Tag Archives: WMG

Reduced Battery Degradation Using V2G

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We have previously discussed the work of the Warwick Manufacturing Group on mitigating potential battery degradation by “intelligently managing V2G technology”. In a recent press release the EV-elocity project refers to a new WMG paper on that subject, reporting that:

A number of studies have identified the strategic importance of charging infrastructure to support the introduction of electrified vehicles (EVs) and to underpin consumer acceptance of the technology. For this reason, considerable research has been undertaken to evaluate the different facets of the technology, including the ability to charge at higher rates of electrical power, the introduction of smart charging (V1G) that allows dynamic management of the charging process in terms of both power and charge time and vehicle-to-grid (V2G) that enables bidirectional energy flow between the vehicle and the supply. In recent years, the term V2G has become more generalised to V2X, to acknowledge the variability in which the EV may be integrated, either to the grid or behind-the-meter, for example within a local electrical network, such as a building (V2B).

Irrespective of the exact nature of the integration method, understanding the impact of different strategies on battery degradation is a key requirement that may ultimately underpin consumer acceptance. Only a few studies have examined the potential impact of V2G operation on battery degradation. Often their assertion is that the increased charge-throughput will negatively impact battery life. These works often neglect that the battery will equally degrade through a process of calendar-ageing in which the retained capacity of the battery reduces as the battery is stored at no-load.

As highlighted in these results from the EV-elocity project, the nature of the degradation is highly complex with dependencies that crosscut: the state of charge (SOC) of the battery with respect to the optimal SOC storage condition and the duration of the parking interval. To further compound the challenge, experimental results shows that the optimal SOC point varies with battery life.

The paper referred to is open access and entitled “A Study of Reduced Battery Degradation Through State-of-Charge Pre-Conditioning for Vehicle-to-Grid Operations“. The abstract begins as follows:

Transport electrification is a key enabler to reduce fossil fuel depletion and related carbon dioxide emissions. However, critical barriers exist in terms of battery costs and their expected life. Vehicle-to-grid technology can bring benefits to both the electrical power grid and electric vehicle owners, while its practical implementation faces challenges due to the concerns over accelerated battery degradation. This paper presents a comprehensive study on reduced Lithium-ion battery degradation through state-of-charge pre-conditioning strategies that allow an electric vehicle to participate in vehicle-to-grid operations during periods in which the vehicle is parked. Energy capacity reduction of the electric vehicle battery are predicted using semi-empirical ageing models, which have been built and validated to capture the degradation behaviours of the battery with respect to both calendar and cycling ageing. Five charging strategies for battery state-of-charge pre-conditioning have been developed to evaluate the ability to mitigate battery ageing before commencing vehicle-to-grid operations. Simulation studies on battery degradation utilizing such charging mechanisms under two different operational profiles have been undertaken.

At this point you may be wondering exactly what the various charging mechanisms entail? Here’s a summary of the assorted strategies from the press release:

and here’s a summary of the results:

Going back to the abstract from the Bui et al. paper, the brief conclusions are that:

The analytical results show that the proposed charging strategies do not accelerate battery degradation and are capable of mitigating the total ageing process from 7.3 – 26.7% for the first 100 days of operational life and gradually vary to 8.6 – 12.3% for one-year continual operation compared to the reference standard charging approach.

To summarise, leaving your electric vehicle plugged in and “fully charged” is not good for the “state of health” of its traction battery. Here’s a video from Euan McTurk that delivers a similar message:


Can V2G Improve EV Battery Life?

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According to a recent press release from Warwick University:

Researchers discover that by intelligently managing vehicle-to-grid technology, energy from idle vehicle batteries can be pumped back into the grid – and this would improve vehicle battery life by around 10%.

That will come as a surprise to many people! Let’s dig deeper to discover what “intelligently managing V2G technology” means in this context. According to the press release once again:

Dr Kotub Uddin, with colleagues from WMG’s Energy and Electrical Systems group and Jaguar Land Rover, has demonstrated that vehicle-to-grid (V2G) technology can be intelligently utilised to take enough energy from idle EV batteries to be pumped into the grid and power buildings – without damaging the batteries.

This new research into the potentials of V2G shows that it could actually improve vehicle battery life by around ten percent over a year.

For two years, Dr Uddin’s team analysed some of the world’s most advanced lithium ion batteries used in commercially available EVs – and created one of the most accurate battery degradation models existing in the public domain – to predict battery capacity and power fade over time, under various ageing acceleration factors – including temperature, state of charge, current and depth of discharge.

Using this validated degradation model, Dr Uddin developed a ‘smart grid’ algorithm, which intelligently calculates how much energy a vehicle requires to carry out daily journeys, and – crucially – how much energy can be taken from its battery without negatively affecting it, or even improving its longevity.

The researchers used their ‘smart grid’ algorithm to see if they could power WMG’s International Digital Laboratory – a large, busy building which contains a 100-seater auditorium, two electrical laboratories, teaching laboratories, meeting rooms, and houses approximately 360 staff – with energy from EVs parked on the University of Warwick campus.

They worked out that the number of EVs parked on the campus (around 2.1% of cars, in line with the UK market share of EVs) could spare the energy to power this building – and that in doing so, capacity fade in participant EV batteries would be reduced by up to 9.1%, and power fade by up to 12.1% over a year.

This is all still just a trifle vague, so let’s dig deeper still. Dr Uddin and his colleagues have written a learned journal article on the subject at hand, and fortunately for our purposes it’s open access! According to the conclusions to the paper:

The smart-grid algorithm was used to investigate a case study of the electricity demand for the University of Warwick IDL building. Simulation results suggest that the smart-grid formulation is able to reduce the EVs’ battery pack capacity fade by up to 9.1% and power fade by up to 12.1% within the context of the grid topology considered or if the EV is charged to 100% daily. In comparison, if the EV is charged only when the battery is close to depletion, the smart grid optimisation was able to reduce capacity fade by 4.4% and power fade by 9.5%. In conclusion, we show that an EV connected to this smart-grid system can accommodate the demand of the power network with an increased share of clean renewable energy, but more profoundly that the smart grid is able to extend the life of the EV battery beyond the case in which there is no V2G.

I cannot help but think that the opinion of many battery degradation sceptics won’t readily be swayed by “simulation results” based on a “degradation model”, validated or not.