Battery-powered products in green management: potential and problems
Comagarden/Morgan data on sales of garden and lawn care equipment highlight, within a recovering market, the massive success of electrically powered technologies. A survey of the types of products that use the electric motor, from self-propelled machinery with driver on board to equipment carried by the operator. Environmental benefits and the problem of disposal and recovery of used batteries
The debate on climate change has raised awareness on the need to have more green areas, plant more trees, create urban and peri-urban forests. It has also raised awareness on how and with which means to implement the maintenance of green areas respecting environmental sustainability. The constant growth in the use of battery-powered machinery and equipment, which as such are less polluting, reflects this greater sensitivity to environmental issues. Market figures provide a clear indication of that. The data on sales of gardening machinery, in Italy, in the first nine months of 2021 processed by Comagarden/Morgan not only show an overall increase in the sector compared to the same period in 2020 but also highlight how, within each type of machine and equipment, battery-operated models had the highest increases, with peaks of over 45% for lawnmowers and blowers/aspirators.
Machinery and equipment powered by Lithium-ion batteries
The power supply of gardening machinery and equipment is generally provided by lithium-ion batteries combined with other metals. The most frequent combinations are lithium-lobalt oxide, lithium-manganese oxide, lithium-nickel-manganese-cobalt. The use of lithium is due to its low molecular weight and high energy density, so the batteries have a low weight compared to the electrical potential. More specifically, the weight of a lithium-ion battery mounted on a piece of hand-held equipment, such as a brushcutter, amounts to 1-2 kg with a duration that, depending on the working conditions, is between 45 minutes and even more than 1 hour. The most performing batteries carried on a backpack, being heavier (they reach 5-6 kg), last 3-5 hours and more. These batteries have a service life span of 600-900 cycles, with low recharge times. They have no memory, so that they can be charged regardless of discharge rate. In addition, the loss of charge during non-use periods is very low and does not exceed 2%-3% per month. This means that they do not have to be recharged immediately after even prolonged storage. We have mentioned the increasing diffusion of battery power for gardening machinery and equipment. Now let us look at some examples.
Lawnmowers
Mowers with driver on the ground. We have already pointed out that, along with blowers/aspirators, this is the category that in the first nine months of 2021 recorded registration increases of more than 45% compared to the same period in 2020. The engine power of these mowers, usually with horizontally rotating blades, is between 250 and 1,500 W, with cutting widths ranging from 30-35 cm to 80 cm. They can perform both mulching cutting and cut with collection in the basket. The operating range is affected by several factors, such as the terrain orography (slope), density, height and degree of grass humidity. The single or double blades are generally made of hardened steel and operate at a speed of around 3,000 rpm. The geometry of the casing is also very accurate in order to ensure a clean cut and a rapid ejection of the grass. To increase the battery life, some models are equipped with two battery positions so that when the first one is discharged, the second one is activated. Always to increase the autonomy, there are also versions that, in addition to having the two fixed battery positions, through an application, it is possible to add a battery carried on the back by the driver. With an autonomy of around 3 - 3.5 hours, these machines can control a lawn area of up to 3,500-4,000 m2 offering the same performance as an equivalent mower with an endothermic engine.
Mowers with driver on board. The medium-sized models have a cutting width of 60 - 100 cm for engine powers of over 5 kW. These machines have the same performance as those with an endothermic engine, and the cutting height adjustment is electric primarily. The range varies from 2 to 4 hours. With two hours of autonomy, the lawn covered area is around 2,000 m2. They can also be used as a mobile source of energy for users with power less than 1 kW. In the large model class, cutting widths of more than 180 cm can be achieved, even with 7 hours of autonomy and recharge times around 8 hours. Versions also exist with a photovoltaic panel roof to power the battery through solar energy.
