Energy Efficiency, Emissions and Adoption of Biomass Cookstoves

Abstract

Indoor air pollution due to inefficient use of solid biomass fuels in traditional cookstoves causing serious threat to human health and millions of deaths, mainly in developing countries. This chapter reports parameters for measurement of thermal as well as emission performance of biomass cookstoves. The thermal performance parameters include fire power, efficiency, specific fuel consumption and turn-down ratio whereas the emission performance parameters include emission factor or indoor concentration of a pollutant. This chapter also reports about technological improvements in the biomass cookstoves. Since early 1980s, efforts were made by the researchers for development improved cookstoves. These efforts include use of metals as cookstove materials, provision of grate for better air circulation, air preheating, provision of swirl and secondary air, provision of insulation, use of chimney, baffles etc. The improved cookstoves were found to be causing saving in biomass fuel but there was not much improvement in emission performance of these stoves as compared with their traditional versions. The research on advanced biomass cookstoves started in early twenty-first century. While designing these cookstoves, advancements in technologies such as insulating the combustion chamber, supplying correct amount of primary and secondary air at right place into the combustion chamber, use of fan to create draft, use of gasification techniques, use of high density pellets as fuel etc. are being used. Advanced biomass cookstoves are found to be highly fuel efficient and they cause negligible pollutant emissions. Various factors affecting adoption of improved biomass cookstoves such as social, functional, and cultural are discussed in detail. Recommendations for use of energy efficient and clean cooking options are also given.

1. Introduction

Access to clean cooking energy for all, is a major challenge in twenty-first century. In modern cooking practices, people across the globe are using various cookstoves with fuels such as biomass, Liquefied Petroleum Gas (LPG)/ Piped Natural Gas (PNG), kerosene, Charcoal, biogas etc. Other cooking devices such as electric, solar and induction are also being used. About one third of global population does not have access to clean energy mainly due to issue of affordability. The most commonly used cookstoves in the developing nations are the biomass cookstoves. Traditional versions of these cookstoves are highly polluting and very inefficient which results in severe health issues and millions of premature deaths globally.

According to International Energy Agency, in 2018, the global consumption of energy in residential sector was about 88 EJ (1 EJ = 1018 J) which was about 23.3% of the total energy consumption [1]. The components of residential energy are: 32% combustion of bio-fuels & waste, 24% combustion of gas, 21% combustion of coal, 4% combustion of oil and the remaining 26% energy for generation of residential electricity [1]. Since year 2000 till 2019, there is about 48% rise in global energy consumption [2]. The cost of cooking energy is also rising day by day. For example, in India the price of LPG cylinder has been doubled in last 7 years from Rs. 410.0 in 2014 to Rs. 819.0 in 2021 [3]. These statistics indicate that there is an urgent need for conservation of residential cooking energy by using energy efficient cookstoves.

Primitive humans started cooking with fire nearly 2 million years ago [4, 5]. The first method of cooking was probably roasting of a fish or a bird by holding it over an open fire [6]. The different stages of evolution in cooking process as reported in literature are: Prehistoric cooking, ancient cooking, medieval cooking, renaissance cooking, modern cooking and twentieth century cooking [6]. Since prehistoric era till present days, human beings have continued using open fires for cooking purpose. In present days, commonly used domestic cookstoves in different parts of the world can be broadly classified into two groups viz. combustion cookstoves and non-combustion cookstoves. The cookstoves in which direct combustion of solid, liquid or gaseous fuels occur and chemical energy of fuels is converted into thermal energy, are known as combustion cookstoves. The examples of combustion cookstoves are: Biomass cookstove, Gas cookstove, Kerosene cookstove, Charcoal cookstove and their variants. In non-combustion cookstoves, no combustion of fuels occur but solar or electric energy is converted into thermal energy. The examples of these cookstoves are: Solar cooker, Electric cookstove, Induction cook-top and their variants. With reference to the developments occurred in biomass cookstoves over last few decades, they are mainly classified into three categories viz. traditional cookstoves, improved cookstoves and advanced cookstoves. Biomass cookstoves are also classified as: stationary (non-metal cookstoves) and portable (metal cookstoves), natural draft (buoyancy induced) and forced draft (fan or blower driven). The advanced biomass cookstoves are of two type viz. combustion cookstove and a gasifier cookstove. The gasifier cookstoves are further available in four types: updraft, downdraft, cross draft and top lit up draft (TLUD). The detailed classification of biomass cookstoves can be found in literature [7, 8, 9, 10, 11].

