Emission Factors

Emission factors measure the amount of green house gasses released by a process or activity. Typically, there are individual emission factors for each green house gas, although often they are consolidated into the CO2 equivalent emission. Precise emission factors are published by many agencies. We just describe the principles. Emission factors are crucial in determining the carbon footprint of an organisation.

Emissions from Burning Fuels

The burning of most fuels produces green house gas emissions, though in different amounts. Values for CO2e vary from 204t/MWh for natural gas to 329t/MWh for use of coal in industrial processes.

Emissions from Electricity

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To generate electricity, green house gasses are produced during construction of the device or plant as well as during operation. In order to compare different technologies both components must be taken into account over the expected lifetime of the installation. The result is a value that measures the amount of CO2 emitted per kWh of electricity generated. Naturally, these values do not just depend on the conversion technology, but also on factors such as location, thus giving rise to some variation.

The electricity emission factor is the weighted average emission for a particular supplier (utility company) or country, taking into account the fuel / technology mix that is employed to generate the electricity.

Building clean energy capacity will reduce this emission factor. The exact amount, the so-called avoided emissions factor, will depend on which of the existing technologies and how much is substituted.

  Electricity Emission Factor Avoided Emission Factor  
  t CO2e / MWh t CO2e / MWh  
Oregon 0.148 0.781 Low emissions due to use of hydro
Colorado 0.913 0.900 High emission factor due to predominance of coal
Austria 0.197 0.558 Low emission factor due to hydro
UK 0.476 0.643 Balanced energy mix
Germany 0.541 0.829 Balanced energy mix
France 0.083 0.849 Ultra low emission factor due to use of nuclear energy
Peru 0.148 0.826 Low emission factor due to use of hydro
India 1.005 0.900 High emission factor due to predominance of coal

Emissions from photovoltaic cells:

Carbon Emissions from Nuclear Energy The manufacturing of solar cells is energy-intensive; the purer the silicon used the more energy is required. The CO2 emissions from that process, however, are believed to be compensated for after just one year of operation.

Emissions from nuclear energy:

There is a lot of debate about the figures, especially around processing of uranium from mining to enrichment. Additionally, fossil fuels are required for backup generators used during downtime, waste disposal and de-commissioning.



In official fuel disclosure data, however, those emissions from nuclear or renewables can be neglected and assumed to be zero.

Emission Factors for Other Activities

For many processes and activities, it is very difficult to determine exactly how much fuel is burnt. In addition, green house gas emissions do not just stem from burning fossil fuels. They are side effects of many other processes both man-made and natural. Therefore, factors have been published that convert easily observable volume of an activity to estimated emissions. We have lsited some examples:

Category Sub-Categories Observable Unit Emission Factor CO2e
Passenger Transport Size: e.g. Medium Sized Car Distance travelled in km 0.2128 kg/km
Freight Transport Weight class and load factor. E.g. 7.5 - 17t, 50% loaded Distance travelled in km 0.75 kg/km
Refrigerator / Aircondition

Type of refrigerant and type of euqipment

E.g. HFC-134 in a domestic fridge

Installation Weight of euqipment in kg 10 kg/kg
Operation Weight of equipment in kg and time of operation in years 3 kg / (kg year)
Disposal Weight of equipment in kg 8 kg/kg
Supply Chain

Various:

E.g. Paper, Hotel, pesticides, fish, computer services, education - i.e. pretty much everything

Money spent in £

Paper: 1.3 kg / £

 

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