Why environmental dust influences solar energy harvesting

In order to minimize dust effects on optical surfaces related to the solar energy harvesting, adhesion between the active surface of energy harvesting device and the dust particles needs to be lowered. Consequently, the pinning force for the dust particles reduces, and the dust particles can be removed via creating the self‐cleaning effect. The wetting state of the active surface becomes critical towards reducing the pinning force. In this case, hydrophobic surfaces remain favorable reducing the dust adhesion on the surfaces. In the present perspective, characteristics of the environmental dust particles and their effects in humid air ambient are presented. The methods for dust removal from the surfaces and the optical transmittance reduction by the dust particles are discussed. The challenges and future perspectives of surface texturing towards achieving hydrophobicity and optical transmittance are also introduced.     

Solar energy harvesting and self-cleaning of surfaces by an impacting water droplet

The self-cleaning of surfaces via impacting water droplets is examined pertinent to solar energy applications. The mechanism of spreading and retraction of the impacting droplet onto the dust and cleaned hydrophobic surfaces is considered in the analysis. The spreading factor of the impacting droplet is formulated incorporating the energy balance on the hydrophobic surface. High-speed photography is used to monitor the impacting droplet behavior. The functionalized silica particles coating is introduced towards generating hydrophobic wetting state on the glass surfaces. Environmental dust particles are characterized prior to self-cleaning impacting tests. It is found that spreading rate predicted for the impacting droplet agrees well with that obtained from the experiments. The droplet Weber number incorporated in the experiments does not result in droplet breaking on the surface upon impacting. The dusts are dissimilar in shapes and consist of several elements. Impacting droplet gives rise to cloaking of the dust on the surface during spreading and retraction. Almost all the dusts are removed from the surface through the impacting droplets; however, few dust residues are left on the impacting surface, which cover only 0.03% of the total surface area. Hence, we have demonstrated that self-cleaning of a surface can be achieved by an impacting droplet for renewable energy applications.     

Solar energy at various depths below a water surface

The total solar energy at various depths in water has been calculated by adopting two sets of data, namely the extinction coefficient of water in the spectral range of 300–2500 nm, and the solar spectrum at sea level in the same spectral range. With the aid of a computer program designed for this purpose, the solar spectrum at various depths has been reconstructed and the total solar energy has been measured by calculating the area under the spectral distribution curves. A mathematical expression for the integrated solar energy as a function of depth in water has been derived.     

Review of vibration‐based energy harvesting technology: Mechanism and architectural approach

Energy harvesting technologies are growing rapidly in recent years because of limitation by energy storage and wired power supply. Vibration energy is abundant in the atmosphere and has the potential to be harvested by different mechanisms, mainly through piezoelectric and electromagnetic means. Various architectural structures were also designed for several operating conditions, namely, resonance frequency and range thereof, acceleration, and energy extraction from several motions. The advantages and disadvantages were elaborated on, and improvements on ideas from current research were discussed in this review.     

Enhancement of piezoelectric vibration energy harvesting with auxetic boosters

This paper proposes a new concept to enhance the efficiency of the vibration energy harvesting via an intermediate booster. The boosters have auxetic structures and exert extra stretching strain in two perpendicular directions. The concept is tested on a conventional cantilever beam under the base excitation. The problem consists of a cantilever beam subjected to a body load at low frequencies. An auxetic substrate is bonded to the beam with a thin epoxy layer, and the piezoelectric (PZT) element is attached on top of it. Two different auxetic structures are investigated in this study. It is shown that employing these kinds of boosters can remarkably enhance the performance of the energy harvesting system. The harvesting efficiency is numerically evaluated in different load amplitudes and frequencies. A parametric study is then carried out, and effects of different geometrical design parameters of the auxetic boosters on the performance of the energy harvesting system are investigated. Comparing with the case in which the PZT is straightly attached to the cantilever, it is shown that adding such intermediate boosters at low-frequency range can increase the extracted power by factors of 3.9 and 7.0 for the two proposed geometries.     