According to International Energy Agency (IEA) [12], about 2.6 billion people globally (i.e. about 34% of the global population) do not have access to clean cooking energy. They still rely on solid biomass as the only cooking fuel. According to World Health Organization (WHO) [13], every year about 4 million premature deaths occur from the illnesses resulting from household air pollution due to inefficient cooking practices using solid biomass and kerosene cookstoves.

Over a long period of time, the evolutions in design and operation of cookstoves have occurred. The developments in combustion cookstoves are attributed to increase in their overall efficiencies due to improved thermal and emission performance. Also attention is being provided on user friendly designs of the cookstoves.

The present chapter reports parameters affecting thermal and emission performance of biomass cookstoves. It reports emission norms set by national and international agencies for cookstoves using biomass and fossil fuels. It reports the advancements in technologies of biomass cookstoves. It also reports factors affecting adoption of biomass cookstoves. Recommendations are also given on promotion of clean cooking energy options.

2. Performance parameters of biomass cookstoves

In biomass cookstoves, conversion of chemical energy into thermal energy takes place due to combustion of solid biomass. The parameters which affect performance of biomass cookstoves are of two types viz. thermal parameters and emission parameter includes emission factor of different pollutants. The thermal performance parameters include fire power, efficiency, specific fuel consumption and turn-down ratio. The emission performance parameters include emission factor of a pollutant (g/kg or g/kJ or g/MJ) or indoor concentration of a pollutant (ng/m³ or μg/m³ or mg/m³ or g/m³) [9].

The amount of thermal energy produced (kJ) per unit time (s) is known as fire power (kW). Mathematically fire power is defined as follows:

$$\text{Fire power}\left(\mathrm{P}\right)=\frac{\text{mass of fuel burnt}\times \text{Calorific value of fuel}}{\text{Time taken for complete combustion of fuel}}\mathrm{kJ}/\mathrm{s}\text{or}\mathrm{kW}$$E1

Fire power is the total amount of energy available for cooking the food per unit time. The energy actually used for cooking the food will be very small as compared to that of the fire power due to various losses. Figure 1 shows energy balance for a biomass cookstove. Out of the total energy available in the form of fire power (a), some of the energy is absorbed by the cookstove body in the form of an internal energy and some energy is lost form the cookstove body to the surroundings through convection, radiation and to the ground through conduction (b). Heavier cookstoves absorb more energy in the form of the internal energy. Hence, traditional cookstoves as well as modified biomass cookstoves made of mud and brick are found to have poor efficiencies as compared to the metal biomass cookstoves. Some of the energy in the fire is absorbed by the pot and the pot contents (c). During this transfer of energy, some of the energy is lost to the atmosphere with flue gases and some energy is lost in the form of direct radiation and convection (d). Vessel walls also lose some heat to the atmosphere in the form of convection (e). From the top portion of the pot, there will always be evaporative (f) and convective energy losses (g).

Figure 1.

Schematic of energy balance of a cookstove [9]. [Reprinted from Renewable & Sustainable Reviews, Vol. 41, Sutar K. B., Kohli S., Ravi M. R. and Ray A., Biomass cookstoves: A review of technical aspects, 1128–1166, 2015, with permission from Elsevier.].

