Every morning across the globe, small open fires are started and tended by women as part of a daily routine. The fires are essential to households, as they provide hot water and cooked meals. The smell of the smoke from those open fires, in fact, is woven into the texture of life in much of the developing world.

But these open fires require wood or charcoal for fuel and are implicated in deforestation and the smoke pollutes the skies and cause respiratory illnesses. For the past half-century, public and private organizations have developed new and improved cookstoves and have distributed them to nearly 830 million people. Some of these units have been more efficient and less polluting wood stoves; others use gas or liquid fuels to displace biomass.

In spite of these efforts, however, the number of people using open fires is expected to remain unchanged over the next 15 years. One reason for this is because the population is growing faster than the number of cookstoves, and when stoves break people often go back to cooking over open fires.

Ultimately, the problem is one of adoption as well: the people for whom improved cookstoves are designed often don’t use them the way that the engineers had in mind. Sometimes, they don’t use them at all.

Our experiences throughout many of villages across Africa, Asia, and the Americas confirm the largely anecdotal evidence that improved stoves are underutilized. Users tend to adopt improved cookstoves as additional cooking devices rather than replacing open fires. This practice, commonly referred to as “stove stacking,” occurs when users retain multiple cookstoves, each for a specific purpose. Much the way that a Western family might have a gas stove, a microwave oven, a toaster, a waffle iron, and a slow cooker and use each for different, specific tasks, a family in the developing world might see an improved cookstove not as a replacement for an open fire but a supplement to it.

The developers and philanthropists who provide well engineered clean-burning stoves often overlook such cultural considerations. Designing a fuel-efficient, low-emission stove is an engineering challenge, but engineers must also understand local needs and preferences. No matter how efficient an improved stove may be, it won’t reduce fuel consumption or improve public health if it’s not used.

Cookstove technologies shouldn’t just be engineered for efficiency, but also for impact.

A growing body of research indicates that cookstove use and impact are shaped by many factors, from culture and demographics to climate, diet and local infrastructure. Yet most cookstove studies have focused narrowly on the effect of materials and construction on stove performance and emissions. Comparatively little attention has been paid to developing design criteria and constraints informed
by local needs and preferences.

The place of cookstoves in routines of everyday life—that is, the experiences of cookstove users—is generally overlooked yet it is essential to understand the design needs. Cookstove technologies shouldn’t just be engineered for efficiency, but also for impact.

Addressing this challenge begins with in-depth field study. For our part, we traveled to an isolated rural village in sub-Saharan Africa to examine how people there use various cooking technologies. We discovered that the impact of improved cookstoves in this village was minimal, but we also developed some guidelines that might improve the penetration of introduced cooking technology in the future.

Further, we tested and measured fuel use. We discovered that 98 percent of all energy used in the village goes to domestic needs, particularly cooking and space heating. Of that energy, 94 percent comes from wood, of which three-quarters is burned in domestic cookstoves. The village annually consumes 234 metric tons of wood.

Village Life

We made four visits to Nana Kenieba, a village in southern Mali, between May 2009 and December 2010 to examine the human, natural, and infrastructural factors that characterize the dynamics of village energy supply and use. Nana Kenieba is located within the Sahel, a transition region between the Sahara desert and Africa’s mid-continental forests. Mali ranks 160th out of 169 countries on the United Nation’s Human Development Index, which measures life expectancy, educational attainment and income.6Mali also has the world’s sixth-worst mortality rate for children under five years old attributed to water and air pollution.

Farming activity and wood collection by season

All 60 families in the village live on subsistence agriculture. Seasons define rural life and economics, including agricultural activities, wood harvesting and other duties. During the rainy season, for instance, 10 percent of the village’s 770 residents live outside the village proper, in small camps adjacent to their farmland.

Connection to the world beyond the village is difficult. There is no access to the electrical grid and travel along the dirt roads is by foot, bicycle or the small bus that departs daily for the market town 35 kilometers away. Any goods not available in the village can be sourced from the market, however, many of the goods used in the village are supplied by local artisans, including blacksmiths, bakers, tailors, carpenters, furniture makers, brick makers, potters and basket makers.

Homes are commonly built from uncompressed earthen blocks and thatch roofs. Kitchens, which are constructed from mud-daubed wood lattice, are separate structures from the main living space. Families are often polygamous, with several women exchanging familial cooking duties every few days. It’s common for women within the same family to have separate kitchens and cookstoves.

We visited five families, ranging from small (fewer than seven members) to large (more than 22 members). Our study encompassed several different methods, from direct observation and participation with the cookstove users that enabled us to identify factors that may influence cookstove use and impact, to surveys and interviews that allowed us to gather demographic data and information on the types and numbers of cookstoves used, how each stove was used and whether cooking practices varied between seasons.

