Different energy sources (such as coal, gas, oil/petroleum, nuclear, solar, wind & others) have different greenhouse gas footprints when used for electricity generation.
Below, we outline these greenhouse gas footprints across different metrics, and summarise which energy source may emit the most, and also the least.
This guide may complement our separate guide on the fossil fuels that emit the most CO2 and greenhouse gases.
Summary – Carbon Footprint Of Energy Sources & Electricity
Energy Sources Used For Electricity Generation vs Other Uses
Energy sources can be used for a range of different uses
Heating and also as fuels for transport are two examples
But, this guide specifically focuses on the use of energy sources for electricity generation
Important Of Understand Emissions For Different Energy Sources In Electricity Generation
This is important because electricity generation is one of the leading emitting industries globally
In General, Which Energy Sources Emit The Most For Electricity Generation?
Across the metrics listed below, fossil fuels might generally emit the most per unit of electricity generated
Coal in particular might emit the most across several metrics, which is followed by oil, and then natural gas
Even when taking into account lifecycle emissions for stages other than just the power plant or electricity generation stage, renewables and nuclear might emit less than fossil fuels
When taking into account changes in energy technology in the future, hydro and bioenergy may have potential to emit more emissions
Most Emissions At The Electricity Generation Stage Only
Per kWh of electricity generated at the electricity generation stage only, coal might be the largest emitter, with natural gas in second
Renewables and nuclear may emit little to no emissions
One report indicates that wind and nuclear energy may emit less than solar
Difference In Emissions During The Electricity Generation Stage Only vs Lifecycle Emissions (Of All Stages)
We outline the difference between these metrics of emissions in the guide below
Most Emissions When Including Other Lifecycle Stages (Other Than Just The Electricity Generation Stage)
When including other lifecycle stages in addition to the electricity generation stage, the results don’t appear to change much
Coal may be the largest emitter again, followed by oil fired electricity generation, and then natural gas
Geothermal might fall far behind them (emitting very little emissions)
Renewables and nuclear might emit the least, although one report indicates that solar emits more than nuclear and wind specifically
There may be some exceptions with the emissions of renewables
There’s also other comments and qualifications we make about individual energy sources and their lifecycle emissions in the guide below
Most Emissions Including Other Lifecycle Stages, But Adjusting For Future Energy Technology Improvements
When adjusting for future energy technology improvements up to the year 2050 across all energy sources, the emissions results may look similar again
However, two of the main differences might be:
– Hydro energy may emit much more – even more than natural gas
– Bioenergy may be the second highest emitter behind coal
Energy Source Responsible For The Most Emissions In The US
In the power sector, coal emits the most CO2 of energy source in the US by a significant margin, both in terms of total tons, and also % share of total emissions
A Note On Emissions Energy Used In From Transport
We didn’t consider emissions from energy used in transport in this guide.
If we did, petroleum based vehicle fuels (like gasoline and diesel), hydrogen fuels, and other fuels may feature prominently.
Some Asterisks’ In Relation To This Guide
Some asterisks or things we did not consider in this guide that may impact emissions and the overall sustainability of different energy sources might be:
– Variables such as the type of power plant, and the ‘clean technology’ a power plant is using can impact emissions
– The type of coal can impact emissions, mainly black vs brown coal
– Renewable energy may have to use batteries for energy storage, and these batteries may have an emissions footprint to produce and dispose of or manage as waste
– Variable renewable energy sources may have to be used in an electricity grid in conjunction with a backup fossil fuel power plant, so, these emissions should be taken into account
– Different energy sources may lose power in the transmission of energy sources to new locations, such as when being transmitted by power lines
– Efficiency of the different energy sources may be of note
It might be factored into the practical side of energy use, and also the eventual carbon footprint, because it ultimately impacts things such as resource usage and impact on the environment
– Storage of energy sources, and boil off energy losses can also lead to the loss of energy
Average Carbon Footprint Of One Kilowatt Hour Of Electricity – In The US
Before looking at the carbon footprint of the different energy sources, we thought it would be a good idea to look at what the average carbon footprint of a kilowatt hour of electricity might be as a reference and comparison point.
In the US, the average carbon footprint of a kilowatt hour of electricity might be close to a pound of CO2.
This carbon footprint though can obviously differ city to city, depending on the energy mix used.
For each kilowatt hour generated in the U.S., an average of 0.954 pounds of CO2 is released at the power plant (css.umich.edu)
Carbon Footprint Of Different Energy Sources – Electricity Generation Stage Only
The data below is for the electricity generation or power plant stage only
It doesn’t include other lifecycle stages, such as mining or production
Per kWh Of Electricity Produced
Coal might be the largest emitter per kWh of electricity generated
Natural gas might emit around half the CO2 of coal
Renewables and nuclear might emit far less than coal or natural gas – having almost no emissions
From greenbiz.com:
Coal generally … generates more greenhouse gases emissions and other pollutants than any other energy source (about 2.15 lb CO2 per kWh electricity)
Natural gas emits about half the carbon emissions of coal (about 1.22 lb CO2 per kWh electricity) …
Wind and solar energy … generate negligible carbon emissions
From css.umich.edu:
[For each kWh generated in the U.S. …]
Coal releases 2.2 pounds [of CO2e at the power plant], petroleum releases 2.0 pounds, and natural gas releases 0.9 pounds.
