Considering that EVs neither emit GHGs nor any significant air pollutants & with almost twice the energy transfer efficiency, they are much better choice for future of sustainable mobility system. Also, as per one of the research, the overall carbon emissions of an EV are around 17-30% lower than of an ICEV during respective life cycles. For EVs, even these emissions are further reduced when electricity from renewable energy sources is used to power them. With these strong positives, the present-day EVs have an unshakeable footing in current times and that’s why the present focus of the whole mobility system is on them.
Charging Challenges OF EVs
However like everything else in nature, the EV-based mobility system is also not perfect and has its inherent drawbacks. Fortunately, though the battery life (energy storage), which is one of the most critical systems of EVs, is increasingly becoming better still the industry trend is to offer a warranty for 1.5 km run over the 8 years as given below. This is much less than the current technical estimates of battery life which, with average running of 24,000 kms per years, still has an energy holding capacity of 80% but this may not be good enough for EV application (a point which time will only tell).
Fortunately, the batteries technologies are still evolving, hence we can expect the life span & performance of future EV batteries to further improve but it is the other issue, not related to the EV technology, per se which needs to evolve at a much faster rate to increase the acceptability of EVs. This is the charging infrastructure. It is one of the biggest single deterrence in mass acceptability of EVs, creating unwanted “battery-based anxieties” related to “Range”, “Charging Time”, “Battery Life”, “Balance KM Run” & “Charging Compatibility”, similar to what happened, when mobile phones were introduced, about two decades back. As such, these “anxieties: are not out of context yet they must be taken with a pinch of salt since ICEVs can also run out of fuel if the tank is not filled at right time.
Some of these drawbacks (perceived) as well the advantages (real) have been summarized below:
However, the crux of the issue is, that despite all these “New Technology Syndromes”, the EVs are gaining popularity and their sales are growing year by year. It is expected from a study of Deloitte that by 2030 the EVs would be able to share about 40% of automotive market.
With everything in place for EVs, it is the charging infrastructure, which needs to be expanded at much faster rate for sustaining the growth of EV market. Yet this challenge still remains a big concern even in advanced countries, leave aside in developing countries like India. This challenge, coupled with different types of chargers and plugs (there are no universally known common charging standards across the globe in context to EVs, like two kinds of fuels for ICEVs – Petrol & Diesel). Though the government agencies/ policymakers are proposing policies to create these EV charging setups to accommodate all kind of chargers to promote EVs, these challenges become more complex, when someone tries to locate an “EV-matched” charging station on highways/ expressways. Fortunately, as the eco-system of EVs grows, many of these drawbacks, related to charging compatibly, will go away and the battery performance will also improve, it is the basic energy provision to the charging system will remain a challenge.
EV Charging System: With EVs continually gaining popularity all over the world, their numbers have still not crossed critical threshold for mass expansion of related infrastructure, hence depending upon the EV sales volumes in any territory/ country/ zone, different kind/ types of EV charging setups are getting developed to suit that areas’ requirement & needs. This has created a situation of high level of complexity in global EV market. However, there are three generally accepted descriptors for EV Supply Equipment (EVSE), which also include EV chargers e.g.: their Mode, Level & Type.
Battery Charging: Let’s now try to understand a bit of the charging pattern of EV batteries, which provides energy by a chemical process (this would depend upon the chemistry of the cell). The chemical reaction within the battery creates a specific voltage (V), which keeps falling while it feeds current to the connected load (supply of energy). During recharging, this chemical process is reversed to pump back the energy to the battery. The energy flow (withdraw as well as charging) can be done at a specific voltage (V) & Current (I) since it is the energy (V*I) that needs to be handled by the batteries. When fast charging is needed, either the voltage or the current is increased. However, batteries by their intrinsic characteristics, have very strict operating limits, particularly regarding the voltage, which must be maintained to charge the batteries safely7. The charging time will vary depending upon the model, type and the way the battery is getting charged, still, the actual charging time is usually longer than the theoretically assessed time due to many factors associated with the battery, some of which are indicated below:
- Due to differences in “Charge Transfer” & “Mass Transport” or “diffusion” processes between electrodes during the charging. Though the “charge transfer” is fast, it is the “mass transfer” which can take several hours depending upon the capacity, condition & charging status of the cells.
- Due to “parasitic” or “passivation” of the electrodes, “crystal formation” and “gas build-up”.
- Due to the non-linear characteristics of charging & discharging processes, there is a limit on charge rate. When the charge rate exceeds this limit (i.e. more energy being pumped into the cell than the rate of reverse chemicals reactions taking place inside the cell), it can permanently damage the cell (due to polarisation, overheating as well as unwanted chemical reactions).
- Also, the fast charging of EVs’ batteries, forces up the rate of chemical reactions in the cell, hence cells necessarily need “rest periods” during the charging process (for the chemical actions to propagate throughout the bulk of the chemical mass in the cell and to stabilize at progressive levels of charge) and hence the charging algorithm becomes important.
- The battery charging rate is highly dependent on the battery temperature & is most optimum between 20°C and 30°C. The charging rate can be slower if the battery temperature is away from this range. This is certainly a challenge in India wherein temperature varies much beyond these limits.
- The charging rate also depends upon the compatibility of EV’s charging algorithm & that of charging stations.
…To be continued
- Recall 2016, when the fire in the Samsung Galaxy Note 7 had been a source of trouble around the world which later Samsung had claimed, were due to faulty batteries.
Prabhat Khare possesses a BE (Electrical) degree from IIT Roorkee (Gold Medalist). Now, he is the Director of KK Consultants. He is also a BEE Certified Energy Manager and a Lead Assessor for ISO 9K, 14K, 45K & 50K.