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Introduction

Cooking is major necessity for people all over the world. The problem arises when fuel is either scarce or highly expensive. The problems are encountered more pronounced in the developing countries, and particularly in villages and rural areas. Cooking accounts for a major share of energy consumption in developing countries. Most of the cooking energy requirement is met by non-commercial fuels such as firewood, agricultural residues or animal dung in rural areas. The cutting of firewood causes deforestation that leads to desertification. There is a critical need for development of alternative, appropriate, affordable methods of cooking for use in developing countries. There are very favourable climatic conditions in India for all solar energy applications. Solar cookers seem to be a good substitute for cooking with firewood for widespread use in country. The use of solar cookers would not only help in conservation of conventional fuels but also result in the reduction of the release of carbon dioxide (CO₂) into the environment.

Several types of solar cookers have been designed in the past four decades. According to the Ministry of Non-Conventional. Energy Sources (MNES),¹around 340,000 family-sizes, box-type solar cookers were sold by January1995. However, in view of the fact that a majority of the population in rural and semi-urban areas of India has access to non-commercial fuels at rather low prices, it is important that the investment in a solar cooker is financially viable to them. Many technically and economically feasible solar cookers are in operation, no broadly valid basis for comparing the achieved performance of one solar cooker with that of another operating under different conditions has found general acceptance.

Fig. 1 shows the breakup of demand of solar cookers in three continents. Table 1 shows the scenario of solar cookers demand in Asian countries.²

In this chapter, the study has been based on weather conditions of India for evaluating cooking time at various load and compared with Kandpal model. Finally, carbon credit earned by box type solar cooker has been estimated as per norms of Kyoto Protocol.

Description of Box-Type Solar Cooker

A box-type solar cooker (Fig. 2) consists of a rectangular enclosure which is usually fabricated of fiber-reinforced plastic (FRP)/ galvanized iron (GI)/aluminum sheet. A trapezoidal, blackened aluminum tray is housed in the enclosure which absorbs solar radiation. Generally, glass-wool padding of 5 cm thickness is used to insulate the tray from heat loss. The tray is covered with a 3-4 mm thick, double-glass lid having a gap of 1 cm between the glasses. The lower glass is usually toughened to avoid cracking during cooking. A silvered or aluminized glass reflector is attached to the inner side of the cover to enhance input radiation. Blackened aluminum or stainless steel pots are used for cooking.³

Figure 1: Worldwise distribution of ½ billion urgently needed solar cookers Click here to view figure

As per requirement, solar cookers of different sizes may be used. The family-size (aperture area,A_p= 0.25 m²) solar cooker, standardized by the MNES, is reported to be suitable for cooking meals for 4-5 persons.⁴

Analysis of Total Incident Radiation on Solar Cooker

There are two types of radiation incident on the double glass cover of the container of the solar cooker. One is the direct incident and other one is the reflected from the reflector. The total incident radiation (I_T) is obtained from the following relation⁵

Figure 2: Schematic diagram of a box type solar cooker Click here to view figure

Solar radiation incident on horizontal glass cover =I_H...(1)

Solar radiation incident on vertical reflector =I_v

=IBHRb+ IDHRd+ ρ RrIH...(2)

where...(3)

I_BH= Beam radiation on horizontal surface

I_DH= Diffuse radiation on horizontal surface

ρ = ground reflectivity which is equal to 0.2

R_bfactor for eqn. (2) is calculated as


whereθ_iandθ_zare the angles of incidence on inclined and horizontal surfaces respectively.

cos θ_zandcos θ_ifor eqn.(3) may be evaluated fromthe following relations

cosθ_z= cosΦ cosδ cosω + sinδ sinΦ ... (4)

and

cosθ_i= - sinδ+cosΦ+ cosδcosωsinΦ ...(5)

where Φ is lattitude angle (28^o35’N for New Delhi) and hour angle,ωis calculated from local solar time,STas

ω = (ST-12) 15° ...(6)

and declination angle,is found from the following expression

R_dr= 23.45 sin[360/365 (284+n)]...(7)

where n is number of days in a year

RR = 11 cos/22...(8)

where is inclination of the surface

Solar radiation reflected by reflector and received by horizontal glass cover =ρ_gI_v

where ρ_gis reflectivity of glass and is equal to 0.8 Hence total radiation received by glass cover

= I_T= I_H+ 0.8x I_v...(10)

表2显示了平均每小时总入射辐射falling on cooker with air mean temperature.

Figure 3: Cooking time in hours for various load of box type solar cooker Click here to view figure

Estimation of Solar Cooking Time

In present analysis, time for cooking between 10 AM to 2PM from box type solar cooker has been evaluated for various loads viz. 0.5 kg to 2kg from the following relation.⁵

...(12)

The equation is modified as

...(13)

after substituting value T_w= T_band T_wo= T_aand compared to Kandpal model^6,7

...(14)

WhereF₁andF₂^6,7are the two figures of merit of a solar cooker which characterize its thermal performance,His the hourly insolation onAand Σm₁c₁.The total heat capacity of the load (raw foodplus water) as shown in Fig. 3.