From Figure 1, it is clear that actual energy used per unit time for cooking the food (P_u) = {(c)−[(e) + (f) + (g)]}/t. Now, thermal efficiency (η) of biomass cookstove is defined as the ratio of actual energy used by the pot and the pot contents for cooking the food per unit time to the fire power available due to combustion of fuel. Mathematically, thermal efficiency is defined as follows:

$$\text{Thermal efficiency}\left(\mathrm{\eta }\right)=\frac{\text{Actual energy used}\mathrm{per}\text{unit time for cooking the food}}{\text{Fire power}}=\frac{{\mathrm{P}}_{\mathrm{u}}}{\mathrm{P}}$$E2

Specific fuel consumption (SFC) is the mass of dry fuel required (g) to produce a unit output. Here, the unit output is a mass of water remaining in the pot at the end of the test (kg). SFC is expressed in terms of g/kg [14]. Turn down ratio is the ratio of maximum and minimum power between which the cookstove can be operated satisfactorily [9].

Emission factor (g/kg or g/kJ or g/MJ) of a particular pollutant is mass of that pollutant emitted (g) per kilogram of the fuel burnt or per kJ or per MJ of energy released during the cooking task [9]. Indoor concentration of a particular pollutant (ng/m³ or μg/m³ or mg/m³ or g/m³) is defined as the amount of exposure of that pollutant (ng or μg or mg or g) to the user per m³ of the air in the room or cooking space [9].

According to WHO guidelines [15], carbon monoxide (CO), particulate matter of size less than 10 μm (PM₁₀) and of less than 2.5 μm (PM_2.5), nitrogen dioxide (NO₂), formaldehyde, naphthalene, benzene and polycyclic aromatic hydrocarbons (PAH) are found to be major indoor air pollutants. Considering global warming potential of these pollutants, it is very important for the researchers to know the safer limits of these pollutants in ambient air as recommended by the national and international agencies. Table 1 report WHO guidelines on indoor air pollutants resulting from combustion of fuels and also ambient air quality standards set by United States Environmental Protection Agency (USEPA) for USA [16] and by Central Pollution Control Board (CPCB) for India [17]. For a given pollutant, with increase in averaging time, values of its safe limit decrease. For example, as per WHO guidelines, permissible limit of exposure to CO emissions for 1 hour is 35 mg/m³, for 8 hours it is 10 mg/m³, and for 24 hours this limit is 7 mg/m³.

Pollutant	Averaging time	WHO [15]		USEPA [16]		CPCB India [17]
		Value	Unit	Value	Unit	Value	Unit
CO	24 hours	07	mg/m^3	—	—	—	—
	8 hours	10	mg/m^3	09	ppm	02	mg/m^3
	1 hour	35	mg/m^3	35	ppm	04	mg/m^3
				—	—
PM10	Annual	20	μg/m^3	—	—	60	μg/m^3
	24 hours	50	μg/m^3	150	μg/m^3	100	μg/m^3
PM2.5	Annual	10	μg/m^3	12	μg/m^3	40	μg/m^3
	24 hours	25	μg/m3	35	μg/m^3	60	μg/m^3
NO2	Annual	—	—	53	ppb	40	μg/m^3
	24 hours	—	—	—	—	80	μg/m^3
	1 hour	200	μg/m^3	100	ppb	—	—
SO2	Annual	—	—	—	—	50	μg/m^3
	24 hours	—	—	—	—	80	μg/m^3
	1 hour	—	—	75	ppb	—	—
Formaldehyde	30 minutes	0.1	mg/m^3	—	—	—	—
Naphthalene	Annual	0.01	mg/m^3	—	—	—	—
Benzene	Annual	Unit risk of leukemia: 6 × 10^−6 per μg/m^3 of air.		—	—	05	μg/m^3
Polycyclic aromatic hydrocarbons (PAH)	Annual	Unit risk for lung cancer: 8.7 × 10^−5 per ng/m^3 of B[a]P.		—	—	01	ng/m^3

Table 1.

WHO guidelines for indoor air quality [15] and ambient air quality standards for USA [16] and India [17].

USEPA: United States Environmental Protection Agency, CPCB: Central Pollution Control Board, ppm: parts per million, ppb: parts per billion, ng: Nano gram, and B[a]P: Benzo(a)Pyrene.

