What is a Clean Cookstove?
In a broad sense, global solutions to the health, climate, and other risks caused by the incomplete combustion of biomass in cooking stoves should meet four core criteria:
- User needs: Solutions must meet the social, resource, income, and behavioral needs of users.
- Scalability: Solutions must be scalable through markets or other mechanisms.
- Performance: Solutions must substantially improve technology design and performance relative to baseline conditions and – once industry standards are in place, be able to meet any international standards for performance and safety.
- Monitoring: Solutions must stand up to rigorous field monitoring and evaluation to demonstrate actual, in-field impacts.
Any fire creates some pollution. However, there are many fuels and advanced stoves that – at least in controlled settings – represent much cleaner solutions. These solutions might be thought of as moving along a spectrum, often referred to as the energy ladder. At one end of the spectrum is the use of raw, unprocessed solid fuels (e.g., dung, crop residues, humid wood) in open fires or crude stoves, while at the other end of the spectrum are ultra-clean fuels (e.g., natural gas, electricity, solar) or modern cooking devices like propane stoves. In the middle are a wide range of technologies and fuels of dramatically varying performance, durability, safety, and cost.
The Alliance is technology and fuel neutral, but that neutrality must be related to the performance of the solution and its ability to meet established industry standards, as well as an ability to demonstrate broad consumer acceptance to reach significant scale of operations. The Alliance will seek to advance solutions that are as clean and efficient as possible, and will actively pursue intermediate solutions that can bring about real, measurable benefits.
Different elements of the technology and fuel spectrum include: clean fuels, stove technologies, and behavioral and structural solutions.
Different delivery mechanisms for these solutions include various business models, carbon credits, government programs, and humanitarian efforts.
Clean cooking fuels offer the greatest leap in performance, but are not always available or affordable to poorer populations. The fact that they require an ongoing fuel cost in addition to an upfront cost to purchase a stove is perhaps the greatest barrier to universal adoption. Examples of clean fuels include:
Electric Stoves
Cooking with electricity produces zero emissions within a household, and therefore is essentially smokeless from a personal exposure perspective. Emissions associated with the marginal increase in power production must also be considered (and will be more or less depending on the fuel source and emissions controls on the power plant).
Clean Fuels
Gas Fuels – Biogas and Propane (or LPG)
- Health Emissions: 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%.
- Climate Emissions: LPG is a fossil fuel, and thus has a substantial carbon footprint, but it has been estimated that its carbon impact (per unit of energy delivered) is substantially less than the net warming impact from other forms of solid biomass burned in a cooking stove (though very clean burning stoves that use 100% sustainably harvested biomass could theoretically have even less impact).
- Time to Boil: Cooking with LPG depends on the firepower of the stove. Some LPG stoves are faster to boil compared to the open fire.
- Fuel Use: Lab testing results show that cooking with LPG reduces the weighed fuel to cook by nearly 90%, relative to cooking on an open fire.
Liquid Fuels – Ethanol and Kerosene
- Health Emissions: Testing in lab settings indicates about 85% to over 95% reduction (depending on the pollutant).
- Climate Emissions: Kerosene’s net climate impact appears to be worse than that of LPG, but much better than that of traditional stoves fueled by solid biomass.
- Time to Boil: Liquid fuels have a more ambiguous impact on cooking time. The cook can feed more wood into the biomass stove and can boil water very quickly.
- Fuel Use: Lab testing results show that cooking with ethanol and kerosene can substantially reduce weighed fuel used to cook by over 74%, relative to cooking on an open fire.
- Note: Other liquid fuels such as plant oils are in use, but the Alliance is not aware of any independent testing results of stoves using these fuels; US EPA testing of a plant oil stove has been completed, but data is not yet available.
Solar Cookers
Most people using three stone fires live where sunshine is abundant and solar cooking is possible. However, in the sun’s absence there is a need to burn combustibles as well. The two technologies are complementary.
A solar cooker is a device that cooks using only energy from the sun. This sunlight is free. It emits no greenhouse gasses. It protects from smoke inhalation. In suitable circumstances, solar cookers can save time, work, and combustible fuel. They come in a variety of designs and sizes from small, inexpensive household units to large more expensive institutional units. Most solar cookers act like crock pots while others have the intensity to perform like a stove top burner. Nearly all foods can be cooked in some type of solar cooker. However, solar cookers are unfamiliar to most cooks in the developing world who are used to cooking over an open flame, so adaptation to these stoves requires training and follow-up.
Funding for the introduction of solar cookers in the field has been modest which has restricted the formal evaluation of results. However, community sized pilot projects of solar cookers in Africa and Latin America, plus large projects in India and China have demonstrated the viability of the technology. While its in-country manufacture is desirable, advanced components from developed countries may be necessary for optimum performance.
