Solar cookers for outdoors and indoors

The solar cooking process has been investigated to develop safe, simple, portable, and reliable solar cookers. The concept of insulated and vapor-tight pots has been introduced and applied to oven, point-focus and heat-pipe cookers. A new, flat-plate cooker with heat pipes has been developed. It requires no tracking and allows cooking to be done in the shade or indoors. Also, a novel-portable cooker, the Mina Oven, featuring a vapor-tight pot and an integral collector with reflector flaps, has been constructed and tested. A second portable cooker that has been developed is the Arafa Cooker, which comprises a parabolic dish focused at a glazed and insulated receiver. Experiments indicated that all cookers yielded satisfactory performance, with cooking times of 25–45 min per kg of food per m² of solar collection area while operating from 10 a.m. to 4 p.m.     

Development of a domestic concentrating cooker

A Fresnel type domestic SPRERI concentrating cooker was designed and developed. The cooker has an aperture area of 1.5 m² and a focal length of 0.75 m and was found to provide an adequate temperature needed for cooking, frying and preparation of chapatis. The cooker was found capable of cooking food for a family of 4 to 5 persons. Details of development of this cooker and the tests conducted are given in this paper.     

A parabolic solar cooker with automatic two axes sun tracking system

A parabolic solar cooker with automatic two axes sun tracking system was designed, constructed, operated and tested to overcome the need for frequent tracking and standing in the sun, facing all concentrating solar cookers with manual tracking, and a programmable logic controller was used to control the motion of the solar cooker. The results of the continuous test – performed for three days from 8:30 h to 16:30 h in the year 2008 – showed that the water temperature inside the cooker’s tube reached 90 °C in typical summer days, when the maximum registered ambient temperature was 36 °C. It was also noticed that the water temperature increases when the ambient temperature gets higher or when the solar intensity is abundant. This is in favor of utilizing this cooker in many developing countries, which are characterized by high solar insulations and high temperatures. Besides cooking, the proposed cooker could be utilized for warming food, drinks as well as to pasteurize water or milk.     

Multiple use communal solar cookers

Solar cooking in boarding schools and communal centres in isolated areas demands the heating of large quantities of food. It is generally done in large pots of 30–40 litres. In a previous paper (Saravia et al., Energías Renovables y Medio Ambiente, ASADES, 1999, 6, 7–16), the solar cooker presented consisted of two separate units: a concentrator on one side and an insulated box containing the pot on the other. In this paper we introduce some changes which improve its working capacity. At present we can count on three different kinds of absorbers, which have been optimised to fulfill different functions in a concentrator of an area of 2 m². These alternatives allow the possibility of satisfying the needs of a communal dining centre, cooking for up to 30 children, once each concentrator has been installed.     

Gasification of rice straw in an updraft gasifier using water purification sludge containing Fe/Mn as a catalyst

This study investigated the feasibility of gasification of rice straw using an Fe/Mn sludge as a catalyst. The Fe/Mn sludge contained iron and manganese compounds produced from a water purification plant. The gasification temperature and equivalent ratio (ER) was set at 900 °C and 0.30, respectively, with an amended catalyst ratio of 0%–15%. Experimental results indicated that the combustible gas production was increased from 0.61 m³/kg to 0.72 m³/kg with the Fe/Mn sludge addition. The lower heating value (LHV) of combustible gas and energy density (ED) were also increased with an increase in Fe/Mn sludge addition. The LHV and ED increased from 14.76 MJ/Nm³ to 15.82 MJ/Nm³ and from 1.37 MJ/MJ to 1.47 MJ/MJ, respectively. In conclusion, the catalytic gasification of rice straw was more efficient on an energy yield basis with the Fe/Mn sludge addition. The Fe/Mn sludge used in this research has been developed as a potential catalyst for the application of rice straw gasification.     

The performance of a solar cooker in Egypt

A simple, efficient solar cooker was designed and its performance in the Egyptian climate was evaluated. The cooker is of the hot box type with a plane booster mirror reflector. The performance of the cooker was measured experimentally for over two years under different working conditions. The test conditions included experiments with and without adjusting the cooker's position for maximum solar radiation and the tilt angle of the booster reflector for maximum concentration. Formulas for calculating the orientation angle of the oven and tilt angle of the reflector were deduced. The shadow effect caused by the sides of the oven was also calculated. The solar cooker proved to be reliable, trouble free and efficient. All kinds of food were cooked including meat, chicken, rice, peas, beans, potatoes, soup, eggs and cakes. A good meal for a family of four was cooked in 3–4 h. It was established that better heat transfer occurred when the cooking pot was covered with an airtight plastic transparent cover rather than using an ordinary metallic cover. The energy balance of the cooker from heat transfer considerations enabled estimates of both over and food temperature to be made. Calculated values agreed well with the experimental measurements.     

