Capacity data is sourced from the “Global Coal Plant Tracker” by Global Energy Monitor, version January 2019
To estimate the CO2 emissions from the existing and planned coal-fired capacity, we use the following formula:
\[ AnnualCO_2 (Mt) = capacity × capacity factor × heat rate × emission factor × Φ \] where Φ represents a unit conversion factor (3.97347 x 10-9) which basically represents 8760 hours per year (to calculate the annual electricity output) divided by 2202.31 lb/tonne (to calculate the emissions in the standard tonnes unit).
The capacity describes the amount of power a plant can produce and is measured in Megawatt (MW). For each plant in the database, the capacity is given, ranging from 0 to 8000 MW. Information on the capacity is obtained from the Global Coal Plant Tracker database. Additional information used to classify the units include the current status of the plant (‘Operating’, ‘Under construction’, ‘Planned’ and ‘Announced’) and the combustion technology used (‘Supercritical’, ‘Ultra supercritical’, ‘Subcritical’). For more information on the difference between the different combustion technologies read this article.
To convert the capacity into the energy generated by the unit, we multiply the capacity with the capacity factor and the number of hours in the year (8760). This represents the energy generated by the unit in a year. For the purpose of our analysis, we make a distinction between the capacity factors of hard coal and lignite units. We use capacity factors derived from the Current Policies Scenario from the World Energy Outlook (IEA, 2018).
The heat rate describes how efficiently a plant converts energy from coal into electricity and it is usually expressed as the amount of energy used by a power plant to generate one kilowatt hour (kWh) of electricity. This rate is derived by comparing the quantity of energy contained in coal as it enters the plant site to the quantity of energy contained in the electricity that exits the plant side into the grid. The heat rate in our analysis depends on factors like the type of combustion technology, the type of coal and the size of the plant (Sargent & Lundy, 2009).
The emissions factor refers to the average amount of CO2 emissions resulting of burning coal to produce a certain quantity of energy. For our analysis, we use emissions factors based on the International Energy Agency (B.D. Hong and E. R. Slatick, 1994) for the different type of coal that are used in each power plant included in the Global Coal Plant Tracker database:
Based on the formula above we calculate the emissions on a per plant basis, which are then aggregated at a regional or country level and distinguished by their status, taking into account the plants that are either operating, retired, deactivated, under construction, planned or announced.
Moreover, in order to calculate the emissions for each plant, due to some missing information in the GCPT database regarding retirement date, type of fuel, etc. for some power plants we made the following assumptions:
Information on the type of coal burned in the power plant was missing for a considerable part of the planned coal plants. In order not to bias the estimates artificially assigning a too high or too low emissions factor to the plant with missing fuel information we assigned an average emissions factor to those plants, namely (0.0911 kg CO2/MJ), which is the emission factor of subbituminous coal.
For power plants that do not have a commissioning date in the database, calculate the country average opening years by status. Where this information is not available, we use the average value over the region. The following boundary conditions are imposed: for plants under construction we assume the year of commissioning is 2019; for planned power plants (including permitted, pre-permitted plants) foreseeing a 2-year time, i.e. 2021, while assuming a longer 4-year period for announced plants, i.e. 2023.
Additionally, we assume the observed global mean average lifetime of 40 years to be the best estimate of the future observed lifetime of power plants.
Finally, in order to build emissions pathways for the regions in the following decades, we calculated the expected retirement dates of operating power plants by adding the assumed average lifetime (40 years) to the opening year of those plants. However, consistency checks have been done afterwards. If this assumption leads to earlier retirement of currently operating power plants, we applied the following rule to adapt the estimated year of retirement: taking into account that all these power plants were supposed to be retired a while ago we assume they will be online for another 5 years but not beyond that.