Hybrid mowers with helical blades. These machines are mainly designed for golf courses, both for greens and fairways, and come in versions with a driver on the ground and a driver on board. One of the solutions adopted is to replace the hydraulic circuit of the cutting cylinders with an alternator that keeps the speed of the cylinders within the desired value. This allows the engine to operate at a lower speed, thus saving fuel. For cutting widths around 150 cm (3 cutting units), the power required is 15 - 18 kW.
Robot mower. In recent years, it is the machine that has become increasingly popular and widespread, much appreciated by both hobbyists and professionals. Many versions are produced with costs ranging from just over 1,000 euros to over 12,000 euros, to which must be added those of installation around 300 - 400 euros for lawn areas of 1,000-1,500 m2. Depending on the model, the cutting widths range from 20 cm to over 100 cm, with a dominant surface area of between 500 and over 20,000 m2. Once the working perimeter is defined, it moves inside it and, due to the sensors and receivers with which it is equipped, avoids any obstacles (trees, bushes, flowerbeds, etc.) in its path. The battery is automatically recharged by hooking it up to the charging station located in a specific position on the lawn. The range is generally between 60 and 90 minutes, but the automatic recharge allows for 24-hour use and, therefore, also at night. On some models, the installation of a GPS enables to draw a map of the garden and the paths to follow. Through SMS, the user can follow the robot's operation and intervene remotely.
Equipment carried by the operator
This category includes various gardening equipment, such as chainsaws, hedge trimmers, blowers/aspirators, brush cutters. With the same performance as the corresponding models with an endothermic engine, the operator mainly appreciates the lower weight and greater comfort in use.
Chainsaws. The market offers a wide range of models. The user's choice is guided by the price/performance ratio and the machine's weight. This is why manufacturers have reduced weight while improving engine performance. The 2-2,5 kg models, with a bar length of 30-35 cm, do not perform differently from those with an endothermic engine with a displacement of around 45 cm3. In the larger models, with a bar length of 40 - 45 cm and rated power of over 2 kW, the weight exceeds 5 kg. Battery life in first-generation machines was limited. Today the latest generation models last up to a few hours. The cutting chain speed is around 20 m/s, with safety systems (automatic blade stop, etc.) comparable to endothermic models. Ergonomics has also improved with the development of handles that can be oriented 180° or rotated 90° in order to facilitate cutting operations.
Telescopic arm chainsaws. They enable cutting branches and twigs at a certain height of the tree while remaining on the ground. The arm is adjustable from 2.5 to 5 meters, and the cutting length of the chainsaw is 20 to 25 cm, for a weight between 2 and 5 kg.
Hedge trimmers. These machines perfectly meet the user's needs when is engaged in cutting hedges, bushes and tree branches. The weight varies from 3 to 5 kg, while the length of the blade is between 50 and 70 cm. With the batteries mounted on the machine, the autonomy is around 45 minutes. With batteries carried on the back, the runtime increases to several hours. Some models are equipped with an anti-blocking system of the motor when high cutting resistance occurs, implemented by reversing the motion of the blade. The pivoting handle helps orient the blade in different cutting positions. The hedge trimmer can be mounted on a telescopic arm with chainsaws.
Hand operated blowers. They allow to convey, for the following collection, different kinds of material: leaves, paper, cans, paper bags, etc. and, therefore, are used for cleaning streets, lawns, stadiums, etc... The minimum weight is about 2.5 kg, with an air capacity that can be adjusted depending on the material to be collected. Maximum flow rates are as high as 900 to 1,000 m3/hour, with an adjustable speed between 15 and 55 m/s.
Hand-held brush cutters. They are mainly used for cutting grass on mineral surfaces, cutting roadside grass, and trimming after the passage of lawnmowers. They are also used to cut grassy areas of a certain size or located on slopes. They can mount different cutting heads, from trimmers to those with different types of blades. Special protections of the head avoid throwing stones or other material particularly dangerous when working in an urban environment. To prevent this danger without the need for protection, some models have heads with two counter-rotating blades between them. The power varies depending on the model from 200 W to 2.0 kW for working widths of 30 to 45 cm.
