A study of a greenhouse concept on conventional biogas systems for enhancing biogas yield in winter months

A new concept is introduced of using a greenhouse for enhancing the biogas yield from a conventional biogas system in the winter months. If a conventional biogas system is glazed, the trapped solar energy can be used to raise the temperature of the slurry which normally goes low enough to reduce the gas yield appreciably. Numerical calculations have been performed corresponding to the meteorological data on a typical winter day, i.e. 19 January 1981, at New Delhi (India). A comparative study of the performances of conventional and solar-assisted biogas plants using the concept of a greenhouse indicates that the ambient temperature of the slurry can be raised from 18°C to about 37°C, the optimal temperature for anaerobic fermentation.     

Solar assisted biogas plants IV: Optimum area for blackening and double glazing over a fixed-dome biogas plant

The paper presents the economic analysis of a fixed-dome biogas plant of rated capacity 8 m³, above which a part of the ground is blackened and doubly glazed in the cold climate of Srinagar. Blackening and glazing of the ground cannot alone maintain the slurry temperature at 35°C, which is the optimum temperature in the mesophilic range for the anaerobic digestion of cattle dung, and so a part of the biogas must be burnt. The electrical simulation experiments have been performed to determine the loss or gain of heat from the underground biodigestor to the ambient atmosphere through the ground if a part of the ground above is blackened and double glazed. Economic analysis of the system shows that the optimum area to be blackened and glazed would have a radius 1.5 times that of the biodigestor.     

改善全烧式沼气发动机的起动性

沼气中含有大量的二氧化碳，其燃烧速度较慢，且空然比范围窄，热值不高，这些因素导致全烧式沼气发动机的起动性能差在本文的研究中，通过采取提高沼气燃烧速度，确定最佳起动空燃比等措施，较好地改善了全烧式沼气友动机的起动性。     

Solar cell junction temperature measurement of PV module

The present study develops a simple non-destructive method to measure the solar cell junction temperature of PV module. The PV module was put in the environmental chamber with precise temperature control to keep the solar PV module as well as the cell junction in thermal equilibrium with the chamber. The open-circuit voltage of PV module V_oc is then measured using a short pulse of solar irradiation provided by a solar simulator. Repeating the measurements at different environment temperature (40-80 °C) and solar irradiation S (200-1000 W/m²), the correlation between the open-circuit voltage V_oc , the junction temperature T_j , and solar irradiation S is derived.The fundamental correlation of the PV module is utilized for on-site monitoring of solar cell junction temperature using the measured V_oc and S at a short time instant with open circuit. The junction temperature T_j is then determined using the measured S and V_oc through the fundamental correlation. The outdoor test results show that the junction temperature measured using the present method, T_jo, is more accurate. The maximum error using the average surface temperature T_ave as the junction temperature is 4.8 °C underestimation; while the maximum error using the present method is 1.3 °C underestimation.     

Approaches for developing a sizing method for stand-alone PV systems with variable demand

Accurate sizing is one of the most important aspects to take into consideration when designing a stand-alone photovoltaic system (SAPV). Various methods, which differ in terms of their simplicity or reliability, have been developed for this purpose. Analytical methods, which seek functional relationships between variables of interest to the sizing problem, are one of these approaches.A series of rational considerations are presented in this paper with the aim of shedding light upon the basic principles and results of various sizing methods proposed by different authors. These considerations set the basis for a new analytical method that has been designed for systems with variable monthly energy demands.Following previous approaches, the method proposed is based on the concept of loss of load probability (LLP)—a parameter that is used to characterize system design. The method includes information on the standard deviation of loss of load probability (σ_LLP) and on two new parameters: annual number of system failures (f) and standard deviation of annual number of failures (σ_f).The method proves useful for sizing a PV system in a reliable manner and serves to explain the discrepancies found in the research on systems with LLP<10⁻². We demonstrate that reliability depends not only on the sizing variables and on the distribution function of solar radiation, but on the minimum value as well, which in a given location and with a monthly average clearness index, achieves total solar radiation on the receiver surface.     

A sizing method for stand-alone PV installations with variable demand

The practical applicability of the considerations made in a previous paper to characterize energy balances in stand-alone photovoltaic systems (SAPV) is presented. Given that energy balances were characterized based on monthly estimations, the method is appropriate for sizing installations with variable monthly demands and variable monthly panel tilt (for seasonal estimations).The method presented is original in that it is the only method proposed for this type of demand. The method is based on the rational utilization of daily solar radiation distribution functions. When exact mathematical expressions are not available, approximate empirical expressions can be used. The more precise the statistical characterization of the solar radiation on the receiver module, the more precise the sizing method given that the characterization will solely depend on the distribution function of the daily global irradiation on the tilted surface H_gβi.This method, like previous ones, uses the concept of loss of load probability (LLP) as a parameter to characterize system design and includes information on the standard deviation of this parameter (σ_LLP) as well as two new parameters: annual number of system failures (f) and the standard deviation of annual number of system failures (σ_f).This paper therefore provides an analytical method for evaluating and sizing stand-alone PV systems with variable monthly demand and panel inclination. The sizing method has also been applied in a practical manner.     

