One fuel is not like another - at least when it comes to carbon dioxide emissions. Burning lignite, for example, produces around twice as much carbon dioxide in relation to its energy content as burning natural gas. Natural fuels such as peat and wood also have very high specific emissions if they are not used sustainably. Deforestation therefore has a doubly negative effect on the climate. If the amount of wood burned is limited to the amount that can be regrown, its use is neutral, since wood binds just as much carbon dioxide from the atmosphere as is later released during combustion.
If the fuels are used to generate electricity, carbon dioxide emissions increase opposite proportional with the Power plant efficiency. The worse the efficiency of electricity generation, the greater the electricity-specific emissions. For example, if lignite from "Lausitz"-region is burned in a power plant with an efficiency of 35 %, 1,17 kg of carbon dioxide is produced per kilowatt hour of electrical energy (kWhel). In a natural gas combined cycle power plant with an efficiency of 60 %, as another example, only 0,33 kg of carbon dioxide is emitted per kWhel.
Replacing lignite-fired electricity with electricity from natural gas can therefore save over 70% of the direct carbon dioxide emissions. In order to properly understand this benefit, the upstream chain emissions and the resulting greenhouse effect must also be taken into account.
Methane, as the main component of natural gas, has a particularly high global warming potential (GWP100= 25 to 28; IPCC WG1AR5, s.714). The transport leaks have a high impact on the total GWP of the Natural Gas based power supply and therefore must be considered. Independent surveys of current methane emissions from gas production, transport and use are not yet available for Germany. The following calculation serves as an illustration of the greenhouse effect of natural gas in electricity production, including fugitive methane emissions.
For long-term climate protection, only emission-free energy supply, based on renewable energies and sustainably biomass is an alternative. By getting out of natural gas-fired power generation, it is possible to stop the methane leakage emissions and therefore reduce the global warming potential.
[kg CO2 / GJ]
|... Central Germany||104,0|
|Liquid petroleum gas||63,1|
*) not sustainable use without reforestation
Source: Fachbuch Regenerative Energiesysteme and UBA
|Fuel||Power Plant Efficiency|
|CO2 Emissions 1) |
[g CO2 / kWhel.]
|->New turbine KW||39.2||619|
|->New construction CCGT||59||411|
Total Greenhouse Effect
Direct 2) + Fugitive Emissions 3)
|CO2 Emissions |
[g CO2-eq. / kWhel.]
|-> 1 % methane leakage||(100+25) % . 204 g/kWhel. =||503|
|-> 2 % methane leakage||(100+50) % . 204 g/kWhel. =||603|
|-> 3 % methane leakage||(100+75) % . 204 g/kWhel. =||704|
* Mean net electrical efficiency (UBA 2017)
** Mean gross electrical efficiency (UBA 2019)
1) Own calculation from "CO2 emission factor including upstream chain emissions" (UBA 2019, p.43) / "power plant efficiency"
2) Own calculation of direct CO2 emission factor for natural gas: 201 gCO2/kWhPE (excluding upstream chain emissions); assumption for net electrical efficiency = 50%: (201 g/kWhPE ) / 0.5 = 402 g/kWhel.
3) Own calculation of fugitive emissions: The release of 1% of the amount of methane needed for 1 kWh of electricity (145 g/kWhel. at 50% efficiency) corresponds to CO2eq. of 36 grams at GWP = 25.