Design, Development and Testing of a Portable

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Renewable Energy 32 (2007) 257–266

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Design, development and testing of a portableparabolic solar kitchen

Jose M. Arenas�

Universidad Politecnica de Madrid (UPM), E.U. Ingenierıa Tecnica Industrial, C/ Rondad de Valencia, 3,

Madrid 28012, Spain

Received 2 July 2005; accepted 31 January 2006

Available online 23 March 2006

Abstract

In this project we describe the design, manufacture and testing of a new portable solar kitchen with

a large, parabolic solar reflector that folds up into a small volume. Technical trials carried out with a

prototype have determined that the solar kitchen reaches an average power scale of 175W, with an

energy efficiency of 26.6%. This power scale provides sufficient energy to cook a simple meal for two

people in an average time of 2 h. Improvements in the design have reduced the weight of the solar

kitchen to less than 5 kg and the assembly and disassembly times to 2 and 1min, respectively.

Moreover, its competitive price (48.62 h) encourages the substitution of solar energy for conventional

energy. The parabolic solar kitchen described here thus provides a portable, inexpensive,

environmentally friendly food heating system that can improve the quality of life of needy people

in the Third World and reduce consumption of conventional energy.

r 2006 Elsevier Ltd. All rights reserved.

Keywords: Parabolic solar kitchen; Portable; Energetic efficiency; Payback period

1. Introduction

Over the past few years, planetary climate change has demonstrated itself in numerousways. One of the most outstanding examples has been the prevalence of prolongeddroughts in the deprived areas of Africa (although also in other regions of Australia,America, etc.). Affected regions have experienced a considerable loss of vegetation, due not

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ARTICLE IN PRESSJ.M. Arenas / Renewable Energy 32 (2007) 257–266258

only to the drought itself but also to the extensive forest fires that these conditionsprovoke. The population of these regions is generally nomadic, has little or no access toresources, and uses wood fires to heat food. The persistent droughts therefore add the lossof capacity to heat food to an already precarious situation.With the objective of contributing to a resolution of this situation, various sophisticated

(and normally expensive) techniques have been developed. The most satisfactory systemsare those based on the use of renewable energy (wind, tides, sun, etc.), since they give cleanand inexpensive energy if selected with due consideration to their intended surroundings.In this spirit, it would seem advisable to analyse solar energy possibilities as a means of

heating food in drought-affected areas since the regions in question normally haveabundant solar radiation. In India, for example, the arid areas have an annual radiation ofbetween 7600 and 8000MJm�2 [1].

1.1. Historical background of the solar kitchen

The first solar oven was made by the naturalist Louis Leclerck (1707–1788).Nevertheless, Horace-de-Saussure (1740–1799) was the first technician to use solar energyto heat food. The French physicist Augustin Mouchot described the first solar kitchen inhis book ‘‘La chaleur-solaire’’, published in Paris in 1869. This same book indicates thatthe British astronomer Sir John Herschel created the first solar kitchen in South Africabetween 1834 and 1838.Since that time, a great deal of work has been put into improving solar kitchens. The

developments made during the second half of the 20th century are particularly important.At the beginning of the 1950s, a large solar kitchen was designed and manufactured using areflector [2,3]. Later on in the 1960s and 1970s, new types of reflectors were made thatimproved the technical characteristics of the solar kitchen [4–7].The limitations of these first reflecting solar kitchens (the requirement of constant re-

adjustment towards the sun, complex design, etc.) motivated the almost simultaneousdevelopment of other solar kitchen systems. Among these, the most used were the solaroven and the ‘‘solar hot box’’.In the solar oven design a solar collector was installed on the outside of the house, while

the cooking chamber was located inside [8,9]. Although the energy output of the solar ovenwas good, it still needed constant re-adjustment towards the sun. It was large in volume,complex, and above all had a very high economic cost.The solar hot box was a closed, thermally insulated receptacle heated by a flat reflector

oriented towards the sun [10–12]. This system also needed constant re-adjustment towardsthe sun, and was greatly affected by the intermittence of solar radiation.For these reasons, over the past few years, investigation of solar kitchens has been

focussed on improving technical performance (less frequent re-adjustment towards the sun,improved thermal insulation, etc.) and reducing manufacturing costs.

1.2. Portable solar kitchens

A common characteristic of potential solar kitchen users is that they travel frequently(from their house to arable land, to the mountain, etc.). On many occasions, the areas theygo to also change depending upon the agricultural or livestock season.

