Exploring the role of coal consumption, solar, and wind power generation on ecological footprint: evidence from India using Fourier ADL cointegration test

The transition to renewable energy sources has been identified as crucial to combating climate change on a global scale. India’s future energy vision is becoming increasingly focused on renewable markets, particularly solar and wind power, which would improve energy efficiency and allow the country to shift from a coal-based economy to a renewable-based economy by 2030. In this context, the present study intends to investigate the impact of India’s considerable investments in solar and wind power plants on mitigating environmental degradation by reducing reliance on coal-fired power. To this end, this study adopts the Fourier Autoregressive Distributive Lag (ADL) cointegration test and Fully Modified Ordinary Least Square (FMOLS) to assess the relationship between coal consumption, solar power, wind power, and ecological footprint in India using data from 1995 to 2018. The empirical results show that solar and wind power are significant and negatively related to ecological footprint, indicating that they lessen the environmental degradation. However, coal consumption is significant and positively related to ecological footprint. The study findings confirm the constructive role of solar and wind power in mitigating environmental degradation that is caused by the domination of coal-fired power generation in India, and solar and wind power are cleaner alternatives to replace coal-fired power.


Introduction
Renewable energy sources play a crucial role in environmental and sustainable development issues, such as mitigating environmental degradation, improving traditional primary energy-related carbon emissions, increasing efficiency, and economies of scale. It is obvious that using traditional energy sources in production process have detrimental effect on environment and cause climate change. The three warmest years in our history were recorded to be 2015, 2016, and 2017, even though 2016 had the greatest level of atmospheric carbon emissions in the past 800,000 years. Meanwhile, due to the increasing proportion of greenhouse gas (GhG) emissions by developing countries, it has attracted the growing attention of policy makers and environmentalists to urgently work on energy regulation measures and find a remedy for environmental sustainability. They indicated that renewable energy sources are remedies for sustainable development goals and that power generation by using traditional fossil fuel sources is a major cause of environmental degradation (Udemba and Tosun 2022). Therefore, according to sustainable development goals and international treaty agreements on climate change such as the Paris agreement, countries have begun to prioritize environmental sustainability and increase the share of renewable energy sources in the energy mix by investing more in their potential renewable energy sources (IRENA 2020;BP Energy Outlook 2020). In this context, the integration of new generation renewable energy sources into power generation systems has rapidly increased in the world. According to the International Energy Agency (IEA 2019), the power generation system that uses traditional energy sources accounts for almost 40% of carbon emissions throughout the world, and, nowadays, it continuously declines depending on increasing investment in renewable energy generation. In 2019, renewable energy generation accounted for 26.2% of total generation globally. This raises this proportion in the energy mix of the countries, mainly depending on the rapid increase in investment in solar and wind energy capacities. Solar power generation has become the most widely used power generation in the world, accounting for more than 50% of total renewable energy expansion in 2021, followed by wind power generation. Furthermore, it is predicted that these renewable energy sources will take the place of using traditional energy sources for power generation by 2035 (IEA 2018(IEA , 2019(IEA , 2021aREN21 2019;BP Energy Outlook 2020). Although India is one of the world's largest coal consumers, it is also the world's second largest renewable energy investor after China (Martinot 2009).
