There is a debate about the environmental aspects of installing large wind energy converters, which raises a concern for investors and authorities to construct wind power plants. Life cycle assessment (LCA) is an international standard (ISO) approved tool devised to compare different energy systems or technologies and assess their environmental impacts through life cycle in order to help decision makers to choose best technology to be used. It addresses environmental aspects, including emissions footprint, and secondary raw material extraction at the end of life by introducing the circular economy (CE) approach.
LCA of wind turbines, onshore and offshore wind farm was tackled in several studies. Crawford (Crawford, 2019) studied the effect of the size of the wind turbines on their life cycle and greenhouse emissions and concluded that the size of wind turbine is not an important factor to optimize the life cycle energy performance, while Tremeac and Meunier (Tremeac & Meunier, 2009) compared two wind turbines with considerably different capacities, one of 4.5 MW and the other is 250 W, and concluded that, the larger the rated output power of the wind turbine, the lower the CO2 emissions per kWh generated. Guezuraga et al. (Guezuraga et al., 2012) compared two different wind energy technologies, one is 1.8 MW gearless and the other is 2 MW with a gearbox. They used Global Emission Model of Integrated System (GEMIS) simulation software to assess the life cycle of the wind turbine, and found that energy requirement of manufacturing phase represents the highest share 84% of the total life cycle and the tower accounts for 55% of total wind turbine production. They estimated the energy payback time as 7 months and the CO2 emissions as 9 g/kWh, concluding that renewable energy and specifically wind energy is the cleanest source of energy, this is conclusive with other studies (Web, 2021a). Rashedi et al, (Rashedi et al, 2013) performed a life cycle impact analysis (LCIA) of three wind farms: one onshore with horizontal axis wind turbines, one offshore with horizontal axis wind turbines, and another is vertical axis wind turbines wind farm. They concluded that vertical axis wind farm generates lowest impacts per unit electricity followed by horizontal offshore and last the horizontal onshore farms. Wagner et al. (Wagner et al., 2011) and (Weinzettel et al., 2009) studied floating offshore wind turbines by LCA means. In terms of the size of wind turbines, again, the study revealed that the larger the rated output power of the wind turbine, the lower the CO2 emissions per kWh. In contrast, (Kadiyala et al., 2017) performed a statistical evaluation of wind energy LCA studies and determined that for wind turbines greater than 0.25 MW capacity, onshore turbines have higher GHG emissions (15.98 - 17.12 gCO2eq/kWh) compared to offshore wind turbines (12.9 - 7.61 gCO2eq/kWh). Lenzen and Wachsmann (Lenzen & Wachsmann, 2004) indicated that that the location and geographical variability play a major role in determining the life cycle environmental impacts of wind farms. They determined that in addition to geographical location, the life cycle environmental impact of wind energy is also dependent on major parameters such as type of wind turbine axis of rotation (horizontal or vertical), capacity factor, and rated power.
In the US, Chipindula et al, (2018) conducted a LCA study in Texas, USA, with attempts to quantify the relative contribution of different phases of life cycle impacts for three different sites (onshore, shallow-water, and deep-water, in Texas) using software (SimaPro). They indicated that material extraction and processing have the dominant impact with contribution of 72% for onshore site, 58% for shallow water and 82% for deep-water location across the 15 midpoint impact categories. The payback period for CO2 was estimated as 6 to 14 months and energy payback period 6 to 17 months with shorter payback periods to onshore sites. The greenhouse gas emissions (GHG) were in the range of 5–7 gCO2eq/kWh for the onshore location, 6–9 CO2eq/kWh for the shallow-water location, and 6–8 CO2eq/kWh for the deep-water location. Haapala and Prempreeda (Haapala & Prempreeda, 2014) made an LCA for two 2 MW onshore wind turbines located between the states of Oregon and Washington. They suggested that the manufacturing phase accounts for the highest share (78%) of the life cycle environmental impact for supply chains in the U.S. They estimated the energy payback period to be 5.2 and 6.4 months for the two turbines and identified that the tower has the highest contribution to environmental impacts followed by the rotor and nacelle. In Brasil, Kerstin B. Oebels and Sergio Pacca (Oebels & Pacca, 2013), assessed the life cycle of an onshore wind farm on the northeastern coast of Brazil, with aim to identify the main sources of CO2 eq emissions. They found that CO2-intensity during the life cycle of the wind farm is 7.1 g CO2/kWh and the bulk emissions are from production phase over (90%), while the transportation phase contribution only 6% of the CO2-emissions. In South Asia, (Nian et al, 2019) calculated LCOE of offshore wind in Singapore and found that offshore wind is less competitive than PV and that it could reach parity with solar PV at a distance of 300 km offshore under annual mean wind speed of 6-8 m/s. In India (Jani & Rangan, 2018) Jani Das .. et al performed life cycle analysis of energy requirement and carbon footprint for two large scale grid connected wind farms with two different technology wind turbines at two different locations to study the impact of load factor, recycling and transportation.
Several case studies were conducted in Europe. Pavel Petruneac ( Pavel Petruneac, 2015) compared onshore and offshore wind turbines in UK and concluded that CO2 emissions is the most important parameter in the LCA and the major contribution of these emissions from manufacturing and transportation processes and the payback period for onshore is 0.47 year while for offshore is 1.94 or almost two years and in general the carbon footprint is far less than conventional electricity. Martínez et al (Martínez et al, 2008) analyzed a 2 MW wind turbine that was installed in Munilla wind farm in Spain; during its life cycle from cradle to grave, considering all phases. They evaluated the environmental advantages and impacts of manufacturing and recycling process. In France (Palomo & Gaillardon, 2009) LCA has been carried out to evaluate the potential of environmental impacts associated with electricity generation from a French onshore wind farm consisting of five units of 3MW each. They calculated the energy payback time (EPBT) as (1.03 yr.), the energy intensity (EI) as (0.051 kWh used/ kWh produced) and CO2 intensity (11.77 g of CO2/ kWh produced) for wind turbine life time of 20 years and performed sensitivity analysis for life time of 40 years. In Italy (Ardente, 2008) a case study of a wind farm located in the South Italy (Sicily) was conducted to investigate the different steps of the life cycle. In Greece (Abeliotis & Pactiti, 2014) Abeliotis & Pactiti assessed the environmental impact of an onshore wind farm of 4 wind turbines 850 kW each and determined the CO2 intensity as 4.1 kg/ MWh and the energy payback period as 7 months.
There is a lack of LCA studies to assess wind energy projects in Africa and specifically in North Africa, only two studies were conducted; one in Libya (Al-Behadili & El-Osta, 2015) and the other in Ethiopia (Karkour et al., 2021). In Libya, Al-Behadili and El-Osta evaluated the primary energy consumption and carbon footprint to a wind farm on the northern coast of Libya (Dernah) and assessed the effect of recycling. The LCA revealed that energy payback period is 5.7 months, and the pay back ratio is 42. The CO2 intensity is 10.4 g/kWh without recycling process while with recycling is 4.65 g/kWh of energy generated. This study, in addition to previous one, will provide knowledge of such practice in this region.