Biogas is a methane rich gas produced through the anaerobic (without air) digestion of organic wastes. It can be generated from animal and kitchen wastes, as well as some crop residues. For cooking and other thermal household tasks, biogas can be used directly in conventional low-pressure gas burners. Biogas is used for many different applications worldwide. In rural communities, small-scale digesters can provide biogas for single-household cooking and lighting. Large-scale digesters can utilize biogas for electricity production, heat and steam, chemical production, and vehicle fuel.
Health Impacts: Users of biogas technology yield tangible health effects with regards to smoke reduction in the kitchen. Individual studies have found that biogas plant installation can significantly reduce respiratory diseases, including decreases in respiratory illness, eye infection, asthma and lung problems.
Climate Impacts: Unlike fossil fuel combustion, biogas production from biomass is considered CO2 neutral and therefore does not emit additional greenhouse gases (GHG) into the atmosphere. However, if biogas is not recovered properly it will contribute to a greater GHG impact than if methane is simply combusted. Several biogas programmes in Asia have managed to generate carbon revenues through the compliance and/or voluntary market.
Fuel Efficiency: The primary domestic uses of biogas are cooking and lighting by means of a gas mantle. The efficiency of a biogas cookstove ranges from 50 to 65 percent, depending on the gas pressure and the stove design.
Fuel Availability: Biogas is best suited for the estimated 155 million households and commercial farms where sufficient animal manure can be collected on a daily basis. However, fuel collection can prove challenging, particularly for farmers who do not keep their livestock in one location. Biogas systems can function under a variety of climatic conditions, yet widespread acceptance and dissemination of biogas technology has yet to materialize in many countries. One primary reason is the high investment capital necessary for a biogas plant, which often can only be afforded by better-off farmers. Even for small biogas units, the up-front costs may not be affordable for poor households. Even so, approximately 48 million domestic biogas plants have been installed since the end of 2011, of which 42.8 million are in China and 4.4 million in India.
Approximately half of the world's population still depend on coal and biomass fuels, (mainly wood, charcoal, dung, and crop residues), for their home cooking and heating. Biomass is the oldest source of renewable energy known to humans and is used for household energy production either through growing energy crops, plants specifically grown for energy use, or by using biomass residues from plants with other applications. Wood is still the largest biomass energy resource today, though other sources of biomass include food crops, grassy and woody plants, residues from agriculture or forestry, and the organic component of municipal and industrial wastes.
Health Impacts: Burning biomass indoors over open fires or on crude stoves can lead to high concentrations in air of substances harmful to health. The known adverse effects of biomass combustion for household energy use include common respiratory diseases, along with low birth weight and increased infant mortality. In developing countries, women are traditionally responsible for cooking and have the highest levels of exposure, as well as infants and young children, who are often carried on their mother's back.
Climate Impacts: Burning biomass releases approximately the same amount of carbon dioxide as burning fossil fuels. While fossil fuels release carbon dioxide (CO2) captured by photosynthesis millions of years ago, biomass releases CO2 that is largely balanced by the carbon dioxide captured in its own growth (depending upon the amount of energy used to grow, harvest, and process the fuel). Replacing harvested biomass results in a sustainable cycle of carbon dioxide emission and sequestration. However, burning biomass also releases pollutants including black carbon and methane, which have short life spans but significant consequences for the climate. Black carbon, which results from incomplete combustion, is estimated to contribute the equivalent of 25 to 50 percent of CO2 warming globally. Methane emissions are the second largest cause of climate change after carbon dioxide.
Fuel Efficiency: Biomass is often burned over open fires or in crude stoves, which yields negative health and climate impacts. Use of clean and efficient biomass cookstoves results in fuel saving, improved fuel efficiency and reduced emissions
Fuel Availability: Biomass availability varies in regions throughout the world from sustainable harvesting in some areas to many areas where biomass use is unsustainable, leading to deforestation, desertification, and land degradation. The type of biomass used varies from region to region according to climate, soils, geography and population.
