Performance assessment of an improved cook stove (Esperanza) in a typical domestic setting: implications for energy saving
© The Author(s). 2017
Received: 24 October 2016
Accepted: 8 June 2017
Published: 3 July 2017
Much of the Malawi’s energy source, which is biomass, is consumed using traditional household technologies. These technologies contribute to over consumption of biomass leading to increased forest degradation, and they release various gases and particulate matter that often cause indoor air pollution which is a health hazard to the users. To combat deforestation and pollution, improved cookstoves were introduced in Malawi from early 2000. A number of improved stoves were introduced including Esperanza which is reported to have 60% wood fuel saving under controlled conditions compared to the traditional 3-stone stove. The efficiencies of improved stoves were obtained through controlled cooking test, but very limited studies have evaluated them under normal household settings. Therefore, this study sought to compare the performance of the Esperanza stove with a 3-stone stove in a typical domestic setting.
A Volunteer in Technical Assistance (VITA) standardized questionnaire was administered to households that were using the Esperanza stove. A cross-sectional Kitchen Performance Test (KPT) was conducted to compare the wood-saving performance of exclusive use of Esperanza stove and the 3-stone stove using the VITA KPT tool.
In the study area, a policy of banning household use of other cooking technologies has been in place with the main goal of encouraging the use of new technologies. There is evidence that the Esperanza stove was used more often, though it was used in combination with other technologies. Although Esperanza stove had earlier been reported to be more fuel efficient than the 3-stone stove, results revealed that due to improper use, the Esperanza stove consumed 86% more wood fuel compared to 3-stone stove.
Three-stone stoves are still the preferred mode of cooking technology in most rural and peri-urban environments in Malawi. The shift to the improved stove technologies therefore requires urgent government intervention to ensure total use of these technologies that save energy and the environment. Additionally, the optimum efficiency of the Esperanza stove can be viable with training to new users. Thus, the importance of training on the proper use of Esperanza stove is recommended in order to optimize its performance and maximize energy saving.
It is estimated that around two-thirds of the population in developing countries rely on biomass fuel (wood, dung, and fiber residues) for cooking and heating . Malawi is a developing country with 84% of 2.3 million households living in rural areas where biomass supplies about 99% of household energy demand. The household sector is the most dominant energy consumer, accounting for about 84% of total energy consumption in Malawi . An estimated 48% of wood fuel is from sustainable yield while 47% is taken from natural woodlands that are quickly varnishing without replacement. The remaining 5% comes from other biomass sources that include crop and industrial residues .
Most of Malawi’s biomass energy source is consumed in traditional end-use technologies, whose efficiencies are low; around 10–12% . High dependency on the use of technologies that have relatively low conversion rate of biomass to energy is one of the factors that is contributing to the overconsumption of biomass. Thus, traditional cookstoves (specifically the 3-stone stove) use more biomass that leads to increased rate of forest degradation . Moreover, these inefficient stoves release various gases and particulate matter that often cause indoor air pollution, leading to potential health hazard to the users .
Research on improved technologies for energy conservation in developing countries is a continuous process which has resulted in the design of several types of improved cookstoves for use by rural households . Compared to a basic 3-stone stove with 10–15% thermal efficiency, improved cooking stoves can easily halve the fuel requirements of the cooking process . However, before any stove is introduced on the market, it is first evaluated for its efficiency and usability against set international standards . These tests provide reliable information about stove performance that informs the stoves committee on how to select a locally appropriate and energy-efficient stove for each cooking task.
The key principle behind these stoves is to reduce biomass consumption for each cooking task by improving efficiency . Thus, information on energy saving of these stoves help organizations to make informed decisions on which stoves to adopt compared to others in order to save more wood fuel. In addition, provided that sufficient training is given, the potential wood fuel saving of the improved stoves could negate the reported energy saving and fuel efficiency.
The Esperanza stove was introduced in the Phalombe and Mulanje districts as part of an intervention to preserve the fast degrading environment around Mulanje Mountain. In 2006, it was reported that in Mulanje alone, the total energy consumption was estimated to be 3.12 million GJ; out of which, 97.5% was biomass energy . To get maximum efficiency from the Esperanza stove, specific rules need to be disseminated through training to the potential users and the stove user guide. This training is on how to operate the stove before starting it and during its use. Users are encouraged to consult and follow instructions in the stove user guide to ensure maximum energy saving and fuel efficiency. The instructions include removing ash each time before starting fire to prevent the ash from choking the stove. The ash hole has to always be kept closed on the outside of the stove when cooking to prevent entrance of cold air into the combustion chamber and escaping of heat from the combustion chamber. When cooking, it is important to ensure that the wood fuel is not burning outside the stove fire entrance. Also, the use of pots that do not leave big gap around the pot skirt of the stove are recommended to increase the transfer of heat to the cooking pot thereby preventing wastage of generated heat, which consequently could reduce the efficiency and wood-saving aspects of the stove.