ARTICLE IN PRESSJ.M. Arenas / Renewable Energy 32 (2007) 257–266 259

In addition, these users generally have little economic capacity and the cost ofpurchasing a solar kitchen must therefore be minimal. An increased use of free solar energyrather than conventional sources (coal, oil, etc.) will also improve the economic capacity ofthe population and reduce atmospheric contamination.

Nevertheless the majority of solar kitchens are not conceived using these criteria, insteadhaving complex designs and high manufacturing costs. Over the past few years, however,research has been carried out along these lines focussing basically on closed box systemswith a parabolic reflector [13].

In the case of closed box solar kitchens, efforts have been made to improve the thermalinsulation of the receptacle and to increase its energy efficiency [14–16]. Standing out inthis field is the contribution of Nahar [17,18] who proposed the use of a double reflector todecrease the frequency of solar re-adjustment and a new transparent insulation material(TIM) to minimise convection losses in the solar kitchen. Although the solar kitchenproposed by N.M. Nahar is reasonably priced (approximately 50 h in materials), itsexcessive weight (around 20 kg) and volume (560� 560� 180mm3) make it difficult for theuser to travel long distances without consuming additional transport resources. Moreover,the design does not improve on the typical closed box limitation of restricting access to thefood during the cooking process, which in practice limits its use to baking.

On the other hand, solar kitchens with a parabolic reflector require large reflectionsurfaces to obtain a sufficiently high temperature. This imposes a complex design and tendsto increase both weight and volume.

For this reason most research has been carried out on fixed solar kitchens, focussing onimprovements in design such as the incorporation of new reflector materials (aluminiumfilm, silver-polymer/silver-steel technology and stretched membrane technology) and thereduction of manufacturing costs [19,20].

However, the increasing demand for portable solar kitchens has encouraged researchersto open new lines of investigation that are attempting to find a satisfactory solution to theproblems previously described.

The most outstanding progress in this field took place in the nineties, when updatedreflector designs were put forward based on concave parabolic cylinders [21,22], the use oflighter reflecting materials [23,24], or modular construction to make assembly anddisassembly easier [25].

Despite the specific advantages given by these new designs, however, a satisfactorygeneral solution was not found. In the present project a new solar kitchen with a foldablesolar reflector is therefore proposed, combining a large reflection surface with a smallvolume when folded up.

With reduced cost, minimum weight, and easy assembly and disassembly the proposedsolar kitchen is very competitive when compared with other energy sources and solarkitchen designs.

2. Design

The design of the kitchen incorporates both systemised design tools [26] and qualityimprovement techniques [27]. CAD (Inventor system) advanced techniques have been usedin its design, allowing a three dimensional construction by means of solid molding.

The parabolic solar collector is designed to be both adjustable and totally dismountable,with a screen and heat concentrator made from reflective, elastic aluminium film and


having light, rigid, metallic parabolic rods to extend and fold up the screen as required.The solar collector is divided into two units: the support and the reflector. The reflector inturn is divided into three sub-units: the parabolic dish, the tray and the handle (Fig. 1).A prototype conceptual design has been achieved by means of three-dimensional CAD

techniques and the simulation of various materials and joint movements. CAD systemutilities allow the automatic production of blueprints for the manufacture of the solarcollector components.The support is a tripod made with round aluminium tubes and flat aluminium bars

(alloy 6061, commercially named Simagaltok 61). The triangular structure has telescopic

Fig. 1. Schematic solar kitchen design: (a) support with telescopic legs, (b) assembly of reflector on support, (c)

automatic reflector opening, (d) assembly of grid, (e) solid solar kitchen model.


legs (maximum length 100 cm), giving the solar kitchen a stable footing on uneven groundand allowing any necessary inclination for the reflector.

The structure of the parabolic reflector is made up of a central body (where theautomatic opening mechanism is located) and a set of metal rods (some parabolic shaped,others straight) allowing the opening and closing of the reflector. All the elements areconstructed from aluminium (alloy 6061), and each parabolic rod has a length of 57 cm.The assembly achieves a reflection surface 100 cm in diameter when the structure iscompletely open. To facilitate the automatic opening and closing of the structure, a specialaluminium tube handle (alloy 6061) has been designed that screws into the central body.

Fig. 2. Solar kitchen components and assembly: (a) kitchen components and (b) ready for cooking.


