Greening Electricity Grids through Wind, Solar, or Both? – A Discussion From an “Energy-Drought” Perspective

Wind installation near Hassan, Karnataka, India (Photo provided by the author)

Greenhouse gases generated by the electricity sector are a major concern for climate change mitigation. Decarbonising the electricity sector is essential to reach "Net-zero" targets worldwide. Therefore, the proportion of green renewable (wind and solar) power capacity in the energy mix is increasing rapidly. However, wind and solar are weather-dependent sources. Variations in generation can occur in different timescales, starting from minutes to hours and to days. When there is no renewable generation for a longer than average duration, balancing electricity demand with the available generation in a renewable-rich grid becomes challenging. We define these events as "energy droughts." These are rare but large impact events.

We analysed India's wind, solar, and hybrid energy droughts for the first time using a stochastic weather generator. While previous studies use available short-time series data, we simulated 5,000 years of possible wind solar generation dataset to estimate rare energy droughts. We show that wind droughts are more intense than solar droughts in India. Our work shows that the hybridization of wind and solar makes renewable energy droughts rarer. However, we found that the benefits of hybridization are regionally dependent. In South India, hybrid plants have advantages over either wind or solar plants alone. In comparison, for Rajasthan in northern India, the benefits of hybridization are limited. This is because, while windy days are cloudier in South India, in Rajasthan, the opposite occurs, and high wind days are less associated with cloud cover. This means that most of the time, wind and solar generation are negatively correlated in South India, but are positively correlated for Rajasthan. We also found that when one of the regions (South India or Rajasthan) has a renewable drought, the other region has only a 10% probability of having a similar drought (Gangopadhyay et al., 2022). 

It is vital to examine the policy changes required to incentivise the installation of wind-solar hybrid plants, especially in those regions where the possibility of combined drought reduction exists. The drought mitigation impacts of wind-solar hybridization remain unexplored in available literature. Based on our analysis, it would be beneficial to encourage the strategic installation of hybrid plants to mitigate renewable energy droughts. Renewable energy droughts are an important and growing challenge in a deeply decarbonized electricity grid. 

In addition, a policy framework needs to be established to assist in the strengthening of grid interconnections across India. These would result in balancing regional-scale extreme renewable energy droughts. India has five grid regions, and they have limited interconnections. Inter-regional grids need to be strengthened to mitigate regional-scale renewable energy droughts in a renewable-rich grid, and inter-regional energy trade needs to be encouraged.

Energy droughts are only one of many factors for evaluating the optimal energy mix and electricity capacity planning within a country. Factors such as total electricity supply, avoiding over-generation or surplus power, balancing generation with demand, limiting fuel import costs, minimizing per capita emissions from the life cycle of energy generation, managing the demand for land, and minimizing total energy and electricity systems costs also need to be considered when evaluating various energy mix options (Saraswat and Digalwar (2021), Laha et al. (2020)). Rose et al. (2020) argue that wind resources are better correlated than solar resources with the seasons and times of day when energy demand is high. However, they agree that wind resources experience very high seasonal variability. Increasing wind capacity typically involves accompanying investments in gas generators and storage to provide continuous power supply during periods of low wind speed. 

Reference: 

1. Gangopadhyay et al., 2022: A. Gangopadhyay, A.K. Seshadri, N.J. Sparks, R. Toumi,
The role of wind-solar hybrid plants in mitigating renewable energy-droughts, Renewable Energy, Volume 194, 2022, Pages 926-937, ISSN 0960-1481,

https://doi.org/10.1016/j.renene.2022.05.122.


2. Saraswat and Digalwar, 2021: Saraswat S.K. and Digalwar A.K., Evaluation of energy alternatives for sustainable development of energy sector in India: An integrated Shannon’s entropy fuzzy multi-criteria decision approach, Renewable Energy, Volume 171, June 2021, Pages 58-74 available at https://doi.org/10.1016/j.renene.2021.02.068 accessed on 3 Nov. 21


3. Laha et al., 2020: Laha P., Chakraborty B., and Østergaard P.A., Electricity system scenario development of India with import independence in 2030, Renewable Energy, Volume 151, May 2020, Pages 627-639, available at https://doi.org/10.1016/j.renene.2019.11.059 accessed on 3 Nov. 21


4. Rose et al., 2020: Rose A., Chernyakhovskiy I, Palchak D,Koebrich S., and Joshi M.,Least-Cost Pathways for India’s Electric Power Sector, National Renewable Energy Laboratory, Technical Report, NREL/TP-6A20-76153, 2020, available at https://www.nrel.gov/docs/fy20osti/76153.pdf accessed on 3 Nov. 21

Author: Anasuya Gangopadhyay, GAUC Global Youth Ambassador and PhD student at India Institute of Science (IISc).
Editor: Jeffrey Tykot

The article reflects the opinions of the author and not necessarily that of GAUC