Are Renewables Emission Free?
Renewable energy sources like solar, wind, and hydro are often described as “emissions-free” or “clean energy”. However, renewables do still have some carbon emissions over their lifecycle, from manufacturing to end-of-life disposal. While renewable energy has very low emissions compared to fossil fuels, calling them completely “emissions-free” can be misleading.
This article analyzes the lifecycle emissions from major renewable energy sources, including solar PV, wind, biomass, and hydropower. It compares the emissions from renewables to fossil fuels like coal and natural gas. The analysis shows that while renewables have very minimal emissions compared to fossil fuels, they are not completely “emission-free” when considering their full lifecycle. Describing renewables as “emission-free” is an exaggeration, but they play a critical role in climate change mitigation and displacing fossil fuel energy sources.
Lifecycle Emissions from Solar PV
Solar photovoltaic (PV) panels produce emissions through their manufacturing process and raw materials extraction. Producing solar panels requires energy-intensive processes like mining silica and smelting metals. Transporting materials and manufacturing solar panels also consume fossil fuels for energy. According to a 2013 National Renewable Energy Lab report, the global warming potential of crystalline silicon solar panel production is estimated at 45 gCO2eq/kWh. Thin-film solar panels have slightly higher emissions during manufacturing at 60 gCO2eq/kWh. While solar panels create emissions during production, they can offset much larger amounts over their working lifespan by generating clean renewable electricity. One analysis found solar PV systems offset their life cycle emissions within 2-3 years for most regions.
Lifecycle Emissions from Wind
The manufacturing, installation, and maintenance of wind turbines does generate some greenhouse gas emissions. However, most emissions associated with wind power occur during the manufacturing stage. Once wind turbines are operational, they emit very little carbon pollution.
According to a 2013 lifecycle assessment, manufacturing a 2MW onshore wind turbine emits around 4.64 grams of CO2 equivalent per kWh of electricity it produces over its lifetime. The bulk of emissions come from materials like steel, fiberglass, copper, and concrete needed to construct the wind turbine (Yale Climate Connections).
In contrast, coal-fired power plants emit around 980 grams of CO2 per kWh generated. As a result, wind energy helps avoid a significant amount of emissions once operational (U.S. Department of Energy). Overall, wind power generates around 11 grams of CO2 per kWh, over 90 times less than coal.
Emissions from Biomass
When biomass like wood or crop residues is burned for energy, it releases carbon dioxide (CO2) into the atmosphere just like fossil fuels. The key difference is that the CO2 released from biomass comes from carbon that was absorbed as the plants grew, so it may be considered carbon neutral. However, recent research challenges the idea that biomass is truly carbon neutral.
A 2021 report found that many biomass plants in the U.S. South are sourcing wood from whole trees and residues from logging operations[1]. Burning these residues emits CO2 that would otherwise stay locked up in forests. The report estimates biomass emits more CO2 per megawatt-hour than coal. Another study found it takes decades for new forest growth to re-absorb the carbon released from burning biomass[2].
Whether biomass can be considered carbon neutral depends on the feedstock source, harvest methods, and regrowth time. While biomass can provide low-carbon energy, it may not offer the climate benefits of zero-emission renewable sources like solar, wind, and hydroelectric power.
Emissions from Hydroelectric
While hydroelectric power does not directly burn fossil fuels, the reservoirs created by hydroelectric dams lead to emissions of methane, a potent greenhouse gas. When areas are flooded to create reservoirs, decaying organic matter in flooded soils and vegetation leads to methane production. According to research from the U.S. Department of Energy, “All inland waters naturally produce some GHG emissions. However, when human-made reservoirs are constructed for hydropower facilities, they change the way gases, like methane, escape from the system” [1]. Some estimates suggest reservoirs used for hydropower emit over 25% of global methane emissions from human activities [2]. Methane has over 80 times the global warming potential of carbon dioxide over a 20 year period, so even small amounts can have a significant climate impact. Strategies like degassing methane through turbines has been proposed, but substantial emissions remain an issue with large reservoirs.