Studies have shown that there is over dependence on wood fuel and charcoal sources in Mulanje and Phalombe. To address the problem, GTZ-ProBEC designed various types of improved cooking stoves. The performances of these improved stoves had initially been assessed in the laboratory, through controlled cooking tests (CCTs) , and were found to be higher than that of the 3-stone stove. Laboratory testing provides a cost-effective means of evaluating cookstoves while controlling variables that are difficult or impossible to control in the field. Despite such advantages, controlled laboratory testing cannot fully duplicate field testing but should emulate field conditions to the greatest extent possible. Although, this had been the case, very few studies have evaluated these improved stoves under normal household conditions . Thus, it is important to investigate the performance of improved stoves under household conditions as efficiencies could differ from the CCT results as it was observed with plancha stove in Guatemala. For example, in standard water boiling and cooking tests, the plancha consumed more fuel and took longer than the open fire, but in 5-day tests of routine cooking, the plancha was found to use 39% less wood fuel than that of the open fire . Therefore, the objective of this study was to assess the performance of the Esperanza stove in a typical domestic setting.
This paper begins with an introduction to the sources of energy and the traditional technologies that are used and their impacts on the environment and health. It discusses improved technologies that are meant to address the problems that are caused by the traditional technologies. The Esperanza stove is an example of improved technology and this study compares the performance of the improved technology with the traditional 3-stone stove. The analysis is based on the usage and consumption of wood fuel in estimating variations in wood fuel savings. The last section provides the conclusion and recommendations for future research studies.
Description of the study area
In this study, the Esperanza stoves are fixed in kitchens of tea estate houses used by the estate workers. The workers do not pay for the stoves as it was a policy of the Eldorado Tea Estate that every house has to be fitted and use an Esperanza stove. It is required that every household that has Esperanza stove in its kitchen should be trained on how to use it and a user guide was left with them. When the stoves are installed in the kitchens, all the households and some trainers of trainers are trained on how to use the stove. The training has to be continuous because tea estate workers are seasonal; whenever there are new occupants, they have to undergo the training process.
The study involved field experiments and administration of questionnaires to households that had Esperanza and 3-stone stoves only in their kitchens. Purposive sampling was used in selecting one tea estate out of the 15 in the Mulanje district. The Eldorado Tea Estate was chosen because it had a higher number of Esperanza stoves compared to other estates. Cluster sampling method was then used to sample two compounds from the estate (Mimosa chithando and Mpumula chithando) where the study was conducted. A cross-section study design was adopted in between two groups of households, one using a 3-stone stove and the other using the Esperanza stove. Using the cross-section design ensured that experiments were simultaneously carried out from both types of stoves .
Controlled cooking tests (CCTs) were conducted to compare the wood fuel saving of the Esperanza stove to the 3-stone stoves at GTZ-ProBEC laboratory and some selected households in Mulanje. The CCT measures the wood fuel consumption of stoves in controlled conditions. Field experiments were done using the Kitchen Performance Test (KPT) based on the Volunteer in Technical Assistance (VITA) protocol . The KPT measures the relative rate of wood fuel consumed by each stove as they are used in the normal household environment. The KPT was conducted for four consecutive days. Each day involved recording the weight and moisture content of the wood fuel that the household presumably would use for cooking per day. After a day’s cooking, the remaining wood fuel’s weight and moisture content was also measured. If the remaining wood fuel was not sufficient for the next day, extra wood fuel was weighed, recorded, and added to the remaining wood fuel. The study was conducted on 21 Esperanza stoves and seventeen 3-stone stoves. All data were recorded on KPT Daily Data Forms during the study period. The data were then entered in the VITA KPT data calculation sheet for analysis.
In addition, an assessment of the effect of leaving the ash-removing hole open on the Esperanza stove was also conducted. The ash-removing hole runs from the combustion chamber to the outside of the stove. If left open, it allows heat to escape to the outside and cold air to flow into the combustion chamber. This assessment was done by recording temperatures using a thermocouple, whose probe was put at 5 cm from the outside surface of the stove into the ash-removing hole. The temperature was monitored for 60 min at 10-min intervals from the time the fire was started for three consecutive days. The results were recorded and plotted on a graph.
