Author: Rohan Choukkar, Centre for Innovation Incubation and Entrepreneurship, IIM Ahmedabad
The growing consciousness on renewable energy has helped increase adoption of the wind and solar energy and created an environment for newer models of generating the same, in recent years. India is looking at a radical overhaul of its generating mix and plans to derive 60%* of its power needs from non-fossil sources by 2027¹. In a heartening shift, it’s not just policy or dialogue on climate change but the proliferation of cost competitive options that are responsible for increased adoption.
Solar photovoltaic (PV) modules, in fact, have their own version of Moore’s Law – Swanson’s Law avers that solar PV module prices drop near 20% with the doubling of cumulatively shipped volumes. This mag
nitude of price drop tears up rulebooks for the electric utility industry, but this relentless progress comes with an inbuilt bug. Our grids have been built over the 20th century, structured around baseload power generators³. The intermittency inherent in wind and solar, because of their dependence on weather, coupled with a lack of effective demand forecasting, makes the effective integration of a large amount of renewable power a significant challenge. Finding the means to store the energy will spur adoption of renewables in our generation mix.
Lithium ion for energy storage
The gold standard today for energy storage, even at a utility scale, is the ubiquitous lithium-ion battery. The battery’s chemical properties allow high energy density with good efficiency making it ideal for smallest devices and large grid-scale battery farms. Lithium ion, however, cannot solve every storage problem.
For one, scaling is a major challenge. Lithium ion batteries have rather high active material costs and degrade due to cycling over time. After all, all mobile phone users battle with a poor life of their phone battery which only reduces with time. The life and performance of a battery reduce with each charge-discharge cycle as conductive channels within the battery that move these ions break down further. Clearly, this technology class is a sub-optimal solution if the need is of a long duration storage that exceeds four hours, and many charge-discharge cycles.
There have been some long-standing ways to store surplus energy for use during periods of high demand, but their adoption has been slow for several reasons. Ninety-five percent of all storage facilities today are pumped hydroelectric projects, the first of which date back as far as the early 1900s. The premise is fairly simple – water is pumped to an elevated reservoir from one at a lower elevation during periods of surplus power. This can then be used for load balancing but comes with very obvious geographic limitations. Thermal storage technologies are also long established, using media as disparate as liquefied air and molten salt, but these have faced challenges when scaled up – large space, high cost and elevated thermal losses are hallmarks of bigger projects.
Fortunately, there are some interesting technologies on the horizon which promise to make large-scale, long-duration storage cheaper. Among the most well-known are flow batteries. Flow batteries essentially comprise two tanks of liquid that are made to flow past each other while separated by a membrane. While their energy densities are relatively low, these batteries enjoy a substantial scaling advantage. More capacity simply means adding more (or bigger) tanks of electrochemical fluid. In addition, many of these are basic redox reactions and hence ensure little degradation in the fluids and therein longer charge-discharge cycles and significantly longer lifespan of the battery making them ideal for large grid storage applications if one were to overcome certain engineering challenges. For one, the amount of parasitic power# is very high, as the pumps need to maintain circulation of the electrochemical fluid circulating on-site. Current technological advances focus on making more stable and non-corrosive fluids, to bring down costs while improving safety and environmental friendliness.
Lithium-air batteries are frequently described as the holy grail of energy storage, but they are a long way away from leaving the confines of a laboratory. Zinc-air batteries, the poorer cousin of lithium-air, have been known for a century and are now making a comeback. Traditional zinc-air batteries have been non-rechargeable, but substantial progress has been made in reducing electrode corrosion and increase cycle life, to reduce their use-and-throw nature. If efforts to scale up this technology are successful, zinc-air batteries promise to provide storage at a fraction of the cost of lithium-based batteries, and in some cases becoming cost competitive with lead acid batteries. Zinc-air batteries also show very little degradation under zero charge conditions – unlike lithium batteries – making them very useful for niche applications like microgrids.
In conclusion, exciting times are in store for the energy storage market. Longer-duration storage technologies will play a pivotal role in ensuring energy generation and storage is sustainable and environment-friendly.
#Parasitic power represents the power consumed even when the appliance is shut off, that is standby power *http://www.cea.nic.in/reports/committee/nep – Chapter 5 ¹https://www.theguardian.com/world/2016/dec/21/india-renewable-energy-paris-climate-summit-target ²http://www.abc.net.au/news/2017-03-11/could-the-tesla-powerpack-really-solve-sas-energy-woes/8345864 ³Base load power generator is a large, centralised power plant, primarily coal that provides steady and consistent output
About the Author:
Rohan is an alumnus of the University of Pennsylvania, with a background covering renewable energy technology, advanced manufacturing, optimisation methods and supply chain management. He is driven by the challenges of scaling up emerging business and market models.