In detail, as the third-largest carbon emitting country in the world, India emitted 6.8% of the global carbon emission level in 2019. Besides, it is also positioned as the third-largest energy consumer due to rapid population and economic growth with a high industrialization level. Rapid population growth (1.36 billion inhabitants, 2019) and intensive industrialization have created enormous demand for energy in the country. Hence, India satisfies 80% of its energy needs by heavily utilizing traditional fossil fuels such as coal and oil (Franco et al. 2017;Crippa et al. 2020;IEA 2021b). On the one hand, although India is the second-largest coal-abundant market in the world, its coal reserves are insufficient to satisfy its increasing energy demand. Domestic demand for coal has more than doubled, reaching 60% in 2019, up from 25% in 1990, in the country's energy mix. Consequently, more than 80% of coal-fired plants in India are faced with a critical stock availability level in 2021. Thus, increasing demand for energy and facing the scarcity of coal resources have led India to invest in its potential alternative energy sources for power generation (Kumar and Majid 2020;IEA 2021aIEA , 2022. On the other hand, utilizing coal-fired technologies for power generation worsens the environmental sustainability and air quality in India. The level of carbon emissions caused by these technologies accounts for almost 45% of total energy-related emissions in India (Sholapurkar and Mahajan 2015). Consequently, energy policies in India play a vital role in mitigating carbon emissions and improving local and global environmental quality in line with global environmental agreements and the country's own sustainable development goals.
Although coal-fired generation still has a massive share in the energy mix, India is highly endowed with the remarkable potential of renewable energy sources such as solar and wind power. In this regard, India aims to increase the utilization of solar and wind power to reduce the rising dependency on importing coal and, accordingly, try to mitigate environmental problems created by coal-fired power (Wang and Liu 2021). Besides, they are fully cost-competitive and cost-effective green energy resources compared to fossil-fuel fired technologies. In particular, wind power is approximately 35% cheaper compared to coal-fired power, where this number is accounted for as 30% for solar power generation (GWEC 2020; Indian Institute of Science 2021). Accordingly, the Indian government intensified its project developments and investment in increasing the capacity of power generation from its potential renewable energy incorporation with the Ministry of New and Renewable Energy (MNRE) (REN21 2021; Shekhar et al. 2021). Since 2014, the share of renewables in terms of installed capacity has doubled while the share of coal capacity has regressed. Owing to the remarkable progress of India's energy transition by renewables deployment, the total installed capacity of solar and wind power has reached 49 GW in the 2015-2019 period (IEA 2021a). Moreover, according to a report by the Indian Institute of Science (2021), the total installed capacity of renewable energy has reached 86 GW, of which solar power accounted for 34 GW, with wind power adding a further 37.5 GW by the end of 2019. Additionally, in 2020, wind power installed capacity accounted for 43.3% of the total energy mix. That was followed by solar power with a share of 39.8%. According to the Renewable Global Status Report (2020), India has become one of the world's leading investor economies in renewable energy. At the end of 2020, India was ranked fourth according to its wind power installed capacity and fifth according to solar power installed capacity (Energy Statistics 2021).
Acceleration in investment and a rapid increase in installed capacity of renewables have led the Indian government to set a target to raise its renewable energy generation capacity to 450 GW by 2030 under the conditions of the Paris Agreement (IEA 2022). In addition, they have committed to an emission mitigation target to reduce harmful emissions and their intensity by 43% and 60% in 2030, respectively. According to the IEA report published in 2018, the share of renewable energy sources in India is expected to rise to 38% by 2040 due to the priority given to new power generations, led by solar and wind power in particular. Apart from this, coal-fired power generation is targeted to decline from 74% in 2017 to 57% by 2030 (IEA 2020). To this end, according to 2030 development goals, the upward trend of solar and wind power generation systems will keep growing in the near future. Therefore, based on these expectations, it is important to see how far India can go beyond its targeted level to make the new power generation pathway consistent.
