Comparing CO₂ emissions from different energy sources

20.09.2023

When you produce electricity, you generate greenhouse gas emissions – and 02this is true for fossil-free energy sources as well. Even if the actual production of electricity does not generate emissions, there is a life-cycle perspective to consider.

If we are to find ways to reduce emissions from different parts of our energy system, we must take a bird’s eye perspective and analyse the emissions from the whole life cycle of the energy sources we use. Make no mistake, wind power generates very low emissions of greenhouse gas (GHG) during its life cycle compared to fossil-fuel sources. But wind power does come with a climate footprint, and when making decisions it is important not to compare apples and pears. 

We think that is a good example of the importance of life-cycle assessments so let us get to the bottom of how it all adds up.

How do emissions arise? 

A wind turbine converts the kinetic energy of the wind into electricity. This process does not generate any GHG emissions. Instead, emissions occur at different stages of the wind turbine's life cycle:

• When the raw materials for the wind turbine are mined and processed. 
• When the wind turbine is produced in the factory.
• When the wind turbine is assembled and erected.
• When maintenance and repair works are carried out.
• When the wind turbine is dismantled and its materials are recycled.

"We need to be aware of where emissions are generated. To give you a real-life example, an electric car emits zero CO₂ when driving and is labelled emission-free. But emissions are generated when the car and its battery are made. The electricity mix and emissions from the electricity production are other important sources of emissions," says Anna Berggren, Senior Business Development and Sustainability Director in COWI Sweden.     

Life-cycle assessment – the method for determining emissions 

To determine and compare the level of emissions and the climate impact of different energy sources, a method called life-cycle assessment can be used. GHG emissions are measured in grams of carbon dioxide equivalent per kilowatt hour (g CO2e/kWh). Carbon dioxide equivalent is a measure used to compare emissions of different greenhouse gases. 

This is how much each type of power emits during its life cycle*:

• Hydropower: approximately 4 g CO2e/kWh
• Wind power: approximately 11 g CO2e/kWh
• Nuclear power: approximately 12 g CO2e/kWh
• Solar power: around 41 g CO2e/kWh
• Natural gas: 290-930 g CO2e/kWh
• Oil: 510-1170 g CO2e/kWh
• Coal: 740-1689 g CO2e/kWh.

Source: IPCC

Why such large differences?

The reason is that the efficiency of fossil fuels varies, depending on how efficient the power plants are and how the fuel is extracted. From a life-cycle perspective, GHG emissions from wind power are extremely low compared to all other forms of power generation.

"The demand for electricity will increase dramatically in the coming decades, and at the same time, we need to cut GHG emissions. This is not an easy problem to solve, but at COWI we are dedicated to helping our customers make this green transition a reality. It’s clear that wind is a power source that will play an important part in this transition, even if we have to find ways of limiting the climate impact of wind turbines as well,” says Anna Berggren.

*(IPCC) in its synthesis report (AR5), Swedish Energy Agency.