1. Introduction
At present, the introduction of renewable energy is being promoted in electric power sectors worldwide to respond to the issue of climate change [
1]. In 2022, global wind power generation increased by 265 TWh, reaching 2100 TWh [International Energy Agency (IEA) [
1]]. By 2030, more than 500 GW of new renewable energy is planned to be added [
1,
2]. Among renewable energy sources, solar power generation is becoming more prominent, while wind power generation is also being developed not only onshore but also offshore [
3]. Furthermore, many countries have ratified the Paris Agreement adopted at COP21 [
4]. The Intergovernmental Panel on Climate Change (IPCC) has been conducting multiple scenario analyses and presented the low energy demand (LED) scenario in its integrated report in 2019 [
5].
However, wind power generation equipment has a lifetime, and a large amount of waste is predicted to be produced at the end of that lifetime [
6,
7,
8,
9]. The previous study established multiple-scenario life cycle stages, such as manufacturing and operation and management (O&M), of wind power generation [
6].
With regard to wind power generation, the disposal of waste from wind blades is considered a problem [
6]. Wind blades are made from glass-fibre-reinforced plastic (GFRP) and carbon-fibre-reinforced plastic (CFRP), which are extremely lightweight, allowing for the production of strong structural components [
10]. To date, several previous studies have discussed how wind blades can be disposed of at the end of their lifetime, including landfilling after cutting, incineration, thermal recycling (energy recovery), mechanical recycling, and chemical recycling [
10,
11,
12,
13,
14,
15,
16,
17,
18]. However, given the physical properties of GFRP/CFRP, two challenges exist in the recycling of materials and making secondary use of recovered materials. The first problem is a decrease in the strength of recycled materials. GFRP and CFRP cannot be reformed because they are cross-linked [
19], and obtaining the same strength as the primary material is difficult for materials recovered through mechanical recycling [
16]. The strength of recycled glass materials recovered through thermal recycling can be reduced by up to 80% [
20]. The second issue is the low economic incentive for recycling. The cost competitiveness of materials obtained by recycling is low [
21]. The widespread use of materials recovered from mechanical recycling requires significant financial support [
7]. Chemical recycling can be costly compared with other methods [
20]. For these reasons, incineration and landfilling have been suggested to continue as the primary treatment options for wind blade waste [
9,
17,
18]. Even if wind blade waste is recycled, a possibility exists that the recovered materials will not be properly recycled.
Japan is one of the world’s largest energy consumers and importers, and it relies on imports from other countries for nearly 96% of its primary energy supply at the national level [
22]. Thermal power generation accounts for 72% of Japan’s electricity sector and is seen as a challenge [
23]. In 2020, the country declared that it will aim for carbon neutrality (a concept that means net zero in terms of greenhouse gas [GHG] emissions and absorption) by 2050 [
24]. To achieve carbon neutrality, effort in the energy sector, which emits 85% of GHGs, is important, and Japan’s 6th Basic Energy Plan sets the goal of rapidly increasing renewable energy use in the power sector in the future [
25]. To achieve this goal, Japan is conducting multiple energy scenario analyses to review its power source mix with the aim of achieving decarbonisation by 2050 [
26,
27,
28,
29]. At present, solar power generation in Japan is being introduced through subsidy systems, such as the feed-in tariff (FIT) system, which started in 2012, and the amount of solar power generation rapidly increased from 6613 GWh to 94,801 GWh from 2012 to 2022 [
1]. Meanwhile, the amount of wind power generation in 2022 was 9603 GWh [
1], and the introduction of wind power generation has been delayed. In the future, plans are underway to introduce not only onshore wind power but also offshore wind power in large quantities, and wind power generation is predicted to increase [
3].
Therefore, the waste generated from solar power generation and wind power generation equipment, which is discharged after its lifetime ends, should be considered. Regarding waste treatment for solar power generation, only a few countries other than the European Union market regulate waste solar panels; however, Japan is actively involved in the research and development of recovery technologies and manufacturers’ recycling effort [
30]. In Japan, where the large-scale introduction of wind power generation is predicted to occur in the future [
31], no studies (to the authors’ knowledge) have yet predicted the future amount of wind blade waste and CO
2 emissions from its treatment processes. Furthermore, wind blade waste from wind power generation has not been considered in multiple energy scenario analyses for Japan [
29,
31] that are currently being conducted. After considering Japan’s unique wind power generation lifetime, estimating the future disposal timing of wind blades and the amount of CO
2 emitted during their disposal from the energy scenarios [
5,
31] devised by IPCC is important to achieve low carbon emissions in the future. In addition, by considering the blade waste generated from all stages of a wind blade’s life cycle (manufacturing, service, and end-of-life stages), estimating the total amount of wind blade waste is possible. Japan, where the wind power generation industry is not yet fully developed, is currently engaged in debates on how to dispose of blade waste, referring to Europe and other countries with advanced wind power generation sectors [
32].