Strengths
There are many reasons why hobbyists and green maintenance professionals are increasingly turning to battery-powered electric machinery and equipment. For equipment carried by the operator, as has already been pointed out, one of the reasons is the lightness and consequent greater ease of maneuvering. Another reason is greater comfort, both in terms of sound and hand-arm vibrations level. In fact, the sound level does not exceed the maximum values of 80-90 dB, which benefits the operator and the community. When working in an urban environment and in other sensitive areas (hospitals, schools, rest homes, etc.), the vehicle's environmental impact is, in fact, reduced. The lower weight and reduced hand-arm vibrations minimize the operator's risk of injury and muscular-skeletal diseases. Other advantages are the high battery life that allows continuous use for several hours and also the ease with which the start-up is implemented as just press a button. Moreover, they require low maintenance and, in general, have a longer lifespan compared to similar models with an endothermic engine, so the operating costs are lower. However, the most qualifying strength is environmental as their use does not involve direct emission of CO2 and other polluting gases. The purchase of a battery-powered machine and equipment addresses actions leading toward the desired energy transition.
Weaknesses
In the current lithium batteries, the electrolyte, always lithium, is in the liquid state. This can lead to overheating the battery under certain conditions, resulting in a fire hazard. Cases of self-fire of lithium batteries are not uncommon in storage areas not properly managed. One of the solutions to this problem is to make batteries with electrolytes, always lithium, but in a solid-state. This allows not only to reduce the risk of fire but also to increase the energy potential and, therefore, the duration of the use time of the batteries after each recharge. Cobalt is an essential component of the cathode of lithium batteries and thus has a growing market. The World Bank expects demand for cobalt, between now and 2050, to grow by 585%. The reason lies in the automotive sector, i.e., in the growing popularity of electric cars. As a matter of fact, in the batteries of an electric vehicle, cobalt can weigh up to 14 - 15 kg. Besides the increasing cost, of concern is that 60 - 70% of the world's total cobalt is found in the south of the Democratic Republic of Congo. The reasons for concern are the mistreatment and exploitation of labor employed in the mines and the fact that the companies used in the extraction are almost all from China. Hence the search for lithium batteries without cobalt is replaced by other metals such as nickel, iron-phosphate, manganese. Another problem created by the growth in the number of electric vehicles is the disposal and recovery of exhausted batteries. This is why Consortia and private companies deal with the disposal of batteries and accumulators that have reached the end of their life.
Battery disposal and recovery.
The ways to implement proper storage of lithium batteries to avoid possible fires are the subject of regulation and guidelines by a working group consisting of the Fire Department, ENEA, and university institutes. The possibility of prolonging the life of those batteries that, although no longer able to power an electric car, still maintain a certain charge is also being evaluated. The idea is to assemble these accumulators to implement energy storage from renewable sources (solar, wind, ...). At the same time, solutions are sought for the recovery of components. Electric vehicle batteries are difficult to process due to the flammability of lithium and the fact that elements such as cobalt and even nickel have chemical-physical characteristics that require complex procedures for their recovery. This makes the process that leads to a second life of the components, destined to other applications (photovoltaic panels, for example), costly and profitable only under certain conditions. However, driven by the market value of the components and the constant increase in the number of batteries to be disposed of, the road to a circular economy for these products is already open and offers interesting prospects. One of the recycling systems involves, after prior discharge, grinding to obtain the material from which to implement the recovery of lithium, cobalt, nickel and other heavy metals (not graphite). The process used, called hydrometallurgical, involves a chemical treatment of leaching carried out with acids (sulfuric, hydrochloric or nitric) or bases at certain temperatures. It is, however, a process that requires a lot of energy. Another system is based on a delamination technique, implemented with ultrasound, which allows detaching from the electrode, both the graphite oxides and the oxides of lithium, cobalt, nickel, etc… without the need to grind the batteries. Battery recycling is relatively recent and evolving activity. The countries where the recycling process is more advanced are China and South Korea. However, the USA and EU are also moving in this direction by promoting significant experiences.
