The use of battery power for agricultural vehicles and machinery promises to revolutionise the agricultural industry by lowering costs and improving production. From battery powered large tractors to autonomous small electric robots, battery and solar power are changing the face of agriculture.
Agriculture is under pressure to produce more food using a declining availability of additional arable land and water resources. Mechanised farming can improve food production in Africa, but requires energy, an increasingly costly input to the food production process. There is a need to control energy costs, as in any other industry, by the use of more efficient methods and machinery.
Agriculture is going through a revolution, brought about by new technology, moving to what is known as precision farming (PF), which uses satellite imagery, drones, ground based sensors, GSP systems and agri-robots to control the planting, growth and harvesting of crops. The traditional method of crop management involves blanket application of herbicides, pesticides and fertilizer, while PF makes use of automation and artificial intelligence to precisely control the amounts of fertilizer, herbicide and insecticide applied to crops, with resultant increased yield and greatly reduced use of the above. PF also reduces the energy used by agricultural machinery by directing action only where it is needed and focusing activities on specific areas only.
Much of the ground based equipment used in PF has only been made possible by the decreasing cost of storage and solar power devices, which allow small autonomous electric powered robots to operate for long periods of time and with reduced weight and cost. PF can be operated on a large scale without such robots, but this restricts it to separate fields, whereas with the use of robots, this can be applied to individual plants.
The transition to electric power in agriculture
Agriculture is energy intensive, and the use of large machinery results in high fuel consumption. Farm machinery used for crop management conventionally consists of diesel or petrol engine powered tractors. Energy forms a large component of the cost of production, which is increasing.
As in many other industries, attention has been given to changing from internal combustion engine drives to electric driven farm vehicles, and a number of battery powered farm vehicles are now available. Electric vehicle drive systems are well developed in the motor and industrial vehicle industry, and the challenge has been in adapting the existing technology to the needs of agricultural machinery. Electric driven farm vehicles are nothing new. They were common in the 1930s but were tethered to the supply by trailing cables. The difference is that the current generation are battery powered.
One of the claims of the industry is that electric farm vehicles are more energy efficient and cheaper to run than diesel powered machinery. The critical factor is the price of electricity versus the price of diesel. The use of electric driven vehicles is also influenced by a growing application of own generation on farms, using solar, wind, biomass or small hydro. The cost of own generation is decreasing, making the use of electric powered farm vehicles more attractive.
The electric powered farm vehicle
The primary vehicle used in agriculture is a tractor, with most performing high energy tasks using, for example, plow disks and subsoilers. This leads to tractors being oversized for medium and low-energy demand applications, resulting in unnecessarily high fuel consumption on lighter-duty tasks and under-utilisation during other times. One of the challenges facing development of electric farm vehicles is the need for sufficient stored energy to run a large vehicle for a full day on a single charge. This has currently restricted the sector to small to medium sized vehicles, comprising farm runabouts, orchard vehicles and smaller tractors.
Farming requires powerful machinery to perform ground preparation functions such as plowing, tillage and other energy intensive operations, so the tractor is the heart of most farming operations, and is the primary target for conversion to electric operation. The tractor not only provides transport and traction power, but is also used to drive attached machinery in a stationary operation. Several agricultural machinery (AM) manufacturers have introduced battery powered tractors into the market. Examples are given in Table 1.
Table 1: Battery powered tractors on the market or under trial.
Solar powered electric tractors
Apart from numerous DIY versions that actually run directly on power derived from PV panels attached to the tractor, all of the so-called solar powered tractors are powered from a stationary array plus batteries. This allows the array to be dimensioned to charge both the tractor and run other stationary machinery and appliances as well as lighting. Options for battery swap out are also being considered, i.e. one battery can be on charge during the morning session and swapped at the midday break for a second battery that would then charge during the afternoon shift.
While even just a few years ago the idea of a solar powered practical electric tractor may have been a pipe dream, the combination of cheap solar panels and the evolution of lithium batteries and other associated technologies are changing everything. Typical of the solar powered tractors is the Seletrac. While not directly powered by the sun, it is recharged via an 8 kW rooftop solar power system which also supplies the power needs for the farm.
An electric tractor concept touted to be a game changer is the AgBot. Instead of having a single large tractor, farms of the future may have a fleet of autonomous smaller tractors completing various tasks simultaneously. Small tractors also have an advantage of reducing soil compaction and unlike their larger counterparts, can be used in wet conditions without creating as much damage (or getting bogged down). The ability to work just after rain when weeds are beginning to sprout can translate to less herbicide being needed.