Fabrication of and performance studies on a low cost solar cooker having an inclined aperture plane

A low cost box-type solar cooker made of two paper carton boxes with crumpled newspaper balls as insulation has been fabricated with a tilted aperture plane. Comparative tests of this cooker have been conducted against a normal type costlier solar cooker with 1000 ml load of water in each of the cookers. It has been observed that on a sunny day water temperature initially increases more rapidly in the new cooker compared to the normal type cooker. But at temperatures higher than 90°C both the cookers perform similarly. Two figures of merit F₁ and F₂ have also been found to be satisfactory. An arrangement of low cost auxiliary heating using a 100w electric bulb inside a blackened metal casing allows the carton box cooker to reach cooking temperatures under cloudy conditions with ease when the normal type solar cooker fails. The cost of materials for the new cooker is within US $10 and has been observed to be as effective as the normal type solar cooker which requires between US $40 and $65 to fabricate.     

Electricity generation from rice straw using a microbial fuel cell

This study demonstrated electricity generation from rice straw without pretreatment in a two-chambered microbial fuel cell (MFC) inoculated with a mixed culture of cellulose-degrading bacteria (CDB). The power density reached 145 mW/m² with an initial rice straw concentration of 1 g/L; while the coulombic efficiencies (CEs) ranged from 54.3 to 45.3%, corresponding to initial rice straw concentrations of 0.5–1 g/L. Stackable MFCs in series and parallel produced an open circuit voltage of 2.17 and 0.723 V, respectively, using hexacyanoferrate as the catholyte. The maximum power for serial connection of three stacked MFCs was 490 mW/m² (0.5 mA). In parallelly stacked MFCs, the current levels were approximately 3-fold (1.5 mA) higher than those produced from the serial connection. These results demonstrated that electricity can be produced from rice straw by exploiting CDB as the biocatalyst. Thus, this method provides a promising way to utilize rice straw for bioenergy production.     

Evaluation of low cost cathode materials for treatment of industrial and food processing wastewater using microbial electrolysis cells

Microbial electrolysis cells (MECs) can be used to treat wastewater and produce hydrogen gas, but low cost cathode catalysts are needed to make this approach economical. Molybdenum disulfide (MoS₂) and stainless steel (SS) were evaluated as alternative cathode catalysts to platinum (Pt) in terms of treatment efficiency and energy recovery using actual wastewaters. Two different types of wastewaters were examined, a methanol-rich industrial (IN) wastewater and a food processing (FP) wastewater. The use of the MoS₂ catalyst generally resulted in better performance than the SS cathodes for both wastewaters, although the use of the Pt catalyst provided the best performance in terms of biogas production, current density, and TCOD removal. Overall, the wastewater composition was more of a factor than catalyst type for accomplishing overall treatment. The IN wastewater had higher biogas production rates (0.8–1.8 m³/m³-d), and COD removal rates (1.8–2.8 kg-COD/m³-d) than the FP wastewater. The overall energy recoveries were positive for the IN wastewater (3.1–3.8 kWh/kg-COD removed), while the FP wastewater required a net energy input of −0.7–−1.2 kWh/kg-COD using MoS₂ or Pt cathodes, and −3.1 kWh/kg-COD with SS. These results suggest that MoS₂ is the most suitable alternative to Pt as a cathode catalyst for wastewater treatment using MECs, but that net energy recovery will be highly dependent on the specific wastewater.     

