Performance test of a box‐type solar cooker: effect of load on the second figure of merit

In this paper thermal performance test experiments for first figure of merit (without load) and second figure of merit (with load) of a box‐type solar cooker were conducted as per Bureau of Indian Standards. The values of second figure of merit (F₂) were determined for different loads of water and the results show that F₂ depends on the quantity of water loaded in a solar cooker. Therefore, it is recommended that the performance test method should specify the amount of water which is to be taken. Copyright © 1999 John Wiley & Sons, Ltd.     

Evaluating the optimum load range for box-type solar cookers

This paper introduces a new concept of Optimum Load Range (OLR) for solar cookers. OLR gives the load values for which cooker preferably shows good thermal as well as good cooking performance; it may be considered a crucial parameter for solar cookers. This OLR concept is based on the dependence of rate of rise of load temperature on different heat transfer processes between load and cooker interior. This concept illustrates solar cooking in two simple steps. The total time required to complete these steps puts an essential constraint for cooking of any load amount. The maximum value of load (upper limit of OLR) till which cooker shows satisfactory cooking may be determined from this constraint. This constraint requires determination of two OLR parameters which are t_{step I} and t_{step II}. The load for which cooker remain almost 30% efficient, may be referred as lower limit (minimum value) of OLR. For the verification of OLR, experimental studies have been conducted with a solar cooker named SFSC. The OLR parameters along with different thermal performance parameters (TPPs) (second figure of merit (F₂), utilization efficiency (η_u) etc.) suggested by different researches for solar cookers in water load condition have been computed from the measured thermal profiles of different loads (0.8–3.0 kg). From the curve analysis of different TPPs with load, the existence of upper limit of OLR is observed. The values of rate of rise of load temperature at water temperatures 80, 85 and 90 °C for different loads also confirm the same. The OLR of SFSC is found to be 1.2–1.6 kg.     

An investigation into sky temperature estimation,its variation,and significance in heat transfer calculations of solar cookers

The determination of sky temperature assumes great importance in engineering applications such as radiative cooling of buildings. Many studies that involve a radiative exchange with the sky employ different reported models of sky temperature interchangeably. However, until now, hardly any systematic study has been done to quantify the errors/variations that might be encountered in calculating this radiative exchange employing these different correlations. In the current paper, first, a thorough analysis has been presented on the sky temperature correlations and a possible range of variation in sky temperature based on the estimation of sky emissivity is computed. Both diurnal‐nocturnal variation in sky temperature and seasonal disparities in sky temperature have been reported. Next, the case of a box‐type solar cooker has been taken up for investigation with respect to the possible influence of the sky temperature estimation in predicting its performance parameter, first‐figure‐of‐merit on a daily, seasonal, and climatic basis. Our observations show an enormous difference in sky temperature depending upon the expressions of emissivity from which it is derived. The variability of sky temperature has a nominal influence on the prediction of first‐figure‐of‐merit, although a marked discrepancy is observed across the seasons at the same location.     

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.     

Enhancement the solar box cooker performance using steel fibers

The use of fossil fuel and wood for cooking poses health, environmental, and economic challenges, especially with the growing population. This has led to an increase in the trend towards the use of clean and sustainable cooking sources, including solar cookers. This experimental study aims to contribute by enhancing the performance of a solar box cooker (SBC) according to the concept of porous media via adding steel fibers inside the box as a modified SBC and comparing it with a conventional SBC. The stagnation test to determine the first figure of merit and the load test to determine the second figure of merit, standard boiling time, and cooker optothermal ratio were conducted under the outdoor conditions of Baghdad city. Also, an energy and exergy efficiency analysis, and calculating the rate of heat loss by three water loads heating and cooling tests. The results revealed that the modified SBC has a higher thermal performance than the conventional SBC.     

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.     

Optimum design criteria for solar hot water systems

This paper is concerned with the optimisation of some design criteria of SHW systems intended for residential and hotel applications. For this purpose, a system model based on TRNSYS programme has been used to correlate the performance and cost effectiveness of the system with a number of key design criteria which include the Collector to Consumer Factor (FCC) expressed in m² of collector per consumer and the Collector to Load Factor (FCL) expressed in m² of collector per annual GJ of thermal load.     