The reflecting material is a film of metallised polypropylene 45 mm thick, with a lightreflection index of 99.9% and traction resistance of 45N/mm2 (MOPP CST 45, Type Ddesignation).A parabolic framework for the reflective surface is created using ten circulars sections,

which are joined to the parabolic rods with double reinforced beading.Saucepans and frying pans can be placed on the tray, which is provided with a grill and

an adjustment mechanism. Made of aluminium (alloy 6061), it is large and strong enoughto allow the use of saucepans (preferably black) of up to 25 cm in diameter with amaximum capacity of 5 l.The low weight of this solar kitchen (4.75 kg all included), together with its low volume

when folded (approximately the same as a conventional umbrella) make the kitchen easy totake anywhere. Additionally its simple design based on the use of threaded joints hasreduced the assembly (2min) and disassembly (1min) times of the solar kitchen to aminimum. In Fig. 2 the solar kitchen is shown before and after assembly.

2.1. Performance and trials

Numerous trials have been carried out to verify the performance of the solar kitchen.A black aluminium saucepan with 1.5 l of water was used in each trial. The ambienttemperature was measured with a digital thermometer, and the temperature of the waterwas measured using a thermopar probe (transmitting the measurement to an electronicscreen). The exposure time was 120min, with a re-positioning of the reflector every 20min.Fig. 3 shows the temperature variation of the water over time for one of the trials (the

15th of April at 13:00 h in Madrid). Throughout the trial duration, the solar radiationreceived by the reflector was measured using a calibrated photovoltaic solar panel.A simple analysis allows determination of the efficiency of the solar kitchen by means of

the following equation:

Z ¼Thermal energy used

Solar energy received� 100 ¼

ðmaca þmcccÞðtf � tiÞ

SR T

0 I dT� 100 ¼ 26:6%, (1)

0

20

40

60

80

100

0 10 20 30 40 50 60 70 80 90 100 110 120

time (min)

Tra

. (°C

)

600

650

700

750

800

850

900

950

1000

Rad

iati

on

(W

/m2 )

Tra. water °C Tra. Amb °C Radiation W/m2

Fig. 3. Variation of ambient temperature and water in the solar kitchen.


where ma is the water mass in saucepan (kg), ca the specific heat of water (J kg�1

1C�1), mc

the saucepan mass (kg), cc the specific heat of saucepan (J kg�1 1C�1), tf the final watertemperature (1C), ti the initial water temperature (1C), S the reflector cross-sectional area(m2), I the solar radiation (Wm�2min�1), T the time elapsed up to reaching a suitablecooking temperature (min).

An analysis of the remaining trials reveals that this solar kitchen design has an averagepower output of 175W and reaches suitable cooking temperatures after 35–40min ofexposure.

The results obtained confirm the ability of this solar kitchen to feed one or two people.A new prototype is being designed for larger groups, with a larger foldable parabolicreflector.

3. Manufacturing costs of the solar kitchen and capital payback period

The cooking time of a typical meal on a solar kitchen can be estimated as being 2 h, withan average energy consumption of 1260KJ (for two persons).

Considering an average use of 320 days a year (number of sunny days a year and twomeals a day), the energy saving that can be obtained from a solar kitchen is 806.4MJa year.

Table 1

Manufacturing cost of the solar kitchen

Solar kitchen sales price

Type Description Quantity U. Cost Total

Direct costs

Materials Aluminium tube 6061—Ø 25� 21 1.5m 3.6 h/m 5.40

Aluminium tube 6061—Ø 20� 15 1.5m 1.98 h/m 2.97

U shape aluminium strip 6061—25� 15� 2 0.3m 17.1 h/m 5.13

Round aluminium 6061—Ø 30 0.4m 4.9 h/m 1.96

Aluminium flat strip 6061—90� 55� 40 0.1m 8.22 h/m 0.82

Aluminium angle 6061—15� 15 0.8m 1.35 h/m 1.08

Aluminium rod 6061—Ø 5 10m 0.2 h/m 2

Aluminium flat strip 6061—60� 45� 5 0.1m 3.0 h/m 0.3

Metallised sheet MOPP CST 45 1.5m2 4 h/m2 6

Various (screws, nuts, split pins, etc.) — — 2.40

Total materials 28.06

Labour costs Assembly line (3 workers, 0.1 h, 25 h/h) 7.50

Use of machinery Amortisation costs of lathe, saw, planer, etc. (10% cost of material) 2.8