3. Traditional and improved biomass cookstoves

Figure 2(a and b) shows images of traditional biomass cookstove and improved mud cookstove. Average efficiency and CH₄ emissions of traditional biomass cookstoves used in Asian countries were reported to be about 11% and 0.52 g/MJ of energy delivered by wood fuel [18]. Since early 1980s, some researchers reported ways of improving thermal performance of the traditional biomass cookstoves by modifying their designs [19, 20, 21, 22, 23, 24]. These ways include: use of metals as cookstove materials, provision of grate for better air circulation, air preheating, provision of swirl and secondary air, provision of insulation, use of chimney and baffles [18]. Average efficiency and CH₄ emissions of improved biomass cookstoves used in Asian countries were reported to be about 24% and 0.408 g/MJ of energy delivered respectively with the wood fuel [18]. Thermal performance of improved biomass cookstoves was found to be better than the traditional cookstoves; but there was not much improvement in their emission performance as compared with traditional ones. Researchers have found that improvement in efficiency of biomass cookstove does not always ensure reduction in emissions. There exists a certain range of power levels where the correlation between efficiency and emissions is positive, while elsewhere it will be negative [18].

Figure 2.

Images of traditional biomass cookstove and improved mud cookstove.

Improved biomass cookstoves are known as fuel efficient cookstoves as they reduce fuel consumption by 20–50% as compared with the traditional biomass cookstoves [25]. Some of the examples of improved biomass cookstoves are: Swosthee cookstove [26], rocket cookstove [27], Patsari cookstove [28], Envirofit cookstove [29], Jiko cookstove [30] etc.

4. Advanced biomass cookstoves

To improve thermal and emission performance of metal biomass cookstoves, efforts have been made by the researchers which include: application of scientific principles for designing the cookstoves, insulating the combustion chamber, supplying correct amount of primary and secondary air at right place into the combustion chamber, use of fan to create draft, use of gasification techniques, use of high density pellets as fuel etc. [31, 32, 33, 34]. Such efforts have helped in accelerating the process of design of advanced metal biomass cookstoves, both in natural and forced draft versions, across the globe.

According to method of combustion of biomass fuel into combustion chamber, advanced biomass cookstoves can be classified into two types viz. normal combustion cookstoves and gasifier cookstoves. The best example of the biomass cookstove which can efficiently operate in both these modes is Philips forced draft biomass cookstove [34].

During normal combustion mode, the biomass is fed in terms of small batches to the combustion chamber (oven). The pyrolysis products burn near the top of the combustion chamber using secondary air whereas the char combustion occurs using primary air at the bottom of the oven. During gasification mode, the whole combustion chamber is filled with the biomass fuel. The cookstove is lit at the top and the fire slowly passes to the bottom of the combustion chamber. Unlike the combustion mode, no fuel is added to the cookstove until the fire goes off. This gasification mode of operation of cookstove is also known as Top Lit Up Draft (TLUD) gasification, as the cookstove is lit at the top and the flow of both primary as well as secondary air goes in upward direction. Figure 3 shows schematic diagram of Philips forced draft cookstove.

Figure 3.

Schematic diagram of Philips forced draft cookstove [34]. [© 2006, Royal Philips. Password, Philips Research innovation magazine, issue#28].

Jetter et al. [35] conducted experimental studies on 22 biomass cookstoves and reported that the efficiency of Philips forced draft cookstove was about 38% where as its CO and PM_2.5 emissions were very small. The authors also reported that cookstove operating on TLUD mode showed the lowest CO and PM_2.5 emissions. Some examples of TLUD gasifier cookstoves are rice husk gas cookstove [36], Oorja cookstove [37], pellet-fed gasifier cookstove [38] etc. The main advantages of using TLUD type of gasifier cookstoves are: highly efficient operation, clean combustion with negligibly small levels of emissions, use of densified pellets made up of crop residues and other biomass wastes for waste to energy conversion.