Therefore, the objective of this study is to quantitatively estimate the total amount of waste emitted during each life cycle of wind blades (from manufacturing to disposal) and the amount of waste disposed of when large quantities of onshore/offshore wind power are introduced in Japan towards achieving a low-carbon society. When calculating the CO
2 emissions of the blade waste treatment process, European recycling or treatment processes [
10,
11,
12,
13,
14] were considered.
Recycling methods for GFRP/CFRP, which constitute wind blade waste, have been studied [
10,
12,
13,
14,
16]. However, the recovered materials have low material strength [
16,
19,
20], and economic incentives are small [
7,
20,
21], so recycling methods are not widely accepted by society [
9,
17,
18]. Therefore, in this study, CO
2 benefits from secondary use were not included in the system boundary, and the global warming potential (GWP) [tCO
2eq] was calculated quantitatively to predict CO
2 emissions in line with the actual situation.
4. Conclusions
This study quantitatively estimated the amount of CO
2 emissions during the processing of waste generated in each life cycle of wind blades (from manufacture to disposal) when mass-introducing onshore/offshore wind power toward low carbonisation while considering recycling or treatment processes used in Europe [
10,
11,
12,
13,
53]. When recycling wind blade waste, the strength of GFRP/CFRP is reduced and the cost of recycling is increased, and thus, the secondary use of materials has not actually progressed. In this study, calculations were performed on the assumption that although the recycling method for GFRP/CFRP in wind blades has been socially implemented, the usefulness of secondary materials cannot be established.
We calculated the installed/decommissioned capacity of wind power generation in Japan until 2100 by considering the LED scenario (AIM). The life cycle of wind blades was divided into the following stages: manufacturing, service (O&M, replacement), and end-of-life, by considering European recycling or treatment processes. The total amount of blade waste by 2100 was calculated. When the average lifetime () is 20–25 years, the installed capacity will sharply increase from 2031 to 2040 (21.5–22.0 times), reaching its maximum value in 2040. However, installed capacity will decrease sharply from 2040 to 2041 (0.084–0.12 times) and remain stable from around 2060. Meanwhile, when the average lifetime () is 20–25 years, decommissioned capacity will gradually increase and reach its maximum value from around 2030 to 2065, and then it will decrease thereafter. To achieve carbon neutrality in 2050, rapidly introducing a large amount of wind power generation from 2031 is necessary. In particular, offshore wind power is predicted to expand or wind turbines will become larger than those used in onshore wind power.
Nine calculations were performed by combining three cases of parameter (
) representing the damage rate of wind power generation and three cases of the wind blade waste emission factor at each life cycle stage. The base case, in which values that were intermediate for both parameters were chosen, shows an exponential increase until 2065 and then a decrease. Meanwhile, in the two cases that combine the parameters (
= 4.07) in which wind blades are less likely to be damaged, the value will be smaller than that of the base case after 2030. After that, however, one will cross the base case in 2053 and the other in 2055, and then reach the maximum value in all the cases in 2060 and the minimum value in all the cases in 2073. On the basis of the 2020–2100 LED scenario (AIM) [
31], the amount of wind power blade waste was calculated, and the maximum value was 0.15–0.17 Mt.
At present, the options for processing wind blade waste are landfilling and incineration. However, even when recycling is considered, the GWP of wind blade waste treatment process in 2050 (150.2–188.3 MtCO2eq) remains extremely large, accounting for approximately 63.9–80.1% of total GHG emissions in 2050 under the LED scenario (approximately 235 MtCO2eq). Moreover, the cumulative GWP of the wind blade waste treatment process until 2100 is 11.4–12.9 GtCO2eq. Even when thermal power generation was replaced with wind power generation, the GWP of the wind blade waste treatment process accounted for 82.5–93.6% of the GWP reduction due to the substitution. Therefore, this study revealed for the first time that the amount of CO2 emissions contributed by the wind blade waste treatment process is too large to be disregarded. However, the results of this study do not consider the environmental benefits of secondary use, reflecting the current situation where secondary use is difficult to implement owing to the reduced strength and low economic value of recycled materials during recycling. However, as technology develops in the future, where strength is maintained and costs decrease, the secondary use of recovered materials may become widespread. In this case, the calculated GWP during blade waste processing would be based on the fact that primary materials would be reduced through the secondary use of recovered materials, and CO2 emitted during this process would be reduced.
Accordingly, several issues, such as the quality and economic efficiency of secondary materials [
7,
17,
19,
20,
21], must be urgently resolved to realise a low-carbon society.
In this study, predictions were made in accordance with the LED scenario [
31], but the amount of power generation equipment that can be installed in 1 year is considered to be limited by the population involved in the wind power generation sector, costs, and construction period. Therefore, future work is expected to incorporate these constraints into the model and examine them closely.