Solar energy is an alternative renewable energy that is increasingly becoming mainstream due to cost feasibility and higher efficiency. Apart from producing power for offices and households, solar energy can be used to power dryers, cookers, solar stills, lighting, refrigeration and even air conditioning. There is increasing usage of solar energy for agricultural purposes, which consumes considerable amount of power in India.
Solar power technology would be a reasonable choice for agricultural tools. Solar Photovoltaic cells (SPV) directly convert the light energy from the sun into electricity. Concentrated solar power (CSP) systems use an indirect method for the conversion process. Other than SPVs and CSPs, there are other new techniques such as dye-sensitized solar cells, luminescent solar concentrators, bio-hybrid solar cells, photon enhanced thermionic emission systems, etc. All these tools can be produced in small volumes; they are portable which makes it easier to use them in agriculture.
Solar farming uses power generated from solar energy to operate agricultural or farming tools. It is simple, cost effective, reliable and long lasting. Most common agricultural tools such as tractors, watering systems, rotator, roller, planter, sprayers, broadcast seeder etc. work on battery power and fuel oil. In solar farming, the battery power is replaced with solar power, so that the usage of electricity from grid-power and non-renewable sources can be reduced. Here is a list of agricultural tools that are currently being operated in India using solar energy:
Solar Water Pumping System
A solar photovoltaic (SPV) water pumping system consists of solar panels, an on-off switch, a control & tracking mechanism, and a motor pump. This system essentially uses SPV cells for converting solar energy into electric current. A SPV cell array capacity can range around 200 watts to 5KWp (kilowatt-peak) based on the needs of different water sources such as bore-wells, open wells, reservoirs, streams, etc.
Parameters such as the daily water requirement, water source and geographic location must be kept in mind before selecting a suitable solar pump. Although its operation is similar to other pump systems, the duration and quantity of pumping water might vary, depending on the solar radiation intensity, location, season, etc. A system with 1,000Wp capacity can irrigate about two acres of land, pumping approximately 40,000 liters of water per day. A solar pump system with 5HP capacity costs around INR439,000. Some states in India offer subsidies of up to 80% to farmers for encouraging the use of solar energy. Several manufacturers such as Kirloskar, Schneider Electric, Tata Solar, etc. offer a wide range of solar pumping systems in India.
Solar water pumping requires less power and is cost-effective because they do away with the need for expensive fuel like diesel to operate. A solar pumping system with 1,000Wp capacity can give savings of up to INR45,000 per year as compared to a diesel-operated pump. The system’s environmental impact is nearly zero since there is no internal combustion engine as found in regular motors.
Solar dehydrators or dryers are used in farms to dry crops before sending them to the market. These dryers commonly use passive solar panels for generating energy. A large-scale solar dryer usually consists of a shed, drying racks and a solar collector (panels). The crops are dried when hot air is circulated through the shed by natural convection or using a fan.
Domestic and compact solar dryers can handle farm produce like vegetables, fruits, spices, etc. Solar cabinet dryers can be used for drying perishable, semi-perishable and wet processed food material (such as potato chips, leafy vegetables) without contamination. Forced circulation solar dryers use an array of solar collectors connected together to maximize airflow. This type of dryers have components such as solar air heaters, an electric blower, connecting ducts, a drying chamber and control systems for air temperature and flow rate. These dryers are used to dehydrate high value products.
Natural convection solar tunnel dryers are another type that can be used for drying bulk material with high moisture content. These dryers have exhaust fans at the upper end of the tunnel to drive away humid air. Adequate insulation is ensured on the floor and upper sides of the dryer to prevent heat loss. Dryers are sold in India by various manufacturers within a cost range of INR15,000-20,000. Subsidies are also available for dryers just like any other solar installations.
Solar Greenhouses make optimum use of solar energy for providing heating and insulation. Specialized solar greenhouses can collect and store energy for night-time use or during cloudy weather. SPV cells can be used to collect solar energy for additional insulation in colder climates. Another solution is to use water tanks heated by solar power for circulating heat, which maintains the temperature at a level suitable to grow vegetables throughout the year, enabling vegetable production during off-seasons. Such greenhouses using passive solar technology have been built for costs starting at INR30,000 in Ladakh.
In warmer climates, solar greenhouses can be used to create a cooler zone required for certain crops. Cooling pumps can be powered by SPV cells placed either on top or along the sides of the greenhouse. Greenhouses also require proper ventilation with exhaust mechanisms to reduce humidity and get fresh air inside. Solar energy can be used for such ventilation systems. Simple vents using natural convection and heat from the sun is one option and another is to have a solar-powered exhaust fan.
Solar Electric Fence
Solar powered electric fences are highly effective and dependable for large fields and cattle farms. These fences typically consist of a SPV unit as a source of power, an energizer that produces high voltage impulses (8kv) emitted in intervals of 0.9 to 1.2 seconds, along with a 12V battery. The impulse carries 10 mA of current and delivers a shock lasting for a fraction of a second. The batteries can be recharged using readymade solar fence chargers. Battery operated solar fences may cost from INR45,000-50,000 per acre. Cheaper versions costing as low as INR10,000-25,000 per acre have been developed using locally made materials in some places in India.
Solar Milking Machine
Milking machines for cows operated on solar power instead of diesel or electric power are another innovation. A SPV module connected to batteries powers the machine. A mobile milking machine along with solar panels and battery backup is available for INR70,000. Some states like Karnataka provide subsidies of up to 50% for these machines. There are manual milking machines that can be either hand operated or connected to solar power as well.
Solar Mowers & Tractors
Solar electric mowers are available with cordless and rechargeable battery options. These lawn mowers do not emit toxic fumes and do not require frequent refueling to run. Only a few hours of recharging from a solar-powered battery charger are required. It is also possible to convert an existing fuel or electric lawn mower into a solar mower.
Similarly, tractors and planting machines are available with solar panels on top to power them. Solar-powered tractors can easily handle non-energy intensive operations like planting and harvesting. Their operating costs would be a fraction of those of conventional tractors. However, the technology is relatively new in India and used in a few places along with conventional tractors. May be in a decade, we will have fully solar-powered agricultural machineries.
Latest update in tractors
Sonalika Motors has launched Sonalika Tiger Electric, India’s first field-ready electric tractor in December 2020. This state-of-the-art tractor is powered by a 35HP engine and 25.5 kw naturally cooling compact battery. The energy-efficient, German design etrac motor offers high power density and peak torque with a top speed of 24.93 kmph and a battery backup of 8 hours.