Energy Harvesting Technologies for Achieving Self-Powered Wireless Sensor Networks in Machine Condition Monitoring: A Review <s> Light Energy Harvesting <s> Batteries used in photovoltaic applications are required to have particular properties in order to minimize the system cost, in addition to meeting stringent reliability requirements associated with PV system installations. The battery sizing, installation, operation and maintenance, thus, are fundamentally different from those used in several other energy storage applications. The current paper gives an overview of battery systems commonly used in PV installation, as well as several new options which are found suitable or have been modified suitably to meet PV energy storage requirements. The systems are discussed briefly with respect to their construction, performance characteristics and compatibility with PV systems. The battery sizing procedures are also reviewed. <s> BIB001 </s> Energy Harvesting Technologies for Achieving Self-Powered Wireless Sensor Networks in Machine Condition Monitoring: A Review <s> Light Energy Harvesting <s> Nanotechnology is an enabling technology that provides an extensive range of resources to resolve the energy-related problems, as the developing components and appliances are smaller than 100 nm they provide the new ways to catch, store and exchange energy. Every day, the sun shines a huge amount of energy which is generated through a process of nuclear fusion. Even the sun radiates more energy in one second than people have practiced since the beginning of time. It has been noted that the technical potential of solar energy all over the world is many times larger than the current total primary energy demanded. In this study, the solar harvesting technology with the help of nano-materials has been thoroughly studied. The different types of modern solar collecting technologies that use the nano- materials effectively and successfully have been discussed. Among a number of devices, the solar collector, the fuel cell, photocatalysis and solar photovoltaic have used the nanomaterials to increase the efficiency. It is found that by using nanomaterials the incident radiation can be increased by 9 times while the efficiency of the solar collector is 10% higher compared to that of a conventional flat plate solar collector. The generation ways solar cell technologies have been also discussed here. At the end of this article, few challenges in using nanotechnology are also addressed in detail. <s> BIB002 </s> Energy Harvesting Technologies for Achieving Self-Powered Wireless Sensor Networks in Machine Condition Monitoring: A Review <s> Light Energy Harvesting <s> Abstract Solar-powered airplanes are studied in this research. A solar-powered airplane consumes solar energy instead of traditional fossil fuels; thus it has received a significant amount of interest from researchers and the public alike. The historical development of solar-powered airplanes is reviewed. Notable prototypes, particularly those sponsored by the government, are introduced in detail. Possible future applications of solar-powered airplanes in the civilian and military fields are proposed. Finally, the challenges being faced by solar-powered airplanes are discussed. This study proposes that the solar-powered airplanes are potential alternatives to some present technologies and that they complement current satellites, traditional airplanes, airships, and balloons. However, these planes require further development and enormous technical obstacles must be addressed. <s> BIB003 </s> Energy Harvesting Technologies for Achieving Self-Powered Wireless Sensor Networks in Machine Condition Monitoring: A Review <s> Light Energy Harvesting <s> Abstract In this work we describe a passive screen printed flexible tag for gas monitoring that can be used in sealed environments. The developed measurement system is based on chemical sensors that are sensitive to gases concentration presenting optical response, luminescent or colourimetric. The measuring electronics consist of a LED for optical excitation of the sensing membrane and a high resolution digital colour detector for the reading of the optical signal. A microcontroller receives and processes the data enabling the detection threshold for the corresponding gas. The whole system is powered by two miniaturized solar cells that provide 4 V and up to 250 μA each one. This system can run in sunlight or using a bright artificial light as the only energy source. The information of the inner environmental conditions regarding the gas concentration is transmitted to the user through a simple optical code using colour light-emitting diodes. These LEDs are activated to indicate whether the concentration of the monitored gas is within the expected limits, or not. Two prototypes based on this architecture and only changing the sensing module have been developed and applied for the determination of two common gases: oxygen and carbon dioxide. In the first case, a luminescent chemical sensor is used while in the second, the sensing membrane presents a colourimetric response. Both types of sensors can be used in this design. Resulting limits of detection are compatible with assessment of modified atmosphere packaging. <s> BIB004 </s> Energy Harvesting Technologies for Achieving Self-Powered Wireless Sensor Networks in Machine Condition Monitoring: A Review <s> Light Energy Harvesting <s> Key issues relating to the past, current and upcoming technologies of solar-powered aircraft are reviewed with the intent to assess the technology trend and offer a prediction for the next decade. The paper looks into the design issues comprising of structures, systems, propulsion, aerodynamics, and system integration for solar-powered aircraft. Additionally, the technological status which includes structural materials, photovoltaic systems, battery and power management systems in the case of solar aircraft, would be considered. Finally, technology trend issues would be assessed