Research groups, non-government agencies and some government departments have developed protocols for testing the thermal and emission performance of biomass cookstoves. Comparative studies on testing protocols for biomass cookstoves are available in literature [9, 39]. An ISO technical committee comprising of experts from 45 countries and 8 international organizations published voluntary performance targets for biomass cookstoves in 2018 [40] in the form of a document called ISO Workshop Agreements (IWA) [41]. These targets cover five performance indicators viz. thermal efficiency, fine particulate matter emissions, carbon monoxide emissions, safety, and durability of biomass cookstoves. For each indicator, laboratory test results are rated along 6 tiers (0: for lowest performing cookstove to 5: for highest performing cookstove). Table 2 reports default values of these voluntary performance targets. The three types of biomass cookstoves viz. traditional, improved and advanced can easily be categorized as per the tier rating. Most of the traditional cookstoves fall in tier 0 to 1 categories. The improved biomass cookstoves will have tier rating of 2–3 whereas the advanced biomass cookstoves shall be given the tier rating of 3–5. With increase in tier rating of the cookstove, its efficiency increases, CO and PM emissions decrease, its safety score increases i.e., it can be operated safely and its durability score decreases i.e., it becomes durable.

Tier	Thermal efficiency (%)	CO (g/MJd)	PM (mg/MJd)	Safety score	Durability score
5	≥ 50	≤ 3.0	≤ 5.0	≥ 95	< 10
4	≥ 40	≤ 4.4	≤ 62	≥ 86	< 15
3	≥ 30	≤ 7.2	≤ 218	≥ 77	< 20
2	≥ 20	≤ 11.5	≤ 481	≥ 68	< 25
1	≥ 10	≤ 18.3	≤ 1031	≥ 60	< 35
0	< 10	> 18.3	> 1031	< 60	> 35

Table 2.

Default values of voluntary performance targets for biomass cookstoves [40].

MJ_d: Mega Joule of energy delivered.

5. Adoption of biomass cookstoves

On one side, the design and development of biomass cookstoves is being done by the researchers in research laboratories but on the other side, dissemination of these cookstoves to the end users is a very important task. For successful dissemination and adoption of a cookstove, it must be locally manufactured, easy to operate, durable and it must result in clean combustion [42].

Bielecki & Wingenbach [43] reported that adoption of improved cookstoves depends on three factors viz. social, functional, and cultural. The social factor includes family size and meal occasion; functional factor includes ability of improved cookstove to provide space heat and ambient light, and the cultural factor includes local norms and traditional foods.

Adane et al. [44] categorized the factors affecting adoption of biomass cookstoves into four types: (i) household and setting related factors, (ii) cookstove technology related factors, (iii) cookstove users’ knowledge and perception related factors, and (iv) financial and market development related factors. Household and setting related factors include: gender of the household head, educational level of the household head, family size of the household, house ownership, location of cooking quarter, and source of fuel. Cookstove technology related factors include: fuel processing requirement, durability of cookstove, fuel saving benefit of cookstove, health benefit of cookstove, time saving benefit of cookstove and safety benefit of improved cookstove. Cookstove users’ knowledge and perception related factors include: optimistic previous social interaction, traditional suitability of cookstove and live demonstration experience. Financial and market development related factors include price and availability of the cookstove.

Nzengya et al. [45] reported that cost of cookstove, availability of cookstove, cost of fuel, availability of fuel, design of cookstove, time required for starting the cookstove, and time required for cooking the food are the factors affecting adoption of a biomass cookstove.

According to Jan [46], following factors act as key barriers to the adoption of improved cook stoves: lack of education of the women, non-participation of women in household decision making processes, low family income, lack of knowledge of health and environmental impacts associated with inefficient use of biomass, insufficient funds allocated by governments and NGOs for such programs, and poor monitoring system for the long-term cookstove use.

Jauland et al. [47] reported the evidence of saving in cooking time and fuel saving in the households which started using improved cookstoves. The authors did not find any evidence of health benefits in these households.

