA) data to track balancing actions 
and contrast it with the unit’s submitted FPN. Solar 
data is also considered, data is collected from 
Sheffield Solar found here.  
This metric does not include the balancing actions 
of interconnectors or small BMUs. Interconnectors 
are connected to two energy systems and 
therefore NGESO is not wholly responsible for 
control actions. Interconnectors also do not receive 
instructions via BOAs. 
It is important to note that the NGESO control 
room does not make dispatch decisions on the 
carbon intensity of BMUs. The remit is to balance 
the system and maintain system security in the 
most economically way possible. 
 
Methodology 
The methodology behind the carbon intensity of 
balancing actions is relatively straightforward. 
Each Balancing Mechanism Unit (BMU) belongs to 
a fuel type category and each fuel type has an 
associated carbon emissions factor, with the unit 
gCO2/kWh. 
BMUs submit a FPN, which is a plan of their 
committed schedule (barring faults). The FPN 
details if a unit is planning on ramping up/down or 
staying at a fixed level. 
BOAs are balancing actions made against the 
submitted FPNs. Bids reduce the energy supplied 
by a BMU when compared to the energy that 
would have been supplied had it followed the FPN 
schedule.  Offers are the reverse, offers increase 
the energy supplied by a BMU. 
As the carbon emission factors of all BMUs are 
known, it is possible to make a comparison 
between the carbon intensity had all BMUs 
followed their FPNs and the carbon intensity with 
all BOAs applied. 
For example, if wind is curtailed due to a constraint 
on the network the control room will instruct the 
wind BMU down with a bid and may compensate 
by instructing a gas plant up with an offer. This will 
result in the carbon intensity of the BOA profile 
being higher than that of the FPN profile.  
It is important to note that this metric is not a 
measure of emissions but instead tracks the 
difference of carbon intensity. The carbon intensity 
𝐶𝑡 at time 𝑡 is found by weighting the carbon 
intensity 𝑐𝑔 for fuel type 𝑔 by the generation 𝑃𝑔,𝑡 of 
that fuel type, where 𝑃𝑔,𝑡 is either the FPN level or 
BOA level. This is then divided by national 
demand 𝐷𝑡 to give the carbon intensity for GB: 
𝐶𝑡=
∑
𝑃𝑔,𝑡
𝐺
𝑔=1
× 𝑐𝑔
𝐷𝑡
 
Table 1 shows the peer-reviewed carbon intensity 
factors of GB fuel types used in this methodology. 
Carbon intensity factors are based on the 
Carbon Intensity 
Balancing Actions 

 
 
 
 
Publicly Available 
 
2 
outputweight average efficiency of generation in 
GB and DUKES CO2 emission factors for fuels [4]. 
On average, the difference between the two 
profiles will not vary by a great deal. The number 
of BOAs and the volume of energy instructed will 
be small in comparison to the levels of national 
demand and generation. 
This rule of thumb may not apply when the 
national carbon intensity is approaching low levels, 
considered below 150 gCO2/kWh. Carbon intensity 
is lowest when there are high levels of nuclear, 
wind and solar generation. Under these conditions, 
the control room may need to instruct bids to 
renewable sources for network constraints and 
stability concerns. Conventional fossil types 
(gas/coal) may be required to balance the system. 
This situation is shown below in figure 1. 
Figure 1: Graph of the carbon intensity of balancing 
actions under high renewable generation conditions. 
 
Table 1: Carbon intensity factors for each fuel type and 
interconnector import [2][3]. 
Fuel Type 
Carbon Intensity 
gCO2/kWh 
Biomassi 
120 
Coal 
937 
Gas (Combined Cycle) 
394 
Gas (Open Cycle) 
651 
Hydro 
0 
Nuclear 
0 
Oil 
935 
Other 
300 
Solar 
0 
Wind 
0 
Pumped Storage 
0 
 
References 
[1] Carbon Intensity API (2017): 
www.carbonintensity.org.uk  
[2] GridCarbon (2017): www.gridcarbon.uk 
[3] Staffell, Iain (2017) “Measuring the progress 
and impacts of decarbonising British electricity”. In 
Energy Policy 102, pp. 463-475, DOI: 
10.1016/j.enpol.2016.12.037  
[4] DUKES (2017): 
www.gov.uk/government/collections/digest-of-uk-
energy-statis

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