Comparing Emissions: Renewables vs Fossil Fuels
Lifecycle emissions from renewables are a fraction of those from coal, oil, and gas. According to the World Resources Institute, renewable energy sources typically emit about 50g or less of CO2 per kWh over their lifetime, compared to around 1,000g per kWh for coal and natural gas [1]. The UN also notes that renewable sources like wind and solar emit little to no greenhouse gases and are cheaper than fossil fuels [2]. Amigo Energy highlights that renewables like solar and wind apart from construction and maintenance emit far less CO2 than fossil fuels [3]. In summary, the lifecycle emissions from renewable sources are substantially lower than those from coal, oil and natural gas.
Why “Emission-Free” is an Exaggeration
While renewable energy sources like solar, wind, and hydroelectric produce minimal emissions during their operational lifetime, calling them “emission-free” is an exaggeration. Renewables do still have some associated emissions from manufacturing, construction, maintenance, and decommissioning.[1] However, lifecycle analyses show that the emissions from renewables are drastically lower than those from fossil fuels.
For example, solar PV emits about 60 grams of CO2 per kWh over its lifespan, while coal emits around 1,000 grams per kWh.[2] So renewables are not completely emission-free, but their emissions are very low, especially in comparison to fossil fuels. Terms like “low-carbon” or “near zero-carbon” are more precise than “emission-free.”
That said, renewables still play a critical role in climate change mitigation. Phasing out fossil fuels and replacing them with renewables (in combination with nuclear, hydro, and other low-carbon sources) is a key strategy for deeply decarbonizing the energy system.
[1] https://climate.mit.edu/explainers/renewable-energy
[2] https://www.ipcc.ch/site/assets/uploads/2018/03/Chapter-7-DS-SNP.pdf
The Role of Renewables in Climate Change Mitigation
Renewable energy sources play a critical role in climate change mitigation by providing an alternative to fossil fuels which are major contributors to greenhouse gas emissions. According to the UN, “Renewable energy sources, such as wind and solar, emit little to no greenhouse gases, are readily available and in most cases cheaper than coal, oil or gas.” (https://www.un.org/en/climatechange/raising-ambition/renewable-energy) Transitioning electricity generation, heating, and transportation to utilize renewable sources can significantly reduce global carbon emissions.
As the World Wildlife Fund notes, “Renewable energy minimizes carbon pollution and has a much lower impact on our environment.” Renewables like solar, wind, geothermal and hydropower produce negligible lifecycle emissions compared to natural gas or coal power plants. Increasing the share of renewables in the energy mix is critical for phasing out fossil fuel infrastructure and meeting global climate targets. WWF emphasizes that renewable energy is “having its moment in the sun” as costs have declined dramatically in recent years, making it more feasible to transition energy systems. (https://www.worldwildlife.org/magazine/articles/importance-of-renewable-energy-in-the-fight-against-climate-change–3)
Future Outlook
The outlook for future emissions reductions from renewable energy is promising, as technology improvements will further reduce lifecycle emissions.
Many studies predict that as renewable energy technology matures, emissions associated with raw material extraction, manufacturing, construction, and end-of-life disposal will decrease. For example, one analysis found that by 2050, emissions from solar PV could fall by up to 90% compared to today’s levels, as manufacturing becomes more efficient, panels become thinner, and end-of-life recycling improves [1].
Advances in wind turbine design are also expected to lower emissions through larger, lighter turbines and more efficient manufacturing. Studies estimate emissions from onshore wind could fall 10-20% by 2050 [2]. Offshore wind emissions are predicted to fall even further with optimized logistics and larger turbines.
Overall, the emissions benefits of renewable energy are likely to improve in the future as technology matures, further strengthening the climate change mitigation potential.
Conclusion
In summary, while renewables like solar, wind, hydro, and biomass are not completely emission-free over their full lifecycles, they produce dramatically fewer emissions than fossil fuel sources. Though manufacturing solar panels and wind turbines does require energy and create greenhouse gases, the operational emissions from renewables are negligible. This makes them an essential tool in reducing carbon emissions and mitigating climate change compared to coal, oil, and natural gas. Describing renewables as “emission-free” may be an oversimplification, but their vast emissions reductions compared to fossil fuels show why they will play a key role in a low-carbon future.
