The box solar oven in Malawi. Feasibility study on design and use

TABLE OF CONTENTS

Table of Contents

ACKNOWLEDGEMENTS

ABSTRACT

TABLE OF CONTENTS

LST OF TABLES

LIST OF FIGURES

ABBREVIATIONS AND ACRONYMS

CHAPTER 1
1.0. INTRODUCTION AND OBJECTIVES
1.1.0. Introduction
1.1.1. Status of Biomass Utilization in Malawi
1.1.2 INNOVATED SOLAR BOX OVEN
1.1.3 THE STRATEGY BEHIND THE OVEN PROJECT
1.2 PROJECT OBJECTIVES
1.2.0 GENERAL OBJECTIVE
1.2.1 SPECIFIC OBJECTIVES

CHAPTER 2:
2.0 LITERATURE REVIEW
2.1.0. PRINCIPLES IN OVEN OPERATION
2.2 ENERGY ENVIRONMENTAL POLICY IN MALAWI

CHAPTER 3
3.0 MATERIALS AND METHODS
3.1.0 DESIGN

CHAPTER 4
4.0 RESULTS AND DISCUSSION
4.1.0 Conversion Efficiency
4.1.1. Rate of Energy Released by the oven
4.1.2. The standard stagnation temperature
4.1.3. standard sensible heating time
4.1.1 DISCUSSION

CHAPTER 5
5.0. IMPACTS

CHAPTER 6
6.0 CONCLUSIONS AND RECOMMENDATIONS
6.1.0 CONCLUSIONS
6.1.1 RECOMMENDATION

REFERENCES

APPENDIX

ACKNOWLEDGEMENTS

It has been a journey travelled many times in dreams towards the Bsc. degree. I would have not reached this point had I embarked alone. Many have played a great role in my moments of lost, weary, complacent and watched from the sidelines with cheering. To all these people I am forever grateful.

Sincere appreciation is expressed to the Department of Physics and Biochemical sciences for giving the opportunity and the necessary financial support to complete the project.

I would like to thank the supervisor Miss E. Katengeza for her guidance, knowledgeable criticism, constant encouragement and unfailing support. I acknowledge Mr. Masache as a project coordinator for the valuable support, encouragements, enjoyable company and all my friends at the college with gratitude.

I also recognize the work of Mr. Adams Chavula of the Meteorological department of Malawi for playing in the background by providing necessary information towards the project. I would also like to thank Mrs. T. Mlowa of the Physics and biochemical department at Polytechnic College for the special advices on carrying the project.

Special acknowledgement goes to my parents, Mr. and Mrs. Kaselema together with my brothers and sisters for all their prayers and for giving me valuable moral support, power, strength and continuous love to survive the pressure of ‘Polytechnic life'.

ABSTRACT

The solar oven was tested using the American Society of Agricultural Engineering Standards (ASAE S580) developed by Dr. Paul Funk and also used were the suggestions by Shawn Shaw of Rensselear Polytechnic Institute. The design showed that the reflector arrangement played a great role in radiation absorption by the oven. A temperature rise of 66°C was reached within an approximate period of one hour even though the water never reached the boiling point as the oven only managed to register a highest temperature of 90°C. Testing the oven illustrated the essence of the new design as the thermal conversion efficiency of the oven was 18.2%.

The oven was made of two plywood boxes one inside the other with the cavity being filled by cotton wool in additional to newspapers which are mostly used.

This research conclude that the oven performance greatly depend on meteorological conditions and also that it can only preferably be used around noon hours.

Carrying the project faced some hurdles and among them includes variation in weather conditions and lack of recording equipment. For example mercury-in-glass thermometers had to be used instead of thermocouple thermometers.

The project therefore recommends that a similar project be carried at a different location under different meteorological conditions . It also recommends the use of handles on the glass absorber plate to avoid hand burns and emphasize the need for lid on cooking pots as evaporating water could broke the ability of sun radiation to enter the chamber after condensing on the glass.

LST OF TABLES

Table 1: controllable variables in oven testing.

Table 2: Comparison between old and new model

Table 3: Results of the water boiling tests on an open fire stones stove

Table 4: Annotated results of temperature as were recorded during the testing period

LIST OF FIGURES

Figure 1: energy distribution of Malawi

Figure 2: dimensions of the design and framework of the cooking chamber.

Figure 3: reflectors plan.

Figure 4: Schematic diagram of the final new solar oven

Figure 5: Picture showing the box type solar oven

Figure 6: experimental setup at the project site

Figure 7: Solar oven tests showing water temperature as a function of time.