Studies on semi-cylindrical solar tunnel dryers: year round collector performance

In this paper, the results of year round thermal performance of collector of semi-cylindrical solar tunnel dryers (STD) has been presented. The calculations have been made under natural circulation and forced circulation mode. The day-long average of solar irradiance, ambient temperature, rise in the inlet air temperature, natural circulation volume flow rates, and collector efficiency have been calculated for each month of the year. The effect of collector length, cover radius, collector inclination with horizontal have been made for rise in inlet air temperature, volume flow rate and for the efficiency. All calculations have been made for Delhi climate. © 1998 John Wiley & Sons, Ltd.     

Development of thermodynamic cycles for concentrated solar power plants

Solar thermal power is a promising ‘green’ technology that could contribute significantly – in countries where it may be applicable due to available resources – towards meeting the 2020 and 2050 targets for the free energy production of emissions [Viebahn, P., Lechon, Y., and Trieb, F., 2011. The potential role of concentrated solar power (CSP) in Africa and Europe – a dynamic assessment of technology development, cost development and life cycle inventories until 2050. Energy Policy, 39 (8), 4420–4430]. Especially for the regions where solar radiation is significant, the technology of concentrated solar power (CSP) plants seems to have a great potential, once cost-related issues are resolved. The thermodynamic process, on which the component design of the plant is based, plays a significant role in the optimisation of the efficiency of the derived configuration. This paper aims to present a route for the design of thermodynamic cycles for a CSP, starting from the simplest processes and heading towards more complicated ones. For a reference output capacity, the obtained efficiencies are presented, illustrating the technical benefits of shifting to more advanced thermodynamic processes.     

Novel mixed solar cooker: Experimental,energy, exergy,and economic analysis

This work focuses on the structure, working, and testing of a new mixed solar cooker using a linear Fresnel collector, evacuated tube and box-type cooker. The low-cost components used in the construction of this cooker can help it satisfy the needs of both urban and rural inhabitants who need steady cooking temperatures above 140°C. A family of five can prepare four meals using this modified solar cooker, which costs about $250. The designed solar cooker was tested by conducting no-load and full-load tests. For the no-load test, the maximum temperature of the absorber plate and oil for the new mixed cooker was recorded as 160.26°C and 172.72°C, respectively. The absorber plate of the new mixed cooker and its oil both reached their highest temperatures during the full-load test at 141.14°C and 157°C, respectively. The energy efficiency of the new cooker is 58.776%, while its exergy efficiency is 13%. The heat transfer coefficient increased to 100.16 W/m² °C. This cooker provides an additional time savings of 60 min. An improvement of 27.5% in the highest temperature reached was seen when the developed cooker's performance was compared with those reported in the literature. Additionally, the new cooker's heat-storing capability enables up to 3 h of autonomy. The Levelized Cost of Cooking a Meal for the innovative mixed solar cooker is $0.034 per meal.     

Efficiency assessment for a small heliostat solar concentration plant

In this paper, a small non‐imaging focusing heliostat is presented, and an analytical model for assessing its performance is described. The main novelty of the system lies in the tracking mechanism and the mirror mount, which are based on off‐the‐shelf components and allow a good trade‐off between accuracy and costs. The concentrator mirrors are moved by this two‐axis tracking machinery to reflect the sun's rays onto a fixed target, the dimensions of which can be varied to suit the user's needs. A prototype plant to be located in central Italy was designed and simulated with a ray‐tracing algorithm, and it comprises 90 heliostats for a total reflective area of 7.5 m². The reflected solar rays are tracked taking the mechanical positioning errors of the tracking system into account. The total flux of radiation energy hitting the target was determined, and intensity distribution maps were drawn. Simulations showed that the system's optical efficiency can exceed 90% in summer, despite the tracking errors, mainly because of the smaller distance between the heliostats and the receiver. The solar concentration ratio over a receiver of 250 mm in diameter reached 80 suns with a very good uniformity. Over a 400‐mm receiver, the concentrated radiation was less uniform, and the solar concentration ratio reached 50 suns, with a higher optical efficiency and collected solar radiation. The present concentration ratio is still suitable for many applications ranging from the electric power production, industrial process heat, and solar cooling. Copyright © 2014 John Wiley & Sons, Ltd.     