Based upon the given information above, this study investigates coal consumption, solar, and wind power generation, and their significance for environmental sustainability for India for three main paradoxical reasons. First, India is one of the world's biggest coal consumer countries for power generation. Second, it is ranked as the third top global carbon emitter country, and lastly, it is ranked as one of the world's top three leaders depending on installed renewable energy capacity. In fact, this study aims to contribute to the existing energy and environmental economics literature with several novelties. First, to the best of the authors' knowledge, this is the first attempt to answer the question of how the use of renewable and non-renewable energy sources in India affects environmental sustainability. This is important to be determined to assess whether the intensive investments made for renewable energy sources work to reduce environmental deterioration levels in India. To do this, the ecological footprint, which is a comprehensive indicator, is first used to measure environmental sustainability in India and then regressed on different renewable energy potentials. In other words, if, as the literature suggests, solar and wind energy sources are the primary drivers of the environment, then controlling the aggregate level of emissions through these indicators may be feasible. This is also the first study to use disaggregated data for renewable energy and link coal consumption, solar and wind power energy, and ecological footprint into a single analysis. Thirdly, India is one of the biggest contributors to the world's emissions and environmental deterioration due to its dependence on fossil-fuel fired generation systems and carbon emissions from fossil-fuel generation, which grew tenfold from 181 MtCo2 in 1971 up to 2161 MtCo2 in 2017 (IEA 2019). To this end, from a theoretical standpoint, if environmental degradation due to GhG emissions, mainly carbon emissions, is strongly sensitive to the changes in coal consumption, this study will be a light for policy makers, energy, and environmental economists to pay strong attention to the country's specific energy revolution for integrating renewable energy sources for power generation to reach the sustainable development goals of India. Also, the findings of this study could be especially useful for the continuity of the renewable generation target and to lessen the adverse environmental effects of fossil fuels in India. Fourth, although few studies have investigated the wind power-carbon emissions nexus in the literature, no studies have yet examined the wind powerecological footprint nexus for India. Fifth, as an empirical and methodological contribution, this is the very first study that employs the newly developed advanced data testing method, the Fourier ADL cointegration test, to empirically analyze the steady-state association between ecological footprint and disaggregated renewable and non-renewable energy sources. This empirical technique differs from traditional cointegration techniques by considering the number of structural breaks and gives robust results accordingly. Lastly, this study extends the data set used in the literature and covers the years from 1995 to 2018, which is also the whole available data. Upon careful empirical and methodological analysis done to answer our research question, effects and implications will be recognized and designated for better identification of the workings of sustainable development. Accordingly, policy recommendations will be provided to achieve the sustainable development goals of the country.
The organization of this paper is listed below: After the introduction, Section 2 introduces the empirical and theoretical literature and is followed by Section 3, which assesses the data and the econometric methodology applied. Section 4 discusses the findings of the study, and Section 5 delivers the conclusion and policy implications.

Empirical and theoretical literature
The sustainable development issue has been widely examined in the literature. The Brundtland Report (1987) and Goldemberg et al. (1988) can be demonstrated as a starting point for this examination. Sustainable development as a concept has been constructed along with social, economic, and ecological dimensions. The Brundtland Report (1987) determines it as a development issue and signifies the needs of the current generation without wasting the resources for future generations to meet their needs. However, other studies illustrate this point as inherently a dynamic process and not a fixed condition (Mog 2004). Meadows (1998) stated that it is a dynamic concept and depends on people's values and awareness. Although there are lots of debates and arguments about this three-dimensional concept, nowadays, the sustainability of satisfying society's needs is prioritized over the sustainability of the economy and environment. However, it is well known that both society and the economy are interdependent on the environment as an essential resource supplier.
Besides this, the current and forecastable fossil fuel crisis on the national front, along with GhG emissions, especially carbon emissions, methane, and nitrous oxide, which cause an increase in global heat, leads not only India but also other countries to rethink and restructure their infrastructure and their energy dependencies. As it is mentioned earlier, the increasing global temperature and the rapid increase in the Indian population and its energy demand led India to focus on sustainable and economically efficient energy supply and improve its energy efficiency measures with the integration of renewable energy into its energy mix. Therefore, due to the rapid increase in energy demand in India, it can be stated that the most significant environmental problem in India is building up an efficient infrastructure for its energy supply to meet its social and economic goals. To this end, this study aims to clarify the debates in the literature by evaluating the significance of the potential alternative energy resources on environmental sustainability and recommending some policies to achieve development goals. Accordingly, this section is organized into three sub-sections to give the reason for the selection of the variables and empirical analysis.

