Sustainable Energy Use in the Rice Value Chain

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Rice is a major food staple and a mainstay for the rural population of many countries. It is mainly cultivated by small farmers in holdings of less than one hectare. Vital for the nutrition of much of the population in Asia, as well as in Latin America and the Caribbean and in Africa, it is central to the food security of over half of the world population. Developing countries account for 95 percent of the total production.[1] However, the negative impact of rice on the environment is also considerable, accounting for 5 to 10 percent of global methane gas emissions and consuming 3,000 to 5,000 liters of water per kilogram of rice produced.[2]

Source: Shrestha, 2012
Rice Value Chain (Shrestha, 2012)


Rice can grow in a wide range of environments, even in areas where other crops would fail. Rice can be classified depending on the altitude where it is grown (upland or lowland) and the water source used (irrigated or rainfed). Irrigated rice environments are the most important rice production systems, providing 75 percent of the world’s rice production. Grown in paddies, surrounded by a small embankment that keeps the water in, the main irrigation approach used is flood irrigation. As rice is extremely sensitive to water shortages, most farmers opt for this method, ensuring enough water for the crop[3]. Flood Irrigation, also known as surface irrigation, is the application of water by gravity flow to the surface of the field. The management of these types of irrigation is easy and does not require modern technology. They do not require high financial input and adapt easily to flat topography. Especially for short-term water supplies these systems work well and adapt well to moderate to low infiltration rates, allowing easy leaching of salts. Read more…


Unmilled rice known as “paddy” is harvested when the grains have a moisture content of around 25 percent. As a product of smallholder agriculture, it is usually harvested manually. This process is followed by threshing within a day or two, which is also carried out by hand in many countries. This process consists of whacking the rice against some hard object, so the grains scatter. They are then caught in some container or just on a woven mat. This procedure does not excessively increase the amount of foreign material such as stones and mud clods in the paddy, but it will still contain chaff and empty grains that will need to be winnowed out. However, most whacking threshing operations will leave 10 to 15 percent of grain behind.[4] There are small mechanical threshers that can effectively recover this grain. One is the axial flow thresher, designed by IRRI.[5]

ASI Thresher

The ASI thresher separates the rice grains from the panicle mechanically without damaging the grains. It reduces the loss of grains and saves labour and time for threshing operations, especially for women. The paddy produced is clean and not broken, enhancing rice quality. The ASI thresher is easy to build and can operate at the village level. Local manufacturers can download the technical design from the RiceHub and use local materials to build and adapt the machine to local conditions. A locally manufactured ASI thresher costs about 4,500 USD including the engine. Read more…

The ASI Thresher requires an engine of 18-24 CV as a power source. While it is often powered using diesel fuel, it can be powered with solar panels. This ensures more cost-efficiency in the long-term and prevents added GHG emissions. Read more…


Parboiling is a process of soaking, briefly heating, and drying paddy before it is milled. The process swells the grains, loosens the hulls, and toughens the grain. All this allows for a substantial increase in milling recover from about 67% to 75%, which improves food security. Also, during this process some of the nutrients in the bran will leach into the endosperm providing for a somewhat more nutritious final product. This is most noticed in the additional amounts of Calcium, Phosphorus, and Potassium as well as the vitamin Niacin and the Amino acid Proline while containing less Sodium. In addition, grains become harder than raw rice providing a less sticky texture on cooling that some people object to.[6]

GEM Parboiler

An improved parboiling technology called grain quality-enhancer, energy efficient and durable material (GEM) parboiling technology combines the use of a uniform steam parboiler and an improved parboiling stove. When the quantity of paddy to be parboiled is more than 50kg per session, other components (paddy soaking tank, labour saving devices and improved drying surface) are required. The GEM parboiling technology is not only about the equipment but also the process. It is suitable for both rainfed and irrigated rice, but its profitability is higher in irrigated areas. As parboiling is usually carried out by women, the GEM parboiler was co-developed with women from the Glayoue Innovation Platform in Benin. Besides enhancing parboiling efficiency, it has reduced the risk of heat burns and exposure to smoke, and furthermore, increased revenues of its users. Read more…


Subsequently, the rice needs to be dried to bring down the moisture content to no more than 20 percent, making it suitable for milling. One common approach is laying the rice out to dry along roads on the ground.[7] Drying is the most critical operation after harvesting a rice crop. Delays in drying, incomplete drying or ineffective drying will reduce grain quality and result in losses.[8]

The drying process can be improved by using renewable energies, for example solar energy, to power more efficient drying systems.

Solar Bubble Dryer

One innovation that allows safe and efficient drying conditions using solar energy is the solar bubble dryer. The technology consists of a 15 to 26 metres long plastic tube where the rice is laid out. The transparent upper side of the tube allows the sun’s rays to penetrate, building up heat inside and drying the product. The heat is distributed uniformly by solar-powered fans that make the air flow, removing the moisture. For optimized drying, the rice is turned regularly using a rolling bar. Being currently optimized energetically and trialled in different countries, the bubble dryer can cost between € 1,200 and € 3,400.[9] Read more ...