加快发展河北省太阳能光热发电的建议和对策

太阳能作为一种可再生的新能源,越来越引起人们的关注。我国每年太阳能资源理论储量折合标准煤达17000亿t,而包括风能、水能、生物质能、地热能在内的其它所有可再生能源折合标准煤不到60亿t,太阳能利用潜力巨大。太阳能发电主要有光伏发电和光热发电。太阳能光热发电比光伏发电具有更多的优势。阐述了太阳能光热发电的国内外发展现状,分析了河北省太阳能的资源潜力,并提出了河北省发展太阳能光热发电的建议和对策.     

太阳能半导体制冷性能改进的技术策略

本文在介绍了太阳能半导体制冷的原理及系统结构的基础上,对影响太阳能半导体制冷性能的主要因素进行了系统分析,主要有太阳辐射强度和电池板的光电转换效率、材料的优值系数、电臂的优化结构设计、热端强化散热以及半导体最优工况。其中半导体材料的优值系数和半导体制冷热端散热这两个因素是影响太阳能半导体制冷性能的关键因素。从优值系数方面讲,可以通过半导体材料的性能改进及其加工、制造工艺的完善提高优值系数,从而提高半导体制冷性能。而寻找合理的半导体制冷热端散热方式对制冷性能也有着很重要的影响,随着散热强度的不断增强,半导体制冷的性能有所提高,但最终趋于恒定。     

Performance evaluation of a small‐scale sodium carbonate salt gradient solar pond

In this study, thermal performance of the salt gradient solar pond (SGSP), which of density gradient is artificially with sodium carbonate solution, was tested under Karabuk prevailing weather conditions in Turkey. A small‐scale prismatic glass tank was constructed with an area of 0.45 × 0.20 m² and a depth of 0.25 m as solar pond. A series of experiments with four different density levels were conducted in July–August 2004. The variations of the temperature and density profiles were observed for each of experiment for a week. It was found that the maximum temperature difference between the bottom and surface of the pond is 21°C and maximum temperature in the lower convective zone (LCZ) has been measured as 49°C at the first experiment. The efficiency of the pond was evaluated 13.33% weekly mean radiation intensity of 524 W m^?2 for the first experiment. Copyright © 2006 John Wiley & Sons, Ltd.     

Recommendations for the market introduction of solar thermal power stations

Until 2010, solar thermal power stations based on parabolic trough concentrating collectors can become a competitive option on the world's electricity market, if the market extension of this mature technology is supported by a concerted, long-term programme capable of bundling the forces of industry, finance, insurance and politics. Technical improvements based on the experience of over ten years of successful operation, series production and economies of scale will lead to a further cost reduction of 50% and to electricity costs of 0.06 - 0.04 US$/kWh for hybrid steam cycles and hybrid combined cycles, respectively. Until 2010, a capacity of 7 GW will be installed, avoiding 16 million tons of carbon dioxide per year. The programme comprises an investment of 16 billion US$ and requires external funding of 6%.     

Exergetic utilization of solar energy for feed water preheating in a conventional thermal power plant

This communication is based on exergy concept for the utilization of solar thermal energy in a Rankine cycle‐based fuel‐fired thermal power plant (FFTPP). It has been shown that solar thermal energy as an aided source for feed water preheating helps to reduce the exergy loss in feed water heater (FWH) of Rankine cycle and develops more work than that could have been produced in a solar thermal power plant (STPP). It has been found that this enhancement in work increases for low‐pressure FWHs. For further illustration, a case study has been carried out of a typical 50 kW STPP and a 220 MW FFTPP. The effect of utilizing the same input solar thermal energy of typical STPP, if used as an aided source in a 220 MW FFTPP for feed water preheating is investigated. The work output of STPP is 59.312 kW, while the extra work output of FFTPP by using solar thermal energy of STPP is 90.27 kW. It has been found that the efficiency of work conversion of aided solar thermal energy in FFTPP is higher than the efficiency of work conversion in STPP. Copyright © 2009 John Wiley & Sons, Ltd.     