Coal consumption and environmental degradation
Coal is the most cost-effective option compared to other forms of fossil fuels, and it is regarded as a reliable energy source (Apergis and Payne 2010). However, the reliance on coal has raised environmental concerns in terms of emissions. Coal-fired power technologies account for the vast majority of global emissions, and they are the main sources of pollutants such as sulfur dioxide (SO 2 ), oxides of nitrogen (NO 2 ), and particular matter (Shahsavari and Akbari 2018). Therefore, they have detrimental consequences on the environment. Wang et al. (2018) highlight that SO 2 and NO 2 are the major dangers in the life cycle of coal-fired power generation, and environmental emissions from coal-fired technologies are generated during power generation phases. In research conducted by Dunmade et al. (2019) for South Africa, it is determined that the country's coal consumption has a 95% potential to contribute to global warming. Additionally, Wang et al. (2008) indicate that coal mining has harmful effects on groundwater and vegetation. In their study, Shearer et al. (2017) assesses the future emissions of coal-fired plants under construction in India. They indicate that the country's low-carbon target could be threatened by emissions from new coal-fired power plants.
Coal consumption is a widely used source of energy in the world, and there are numerous studies done on the subject matter in the literature. In this regard, researchers have extensively used carbon emission (Long et al. 2015;Pata 2018;Joshua et al. 2020;Munir and Riaz 2020;Ansari et al. 2022;Kanat et al. 2022) to assess the environmental situation based on coal consumption. The empirical results of all these studies report that coal consumption significantly contributes to environmental damage. Recently, limited studies have considered ecological footprint as a holistic measure of environmental deterioration (Adebayo et al. 2022;Gorus and Karagol 2022;Hassan 2022). The common conclusion of these studies indicates that consumption of coal causes a rapid degradation of the environment. In the case of India, the same result is obtained by Tiwari et al. (2013), Ahmad et al. (2016), Gyamfi et al. (2021), Pata and Kumar (2021), Magazzino et al. (2021), and Adebayo et al. (2022). In short, all the existing research agrees that using coal has a negative effect on the health of the environment.

Solar power and environmental degradation
Considering its clean nature and low emissions potential, solar power is one of the important alternatives to fossil-fuel technologies (Dogan and Seker 2016). It also has long-term advantages in terms of sustainability, environmental protection, and greater potential for expanding access to reliable energy (Heffron et al. 2021). There are two main strands of literature on the relationship between solar power and the environment.
The first strand of studies has emphasized the environmental risk of solar power. Unlike the other sources of energy, solar power is free and inexhaustible because it uses sunlight to generate energy (Evans et al. 2009). However, solar power has a high degree of intermittency, which indicates that the performance of solar systems is strongly influenced by the meteorological conditions/weather fluctuations (Yasmeen et al. 2022;Yuan et al. 2022). This can be seen as the main disadvantage of solar power. Furthermore, solar power has environmental externalities such as land degradation, water use, soil pollution, solar radiation fluctuation, and hazardous substances (e.g., solvents and acids) used in the manufacturing phases of solar panels (Shahsavari and Akbari 2018;Al-Shetwi 2022). In this regard, Lambert et al. (2021) prove the negative impact of solar panels on soil quality. Bakirci and Kirtiloglu (2022) highlight that solar radiation levels gradually increase in regions with normal weather conditions, while they decrease in regions with cloudy weather conditions. In fact, most of these consequences can be corrected with well-planned management.