ABBREVIATIONS AND ACRONYMS

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CHAPTER 1

1.0. INTRODUCTION AND OBJECTIVES

1.1.0. Introduction

The inexorable need to cook food for nourishment is fundamental to nearly every society and there is an upsurge requirement of the expenditure of energy in some form due to an increase in human population. These form of energy include solar energy technology. It can be harnessed to meet the energy need for food preparation without the environmental and health problems associated with biomass fuels mostly used by Malawians. For period immemorial, societies have been using solar energy directly or indirectly to dehydrate, warm, and dry different food items. This brings into confusion as to why there is little acceptability by the communities in using solar devices. There are a wide variety of devices designed to capture the sun's energy and harness it for different purposes and includes solar heater , solar cooker, solar dryer, solar still and solar air heating systems. Also peculiar and of concern in this project is the solar oven. Many are the projects that have been carried out around the world with others still in progress. This project was conducted at the University of Malawi, Polytechnic in the department of physics and biochemical sciences.

Among other objectives the preliminary idea in conducting the solar oven project was to determine if they can effectively be used in Malawi. The idea to carry a feasibility study on design and use of the solar oven was initiated since by the time of carrying this project, no published literature about box type solar oven projects in Malawi was available. It was discovered that other countries have societies pertaining to solar cooking technology despite the effort by the Illinois, USA company in distributing solar ovens in Malawi (www.sunoven.com: 21/8/2014). This causes wonders as to why Malawi was not embarking on solar oven project as research about insolation levels about the country had shown to be effective enough for solar cooking. For example research report by Gregory E.T Gamula et al (December, 2012) showed that Malawi has an insolation of 900W/m[2] in cold season and 1200W/m[2] during warm season.

There are three types of solar ovens currently in use globally and literature review showed that there is clear room for improvement. The research focused much on box type of solar oven and a new type was designed to address some of the perceived weaknesses and determine if ever it can be applied in Malawi. This new solar oven incorporates a number of strategies drawn from thermal performance of the solar ovens and cookers, which were normalized with a set of standard environmental conditions. Observations based on ergonomics and safety were also given consideration in designing the oven in this scenario.

Electricity and gas are only intermittently available and considered too expensive for cooking. For example electricity tariffs in Malawi were raised by 37.28% in 2014 (Chimwemwe Mangazi and Elita Soko, capital radio Malawi: April, 2014) and the price for gas is not fixed with the introduction of automatic fuel pricing methodology. Firewood provides over 50% of the urban cooking and almost 100% in the rural areas where in all settings three stones open stoves and braziers are used. Therefore there is need to introduce conveniently affordable uncarbonized energy sources to prepare meals as these stoves cause smoke related illnesses and also contribute to deforestation. Sympathetically charcoal and firewood used are unsustainably produced and collected from trees in forest reserves and national parks. Hence the solar oven proves to be a viable option in alleviating problems related to biomass usage like deforestation, soil erosion, smoke related diseases etc.

1.1.1. Status of Biomass Utilization in Malawi

Malawi is an increasingly energy depressed country due to its relatively small land-mass, large population and heavy dependence on biomass. The national energy policy estimates that 93% of households consume 84% of the total primary energy. A staggering 99% of the household energy is supplied by biomass. This, with increasing population growth currently at the rate of 3.33% [ Malawi national census report: August, 2014], is exerting significant pressure on the country's forest resources, leading to forest degradation and deforestation at the rate of 2.6% per year. However the percentage of people connected to the national grid's demand far exceeds the supply of 320MW installed capacity. Thus, load shedding is frequent. The chart below depicts the energy usage distribution in Malawi.

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Figure 1: showing the energy distribution of Malawi (adapted from: terminal report on dissemination of improved institution cookstove, K.J Gondwe et al; July, 2003 )

1.1.2 INNOVATED SOLAR BOX OVEN

An oven is an enclosed compartment, usually part of a cooker, for cooking food. It can also be referred to as the small furnace or kiln (Concise oxford dictionary, 10th edition). The box type was chosen because it allows to hold multiple pots, making it a good style of cooking for large households or when preparing separate dishes. The box oven has also the ability to use different types of cook wares making them adoptable for households as they do not require distortion in buying cook wares unlike other ovens which needs special wares.