Innovative configuration of a hybrid nuclear-parabolic trough solar power plant

This paper proposes a combination of a nuclear and a concentrated solar power (CSP) plant. Most of today’s operating nuclear reactor systems are producing saturated steam at relatively low pressure. This, in turn, limits their thermodynamic efficiency. Superheating of nuclear steam with solar thermal energy has the potential to overcome this drawback. An innovative configuration of a hybrid nuclear-CSP plant is assembled and simulated. It brings together a small pressurised water reactor and a parabolic trough solar field. The solar heat is transferred to nuclear steam to raise its temperature. Continuous superheating is provided through molten salts-based thermal energy storage (TES). The results from design point calculations show that solar superheating has the potential to increase nuclear plant electric efficiency significantly. Solar heat to electricity conversion efficiency defined as the ratio of extra generated power to collected solar energy reaches unprecedented rates of 52%. An off-design model was used to simulate 24-h operation for one year by simulating 8760 cases. Due to TES non-stop operation is manageable.     

Performance analysis of direct solar dryer driven by photovoltaic thermal energy recovery and solar air collector for drying materials and electricity generation

The direct-type solar dryer is characterized by very simple construction, less maintenance, cost-effectiveness, and is easy to handle. The present study aims to enhance the performance of a direct-type solar dryer. To achieve this, the photovoltaic (PV) panels with thermal energy recovery and solar air collector were integrated with the direct-type solar dryer. In this study, the PV panels with thermal energy recovery and solar air collector were utilized as preheating units to raise the air temperature before entering the direct solar dryer. Moreover, the PV panels were utilized to drive the air blower. In this study, three incorporated models are suggested to study the performance of the solar dryer integrated with PV panels with thermal energy recovery and solar air collector. The model of each component was validated by the previously recorded empirical data. The results confirmed that the dual utilization of the PV panels with thermal energy recovery and solar air collector as a preheating unit raised the air temperature entering the direct solar dryer by the rate varying between 29°C and 42°C within the period 9:00 a.m.–4:00 p.m. Also, the moisture content of banana samples inside the direct solar dryer reduced from the initial value of 72% (wb) to the value of 33.4% (wb) within 7 h (9:00 a.m.–4:00 p.m.). During this operating period, moisture removal from the banana samples varied between 110 and 400 g/h.     

Novel symmetric squaraine chromophore containing triphenylamine for solution processed small molecule bulk heterojunction solar cells

New symmetrical low band-gap small molecule materials, SQ-bis[HP-HT2-TPA] and SQ-bis[HP-HT2-BT] incorporating as novel derivative of squaraine-pyrrole framework and π-extended thiophene with triphenyamine (TPA) and benzothiophene (BT) end group, have been synthesized and characterized. The effects of TPA moiety were investigated. Compared to SQ-bis[HP-HT2-BT], SQ-bis[HP-HT2-TPA] exhibited three times improved transporting property of hole carrier and four times enhanced absorptivity by more efficient intermolecular π−π interaction for high-efficiency bulk heterojunction (BHJ) device, suggesting that TPA contributes to a better hole mobility. The bulk-heterojunction photovoltaic devices fabricated with SQ-bis[HP-HT2-TPA]/C₇₁-PCBM BHJ film had an average power-conversion efficiency of 1.83%(±0.12) under 100 mW/cm², with a short-circuit current (J_sc) of 9.32 mA/cm², fill factor (FF) of 0.30, and open-circuit voltage (V_oc) of 0.65 V, which has ∼42% higher efficiency compared to SQ-bis[HP-HT2-BT]/C₇₁-PCBM BHJ films.