The second strand of studies discusses the impact of solar power on the environment in terms of carbon mitigation. For instance, Gao et al. (2021) investigate the environmental impact of solar power during its lifespan from the emissions and ecological footprint perspective. Their results show that solar power generation emits a significant amount of emissions and leaves a significant ecological footprint during the manufacturing phases, and the environmental impact of the other phases is very small. When the manufacturing phase is completed and fully installed, solar power plants are completely safe for the environment. Kotrikla et al. (2017) also report that a large amount of emissions can be removed by using solar power. Accordingly, solar power can be described as pollution-free because it emits 99% fewer emissions than coal-fired technologies and does not require fuel to operate (Sharif et al. 2021b). Additionally, recently, several studies to date almost agree that solar power is highly effective in reducing carbon emissions. These include Zhang et al. (2020) for China, Zaman et al. (2021) for Saudi Arabia, Chien et al. (2022) for China, Güney (2022) for 35 countries, Yasmeen et al. (2022) for the USA, Yu et al. (2022) for top ten solar energy consuming countries, and Zhao et al. (2022) for G7 countries. In the same line, Sharif et al. (2021b) reach the same result for the top-ten solar energy consuming countries by using ecological footprint as a comprehensive parameter for environmental deterioration.

Wind power and environmental degradation
This section discusses the environmental effects of wind power. Wind energy is one of the most feasible forms of renewable energy, and it is mainly a domestic energy source; it is unlimited and cost-effective (Chien et al. 2021;. Evans et al. (2009) state that wind power is considered the most powerful energy source among the other energy sources in terms of sustainability, and their results highlight the necessity for wind power investment to minimize environmental concern over the world. In this line, Gao et al. (2021) reveal that wind energy provides the fastest return on investment among biomass, thermal, and solar power.
Although wind power technologies have a lower environmental impact compared to traditional energy sources, they have negative externalities such as noise and habitat destruction. In addition, wind power inevitably releases pollutant emissions, which are typically formed during the production, material transportation, and installation phases (Weisser 2007; Xue et al. 2015;Xu et al. 2022). These effects are regarded as minor and can be mitigated with careful management and monitoring. In fact, wind power emits significantly fewer emissions than other power generation sources (Li et al. 2012;Wang and Sun 2012). From the life-cycle perspective, Miller et al. (2018) document that wind power emits less carbon than fossil-fired based technologies. More specifically, Marimuthu and Kirubakaran (2013) report that wind power decreases emissions compared to a coal-fired power plant, but solar power plants have a higher carbon intensity than wind power plants. Likewise, Li et al. (2020) investigate the environmental emissions caused by wind power generation in China. The life cycle assessment method reveals that wind power generation diminishes the environmental emissions, which are carbon emissions, sulfur dioxide (SO2), nitrogen oxide (NOx), and carbon monoxide (CO). Moreover, Forbes and Zampelli (2019), in their study, report that in the absence of wind power, carbon emissions would have been 14.6% greater in Ireland. Their findings also highlight that higher penetration levels of wind power leads to a large reduction in emissions. In the same way, Oliveira et al. (2019) conclude that the investment in wind power results in a reduction in total carbon emissions in Ireland.
Few studies have investigated the impact of wind power on the environment at a national or cross-national level from a climate change perspective. For instance, Destek and Aslan (2020) for G7 countries, Sharif et al. (2021a) for the USA, Güney and Üstündağ (2022) for 37 selected countries, Bargaoui (2022) for 36 OECD countries, and Zhang et al. (2022) for E5 countries indicate that wind power generation improves environmental quality, preventing harmful effects of emissions. In addition to these studies, Aydin and Pata (2020) stated that there is a path dependence in energy demand for wind power in the USA. That is, wind power has long-term effects in the USA, and energy policies can be implemented for this energy source.

Data and methodology
Given the expectation of increasing global energy demand threefold due to an increase in population, productivity, and living standards by 2050, most countries plan to improve their energy production capacity by investing in renewable energy sources. For instance, the Indian government invests in solar and wind energy to enhance the share of renewable energy sources in the energy production mix. In recent years, these two renewable energy forms have seen the most rapid expansion in India, and they serve as the structural pillars of the clean energy system. India has reached fourth place with the largest installed wind power capacity and fifth globally in terms of solar power capacity. In this context, in this study, we aim to explore the long-run association between coal consumption, solar, and wind power generation and the ecological footprint in India. The investigated relations can be presented as below: Therefore, a comprehensive indicator for environmental sustainability, i.e., ecological footprint (EFP), is used and measured as global hectares per person (gha). It comprises forestry, cropland, fishery, and grazing land along with CO 2 emissions. The data has been obtained from Global Footprint Network official website (2022). Besides, the data for coal consumption (COAL), solar power generation (SOLAR), and wind power generation (WIND) are acquired from British Petroleum statistical review of world energy (2022) and measured as terawatt per hour (www. bp. com). The annual data is restricted for the time period of 1995-2018, due to the data availability of ecological footprint. To increase the reliability of the results and decrease the heterogeneity of the series, the logarithmic forms of the variables are used for estimations. Table 1 details the descriptive statistics and correlation matrix for investigated variables.