Charcoal is charred wood, which has lost all moisture and most volatile contents in the production process. It is an energy-dense, light-weight, easy-to-handle, and convenient fuel, which burns without producing much smoke (visible emissions) other than during lighting. These properties make it a preferred fuel especially in urban and peri-urban areas. However, the process of turning wood into charcoal usually wastes over half of the energy in the wood,
Health Impacts: While low in particulate matter emissions, charcoal often has high (odorless and colorless) monoxide (CO) emissions which can kill if room concentrations reach critical levels.Use of charcoal for household energy can lead to high concentrations in air of substances harmful to health, particularly for women and children. Lab testing indicates that improved charcoal stoves can significantly (by 75% and possibly much more) reduce particle emissions released by an open fire. However, most charcoal stoves significantly increase carbon monoxide emissions. Lab testing comparing improved charcoal stoves with traditional charcoal stoves showed mixed results, with some “improved” charcoal stoves slightly reducing emissions and others increasing these emissions.
Climate Impacts: Lab tests of charcoal stoves for climate forcing emissions found that these stoves—relative to an open fire – achieved modest reductions of climate forcing of about 20 percent, when taking into account CO2. However, this analysis does not take into account the net life-cycle impacts, which would also include the substantial climate impacts related to charcoal production. Lab testing comparing improved charcoal stoves to a traditional charcoal stove showed that most (but not all) “improved” charcoal stoves reduced CO2 emissions to varying degrees.
Fuel Efficiency: Most traditional charcoal stoves are made of scrap metal with no option to regulate the burn-rate of the fuel and often without pot-rests, so that the pot sits directly on the charcoal. This causes high emissions of potentially lethal carbon monoxide and wastes a significant amount of fuel. The inability to regulate the air supply and turn down the heat also leads to unnecessary waste of fuel. Lab testing indicates that improved charcoal stoves can reduce fuel use substantially.
Fuel Availability: Charcoal is often produced in rural areas as an income generating activity and then sold in urban markets where firewood collection is less feasible and people have more purchasing power to buy fuel. The price of charcoal is consequently linked to the size of cities, the distance to exploitable forests, and the price of the fuel required for transport. Thus, as cities expand and forests retreat, the cost of charcoal climbs upwards, often resulting in a heavy financial burden on urban households.
Coal is a black, solid, carbon-rich material found underground and is among the most important fossil fuels. In the household energy sector, coal is often used in countries where cooking and heating are combined, particularly in China.
Health Impacts: Coal combustion tends to emit other pollutants, in addition to products of incomplete combustion, such as sulfur dioxide, nitrogen oxides, and mercury compounds. Coal has additional pollutants that may include sulfur, arsenic, mercury, and fluorine that make it a particularly dangerous solid fuel to cook with. However, if local realities are such that coal will be used as a household cooking fuel, processed coal briquettes in combination with advanced coal stoves (especially with a chimney to lessen immediate individual exposures) appear to be a much cleaner way to cook with coal. Lab measurements indicate that the combination of using improved stoves with processed coal briquettes could have a dramatic impact on particle emissions, in one case reducing emissions by over 60 percent.
Climate Impacts: Burning coal for cooking and heating yields carbon dioxide, black carbon, and methane emissions, while coal mining and abandoned mines emit methane, all of which affect climate. Coal and coal waste products contain many heavy metals, which are dangerous if released into the environment.
Fuel Availability: While coal is not used widely as a source of cooking fuel around the world, it is a significant household energy source for China, where strong domestic coal production influences availability of the fuel for cooking and heating.
Ethanol is a clean liquid bio fuel that can be made from a variety of feedstocks including sugary materials such as sugar cane, molasses, sugar beet, or sweet sorghum, starchy materials such as cassava (manioc), potatoes, or maize, or cellulostic materials such as wood, grasses, corn stover and other agricultural residues. Many new feedstocks are under development, such as algae, kelp and other wild or non-cultivated crops such as cattails (bulrush).
