This is part III of a blog series - A Primer on 2006 IPCC Guidelines for Emission Inventories. 

Introduction

The energy sector accounts for the largest share of emissions across the globe and is therefore one of the most important sectors in the emission inventory. The combustion of fossil fuels primarily causes release of carbon dioxide (CO2), along with other gases like methane and nitrous oxide. Fugitive emissions from fossil fuel mining/refining also cause a release in these emissions. While burning fossil fuel, stationary combustion activities like electricity & heat generation or manufacturing industries play a major role in emissions. Mobile combustion activities including various modes of transportation form the second highest GHG emitting sub-sectors. IPCC also includes carbon dioxide transport and storage as a possible source of emissions. 

Emission sources

IPCC divides emissions from the energy sector into three main categories; (1) Fuel combustion activities, (2) Fugitive emissions from fuels, (3) Carbon dioxide storage and transport. 

Fuel combustion activities

IPCC describes fuel combustion as ‘the intentional oxidation of materials within an apparatus that is designed to provide heat or mechanical work to a process, or for use away from the apparatus’. 

In simpler terms, any activity that uses fuels for heat or energy purposes is called combustion of fuel and is a potential source of emissions. In this case, fossil fuel combustion causes the release of gases like CO2 and CH4. These activities include heat and electricity generation, transportation activities, residential energy usage or use of fossil fuels in manufacturing industries. 

Electricity generation is one of the highest GHG emitting sources and a major contributor to climate change for most countries. If fossil fuels form a significant part of the energy mix, it is important to calculate the emissions from each of these sources. It is also important to note that fossil fuel can be used in industrial processes for non-energy purposes as well. It is therefore necessary to ensure that double counting is avoided. 

Apart from this, the transport sector forms an important source of emissions. All the modes of transport such as aviation, road transport, railways and water borne navigation are included under this sub-sector. Emissions from international aviation can be controversial due to multiple countries being involved. IPCC clearly states that ‘Parties to the UNFCCC have not made a final decision yet on the allocation to national GHG inventories of emissions from fuels used for international aviation and from international marine bunkers. For the moment, all emissions from these fuels are to be excluded from national totals, and are to be reported separately’ 

Fugitive Emissions from fuels

This category includes all the GHG emissions that occur during the extraction, processing or handling of fuels (coal, natural gas, petroleum etc). A good example for such emissions is the release of methane gas during coal mining. Fugitive emissions form a small portion of the total emissions inventory except in cases where the production and handling of fossil fuels is in significant quantities.

Carbon dioxide storage and use

The 2006 IPCC guidelines have introduced carbon dioxide storage and use as a part of the emissions inventory. The technology includes capturing of carbon dioxide gas, usually from large scale point sources like power plants or industries. This captured gas may either be compressed and transported to other sites or may be injected deep into the earth. 

It would be beneficial to understand the effect of this technology on reducing carbon dioxide emissions and the resultant reduction in total emissions. This technology is not very prevalent, though it has gained some impetus in recent years. 

Data collection, consistency and uncertainties

The activity data for the energy sector is the amount of the fuel consumed for combustion. In order to ensure consistency and comparability in data, it is important to ensure the type of fuel is clearly defined. IPCC has provided a list of fuel types based on the definitions given by the International Energy Agency (IEA). On similar lines, to ensure the comparability of data, the units should be expressed consistently in Joules. Since most of the fuel amount is expressed in tonnes or cubic metres, it has to be converted to Joules using the net calorific value (NCV). 

Challenges with double counting

There are certain fuels which have the potential to be double counted in other sectors as well. IPCC has provided clarification on all those fuels to avoid the issue with double counting. 

Biomass

Under the energy sector, there is a provision for biomass burning to be counted as an emission source. However, since biomass burning is usually a very informal residential or agricultural activity, it becomes a challenge to collect data for this activity. Volume four of the IPCC guidelines (AFOLU sector) provides an alternative method to calculate emissions from fuelwood consumption. 

Waste

When waste is burned without consuming the heat as an energy source, then such emissions are considered under the waste sector. However, if waste is incinerated and the resultant heat is utilised as an energy source, then such emissions are calculated under the energy sector. 

Non-energy use of fuels

In certain cases, fossil fuels are used for non-energy purposes like solvents, feedstock or solvents in industrial processes. In such cases, the emissions occurring from these activities are calculated under the IPPU sector. In case the fossil fuel is burned for heat or power generation, the resultant emissions are counted under the energy sector. 

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