Solar parks can generate a lot of renewable energy, but provide inconsistent energy production. For instance, the energy production of solar panels depends on the strength of the sun, among other things. An energy storage system can provide a solution and accommodate peaks and troughs in energy production. Using discarded batteries from electric vehicles makes such a storage system more economically viable.
This is according to research by MIT. With the increasing popularity of electric cars, battery packs are increasingly common. The performance of these batteries declines the longer they are in use. For instance, the capacity of the batteries is declining, so they offer a shorter range than before.
Declining capacity
Batteries in electric cars are therefore often replaced as soon as their capacity drops below 80%. However, the fact that they are discarded does not mean that these batteries are no longer usable. For instance, research by MIT shows that the batteries are still perfectly usable for energy storage at solar farms.
A solar park consists of a large number of solar panels, which generate energy only if enough sunlight is available. This means, among other things, that during bad weather conditions and during the night, less to no electricity is produced. This creates peaks in the supply of solar energy; where the amount is high during the day and low at night, for example.
Capturing peaks
Energy storage systems can help by capturing these peaks. By storing electricity generated by solar panels in batteries, it is available at times when production is lower than demand. However, batteries are relatively expensive, making energy storage systems for large solar farms costly.
By reusing discarded batteries from electric cars, it is possible to reduce these costs substantially, MIT argues. Since the batteries are no longer usable for their original application, the batteries are available relatively cheaply.
Three scenarios
The study examined different scenarios for solar farms, using local conditions in the US state of California as a starting point:
- a stand-alone 2.5 megawatt solar farm;
- an identical solar farm including a new energy storage system based on lithium-ion batteries;
- an identical solar farm with an energy storage system based on discarded batteries from electric cars.
The analysis shows that an energy storage system with new batteries does not offer a reasonable return on investment for solar parks. However, if the same system is realised with used batteries from electric vehicles, it is profitable. MIT states that such an investment can be profitable as long as the discarded batteries are available for less than 60% of their original purchase price.
Challenges
Using batteries from cars for an energy storage system presents several challenges. Postdoc Ian Mathews explains, "There are many challenges at the technical level. How do you screen the batteries you remove from a vehicle to ensure they are reusable? How do you combine batteries from different cars so that they work well together, and the poorer quality of one battery does not negatively affect the performance of the system?"
Economically, Mathews also sees challenges. "Are we sure that these batteries still provide enough value to justify the cost of removing batteries from cars, collecting them and reprocessing them into a new application?" He also points to unwarranted previous assumptions, such as that maximising battery charging will deliver the most value. This turns out not to be true; research from MIT shows that it is precisely maximising the lifetime of batteries that helps maximise their value.
Lifetime
Another key issue that MIT does not yet have a concrete answer to is the lifetime of the discarded batteries in their new application. In the study, the team assumes that batteries are used at 80% of their original capacity until their capacity drops below 70%. Mathews points out that this is an assumption. In practice, therefore, it may turn out that batteries remain usable in energy storage systems up to 60% capacity, for example.
The decrease in battery capacity is difficult to predict as several factors influence this process. These include how the batteries are controlled. Mathews expects that machine learning can help discover the most optimal control of batteries.
Refurbishment is not easy
McKinsey agrees on the potential of discarded batteries from electric vehicles for energy storage systems. Like MIT, the research firm does foresee several challenges:
- Current battery packs in electric vehicles vary in size, capacity and electrode composition, among other things. The number of battery packs available will only continue to grow in the future; McKinsey expects there to be 250 different models of electric vehicles from over 15 different manufacturers by 2025. The design of battery packs will be tailored to these specific car models, making refurbishment a challenge.
- As new batteries become cheaper, the price difference between new and used batteries is shrinking. Whereas in the mid-2020s the price differential was still expected to be 30-70%, by 2040 it is likely to be down to 25%. Only if the price difference remains large enough will the use of used batteries be relevant. Industrialising refurbishment processes can help reduce these costs.
- Stricter standards are needed for the quality, safety and performance of end-of-life batteries. Different parties including OEMs and battery refurbishment companies are working on standards in this area. Such standards provide more transparency.
- Currently, there are no regulations for recycling and reusing batteries from electric vehicles. This leads to regional differences and uncertainties for both companies involved and customers about the responsibility for such batteries.
More information about MIT's research is available here. You can read more about McKinsey's view here.
Author: Wouter Hoeffnagel