Processed Solid Fuels: Charcoal, Pellets, Coal
For the majority of the developing world that either does not have access to or cannot afford LPG or liquid fuels, burning solid biomass is the only option.
Charcoal
Charcoal is by far the most common processed solid fuel used today, and improved charcoal stoves are on the market across the globe. While turning wood into charcoal wastes over half of the energy in the wood, charcoal does have its advantages.
- Health Emissions: Lab testing to date indicates that improved charcoal stoves can significantly (by 75% and possibly much more) reduce particle emissions relative to an open fire. However, most charcoal stoves significantly increase CO emissions. Lab testing comparing improved charcoal stoves to traditional charcoal stoves showed mixed results, with some “improved” charcoal stoves slightly reducing emissions and others increasing these emissions.
- Climate Emissions: 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%, 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 the 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.
- Time to Boil: Lab testing has shown mixed results. Testing relative to an open fire show that most charcoal stoves cut time to boil, though only modestly. However, other testing compares newer improved charcoal stoves with a traditional stove, and in those cases, the so-called “improved” stoves all significantly increased time to boil, even for some of the newer designs.
- Fuel Use: Lab testing to date indicates that improved charcoal stoves can reduce fuel use substantially.
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 developed countries. However, few stoves are dedicated to these fuels alone – that is, they are typically used in conjunction with an improved biomass stove. Results from testing of such stoves is noted under the Stove Technologies portion of this website. Broadly speaking however, these fuels can lead to substantial improvements in efficiency and emissions although providing adequate supplies of the pellets or cakes at affordable prices and at large scale has proved challenging in previous settings. 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.
Coal
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%.
Clean Stove Technologies
Clean, efficient, durable, safe, and affordable stoves are – along with clean fuels – central to most solutions to the health, environmental, and other risks inherent in cooking with fire. Advanced stoves are much more likely to achieve the more dramatic health and climate benefits that the Alliance seeks, while other so-called “rocket” stoves achieve important, but more modest progress and are therefore best thought of as intermediate solutions. Still other stoves on the market claim to be “improved,” but once tested may offer only very modest benefits.
Advanced Biomass Stoves
There are two primary types of advanced biomass stoves that can achieve high levels of performance: forced air and gasifier stoves, both of which can run on processed or raw biomass. Forced air stoves have a fan powered either by a battery, an external source of electricity, or a thermoelectric device that captures heat from the stove and converts it to electricity. This fan blows high velocity, low volume jets of air into the combustion chamber, which results in much more complete combustion of the fuel.
Gasifier stoves force the gases and smoke into flame above the fuel where almost complete combustion then occurs. In a typical gasifier stove a batch of fuel is top lit. When the fuel underneath the flame gets hot the combustible products have to pass through the flame front. In a fan stove the jets of air create the superior mixing of flame, gas, and smoke seen in the Top Lit Updraft (TLUD) gasifier stoves.
- Health Emissions: Lab tests of advanced biomass and gasifier stoves on the market today indicate the potential to eliminate key emissions by over 80% in all cases, and by as much as 98% for the better performing stoves. New advanced stoves under development today should be able improve on this potential, though substantial questions remain as to the replicability of these figures in actual operating conditions. Advanced stoves that are optimized for and fueled by a processed (uniform) fuel will very likely have much better results in field conditions.
- Climate Emissions: Lab tests of advanced biomass stoves for climate forcing emissions found that fan stoves reduced net warming impact by nearly 60% and gasifier stoves by about 40%, when CO2eq was considered. If the biomass was considered to be harvested sustainably, fan stoves reduced overall warming impact by about 95% while gasifier stoves reduced warming impact by about two-thirds. These analyses took into account both greenhouse gases and aerosols such as black carbon.
- Time to Boil: Lab testing indicates that gasifier and fan stoves may reduce time to boil compared to an open fire.
- Fuel Use: Lab testing of forced air fan stoves demonstrates reduced fuel use (relative to a 3-stone fire) ranging from 37% to 63%. Gasifier stoves also appear to save on fuel use, though generally less than the fan stoves.
Rocket Stoves
Rocket stoves are defined by an insulated L-shaped combustion chamber that allows for partial combustion of the gases and smoke in a stove, and thus achieve important emission benefits compared to open fires or crude stoves. These stoves can be centrally mass-produced products, locally artisanal products, or anything in between.
- Health Emissions: Lab tests to date show a wide variety in performance of these stoves, even in laboratory settings. The better rocket stoves on the market achieve in these laboratory settings emissions reductions of roughly 70% or more (for carbon monoxide) and over 50% for particles. Few field studies on emissions performance of these stoves have been completed to date, and performance in the field is likely to be highly variable, depending on the stove, the fuel quality and the individual user. Some field studies of the plancha version of these stoves often used in kitchens in Latin America – a raised wood-burning stove with a chimney, typically designed with a flat griddle to make tortillas – can reduce indoor concentrations of key pollutants by two-thirds or more.
