The Future of Grid Storage: Can EV Batteries Meet Short Term Demands?
13-02-2023 | By Liam Critchley
There’s been a lot of talk over the years around how new renewable energy generation devices are going to fit in with existing grid architecture around the world―as many of the world’s electrical grids were built decades ago and have not been designed to work with renewable energy sources. Nevertheless, transitioning towards a grid that can also utilise renewable energy sources is going to be key in the coming years as renewable energy technologies are being rapidly deployed around the world to phase out the reliance on coal and other fossil fuels.
However, the task is not a simple one because there are several commercial renewable energy technologies, all of which have varying power generation based on environmental factors (such as wind or the sun) that can lead to large amounts of energy being created at certain time periods, but a lack of energy being produced at others. If there’s to be a status quo switch to renewables over fossil fuels, then the variability of power, alongside current grid architecture and electrification demand, could present issues regarding grid stability and security of supply.
To overcome this, there needs to be some form of short-term energy storage solution that can store large amounts of renewable energy when the stimulus is strong, as this extra energy could be released during low energy generation periods. Without an effective short-term solution, renewable energy is not likely to become a dominant energy generation technology for large portions of the population―and would continue to be used for smaller-scale or localised energy needs.
There have been a number of ideas proffered to solve the short-term storage conundrum, including different energy storage devices, electricity generators, long-distance electricity transmission, over-building renewable energy sources that would still provide enough power in low periods, and power-to-gas technologies. Out of all the solutions, the option that makes the most economic sense in today’s market is energy storage devices, namely batteries. Battery costs are constantly coming down, including the large rechargeable batteries that are now used in electric vehicles (EVs), and it’s thought that the relatively large storage capacity of EV batteries could be a good solution for the storage of electricity in the short-term for electric grids.
Why EV Batteries?
EV batteries are getting better and better to meet the range demands of consumers, but they could also play a part in grid storage. It’s thought that it could manifest while the batteries are still in the vehicle via vehicle-to-grid approaches, but there’s also the potential to use the batteries at the end of their vehicle life (EoL).
For vehicle-to-grid approaches, there are smart ways of charging EVs that offer a dynamic way of charging, but the EV can also be used as a means to store electricity and feed it back into the grid when required. This approach relies on a number of human factors, including standards, market arrangements to facilitate dynamic energy pricing (so that the vehicle owner can benefit financially), and of course, human participation in the initiative.
This is just one way that EVs could be facilitated. The other is when the batteries have reached the useful lifetime in the EV, and the battery is no longer considered efficient enough to warrant keeping it in the car over replacing it for a newer, higher capacity battery. For EV batteries, this stage comes when the battery capacity is around 70-80% of its original capacity, and while these batteries may be unsuitable for EVs, they could still have a lot of useful life in less demanding stationary energy storage applications―such as in the electrical grid.
Using EoL EV batteries could offer a way of improving the flexibility of supply, provide a way for recycling old batteries, and could reduce the capital costs and emissions associated with building extra energy storage and power-electronic infrastructure. However, how much of an influence and potential EV batteries could have on the storage capabilities of the grid relies on a range of socioeconomic and technical factors, including the business models of companies and their willingness to participate in providing the EV batteries, battery degradation, and how well the vehicle owners look after the battery regarding charging and driving behaviour (and the effect that this has on battery performance). For vehicle-to-grid approaches, it also relies on the regular participation of owners and whether they will reliably allow the facilitation of renewable energy in and out of their EVs.
Could EV Batteries be the Solution?
So, could they be a solution? It certainly appears so, and a study has recently been performed by Xu C. et al, looking at the feasibility of using EV batteries for short-term grid storage using socio-technical parameters and constraints that factored in EV battery deployment, battery degradation over time, and market participation. The researchers created an integrated model considering all these different factors, looking at both EoL and vehicle-to-grid approaches and deduced some key findings. The study only looked at short-term storage because EV batteries are not suited to long-term storage due to self-discharging over time.
The aim was to look at the global grid storage opportunities for EV batteries by 2050 for both vehicle-to-grid applications and EoL approaches. The study took into account the main EV battery markets (China, India, EU, and US) and combined the rest of the world’s markets into a ‘rest of the world’ category. The approach utilised a dynamic battery stock model to estimate future battery demand, and these demand estimates were based on EV driving and charging behaviour models for small, mid, and large-size battery EVs (BEVs) and plug-in hybrid EVs (PHEVs) and the driving distances typically seen in each of the regions. The model was then combined with battery degradation models for region- and chemistry-specific batteries.
From a capacity perspective, the models show that cumulative vehicle-to-grid and post-EoL use will grow by a factor of 13-16 between 2030 and 2050. Pitting this growth against future demand for grid storage showed that the estimated growth is expected to increase as fast, if not faster, than the short-term grid storage capacity demand.
Looking at vehicle-to-grid batteries alone, it’s thought that between 21% and 26% of the global theoretical battery capacity could be available for vehicle-to-grid services by 2050. The only major limiting factor that could affect the prospects of this approach is the battery capacity required to meet consumer driving demand. However, on the positive side, it’s been modelled that only 5% of the theoretical capacity would be lost due to battery degradation by 2050, so it is not a major barrier. Overall, it’s thought that vehicle-to-grid approaches could contribute anywhere between 18-30 TWh of technical capacity by 2050.
As far as EoL batteries go, it’s been assumed that around 2.1-4.8 TWh of retired batteries will become available for use in the electrical grid by 2050, which could reach a cumulative second-use capacity of anywhere between 14.8–31.5 TWh by 2050 if the batteries have, on average, an extra 10 years of usable life. There are a lot of variables with EoL batteries, especially around their condition and how they’ve been treated over time, and it’s also thought that the utilisation rate of retired batteries would need to be anywhere between 32% and 68% to achieve these levels of capacity.
Overall, if you combined the potential of both EoL and vehicle-to-grid approaches together, then it could contribute a total technical capacity of anywhere from 32-62 TWh by 2050. The capacity could come from a number of configurations around vehicle-to-grid and EoL use depending on society at the time, but it’s thought that participation rates will only need to be anywhere from 12% to 43% to provide the required short-term grid storage demand around the globe. The participation rates necessary could even be less than 10% if around half of the EV batteries at EoL are used as stationary storage. The study also concludes that while 2050 is the target, the short-term grid storage demands could be met as early as 2030 in most regions (with the estimates being generally conservative).
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