Rechargeable Lithium Batteries, Powering Agricultural Robotics

Battery power for mobile applications is in itself not new but for agricultural robotics there are a number of specific requirements and unique challenges which need to be considered. Battery power should always be accessible, reliable, long-lasting and convenient and in many cases capable of fast recharging. Having high energy density and in some cases high power capability is a typical requirement. Cost will become an ever increasing factor for the OEM’s of robotics systems to the market as the business scales up. In Agricultural-robotics this cost factor is especially sensitive in a market where consumer pricing is extremely sensitive and subsidies from governments are common.

As in most new markets, Agricultural-robotics applications have initially been satisfied by a lead-acid battery technology because it is available, relatively simple to integrate into the system, end-users can readily source a replacement, the overhead of control and charger electronics is relatively simple and requires minimal design effort. When they decide to step out of the lead-acid solution (for reasons of energy density or performance) most designers in Agricultural-robotics progress to Lithium-Iron Phosphate (LFP) technology as the charging algorithm is close to lead-acid and the cycle life performance is a good match with their expectations and business model. As volumes grow and the battery performance becomes even more critical to the performance of the product so the move from LFP to NCA (Lithium nickel cobalt aluminium) or NMC (Lithium Nickel Manganese Cobalt) technology will accelerate as it has done in many other markets such as eBike and EV, Grid Scale & “Behind the Meter” Energy Storage Systems, robotics, material handling, AGV and many more.

Even at VARTA when we started our residential energy storage system business in 2011 we followed a similar trajectory. In this business VARTA designs and manufactures fully integrated single box energy storage systems containing a battery and inverter together with an energy meter and control electronics which is sold, under the VARTA brand, to end users who have solar panel installed on their roof and who want to either shift the time of use of the energy by storing it in a battery or sell it back to the grid when it is financially advantageous to do so. With over 30 years’ experience in lithium ion technology, VARTA still started with lead-acid technology making it fast and easy to prove the rest of our concept and to get a product on the market which could be evaluated by customers and allow VARTA to get feedback from the market on system improvements and enhancements. This was followed by a move to LFP technology in order to enhance the battery performance, reducing the size and weight, increasing the energy density and allowing VARTA to begin to commercialise the system and increase the volume of sales to the market.

However, the real step change in volume and market acceptance did not occur until VARTA, along with the majority of our competitors, switched to NMC technology which provided a quantum leap in terms of energy density and where, by limiting the internal charge voltage, we could both enhance the overall efficiency of the system and at the same time offer our customers an extended warranty covering 10 years or 10,000 cycles which makes the return on investment for the end customer a much more realistic proposition. Using NMC VARTA was able to become more agile as well, for example introducing a wall-mounted system as well as a free-standing system which would never be possible with the other, less energy dense, battery technologies.

We therefore see an exciting innovative future for Agricultural--robotics supported by NMC / NCA technology because of the ruggedized nature of the business together with the demands for long life and return on investment that require high energy density, long cycle life and flexibility in design. Utilising cylindrical 18650 or 21700 cells increases the granularity of the battery system and allows the designer to create much more flexible battery modules that can be interconnected in the Agricultural-robotic system to power the AGV or robotic system. This flexibility also extends to allow the designer to offer the end customer options such as a standard capacity battery than can later be

upgraded to a high capacity solution just by adding additional modules. Further benefit is also possible when modules can be replaced in the field and common modules used across a range of different systems leading to high volumes, higher reliability and ultimately to lower costs.

There is an additional advantage when these modules can be designed in such a way as to make a modular system possible and modules can then be connected in series and parallel to either increase the system voltage or to increase the overall capacity. Moreover, with integrated communications and smart controls, the OEM can extract some flexibility of performance from a standard module and have access to detailed performance and function data. In cases where a number of robotic solutions products are within the portfolio, even if they have different power requirements, they can ultimately be served by one single battery at the module-level. This reduces design-in efforts from one robot to the next and reduces inventory-holding to one single base module to serve all machines. Once the modules are used universally across multiple applications and end users, then real economies of scale can be achieved.

Utilising NMC / NCA cylindrical cells in this way also allows the possibility to collect data from the battery, transfer it to a cloud, analyse the data and to compare the performance of one module versus another over time. Such analysis allows the end-user to be informed about the battery performance, to predict when maintenance is required and to optimise when the battery or module should be replaced. Additionally alternative business models are also possible such as instead of the end user purchasing the battery they pay either only for the energy throughput or a fixed fee based on a predetermined energy throughput.

As well as this, the source of energy to recharge the batteries is frequently a challenge because access to the grid can be either be limited or zero (for practical purposes). With no buildings or grid access out in the field and sometimes remote buildings for animals without power then providing this opportunity to recharge across the whole agricultural segment, will be an which issue will receive a lot of attention in the future.

Plans to address this are varied but VARTA, as an expert in static Energy Storage Systems for renewable energy, sees a future which integrates renewable energy sources which are either already situated on many farms (like solar panels or windmills) with mid-to-large scale Energy Storage Systems to overcome this. This has the potential to be an elegant solution, with solar panels added to existing farm buildings or constructed within low-cost structures where robotic vehicles can return from the field to recharge. Depending on the type of vehicle and application, these would range in size from relatively small huts to shield and charge the robot up to pre-existing or newly constructed barns for large (tractor sized) equipment and ancillary storage purposes. This long-term approach to infrastructure provides the best possible environmental outcome, the best possible charging opportunity and therefore practical implementation and the lowest long-term cost with the possibility of entirely free of charge energy at the point of delivery.

To find out more about VARTA’s current and future products which are specifically developed for the agricultural market and other mobile/robotics applications visit our website at www.vartastorage.com/asb or contact alex.stapleton@varta-storage.com.