The typical daily activities for an adult woman leave little free time to pursue leisure activities or wage-earning ventures. Most socializing occurs when gathering wood, collecting water or waiting in line for the diesel-powered grain grinder. Due to cultural practices, only married women with children perform cooking duties; unmarried women and women without children do not cook.

More detailed data on the cooking process were captured using activity diagrams and minute-by-minute time-series accounts of each cooking task. These data show how women completed multiple activities while cooking, such as preparing ingredients, tending to children, cutting tinder and shelling peanuts. Such parallel activities are often completed outside the kitchen, drawing the cook’s attention away from the fire for periods as long as up to 15 minutes.

To keep an unattended fire from smoldering, women in the village prefer to stoke a fire with large amounts of wood. Improved cookstoves, however, don’t allow for that. Since they are engineered with an eye toward better performance and reduced emissions, improved cookstoves generally have small, well ventilated combustion chambers, meaning they require regular attention. Participant observations suggested that the constant attention they require is part of the reason these ostensibly improved stoves were used infrequently in the village.

Other notable “day in the life” observations included the time and effort expended to collect wood—up to two hours per day, with bundles weighing from 14 to 22 kilograms carried distances of up to 4 kilometers—and the varied methods, from lighting straw or plastic to borrowing burning coals used to start fires. Women also preferred to prepare meals inside a kitchen and hot water outside the kitchen and they used multiple cookstoves for different types of meals and meal sizes (the three-stone fire is most commonly used).

Perhaps the most notable observation, however, is that the culinary chain—gathering wood, preparing cooking ingredients, cooking meals, serving food, eating and cleaning—constitutes 65 percent of time that a married mother spends on daily chores and activities.

These findings and data suggest that cookstove adoption might increase if women believed, on balance, that the cookstove reduced their workload relative to existing practices.

Stacking Stoves

After participant observations suggested a high prevalence of stove stacking—the use of multiple cookstoves, each with a specific purpose—we looked to quantify the extent of stacking using data collected from surveys of cookstove ownership and use. These surveys were accompanied by in-depth interviews to understand owner decisions.

Cooking in the village spans six types of meals and five other non-meal cooking tasks. The meals include two different types of breakfast porridges and lunches and dinners involved either a thick or thin porridge with a sauce or steamed rice or couscous, with variations on each. The tasks include chores such as heating water, roasting peanuts, or making medicine.

We found five types of cookstoves in the village. Most prevalent was the traditional three-stone open fire—as shown in the cover image—with the cooking vessel balanced on stones over the burning wood. Another traditional type of stove is the gakourouwana, where the cooking vessel rests on a U-shaped support of mud or clay. There were also hand-crafted metal cookstoves made in Mali, and two types of improved stoves—a low-thermal-capacity stove made from clay and straw blocks and a manufactured metal cookstove that has been distributed worldwide. The two kinds of improved cookstoves had been given away by a non-governmental organization one to two years before our study.

Around half the women we surveyed engaged in stove stacking (they owned more than one stove). Nearly all own a traditional three-stone fire or a traditional gakourouwana cookstove, about 15 percent own both types of traditional cookstoves and 43.9 percent own a traditional cookstove as well as an improved cookstove. Interestingly, approximately 40 percent of women shared cookstoves. Due to the extended family structure in the village, there are often multiple cooks per household.

Often, women owned two or more three-stone fires so they could cook both indoors and outdoors. Meals were usually prepared in the enclosed kitchen, but during especially hot weather they were prepared outside. Hot water was generally prepared on an outdoor fire. Portable improved cookstoves were used more frequently than stationary cookstoves in the hot season because the stationary cookstoves could not be moved outside the kitchen.

Not a single woman in the study owned only improved cookstoves—one of several strong indicators that improved cookstoves do not address all cooking needs in the village

Not a single woman owned only improved cookstoves—one of several strong indicators that improved cookstoves do not address all cooking needs in the village. No one who owned an improved cookstove used it frequently. Improved cookstoves were used to heat water and cook meals, but only traditional fires were used for activities such as roasting peanuts, making medicine and processing shea.

What’s more, families with over 15 people, which accounted for approximately one-half of the village population, rarely used improved stoves because their large meals and large pots exceeded weight and size limitations of the improved stoves. The improved stoves were also too small or lacked the durability required to support large pots used for shea processing and to heat bathing water for large families.