Figure 4: Payback period of solar cooker Click here to view figure

Energy Conservation

In comparison with open fire, saved primary energy by using solar cooker can be written⁸as:

E[T_bT_aC_pm]per day...(15)

This givesE=[(100-20) K 4.18kJ/kg/ K 3kg] =1003.2 kJ per day

Therefore primary energy saved per

person=E/ =3.4MJ per day...(15a)

where η₀is the overall efficiency

If sun is available for 300 days in a year. Then annual saved primary energy for a family of 5 persons is:

SPE_annually= (E/₀) 300×5 = 3.4 MJ×300×5

= 5100 MJ per family...(15b)

If the meal cooked by the solar cooker for a single household, then amount of fuel saved per year is calculated from the following relation

where

m_f= mass of fuel saved per year, kgH.V. = Heating value of the fuel, KJ/kg

= Burning efficiency of the fuel device in % age

Figure 5: Variation of carbon credit earned by solar cooker with of rural household Click here to view figure

CO₂Mitigation

By considering different fuels (firewood/ dung cake/charcoal/kerosene etc.), the CO₂emissions for each fuel is calculated_.In order to estimate CO₂emissions from different fuel for a single household energy (SPE_annually), the following expression is adopted [9] as:

₀log[(M) /(a b)] log[(E M) /(a b)_10,11C]
^{___________________________________}

log[(1a) /(1b)] ...(17)

wherec= Fraction of carbon contents multiplied by 44/12. From the eqn. (17), CO₂emissions are calculated for different fuels. The

Table 3 shows fuel saved in Indian Rupee and CO₂emissions in kg for a single household.

Table 1: Demands of solar cookers in Asian countries by 2050 Click here to view table

Table 2: Mean hourly solar radiation on solar cooker Click here to view table

There are 602 districts and 127800 villages in India based on 2005 statistics and as per 2001 census. Each village has more than 1000 population. Most population of India lives in rural areas. Therefore total population of rural areas was 127.8 million in the year 2001.

Present population is given by the equation¹⁵

where is population in thenth year,P₀

population in the 0^thyear (the year 2001;P₂₀₀₁=127.8 million) andiis the annual growth rate in the population, which equals to 2%.

The rural population in the current year will be as

P₂₀₀₉P₂₀₀₁(1 0.02)⁸P₂₀₀₁1.1717

=127.8 million1.1717

=149.743 million

Then total number of families in rural areas

= 149.743 million

= 29.95 million. ...(20)

Carbon Credit Earned by Solar Cooker

Using eqn. (15b) and eqn. (20), the annually primary energy saved in rural areas is 29.95 million 5100 MJ =152745×10 ³ GJ or 42430×10 ⁶ kWh.

The average CO ₂ equivalent intensity for electric generation from coal is approximately 0.982 kg of CO ₂ per kWh at source ^16,17 . However, 40% is transmission and distribution losses and 20% loss is due to the inefficient electric equipment used. Then the total figure comes to be 2.04 kg of CO ₂ / kWh.

So, the CO ₂ emission reduction = 2.04×4243010 ⁶ kg = 86557.210 ³ ton. Then CO ₂ emission reduction by solar cookers ¹⁴ comes to USD (86557.2×10 ³ ×21×1.14165) = USD 2075.2 million per annum. Variation of carbon credit earned with household in rural areas is mentioned in figure 5.

Table 3: Quantity of Fuel and CO2 emissions per annum Click here to view table

Results and Discussion

Eqn。(1)和(2)计算使用MATLAB的software for evaluating the hourly total incidence radiation falling on solar cooker by considering Indian climate conditions. The results are tabulated in Table 2. The eqn. (13) and (14) have been used for calculating monthly cooking time from solar cooker. The comparisons are shown in Fig. 3. Figure shows that lowest cooking time is in the months of April and May and maximum in July and August due to the availability of solar radiation. From the Table 3, it is observed that CO2 emitted by LPG is minimum followed by biogas, kerosene, charcoal and firewood. There is a need to promote renewable energy in rural areas because of non-availability and costlier LPG. The saving of CO2-emission is credited to those who use the solar cookers. Moreover interior cooking enhances the risk of lung and eye diseases that affect millions of people world wide. Free energy will give extra profit for food sellers who use solar cookers for cooking. Assembling, spreading and using of solar cookers create jobs. Indeed, we need to encourage future projects and to multiply clean development mechanism solar cooker projects.

The figure 4 shows that the payback periods based on economic analysis are in increasing order with respect to fuel: charcoal, firewood, LPG and kerosene etc whereas the value of payback period for kerosene fuel is highest, i.e., 1.08.

Conclusion

This paper gives the detailed analysis of box type solar cooker .The cooking time for various loads has been evaluated. The results are compared with Kandpal model as shown in Figure 3. Conventional fuel cost saved for domesting cooking and CO ₂ reduction per annum are tabulated in Table 3 If this type of project is installed only in 20% of the Indian rural areas then the carbon credit earned by the system is USD 415 million (Indian Rs. 199 crores) annually.

The total carbon credit earned by the system is USD 2075.2 million (Rs. 995 crores) installed in rural areas annually.

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