Panel A of Table 1 shows that the mean value of EFP is − 0.065, that is between 0.173 and − 0.217. The standard deviation of the ecological footprint is 0.125, which suggests a low level of dispersion from the mean value. Furthermore, the means of coal, solar, and wind power generation are 2.274, − 2.511, and 1.898, respectively. Additionally, the Jarque-Bera (JB) statistics designate that variables are (1) lnEFP t = + 1 lnCOAL + 2 lnSOLAR + 3 lnWIND + t normally distributed and positively skewed except for wind power generation. Furthermore, the correlation matrix analysis in Panel B of Table 1 reveals that coal, solar, and wind energy sources are positively correlated with ecological footprint in India at a 1% significance level, while they are positively and highly correlated with each other.
Furthermore, the Augmented Dickey-Fuller (ADF), developed by Dickey and Fuller (1979), and Phillips and Perron (PP) (1988) stationarity tests have been employed to determine the integration order of the variables as a precondition for investigating the long-term association among studied variables. However, traditional unit root tests can prohibit structural breaks and may occasionally yield ambiguous results when the data has structural breaks. Therefore, the Zivot-Andrews unit root test has been employed to check for structural breaks and determine the stationarity level of variables under this condition. Furthermore, in the energy-environment literature, the authors mainly used dummy variables to avoid misleading results and to capture the effect of rapid changes in data. However, this is insufficient to capture the slower changes, such as economic reforms, in series. Economic reforms, e.g., supply-side policies, are long-term policies and have small and long-term effects on other variables. Therefore, they may not be captured with traditional unit root tests. To avoid these deficiencies and improve the strength of the results while testing the cointegration relationship among examined variables, a newly developed model, i.e., Banerjee et al. (2017), has been utilized. This method uses the Fourier function to estimate the results and can capture multiple breaks (Gallant 1981;Gallant and Souza 1991). It was developed model of Banerjee et al. (1998) and can be presented with the following equation (Eq. 1). where deterministic trend is depicted with d(t) and can be defined as below: where t depicts for trend, and N indicates for the no of observations. Moreover, stands for particular number of frequencies. It can be determined with the minimum sum of squares method. Then, Eq. (2) was implemented into equation one, and the following model was generated.
Then, the null hypothesis of no cointegration relationship among investigated variables ( ∅ 1 = 0) was tested against the alternative hypothesis which states for cointegration association among investigated variables ( ∅ 1 < 0) . The following test statistic was used for this purpose.
where ∅ 1 and se ( ∅ 1 ) indicate ordinary least squares estimators and standard error term of ∅ 1 , respectively. This test is recently commenced to the literature, and yet none of the studies investigated the cointegration relationship of renewable energy potentials of India, i.e., coal, solar, and wind energy, with its environmental sustainability indicators, i.e., ecological footprint by employing Fourier model estimation. Therefore, this technique distinguishes our paper from the previous studies in the energy-environment literature. Moreover, Bounds test has been utilized to confirm our results obtained from the Fourier cointegration test. Lastly, to capture the direction and magnitude of the effect of wind power generation on environmental sustainability in India, FMOLS model has been utilized. This model was applied to examine the robustness of the outcomes under the condition of small sample size and serial correlation and endogeneity problems in the regressors.

