At this week’s seminar Prodip Chatterjee from the SolarBox project discusses how this early stage open source initiative is creating low cost energy storage products with used consumer electronics batteries for rural electrification with an initial focus on India. To complement his talk he has written us this blog about his experiences with second life energy storage applications and the opportunities they provide. You can also download his slides as a PDF.
The significant advancements in electro-chemical storage especially in terms of energy density, particularly with Lithium-Ion batteries, have paved the way for an unprecedented variety of battery powered device across every aspect of our daily life.
These devices impact can be broadly separated into two categories:
- Mobility applications for exmaple electric vehicles, e-bikes and e-scooters.
- Portable electronics devices like laptops, smartphones, powerbanks, wireless headphones, smartwatches and power tools.
In 2018 alone, more than a billion smartphones have been sold worldwide and more than an additional billion devices of portable electronics devices. In the mobility space, especially electric vehicles are gaining popularity across the world at an unprecedented pace.
Although cumulatively only 4 million electric vehicles (EV) had been sold up till Quarter 2 of 2018 (versus 81 million gasoline cars in 2018 alone), the projected volume of EV is forecasted to be 11 million by 2025 and 30 million by 2030. As a consequence, customers are buying and using battery powered devices more than ever before.
It turns out that mobility applications (like EVs) need to replace their batteries when its remaining capacity still is at approximately 80% State of Health (SoH), because below that SoH treshold the surge current drawn in the first few milliseconds during acceleration from the battery pack is too high for the drained battery. Another element is the decreasing range of the car, which degrades with increased usage.
In the case of portable electronics devices, the replacement rate of consumers and corporate customers on upgrading to new generation of devices is leading to an increased number of old devices that have hardly been used in their product lifecycle (which includes the battery inside the product).
This phenomenon is also driven by the industry, attracting customers to upgrade towards new product generations once they are launched instead of staying with their existing devices which in return leads to an increased volume of electronic waste (E-Waste) across the globe. According to the United Nations, 41 million metric tons of E-Waste have been created in 2017 at a growth rate of between 6 and 8% per annum. Developing countries often have no proper E-Waste recollection and recycling infrastructure, leading to an increased and unsolved problem.
From a top-level perspective, we have asked ourselves at the beginning of our project work in 2017 if the batteries from the above mentioned applications (especially power electronics like laptops and smartphones) after being discarded can be reused in a smart and sustainable way by aggregating these used battery cells into a stationary storage device.
Low cost energy storage is the need of the hour; it is regarded as key component in order to transition to a world with renewable energy sources like solar or wind energy. It is also essential to provide decentralized energy in remote areas especially in developing countries where a traditional grid is not economically feasible as well as for small solar home systems providing electricity for those 1.3 billion people who have less or no access at all to energy.
The most affordable energy storage device one can buy today are tubular lead acid batteries at the price of around 128€/kWh. These batteries are having a number of disadvantages for users ranging from their limited lifetime at approximately 400 cycles, its heavy weight and poor C-Rate performance. However, due to their robustness, high recycling rate and robustness in difficult conditions it is till today dominating energy back-up systems. There is also no transparency for most users about degradation and the right time to replace the batteries in return for a new system.
Reusing Lithium-Ion batteries for stationary energy storage is not an entirely new phenomenon. In the formal economy there has been plenty of research and pilot projects of repurposing used EV batteries into grid-scale stationary energy storage across the large automotive companies like Audi, BMW, Mercedes Benz, Jaguar LandRover, Nissan, Toyota and many more. Due to the nascent EV market leading to an initially small amount of used battery packs, the majority of projects are in pilot stage.
However, there has been a lack of work both in academia as well as research around the potential reuse scenarios of used Lithium-Ion batteries from a vast array of consumer electronics devices (like laptops, smartphones and powerbanks.) Over the course of our work we have found out that used consumer electronics batteries are reused in different applications such as solar lights, counterfeit products, toys and many more in emerging economies like India.
An established informal sector is operating in developing countries like India that is positive in terms of resource efficiency but triggers significant downsides due to a lack of product safety, missing certifications, poorly designed products and most importantly these used batteries usually don’t end up in a formal recycling process after its end-of-life but instead in landfills causing hazards in the soil.
We have been testing 600+ used Lithium-Ion batteries from old laptops (cylindrical cells, 18650 type) and smartphones (pouch cells) of all major brands that have been sourced randomly from various electronic waste dealers in India. We conducted charge-discharge-charge (CDC) tests with various C-Rates with all of these cells and also measured further parameters like internal resistance (IR) and temperature.
The figure below shows a summary of the data points we have gathered and the distribution of performance between laptop and smartphone batteries.