Nuclear, solar, wind, and hydroelectric release no CO2 when they produce electricity [but there are emissions upstream to consider]
Difference In Emissions At The Electricity Generation Stage Only vs Emissions Across All Lifecycle Stages
Emissions can be measured at the electricity generation stage only.
But, they can also be measured across the electricity generation stage, as well as other upstream and downstream lifecycle stages
– Electricity Generation Stage
An example of this is the emissions at a coal power plant.
– All Lifecycle Stages
Examples of emissions at other lifecycle stages include:
Emissions during mining (such as during the drilling for natural gas)
Emissions during production (such as the production of solar panels, wind turbines, nuclear reactors, etc. – and, this can be for the materials used, the electricity used in production, and more)
Emissions during transport (such as the transport of natural gas products in pipelines)
Emissions during decommission a power plant or reactor (such as decommissioning of a nuclear plant)
Emissions during waste management (such as managing the waste of solar panels when they reach the end of their lifetime, or managing spent nuclear fuel)
– Some Noteworthy Examples
Solar panels may not emit greenhouse gases whilst generating electricity, but may have emissions associated with the manufacture of solar PV panels
Nuclear energy may emit few emissions during electricity generation, but nuclear reactors may have emissions during construction for the cement, steel and other materials that are required
Natural gas may have emissions associated with methane leaks during both drilling, and also transporting natural gas products in pipelines
Carbon Footprint Of Different Energy Sources – Including Other Lifecycle Stages
The information below considers the emissions footprint of different energy sources for the electricity generation stage, but also the other ‘upstream’ or ‘downstream’ stages
Another way of saying that, is that it considers emissions across all lifecycle stages
CO2e Per kWh Of Electricity Generated
Coal might be the largest emitter when considering lifecycle emissions of CO2
Oil may be in second
Natural gas using certain types of gas power plants might be in third, and might produce only about half the emissions of some conventional coal power plants
Geothermal might emit far less than both coal and natural gas, and also oil
Renewables tend to feature low in terms of lifetime emissions, as well as nuclear
One report indicates that solar emits more than nuclear and wind specifically
There can be exceptions to renewables, such as the higher emissions when hydro is using pumped hydro methods (that use fossil fuels for pumping), or when accounting for methane from decaying matter in reservoirs
The wikipedia.org report in the resources list shows the life cycle CO2 equivalent from electricity supply technologies in terms of median gCO2eq/kWh
A paraphrased summary is:
[Coal (PC) topped the list in terms of the most emissions by a significant margin]
[Gas (combined cycle) was in second]
[Dedicated Biomass was in third]
[Solar PV, geothermal, hydropower, offshore wind, nuclear, onshore wind, and ocean (tidal/wave) produce the least emissions]
[One outlier was the maximum emissions hydropower can produce under some setups. One example might include when it has to use pumped hydro with fossil fuels]
From parliament.uk:
In the UK, the lifecycle carbon footprint of different energy production sources is (in terms of gCO2eq/kWh):
Conventional Coal Combustion [… results in emissions of] >1,000 gCO2eq/kWh (CO2 equivalent per kilowatt hour)
Newer gasification plants [… result in emissions of] <800gCO2eq/kWh
Oil-fired electricity generation plants [… result in emissions of] ~650gCO2eq/kWh
Current gas powered electricity generation [… results in emissions of] ~500gCO2eq/kWh)
[All of these energy sources had carbon footprints far higher than biomass (combustion), photovoltaic power systems, wave and tidal, biomass (gasification), hydro (storage), offshore wind, nuclear, hydro (run of river), and onshore wind – all in that order from most to least emissions]
From css.umich.edu:
Nuclear, solar, wind, and hydroelectric release no CO2 when they produce electricity but emissions are released during upstream production activities (e.g., solar cells, nuclear fuels, cement production).
ucsusa.org compares geothermal to both natural gas and coal:
Enhanced geothermal systems, which require energy to drill and pump water into hot rock reservoirs, have life-cycle global warming emission of approximately 0.2 pounds of carbon dioxide equivalent per kilowatt-hour
To put this into context, estimates of life-cycle global warming emissions for natural gas generated electricity are between 0.6 and 2 pounds of carbon dioxide equivalent per kilowatt-hour and estimates for coal-generated electricity are 1.4 and 3.6 pounds of carbon dioxide equivalent per kilowatt-hour
More lifecycle carbon footprint stats of different energy sources can be found in the ‘environmental impact’ wikipedia.org resource
More Information On Solar Energy
Some reports indicate that solar PV energy may be reducing it’s lifetime carbon footprint over the decades, and some of this is related to improvements in technology and efficiency of the panels.