Results and discussion
Assessing usage of the Esperanza stove in days/week
Estimating wood fuel saving of the Esperanza stove
Estimating daily average wood saving of the Esperanza and 3-stone stoves
Fuel use (kg)
Fuel use/capita (kg/person)
Energy use (MJ)
Energy use/capita (MJ/per)
The results in Fig. 8 indicate that the Esperanza stove used more dry wood than the 3-stone stove. Wet wood consumption at an adult equivalent of 2.3 shows high consumption of the Esperanza stove (9.4 kg) compared to the 3-stone stove (4.4 kg). These results agree with the results that were found in Guatemala; wherein standard water boiling and cooking tests, unimproved plancha consumed more fuel and took longer than the open fire. Smith  showed that improving baffle design of the plancha increased thermal efficiency of the plancha by 12% .
The result in Fig. 10 shows that temperature increased with time. For instance, at time 0, the temperature was >30 °C and at 60 min it had increased to 40 °C, recording an increase of 10 °C within an hour. These findings confirm that a lot of heat is lost during cooking if the ash-removing hole is open, resulting in high wood fuel consumption and low thermal efficiency per cooking session. In a 3-stone stove, 85 to 90% of the energy content in the wood is lost as heat to the environment outside the cooking pot [14, 21]. When users of the Esperanza perpetuate 3-stone practices, energy saving potentials with improved cooking stoves are far smaller and less cost-efficient. This low efficiency not only wastes natural resources, but also boosts air pollution and greenhouse gas emissions because of incomplete combustion . Hence, the need to keep the hole closed so that heat is kept inside the combustion chamber of the stove is imperative. This is important because high temperatures are required in a stove for complete combustion and for increased stove efficiency.
Three-stone stoves are still the preferred mode of cooking technology in most rural and peri-urban environments in Malawi. Despite the reported wood fuel saving of 60% of the Esperanza stove compared to the 3-stone stove in a laboratory controlled condition test; the results of this study in a typical domestic setting showed high wood fuel consumption. This was attributed to home occupant turn-over and lack of training to new users. The cooking practices inherent for the 3-stone stove increases heat loss and wood fuel consumption such that if the users of the Esperanza stove (or any other improved cookstove) are not trained, the improved stoves will still be less efficient. The shift to the improved stove technologies therefore requires an integration of the users’ experiences and expectations to ensure proper use of these technologies that save energy and the environment. Thus, the importance of training on the proper use of the Esperanza stove is recommended in order to optimize its performance and maximize energy saving. There is also a need to carry out studies on the ideal type of wood fuel that is suitable for use in the Esperanza stove.
Although the KPT is difficult to control, leading to data with high variance, it has the advantage of reflecting the true fuel consumption in study households as they proceed with their everyday cooking activities. Laboratory-based investigations such as the water boiling test (WBT) can be employed as a screening procedure to identify inefficient stove designs prior to dissemination and adoption. Such results should not be relied upon as the only method of efficiency assessment but it is worthwhile to consider changes in the KPT protocol that could be adopted to generate more significant results.
The study was conducted in an area where most of the users did not have knowledge on how to use the Esperanza stove as they did not have any training. For future study, there is need to have a set of trained users of the Esperanza stove using it in the typical domestic setting for the results to be used as a benchmark or a model performance of the Esperanza stove.
The study was possible through financial assistance from the Malawi Environmental Endowment Trust (MEET). Most importantly, we thank the residents of the Eldorado Tea Estate who participated in this study. The authors would like to thank the Mulanje Renewable Energy Agency (MuREA) for the use of their measuring equipment and the anonymous reviewers for their inspiring and constructive comments on the paper.
MFLC is the lead author and made a substantial contribution to the conception and design of the manuscript; MFLC also drafted the article. CK administered the VITA questionnaire to households within the study area and also analyzed the data. JM contributed to the field work, specifically the efficiency testing of stoves and analyzing the results. CM designed the experiment that was used for testing the heat losses from a cleaning hole on the improved cooking stove. LGP critically revised the manuscript for important intellectual content. She also formatted the paper to conform to the specifications of the journal. All authors read and approved the final manuscript.
The authors declare that there are no financial or personal relationships which may have inappropriately influenced them in writing this article.
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