Empirical results
As mentioned before, ADF and PP unit root tests have been utilized to determine the integration order of the variables as a prior condition for the cointegration test. The minimum (2) Δy it = d(t) + ∅ 1 y 1,t−1 + � y 2, t−1 + Δy 2t + t value of the AIC criterion is used to determine the optimal lag length for these tests. The results of the unit root tests are provided in detail in Table 2. Consequently, all of the studied variables have a unit root at their level form and are stationary at integration order one, I(1), at different significance levels. In addition, the Zivot-Andrews unit root test is conducted, and the structural break for ecological footprint occurs in 2013, coal consumption in 2014, solar energy generation in 2007, and wind power generation in 2004. In these years, India has reiterated its reforms on the economy and eliminated its rules and deregulated the market for more foreign direct investments. To this end, India aims to catalyze economic growth which causes significant deteriorations on environment and energy sector. These results satisfy the precondition of the Fourier ADL cointegration test. A second step is the verification of long-run equilibrium associations among the variables examined with newly established, Fourier ADL cointegration test. Also, Fourier ADL test results are verified by conducting the ARDL Bounds test. Table 3 gives the outcome of the cointegration tests. Accordingly, the trace statistics show the cointegration relationships among studied energy sources with ecological footprint level at 1% significance level for both tests. In other words, these results indicate that coal consumption, solar power generation, wind power generation and ecological footprint have long-run steady-state relationship in India.
To test the significance and the magnitude of the effect of studied energy sources on ecological footprint in the long run, FMOLS model has been utilized. The empirical outcomes are tabulated in Table 4. Based on the findings, it is clear that all the studied variables have a statistically significant effect on ecological footprint in India.
According to the results, coal consumption is positively related to the ecological footprint, which infers that coal consumption leads to environmental degradation. More specifically, an increase in coal consumption by 1% causes a surge in environmental degradation by 0.713% in the long run. Given India's heavy reliance on coal to satisfy its high energy demand, this is an expected outcome, and it shows that dependence on coal has adverse environmental consequences. As a result, environmental degradation in India has accelerated as the country's coal production has expanded to meet the rising need for energy. This fact has an important implication for the energy target of the Indian government, which is the necessity to shift the country's energy use toward clean energy sources with little or no    Magazzino et al. (2021), Gyamfi et al. (2021), Pata and Kumar (2021), and Adebayo et al. (2022). Regarding the coefficient of solar power, it is statistically significant and negatively associated with ecological footprint. A 1% rise in the proportion of solar energy generation leads to a 0.016% decline in the environmental degradation level. As a clean and sustainable energy source, solar power can help contribute to reducing environmental degradation. This is because solar power does not rely on the combustion of coal-fired power and other harmful materials. Also, it can decrease both the level of dependence on coal-fired power and environmental problems caused by coal-fired power generation in India. Given this, solar energy is worth investing in in India, and further developments in solar capacity may provide even greater environmental advantages. This finding is supported by the empirical result in the study of Wu et al. (2021), in which solar energy is the promising carbon-neutral option compared to coal-fired generation. This result is in line with Zhang et al. (2020) for China, Sharif et al. (2021a) for USA, Yasmeen et al. (2022), and Yu et al. (2022) for top-ten solar-consuming countries, and Zhao et al. (2022) for G7 countries. However, this contrasts with the views of Destek and Aslan (2020) for G-7 countries, and Magazzino et al. (2021) for India who reported the insignificant effect of solar power on environment.
Finally, wind power has a significant negative effect on the ecological footprint. For every 1% increase in wind power generation, there is a decline of 0.072% in the level of environmental degradation in the investigated period. The results show that wind power has the potential to be considered as one of the best alternatives among potential renewable energy sources to fossil fuels. Also, findings support the view that wind power is an eco-friendly energy source. This is because the process of transforming the kinetic energy of the wind directly into energy does not produce any pollution or emissions. This would help India ensure a better environment and reach its environmental sustainability targets. Wind-generated energy is therefore highly recommended for the Indian economy. Furthermore, this result can be supported by the findings provided in the recent study by Li et al. (2020), in which wind power generation is more effective at controlling emissions than coal-fired power. The empirical finding can also be justified by a study like Zhang et al. (2022) for selected five emerging economies, including India.
