With most major original equipment manufacturers (OEMs) set to cut ties with combustion engines in the next five years and more stringent government policies on air pollution, we are set to witness an exponential uptake in electric vehicles; however, prolonged charging times and grid stability remain uncertainties, writes Alan Spillane.

This article will focus on what a Battery Swapping System (BSS) and Battery Sharing Station (BShS) is while discussing some key features of how the system operates, providing readers with an introduction to such charging methods and opening discussions for alternative forms of EV charging in the future.

Exponential uptake in electric vehicle ownership on the way

Electric vehicles have been backed by auto industry experts and OEMs as being the future of mobility globally, where privately owned vehicles will be battery powered and the larger fleets look set to be powered by fuel cells, be that hydrogen or some other fuel source. This has been reflected by many national government targets and climate plans.

The Irish government set a target that 10% of the 2.7 million vehicles estimated to be on the roads in 2020 will be electric vehicles – meaning that there will be 270,000 EVs on the road by 2020 (there are about 5,000-6,000 registered BEVs on Irish roads as of October 2019...). Ireland has also set itself the target of ending the sales of fossil fuelled combustion engine cars sold by 2030.

In addition, the climate plan proposes to add more incentives to people thinking of a change to an electric vehicle. The plan aims to have a charging network capable of catering for about 800,000 electric vehicles in place by 2030.

From this, it is obvious that large-scale adoption of EVs is inevitable and has significant potential to not only reduce transport's huge CO2 footprint, but to also provide much needed energy storage to a decentralising electricity grid and also the ability to combat the intermittency of renewable energy penetration.

So, what does it mean for the future of EV charging?

The current EV market is seeing an exponential increase in EV adoption and a demand that all electric vehicle OEMs are struggling to keep up with.

This sudden surge in EV uptake that we are all set to witness in the next few years poses significant technical challenges in electrical distribution systems and, in particular, grid reliability issues as the current generation capacity and distribution networks are not designed to support the load profile of this number of EVs being charged through traditional methods.

According to the UN's Intergovernmental Panel on Climate Change, it estimates that by 2040, the world's energy consumption will have increased by 40%, that's an increase of about 46,000TWh from 2018's final energy consumption figures.

With regard to electric vehicles one of the uncertainties is the charge time of the battery packs and, of course, the reliability of each vehicle’s battery pack.

Consumers are used to fuel replenishment in about five minutes, meaning a high demand for DC fast charging, which is currently most common at 50kW.

This is another EV charging concept that poses significant technical challenges to the transmission grid as this type of charging can lead to unsustainable load spikes on the distribution network, especially while at peak-load periods.

In these circumstances, fast charging will either require that spare capacity be available at connected busbars to meet these requirements or that EV customers be put in a queue system until capacity becomes available. Neither option is desirable.

For EVs to be adopted at scale, the charging infrastructure and integration with the distribution and transmission networks must also evolve rapidly.

A solution may be to entice EV customers to lease their battery packs from their electric vehicles as opposed to owning the battery to be used in an optimised battery swapping station (BSS) designed to offer EV customers the convenience of replenishment of energy within three to eight minutes (similar, if not quicker, than its combustion engine counterpart).

The battery swap explained

This Battery Swapping System (BSS) approach entails using the Battery as a Service (BaaS) model where EV drivers will either lease their battery packs or not own them at all.

In return, receiving a service from a third-party BSS platform operator that allows for easy access and exchanging of Universal Battery Packs (UBPs) for quick and efficient fuel replenishment in the same time it would take to refuel an ICE vehicle.

Some auto-makers and startups have tested BSSs similar to this including Tesla Motors which introduced an internal battery swap programme in 2013 but shut down its service three years later in 2016 due to reports of its onboard Nvidia GP100 processing chips at the time being unable to differentiate different battery packs of each swap and assuming that the original trip totals were continuing.

Read more about the programme here and note that there have been heavy rumours recently regarding the OEM, planning to relaunch its battery swapping programme soon.

Innovative Chinese automaker NIO is also deploying some similar models at selected locations in China and offers battery swaps within three minutes using individual stations.

Engineer Einar Aarseth filed patents in 2011 outlying plans for an electric vehicle service centre and method for exchanging and charging vehicle batteries. A simple flowchart from Aarseth’s plans below provides an easy-to-follow method of the system in operation.

Battery sharing stations (BShN)

With forecasters expecting an exponential increase in EV market share in the next few years, growing from roughly 1% today to about 30% in Europe and 15% in the US by 2025, totalling 130 million EVs, it is unquestionable these increases in such a short space of time pose significant technical challenges to grid security and reliability as current generation capacities and distribution networks are not designed to support the load profiles of this number of EVs.

Battery Sharing Stations (BShSs) seem to have some potential as a solution to mitigate the impact of an exponential growth in EVs while, more interestingly, having the ability to act as a battery energy storage plant (BESS).

This would be where the curtailed direct and indirect solar energy can be used to charge the depleted battery packs, further allowing the BShN to act as an energy storage aggregator that can use the stored excess renewable energy to then competitively participate in electrical energy markets, providing services to the Distribution System Operator (DSO) and Transmission System Operator (TSO) such as voltage support, demand response and energy arbitrage.