summarizing into a predictive outlook. The applicable technologies in the design of solar powered aircraft has evolved over the years, hence an overview is presented. <s> BIB005 </s> Energy Harvesting Technologies for Achieving Self-Powered Wireless Sensor Networks in Machine Condition Monitoring: A Review <s> Light Energy Harvesting <s> Abstract Future solar cells may produce electricity in all weathers. We present here a cost-effective and high-efficiency graphene based conducting composite tailored all-weather solar cell that can be actuated with raindrops and sunlight. Due to the formation of π-electron|cation double-layer pseudocapacitance at conducting composite/raindrop interface, the delocalized π-electrons on graphene can migrate along percolating pathways forward at spreading process and backward at shrinking periods, resulting in charging and discharging of the pseudocapacitor. The optimized solar cell yields a photoelectric conversion efficiency of 9.8% under simulated sunlight irradiation (air mass 1.5, 100 mW cm −2 ) as well as current over several microamps and voltage of hundreds of microvolts under simulated raindrops. This work could extend our knowledge of future all-weather solar cells. <s> BIB006 </s> Energy Harvesting Technologies for Achieving Self-Powered Wireless Sensor Networks in Machine Condition Monitoring: A Review <s> Light Energy Harvesting <s> The purpose of this article is to understand the state of art of photovoltaic solar energy through a systematic literature research, in which the following themes are approached: ways of obtaining the energy, its advantages and disadvantages, applications, current market, costs and technologies according to what has been approached in the scientific researches published until 2016. For this research, we performed a qualitative and quantitative approach with a non-probabilistic sample size, obtaining 142 articles published since 1996–2016 with a slitting cut. The analysis result of this research shows that studies about photovoltaic energy are rising and may perform an important role in reaching a high-energy demand around the world. To increase the participation of photovoltaic energy in the renewable energy market requires, first, to raise awareness regarding its benefits; to increase the research and development of new technologies; to implement public policies a programs that will encourage photovoltaic energy generation. Although crystal silicon solar cells were predominant, other types of cells have been developed, which can compete, both in terms of cost reduction of production, or in terms of greater efficiency. The main applications are dominated by telecommunications, water pumping, public lighting, BIPV, agriculture, water heating, grain drying, water desalination, space vehicles and satellites. The studies found on photovoltaic solar energy are all technical, thus creating the need for future research related to the economic viability, chain supply coordination, analysis of barriers and incentives to photovoltaic solar energy and deeper studies about the factors that influence the position of such technologies in the market. <s> BIB007 </s> Energy Harvesting Technologies for Achieving Self-Powered Wireless Sensor Networks in Machine Condition Monitoring: A Review <s> Light Energy Harvesting <s> Solar cells are considered as one of the prominent sources of renewable energy suitable for large-scale adoption in a carbon-constrained world and can contribute to reduced reliance on energy imports, whilst improving the security of energy supply. A new arrival in the family of solar cells technologies is the organic-inorganic halide perovskite. The major thrust for endorsing these new solar cells pertains to their potential as an economically and environmentally viable option to traditional silicon-based technology. To verify this assertion, this paper presents a critical review of some existing photovoltaic (PV) technologies in comparison with perovskite-structured solar cells (PSCs), including material and performance parameters, production processes and manufacturing complexity, economics, key technological challenges for further developments and current research efforts. At present, there is limited environmental assessment of PSCs and consequently, a methodologically robust and environmentally expansive lifecycle supply chain assessment of two types of PSC modules A and B is also undertaken within the context of other PV technologies, to assess their potential for environmentally friendly innovation in the energy sector. Module A is based on MAPbX3 perovskite structure while module B is based on CsFAPbX3 with improved stability, reproducibility and high performance efficiency. The main outcomes, presented along with sensitivity analysis, show that PSCs offer more environmentally friendly and sustainable option, with the least energy payback period, as compared to other PV technologies. The review and analysis presented provide valuable insight and guidance in identifying pathways and windows of opportunity for future PV designs towards cleaner and sustainable energy production. <s> BIB008 </s> Energy Harvesting Technologies for Achieving Self-Powered Wireless Sensor Networks in Machine Condition Monitoring: A Review <s> Light Energy Harvesting <s> Abstract The utilization of solar energy into the rechargeable battery, provides a solution to not only greatly enhance popularity of solar energy, but also directly achieve clean energy charging, especially the simplified solar-powered rechargeable batteries. This concept has been demonstrated via the employment of high-efficiency nanophotocatalysts for capturing solar energy into batteries. In this review, we give a brief generalization on the conventional applications of solar energy, and systematically discuss the new-type applications for rechargeable batteries. Additionally, the challenge and outlook of solar-powered rechargeable batteries have been proposed. The development of solar-powered rechargeable batteries would