Solar Rice Bubble Dryer in Burkina Faso (©Mgummert)

GrainSafeTM Dry (GSD) Development

In collaboration with the International Rice Research Institute (IRRI) and the University of Hohenheim, GrainPro, Inc. have designed the GrainSafeTM Dry (GSD). The GSD combines in-store drying with hermetic grain storage. In-store drying aims to control the relative humidity of the drying air, so that all grain layers in the deep bed reach equilibrium moisture content. This is possible as a blower that runs on solar power, pushes warm air at the bottom of the device into the grain bulk until the desired humidity level is reached. In hermetic storage the grains are enclosed in an airtight container made from material with very low oxygen permeability, protecting the grains from insects and water reabsorption. Combining the in-store dryer with the hermetic storage properties allows drying and storing food in a protected environment. Including a drying controller allows increasing energy efficiency adapting the blower speed to the relative humidity. With a capacity of 1 to 5 tons of rice, and anticipated system costs of $ 1,100, the GSD still needs to be tested and optimized before a commercial prototype can be developed.


Milling is a crucial step in post-production of rice. The basic objective of a rice milling system is to remove the husk, and produce an edible rice grain that is sufficiently milled and free of impurities. If only the husk is removed, then ‘brown’ rice is the product. If the rice is further milled or polished then the bran layer is removed to reveal ‘white’ rice.[10] Milling can be either done manually or mechanically at large mills. Using renewable energy to mechanize the process makes milling both efficient and emission-free.

Solar Agro-Processing Power Stations

Introducing solar mills in rural areas through microfinancing programs has increased income and saved manual labour. VIA have deployed different types of solar mills to different countries of the Global South, improving the livelihoods of farmers, especially women, who are often involved in manual processing. Read more…

Milling as a Productive Application in Green Mini-Grid Systems

Productive Use (PU) activities, which refer to the utilisation of electricity for income and employment generation, can catalyse rural development and sustainable economic growth. The increasing demand for energy and the increasing household income can accelerate the success of green mini-grid (GMG) projects. The presented guide is designed to help practitioners assess whether milling is an appropriate and financially viable application both for a community and for a mini-grid developer. It also provides guidance on how to operationalize a milling PU. It is organized as a series of tools that help establish a set of best practices for off-grid electrification initiatives. The tools should be used during the feasibility stage of development for mini-grid developers, as they offer important considerations that will help in the decision-making process. However, the tools can be applied independently or together, based on the individual needs of the practitioner. Read more…

Energy Production

The main by-products of rice are rice straw, rice husks or hulls, and rice bran. With proper management, each by-product can be utilized for better purposes such as for energy and non-energy uses (e.g., for agriculture sector and animal fodder production).[11]

Biomass and Solar PV Hybrid Minigrids for Off-Grid Farming Communities

Rural off-grid communities that rely on solar PV systems have limited access to electricity and therefore limited hours for agricultural operations. As diesel generators and battery back-ups are expensive to operate, the innovator Husk Power has developed a hybrid solution that combines biomass gasification with solar power.

The biomass plant converts abundant agricultural residue, such as maize cobs, rice husks, coffee husks and cotton stalks into electricity, powering a mini grid for residential and agricultural uses. The electricity is distributed to rural households and micro-enterprises, allowing a better quality and providing a low-cost option for meeting their energy needs. It powers irrigation pumps, agro-processing mills, and drying and heating processes. As both resources are abundant in rural communities, the processing operations will be able to continue during night time, as the biomass plant will provide power when the solar PV system is not operating. Read more…

Case Studies

Costs and Benefits of Clean Energy Technologies in the Philippines’ Rice Value Chain

Small-scale rice farmers from the Global South often face difficulties in reaching milling services and usually do not have access to grid electricity. Local renewable energy systems can provide electricity and heat for productive activities, hence improving production and reducing food losses in remote rural areas. In off-grid areas the gasification of rice husks and solar-powered domestic rice milling interventions, assessed here as case studies, can be financially viable as well as provide social and environmental co-benefits. Adoption of clean energy technologies in the rice value chain can be facilitated through targets and strategies for rural electrification, the introduction of financing and insurance products, technical assistance to manufacturers and consumers, capacity building and improving energy literacy. Read more ...

Publications & Tools

Costs and Benefits of Clean Energy Technologies in the Milk, Vegetable and Rice Value Chains

Building upon the report Opportunities for Agri-Food Chains to become Energy-Smart, a second part presents the economics related to the energetic transition aimed in sustainable agri-food systems. The subsequent study, presented in this report, focused on the same three value chains as the original report and concentrated on similar key clean energy technologies. The costs, benefits, sustainability potentials and unintended impacts are analysed here at the intervention level (e.g. at famer or food processor level). A methodological approach was developed to provide a sound and comprehensive cost-benefit analysis (CBA). It highlights hidden environmental and socio-economic costs of interventions, such as government-subsidized fossil fuel. The potentially added value of these technologies for different stakeholders was then considered using selected case studies for the same agricultural value chains. Read more…