Saving Fuel

We also investigated the effects of cooking systems on fuel usage. We wanted to gather data on factors from the entire cooking environment rather than only the cookstove. We looked at 17 factors ranging from mass of the water and ingredients being heated and the size of the cooking vessel to the species and water content of the wood being burned.

Data on these factors were recorded in the 155 cooking tests completed across all meal types and stove types. The tests were strictly observational. No wood or food ingredients were provided and no instructions given to respondents. This allowed respondents to cook as if it were a typical day.

Multiple regression analysis with forward selection was used to analyze the data. Six factors proved to be statistically significant in estimating energy use: the type of cookstove application, family size, total mass of wet and dry ingredients, mass of dry ingredients, the use of burning embers as an igniter, and the number of fires used during a cooking event. The smallest families, for example, used almost twice as much energy, per person, as families of 20 people.

The impacts of cookstove improvements may depend more on factors in local cooking systems than on improvements in thermal efficiency.

It has been proposed that reducing grain flour size would reduce energy use in this village, the thinking being that smaller grains would cook faster. We didn’t find any evidence to support that. The diameters of the various grains used in breakfast porridges, for example, differ by about a factor of two. However, there was no statistical difference in the energy used to cook them. While smaller particles cook faster, families cook each meal to a thickness defined by cultural preferences.

Most interestingly, little evidence was found to suggest that improved cookstoves significantly influenced cooking energy use after accounting for other factors. Only one stove had a statistically significant effect on energy use. Though the specific numbers in our findings may not apply directly to other settings, they may suggest a general lesson: the impacts of cookstove improvements can depend more on factors in local cooking systems than on improvements in thermal efficiency. The actual fuel savings demonstrated by improved cookstoves in this case study were far smaller than savings measured in laboratory tests.

Actual savings can be calculated using the rated fuel wood savings in the laboratory, the adoption rate for the cookstove, how often each cooking task is performed, and the rate the cookstove is used for each task. Fuel wood savings for a consumer group can be calculated using the following equation:

(rated fuelwood savings) × (cookstove adoption rate) × (rate of each cooking task) × (rate the cookstove is used for each cooking task) = actual fuel wood savings

Taking the data on cookstove use and a rated fuel wood savings of 50%, the actual fuel wood savings for the low-thermal-capacity cookstove for this group of consumers equates to

(50%) × (100%) × (1.13% × 50%) × (100%) = 0.28%

The low-thermal-capacity cookstove was only used to cook porridge and sauce, which constituted only 1.13 percent of meals in the village. That rate was reduced by an additional 50 percent because that improved cookstove was used only in the sauce component of the meals; the grain component was prepared on a traditional stove. Although not completed here, a similar procedure can be used to calculate the realized reduction in emissions.

Engineering for Impact

We found that in practice, consumer behavior significantly reduces the theoretical impact of improved cookstoves. For this village, the effect that cookstoves can have on fuel use is further reduced when considering that improved cookstoves are rarely used for non-meal activities. With only 64.5 percent of fuel used for cooking meals, the total fuel wood reduction for all domestic cooking and heating activities is just 0.18 percent for the selected group of women.

The adoption of other technologies, such as solar hot water heaters, may have comparable or greater impact on wood reduction and human health. For example, consider a group of families that use a solar water heater for 50 percent of their bathing water needs. For this group, heating water accounts for 27.4 percent of cookstove energy use, the solar water heater would reduce domestic wood usage by 13.7 percent.

We suggest that the engineering challenges posed by cookstoves be approached by in-depth studies of human, natural, and built system factors, and a comparison of how these factors affect technology impact. The investigation can improve the health and environmental impact of cookstove programs by offering guidance in stove design and implementation.

Our findings suggest a variety of technical and programmatic guidelines for increasing the impact of cooking technology programs. While specific guidelines, like the 0.28 percent fuel wood savings, may be unique to this village rather than universal, the systemic approach they represent may apply broadly.

It also seems reasonable to expect that no single cookstove option will replace the three-stone fire in the village we studied. After all, consumers in the developed world also utilize different technologies for making soup, cooking vegetables, baking bread, making toast, grilling meat, and heating our bathing water.

In noting this, we can take a lesson from our own kitchens when designing cookstoves for the developing world: we should consider designing multiple technologies to meet needs that are as varied as our own.

This case study was written by Nathan Johnson and Kenneth Bryden.

Nathan is an assistant professor in the Department of Engineering and Computing Systems at Arizona State University. He is an active researcher and teacher of sustainability, multidisciplinary design, and global development.

Kenneth is an associate professor of mechanical engineering at Iowa State University. He is president of Engineers for Technical and Humanitarian Opportunities for Service, a NGO focused on the issues of household energy in the developing world.