نشریه انرژی های تجدیدپذیر و نو
سال پنجم شماره 1 (پیاپی 9، تابستان 1397)

It is the aim of this paper to determine the parameters affecting thermal performance of flat plate solar collectors. As a first step, theoretical models for different configurations of a flat plate collector are introduced. These include riser tubes below the absorber plate, tubes above the absorber and tube in between.
A comparison is then made between the theoretical results and real experiments which were implemented in solar energy laboratory at South Tehran Branch of Islamic Azad University.
According to the results, the maximum absorbed energy is for the case where tubes are below the absorber plate. Decreasing the distance between the riser tubes , applying low emissivity glass and increasing insulation thickness are among the parameters which increase collector thermal efficiency. In addition, decreasing the pressure of the gas between the absorber plate and collector glazing increase collector efficiency. Insulation material and working fluid also affect the collector thermal efficiency.

This paper presents the thin layer drying behavior of Dill by a solar hybrid dryer. Experiments were carried out at the air temperatures of 40ºC, 50ºC, 60ºC, 70ºC and air velocity of 1m/s, 1.5 and 2 m/s. 5 different thin layer drying models were fitted to experimental data. The high values of coefficient of determination and the low values of reduced chi-square and root mean square error indicated that the Aghbashlo et al. model could satisfactorily describe the drying curve of Dill. According to resultsThe drying rate increased with an increase in the drying air temperature and drying air velocity. Also the effect of the air velocity on the drying time at a low temperature is greater than that at a high temperature. Based on the results, the mean values of increasing in air temperatures by solar radiation for cloudy, partly cloudy and sunny conditions were 11.76, 15.89 and 19.11ºC, respectively.

Upswing trend in society GDP requires a communication development and increasing the energy consumption. Communication development, itself, incurs increasing the energy consumption. About 7% of power generation is of renewable type in Iran which is less than its average in the world. Supposing 2% of electric power in Iran consumes in ICT, we find 4748 million kwh energy consumption in ICT domain which in turn, generates environmental pollution. Thus, in addition to developing the renewable energy usage in the country, operators should be requested to use these energies more day-to-day. In line with that, using the green equipment is our first strategy for operators to consume the energy less. The second strategy is a stepwise one which requires the operators to substitute the fossil fuels with renewable energies.

Solar collectors play key role in solar thermal systems and their efficiency has more effect in the system performance. The shape and geometry of solar collectors is an important factor to increase their efficiency. In this paper, two collectors, a 3-D stationary solar collector which is called solar conical collector and flat plate collector has been investigated. These two solar collectors have the same absorber area and designed and tested in the same conditions. The performance of solar collectors was experimentally studied by the use of ASHRAE standard. Experiments were performed with water as a working fluid in the south of Iran with deference outdoor conditions and the best data has been selected. The results show that the average of thermal efficiency of a solar 3-D collector is about 59% while this value was about 53% for flat plate collector. The performance of both collectors versus radiation, flow rate, temperature variation was studied and the experiments indicated that the efficiency of the 3-D conical collector has better than the flat plat collector.

Mighty whale is a floating wave power device that designing is wave base. This device convert wave power to electricity with some turbines and generators. Prosperity of costal environment due to installing it into cost. It be moored by chains in to keeping from excessive movements. First prototype of Mighty whale had been designed commissioned from 1998 to 2000 by Japan and the total generated of 83.65 MW or 6.37 kWh during 731 days was its result. In this paper we will intend to investigate on condition of Neka and Amir Abad station in Caspian Sea with data which is prepared by National Oceanic and Atmospheric Research Center and also with equations that is obtained from commissioning the prototype in addition to illustrating procedure of installing and commissioning of prototype. Achievements illustrate appropriate condition in Neka station in order to commissioning of Mighty whale due to appropriate wave parameter like period and high in that place. Also it is evaluated low the efficiency of the device in Amir Abad station.

Much of the energy consumed in the world is fed by fossil fuels. These fuels have a variety of toxic and hazardous pollutants. Through various means to the environment and finally enter the human food chain. Although the environmental impacts of the use of fossil fuels on surface water, groundwater, soil, air, vegetation, and so on are numerous. But the topics of air pollution, greenhouse effect and particles and their cooling effect More attention is being paid. Maintain current situation of life in human society in the future without regard to cost-effective energy supply is not possible. Environmental impacts associated with each energy production at the current rate continues to unacceptable conditions and the harmful environmental effects are expanding extensively. Renewable energy as a power source and free of environmental pollution can Play an important role in reducing pollutant emissions such as carbon dioxide and other greenhouse gases. Therefore, in this research, we try to investigate the role of various renewable energies in reducing environmental pollution.

