Energy for Agriculture

Introduction

Modern agriculture needs modern energy - the two are closely linked. For many developing countries, agriculture is the dominant sector in developing the economy. Increasing productivity and the modernisation of agricultural production systems are the primary drivers of global poverty reduction and energy plays a key role in achieving this. Energy input to modern and sustainable agricultural production and processing systems is a key factor in moving beyond subsistence farming towards food security, added value in rural areas and expansion into new agricultural markets.

In many cases, renewable energy technologies and hybrid systems can provide energy services that neatly support the production process, e.g. by providing irrigation (pumps) or post harvest treatment (cooling) or processing (drying, milling, pressing). The requirements of mechanical energy in the agricultural production process are also of critical importance and include human and animal labour as well as fuels for mechanisation, pumping and other activities, and indirectly the production of fertilisers and agrochemicals.

The agricultural production chain involves the following steps:

• Production
• Postharvest and storage
• Processing
• Commercialisation.

Production

Land preparation, cultivation, harvesting and threshing

The power necessary for agricultural production is provided by human labour, draught animals or engine-driven machinery. Mechanisation is a key input in any farming system applying tools, implements and machinery to improve the productivity of farm labour and land. Based on the power source, the technological levels of mechanisation have been broadly classified as hand-tool technology, draught animal technology and mechanical power technology.31
The bulk of direct energy inputs in smallholder production is provided by human and draught animal power (DAP). Agriculture in developing countries relies heavily on the physical capability of farmers, with often limited output, depending on the physical energy available. A fit person consumes around 250-300 W in terms of energy, depending on climate and with a rest of 10-30 minutes/hour. The efficiency of energy conversion is only 25 per cent, with a maximum power output of 75 W. Operations involving human skill include activities such as planting, weeding, spraying and harvesting and using hand tools. Most horticultural commodities are harvested manually, including those grown in highly industrialised nations. Energy requirements during harvesting include mechanical energy for digging up root and tuber crops. For example, a simple, labour-saving cassava harvesting tool was introduced to Thai farmers by the International Centre for Tropical Agriculture (CIAT) reducing person-days from 15-40 (depending on the type of soil and the yield) to 5-10 days only. The tool costs 2.50 USD, is produced by local manufacturers and can be used collectively by farmers.32 Harvesting early in the morning when air temperatures are cooler also helps to reduce energy requirements and cooling costs.

Activities such as ploughing, soil preparation, water lifting, pulling inputs and threshing require fewer skills but greater energy input and are hence mostly powered by draught animals such as buffalos, horses, donkeys, camels or oxen. Power output ranges from 200 W for a donkey for 4 hours daily work to over 500 W for a buffalo (FAO 2000a). Draught animal power can alleviate human drudgery and is generally considered to be an affordable and sustainable source of power for smallholders, also given its great potential for diversification and expansion e.g. for transport and non-farm work. Efforts to expand the use of draught animal power should include work on animal efficiency, which can be improved through modernisation of equipment, better breeding and animal husbandry, feeding and veterinary care.

In sub-Saharan Africa (SSA), human effort contributes about 65 per cent of the power required for land preparation and subsequent weeding, the principal demand peaks in the farming cycle. An example comparison shows that a typical farm family relying solely on human power can cultivate only 1.5 hectares per year. This rises to 4 hectares if animal power is available and to over 8 hectares if tractor power can be accessed (FAO 2006).

Transition to increased mechanisation of agricultural operations occurs using diesel or gasoline-powered tractors and harvesters. Fuel powered two-wheel tractors are often used for agricultural production, with different attachements for tillage, bed planting, row planting, harvesting and threshing. In Bangladesh, power tillers (12-15 hp) are used for about 70 per cent of farm work because of their versatility (UNDP/PA 2009). The fuel requirements for digging up root and tuber crops, e.g. of a potato digger are 0.57 gallons of diesel fuel per ton of product (1.96 litres/MT) (USAID 2009). Energy use depends mostly on the speed at which activities are carried out. As tillage operations within arable farming systems often have the highest energy requirements and lead to soil degradation, the reduction of mechanical tillage is promoted by the approach of conservation agriculture (CA).

In general, a four-wheel tractor will not be economically feasible for a smallholder with a typical land holding of up to 5 hectares. Government-run tractor hire schemes in SSA countries have not been able to increase farm productivity. On the other hand, the concept of a rental market for privately owned and operated tractors has potential that may increase in the future (FAO 2006).

In general, a four-wheel tractor will not be economically feasible for a smallholder with a typical land holding of up to 5 hectares. Government-run tractor hire schemes in SSA countries have not been able to increase farm productivity. On the other hand, the concept of a rental market for privately owned and operated tractors has potential that may increase in the future (FAO 2006).