Health Impacts: Ethanol burns very cleanly, without the production of harmful gases and fine particulates (soot). Burning ethanol produces significantly less carbon monoxide (CO) than kerosene or solid fuels. Studies conducted in a number of countries, both in the laboratory and in household field tests, have shown the benefit of alcohol stoves in dramatically reducing indoor air pollution as compared to wood, charcoal and kerosene stoves.
Climate Impacts: Greenhouse gases released in the production and consumption of ethanol fuel are reabsorbed during the growth cycle of the plant material used to make the fuel. Especially damaging greenhouse gases like carbon monoxide and VOCs (volatile organic compounds) are not produced or produced only at extremely low levels. Black carbon aerosols, a potentially potent climate forcer, are essentially not produced by the combustion of ethanol and methanol.
Fuel Efficiency: Ethanol fuel functions in a range of efficiencies when used in alcohol stoves, with gelfuel generally somewhat less efficient and liquid fuel somewhat more efficient. In the most efficient alcohol stoves, ethanol is more efficient than solid fuels and kerosene, and generally comparable to LPG. Although ethanol fuel has a lower energy content by volume than kerosene, ethanol tends to combust more efficiently in a simple cook stove than kerosene does and therefore gains in efficiency what it lacks in energy. Ethanol with lower water content contains more energy; thus 95% ethanol produces more heat per volume of fuel consumed than 80% ethanol, although flame temperature remains reasonably constant.
Fuel Availability: Ethanol is made on every continent and in most countries. World production of ethanol has topped 100 billion liters annually, with the U.S. and Brazil the largest producers. Other important producers include Colombia, South Africa, India, China, Pakistan, the European Union, Canada and Australia. In Africa important producers include South Africa, Sudan, Ethiopia, Zimbabwe, Mozambique, Cameroon, Nigeria, Senegal and others. Global growth in production capacity has topped 18% in recent years. However, the price of ethanol is still high, in part due to the demand created by its use as a transport fuel.
Kerosene, also called paraffin in some countries, is a liquid product of crude oil with a high energy density. Kerosene is widely used in urban households for cooking, heating, and lighting, but is flammable and causes a high number of fires and deaths each year. Kerosene is sometimes improperly stored in soda bottles leading to accidental poisoning of children.
Health Impacts: In lab testing, emissions from kerosene stoves were low, though appreciably higher than alcohol or propane. Kerosene is not as clean as gaseous fuels and produces more emissions than LPG. Additionally, kerosene fuel use carries a higher risk of injury than many other household cooking fuels.
Climate Impacts: While kerosene has a net climate impact worse than that of LPG, it is much better than that of traditional stoves fueled by solid biomass.
Fuel Efficiency: The energy content of kerosene is 47 MJ/kg. The release of energy from this fuel is dependent of the technological advancement of the appliances used.
Fuel Availability: Kerosene can easily be transported in bulk and does not need to be transported in pressurized containers, in contrast to LPG. Thus, the logistics of distribution and retail are simpler and access to kerosene in rural and peri-urban areas is often widespread. In addition, distribution of kerosene is efficiently controlled by market mechanisms and does not require project support (although its use is subsidized in some countries). However, kerosene must be purchased and the high price frequently prevents its use, particularly amongst the rural poor. This is especially true where fuelwood can easily be gathered.
Liquefied Petroleum Gas (LPG)
Liquefied Petroleum Gas (LPG) is a clean-burning, portable, sustainable, and efficient fuel. LPG is a co-product of natural gas and crude oil production and usually consists of a mixture of propane and butane for standard heating and cooking purposes. Its unique properties make it a versatile energy source – it is a multi-purpose energy with many applications, is portable, and can be used virtually anywhere in the world.
