The Tehesh efficient biomass stove, Tigrai, Ethiopia

by Mr. Tsige Abreha, Mekelle Rural Technology Promotion Center, PO Box 556, Mekelle, Tigrai, Ethiopia Fax: 04 40 37 10

Introduction

The region of Tigrai is one of nine regions situated in the North of Ethiopia. The population is mainly rural, with 83% of the population living in rural areas. Biomass has traditionally been a 'free' resource (Figure 1), mainly as fuelwood and charcoal, and to a lesser extent as crop residues and dung. This energy supply is now under threat, due to its continuous and uncontrolled use. Although diminishing supplies were evident to women in the region, the energy situation of the region was not monitored because of a long-lasting war and political instability. It was not until after the fall of the previous regime that the energy sector was given emphasis.

Figure 1: Woman carrying fuelwood accompanied by daughter

RTPC

Under the auspices of the Bureau of Agriculture and Natural Resources (BOANR), the Rural Energy Development Team (REDT) of the Rural Technology Promotion Center (RTPC) is one of the organisations that has been making substantial efforts to confront the energy crisis in rural areas. Among these initiatives are the construction of biogas plants, and the testing and evaluation of currently available biomass stoves.

In 1997-98, the team conducted a base-level study of rural household energy consumption and determined that the average consumption per household comprised the following:

· Fuelwood	62%
· Dung	24%
· Crop residues	12%
· Kerosene	2%

Based on these results, the team determined that most benefit could be gained from focussing on biomass stoves.

Stoves must suit the type of food

Injera is the staple food that is made every day or two from well-fermented wheat, teff, sorghum or maize flour. It is a large, flat, type of bread (50-56 cm in diameter), which is baked on a ceramic plate (about 1-2 cm thick) known locally as a mogogo in the Tigriana language and as a mitad in Amharic (Figure 2). It is eaten with a sauce made from either vegetables and bean or chick-pea flour, or from stewed meat.

Figure 2: Mogogo under construction

RTPC

Recent studies have shown that injera baking is the major component of household energy use in this area, as shown below:

· Injera 56%
· Sauce and coffee 40%
· Other (including lighting) 4%

Especially in the lowland areas, where injera is baked every day, there is a need for a stove with better performance in terms of fuel economy and smoke dispersal.

Types of stove

Stoves are designed to accommodate the type of food which is being cooked, and the designs of stoves needed to bake injera in Tigrai are unique. The stove for the mogogo is constructed either in a separate kitchen or out of doors.

A small kitchen laboratory has been set up by the Rural Energy Team of the RTPC at the Rural Technology Promotion Center at Mekelle to improve the stoves, assisted by a consultant from GTZ. Several types of stove are currently being tested, including traditional stoves and an improved stove being disseminated currently by the Rural Women's Desk of BOANR.

Conclusions

The traditional stoves had lower efficiencies than the Tehesh stove, as the distance from the fire to the mogogo was found to be too large and there was considerable pollution as there was no chimney to vent the hot gases.

Table title required

Name of stove	Features
Traditional stove	No chimney; single walls; mud and stone
BOANR improved stove (Figure 3)	Chimney; single walls; mud and stone
Jet stove (Figure 4)	Chimney; double wall, with insulation between the walls and under the grate (straw between the walls traps the insulating air during construction); Baffle to reduce velocity of flue gases; Small clearance (1.5-2 cm) between inner wall and the mogogo to utilize the heat contained in the flue gases to the maximum
Tehesh stove (Figures 5 & 6)	It was found that only two of the seventeen women involved in making the jet stove could construct it correctly. The Tehesh stove is similar to the jet stove except that the clearance between the inner wall and the mogogo is reduced, making construction simpler. Instead, there is a 40 cm baffle and the two walls are joined at the top (Figure 6). Tehesh means 'easier to construct'

Figure 3: Improved stove in use

RTPC

Figure 4: Jet stove (illustrated without mogogo)

RTPC

Figure 5: Tehesh stove under construction

RTPC

Figure 6: Line drawings of Tehesh stove (dimensions in mm)

The improved stove had less height between fire and mogogo and a chimney diffused some of the smoke. However, because there is no baffle, a lot of heat is wasted as the smoke goes straight up the chimney.

The Tehesh stove was found to be more efficient for two reasons:

· Increased heat retention due to double walls, reducing heat loss to the surroundings, and producing useable heat some time after all the fuel is consumed

· Reduced flue gas temperatures as baffle prolongs retention time of the gases around the mogogo

The Tehesh stove is recommended for those for whom wood is their major fuel. It can be simply adopted by the stove user if it is accompanied by training in construction and application. Acceptance levels of the Tehesh stove in this region are encouraging.

References

Krishna, C.V. Woodstove Evaluation and Promotion, 1990

Usinger, Jurgen: Workshop on Improved Injera Stove, Indaslasse; Ethiopia Design and Pilot Project, 1996

Gebre G/tsadik: Tigrai rural household energy development, issues and strategies, 1998

Rural Energy Development Team & Rural Women's Desk; Biomass stove (Mogogo stove) test report, 1998