Carbon Footprint Of Energy Sources & Electricity

Different energy sources for electricity production emit different amounts of greenhouse gases.

This results in different carbon footprints for different energy sources.

In this guide, we look at the carbon footprint of electricity in general, but also of individual energy sources like coal, gas, petroleum/oil, nuclear, solar, wind and others.

 

Summary – Carbon Footprint Of Energy Sources & Electricity

Electricity production is one of the leading emitters as an industry globally, and there are different energy sources that are used for electricity production (energy sources are used for heating and also as fuel, but this guide specifically focuses on electricity production)

Energy sources can emit greenhouse gases not only directly at the combustion stage, but indirectly also across the whole lifecycle of the energy source

We’ve included examples of direct and indirect emissions at the bottom of this guide

There’s various ways to measure the carbon footprint of different energy sources

One way is the total emissions in terms of quantity (tonnes) of the different energy sources, and also break that down into a % share of total emissions for a country, or on a global scale.

Doing this for the US in 2017, majority of carbon emissions in electricity production came from coal followed by natural gas, at 69% and 29% respectively (it’s worth noting that these figures can change when accounting for all energy uses – such as heating, and also fuel for transport. But, these are the amounts for electricity production)

Another way to measure the carbon footprint of different energy sources for electricity production specifically is by CO2e (carbon dioxide equivalent) per kWh of electricity produced

When taking this into account, coal tends to be the heaviest emitter by a significant margin, followed by natural gas at two third to half of the per kWh hour value of coal

Biomass and bioenergy can vary, but dedicated biomass can feature behind coal and natural gas in third according to some estimations

Renewables (solar PV, geothermal, hydropower, offshore wind, onshore wind, and ocean tidal/wave), and nuclear, tend to produce minimal emissions or almost no emissions at the operation stage

Solar in particular has become far more emission efficient since 1975 according to one data set

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. Methane from decaying matter in reservoirs can also be an issue

These trends tend to hold consistent for both operational, and life cycle carbon footprints per kWh of electricity produced

Oil is close to on par with coal, but is obviously primarily used in transport. Some sources also put diesel and fuel cells near the top of the list, but again, they are primarily used in transport

A future adjusted set of data, allowing for technology advancements in energy and electricity production, shows similar trends and results (fossil fuels higher and renewables and nuclear lower in emissions), except hydro appears higher in the list

One source indicates that just for combustion, natural gas emits 50 to 60% less greenhouse gases compared to coal

It should be noted though that there emissions involved in making equipment such as solar panels/solar cells, wind turbines (cement and steel), and the construction of a nuclear plant (especially cement and steel manufacturing)

There’s also energy used in decommissioning of a nuclear plant, and disposing of waste when a solar panel’s lifetime is up as well

So, there’s more than just the operation stage to consider

The type of equipment used to produce electricity (e.g. a new vs old coal power plant), and emissions control technology installed at a plant (e.g. carbon capture technology vs no carbon capture technology), can have an impact on the emissions footprint

Different research shows that new coal plants might contribute less emissions than old ones

Further technology advances might keep changing emissions for different energy sources

Something else that might be considered is black vs brown coal, and their respective emissions

There’s an asterisk on renewables when used in an electricity grid – they may have to be used in conjunction with a backup fossil fuel power plant, so, these emissions should be taken into account

Another asterisk on the carbon footprint of different energy sources is energy lost in the transmission of energy sources to new locations. Natural gas might be one of the most efficient energy sources, compared to hydrogen, coal, nuclear and oil. Storage of energy sources, and boil off energy losses can also lead to the loss of energy. So, efficiency 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

In this guide, we specifically outline the emissions from different fossil fuels across different measures

 

Average Carbon Footprint Of One Kilowatt Hour Of Electricity

The average carbon footprint of a kilowatt hour of electricity might be close to one pound.

But, it might also depend on the energy mix of a city.

 

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)

 

Emissions Rates Of Different Energy Sources, Per kWh Of Electricity Produced

In terms of general rates of emissions during operation, coal is the major emitter.

Natural gas is in second.

Renewables and nuclear are the lowest emitters.

 

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

– greenbiz.com

 

… [In terms of electricity] Coal releases 2.2 pounds, 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 emissions are released during upstream production activities (e.g., solar cells, nuclear fuels, cement production).

– css.umich.edu

 

Wind vs nuclear vs solar:

Wind energy and nuclear produce around the same amount of emissions, and solar power produces four times more than nuclear

 

Wind energy:

The greenhouse gases produced during the manufacture of wind turbines is expected to be recouped within 9 months of clean operation in some instances

 

Geothermal:

Geothermal can be a low emitting energy source during operation if used in a closed loop system, where carbon dioxide is injected back into the Earth 

 

Geothermal:

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

– ucsusa.org

 

Lifecycle Carbon Footprint Of Different Energy Sources, Per kWh Of Electricity Produced

Life cycle carbon footprints take into account mining through to waste emissions i.e. emissions at more than just the operations stage.

Coal tends to come out in front according to most calculations, with natural gas in second, but only producing about half the emissions of coal on a per kWh basis.

Renewables tend to feature low in terms of lifetime emissions too.

