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Carbon Lifecycle of Wind Turbine

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Introduction

Wind turbines are one of the most recognisable forms of renewable energy currently being used and developed worldwide for producing electricity. They have the ability to produce vast amounts of energy by converting wind’s kinetic energy into electrical energy by the rotation of a generator, powered by massive fan blades. The largest wind turbines have a rotor diameter of over 240m (NES Firecroft, 2021), the equivalent to 3 football pitches or 22 London busses. Around the world as of 2020, wind turbines can produce a staggering 650 gigawatts of power (WWEA, 2020), enough to power the whole of India.


The scale and productivity of wind turbines makes them immensely beneficial to the economy, particularly with regards to their manufacturing, installation, operation, and maintenance. They also benefit the environment by producing low carbon electricity. That is not to say they do not have downsides, critics routinely highlight that their appearance makes them a blemish on areas of natural beauty (Lo, 2012), and some even go as far as to suggest that they are bad for the environment. These arguments are supported by the fact that they are often placed in remote parts of the countryside or offshore. While this is required to improve energy efficiency and reduce the cost of wind power generation, both on land and at sea (Lo, 2012), this has not prevented criticism.




History of Wind Turbines


Wind turbines have a rich history, spanning over 2 millennia. The last 150 years have seen wind turbines move from being a source of rotational power for grinding wheat or pumping water to full scale offshore windfarms capable of producing 1.2 giga-watts of electrical power (1.2 million kW) (Ørsted, 2020).


The first use of a wind powered machine for practical use was in 7th century Persia (Yūsuf, 1986). Rectangular sails were arranged around a vertical axis, using the wind to create rotational force for the grinding of grain or for drawing water from wells. Similar structures were utilised globally for these purposes. In terms of energy creation, the first electricity producing wind turbine blade was built in Scotland in 1887 by Professor James Blyth (Price, 2005) at his holiday cottage, Marykirk, in Kincardineshire and used to power his lights. Blyth offered his surplus electricity to the people of Marykirk for lighting the main street, but this was declined as they thought electricity was ‘the work of the devil’ (Price, 2005). It wasn’t until 1931 that the first utility scale wind turbine was developed in the Soviet Union, near Yalta. This wind turbine produced 100 kW of energy (Hau, 2003), enough to power up to ten average UK homes today.


Large increases in energy production followed: the first ‘megawatt’ turbine was the Smith–Putnam wind turbine based in Grandpa’s knob in Castleton Vermont, producing over 1250 kW or 1.25 MW of power. This was the largest wind turbine for over 30 years (Changing Times, 1988). Since then, wind turbines have improved significantly with the largest wind turbines producing nearly 20 MW of power and over 80’000 MWh annually (NES Firecroft, 2021). Eventually, it became clear that by moving windfarms offshore, larger amounts of energy could be generated due to the higher wind speeds at sea than on land. This means that offshore farms generate more electricity per amount of capacity installed over the same time period than their onshore counterparts (BTM Consult ApS, 2010). As a result, in 1991, the first wind turbine was installed as part of the Vindeby offshore wind farm of the coast of Denmark. The Vindeby offshore windfarm operated for 25 years until 2017, producing 9.61 GWh per annum on average and a total of 243 GWh in its lifetime. Since decommissioning, the blades from the Vindeby turbines have been recycled into noise barriers for one of the busiest highways in Copenhagen (Wind Denmark, 2019). Another benefit to offshore wind farms is that they are often out of sight and do not impact the natural beauty of the countryside, so are less criticised.




The Green Problem of Wind Turbines


While wind turbines produce vast amounts of power without burning any fossil fuels, a lot of energy is required to manufacture, install, maintain, and decommission a modern wind turbine. Manufacturing of wind turbines uses energy intensive material (Crawford, 2007), not all of which can be recycled. For instance, the blades and nacelles (please see Figure 1 below for an illustration of these components) are manufactured from fibre reinforced plastic (FRP) and the generators contain many rare earth elements. FRP blades are manufactured from a mix of glass and carbon fibre bound in a polymer matrix, making them very energy intensive to produce and incapable of being recycled in a profitable way. The construction of the generators on the other hand requires large amounts of rare earth elements. On average, a tonne of Neodymium is used (Carter, 2021), which takes an equivalent of 66’000 kg of CO2 to mine and refine (P. Koltun, 2014), the equivalent of driving the average UK car 460’000 km (Yurday, 2021). A related problem is that wind turbines are very heavy and require large amounts of energy to move and install at site. The largest wind turbines weigh over 500 tons just in the nacelle alone (Ocean Energy Resources, 2020) which takes many lorry loads to transport. In the case of offshore windfarms an installation vessel is required. Both of these vessels emit pollution from internal combustion engines. All this has caused some commentators to consider wind turbines to be bad for the environment, instead of the force for good that they clearly are.