Besides direct energy demand in agriculture there are also indirect energy inputs in the form of sequestered energy in fertilisers, herbicides, pesticides, and insecticides, all of which require energy in their production, distribution and transport processes. Fertilisers form the largest of these energy inputs to agriculture, whilst pesticides are the most energy-intensive agricultural input (on a per kg basis of chemical) (FAO, 2000).

Need for these inputs however can be reduced by the use of farm-own organic manure or by agro-industry based bio-fertiliser production, e.g. generated from biogas plants (at household or industrial level). The promotion of locally produced organic fertiliser also has the advantage of avoiding the negative environmental impact of mineral fertilisers and benefits from the shorter distances required for distribution, thus reducing energy requirements and fuel costs.

Past experience in Asia indicates that the key factors driving mechanisation and consequently power for agricultural development are guaranteed markets and farm prices for key crops, favorable government policies and availability of credit. The example of India shows that favorable government policy and farmer demand have led to increased availability of appropriate and locally manufactured farm machinery and ultimately to India becoming the world‘s largest tractor manufacturer.

A very comprehensive comparison of Energy Use in Conventional and Organic Cropping Systems has been carried out by the National Sustainable Agriculture Information Service (ATTRA) of the US National Centre for Appropriate Technology (NCAT). The report shows, in a review of existing studies, that there are many complexities involved in comparing energy consumption in conventional and organic cropping systems. Certain research indicates that organic agriculture is more energy-efficient than conventional agriculture, but not in all cases. In some cases, organic agriculture may be more energy-intensive, depending on the specific farming operation, the crop produced and the post-production handling. It is important to assess the energy-intensiveness of food systems in a holistic manner that incorporates energy consumption for the entire life cycle of the food product.

Irrigation

Access to water is a major determinant of land productivity and active water management through irrigation offers an important opportunity to stabilise yields. Irrigation is therefore of the utmost significance in the agricultural production process and this chapter is consequently accorded great importance. Irrigated land productivity is more than double that of rainfed land. In sub-Saharan Africa, only 4 per cent of the area in production is under irrigation, compared with 39 per cent in South Asia and 29 per cent in East Asia (World Bank 2007). With growing water scarcity and costs of large-scale irrigation schemes rising, there is a need to enhance productivity by improving existing schemes, expanding small-scale schemes and developing water harvesting.

―Irrigation‖ refers to the distribution of water for growing crops, including the use of water storage and pumping, where appropriate. The energy demand for irrigation purposes is the energy required to lift water by pumping from surface sources, such as ponds, streams, or canals; or from below-ground sources using open wells or boreholes. This water is typically pumped to surface canals, reservoirs, or elevated tanks. The energy demand for water lifting is calculated by multiplying the head (the vertical distance from the water source to the field in metres) by the volume of water to be raised in cubic metres (m3). Pumping energy needs are typically expressed in units of m4.
Decisions about energy and irrigation should be made on the basis of three key sequential steps:

1. Choosing the right irrigation technology: understanding the irrigation system needs for a given context,
2. Choosing the right pump technology: understanding the various pumping technologies available,
3. Choosing the right energy source: assessing which power sources are possible, desirable, and locally available to provide the necessary energy for that system.

Choosing the right irrigation technology

The question of which irrigation water distribution system is most suitable will depend on several factors including the crop(s) cultivated, climate, location, scale/area of agricultural production, quantity of water required over time, system cost, access to capital, local agricultural workers‘ technical capacity, local availability of equipment, maintenance and repair services and availability of spare parts. Irrigation systems differ in their peak and average water requirements, the need for water storage (e.g. tanks, cisterns), and the ultimate need for pumping and energy. Where small producers (<two hectares) are targeted, the more expensive irrigation technologies may only be accessible through membership of cooperatives and farmers‘ associations, who have sufficient ability to raise capital, as well as having the management capacity for technology adoption, operation, maintenance, and replacement. The reliability of the selected irrigation system and the ability of its maintenance is of primary importance for farmers.