Jana and Bhattacharya [48] reported sustainable cooking energy options for rural people in Bargaon block of Odisha, India. Assessment of different cooking options such as traditional biomass cookstoves, improved cookstoves, gasifier cookstoves, biogas cookstove, LPG cookstove, electric cookstove and kerosene cookstove was conducted in terms of levelized cost of each cooking device per unit of useful cooking energy. While calculating the levelized cost of cookstove, the factors such as its capital cost, maintenance cost, estimated life, efficiency, cost of fuel, interest rate and energy equivalent per unit of energy source were considered. The levelized costs of different cooking devices per MJ without subsidy were: 1.3- traditional cookstove, 0.87-improved cookstove, 3.49-briquette gasifier cookstove, 2.72-kerosene cookstove (1.06 with subsidy), 1.88-LPG cookstove (1.33 with subsidy), 2.49-electric heater and 1.92-biogas cookstove (1.65 with subsidy). The authors found that the cookstoves using kerosene, LPG, briquettes, electricity and biogas were beyond reach of the poor people due to their high levelized costs though they could become cleaner cooking options for traditional and improved cookstoves.

6. Recommendations for promotion of clean cooking energy options

Petroleum Conservation Research Association (PCRA) [49] has given some guidelines for about 30% saving in LPG and kerosene fuels. These guidelines will be very useful for all types of cookstoves. These guidelines include: plan before you start actual cooking; use pressure cooker of capacity corresponding to the family size; use optimum quantity of water; reduce the flame when boiling starts; soak the rice and pulses for about 15 minutes prior to their actual cooking; use shallow, wide vessels while cooking the food; put the lid to avoid heat losses; use small burner which saves fuel; use ISO/ISI marked cooking devices.

Council on Energy, Environment and Water (CEEW), India has published a report on roadmap for access to clean cooking energy in India [50]. Recommendations given by the authors in this report will be very useful for promotion of clean cooking energy options among the end users. These recommendations given for different cooking energy options along with author’s own views are as reported here.

6.1 Biomass cookstoves

• Advanced biomass cookstoves are tier 4 and tier 5 cookstoves which are very expensive and are beyond reach of the common people. Most of the improved cookstoves found today are of tier 2 or tier 3 which are cheaper than the advanced biomass cookstoves and can be affordable to the poor people. In such a case the government must encourage use of tier 3 improved cookstoves equipped with chimneys for adequate ventilation. Also, to encourage use tier 4 and 5 cookstoves, subsidies must be provided to them.

• Labelling cookstoves with their efficiency and emissions rating will aid customer awareness and also will help them in taking decision on selection of cookstove for their family.

• Government shall provide subsidized training in pellet manufacturing and improved cookstove manufacturing, assembling, and marketing to local entrepreneurs and workers. This will help in enhancing local employment. It will reduce the cost of transportation and overhead charges. It will reduce the cost of pellets and initial cost of the cookstoves.

• It is observed that two third of the households using LPG cookstoves for cooking also use traditional cookstoves for heating of water and for space heating due to freely available biomass fuel and to ensure long lasting of LPG cylinder due to its high refill price. Hence, to fully eliminate household air pollution, it is important to address space heating and water heating for bathing using biomass cookstoves.

6.2 LPG

• Providing subsidy on the basis of socioeconomic characteristics will improve affordability of LPG among households.

• The thermal efficiency of the LPG cookstoves is about 55–57%. Research and development with a focused target of improving efficiency of LPG burners by about 10% must be undertaken. It can be done by modifying burner size, burner material, number of ports in a burner and also by improving burner pot interaction. The spacing between burner top and pot bottom can also be optimized. For a particular family size and for a given cooking process, pot sizes can be standardized.

• Sutar et al. [51] conducted preliminary experiments on domestic LPG stove to investigate the best combination of pot size for common cooking processes viz. heating of milk, making of tea and cooking of rice. During experimentation, a fixed amount of food item was used for each type of cooking process. The quantity of these food items was decided as per need of a family of four members based on the survey conducted in 80 LPG using households. The major findings were: LPG consumption was found to be more for larger pressure cookers as compared with smaller ones on account of higher thermal mass and higher convective and radiative losses through them; a pressure cooker of 1.5 liter capacity was found to be optimum for a family size of four members; round bottom pots caused reduction in LPG consumption than flat bottom pots of same sizes; it was estimated that for a four member family, use of optimum pot size, low flame setting and smaller burner will result into saving in about 14 kg of LPG annually.