Experimental testing of a box-type solar cooker using the standard procedure of cooking power

A box-type solar cooker with one (Model I) or four (Model II) cooking pots was constructed and tested under Tanta prevailing weather conditions. Experiments were performed during July 2002 using the cooker with or without load. The obtained results were employed to calculate the two figures of merit, F₁ and F₂, as well as the utilization efficiency η_u and the specific t_s and characteristic t_c boiling times. The obtained values of F₁ indicate that the cooker can be used twice a day for consecutive cooking. F₂ was found to increase almost linearly with the mass of the cooking fluid M_f. The cooker is able to boil 1 kg of water in 15 min when its aperture area equals 1 m². Furthermore, experiments also considered the requirements for the international standard test procedure for solar cookers. The cooking power P was correlated with the temperature difference ΔT between the cooking fluid and the ambient air. Linear correlations between P and ΔT had correlation coefficients higher than 0.90 satisfying the standard. The obtained values of the initial cooking power, heat loss coefficient and the cooking power at a temperature difference of 50 °C agree well with those obtained for small solar cookers. The present cooker is able to cook most kinds of food with an overall utilization efficiency of 26.7%.     

Design and development of efficient multipurpose domestic solar cookers/dryers

A truncated pyramid-type solar cooker is designed, fabricated and tested. The truncated pyramid geometry concentrates the incident light radiations towards the bottom and the glazing glass surface on the top facilitates the trapping of energy inside the cooker. One of the salient features of the proposed design is to completely eradicate the need for tracking the sun during cooking, as tracking of sun does not yield better performance. During testing, the highest plate stagnation temperature, under no-load condition, approached 140 °C and under full-load condition, water temperature inside the cooker reached 98.6 °C in 70 min. Two figures of merit, F₁ and F₂, were calculated and their values were 0.117° C m²/W and 0.467 °C l, respectively, meeting the standards prescribed by the Bureau of Indian Standards for solar box-type cookers. Minor modifications in design are recommended to achieve higher temperatures and reduce cooking times. The design also allows trays to be retained for use as a household dryer.     

Design and fabrication of low cost solar water heaters

We designed two types of very low cost solar water heaters which do not need a water supply connection. The first one consisted of two plastic bowls, one inside the other with 5 cm thickness of insulation in between. A transparent plastic cover was tied around the smaller vessel. It was found that water placed inside the smaller vessel had its temperature raised by 18°C from the ambient temperature within four hours when the average insolation was about 600 kWh/m². The second one consisted of two earthen vessels in place of plastic bowls. The water temperature rise was 20°C under the same radiation. If either of the heaters was covered with cotton-wool insulation in the afternoon, the temperature remains 13°C above the ambient early next morning. The cost of the material was around US$ 4.50 for the plastic bowl heater while this is around US$ 3.50 for the earthen vessel water heater.     

Performance evaluation of a hot‐box reflector solar cooker using a microcontroller‐based measurement system

The performance of a low‐cost compound box‐reflector solar cooker designed and constructed by the department of Mechanical Engineering, at the University of Zimbabwe, was investigated and evaluated using a microcontroller‐based measurement system over a period of 3 months. Solar radiation and temperature measurements are sent directly to the computer for monitoring and subsequent analysis using a spreadsheet program. The system is connected to the computer through the RS232 port. Temperature was measured by LM335 temperature sensors, whereas solar radiation was measured by a Kipp & Zonen CM3 thermopile‐based pyranometer that was initially calibrated against the Eppley Precision Spectral Pyranometer. Peak temperatures of about 90°C for the food can be attained in about 5 h on a clear day in Bindura, Zimbabwe (18°S, 31°E). A standardized cooking power of 11 W and an overall efficiency of 15% were found for this cooker. Copyright © 2008 John Wiley & Sons, Ltd.     

Current status and prospects of biomass resources for energy production in Lithuania

Basic biomass sources in Lithuania are comprised of wood, straw, biofuel and biogas. The current status and the problems from using biomass for energy production in Lithuania are analyzed. The possibility of utilizing wood waste, firewood, straw and biogas for energy is evaluated. Forest comprises about 2.05 Mha or 31.3% of Lithuanian land area. About 4.3 million m³ solid volume of wood per year can be used for fuel (843 ktoe). Wood as fuel is used directly or in processed form (briquettes, pellets and chips).Agriculture produces approximately 1.5–2.0 million tons of straw each year for animal feed, litter and olericulture. Around 30–40% (130 ktoe) could be used as fuel for energy production. Boiler houses for combusting the straw have increased and now comprise about 7 MW. Straw is also used for heating private houses.Sources for biogas production include sludge from water cleaning equipment, animal manure and organic waste in food processing companies. Total volume of operating bioreactors comprises about 24 000 m³, and annual production of biogas is 6.3 million m³ per year (3.4 ktoe). By year 2010 the total volume of bioreactors will increase to 35 000 m³ and about 50 000 m³ by 2040.In Lithuania biodiesel and bioethanol are mainly used in blending with conventional fuel. Following the requirements of the European Union (EU), 2% of total consumed fuel per year is to be produced in 2005. By 2010 biofuel should comprise not less than 5.75% of all fuel existing in the market.     