- Climate Emissions: Limited lab testing of rocket stoves to date suggests that some of the more mass-produced versions of this stove will reduce net warming impact by nearly 60%. Current rocket stoves may have little to no impact on emissions of black carbon, which is less of a criticism (they were not designed to) than an observation. It is not unlikely that current rocket stoves could be redesigned to lead to important reductions in black carbon emissions.
- Time to Boil: The study also showed that the rocket stove was able to reduce time to boil.
- Fuel Use: Fuel use savings vary widely with the type of rocket stove used. Lab tests show that performance can vary from increasing fuel use for poorly designed rocket stoves of high mass, to saving up to 50% of fuel. Limited independent field testing of these stoves has found that several leading rocket stoves do in fact achieve substantial (40% to 50%) reductions in fuel use.
Behavioral and Structural Solutions
Many behavioral and structural steps can be taken to reduce human exposures to cookstove smoke. These include:
- Chimneys: Using and maintaining a chimney is always a good idea, since even advanced stoves or clean fuels lead to some combustion by-products that are best ventilated to the outdoors. If less advanced solutions are in place, chimneys can dramatically reduce immediate personal exposures, though they do not reduce the amount of pollution that contributes to poor outdoor air quality. The effectiveness of chimneys depends in large part on maintenance.
- Cooking Outdoors: Cooking outdoors is another means of minimizing situations of extremely high concentrations of household air pollution. However, for cooks – or babies on their laps or backs – that are hovering immediately over the stove, the immediate exposures while tending the stove may still be significant.
- Keeping Children Away from Stoves: This is a social intervention to take children off their mother’s laps or backs during the cooking period, and moved out into a cleaner, safer environment. The goal is to reduce exposures for very young children that are the most vulnerable with regard to cookstove smoke. This intervention has no bearing on the mother’s exposure.
- Ventilation: Adding ventilation to the kitchen via eave spaces or windows can increase the rate at which air circulates through the kitchen and thereby reduces the build-up of smoke in the kitchen. Well-ventilated kitchens may have dramatically lower indoor concentrations of pollution.
Each of these solutions will help to alleviate immediate human exposures to smoke from cookstoves, and are thus to be encouraged as much as possible. However, their health impact may not be as great as envisioned if ambient air is heavily polluted, thereby leading to more chronic, if lesser, exposures to poor outdoor air quality. These solutions will also have little or no impact on cookstoves’ climate impacts or fuel use (and thus local environmental impacts such as deforestation).
Sustainable Business Models
The field has seen the growth of a wide range of businesses that are manufacturing and/or selling improved stoves and fuels. These businesses build off of one of three general business models: centralized industrial mass-production; local semi-industrial production; and local artisanal production.
Industrial Production
In this model, stoves and/or fuels are mass-produced at a central factory, either for export to other countries or for use within the same country. This is a rapidly growing business model for this field, and many of the fastest growing stove efforts in the world build off this model. A twist on this model is to centrally mass-produce some or all components of an industrial stove, then complete the manufacturing and assembly of the stove near the end-user.
- Advantages: A key advantage of this model is that the high-quality production process means that these are typically the highest performing and most durable stoves. Further, due to the centralized production, this model offers the greatest quality control in production (and thus offer a warranty), as well as the greatest potential to quickly ramp up to a very large scale of production (if market demand should grow accordingly). It also offers likely the greatest way to quickly bring new innovations in design and performance to market, by having a sophisticated enough production process to quickly adjust to new designs and then be able to simply substitute new products into the existing supply chains.
- Disadvantages: The downsides of this model are also important – it typically requires a major capital investment up front to build a factory, a typically higher cost to produce the stoves, and the added costs associated with shipping and (if relevant) importing stoves to overseas markets. These factors all contribute to high prices for the consumer in the marketplace and may restrict the potential to reach the poorest populations. This model also requires building distribution chains to take the stoves to market – but those distribution chains also create economic opportunity and jobs (though the production jobs are all centralized).
Semi-Industrial Production
In this model, stoves and/or fuels are made locally in a centralized setting that is capable of making on the order of 500 stoves per month. The production takes place in a central facility, but it is not a factory in the industrial sense. More typically, individuals make stoves in a common fashion using molds or the like, and then assemble the stoves individually by hand. This model can be implemented by an individual outfit, or it can be coordinated centrally as part of a broad network of producers all working off of a similar design and process.