Fig. 2: The prototype electric farm vehicle developed by NMU (NMU).
The batteries on electric farm vehicles can generally be recharged on a slow or rapid cycle.
Problems are foreseen with grid recharging as all farm vehicles would be recharged at the same time at the end of a day, causing a huge spike in demand. This could be overcome by staggered charging or multiple battery systems, where one battery is on slow charge while the other is being used. Recharging of batteries is a challenge as a typical recharge cycle could take up to 8 hrs. In future variable tariffs may allow the farms to charge batteries when tariffs are low due to low demand or over-generation by renewable energy sources.
Solar or wind charging
Charging from a solar system is being used by at least one model at the moment. Solar charging could be an increasing option on large farms where the trend is to install solar PV for other purposes. This approach would favour the multiple battery system. Most farms have extensive shedding; offering the perfect platform for large scale solar power systems.
A study several years ago showed that using biomass to generate electricity was more efficient than using it to produce liquid fuels. There are a large number of small biomass gasifiers on the market and it is common practice to use these to generate electricity on farms. This offers a symbiotic process for the farmer wanting to convert to electric vehicles.
This is an energy source which can run continuously and generate electricity at low cost.
A local study has shown that electric orchard tractors could replace up to 8000 small tractors on horticultural farms, to undertake a diverse array of low-energy applications . The introduction of electric orchard tractors on these farms could do much to reduce the overall total lifetime cost of farm vehicles. In addition, many farming activities are stop-start and low speed, making them ideally suited to electric vehicles with their low-speed, high-torque characteristics.
The demand for electric farm vehicles is seen to be strongest in the small to medium utility or orchard tractor sector. Nelson Mandela University has developed the first prototype of an electric orchard tractor equipped to undertake a range of low to medium energy applications, and to replace small tractors on farms. The research shows that this electric tractor would need to be marketed in South Africa at a price point of between R400 000 and R500 000. The market for such vehicles is estimated at 1430 p/a by 2030 . The prototype has a 35 kW motor and a run time of five to six hours per charge, with a load capacity of 1 t and a tow capacity of 1,5 t.
The study showed that the cost of ownership of a 20 kW electric utility vehicle was approximately 50% of that of a 35 kW diesel powered tractor.
Fig. 3: Small planting robots operating in swarms (Fendt).
Autonomous or self-drive agricultural machines
While the automotive industry is toying with the idea of self-drive autonomous cars and other vehicles, and struggling to manage the complexity of such a concept, self-drive farm vehicles are well developed and taking advantage of electric power. Granted, the autonomous farm vehicle has a much simpler function to perform, and much simpler programming, but has to follow a designated path very accurately. The use of electric motors, especially when applied as all-wheel drives, allows the accurate positioning required for precision agriculture. There is also a move towards semi-autonomous (SA) operation, where the farm vehicle only performs operations selected by a supervising operator, who can step in and change parameters or correct problems. A single operator can control several machines. Master-slave operations are also possible, with the operator in the master machine. SA operation appears to be the solution of choice at the moment, allowing a hands-on approach to automated farming.
One of the biggest impacts of the decreasing cost of solar and the increased capacity of storage batteries is in the field of agri-robots (AR). AR range from small low weight machines powered entirely by solar and used for weed eradication, to larger machines using stored energy for more complex tasks, such as sowing, fertilization, crop assessment, harvesting and trimming and pruning. AR use a very small amount of power, and being driven by electric motors, can be positioned very accurately, a feature required for precision agriculture. One of the advantages of battery powered AR is that they can work continuously and do not require daylight for operation.
Precision agriculture is one of many modern farming practices that make production more efficient. With precision agriculture, farmers and soils work better, not harder. Precision means being ‘site-specific’ and ‘information-specific’, as in the most precise way of informing farming decisions. Farmers are able to take large fields and manage them as if they are a group of small fields through gathering information from the fields in real-time by observation and measurement, then responding to inter- and intra-field variability in crops. This reduces the misapplication of inputs and increases crop and farm efficiency.
Fig. 4: The Ecorobotics autonomous weeder. (Ecorobotics).
Precision agriculture practices are used to apply seeds, nutrients, water, and other agricultural inputs to grow more crops in a wide range of soil environments. Precision AR can provide information on how much and when to apply these inputs. Although PA is being adopted in South Africa, it has not yet extended to the use of ARs . AR robots have the advantage of small size and low weight, causing less soil compaction than would happen if tractor based planters and cultivators were used, as well as a massive savings in time and energy.