 

Commonly Used Irrigation Technologies

Irrigation system	Technology	Advantage	Disadvantages
Manual irrigation	Using buckets or watering cans	Low infrastructure and technical equipment requirements	High labour inputs
Surface irrigation	Water moves over and crosses the land by gravity flow; water level can be controlled by simple soil dams; water in ditches can be pumped or lifted by human or animal power to the level of the field.	Low cost and simple technology	Inefficient use of water, potentially high evaporative losses, can lead to increased soil salinity
Sprinkler/ overhead irrigation	Piping water to one or more central locations within the field and distributing it by high-pressure sprinklers or guns. Numerous system types exist, including centre pivot, rotating, traveling/water-wheel, lateral move/side roll/wheel line.	Potential labour savings and more efficient use of water than in surface irrigation.	These systems can be expensive and require technical capacity to operate and maintain.
Drip irrigation/Micro irrigation	Delivers water directly at or near the root zone of plants, drop by drop.	Highly water-efficient method of irrigation, since evaporation and runoff are minimised (also reduces chemical input if required); any pumps can be used; saves labour; lower water pressure and energy use are required compared to other automated systems.	Difficult to regulate the pressure in sloped sites; system maintenance can be higher than other irrigation systems (if water has to be filtered to remove particles that may close the tubes); the system can be fairly costly to install, esp. higher end automated technologies (although some very low cost models exist which require much more labour).

 

In general, the scale of production, costs of the technology and organisational capacity of the farmers will drive decisions about which irrigation approach to use. The size, cost, and capacity of suitable technologies increase along with the scale of production. The following table provides some guidance for the selection of irrigation technologies based on key criteria such as production scale, energy source, and budget.

Comparative Analysis of Irrigation Methods

Irrigation Method	Irrigated Area	Water Requirements	Energy Requirements	Capital Cost	Operating Cost
Manual	<0.5 ha	Low to High	Low (manual only)	Low	Low to Medium
Surface / Gravity fed	Unlimited	High	Low (manual only)	Medium	Low
Sprinkler	Unlimited	Medium	High	High	High
Drip / Micro-irrigation	Unlimited	Low	Medium	High	Medium

 Choosing the right pump technology

There are a wide variety of pump technologies available for irrigation, but not all are appropriate for every type of irrigation system. Pumps differ in their pumping approach, size and capacity, the type of water source they are suitable for (groundwater or surface water), the scale/area of irrigation possible, their cost and technical complexity.

Pumps can be classified into three categories: hydraulic, manual or motorised. The table below offers guidance regarding the most appropriate type of water pump, given the area to be irrigated, combined with the water table depth.

Appropriate Irrigation Water Pumps for Different Irrigation Areas

Irrigated Area	Water Table < 8 m	Water Table > 8 m
< 2 ha	Manual Pump: Hand pump Treadle pump (~ 1 pump/0.5 ha) Motorised Pump 3 – 5 hp mechanical pump < 5 hp electric pump	Motorised Pump: 3 – 5 hp mechanical pump (submersile only) < 5 hp electric pump (submersible only)
2 - 4 ha	Motorised Pump > 5 hp mechanical pump > 5 hp electric pump	Motorised Pump: 3 – 5 hp mechanical pump (submersile only) < 5 hp electric pump (submersible only)
> 4 ha	Motorised Pump > 5 hp mechanical pump > 5 hp electric pump	Motorised Pump: 3 – 5 hp mechanical pump (submersile only) < 5 hp electric pump (submersible only)

 Choosing the right energy source

Different pump technologies are often flexible regarding the type of energy source powering them. There follows an overview of the different energy sources available for motorised pumping, and the definition and characteristics of each.  

Grid electricity

Where grid connection is available an electric pump can be powered directly. However, the cost, availability, reliability, and quality of local electricity supplies determine the use of this energy source.

 

Fuels for combustion engines

Motorised pumps can be powered by fossil fuels (diesel, gasoline), either through generators that create electricity, or by transmitting power to the pump through a drive belt and vertical rotating shaft. In addition, some submersible pumps (i.e. progressing cavity pumps) operate by direct displacement, like piston pumps. The pumps tend to be more expensive but nevertheless more efficient than centrifugal pumps. The use of biofuels (plantoil, biogas) is still limited. A few experiments are underway, e.g. in India with biofuels made from local oilseeds (UNDP/PA 2009), in the GIZ PSDA program in Kenya with biogas (GTZ/HERA 2010b) and in Nepal, where Winrock International is supporting community-grown jatropha oil for irrigation pumps.