Development of an energy harvesting damper using PVDF film

We report an energy harvesting damper composed of a composite of piezoelectric polyvinylidene fluoride film and silicone rubber for applications in offshore structures. We describe the generation efficiency of sandwiched and coiled sheet geometries. Piezoelectricity was generated by cyclic compressive loading with frequency of 2 Hz and a displacement of 3 mm using a fatigue‐testing machine, and the voltage and power were measured. We used digital image correlation and finite element method modeling to investigate the deformation of the silicone matrix. The coiled sheet specimen exhibited higher power with larger and more uniform deformation; however the sandwiched geometry exhibited better durability. The lower power of the sandwiched geometry was attributed to localized deformation because of friction at the interface between specimen and fixture, and the performance of this design was improved via the use of a lubricant. Copyright © 2015 John Wiley & Sons, Ltd.     

On the comparison of energy sources: Feasibility of radio frequency and ambient light harvesting

With growing interest in multi source energy harvesting including integrated microchips we propose a comparison of radio frequency (RF) and solar energy sources in a typical city. Harvesting devices for RF and solar energy will be competing for space of a compact micro or nano device as well as for orientation with respect to the energy source. This is why it is essential to investigate importance of every source of energy and make a decision whether it will be worthwhile to include such harvesters. We considered theoretically possible irradiance by RF signal in different situations, typical for the modern urban environment and compared it with ambient solar energy sources available through the night, including moonlight.Our estimations show that solar light energy dominates by far margin practically all the time, even during the night, if there is a full moon in the absence of clouds. At the same time, in the closed compartments or at the new moon RF harvesting can be beneficial as a source of “free” energy.     

Efficient study of a coarse structure number on the bluff body during the harvesting of wind energy

In the present study, an energy harvester with coarse passive turbulence control (PTC) structure is represented to harvest piezoelectric wind energy. Wind tunnel experiments are conducted to investigate the influence of the PTC on the vibrational amplitude of the vortex-induced vibration and piezoelectric power output. Parametric studies of the PTC numbers and sizes are presented to determine the optimized PTC structure to enhance the efficiency of piezoelectric energy harvesting. The experimental results show that the specific parameters of θ= 60^° and W = 8 mm are the most efficient PTC group for designing a vortex-induced vibration-based energy harvester with the coarse surface device.     

The relation of efficiency of excitation energy transfer and ring size of ring-shaped light harvesting complex

The existence of various ring sizes of peripheral light harvesting complex (LH2) in photosynthetic bacteria was reported recently. To investigate the dependence of LH2’s functions as an excitation energy transfer (EET) carrier on its structure, the relation of EET in the systems consisting of ring-shaped aggregates and their ring size is evaluated. Setting the square simulation area (70 nm × 70 nm), we defined the EET efficiency as the rate of population transferred from the area irradiated by the incident light to another area, which is separated by ∼20 nm from the former area, by the time corresponding to the dephasing time of pigments (∼4 ps) after the irradiation of the incident light pulse. As the result, the system composed of large ring with 28 pigments realizes the EET efficiency of 5.3%, 7.0%, and 8.8% in the randomly distributed system of rings when the ring number is 15, 20, and 25, respectively. These values are ∼1.5 and ∼3 times higher than the EET efficiency in the systems composed of rings with 18 pigments and 10 pigments, respectively, when the total numbers of pigments in the simulation area are the same. In the lattice structures, on the other hand, the EET efficiency of the three types of systems shows the similar value of ∼20%. The results suggest that forming a large ring as the unit of EET carrier could be effective to realize efficient EET in the systems containing randomness in distribution of units, whereas in the lattice structure, the EET efficiency may be not critically affected by the ring size of ring-shaped unit carrier.     

Renewable energy harvesting with the application of nanotechnology: A review

It is believed that fossil fuel sources are exhaustible and also the major cause of greenhouse gas emission. Therefore, it is required to increase the portion of renewable energy sources in supplying the primary energy of the world. In this study, it is focused on application of nanotechnology in exploitation of renewable energy sources and the related technologies such as hydrogen production, solar cell, geothermal, and biofuel. Here, nanotechnologies influence on providing an alternative energy sources, which are environmentally benign, are comprehensively discussed and reviewed. Based on the literature, employing nanotechnology enhances the heat transfer rate in photovoltaic/thermal (PV/T) systems and modifies PV structures, which can improve its performance, making fuel cells much cost‐effective and improving the performance of biofuel industry through utilization of nanocatalysts, manufacturing materials with high durability and lower weight for wind energy industry.     