greatly contribute to building resource-conserving society. <s> BIB009 </s> Energy Harvesting Technologies for Achieving Self-Powered Wireless Sensor Networks in Machine Condition Monitoring: A Review <s> Light Energy Harvesting <s> Abstract This paper aims to develop a high-altitude solar-powered hybrid airship, which combines aerodynamic lift and buoyancy with buoyancy force and cruises continuously. A multi-lobed configuration is employed and the solar irradiance and photovoltaic array model are proposed. After introducing all the parts mass of the hybrid airship and design procedure, an optimal problem with the constraint of energy and the equilibrium between buoyancy and weight are proposed. Through a hybrid optimization search method, the solution is obtained and the sensitivities of geographical location and seasons are discussed. The results show a comprehensive influence of the constraint both in latitude and wind field environment. <s> BIB010 </s> Energy Harvesting Technologies for Achieving Self-Powered Wireless Sensor Networks in Machine Condition Monitoring: A Review <s> Light Energy Harvesting <s> Abstract For almost sixty years, solar energy for space applications has relied on inorganic photovoltaics, evolving from solar cells made of single crystalline silicon to triple junctions based on germanium and III-V alloys. The class of organic-based photovoltaics, which ranges from all-organic to hybrid perovskites, has the potential of becoming a disruptive technology in space applications, thanks to the unique combination of appealing intrinsic properties ( e.g. record high specific power, tunable absorption window) and processing possibilities. Here, we report on the launch of the stratospheric mission OSCAR, which demonstrated for the first time organic-based solar cell operation in extra-terrestrial conditions. This successful maiden flight for organic-based photovoltaics opens a new paradigm for solar electricity in space, from satellites to orbital and planetary space stations. <s> BIB011 </s> Energy Harvesting Technologies for Achieving Self-Powered Wireless Sensor Networks in Machine Condition Monitoring: A Review <s> Light Energy Harvesting <s> A technology drift is currently taking place from traditional battery-powered sensor networks, which exhibit limited lifetime, to the new Energy-Harvesting Wireless Sensor Networks (EH-WSN), which open the way towards self-sustained operation. However, this emergent modality also brings up new challenges, especially due to the time-varying nature and unpredictability of ambient energy sources. Most proposals for implementing EH-WSN rely on heuristic approaches to redesign the duty-cycling mechanism at the MAC layer, with the ultimate goal of optimizing network performance while preserving self-sustained and continuous operation. In contrast to the common system-wide reduced duty cycle of battery-powered sensor networks, the duty cycle in EH-WSN is much larger and adapted to the energy harvesting rate and traffic load of each node in the network. In this paper, we focus on solar-based EH-WSN devoted to environmental monitoring. In contrast to current works, we follow an analytical approach, which results into closed-form expressions for the duty cycle and initial energy storage that guarantee self-sustained operation to any node in a solar-based EH-WSN. To center the analysis, we consider TinyOS sensor nodes, though we postulate that the essential components of the obtained formulation will contribute to further develop duty cycle adaptation schemes for TinyOS and other software platforms. <s> BIB012 </s> Energy Harvesting Technologies for Achieving Self-Powered Wireless Sensor Networks in Machine Condition Monitoring: A Review <s> Light Energy Harvesting <s> Abstract Diesel-powered pumps are widely employed in farming and grassland irrigation. However, there can be problems of reliability and availability where fuel supply is erratic and expensive, high maintenance cost, and short life expectancy. These and recent concerns for the environment associated with the diesel engines call for a viable alternative source of power for irrigational water pumping. Renewable energy sources have gained a lot of attention as a replacement for fossil fuels or as a supplement in hybrid systems. Solar-powered (photovoltaic) systems are one of the viable alternatives that have attracted considerable attention in this regard. They have been deployed in many remote regions for various applications, ranging from rural electrification and community water supplies to irrigation and livestock water supplies. Although photovoltaic (PV) systems generally have a high investment cost, it has many features which make it attractive as an alternative source of power for water pumping. It is clean, as it produces no carbon emission, it generates no noise, and it has low operational and maintenance cost. This manuscript presents a detailed intensive review of solar-powered water pumping systems as reported in the literature to serve as a quick reference to researchers and engineers who are working or interested in the subject. <s> BIB013