 

Solar Energy (PV)

see PV-Pumping

 

Wind Energy

Wind can be used to power both mechanical and electric pumps.
Mechanical wind-powered pumps use reciprocal non-motorised submersible pumps and require wind speeds of 2.5 m/s minimum up to 4 m/s optimum. Capacity is much lower than for motorised centrifugal pumps, in the range of 1 m3/hr at depths of 20 metres or more.
Mechanical wind pumps require the availability of local maintenance and repair facilities to be able to respond quickly to mechanical failures. Adequate wind speeds must be present at the location of the wells. One advantage is that they can pump day or night as long as there is sufficient wind, and can be used independently of electricity or fuel supplies. A disadvantage is that they must be located directly above the well, a location that may not be optimal in terms of local wind resources. Wind pumps are appropriate in windy areas without other sources of power, and only for small irrigable areas.
Wind electric turbines convert the kinetic energy of the wind into rotational mechanical energy that drives a generator to produce electricity, e.g. for pumping water for irrigation. Windmills are positioned for optimal wind conditions, providing greater site flexibility and in addition facilitating electricity production for other uses. Water-pumping applications generally make use of wind turbines with rated output between 1 kWe and 10 kWe. A wide variety of small wind electric turbines is commercially available, with rated outputs ranging from a few tens of watts to 100 kilowatts, and is used worldwide to provide electricity in locations where alternatives are unavailable or are too expensive or difficult to provide.

 

Hybrid Systems

Small-scale hybrid power systems, also a mature technology, are used worldwide. By combining different energy sources (solar-diesel, wind-diesel) hybrids can provide widespread and highly reliable electrical supply. These small hybrid systems are easy to install—no special tools or concrete are required.

Post-harvest and storage

Packing

The best precondition for storage is a proper harvest and post-harvest handling. Sorting, grading, and packing produce into storage containers after harvest to prevent losses is important, especially for easily perishable crops such as tuber crops, vegetables and fruits. Reducing the number of times produce is handled between harvest and consumption will reduce mechanical damage and subsequent losses. Packing houses for crops are often simple structures that provide shade and comfortable working conditions for farm workers conducting manual post-harvest operations. Manual handling is recommended for horticultural high-value produce.

Storage

A certain percentage of the farm produce has to be stored before selling at the market, because production is seasonal while demand, particularly for vegetables and fruits, continues year-round. Storage facilities secure agricultural commodities kept for rapid emergency aid and buffer stocks to stabilise domestic prices. Besides storage at central hubs and transportation centres, more localised storage is often necessary.

Dry Storage

To achieve increased production, traditional village stores need to be improved within the means of smallholders to achieve a certain transition to larger and more modern storage systems.43 This requires the management of dry storage facilities, mainly for post-harvest and storage of grain (maize, sorghum, millet, wheat and rice), pulses (beans, peas), roots and tuber crops, and oilseeds, whereas fruits and vegetables require cold storage facilities. For grain, pulses and oil seeds, mechanical damage mostly occurs during harvesting, transport and processing, while insects, mould and rodents damage produce during storage. For such staple foods, energy input or expensive technology is generally. Good storage practice is the key to maintaining quality and value throughout the storage season. A precondition is that crops are in good condition prior to storage, which means well cleaned and carefully winnowed to remove live adult insects. Straw, chaff, weed seeds, stones and dirt must also be removed, as they hold water and their removal will allow grain to dry faster. The grain should be well dried to an appropriate level of moisture content. Good drying is essential because damp grain will become mouldy and spoil. Solar dryers can be used—sun drying will also help get rid of adult insects in the grain. However, as sun drying will not kill all immature stages, such as larvae living inside grains, it is sometimes necessary to treat the grain with insecticide, thus killing the immature stages once they mature and emerge from the grain as adults. Maize is often shelled by hand. This produces better quality grain but is a very slow process. Quicker and effective shelling can be achieved using a variety of mechanical operated machines. The grain must be sufficiently dry both for these and for safe storage. A good store will keep the grain dry and cool and provide protection against rodents and birds. Practising good store hygiene—keeping everything as clean as is practically possible—helps maintain the condition of the crop and the store throughout the storage season. As pests can attack the store at any time, it is important to inspect the store and crop regularly. There are many appropriate technologies and traditional methods for preventing post-harvest losses, varying from location to location. Dry storage facilities range from small-scale, on-farm storage to medium and large-scale facilities of several hundred of tons or more.

Cold Storage

Cold storage in tropical and subtropical climates can generate high energy demand. In general, the initial cooling, processing and cold storage of fresh fruit and vegetables is among the most energy-intensive activities of the food industry. However, for fresh fruits and vegetables, cooling is also one of the most important steps in the post-harvest handling chain to reduce respiration rates, extend shelf life and protect quality. Deterioration of fruits and vegetables during storage depends largely on temperature, so the temperature must be lowered to an appropriate level, to avoid damage and increase the length of storage time. Controlled temperature storage is a critical factor for most perishable agricultural products and a consistent cold chain is necessary to maintain the quality of many high-value agricultural products. Cooling also offers farmers the opportunity to increase income by extending the period for selling and marketing the products when better prices can be achieved. In developing countries, refrigeration in rural areas must often be operated without reliable electricity supply and the provision of a cold chain or store rooms for cooling bigger quantities of produce is often impossible. Three technologies are available for cooling smaller quantities of produce:

