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. --- Publicly Available Carbon Intensity Balancing Actions 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: ∑ 𝐺 𝑔=1 𝐶𝑡 = × 𝑐𝑔 𝑃𝑔,𝑡 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 1 Publicly Available 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 Biomassi Coal Carbon Intensity gCO2/kWh 120 937 Gas (Combined Cycle) 394 Gas (Open Cycle) 651 Hydro Nuclear Oil Other Solar Wind Pumped Storage 0 0 935 300 0 0 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-statistics-dukes Glossary of Terms FPN – Final Physical Notice BM – Balancing Mechanism BMU – Balancing Mechanism Unit BOA – Bid Offer Acceptance NGESO – National Grid Electricity System Operator 2