Which Renewable Energy Has The Lowest Carbon Footprint?
With climate change being one of the biggest challenges facing the world today, there is an increasing focus on transitioning from fossil fuels like coal and natural gas to renewable energy sources like solar, wind, and hydropower. Reducing carbon emissions is crucial to mitigating climate change, so understanding the carbon footprint of different energy sources is important.
This article will examine the carbon footprints of major renewable energy sources to determine which has the lowest emissions. As countries aim to reduce their greenhouse gas outputs, identifying the cleanest renewable technologies is key to building a sustainable energy future.
The central question we will answer is: Which renewable energy source has the lowest carbon footprint?
Defining Carbon Footprint
A carbon footprint is a measure of the total greenhouse gas emissions caused directly and indirectly by an individual, organization, event or product. It is measured in tons of carbon dioxide equivalent. The carbon footprint takes into account greenhouse gas emissions from all stages of a product or activity’s lifetime, including raw material extraction, transportation, manufacture, use and end-of-life disposal.
For energy sources, the carbon footprint is calculated by looking at the amount of CO2 emitted per kilowatt-hour (kWh) of electricity generated. This is also known as the emissions intensity. Each energy source will have a different emissions intensity based on how it is extracted/captured, processed and ultimately used to produce electricity. Sources like coal and natural gas emit CO2 when burned, while sources like wind and solar have minimal emissions during electricity production.
To determine the overall carbon footprint of an energy source, its emissions intensity is multiplied by the total electricity generated from that source over a given time period. Comparing emissions intensities and total carbon footprints provides a way to evaluate the relative climate impacts of different electricity options.
References:
https://www3.epa.gov/carbon-footprint-calculator/
https://justenergy.com/blog/how-to-calculate-your-carbon-footprint/
Fossil Fuels for Comparison
Fossil fuels like coal, oil, and natural gas have high carbon footprints and are major contributors to greenhouse gas emissions globally. According to the EPA, in 2021 fossil fuel combustion accounted for about 74% of total U.S. greenhouse gas emissions, with coal contributing 22%, oil contributing 32%, and natural gas contributing 31% (EPA). The carbon footprint of fossil fuels comes from both the extraction/production process as well as the burning or consumption of the fuels.
Coal has the highest carbon footprint among fossil fuels. Burning coal emits about 228 pounds of CO2 per million British thermal units (BTUs) (EIA). Oil emits about 161 pounds per million BTUs, while natural gas emits 117 pounds per million BTUs burned. In terms of extraction and production, coal mining and oil refining also produce significant greenhouse gas emissions.
Globally, coal accounted for 40% of carbon dioxide emissions from fossil fuels in 2019. Oil accounted for 34% and natural gas 25%. Total global CO2 emissions from fossil fuels reached a record high in 2022, topping 37 billion metric tons (Stanford).
Hydro Power
Hydroelectricity is the largest renewable energy source for electricity generation globally, providing over 16% of the world’s electricity (source). Large-scale hydropower facilities provide consistent, reliable electricity safely and efficiently.
Hydroelectric dams have some of the lowest carbon footprints compared to other electricity generation sources. The reservoirs behind dams emit greenhouse gases like methane and carbon dioxide, but at much lower rates than fossil fuel power plants. According to the U.S. Department of Energy, hydroelectricity produces 60 times fewer greenhouse gas emissions than a coal plant and 10 times less than a natural gas plant per unit of electricity generated (source).
While greenhouse gas emissions do occur from flooded vegetation decaying behind dams, multiple studies show these emissions are negligible compared to fossil fuel plants. Hydropower reservoirs emit 2-8x less greenhouse gases than natural lakes and rivers per unit of surface area (source).
Wind Power
Wind power has become one of the fastest growing renewable energy sources globally. According to the U.S. Department of Energy, wind energy produces around 11 grams of CO2 per kilowatt-hour (g CO2/kWh) of electricity generated, compared with about 980 g CO2/kWh for coal (source). This makes wind power’s carbon footprint nearly 90 times lower than coal. Wind turbines also produce no direct emissions during operation.
At the end of 2020, global wind power capacity reached 743 GW covering over 50 countries (source), making it one of the largest renewable energy sources worldwide. The carbon footprint savings are substantial. According to Yale Climate Connections, if wind energy displaced the global average energy mix, it would reduce CO2 emissions by over 1 billion metric tons per year (source). This demonstrates the massive potential scale and impact of wind power.
With falling costs and rapidly increasing capacity, wind power is poised to grow further and make an even bigger contribution to reducing global carbon emissions.
Solar Power
Solar photovoltaic (PV) panels convert sunlight directly into electricity using semiconducting materials. According to the Solar.com, the carbon footprint of rooftop solar PV is around 12 times less than natural gas and 20 times less than coal. Solar panels emit around 50g of CO2 per kWh produced in the first few years, becoming carbon neutral by year 3 of operation.