 

The Wikipedia resource in the resources list shows the life cycle CO2 equivalent from electricity supply technologies in terms of median gCO2eq/kWh 

According to the estimates:

[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]

 

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 the order of] >1,000 gCO2eq/kWh (CO2 equivalent per kilowatt hour)

Newer gasification plants – <800gCO2eq/kWh

Oil-fired electricity generation plants – ~650gCO2eq/kWh

Current gas powered electricity generation – ~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]

– parliament.uk

 

More lifecycle carbon footprint stats of different energy sources can be found at the environmental impact wikipedia.org resource (in the table under the ‘water usage’ section).

 

Future Adjusted Lifecycle Carbon Footprint Of Different Energy Sources, Per kWh Of Electricity Produced

The only real change here from the above data is hydro appears higher on the emissions list.

 

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):

Nuclear – 4 grammes of CO2 equivalent (gCO2e/kWh)

Solar – 6gCO2e/kWh  (6 grammes of CO2 equivalent)

Wind – 4gCO2e/kWh

Gas – 78gCO2e/kWh

Hydro – 97gCO2e/kWh

Bioenergy – 98gCO2e/kWh

Coal – 109gCO2e/kWh

… It’s interesting to note that the global average target for a 2C world in 2050 is 15gCO2e/kWh.

– carbonbrief.org

 

Carbon Footprint Specifically During Combustion

Compared to coal, natural gas emits 50 to 60 percent less carbon during the combustion process

– chinapower.csis.org

 

Carbon Footprint Of Solar Panels

… 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

– economist.com

 

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)

– carbonbrief.org

 

[Taken from the future adjusted carbonbrief.org list in this guide above]

Solar – 6gCO2e/kWh  (6 grammes of CO2 equivalent)

– carbonbrief.org

 

A few notes on solar panels to be aware of though:

– There are emissions at the manufacture and waste disposal stages

– A panel made in factories in China might have higher emissions because of the amount of coal energy used, compared to panels made in other countries where the energy mix is greener

 

Carbon Footprint Of Wind Turbines

[Taken from the future adjusted carbonbrief.org list in this guide above]

Wind – 4gCO2e/kWh (4 grammes of CO2 equivalent)

– carbonbrief.org

 

But note that wind turbines often need steel and concrete to make, which have have emissions

 

Carbon Footprint Of Nuclear Energy

[Taken from the future adjusted carbonbrief.org list in this guide above]

Nuclear – 4gCO2e/kWh (4 grammes of CO2 equivalent)

[But] Nuclear plants need a lot of steel and concrete … And the centrifuges that separate nuclear fuel also rack up a big electricity bill

– carbonbrief.org

 

Carbon Footprint Of Gas

[Taken from the future adjusted carbonbrief.org list in this guide above]

Gas – 78gCO2e/kWh

– carbonbrief.org

 

Carbon Footprint Of Hydroelectricity

[Taken from the future adjusted carbonbrief.org list in this guide above]

Hydro – 97gCO2e/kWh

– carbonbrief.org

 

Carbon Footprint Of Bioenergy

[Taken from the future adjusted carbonbrief.org list in this guide above]

Bioenergy – 98gCO2e/kWh

– carbonbrief.org

 

Carbon Footprint Of Coal

[Taken from the future adjusted carbonbrief.org list in this guide above]

Coal – 109gCO2e/kWh

– carbonbrief.org

 

How Much Carbon Electricity & Energy Sources Emit In The United States

Coal by far emits the most greenhouse gases in electricity production of any energy source in the US.

 

In 2017:

… the U.S. electric power sector emitted … [about] 34% of the total U.S. energy-related CO2 emissions …

[CO2 emissions from U.S. electric power sector by source were:]

Coal – 1207 million metric tons, and 69% of total emissions

Natural Gas – 506, and 29%

Petroleum – 19, and 1%

Other – 12, and less than 1%

– eia.gov

It’s also worth noting that eia.gov also now has 2019 figures available.

 

Breakdown Of Total Energy Generation By Source, In The US

In 2017 in the United States:

63% of … electricity generation was from fossil fuels (coal, natural gas, petroleum, and other gases).

About 20% was from nuclear energy

… and about 17% was from renewable energy sources. 

Read a full breakdown of total energy generation at eia.gov

 

What’s interesting is that although petroleum and natural gas are used in higher % shares than coal in the US, coal emits more GHGs, and so % of emissions from coal are much higher.

 

How Do Energy & Electricity Emit Greenhouse Gases?

Usually directly, or indirectly.

 

– Directly

At the operation stage, such as the combustion of coal at a power plant.

 

– Indirectly

Emissions that come from another stage of the life cycle of that energy source or electricity production.

For example, a solar panel may not emit greenhouse gases when in operation, but, there were emissions at the manufacturing stage when making the solar cells. There will also usually be an emissions footprint to dispose of the waste once the solar panel has reach the end of it’s lifetime.

Another example is the potential for methane leaks at the oil and gas mining stage when talking about the use of petroleum or natural gas for energy.

There’s more information about oil methane leakage rates and the emissions from different fossil fuels worldwide, and also in China, in this guide

 

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

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