Challenges and opportunities

Battery swapping systems face many challenges in becoming deployed at a large scale, but also provide many opportunities.
• Potential to dramatically reduce price of EVs, making them more affordable and accessible for everybody.
• Leasing/pay-as-you-go model on battery packs is particularly attractive to fleet companies such as ride-sharing and package delivery services who all require their vehicles to drive a significant number of kilometres each day and cannot afford a lot of downtime.
• BSSs allow for controlled/scheduled charging of depleted batteries to off-peak hours on the transmission system, thus acting as a large flexible load from the TSO's perspective.
• More data can be gathered on battery-packs SOC (capacity) and SOH (longevity) using integrated IoT devices in BShNs.
• Acting as a peak-shaving storage plant while having the ability to partake in energy arbitrage.

• Arguably, one of the biggest challenges facing the widespread adoption of BSS is the standardisation of battery packs.
• OEMs would be reluctant to share internal battery architecture designs unless agreed upon or made a requirement across all electric vehicle OEMs.
• Capital cost of grid infrastructure and HV/MV connections. Supplies would need to be fed mainly from wind or solar farms for the BShS to avail of cheap curtailed energy to charge the depleted batteries in their networks, allowing the system to participate in energy arbitrage.

Battery sharing station (BShS) system design

The BShS outlined below is designed to operate within smart grids. A proposed method of this is by using a battery sharing and BaaS model similar to Rotterdam based energy startup Skoon BV, where the Battery Sharing Network (BShN) model co-ordinates the bidirectional flow of power between the BShS and with any potential smart grids in the power grid.

Also worth noting is the CISCO smart grid architectural design as an effective use case for this model. The BShN for these stations consists of several subsystems for communication between the BShS and other systems.The Battery Sharing Network (BShN) model diagram proposes to become a grid utility, providing quick battery energy replenishment and utility services such as peak-shaving and load-balancing.

Station battery storage capabilities

It is well accepted now that battery technology in the form of lithium-ion cells are a well matured, proven and developed technology. With the levelised cost of energy of batteries falling dramatically in the recent decade and improved battery capabilities, these cells can now provide significant utility-scale load-levelling capabilities.

The BShN has the ability to act as a Battery Energy Storage System (BESS). For these systems to effectively contribute to grid balancing and managing renewable curtailment management, many modules will need to be connected per BShN.

EV battery ranges with capacities from 40kWh-60kWh connected via a modular battery storage system are proposed to be used in this scenario, which increases the storage capacity of the plant, allowing it to provide more energy during moments of the peak demand period.

In the case of most traditional electricity networks, the infrastructure was designed to have large centralised generators on one end of the network, and sufficient aggregated loads on the other end with a system of distribution and transmission in between.

This was due to being able to optimally design an efficient electricity generation fleet as short-term variations are typically small and predictable.

However, with increased non-optimised penetration of variable renewable energy, problems such as mismatches between supply and demand, voltage rises and possible reverse power flows at transformers arise. Refer to the above graph for a typical day supply, demand, curtailment and storage statistics.

Proposed battery module assembly within the BShN

It is widely known that lithium-ion cell voltages (VC) are generally quite low. Thus, in order to create a powerful energy storage system from fuel cells, in this case li-ion cells, special series-parallel cell connection is required.

This article is not intended to go into too much technical detail regarding storage unit assembly, although, it is important to note that a certain number of redundant cells are added to BEV battery packs.While the number of cells per battery pack differs to each individual OEM, the Institute of Technology and Engineering (IET) recommends that one redundant cell in five is to be added, allowing for 20% spare capacity per module/pack.

In general, to create a powerful storage system, special series-parallel connections are required. All EV battery packs are proposed to be connected in this manner to pick up for weak single cell voltages in series connections and improve current output by the parallel connections.


Although the successful implementation of these systems may seem like an audacious challenge when looked at generally, they certainly offer a viable alternative to electric vehicle charging that may prove to play a vital role in a decentralising electricity system and, especially, localised grids.

The main takeaway, if nothing else, from this article is to understand how the EV battery packs can be charged from curtailed renewable energy at cheaper, off-peak times on the grid.

If you would be interested in learning more of any concepts discussed in this article, or are involved in this area of study, then I would be delighted to hear from you - I  can be reached at: alanspillane97@gmail.com


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2.) Li, Y (2019). Optimal scheduling of isolated microgrid with an electric vehicle battery swapping station in multistakeholder scenarios: a bi-level programming approach via real-time pricing[research]. Jilin
3.) Ter-Gazarian, AG (2011). ‘Energy Storage for Power Systems’, Power and Energy Series, 63, pp. 136-152, IET.
4.) https://patents.google.com/patent/US5998963A/en
5.) https://www.autonews.com/china/ev-startup-nio-offers-free-battery-swaps
6.) https://www.tesla.com/blog/battery-swap-pilot-program
7.) https://www.iea.org/publications/reports/globalevoutlook2019/
8.) https://www.dccae.gov.ie/en-ie/climate-action/publications/Pages/Climate-Action-Plan.aspx
9.) https://www.engineersireland.ie/EngineersIreland/media/SiteMedia/groups/Divisions/biomedical/Managing-Curtailment-in-2030-02-10-2019.pdf?ext=.pdf
10.) https://www.nio.com/nio-power

Author: Alan Spillane, electrical engineering undergraduate, Limerick Institute of Technology