Enhancement in daily production of biogas system

In this communication, a straightforward analysis of a conventional biogas system (KVIC) integrated with a greenhouse at the top of the dome has been presented. The effect of the use of movable insulation during off-sunshine hours has been included in the analysis. The use of night insulation reduces the heat losses from the top of the system, which causes an appreciable increase in the production of the biogas system. Numerical calculations have been made for a typical winter day in Delhi.     

Multitude of progress and unmediated problems of solar PV in Bangladesh

The aims of this paper are to demonstrate a critical review of the multitude of progress in solar PV research and applications in Bangladesh since its inception in 1996 till 2010. Our studies show that Bangladesh has been experiencing an accelerated shift towards solar PV to meet the gap between demand and supply of electricity along with conventional electricity generation. Despite the present generation of electricity from solar PV is 15-20 MW, both public and private sectors have started several solar PV projects to generate several hundred of MW by the upcoming years. This paper has also tried to identify the critical barriers for widespread dissemination of solar PV in Bangladesh and has discussed possible ways to overcome those barriers as well.     

PV system design for powering an industrial unit for hydrogen production

Needs for hydrogen, as a chemical feedstock, have been growing in the industry, more particularly in the petrochemical industry and in the floating glass technology. Moreover, by its versatility as an energy vector and its renewability, hydrogen has also become an attractive candidate as the vector energy of the future. This has resulted in large surge in demand for hydrogen. However, as hydrogen exists in nature mainly in combination with other elements, the development of its viable and sustainable production technologies has then become necessary.     

Estimation of global radiation using clearness index model for sizing photovoltaic system

A methodology for developing a simple theoretical model for calculating global insolation on a horizontal surface is described in this paper. The input parameters to the model are the latitude of the desired location and the amount of total precipitable water content in the vertical column at that location. Both the parameters are easily measurable with inexpensive instrument such as global positioning system (GPS). The principal idea behind the paper is to have a model that could be used for designing a photovoltaic system quickly and within reasonable accuracy. The model in this paper has been developed using measured data from 12 locations in India covering length and breadth of the country over a period of 9–22 years. The model is validated by calculating theoretical global insolation for five locations, one in north (New Delhi), one in south (Thiruvanandapuram), one in east (Kolkata), one in west (Mumbai) and one in central (Nagpur) part of India and comparing them with the measured insolation values for these five locations. The measured values of all these locations had been considered for developing the model. The model is further validated for a location (Goa) whose measured data is not considered for developing the model, by comparing the calculated and measured values of the insolation. Over the range of latitudes covering most parts of India, the error is within 20% of the measured value. This gives the credibility of the model and the methodology used for developing the model for any region in the world.     

Solar home system electrification as a viable technology option for Africa's development

This paper is based on a review of the effectiveness of solar home systems (SHS) in Africa in meeting users expectations on a service based analytical approach. Various projects have deployed SHS on the promise that they are cost-effective, can meet end-user demands, have ability to alleviate poverty, can save time and reduce emissions. However, a close review of the actual cost of these systems given the services they provide indicates most of the promises remain unmet and hence questions the wisdom of using public funds to support the system at the expense of more appropriate technologies.     

Searching for public benefits in solar subsidies: A case study on the Australian government’s residential photovoltaic rebate program

The Australian Government ran a renewable energy program in the 2000s that provided rebates to householders who acquired solar Photovoltaic (PV) energy systems. Originally called the Photovoltaic Rebate Program (PVRP), it was rebranded the Solar Homes and Communities Plan (SHCP) in November 2007. This paper evaluates both the PVRP and SHCP using measures of cost-effectiveness and fairness. It finds that the program was a major driver of a more than six-fold increase in PV generation capacity in the 2000s, albeit off a low base. In 2010, solar PV’s share of the Australian electricity market was still only 0.1%. The program was also environmentally ineffective and costly, reducing emissions by 0.09 MtCO₂-e/yr over the life of the rebated PV systems at an average cost of between AU$238 and AU$282/tCO₂-e. In addition, the data suggest there were equity issues associated with the program, with 66% of all successful applicants residing in postal areas that were rated as medium–high or high on a Socio-economic Status (SES) scale.     

晶体硅光伏发电技术与市场

本文从太阳能电池的历史和发展现状发展,介绍了太阳能电池的几种新型结构和目前发展水平,以及从实验室向产业化推广的可能性。     

A solar powered wireless computer mouse: Industrial design concepts

A solar powered wireless computer mouse (SPM) was chosen to serve as a case study for the evaluation and optimization of industrial design processes of photovoltaic (PV) powered consumer systems. As the design process requires expert knowledge in various technical fields, we assessed and compared the following: appropriate selection of integrated PV type, battery capacity and type, possible electronic circuitries for PV-battery coupling, and material properties concerning mechanical incorporation of PV into the encasing. Besides technical requirements, ergonomic aspects and design aesthetics with respect to good “sun-harvesting” properties influenced the design process. This is particularly important as simulations show users can positively influence energy balances by “sun-bathing” the PV mouse. A total of 15 SPM prototypes were manufactured and tested by actual users. Although user satisfaction proved the SPM concept to be feasible, future research still needs to address user acceptance related to product dimensions and user willingness to pro-actively “sun-bath” PV powered products in greater detail.