Will offshore wind deliver on its promise?

Reflecting on the net carbon impact of offshore wind assets.

The UK government has pledged to reach net zero emissions by 2050. Further expansion of offshore wind capacity is a key component of achieving this milestone. As a result, the UK government has set a target of 50GW offshore wind capacity by 2030.

At COP26, there was a pledge to make efforts to ensure global warming was kept ‘well below 2°C’. To achieve this, the Global Wind Energy Council (GWEC) has calculated that the average annual wind installation required between 2020 and 2030 will need to be 180GW. This will require a significant increase in global onshore and offshore wind capacity.

Figure 1 - Current market outlook and estimated wind installation to reach 'well below 2°C' target

Source: GWEC, Global Wind Report 2021

However, some critics of wind power have referred to offshore wind as a ‘cheap facelift’. They suggest it is not truly part of the solution to climate change and the emerging energy crisis. This post provides evidence to the contrary, highlighting the low level of emissions from offshore windfarms and their benefit in addressing climate change.

Building an offshore windfarm produces carbon emissions

Offshore wind has been labelled as the “cornerstone” of achieving net zero, driving green energy as a competitive, sustainable energy source. Once an offshore windfarm is in operation, it produces few carbon emissions. However, its construction and decommissioning mean it is far from carbon neutral. The steel, concrete, and carbon fibre needed for wind turbines are largely produced from carbon-intensive processes. To this must be added the diesel burned by ships and trucks in transporting turbine parts, and the energy used during construction, operation, maintenance, and decommissioning to determine the total lifecycle emissions of building an offshore windfarm.

Offshore wind turbines release c.59% more carbon dioxide equivalent emissions throughout their lifetime than onshore turbines due to the volume of material in their floating platforms. However, onshore windfarms produce less energy than their offshore counterparts. This is because planning regulations often limit the height of onshore turbines and the higher wind speeds and consistency in wind direction mean offshore turbines can generate more energy.

Figure 2 - Breakdown of carbon emissions from an offshore windfarm

Source: The Crown Estate, Offshore Wind Report 2021

However, the lifecycle of an offshore windfarm is significantly longer than its carbon payback period

Despite the emissions that are associated with the creation and maintenance of an offshore windfarm, a study by the Carbon Trust found that the carbon payback period for an offshore windfarm in the UK is only 2-3 years. As an offshore windfarm has an average lifespan of 25 years, the carbon savings more than compensate for its initial emissions.

Assuming a 25-year lifetime of electricity production, an offshore wind turbine emits 12g of carbon dioxide for every kilowatt-hour (kWh) of electricity it generates. This represents only 2.45% of the per kWh emissions from a natural gas plant.

Figure 3 - gCO2 equivalent per kWh of different production processes

Source: World Nuclear Association, Carbon Dioxide Emissions from Electricity, 2021

Figure 3 demonstrates the low level of emissions from wind power compared to energy production alternatives.

Moreover, there is room to reduce offshore wind emissions further

Although offshore wind generation has low carbon emissions compared to alternative electricity generation methods, reports by industry specialists have calculated that global wind power lifecycle emissions will reach 55 million tonnes of carbon dioxide equivalent between 2020 and 2050. To put this into perspective, there were 12 billion tonnes of emissions generated by the global thermal power sector in 2020.

As steel makes up 90% of the total materials in an offshore turbine, the carbon intensity of its production is the biggest barrier to reducing emissions. The steel industry accounts for close to 10% of global emissions. This explains why initiatives such as SteelZero have been created, targeting carbon-neutral steel production by 2050. This involves the implementation of new technologies, such as direct reduced iron or hydrogen-based processes, and encouraging the use of sustainable practices, such as the use of recycled materials and the efficient use of resources, throughout the steel production process. Leading offshore wind developers such as Ørsted, Iberdrola and Vattenfall have all announced their commitment to the initiative.

A number of commentators have highlighted concerns about the way turbines are decommissioned, despite them contributing only a small addition to total carbon emissions. There has, however, been some recent progress in this area. In 2021, Siemens Gamesa launched the RecyclableBlade, the world's first wind turbine blade that can be recycled at the end of its life. Reusing blades in other industries is another step towards the creation of a waste-free future for offshore wind. As the blades are made from composite materials that are strong, durable, and lightweight, they are suitable for a variety of applications. For example, the Danish company “B2Sea” has developed a system for creating breakwaters from recycled wind turbine blades.

When assessing the suitability of energy generation, we need to consider factors beyond emissions

Despite the low level of emissions associated with offshore windfarms, there are other negative impacts associated with their construction and operation. One problem is that birds and bats can be injured or killed when they fly into rotating turbine blades. Another concern is that offshore windfarms impact marine species during both construction and operation. Environmental organisations, such as the National Audubon Society in the USA, are looking into ways of reducing these negative wider impacts.

Even without further improvements, offshore wind has a key part to play in helping the UK reach its net zero target. Offshore wind is a source of clean, renewable energy which, due to its reliability and low carbon emissions, makes it a major component of a sustainable energy future. So it is important for offshore wind capacity to increase significantly to support the pledge of keeping global warming ‘well below 2°C’.