A. Total direct costs 38.36

Indirect costs

B. Cost of warehousing, auxiliary staff, etc. (6% direct costs) 2.30

Overheads

C. Company overhead (administration, technical staff, services, etc. 4% of direct and indirect costs) 1.62

Profit

D.Company profit margin (16% of total costs) 6.34

Price of the solar kitchen (A+B+C+D) h 48.62


The manufacturing cost of the solar kitchen is shown in Table 1. The direct costs(material, labour costs, and proportional cost of the machines used) and the indirect costs(warehousing costs, auxiliary staff, etc.) are listed separately. The sum total of the directand indirect costs makes up the cost of the solar kitchen itself. If we add to these costs theoverhead costs of the manufacturing company (administration, technical staff, generalservices such as electricity, water etc.), the total cost is reached.To this cost a profit margin is added, obtaining the profit for the company for each unit

manufactured. Taking into account all these data, the sales price of the solar kitchen is48.62 h (taxes not included).In Table 2, the thermal characteristics and costs of various fuels are shown, as well as the

corresponding economic savings that the use of a solar kitchen offers against theseconventional energies.The solar kitchen capital payback time is obtained by applying the following equation

[16]:

n ¼log½ðA�MÞ=ðr� iÞ� � log½ðA�MÞ=ðr� iÞ � C�

log½ð1þ rÞ=ð1þ iÞ�, (2)

where n is the Capital payback time (years), A the Cost of energy saved per annum (h/year), M the Annual solar kitchen maintenance costs (estimated at 5% of the cost of thekitchen), r the Compound annual interest rate (5%), i the Estimated inflation on energyand annual maintenance (3%), C the Cost of the solar kitchen (h).

Table 2

Thermal characteristics of conventional energy sources and annual economic savings obtained by using the solar

kitchen

Conventional energy sources

Type Heating capacity Efficiency (%) Unit cost (h) Amount necessary

per annum

Annual

saving (h)

Wood 19.89MJ/Kg 17.3 0.12 h/Kg 234.35Kg 28.12

Coal 27.21MJ/Kg 28 0.25 h/Kg 105.84Kg 26.46

Propane gas 45.59MJ/Kg 60 0.55 h/Kg 29.48Kg 16.21

Electricity 3.6MJ/Kwh 76 0.09 h/Kwh 294.73Kwh 26.52

Paraffin 45.55MJ/Kg 48 0.40 h/Kg 36.89Kg 14.75

Table 3

Payback time for conventional fuels

Fuel Capital payback period (years)

Wood 1.99

Electricity 2.14

Coal 2.15

Propane gas 3.80

Paraffin 4.26


In Table 3 the capital payback time for conventional fuels in accordance with Eq. (2) areshown. The lowest payback time is obtained using wood (1.99 years) and the highest usingparaffin (4.26 years).

As most of the material used for the solar kitchen is aluminium, a long life cycle isanticipated (more than 15 years); it should only be necessary to change the metallisedpolypropylene film every 5 or 6 years (a cost included in the maintenance term of Eq. (2)).

4. Conclusions

The principle feature of this solar kitchen is the radial folding of its screen (or parabolicheat concentrator), while the rest of the components can easily be assembled anddisassembled and take up little space.

Once opened the diameter of the screen is 1.00m, giving a solar collection area of0.78m2. The large and strong of the tray and supports allow the use of 250mm diametersaucepans (preferably black) with a capacity of 5 l.

The use of advanced CAD techniques and systemised design improvement methods havesimplified the design of the solar kitchen for the user, reducing the assembly (2min) anddisassembly (1min) times to a minimum. Even with all these improvements, the kitchencan be sold at a reasonable price (48.62 h).

The low weight (5 kg) and volume (approximately the same as a conventional umbrellawhen folded) of this solar kitchen make it easy to take anywhere using conventional meansof transport.

Trials carried out with the prototype have determined that the solar kitchen reaches anaverage power of 175W on a sunny day, assuming that adjustment toward the sun occursevery 20 or 30min. This supplies sufficient energy to cook a simple meal for two in anaverage time of 2 h.

This parabolic solar kitchen therefore provides a portable, inexpensive, andenvironmentally friendly food heating system, which will contribute to improving thequality of life of needy people in the Third World and reduce consumption of conventionalenergy.

Acknowledgements

The author is grateful to professors Rufino Horcajo and Manuel Gavilan of the MadridPolytechnic University, and to the scholar Sergio de Castro for their cooperation andsound suggestions on the design and manufacture of the prototype. Thanks also to theTechnology Transfer Office of UPM for the financing of the present Project (AS 0301).

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Design, Development and Testing of a Portable