1.1.3 THE STRATEGY BEHIND THE OVEN PROJECT

The following benefits were expected to be achieved by the oven:

- Implementation of the solar oven as the source of energy for cooking (energy management).
- To act as a motivating factor in researches on project related to solar oven.

There has been many solar oven projects around the globe with some of them not being properly documented. As such the model adapted is identical to how most of them have been made as a modification to the first model by the Swiss scientist, H.B. De Saussure. The preliminary idea behind conducting the research was basically to analyze if ever the box type of solar oven can effectively be used with environmental conditions of Malawi. These has been done to avoid further complication as modifying a modified oven would have just lead to a more complicated item of which may require high technical knowledge to even use.

1.2 PROJECT OBJECTIVES

1.2.0 GENERAL OBJECTIVE

The general objective of the project was to study the feasibility of designing to construct and use a solar oven as a household cooking energy source with the modification idea to determine if they can be used under the local conditions of Malawi.

1.2.1 SPECIFIC OBJECTIVES

The specific objectives of the project were :

- To modify, design and construct a solar oven using locally available materials.
- To explore the maximum temperature to be reached by the oven.
- To evaluate and determine the efficiency of the solar oven.

CHAPTER 2:

2.0 LITERATURE REVIEW

2.1.0. PRINCIPLES IN OVEN OPERATION

Sun rays are caused to change into heat and conducted into the cooking pot. There is a direct relationship between collected sunlight to the projected area of the collector perpendicular to the incident radiation. The relationship is referred to as the geometric concentration ratio (Kimambo, August 2007).

Where At is the collector area comprising the sum of areas for reflectors and the absorber plate whereas Arc is the area of the receiver/glass absorber aperture. The oven in the project had a total collector area of 1.8225m[2] and the receiver was 0.3504m[2] implying that it had a geometric concentration ratio of:

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Malawi is among the countries with highest insolation and is ranked on level 1 of insolation capacity, justifying the applicability of solar oven even in periods outside the hot dry seasons (SCI, 1919 21s St, Sacramento CA 95814, www.solarcookers.org : 2/9/2014).

History of solar oven

Initiatives are around the world to disseminate knowledge about solar energy as a source of cooking. Examples of these projects include:

i. GTZ Projects

- SADC region program that manages and stimulates the establishment of various projects based on basic energy conservation (ProBEC).
- Mekhe solar cooker project published on January 04, 2012.
- Illinois solar oven projects introduced in March 2011, Malawi.

ii. AFRICA SOLAR OVEN PROJECT

Projects on solar ovens have been carried around the world. For example in 2011 Chris Rapp of Salt Lake city, Utah, did a project on enhanced angle and reflectors. He was actually interested to determine amount of additional power to be reached and used eight reflectors composed of four rectangles and four triangles pieced together and covered with mirror vinyl attached with very small clamps. He could reach a maximum temperature of 230.5°C and maintained a cooking temperature of up to 195.5°C (Retrievedfrom: www. Solarcooker-at-cantinawest.com: 10/3/2014 ).

In 2013, Joshua Folaranmi, from the department of Mechanical Engineering at Federal University of Technology, Niger state, Minna Nigeria, conducted a research which aimed at evaluating the performance of double glazed box type of solar oven with reflectors. (Retrieved from: www.hindawi.com: 4/4/2014).

In March 2011, Sun Ovens, an Illinois, USA company joins forces with the rotary club of Naperville, to help promote solar cooking for the people of Malawi. The project aimed to assist people living with HIV. The global sun ovens they brought in were to provide slow cooking of the ‘seven grains' diet given to people living with AIDS. Prior to the introduction of solar ovens, people would use huge amount of fuel like charcoal or firewood to soften these grains. By then all they had to do was to harness the power of sun to cook their food which minimizes their exposure to cooking fumes and reduce time spent to gather fuel wood.

iii. ENERGY RESEARCH SECTOR

Different energy programs in Malawi address the issue of energy efficiencies at household level. This is basically because institutions and commercial catering establishments are much fewer in relation to households. As such the research was designed in target and much emphasis to households because their need for fuel wood affect even small tree shrubs and have great impact in diverting ecosystem.

2.2 ENERGY ENVIRONMENTAL POLICY IN MALAWI

As of 2003, part IV (Energy Demand Sectors) Section 4.2.1(Urban Household Energy Demand) outlines what the government of Malawi considers to be the most relevant challenges to the energy sector. The policy document indicate Government's interest to reduce the proportion of households using three stones stoves to 50% by 2020 (Gondwe K.J and Taulo J.L: July, 2003).