Spectral transmittance of water and sodium chloride water solution as working substance for a solar pond

The transmission properties of water and sodium chloride water solutions with various salt concentrations were investigated. This paper concerns the measurement of the spectral transmittance and the calculation of the total transmittance for water and NaCl water solutions. The spectral transmittance of the NaCl water solutions over the infrared and nearby regions increased with increasing salt concentration for constant specimen thickness and air mass. The spectral transmittance was found to be useful for precisely calculating the thermal performance of a solar pond, and by using an effective absorption coefficient, a five-partition method dividing the wavelengths into five bands by which the total transmittance up to a water depth of 3 m could be calculated, was found to be important as a practical method of solar pond technology. © 1997 Scripta Technica, Inc. Heat Trans Jpn Res, 26(1): 1–15, 1997     

空气集热器透明蜂窝透过率的二维理论推导

透明蜂窝的太阳透过率是衡量平板式太阳能集热器性能的主要参数.本文考虑入射光线所在平面垂直于集热器表面的情况,从而将光线在蜂窝内部的复杂的传播过程简化为在一个矩形单元内的二维多次反射.根据几何光学原理,推导出蜂窝的有效透过率的计算公式:τe=[(1-Atanθ+N)+(Atanθ-Nρe]τ2ρNe.根据公式,透明蜂窝的有效透过率为入射角θ、材料的透射率τ和反射率ρ、以及蜂窝单元的高宽比A的函数,与蜂窝的具体尺寸无关.该公式提供了计算透明蜂窝透过率的一个简单而有效的方法.     

Vibration energy harvesting in vehicles by gear segmentation and a virtual displacement filtering algorithm

In this study, vibration straight‐line displacements occurring during electric vehicle operations are changed into reversely rotating displacements and divided into small segments by a gear unit. Piezoelectric bending elements are used to form a cantilever beam–based energy feedback mechanism for converting vibration energy into electrical power within an allowable displacement range. A virtual vibration displacement filtering algorithm is proposed to effectively filter virtual displacements that cannot excite the energy harvester and generate electrical power. The average speed of the gear exciting the bender has an accuracy 30%, which is increased using this algorithm compared with 2 other algorithms and directly affects the accuracy of calculating the average power generated by the calculation of piezoelectric bending elements. Theoretical and experimental analyses are conducted for the impact of gear pitch on the regeneration power value by changing the gear pitch at a fixed driving speed. Experiments show that when a vehicle is operated at a fixed speed, the proposed method can be used to obtain the maximum average power of a single piezoelectric bending element through determination of a rational gear pitch. Specifically, when the test vehicle operated at 20 and 60 km/h, the gear pitch should have been 7 and 10 mm.     

别墅型太阳能中央热水系统

介绍了别墅型太阳能中央热水系统的组成、工作原理和性能特点,并与其它形式的热水系统的综合性能进行了比较.实际工程应用表明:别墅型太阳能中央热水系统是一种节能、环保、安全、高效的热水装置,每平方米太阳能热水器的年平均获热量(每年按360 d计)相当于1 200 kWh的电力、500 kg煤和180 kg液化气通过相应装置得到的热量.     

Optical properties and stability of water-based nanofluids mixed with reduced graphene oxide decorated with silver and energy performance investigation in hybrid photovoltaic/thermal solar systems

The present work investigates the effect of the nanoparticles concentration on the optical and stability performance of a water-based nanofluid in solar photovoltaic/thermal (PV/T) systems experimentally and numerically. A novel nanofluid is formulated with the inclusion of the reduced graphene oxide decorated with silver (rGO-Ag) nanoparticles in water. Five different concentrations of nanoparticles in the range from 0.0005 to 0.05 wt% is suspended in water to prepare the samples. Optical properties are measured using UV-Vis. The UV-Vis absorption analysis reveals that all samples show consistent optical absorption coefficient (α) at higher value (more than 3 cm⁻¹) in the range of 1.5 to 4 eV. The application of optical filtration (OF) using water/rGO-Ag nanofluid in hybrid PV/T system presented more solar energy absorption through the OF. The hybrid system shows better performance at concentrations less than 0.0235 wt% compared to the PV system without integration with optical filtration. The hybrid solar PV/T system with OF using water/rGO-Ag nanofluid is able to produce thermal energy with efficiencies between 24% and 30%.     