The increasing use of the photovoltaiv sources and their low efficiency, makes it very important to study on different ways of anhancing their efficiency. In this paper, after designing a photovoltaic farm, the heat transfer equations in solar cells are investigated. Considering the effect of the wind speed on these equations, a solution is provided to decrease the temperature and then increase the efficiency of the photovoltaic panels. Therefore, by means of the meteorological data and three softwares (System advisor model, Matlab and Meteonorm), the 1 MW photovoltaic farm in climate condition of Yazd province is simulated. Then, the effect of wind speed on the efficiency of the photovoltaic farm is investigated. Results shows that with the increase of the wind speed up to 17 m/s, the output power of the farm is considerably increased. For the wind speed upper than 17 m/s, the output power increase is negligible.

The ground-state crystal structures of the alkali borohydrides MBH4 (M= Li, Na, K, Rb) have been established from first principle calculations by comparison of boron charge densities. Alkali borohydrides are potential hydrogen storage material because of their high capacity of H2. However, their high thermodynamic stability is unfavorable for dehydrogenation processes. Understanding the bonding nature of M-B is essential for predicting their dehydrogenation mechanism and then improving their dehydrogenation performance. Quadrupolar parameters of nuclei can be used as a tool to understand the electronic structure of compounds. In this work the charge density distribution in MBH4 (M= Li, Na, K, Rb) was compared. Thus using calculated Nuclear Quadrupole Coupling Constants (NQCC) of 11B nuclei, their electronic structure was studied. The results show that11B-NQCCs of borohydrides is a criterion of their thermodynamically stability and ball milled alkali metal zinc borohydrides demonstrates better catalytic properties with small 11B-NQCC. Therefore, boron atoms in the studied mixed metal borohydrids have weaker bond with metal and easier condition for dehydrogenation in mixed metal borohydrids are seen. The electric field gradient (EFG) of quadrupolar nuclei were calculated to obtain NQCC parameters. All calculations performed using Gaussian 03 at B3LYP/6-311G* GGGGG GG GGGGGG.

Nowadays absorption chiller systems, because of their advantages, have been very privileged. In comparison with other HVAC&R systems one the most advantages of these systems is the possibility of consuming low cost energy sources such as natural gas or gasoline to decrease the system running costs. Also, renewable energy sources can be used instead of fossil fuels with these systems. Solar energy, as one of the most accessible and suitable clean energy sources, has a lot of potentiality in using with absorption systems. In addition, since the peak of air conditioning and cooling demands are in the same phase with the peak of solar radiation, investigation of the different potentiality of solar energy utilization in cooling systems is very important. Utilization of ground source, as one of the other clean and accessible energy sources, can be very useful. Using this source as an energy reserve or supply source, depend on its deployment, can be very beneficial. In this research firstly the absorption chiller systems, their working cycle and different kind of these systems are being described in brief. After that some of the research in the area of using renewable energy sources such as solar and ground source energy in absorption systems are being reviewed.

Reduction of fossil resources, significant growth of oil and natural gas price and greenhouse gases release enhancement have caused more usage of renewable energies as an unlimited, free, clean and environmentally friendly resources. Due to the vast expanses of wind farms in Iran, there is a good basis for using wind energy as an accessible, unlimited and environmentally friendly source. The variable wind speed and the randomness of the nature of the power generated by wind turbines have made it possible for energy experts to provide sustained and permanent load with wind energy hybrid with other renewable sources. In this regard, since 2007, many studies have been done in Iran on modeling and optimizing hybrid power generation systems based on wind turbines. HOMER software is considered as one of the main tools for modeling these systems by Iranian designers. The present study reviews and analysis these indigenous studies. Reviews show that more than half of the research has been published on how to provide power through the use of the hybrid wind, PV, and generator systems.

One of the challenges of architectural design is to provide natural daylight into the internal spaces. Using proper daylight in building is desirable, not only for reason of energy saving, but for improvement of visual environment This performances can be through the use of daylighting systems. Daylighting systems are developed to provide daylight into the interior of buildings because daylight can only penetrate a limited depth through the window. Many of daylighting systems are available to the building industry but there are challenges in using limitations for reasons such as high initial cost, high maintenance of control systems and general utilization in buildings. The purpose of this paper is an overview of innovative daylighting systems with division into main principles, illustrating sketches, installation of systems and short descriptions of the elements. This category helps to select the right daylighting system for given building conditions.