EV Chapter 6: Energy Storage Systems in EVs
Automobiles release a substantial amount of carbon dioxide into the atmosphere, putting us at risk of pollution and greenhouse gas emissions. Currently, many innovative vehicle technologies are being developed with the aim to wean automobiles off of their need for fossil fuels. Energy storage is the core element that is responsible for the popularization and commercialization of Electric Vehicles (“EVs”).
To enable EVs to become an effective and sustainable transportation option, significant R&D work has been in process around the world to address the primary challenge with EVs, i.e., energy storage and energy generation systems.
Currently, there are four viable energy storage options for EVs i.e., batteries, fuel cells, supercapacitors and ultrahigh-speed flywheels. These energy storage systems have a common problem - they either lack high specific energy (“HSE”) or high specific power (“HSP”). HSE is advantageous for extended driving range, whereas HSP is advantageous for high acceleration and hill climbing capacity.
Batteries: Batteries are essential for all types of EVs including, hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs) and pure electric vehicles (EVs). Electric motors are used to turn the wheels of the cars which are powered by electricity stored in a battery pack. The batteries are refilled using grid electricity, either from a wall socket or a separate charging unit when they get depleted. Pure EVs are solely powered by electricity and do not run on any fuel, however, one has the option to use fuel in case of HEVs and PHEVs. However, for charging the EV, electricity can be generated from a variety of sources including hydropower, wind power, geothermal power, wave/tidal power, solar power and nuclear power. EV integration powered by renewable energy is becoming a preferred approach for mitigating climate change and promoting energy transition, according to studies being done to see how these various sources might be used to recharge the batteries in EVs. India is in the early stages of developing regulations for EV, and it has a great opportunity to ensure that EV charging allows for more usage of renewable energy.
Fuel cells: EVs with fuel cell are powered by hydrogen. They are equipped with advanced technologies to increase efficiency such as regenerative braking systems to capture the kinetic energy normally lost during braking and store it in the battery. They are more fuel efficient than conventional internal combustion engines and release no tailpipe emissions—only water vapor and warm air. In comparison to batteries, fuel cells are less mature and expensive for EV application.
In India, the first hydrogen fuel cell was tested in October, 2020 by the Council of Scientific and Industrial Research and KPIT Technologies. However, the technology is believed to be more suited for commercial vehicles, such as buses and trucks. The first hydrogen fuel cell powered bus was introduced in 2018 by Tata Motors in India.
Supercapacitors: Supercapacitors contain positive and negative electrodes separated by an electrolyte, and instead of storing energy in the form of chemicals, they store electricity in a static state, making them better at rapidly charging and discharging energy. In comparison to batteries, supercapacitors offer a substantially higher power density, allowing them to transmit and absorb energy from the load much faster. However, they offer low specific energy for standalone application. In India, a company, Golden Arrow Wireless, has built an electric sports car, which has a supercapacitor option, and the company has claimed that the supercapacitor would take less than five minutes to charge.
Ultrahigh-speed flywheels: The energy is stored in a flywheel as kinetic energy by spinning the flywheel and released on demand. Flywheels are still immature in terms of technology and still have a long way to go for application to EV’s.
Out of all the energy storage systems, batteries are identified as the major EV energy source presently and in the near future due to their technological maturity and reasonable cost. However, they are very bulky, heavy and costly. Due to which, it has become difficult to make an EV that can effectively compete in all departments with conventional vehicles.
None of the above stated energy sources can meet all of the demands of electric cars in order for them to compete with conventional vehicles. In essence, these energy storage systems are incapable of simultaneously providing HSE and HSP. However, combining these energy storage systems with complementary properties can result in the creation of a hybrid energy system and therefore, instead of using a sole energy storage system, EVs can go for such multiple systems. By doing this, the properties of all the energy sources, such as the technology and reasonable cost of batteries, the high specific energy and fuel efficiency of fuel cells, the high specific power of the supercapacitors, along with the enormous specific power and unlimited cycle life of ultrahigh-speed flywheels, can result in a better technology to support EVs. However, this is still in development stage and as of now, this has just been proposed by the researchers and to demonstrate their viability and enhance their functions, more research and development is required to be done.