Health Impacts: Lab testing confirms that cooking with propane or liquid petroleum gas (LPG) is vastly cleaner than cooking over an open fire – reducing emissions of most key pollutants by over 95%, and reducing energy use by about 50 to 70%. LPG improves both indoor and outdoor air quality by substantially reducing pollutants that are hazardous to health, such as SOx, NOx and particulate matter.
Climate Impacts: LPG is very clean burning and has lower greenhouse gas emissions than any other fossil fuel when measured on a total fuel cycle. However, LPG is a fossil fuel, and thus has a substantial carbon footprint. It has been estimated that the carbon impact of LPG per unit of energy delivered is substantially less than the net warming impact from other forms of solid biomass burned in a cookstove and produced fewer harmful emissions than other fuels such as petrol, kerosene, oil, and diesel.
Fuel Efficiency: LPG is cost-effective, since a high proportion of its energy content is converted into heat. LPG can be up to five times more efficient than traditional fuels, resulting in less energy wasted and less household income spent on fuel for those families currently buying solid fuels for cooking. Lab testing results show that cooking with LPG reduces the weighed fuel to cook by nearly 90%, relative to cooking on an open fire.
Fuel Availability: While there is increasing access to LPG in developing countries, this is often primarily in urban areas. The unit of purchase – a canister – can be difficult for low-income families to afford, unlike other fuels that can be sold varying quantities.
Pellets or Briquettes/Cakes
Pellets or briquettes/cakes made from biomass such as agricultural waste, recycled materials, or other materials such as saw dust, are an increasingly common fuel source in developing countries. However, few stoves are dedicated to these fuels alone and pellets or briquettes/cakes are typically used with an improved biomass stove.
Health Impacts: Broadly, use of these fuels can lead to substantial improvements in efficiency and reduction in smoke emissions. Pellets are a clean fuel requiring no additives in the production, and provide a renewable alternative to coal and other fossil fuels.
Climate Impacts: There has been very little independent testing of these fuels in either lab or field settings to date, but recent testing will be forthcoming shortly, and indications are that the combination of an advanced stove with pelletized fuel may be able to dramatically decrease both emissions and fuel use.
Fuel Efficiency: Under the right conditions, pellets or briquettes/cakes can burn more efficiently than traditional biomass. They are more consistent in composition and size than traditional biomass, and a well-designed stove can burn these processed fuels efficiently.
Fuel Availability: Providing adequate supplies of the pellets or cakes at affordable prices and at large scale has proved challenging in previous settings.
Direct solar thermal energy can be used to power solar cook stoves, which can save time, work, money, and combustible fuel in suitable circumstances. Unlike solar photovoltaic energy, which requires expensive PV cells to convert sunlight into electricity, solar thermal energy can be captured instantly and directly with a solar cooker, which generates zero emissions heat for cooking food and boiling water. By comparison, a one hundred square foot PV array would be needed to power a single hotplate. Solar thermal energy can also be used for solar hot water heaters, sterilizers and food driers.
Health Emissions: Use of direct solar thermal energy to power cookstoves produces no smoke, thus eliminating health impacts associated with cooking over open fires or crude stoves.
Climate Impacts: Solar energy use emits no greenhouse gasses and does not contribute to climate change. Fuel Efficiency: While the efficiency of solar thermal energy for cooking is dependent on sunshine, this “fuel” is available free of charge, making it an extremely cost-effective solution, especially for populations with limited access to other fuel sources.
Fuel Availability: Most people cooking over open fires or on crude stoves live where sunshine is abundant and solar cooking is possible, as indicated by NASA’s solar insolation maps. However, in the sun’s absence there is often a need to burn combustibles as well, in which case multiple stove technologies can compliment each other. In some places solar can be the main source of household energy, while in others it is an excellent back-up energy source. As with other fuel efficient stoves, solar cookers are unfamiliar to most cooks in the developing world who are used to cooking over an open flame, so their adaptation to these stoves requires careful training and follow-up.