Additionally, a panel made in factories in China might have higher emissions than panels made elsewhere because of the amount of coal energy used for electricity during production
From economist.com:
… on average [solar panels emit] … around 20 grams of carbon dioxide per kilowatt-hour of energy they produce over their lifetime (estimated as 30 years, regardless of when a panel was manufactured) [and that is] down from 400-500 grams in 1975
As more solar panels are made and technology is improved – they become more efficient
More Information On Wind Energy
Wind turbines often require steel and concrete to make.
More Information On Wind vs Nuclear vs Solar
More Information On Geothermal Energy
More Information On Nuclear Energy
Nuclear plants may have a carbon footprint for the steel and concrete required to make nuclear reactors
carbonbrief.org also notes that ‘… the centrifuges that separate nuclear fuel also rack up a big electricity bill’, and these may have a carbon footprint
Carbon Footprint Of Different Energy Sources – Future Adjusted Lifecycle
Per kWh Of Electricity Produced
Future adjusted lifecycle emissions account for improvements in technology in the future up to the year 2050 for the different energy sources
The major changes here compared to the above lifecycle emissions results that don’t consider future improvements in technology are that:
– Hydro energy may emit much more – even more than natural gas
– Bioenergy may be the second highest emitter behind coal
Coal is still the top emitter, and wind, solar and nuclear might still be very low emitters
From carbonbrief.org:
[When accounting for emissions during manufacture, construction and fuel supply, and also improvements in technology up to the year 2050, each energy source over it’s lifetime (from manufacture to disposal) has the following emission footprint (measured in CO2e per kilowatt hour of electricity generated]:
Coal – 109gCO2e/kWh (109 grammes of CO2 equivalent per kilowatt hour generated)
Bioenergy – 98gCO2e/kWh
Hydro – 97gCO2e/kWh
Gas – 78gCO2e/kWh
Solar – 6gCO2e/kWh
Wind – 4gCO2e/kWh
Nuclear – 4 grammes of CO2 equivalent
What Might Be A Potential Global CO2e kWh Target?
carbonbrief.org also notes that (paraphrased) the global average target for a 2C world in 2050 is 15gCO2e/kWh
With this in mind, most of the main energy sources above might be above this target
More Information On Solar Energy
The technology, geographic location, and amount/intensity of sunlight can impact the solar energy carbon footprint per kilowatt hour produced
From carbonbrief.org:
The best solar technology in the sunniest location has a footprint of 3gCO2/kWh, some seven times lower than the worst solar technology in the worst location (21gCO2/kWh)
Emissions Footprint Of The Main Fossil Fuels – Coal, Oil, & Natural Gas
We previously analysed the emissions footprint of the main fossil fuels in this guide.
Carbon Footprint Of Different Energy Sources In The United States
Emissions Just From Electricity Generation
In the power sector, coal emits the most CO2 of energy source in the US by a significant margin, both in terms of total tons, and also % share of total emissions
From eia.gov:
[In 2017, CO2 emissions from the U.S. electric power sector by energy source were:]
Coal – 1207 million metric tons, and 69% of total emissions
[Natural gas was second at 506 and 20%, petroleum in third at 19 and 1%, and other at 12 and 1%]
eia.gov also notes that:
… the U.S. electric power sector emitted … [about] 34% of the total U.S. energy-related CO2 emissions …
United States Energy Mix – Energy Source % Shares
Read a breakdown of the US’ energy mix in this guide.
What’s interesting is that although petroleum and natural gas are used in higher % shares than coal as energy sources in the US, coal emits more GHGs in total and as a % share.
Sources
1. https://en.wikipedia.org/wiki/Life-cycle_greenhouse-gas_emissions_of_energy_sources
2. https://www.parliament.uk/documents/post/postpn268.pdf
3. https://www.americangeosciences.org/critical-issues/faq/how-much-us-carbon-dioxide-emissions-are-associated-electricity-generation
4. https://www.eia.gov/tools/faqs/faq.php?id=427&t=3
5. https://www.eia.gov/tools/faqs/faq.php?id=77&t=11
6. https://www.epa.gov/ghgemissions/sources-greenhouse-gas-emissions
7. https://en.wikipedia.org/wiki/Environmental_impact_of_electricity_generation
8. https://www.bettermeetsreality.com/which-energy-source-is-the-most-dangerous-harmful-which-is-safest/
9. http://css.umich.edu/factsheets/carbon-footprint-factsheet
10. https://www.carbonbrief.org/solar-wind-nuclear-amazingly-low-carbon-footprints
11. https://www.economist.com/science-and-technology/2016/12/10/how-clean-is-solar-power
12. https://www.eia.gov/tools/faqs/faq.php?id=77&t=11
13. https://www.greenbiz.com/article/which-energy-resources-are-gulping-down-our-water
14. https://en.wikipedia.org/wiki/Carbon_footprint#The_carbon_footprints_of_energy
15. https://chinapower.csis.org/china-greenhouse-gas-emissions/
16. https://www.ucsusa.org/resources/environmental-impacts-geothermal-energy