The Agri-robot swarm concept
Mobile agricultural robot swarms (MARS) is an approach for autonomous farming operations by a coordinated group of robots. One key aspect of the MARS concept is the low individual intelligence, meaning that each robot is equipped with only a minimum of sensor technology in order to achieve a low cost and energy efficient system that provides scalability and reliability for field tasks. The key advantage of this approach is the energy efficiency compared to other methods using robots.
The robot swarms are coordinated by a centralized entity which is responsible for path planning, optimization and supervision. It also serves as a mediator between the robots and different cloud services responsible for the documentation of the procedure. The swarm approach allows robots to concentrate on areas where action is required and devote less attention to areas not needing attention, whereas individual robots have to cover the whole area.
An entire system, including small robots operating in swarms and a cloud-based system control, is available under the product name Xaver, which fits in with the swarm concept of using a large number of small autonomous machines to do precise agricultural work .
Precision planting and plant care
Planting Agri-robots vary from machines based on a simple planting process to those capable of precise seed planting and recording of the position of each seed. Advanced robots use a cloud-based solution to plan, monitor and accurately document precise planting of seeds. Satellite navigation and data management in the cloud allows operations to be conducted round the clock, with permanent access to all data. The position and planting time of each seed is accurately recorded. Knowing exactly where the seed has been planted opens up new potential for the rest of the process, since subsequent operations over the plant cycle, such as protecting or fertilising plants, can be performed precisely according to the individual plant.
An example of an advanced AR robot used for planting is the Mars robot produced by Fendt. It is battery-operated, with an electrical motor of approx. 400 W, and weighs approx. 50 kg. Autonomous operation allows planting to continue round the clock, seven days a week, and because of the large tyres, ground pressure is almost negligible (approx. 200 g/cm²).
The robots need around 70% less energy to do the same work as diesel driven machinery, and since neither diesel nor oil is required to operate the robots, there is no leakage and there are no local emissions.
Fig. 5: The RIPPA weeding robot (UoS).
Weed control ranks among the top challenges for farmers and the biggest pest control issue. Among different classes of pesticides, herbicide use dwarfs all others including insecticide use. Nobody wants to spray herbicides, but nobody wants to see weeds sucking up all the water and nutrients intended for the crops either .
There are several weed-eating robots on the market, some entirely solar powered and others relying on battery storage. The robots detect the presence of weeds and eliminate them either by a controlled dose of herbicide, mechanical removal, or mechanical destruction (crushing).
Solar powered weeding robots (SPWR)
A typical example would be the machine designed and under test by Ecorobotics of Switzerland. The robot is completely solar powered and can operates by detecting weeds and delivering a controlled amount of herbicide to the weed.
Under ideal conditions, the robot can cover three ha per day, so it’s not really suitable for large farms. The robot is powered by a 380 W solar array, and an on board battery is fitted.It can continue to operate in overcast conditions, albeit at reduced performance. In good conditions, it can operate up to 12 hours a day and it has 2 x 15 l herbicide tanks – more than enough for one day of autonomous operation. The robot is a relative lightweight, at approximately 130 kg.
Fig. 6: The Dino battery powered weeding robot (Naio-technologies).
A second example is the RIPPA designed by the university of Rippa designed by the University of Sydney.
Battery powered weeding robots ( BPWR)
These machines are larger than the SPWR and can cover more ground. Examples are the French-made Dino robot which is guided by accurate GPS signals to follow a pre-programmed route, straddling vegetable beds while two cameras assess the plant growth and identify weeds to be mechanically dug out from crops. Once under way, the battery-powered unit can work for up to ten hours on a full charge, covering up to five hectare in a day, without the need for further human interference – even sending its operator a text message when the job is finished .
Another example is the Bonirob, designed and developed by a Bosch company “Deepfield robotics”. The unit is larger and heavier than the solar powered robots but can also be used with taller crops and in larger fields. The unit can operate for eight hours and can cover up to five hectare per day.
Fig. 7: The Bonirob weed eating robot (Bosch).
One of the processes under development is the use of lasers to eliminate weeds. Research has shown that a controlled laser burst can retard weed growth or eliminate it entirely. Laser equipment may increase the power consumption of the weeder and require larger batteries and larger robots.