Pyrolysis–gasification of post-consumer municipal solid plastic waste for hydrogen production

Post-consumer plastic waste derived from municipal solid waste was investigated using a two-stage, catalytic steam pyrolysis–gasification process for the production of hydrogen. The three important process parameters of catalyst:plastic ratio, gasification temperature and water injection rate were investigated. Temperature-programmed oxidation (TPO) and scanning electron microscopy (SEM) methods were used to analyse the reacted catalysts. The results showed that there was little influence of catalyst:plastic ratio between the range 0.5 and 2.0 (g/g) on the mass balance and gas composition for the pyrolysis–gasification of waste plastics; this might be due to the effective catalytic activity of the Ni–Mg–Al catalyst. However, increasing the gasification temperature and the water injection rate resulted in an increase of total gas yield and hydrogen production. The coke formation on the catalyst was reduced with increasing use of catalyst; however, a maximum coke formation (9.6 wt.%) was obtained at the gasification temperature of 700 °C when the influence of gasification temperature was investigated. The maximum coke formation was obtained at the water injection rate of 4.74 g h⁻¹, and a more reactive form of coke seemed to be formed on the catalyst with an increase of the water injection rate, according to the TPO experiments.     

Impact of direct solar irradiance on heat transfer behind an open-jointed ventilated cladding: Experimental and numerical investigations

This paper is based on the study of an experimental wooden-framed house, equipped with a ventilated cladding, located in France. The focus is on investigating the heat transfer taking place in the ventilated air gap behind the cladding and on estimating their impact on heat transfer in the insulated part of the walls.Preliminary CFD simulation made it possible to describe the airflow in the ventilated air gap when buoyancy was acting as the main driving force. It was found that the airflow velocity could reach 0.8 m s^?1, when exposed to 570 W m^?2 solar irradiance. This was verified experimentally. A correlation to assess airflow rate in the air gap behind the cladding has been developed based on temperature differences and on experimental conclusions. The correlation is adapted to energy performance simulation and efficiently represents the average cavity airflow at different height for various irradiance and temperature conditions.     

Mathematical modeling of a box-type solar cooker employing an asymmetric compound parabolic concentrator

A novel design of solar cooker is introduced. The cooker is of box-type equipped with an asymmetric compound parabolic concentrator (CPC) as booster-reflector. It consists of an insulated box equipped with a vertical double glazing cover on a side, and a vertical absorber plate laid out just behind the transparent cover. The booster-reflector is fixed on the glazed side of the box. The absorber plate and the glazing form a vertical channel, open at the top and bottom, and enclosed at the sides. The two openings allow the inside air circulation. A mathematical model of the heat transfer processes involved with this solar cooker, containing a cooking pot loaded with water and deposited on the box floor; was developed and the effects of various parameters, such as solar radiation, load of water and clouds on the dynamic behavior of the cooker are studied.     

On-line recording of solar cooker use rate by a novel metering device: Prototype description and experimental verification of output data

A metering device for the determination of solar cooker use rate is presented. The device records food temperature, ambient temperature and irradiance. Automatic data evaluation yields the number of cooking cycles, cooking time, food “thermal mass”, as well as the impact on fuel consumption and GHG emission compared to other cooking techniques. Metering results are compared with actual conditions for box-type and concentrating solar cookers and found to be in agreement.     

The boiler concept for combustion of large soya straw bales

In one of the largest agricultural companies in Serbia, with over 2000 ha of soya plantations, there are 4000 t/year of baled soya straw produced. Soya straw biomass is planned to be used as a renewable energy source for heating the greenhouses, with 5 ha in area. Therefore, efforts have been made to develop a technology for utilizing large bales of soya straw for energy production. In the first phase, a demo energy production facility-furnace was developed and built. The facility had been tested in order to examine the quality of combustion of large soya straw bales. Since experimental results of testing of this facility have proved to be very satisfactory, in the second phase of the development, a hot water boiler of similar characteristics (burning soya straw bales, with dimensions 0.7×1.2×2.7 m³) has been designed.