Flexible liquid metal coil prepared for electromagnetic energy harvesting and wireless charging

This paper reported a study on a flexible liquid metal coil (LMC) for electromagnetic collection from the transmission line for self-powered sensor and electromagnetic generation for wireless charging of cellular telephone. The room temperature liquid metal of Galinstan was perfused to elastic silicone tube, which is then terminated with gallium-plated copper wire. The as-prepared liquid metal wire can sustain stretching, twisting, and bending with large deformation, and has a good electrical contact stability with the external circuit. The LMC based magnetic energy harvester was then designed and demonstrated to collect the magnetic field energy induced by a wire carrying alternating current. The power of 260 mW was obtained for the wire carrying current of 10 A. The flexible toroidal inductor was fabricated and tested for magnetic energy harvesting. The flexible spiral-shaped LMC was also designed and demonstrated to power cellular telephone through wireless charging. The present study opens the way for further applications of elastic LMC in electromagnetic energy harvesting and charging.     

Solar Technological Progress and Use of Solar Energy in the World

Solar energy can potentially play a very important role in providing most of the heating, cooling and electricity needs of the world The sun has produced energy for billions of years. Solar energy is the solar radiation that reaches the earth. There are a variety of different technologies used in order to take advantage of solar energy. The primary solar energy technologies include photovoltaics, concentrating solar power, and solar heating and cooling systems. Today solar sources provide around 10% of the energy used worldwide, but in the developing countries their share is still of the order of 40%. In 1999, installed photovoltaic (PV) capacity was 594 MWp in the world. Japan has the highest PV capacity as a result of an important program to support the development of PV markets. Japan had a PV capacity of 205 MWp in 1999.     

An analytical model to estimate the state of charge and lifetime for batteries with energy harvesting capabilities

Energy limitation is one of the major bottlenecks during the operation of many emerging applications, such as electric vehicles, water and gas meters and a number of sensors used in the context of the Internet of Things and cyber-physical systems. Energy harvesting techniques have arisen as a promising solution to minimize the energy issues found in these types of application domains. In energy harvesting systems, a critical challenge is the need to use battery models capable of accurately estimating both the input and output power of batteries. This article proposes a temperature-dependent analytical battery model capable of estimating some output quantities — for example, state of charge, voltage and lifetime — of batteries that use energy harvesting technologies. This model was validated by comparing its analytical results with a dataset called the Randomized Battery Usage Data Set, which is available at the data repository of the National Aeronautics and Space Administration (NASA) website. It is also presented a proof-of-concept application, demonstrating that the use of these technologies can serve as an effective means to extend the operating time of batteries, resulting in significant benefits for a number of applications.     

Energy harvesting from pavements and roadways: A comprehensive review of technologies,materials, and challenges

Energy harvesting from pavements has been a topic of extensive research in the recent past. This domain has attracted not only the research community but also the industry and governmental authorities. The various sources exploited for energy harvesting from pavements and roadways are solar radiation, mechanical energy dissipated due to moving vehicles and pedestrians, geothermal energy, rainwater, and wind. This article presents an exhaustive and updated review of all potential means of energy harvesting from these sources. Following the introductory section, the article sequentially covers the energy harvesting methods and their research progress, materials, development of practical systems, commercial status, comparison of technologies, challenges, and concluding remarks. This study reveals that there is wide scope for further research and feasibility studies, which could lead to a wide‐spread implementation of the various technologies for energy harvesting from pavements and roads.     

太阳能-地源热泵耦合方式的工程应用分析

利用太阳能辅助地源热泵既节能环保又能进一步提高能源的利用率且对环境无污染。从天津地区的太阳光照强度的角度考虑,以利用太阳能提高机组的效率和承担部分建筑物负荷这两种方式辅助地源热泵。从节能和经济性两个角度进行分析并得出结论:在天津地区利用太阳能分担建筑的部分负荷更节能、经济。