Carbon Footprint of Wind Turbines


Because of the energy intensive manufacture, the lack of immediate recyclability and the remoteness of the installation location there is sometimes a misconception that wind turbines are not as beneficial as other forms of renewable energy. To illustrate the effectiveness of wind turbines, it is important to compare them with other sources of electricity such as coal, gas, nuclear and other forms of reviewable energy. This is achieved through consideration of the ‘Lifecycle CO2 equivalent’ of a wind turbine. The Lifecycle CO2 equivalent is designed to show how much CO2 is created to make a wind turbine versus how much energy it produces over its life.


For this comparison to be effective, we first need to identify the type and amount of materials used in the manufacturing of a typical wind turbine. For this assessment we will be using the General Electric 1.6 MW wind turbine which is an evolution of GE's 1.5 MW turbine which is design is most common wind turbine produced, with over 12’000 in service in March 2009 (GE Energy, 2009).


In the table below you can see the typical materials used in a General Electric 1.6MW wind turbine and how much is used by weight:


Table 1- Typical material percentages of a modern wind turbine (Dan Ancona, 2001)


A typical General Electric 1.6MW wind turbine weighs around 375 tons in total; the tower alone weighs about 226 tons, with the rotor assembly weighing 84 tons, and the nacelle weighing 65 tons. The major components can be seen in Figure 1 below.



To add to this, a typical onshore wind turbine will require a concrete base comprised of around 240m3 of concrete, the equivalent of a small swimming pool.


Table 2 - Table 2 - Typical Component weights of a GE 1.6MW wind turbine (Dufferin Wind Power INC, 2012)


In Table 3 below, you can see how many tons of CO2 are produced to manufacture a ton of each given material. This includes CO2 emitted at all stages of the process, including mining, refining, transport, and manufacturing. While every care has been taken to make sure these values are valid at the time of writing, they dochange because of the location and processes used to manufacture.



Table 3 -Tons of CO2 equivalent per Ton to manufacture of various materials in a wind turbine

Knowing the percentage breakdown of materials, the total weight of components and the tons of CO2 equivalent per ton to manufacture, we can calculate how much CO2 is produced to manufacture the General Electric 1.6MW wind turbine. This is summarised in Table 4:



Table 4 -Summary of CO2 equivalency


The total CO2 equivalent to manufacture a General Electric 1.6MW wind turbine is therefore around 1058 tons. This is the equivalent of driving your car 7.6 million km (Yurday, 2021) (for context, this is the equivalent of driving to the moon and back nearly 10 times) or 630 flights from London to New York.


There is no hiding from the fact that this is a very large quantity of CO2, but it must be seen in context; the wind turbine is producing vast amounts of power for long periods without releasing harmful emissions to the environment. To quantify how impactful an electricity generation process is, we use CO2 per kWh manufactured. The lower the amount of CO2 per kWh the better.


This can be calculated below using the equation:


From the study in Table 4 we already know the total amount of CO2 it has taken to manufacture our wind turbine. To calculate how much energy (kWh) the turbine has produced in its life we use the equation:



For a General Electric 1.6 MW wind turbine we can assume a 25-year life span and a typical capacity factor of 35% (University of Michigan, 2021). The total capacity is used to determine the total amount of time the wind turbine is producing electricity. This will never be 100% as there will be periods that are not windy, or even when the wind is too strong, and times where the turbine needs to be stopped for maintenance. Let us plug these values into the above equation:



So, the CO2/kWh for a 1.6mw General Electric wind turbine would be:



Over the lifetime of the wind turbine, on average, the life cycle CO2 equivalent will be 8.84g of CO2 per KW hour produced.


Comparison with Other Ways of Generating Electricity


Now we know that a wind turbine’s Lifecycle CO2 equivalency of 8.84g of CO2 per KWh, we can compare this with other forms of energy production. Table 5 below shows other major electricity production processes


Table 5 -Life cycle CO2 equivalent (including albedo effect) from selected electricity supply technologies according to IPCC 2014 (Thomas Bruckne, 2014)

*Range from IPCC report, it is worth noting that the assessment herein falls within this range, showing validity in assumptions and calculations.


As you can see from Table 5, wind energy is one of the cleanest sources of energy production, second only to nuclear. This is the main reason why wind energy has been developed and championed by many nations. Simply, it is a great way to produce plentiful power with very low CO2 emissions. Importantly, future wind turbine developments are aiming to produce a fully recyclable wind turbine so that the electricity produced is truly net zero.



The Future


A great example of the future potential of wind turbines to be a truly net zero form of energy production is the SusWIND project, which has been launched to drive the future sustainability of wind turbine technology. SusWIND is looking to bring together the largest wind turbine manufacturers, such as Siemens and General Electric, and government research organisations such as the National Composites Centre (NCC) and Oil & Gas Technology Centre (OGTC), to improve the production of wind turbines. For example, the project will discover and demonstrate viable ways to recycle composite wind turbine blades, explore the use of sustainable materials and processes in developing composites for blades, and innovate in design to future-proof the turbine blades of tomorrow. More detail on the SusWIND project can be found here.


Content of tables



Content of Figures



References


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