- Advantages: Experience has shown that this model can succeed at a very impressive scale of sales when the conditions are right. Stoves and fuels used in this model tend to be moderately priced, and thus more accessible to poorer populations than those that are industrially produced. In some cases, the production quality of this model is sufficient that a warranty can be offered. This model leads to very substantial local economic development if done well, where the job benefits from the production, distribution, and sales of stoves all accrue locally.
- Disadvantages: This model typically involves intermediate quality (performance and durability) products that have less ability to achieve dramatic benefits. In addition, the quality control associated with the products is much less than that of industrial production.
Artisanal Production
In this model, stoves are made locally by small enterprises – often by trained artisans building mud stoves in place in people’s homes, typically based on a fixed design. The scale of production here is typically on the order of 100s to low 1000s per year, though aggregation of efforts can lead to a much larger scale of results.
- Advantages: The primary advantage to this model is the low cost of the product – thereby making it affordable to the poorest populations. In this model, the entire suite of economic and job benefits accrue locally, as well. In some cases to date, this model has employed carbon financing to provide revenue to ensure local maintenance – and thus performance and durability – of the stoves.
- Disadvantages: The scale of production implies a much smaller scale of activity, though if replicated this business model can reach impressive scales. However the quality control associated with artisanal stoves is much less certain, leading to greater variability in performance and results – though this variability may be addressed through a hybrid approach of centrally manufacturing key parts of the stoves such as the combustion chamber.
Women-Owned Businesses
A tool that is being increasingly utilized by each of these business models is the inclusion of women and women-owned businesses into the full business chain of cooking stoves and fuels – from production to distribution to sales to service. Women are the primary users of the stoves, and thus often have a much greater credibility as salespeople. Further, developing women-owned businesses has substantial collateral benefits of giving women economic power which in turn leads to greater independence, schooling, and economic development across a wide range of indicators.
Carbon Financing
Carbon financing is a tool that is increasingly being leveraged by all of these models to provide revenue to, for example: lower the price of a stove; fund advertising/awareness campaigns; develop new products; or finance expansion efforts. The financing arrangements vary substantially, but may typically yield about 1 ton of CO2-e per stove per year – which, for a business that can sell durable stoves at a large scale could quickly become a large source of revenue. In addition, carbon financing demands rigorous monitoring, incentivizes large projects, and incentivizes efforts to ensure continued use of the stoves for many years – all great benefits to stove businesses.
However, carbon markets cannot be relied on unilaterally to incentivize advanced solutions that will achieve dramatic black carbon or public health benefits. This is because carbon markets are based on GHG (mostly CO2) emissions, as measured by fuel use. But the differential fuel use benefits of the cleaner advanced biomass stoves as compared to intermediate stoves are minimal. To incentivize advanced stoves, public funds would be required to facilitate carbon financing for cookstove projects, with preferential terms given to efforts that promoted advanced stoves.
Government and Humanitarian Efforts
Government Programs
Governments may engage in solutions to the cookstove issue in any number of ways, including, but not limited to:
- National Program: Several governments have established national programs to accelerate adoption of clean and efficient cookstoves. Typically they set goals, assign staff to implement the program, and work with businesses, NGOs, researchers and others to implement it. These national programs were in the past often based on subsidies and giveaways of stoves, but are increasingly planned in close cooperation with businesses working from the business models noted above.
- Partnership: Many governments don’t have formal national programs, but work in close cooperation with international development agencies to implement cookstove efforts in their country.
- Policy: Another option is for governments that have no formal staff or program devoted to this issue per se, to employ policy tools to encourage efforts in this field. These may include, for example: setting national stove standards; establishing stove testing centers; minimizing duties and tariffs for stoves; or engaging in applied R&D to support this field.
- Targeted Subsidies: Governments could also engage in a more limited operational fashion by targeting specific, highly vulnerable populations such as pregnant women. For example, by giving every pregnant women who goes to a health clinic or hospital a high-quality improved stove (and perhaps even paying her to use them, which is now easily monitorable), a government could effectively protect arguably the most vulnerable populations (pregnant women, fetuses, newborns) in a way that would not undermine any of the other business models. To the contrary, by signaling the importance of a clean stove, the government may well be seeding commercial markets in a very effective fashion.
Humanitarian Programs
Humanitarian agencies and organizations are increasingly investing in this field, and at a very large scale. Motivations may range from reducing the personal risks that women and girls face while leaving refugee camps or safe villages to collect fuel afield, to providing a safe way to cook the food that is provided in disaster relief settings, to providing local economic development opportunities for women. In addition to these primary motivations for this work, given the scale of these efforts, this field could play an immensely important role in catalyzing demand for high-quality stoves. For example, if the United Nations High Commissioner on Refugees or the World Food Programme purchased millions of stoves for use around the world, that could have a catalytic effect in driving up production, and thus reducing cost, for improved stoves to be used in more commercial settings across the globe.