The project was conducted as an initiative towards achieving the government goals in addressing energy problems by promoting nontraditional cooking methods.

Among other goals of the energy sector in Malawi include:

- To promote overall socio-economic development.
- To contribute to poverty reduction through sustainable provision of reliable, efficient, affordable and efficient utilization of the energy resources without compromising environmental, health and safety concerns.

The point in the document that is relevant to this study as outlined in the policy is about the mitigation of environmental, health and safety adverse impact on energy utilization.

Test uncontrollable variables (Meteorological parameters)

The meteorological conditions that has a great impact on oven performance are temperature, wind speed, precipitation and insolation. The illustrations below discusses how the optimum performance is determined by the meteorological conditions:

1. Wind speed should preferably be less than 1m/s and not exceeding 2.5m/s for over 10 minutes during test period.
2. Ambient temperature should be between 20°C and 35°C at the test site.
3. Water temperature should be 5°C above ambient temperature when starting tests and recorded at 5°C below the local boiling point.
4. Preferred insolation is between 500W/m[2] and 1100W/m[2].
5. Precipitation- no test should be done when there is precipitation of any kind (ASAE S580).

Also of paramount knowledge prior to solar oven usage is that the best solar irradiation time is from 9:00am to 4:00pm (Kimambo, august 2007).

Test controlled variables (cooker)

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Table 1: showing the controllable variables in oven testing.

Material analysis

Plywood

Oven made from plywood are durable than those made of cardboard and have the ability to withstand pressure exerted when using for longer periods of time. They prove to be easily modifiable in building oven of any size unlike cardboard where size of the oven is predetermined by the available size of cartons.

Cotton wool

Can easily be found almost in every locality. There is a good number of districts in Malawi which grow cotton. In extreme cases even a piece of cloth made from cotton can also be used and personal experience shows that most clothes designed for cold weather season contain a layer of cotton. The tattered ones can be stripped of the cotton and used for insulating the oven chamber.

Polystyrene plastic

Polystyrene plastics in the oven act as a temperature retention material and usually incorporated as part of insulator. But in this project it was specifically used to protect the oven chamber from dampness caused by water spillage even though it was inevitable to avoid it performing its insulating function. They can easily be found and in this scenario they were obtained from grocery A for free as they were used as kamba puffs packaging bags.

Newspapers

They have been used in many solar oven projects as insulators. Mostly crumpled or shredded and used to fill the cavity between boxes (the Pembina Institute, a renewable energy project kit).

Aluminum metal plate

It was used to cover the inside of the cooking chamber. This was basically to increase the thermal conversion of solar irradiation by the oven as it has a higher thermal conductivity as compared to wood (Serway and Jewett, college physics: 7th edition).

CHAPTER 3

3.0 MATERIALS AND METHODS

The solar oven of which its performance has been evaluated using the ASAE S580 (2003) with suggestions by Shawn Shaw (2008) incorporated was made of two plywood boxes one inside the other. The cavity between boxes was filled with newspapers and cotton wool was used as an additional insulating material. The fitted boxes acted like the cooking chamber and the inside was covered with aluminum metal plate. Polystyrene plastic was used to cover the surface of metallic plate. The inserted metal plate was incorporated to increase thermal conversion of sun light into heat energy. Reflectors were made of cardboard and covered with aluminum tin foil. Wood glue was used to stick the foil to the cardboard surface whereas cardboards were pieced together using ‘bolstic' glue. The chamber was covered with glass plate to act as the receiver and also as a heat retention lid.

The solar oven was tested using the American Society of Agricultural Engineering Standards (ASAE S580) developed by Dr. Paul Funk (1998). However due to inaccuracy of the ASAE S580 procedure in addressing issues like:

- Reproducibility
- Understandability
- Efficiency
- Objectivity,

the procedure however incorporated the New Testing Standards on cooker performance developed by Shawn Shaw ( 2008) of The Department Of Physics, Applied Physics, And Astronomy At Rensselaer Polytechnic Institute.

The research method employed for testing in this report was the absolute performance assessment using a standard test method. The procedure entailed:

a. Cooking performance

The testing reported in this scenario involved the rate at which heat was transferred to water in a cooking pot. It indicates how quickly temperature rise was registered by the oven.

b. Testing to a standard method

The standard test method developed by Dr. Paul Funk (1998) has been utilized in this project though there was no precise following as suggestions by Shawn Shaw (2008) were also incorporated.

- A single number as a measure of oven performance was derived.

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