• In India, only 41% of rural households received LPG cylinders at their doorstep in 2018. Permitting local institutions to stock LPG and to supply directly to households will reduce the distance traveled by users to procure LPG cylinders.

• The typical rural LPG distributor struggles for survival with low demand for LPG refills due to high cost of LPG and uncertainty of subsidies. In India, in 2016, over 80% of households that did not use LPG reported high recurring costs as a barrier [50].

6.3 Biogas

• The main hurdle in accelerating biogas use is the regular maintenance of biogas plants. If regular maintenance and servicing of a biogas plant is provided by an entrepreneur, households need not take on the hassle of operating, cleaning and maintaining the plant.

• It is important to train users to operate biogas plants in a manner that minimizes the need for operation and maintenance.

• A centralized toll-free helpline could be useful for people to lodge complaints regarding any issues with the biogas plants, which shall be immediately addressed by the local entrepreneur.

6.4 General guidelines on promotion of clean cooking energy options

• In rural areas, primary health centers and sub-centers are the closest access points to healthcare for the rural population, and thus could be effective venues for communication regarding the clean cooking technologies [50].

• Reliable information on consumers’ willingness to pay for access to clean cooking energy will solve lot many issues. It will help the government agencies in providing the right cooking technology to right household [50].

• Greater focus on technology development, stricter quality standards and awareness drives to increase usage of new cooking technologies will be very important steps for the adoption of clean cooking technologies [9].

• Government must provide grants for the promotion of new technologies that are less effort intensive and/or more efficient e.g., advanced biomass cookstoves [9].

• Fabrication of cookstoves must involve a stringent quality control to keep the critical dimensions as per the requirement otherwise performance of the cookstoves will be affected adversely during its actual use.

• Performance of cookstove drastically affects due to changes in critical dimensions on account of lack of periodic maintenance [9].

• If trained personnel required for periodic maintenance of advanced cookstoves is available locally, then adoption rate of such cookstoves will enhance.

• Advanced biomass cookstoves generally require pellets or prepared fuels for their optimum performance. Availability and cost of the prepared fuel plays a very important role in the acceptance of the cookstove by the end user.

• The probability of acceptance of the new designed cookstove will be higher if the users are made familiar with the operation or if its operation is very similar to the cookstove they were previously using.

• While designing any clean cookstove, care must be taken that lower the capital as well as running cost of cookstove, higher is its acceptance among the users [50].

7. Conclusions

The present chapter reported four important aspects related to biomass cookstoves viz. energy efficiency, emissions, different designs of cookstoves and their adoption. Following are the conclusions drawn:

• The overall performance of biomass cookstoves is affected by two types of parameters viz. thermal and emission performance parameters. Thermal efficiency is the most important thermal performance parameter whereas emission factor of different pollutants is the most important emission performance parameter. In this regard, knowledge about safer limits of these pollutants in ambient air is very important. Also, knowledge of tier categories for biomass cookstoves is also important.

• Various ways to convert traditional biomass cookstoves into improved biomass cookstoves are: use of metals as cookstove materials, provision of grate for better air circulation, air preheating, provision of swirl and secondary air, provision of insulation, use of chimney and baffles

• Different techniques used by the researchers for development of advanced biomass cookstoves are: application of scientific principles for designing the cookstoves, insulating the combustion chamber, supplying correct amount of primary and secondary air at right place into the combustion chamber, use of fan to create draft, use of gasification techniques, use of high density pellets as fuel etc.

• The factors affecting adoption of biomass cookstoves, reported in literature are also discusses. These factors are: social, functional, cultural, affordability, women education, availability of fuel, availability of cookstove, timely servicing help, training, subsidies and grants etc.

• Recommendations on promotion of clean cooking energy options such as fuel saving guidelines, necessity of research and development in advanced cooking technologies, their promotion among the society, and financial support to the new clean cooking technologies etc. are given.

Conflict of interest

“The author declares no conflict of interest.”