Fuelling rural stoves

Some forms of biomass, such as vegetation or animal dung, can provide safe and convenient energy sources in the form of gaseous and liquid fuels, although there are technological hurdles to overcome in this area.

Biogas ' a mixture of methane and carbon dioxide ' for instance, has been used for past 80 years as a fuel in rural India. The gas is produced by mixing biomass with water in a special gas producer or 'digester'. As the biomass degrades, the gas is given off and can be collected. Biogas can be produced in the home, but the systems used are inefficient. They also require considerable amounts of cow dung and other nitrogen-rich material, which makes them unsuitable for households with fewer than three or four cattle. 

The challenges of biogas production don't end there. Cold weather slows fermentation and if the different types of biomass are poorly mixed, the digestion is less efficient. Because biogas cannot be liquefied and requires very high pressure (more than 100 atmospheres ' 100 times greater than the air pressure at the Earth's surface) to compress it, it cannot be stored for long periods. 

Research and development are needed in two areas. One is in developing extremely efficient biogas reactors, to get as much gas as possible from the biomass. Genetically engineered microbes, for instance, might substantially increase the efficiency of gas production. The second area is the development of appropriate materials for storing biogas at medium pressures. 

Recent experiments by P. Pfeifer and colleagues affiliated to France's National Centre of Scientific Research (CNRS) show that biogas can be stored at medium pressure (fewer than 40 atmospheres). These findings could pave the way for small utility companies to be set up, revolutionizing the way cooking is done in rural areas.

These companies could buy cow dung and other locally available biomass, and use them in a high-tech biogas reactor with sophisticated electronics-based controls and biochemical engineering technology, to generate biogas efficiently. The companies could then store the gas in small metal cylinders much like the familiar propane or butane cylinders, which could be transported to households. 

Although much too costly for most rural households in countries such as India, the entire system would be affordable for a small rural utility company.

Such companies could also use biomass to produce liquid fuels such as ethanol and bio-diesel ' which is obtained from plant oils. Another fuel is pyrolysis oil, produced when dry biomass is rapidly heated to about 600 degrees Celsius in the absence of air. The vapors condense to form the pyrolysis oil, which is similar to diesel.

Such a project could be made feasible by local activities including planting crops such as sweet sorghum that can be used for both food and fuel, meaning that food production is not compromised. Another option is to cultivate high-yielding hybrids of bio-diesel crops, such as Karanja and Jatropha, whose seeds yield oil. 

But stoves need to be adapted to run on bio-diesel and pyrolysis oil. These fuels are sticky and tend to form a lot of soot, so sophisticated combustion science and technology is required to produce an efficient blue flame. 

Getting such stoves to burn with a clean flame will also help in developing 'combustors' that produce light by a flame heating up a lace-like envelope of material, called a mantle, which surrounds it. This heated mantle glows to produce light.

Looking for light

Adequate lighting is a basic human requirement and should be a part of any government's minimum needs program. Light is produced either by electricity, or by burning a fuel such as kerosene or oil to produce a glowing flame.

Many rural people rely on lights that burn liquid fuel. One of the best systems is a pressurized lamp with a mantle, which is lit by kerosene gas. Amazingly, these mantles (made of an oxide called thoria mixture) have not changed at all since they were developed in Germany in the late 1880s. 

The mantles are about one-third as efficient as a 100-watt light bulb at generating light. 

With today's level of materials technology, it should be possible to develop new materials for more efficient mantles. In the 1980s, researchers found that coating the mantles with alternative materials like ytterbium, a metal used in lasers and x-ray tubes, produces promising results. With the latest advancement of materials technology it will be much easier to tailor-make the materials for mantles.

Current mantles are also brittle and break easily. Having to replace them increases the cost of running a lantern. So there is a need to develop stronger and more durable materials such as those based on ceramics and carbon composites. These materials can withstand high temperatures and hence will not break. With such mantles, liquid-based lighting could become robust as well as efficient. 

It might even be possible to develop mantles that are as efficient as light bulbs. A liquid fuel lamp with an efficient mantle and running on locally made fuels like ethanol, bio-diesel or pyrolysis oil could be an excellent distributed light source for rural areas. 

One of the most efficient lighting systems in the world is the glow of the firefly, created when two chemicals called luciferase and luciferin react. The energy from this reaction is converted directly into light. Scientists estimate that it is around 85-90 per cent efficient at converting chemical energy into light. A light bulb's efficiency is just 7-10 per cent. 

Imitating this mechanism could produce the ultimate light source. At the moment it is no more than a dream, but a solar-powered unit producing luciferase and luciferin from biomass could one day be a reality.

As most rural areas have no access to grid electricity, much research and development around the world is being directed at developing decentralized sources of electricity, which range from 5-10 kilowatt (providing light to 30-60 rural households) to 10 megawatt capacity (enough power for a rural population of 200,000).

These systems include: county-level power plants, biomass-gasifier-based (gasifiers produce a mixture of carbon monoxide and hydrogen gas which is used to run an internal combustion engine) equipment and innovative technologies such as gas-powered 20-30 kilowatt micro-turbines and steam engines with a small 30 kilogramme unit that can produce six kilowatts of electric power.

Small but perfectly productive

As well as electricity from local organic materials, there is promising research and development in three micro-technologies for producing electricity. These are human muscle-powered lighting systems, thermoelectric devices and miniature 'nano-engines'. 

For example, recent advances in lightweight and highly efficient 'permanent magnet direct current' (PMDC) motors have made it possible for people to use physical effort to produce a small amount of electricity. This electricity, when combined with rechargeable batteries, can power some of the most efficient and long-lasting light-producing devices ' light-emitting diode (LED) systems. 

Two companies ' Freeplay in Europe and Light up the World in Canada ' have pioneered this system. At the moment, the technology is expensive, with a handheld flashlight costing US$50. Research is needed to develop three specific components: cheap LED units, lighter and more efficient PMDC motors, and efficient ways of storing the electric charge so it can be discharged slowly. 

Using this approach, bicycle-powered units on which household members can take turns to charge the battery, could produce 3-4 hours' worth of light. 

The simple biomass cooking stoves now prevalent in rural areas ' inefficient and smoky, with about 10-15 per cent cooking efficiency ' could also be given a radical overhaul by new developments. Attaching a device that converts heat into electricity to such a stove, for instance, could generate 50-60 watts of power for lighting.

This power could be used to generate light or to run a small fan to increase the stove's efficiency, as well as ensure that less soot is produced. 

Recent developments in nanotechnology and new materials have also shown that efficient devices that also convert heat directly into energy can be developed. For instance, coin-sized 'nano-engines' that can produce ten watts of energy from biomass fuels such as ethanol, are already being developed by researchers at the US-based Massachusetts Institute of Technology and University of California, Berkeley for defence purposes and to power mobile phones..

The devices could also power LED lamps, revolutionizing rural lighting. Such a compact system would bypass the need for bulky and costly batteries, since the liquid fuel itself would store the energy. This could result in an extremely compact and lightweight decentralized lighting source. 

Any technology becomes attractive if it is economically viable, and increasing the efficiency of a technology can make it more economical. This is true for cooking and lighting technology for rural areas. Once the technology is available, industry can find ways to reduce the cost of production and bring the price within reach of the rural poor. 

In rural India, preliminary economic analyses show that lighting and cooking technologies based on liquid and gaseous fuels could become a US$6 billion a year industry. The same could be true for other developing countries. 

These technologies could help increase the quality of life of rural people, and create wealth through fuel production and use. Investing in such technology could help to bring three billion people into the mainstream of development ' which is the best way to create a just and sustainable world.