Consequently, empirical findings support the fact that solar and wind power are cleaner alternatives to replace coal-fired power, and India has started to take advantage of the utilization of these clean sources. Solar and wind power have strong potential to reduce the dependence on coal-fired power and can lessen the environmental damage that is caused by the domination of coal-fired power generation in India. Accordingly, increasing the share of solar and wind power in the energy generation mix and continuing on the path toward achieving a low-carbon economy will enable India to reduce environmental degradation and meet its clean energy target. In this line, solar and wind power have become key components of the energy mix in India, and the change in the energy structure of the economy has been successful in mitigating environmental degradation. As COP26 (2021) says, it is important for the future of the world to use more solar and wind power and less coal-fired power.

Conclusion and policy recommendation
India is currently the third-largest energy consumer in the world, and its energy needs are rising continuously. The energy sector relies heavily on fossil fuels to meet rising demand for energy, with coal-fired power accounting for the vast majority of the country's energy consumption. In 2019, India accounted for 11.8% of global coal consumption; however, demand for coal decreased by 8% in 2020, despite India being the second-largest coal importer behind China (IEA 2021a, b). There is a huge concern regarding the adverse impact of coal-fired power plants on the environment. Therefore, immediate investments in clean energy sources are necessary, and the replacement of coal and other fossil fuels with renewable energy sources is a very important step toward a better environment.
In this context, this study explores the long-term associations between coal consumption, solar power generation, wind power generation, and ecological footprint covering the period 1995-2018 to determine the best alternative resource to fossil fuel energy sources. To this end, the Fourier ADL co-integration test and the Bound test are employed. Both tests revealed the long-run steady-state associations between coal consumption, solar power generation, wind power generation, and ecological footprint. Moreover, the long-run coefficients are estimated by employing the FMOLS method, and the results indicate that solar and wind power generation have a negative and significant association with ecological footprint. In other words, increasing the share of solar and wind power generation in the energy mix leads to mitigating the environmental deterioration in India. Furthermore, the findings also reveal the positive effect of coal consumption on the ecological footprint in India, indicating that coal consumption causes environmental deterioration. These results imply that environmental degradation in India can be reduced by increasing the deployment of power generation from solar and wind power. Because, in contrast to fossil fuel power plants, solar and wind power plants are environmentally friendly, emitting no direct emissions, hazardous pollutants or carbon dioxide during their operating stages.
In light of the results, efficiency measures and fossil fuel conservation policies must be implemented to prevent environmental degradation and achieve sustainability objectives. Moreover, India has a huge amount of energy-generating potential from solar and wind power, which are important for current and future energy security. Accordingly, investments in solar and wind power play a crucial role in ensuring the environmental sustainability of India. The Indian government should therefore establish policies for the transition from fossil fuel-based energy to clean energy sources, especially solar and wind power, to reduce the environmental deterioration level. In this way, it will also help the country to take a strong position to combat the climate change problem. To reach this target, the Indian government should prioritize environmental quality by considering the government budget. They can support and subsidize the private sector to promote the integration of solar and wind power plants, or they can concentrate on public-private collaborations. In addition, corporations that utilize clean energy may be rewarded with subsidies and tax breaks, while those that continue to excessively use fossil fuels could be taxed for their carbon emissions. The proceeds from such a tax might be allocated to these initiatives as a means of promoting the transition to clean energy sources and investing in solar and wind power infrastructure. Therefore, economic, lowcarbon, and sustainable development targets are achievable with an increasing share of solar and wind power in the country's energy mix. To this end, future studies may investigate the same problem at the sectoral level for India to have a detailed investigation and help policy makers design comprehensive policies.