Testing Data results from used Lithium-Ion batteries of Smartphones in Laptops sourced in India (2017):
| < 2011 | 2011 – 2012 | 2013 – 2014 | 2015 – 2016 | Total | ||||||
|---|---|---|---|---|---|---|---|---|---|---|
| Laptop | Smartphone | Laptop | Smartphone | Laptop | Smartphone | Laptop | Smartphone | Laptop | Smartphone | |
| Sample Size | 60 | 42 | 66 | 90 | 82 | 76 | 78 | 95 | 286 | 303 |
| Nominal Capacity (Ah) | 2.38 | 0.90 | 2.33 | 1.5 | 2.36 | 1.7 | 2.19 | 2.1 | 2.32 | 1.55 |
| CDC Capacity (Ah) | 1.82 | 0.60 | 1.6 | 0.98 | 1.56 | 0.94 | 1.53 | 1.02 | 1.63 | 0.89 |
| State of health (%) | 76.47 | 66.66 | 68.67 | 65.33 | 66.10 | 55.29 | 69.86 | 48.57 | 70.28 | 58.96 |
| Internal resistance (Ohms) | 123.82 | 750.33 | 161.14 | 786.82 | 128.7 | 714.85 | 121.09 | 722.8 | 133.69 | 743.70 |
Apart from that we have conducted capacity fading and pulse tests with a much smaller number of cells which provided additional insights.The key takeaway was the remaining SoH of those cells of 67% or 5.11 Wh per cell which was left over on average across all of the cells we tested. The rate of non-functional cells has been 7% (42 cells). Both figures have been better of what we have expected initially.
The team has also built a first prototype which is a 12V storage device that runs on used laptop and smartphone battery cells and is an internet-connected product which can transfer location and performance data to a back-end for remote maintenance and tracking.
Its nominal capacity is around 0.7 kWh and optimal for rural households with a moderate load profile. A key learning of the prototype was the complexity of reusing pouch cell batteries with proprietary connectors, such as smartphone batteries. There are tremendous challenges interfacing these connectors safely in a real product; it works on a prototype stage, but it is an unsolved problem for a commercial product. These pouch cells have not been designed to operate outside the device they were used in their designed application, e.g. a smartphone.
Cylindrical cells have standardized form factors and are significantly easier to reuse also due to its more robust mechanical structure. Safety and performance are essential to make energy storage systems with used consumer electronics batteries work. Based on battery testing data, automatic decisions whether a cell is usable or not usable need to be taken in real time and a matching algorithm needs to characterize and decide based on metrics which cells to be grouped together into a system fulfilling a specific customer requirement. This matching algorithm needs to be constantly improved by monitoring product data as well as external data sources such as weather. The team has undertaken first models on to address those challenges.
On a non-technical side, we have undertaken very detailed analysis on the supply ecosystem of these used Lithium-Ion batteries at scale by interacting with 40+ E-Waste dealers of different sizes and across formal and informal players in India, Germany and the US. It is a very complex ecosystem and supply is uncertain, price points for E-Waste don’t follow unit economics principles but are more driven by informal reuse channels as well as global commodity prices (such as lithium).
According to our studies, the commercial feasibility of making energy storage systems that have a final price point which is 20% cheaper then tubular lead acid batteries at a slightly better cycle life significantly relies on the price and condition of the sources used batteries from E-Waste sources.
However, other cost elements for the storage device such as power electronics, outer casing and overheads have a significant cost contribution based on the total costs as well. Those costs are more or less fixed by market metrics, hence it is essential to bring down the cost of sourcing and making sure that those used cells have a significant residual capacity.
The graphics below show our current estimate on the distribution of costs in order to make a storage system with <2 kWh of capacity with used consumer electronics batteries.
The key challenges and takeaways that needs to be addressed in order to reuse Lithium-Ion batteries at scale are following:
- Supply
Access to large scale and low cost supply for used batteries is key. This can take place by having relationships with E-Waste actors or partnerships with entities using batteries at large scale. - Characterization, Degradation and Safety
Making energy storage systems under the circumstance of cells which are different in terms of its history, vendor, manufacturer and past life is very complex. Matching cells into efficient packs, ensuring cell and system level safety as well as forecasting degradation of the pack is a challenging task which to our believe must be solved by data to be fed in corresponding algorithms. - Dismantling
The used cells will come in different enclosures. Dismantling those at scale at very low cost is important in order to be able processing millions of cells per year. Automation and robots can be a suitable way to solve it. - Load profiles and Users
Given the complex technical challenges, it needs to be carefully considered for which use cases and load profiles storage systems with used batteries make sense. We see a higher chance of success with users requiring back-up systems with <2 kWh of capacity. - Circularity and Takeback
In order to ensure ecological responsibility, one must make sure and take care that the storage systems are returned back by the vendor after end-of-life from its users in order to send the Lithium-Ion battery cells to a certified recycler. Making sure this works with thousands of installed systems is complicated.
If those challenges are solved and any form factor can be reused efficiency, there is a realistic chance towards making energy storage significantly more affordable for everyone while at the same time reducing electronic waste substantially. It can be a role model of a circular product in this critical domain of energy storage. This is a joint effort, requiring more talent and focus on this topic as well as collaboration and sharing of data amongst stakeholders.
Our team is going to work on those challenges alongside university partnerships with a next-generation product to be engineered and deployed in Indian villages. The results are going to be open sources in order to maximize impact. We are happy to have talented battery engineers joining us. More details at www.solarbox.co.in
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