EV Batteries as Storage batteries for Grid Power. Possible, Says MIT Study

If there is one area where the renewable energy industry steals a march over fossil fuel based sectors, it has to be the area of recycling. Unlike thermal and oil/gas based energy generators, renewable technologies have come up in the glare of huge public expectations and appraisal, and having to prove themselves better at every stage. Not just pollution or cost. Thus unlike fossil fuel sectors that seem to act reluctantly only under massive public pressure or proven detrimental impact on the environment, pressure is rising on the need for the renewable energy industry to consider plans for recycling of materials, be it for solar panels past their end life of 25 years, or lithium batteries that are only now truly spreading out.

Which brings us to a new study conducted by researchers at MIT (Massachusetts Institute of Technology). The premise of the study is that lithium ion batteries in vehicles, which need to be replaced as their efficiency drops to 80 percent, owing to the high demands from a vehicle, could find a second hope in grid storage PV projects, where demands are relatively more predictable. In these applications, their lifetime value could be extended by a possible decade.

The study was published in the journal Applied Energy, and carried out by six current and former MIT researchers, including postdoc Ian Mathews and professor of mechanical engineering Tonio Buonassisi, who is head of the Photovoltaics Research Laboratory.

The researchers examined a  hypothetical grid-scale solar farm in California for their study. They studied the economics of alternative scenarios: A standalone 2.5-megawatt solar farm; A solar farm with a new lithium-ion battery storage system; A farm with  battery array made of repurposed EV batteries that had declined to 80 percent of their original capacity, the point at which they would be considered too weak for continued vehicle use.

Predictably, while the new battery installation would not provide a reasonable net return on investment, but at a cost of 60 percent of existing battery prices, used batteries delivered a competitive rate of return.

Besides obvious challenges of collection, arranging possibly different sized batteries and the effort of arriving at a price low enough, the researchers also discovered some other insights. They used a semiempirical model of battery degradation, trained using measured data, to predict capacity fade in the lithium-ion batteries under different operating conditions, and found that the batteries could achieve maximum lifetimes and value by operating under relatively gentle charging and discharging cycles — never going above 65 percent of full charge or below 15 percent. This challenges assumptions  that running Li-Ion batteries at maximum capacity provides the most value, for instance.

Extending the battery life was based on allowing degradation to 70 percent levels, after acquiring them at 80 percent levels to begin with. However, extended tests could prove that even degradation to 60 percent can work, according to the research.

As storage backed solar and wind projects projects become the focus across markets, thanks largely to the higher share of renewable energy, and the need to graduate to an all weather, round the clock source for the grid, India’s jugaad obsessed and cost driven developers will certainly do well to track progress in this area.

Readers will recall the big May news, when Renew power won a storage + renewable bid for supplying 400MW of “round the clock” power at a blended price of Rs 3.60 for 15 years. While that bid has thrown up the usual detractors, we believe the bid is a sign of things to come, especially if it executes well. However “easy” the tender conditions for now. India, with an official plan for 50 GW of lithium ion battery manufacturing, has traditionally been a very high recyling economy, and developing a ready made organised market for efficient use of vehicle batteries in grid storage or even off grid storage, might prove to be a win for all stakeholders yet.

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Prasanna Singh

Prasanna Singh

Prasanna has been a media professional for over 20 years. He is the Group Editor of Saur Energy International

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