• Passive/evaporative coolers: where temperatures between 10-25°C are needed, no energy input is required.
• Absorption refrigerators (heat driven coolers (HDC), requiring temperatures below 10°C; heat as an energy source is used to drive the cooling system (e.g. solar, kerosene-fueled flame).
• Refrigerators, which are electrically driven, use mechanical compression technology. Refrigeration is dependent on a reliable and continous supply of electricity which can be generated from different sources: from the grid, diesel powered compressor, mechanical power generated from a water turbine, by solar energy converted by solar cells into electricity stored in batteries or by solar energy and evaporation.

Commercial PV-powered refrigerators were introduced in developing countries to cut down the use of kerosene or gas-powered absorption refrigerators, which are the most common alternatives but also those with the most negative impact on the environment. First introduced for medical refrigeration they now also constitute an alternative method of storing small quantities of agricultural products for sale. The newest type of solar refrigerator is solar powered but requires neither solar panels nor a battery as it functions on the principle of evaporation. Solar photovoltaic power for refrigerators has great potential for lower running costs, greater reliability and a longer working life than kerosene refrigerators or diesel generators. A life-cycle cost analysis has shown that the costs are approximately the same for solar and kerosene refrigerators, but because they are more reliable and environmentally friendly, solar refrigerators are the preferred option.

 

Energy Sources for Different Produce-Cooling Technologies (USAID 2009)

Categories	Commodities/Technologies	Energy Sources
Low tech (<5 kWh/day)	Field packing of leafy, stem, or fruit vegetables, root, tuber and bulb crops, fruits and berries	Electric grid; Solar power with battery back-up
Basic tech (5 to 25kWh/day)	Packinghouse operations and pre-cooling for tropical and subtropical fruits and vegetables; Evaporative cool storage. (Temperature range 15°C to 20°C)	Solar water heater, Electric grid; Generator (diesel or gas); Hybrid PV/ Generator systems with battery back-up
Intermediate tech (25 to 100 kWh/day)	Cooling and cold storage for temperate fruits and vegetables. (Temperature range 0°C to 7°C)	Electric grid; Generator (diesel or gas)
Modern tech (> 100 kWh/day)	Automated packinghouse operations, pre-cooling and cold storage for any kind of fruits and vegetables. (Temperature range down to 0°C)	Electric grid; diesel back-up generators

 

Processing

Drying of Produce

To add value to fresh fruits and vegetables, they must be dried before packaging and marketing. Drying of fresh produce, which contains up to 95 per cent water, to a safe moisture content of 7-8 per cent requires the application of low heat and ventilation for best results. Processing fruits and vegetables on a small-scale level is therefore less mechanised than other agro-processing activities. It is important that the used equipment is constructed of stainless steel because acids in fruits corrode mild steel. Peeling, cutting, or slicing produce into uniformly sized pieces is usually required for successful drying. This is typically done by hand. Machines are available for larger quantities and can speed up the peeling, cutting, or slicing of produce. For drying commodities (e.g. tea, coffee, copra or abaca) in larger quantities, heat assisted drying is used, with many different types of dryer available.

Direct and indirect solar drying

 Laying produce out in the sun to dry naturally is common in sunny climates and is a very inexpensive drying method. It is still the predominant method for producing raisins worldwide. However, traditional sun drying methods often yield low quality as the produce is not protected against rain and dust and other contaminations.
Indirect solar drying requires a covered dryer that protects produce from direct sunlight while capturing more heat from the sun. With natural air flow inside, an indirect dryer reduces heat and pest damage while speeding up drying.

Heat-assisted drying

In rainy weather regions or humid locations, heat-assisted dryers create warm air flow inside the dryer to speed up drying. Heat sources may be electric, propane, wood, or any other locally available fuel. Appropriate drying temperatures can easily be achieved with low-powered, relatively inexpensive technologies. The majority of energy used in heated air dryers is actually used to heat the air. Electricity for moving air is only a small fraction of the air heating costs, which depend on the initial and final moisture contents of the product. If energy conservation measures such as air recirculation are incorporated into the operation, fuel use can drop significantly.

Solar Drying

see Solar Drying

 

• Grain mills

Further Reading

• GIZ-HERA (2011): Modern Energy Services for Modern Agriculture - A Review of Smallholder Farming in Developing Countries.
• USAID (2009): Empowering Agriculture - Energy Options for horticulture.