Taking Stock

Energy storage technologies for electric vehicle applications

Running parallel to the evolution of the renewable energy sector is the innovation in energy storage technologies, which has caught the attention of the industry as well as policymakers across countries. The importance of efficient energy storage solutions in enabling and advancing the power sector in general and renewable energy in particular cannot be emphasised enough.

The mismatch between peak generation and peak demand time intervals calls for the adoption of these storage solutions. The highly sporadic nature of renewable energy generation leads to unnecessary losses. For instance, solar energy generation is concentrated during midday whereas the peak energy demand is high during the night, placing a heavy load on the grid. The excess solar energy could instead be stored for later use during high demand.

However, the evolution of energy storage solutions has not been very satisfactory. Commercially, energy storage solutions have not been able to scale up to their full potential. Renewable Watch takes a look at the emerging energy storage technology landscape…

Popular technologies

Lead acid

Lead acid has been the most popular technology for energy storage due to many reasons. Lead acid technology is a mature technology since it has been in use for more than 140 years, making it the oldest and most readily available technology in the market. Therefore, lead acid batteries retain the lion’s share of the storage market.

Although this technology has been around for very long, it has a number of shortcomings. Lead acid batteries are heavy and bulky, and pose a risk of overheating during charging. Typically, these batteries have a cycle life ranging from 300 to 500 cycles. Moreover, lead acid batteries are also not suitable for fast charging.

Lithium-ion

Over the past five years, the uptake of lithium-ion batteries has increased. Lithium-ion batteries have begun to dominate particularly in the e-mobility and consumer electronics segment. These batteries have many advantages over other technologies available in the market. There are different types of lithium-ion batteries such as lithium iron phosphate, lithium cobalt oxide, lithium cobalt aluminium, lithium nickel manganese cobalt and lithium titanate. Each type of battery is suitable for different applications.

The higher energy density of lithium-ion batteries makes them viable for longer durations of usage between charges. In addition, these batteries do not face the issue of self-discharge. Further, lithium-ion batteries have the added advantage of longer cycle life. The cycle of different chemistries of lithium-ion batteries can range from 1,000 to 20,000 cycles. Overall, these batteries require lesser maintenance as compared to other batteries in the market.

However, lithium-ion batteries come with their own limitations. Protection is an issue when it comes to these batteries. Besides, these batteries should be prevented from being overcharged and discharged to extremely low levels. Further, the current has to be maintained within safe limits to ensure safety. Lithium-ion batteries are costlier when compared with other traditional technologies.

Sodium-ion

A new development in this segment has been the coming of sodium-ion batteries. These batteries are being thought of as a potential replacement for lithium-ion batteries in the next 5-10 years. The main advantages of sodium-ion battery technology are that sodium is readily available and is inexpensive as compared to lithium.

A team at Stanford University is developing a battery using sodium-based electrode material, which costs only $150 per tonne, compared to $15,000 needed for a tonne of lithium. The team believes that it can deliver the battery for less than 80 per cent of the cost of a lithium-ion battery with the same storage capacity.

Although inexpensive, this technology does not stack up well when compared to lithium-ion batteries in terms of efficiency and performance. They also have shorter lifespan and are unsuitable for applications in smaller systems.

Flow batteries

Flow batteries are generally large in size, which makes them best suited for industrial and utility-scale applications. Due to their size, vanadium flow batteries have limited usage and cannot be used for smaller applications such as in electric vehicles. The most popular flow battery technologies are vanadium redox and zinc bromine. Vanadium flow batteries outperform lithium-ion options for utility-scale battery storage. These batteries are more scalable, safer and long-lasting than lithium-ion batteries.

Vanadium batteries are fully containerised and are reusable over semi-infinite cycles. In addition, these batteries discharge 100 per cent of stored energy and do not degrade for more than 20 years. These batteries use the multiple valence states of vanadium to store and release energy. Meanwhile, zinc bromine flow batteries offer the highest energy density in flow batteries. However, the high cell voltage and the highly oxidative nature of bromine require materials capable of withstanding these chemical conditions. Not only are these materials expensive but bromine is also highly toxic, which requires the maintenance of high safety standards.

Cost versus cycle life

Due to variation in the cycle life of different types of batteries, a comparison of the cost per cycle provides an insight into the true cost of various technologies. While lead acid batteries, which have been dominant throughout, have a very low cost, they also have a comparatively shorter cycle life. Meanwhile, advanced lead batteries offer a longer cycle life but are costlier.

Lithium-ion batteries, although more expensive than lead acid ones, are moderately priced and have moderately high cycle life as well. Flow batteries, on the other hand, generally have longer cycle life and entail higher costs. Meanwhile, the cycle life of sodium-ion batteries is more than that of lithium-ion and less than that of flow batteries.

Cost trends

Apart from lead acid, most other technologies are witnessing a significant reduction in prices, owing to increase in innovation. Lead acid batteries have become stagnant in terms of pricing because cost of materials account for almost 85 per cent of the total cost, hardly leaving any scope for innovation and further reduction in prices. However, many studies are being carried out to increase their charge/discharge rates in order to further reduce the overall cost of lead acid batteries.

Lithium-ion in particular has witnessed a significant drop in cost over the past decade and is expected to touch the $100 per kWh mark by 2018. The commercial viability of lithium-ion batteries has already been established by its use in electric vehicles. However, higher upfront costs in comparison with conventional vehicles has somewhat dampened the uptake of electric vehicles. As per industry estimates, comparable upfront costs are expected to be a reality by 2025.

Challenges and the way forward

The lack of data availability to quantify system-level savings is a major issue facing the adoption of energy storage technologies. Typically, the upfront cost of green technologies and conventional technologies is considered as a deciding factor. However, the additional environmental costs incurred by conventional technologies are far more and should be factored in as well.

Although, the Ministry of New and Renewable Energy and NITI Aayog have taken steps in the right direction, these measures fail to take advantage of the achievements in other government departments. Therefore, there needs to be more coordination among departments in order to capture the externalities of incumbent technologies.

The rapidly changing landscape of energy storage technologies has led to a wait-and-watch approach in their adoption.  Further, the energy storage segment has not been very successful in attracting investments. The segment could benefit from more innovative financing mechanisms in order to gain investor interest.

Despite challenges, the outlook for the segment remains positive. With the increasing uptake of renewable energy, the adoption of efficient energy storage solutions is expected to witness strong growth. Moreover, the costs of these solutions are likely to fall further in the near future. Government support in terms of providing a push to the electric mobility segment should also boost its growth.

Based on a presentation by Dr Rahul Walawalkar, President and Managing Director, and Global Head, Emerging Technologies and Markets, Customized Energy Solutions, at a recent Renewable Watch conference, E-Mobility and Charging Infrastructure

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