Solar PV can be implemented at both small and utility-scale. Research from the Columbia Climate School shows utility-scale solar produces 394-447 MWh per acre annually, avoiding 0.482 to 0.552 tons of CO2 per MWh based on the mix of fossil fuels displaced. This results in 190-246 tons of CO2 avoided per acre per year, significantly more than forestry or agriculture.
With no ongoing fuel costs, solar PV can scale rapidly and displace fossil fuel energy production. Declining costs and supportive policies have driven exponential growth in solar capacity. Total global solar PV capacity reached 760 GW in 2020, supplying about 3% of global electricity demand. With further cost reductions and grid integration advances, solar PV can continue displacing fossil fuel energy sources and reducing emissions.
Nuclear Power
Nuclear power has an extremely small carbon footprint compared to fossil fuel energy sources like coal and natural gas. According to the World Nuclear Association, nuclear power plants produce no greenhouse gas emissions during operation. Over the life cycle of a nuclear plant, including construction, mining and fuel processing, the emissions amount to 4-8g of CO2 equivalent per kilowatt-hour of electricity generated, which is similar to wind and hydropower. (source)
Nuclear is a proven low-carbon energy source that provides about 10% of the world’s electricity. Expanding nuclear power production could significantly reduce global greenhouse gas emissions and help mitigate climate change. According to the London School of Economics, using more nuclear in place of fossil fuels could reduce CO2 emissions by over 5 gigatonnes per year. (source)
However, there are concerns related to costs, safety, waste storage and proliferation risks with nuclear power that need to be considered alongside the benefits. Overall, nuclear has a substantial role to play as a low-carbon baseload energy source but likely requires policy support and public acceptance to grow as part of the global energy transition.
Geothermal Power
Geothermal power utilizes heat from the earth’s interior to generate electricity. It relies on accessing areas with high underground temperatures, such as near tectonic plate boundaries, hot springs, and volcanically active regions. The geothermal energy resource originates from the heat generated when the planet formed over 4 billion years ago and from the ongoing decay of radioactive elements.
Geothermal power plants typically access these underground reservoirs via drilling. High temperature water and steam from deep wells are brought to the surface and used to drive turbine generators. After the steam condenses, the water is returned underground to be reheated.1
Geothermal power contributes a small but growing share of renewable electricity generation globally. As of 2019, geothermal energy produced about 85 terawatt-hours of electricity per year worldwide, meeting 0.3% of global demand.2 However, the geothermal energy potential is enormous – estimated at 200 zettajoules per year globally, over 20,000 times current production.3
In terms of carbon footprint, geothermal power emits very low greenhouse gas emissions when generating electricity. The IPCC estimates 38 grams of CO2 equivalent per kWh from geothermal, including plant construction – about 1% the emissions of coal power.4 This is because no fuels are combusted for geothermal electricity. Emissions mainly occur from surface plant operations.
Comparison & Ranking
When comparing the carbon footprint of different renewable energy sources, studies consistently show that wind and nuclear power have the lowest carbon emissions.
According to research from the University of Cambridge, electricity from wind power results in 2-3g of CO2 per kWh, while nuclear power emits 4-5g per kWh (1). These figures are far below fossil fuel sources like coal (820g per kWh) and gas (490g per kWh).
Another analysis looked at the full life cycle emissions of different energy sources (2). It found that onshore wind emits 10g CO2 per kWh, offshore wind 12g, nuclear power 12g, and solar PV 18-48g. Hydropower and geothermal were higher at 24g and 38g respectively.
Overall, the evidence clearly shows that wind and nuclear offer the lowest carbon footprint renewable options per unit of electricity generated. While debates continue around issues like costs, land use and radioactive waste, they excel in minimizing greenhouse gas emissions and global warming impact.
(1) https://www.carbonbrief.org/solar-wind-nuclear-amazingly-low-carbon-footprints/
(2) https://impactful.ninja/the-carbon-footprint-of-renewable-energy/
Conclusion
To conclude, this analysis has found that nuclear power has the lowest carbon footprint of the renewable energy sources examined. Nuclear power emits between 2.5 and 5.1 grams of CO2 equivalent per kWh, which is significantly lower than other renewable options like hydro, wind, solar, and geothermal. The lifecycle emissions of nuclear from mining uranium to plant operation are minimal with modern reactors. While renewable sources like wind and solar have low operational emissions, their lifecycle emissions from manufacturing and construction are higher than nuclear.
While renewable energy sources are critical alternatives to fossil fuels, their real-world carbon footprints may be higher than expected. Nuclear power stands out as the clear renewable winner when it comes to minimal greenhouse gas emissions over the full lifecycle. If we wish to dramatically reduce global carbon emissions from electricity production, scaling up next-generation nuclear technology could provide an impactful solution with a much lower carbon footprint than other renewables.