Light energy, for example the energy from sunlight or artificial light, is generally renewable and ubiquitous energy source, which can be harvested and accumulated to power sensor nodes through the photovoltaic technique BIB012 . Photovoltaic cells manufactured with semiconductor materials can directly convert the light waves into electrical energy through the photovoltaic effect as illustrated in Figure 5 . Free electrons and holes are produced at PN junctions under the influence of sunlight and then move to the N-type and P-type semiconductors to form a potential difference BIB007 . A current can be generated when an external conductor is connected to the electrodes of photovoltaic cells. The amount of energy harvested from light is related to the illumination level. For example, artificial light, usually an indoor light source, can only generate illumination at a low level of below 1,000 lux. The magnitude of sunlight illumination level (up to 120,000 lux for brightest sunlight) is significantly higher than the artificial one. Figure 6 compares the relationship between the electric output and the illuminance level of Panasonic photovoltaic cells for indoor and outdoor illumination   . The amount of energy harvested from light is related to the illumination level. For example, artificial light, usually an indoor light source, can only generate illumination at a low level of below 1000 lux. The magnitude of sunlight illumination level (up to 120,000 lux for brightest sunlight) is significantly higher than the artificial one. Figure 6 compares the relationship between the electric output and the illuminance level of Panasonic photovoltaic cells for indoor and outdoor illumination   . The amount of energy harvested from light is related to the illumination level. For example, artificial light, usually an indoor light source, can only generate illumination at a low level of below 1,000 lux. The magnitude of sunlight illumination level (up to 120,000 lux for brightest sunlight) is significantly higher than the artificial one. Figure 6 compares the relationship between the electric output and the illuminance level of Panasonic photovoltaic cells for indoor and outdoor illumination   . To improve the performance of photovoltaic cells, many researchers have contributed to the advancement of the photovoltaic materials. Photovoltaic cells are mainly classified into three types according to three types of materials: silicon (a commonly used semiconductor material), semiconductor compounds and novel materials BIB008 . Sampaio et al. BIB007 , systematically examined the development of photovoltaic solar cells with different materials, the worldwide markets, as well as their advantages and disadvantages. Although conventional silicon solar cells dominate the commercial markets, a new types solar cells manufactured semiconductor compounds or novel materials, such as the thin film cells and organic photovoltaic cells, are being developed rapidly due to their characteristics of low cost, high conversion efficiency and flexibility, and low environmental pollution. Because of the inconstant availability of solar energy, the direct use of electricity generated by photovoltaic cells or panels leads to low efficiency and inconvenience. Rechargeable batteries can be used to store solar energy for many applications. They are widely used in portable devices (such as To improve the performance of photovoltaic cells, many researchers have contributed to the advancement of the photovoltaic materials. Photovoltaic cells are mainly classified into three types according to three types of materials: silicon (a commonly used semiconductor material), semiconductor compounds and novel materials BIB008 . Sampaio et al. BIB007 , systematically examined the development of photovoltaic solar cells with different materials, the worldwide markets, as well as their advantages and disadvantages. Although conventional silicon solar cells dominate the commercial markets, a new types solar cells manufactured semiconductor compounds or novel materials, such as the thin film cells and organic photovoltaic cells, are being developed rapidly due to their characteristics of low cost, high conversion efficiency and flexibility, and low environmental pollution. Because of the inconstant availability of solar energy, the direct use of electricity generated by photovoltaic cells or panels leads to low efficiency and inconvenience. Rechargeable batteries can be used to store solar energy for many applications. They are widely used in portable devices (such as watches and calculators) and outdoor applications (like solar street lights and solar heaters). Li et al. BIB009 have conducted a comprehensive survey on the advancement of solar-powered rechargeable batteries and characteristics of two distinctive connection methods: external combination with photovoltaics and internal integration with photo-electrodes. With the assistance of integrated technology and nanomaterials, small solar energy harvesting systems can be built to provide enough power for tiny sensor systems. Promising nanomaterials and nanotechnology applied for the solar energy harvesting have been discussed in BIB002 . Escobedo et al. BIB004 have designed the first printed flexible tag with characteristics of small size, low cost and low power consumption for gas concentration measurement in sealed environments, which can be powered by two miniaturized solar cells with the energy solely harvested from sunlight or bright artificial light. Sunlight is virtually inexhaustible, renewable, clean and can be harvested to power large-scale outdoor machines efficiently and effectively. For example, it is prevailing for solar-powered aircraft systems in the aerospace industry BIB010 BIB011 BIB003 BIB005 . Some scholars have reviewed its utilization powering water pumping systems instead of diesel power in agriculture BIB013 . Nevertheless, in solar energy harvesting, there are some major disadvantages such as instability, time-variance and regional restriction. inevitably affect the conversion efficiency, although some researchers have studied solar cells suitable for all weather applications BIB006 . For machine condition monitoring, micro-scale photovoltaic cells working with storage batteries can power the sensor nodes to monitor the condition variables of outdoor machinery such as vehicles, marine systems, mining machines and offshore equipment. Compared to sunlight, the conversion efficiency of artificial light is much lower due to the low intensity of the excitation source. Indoor light cannot yet supply enough power for WSNs on indoor machine condition monitoring, and only limited references mention the indoor light harvesting application BIB004 . Until major advances are made in photovoltaic technology it is only useful as a backup for other energy harvesting technologies for indoor machine condition monitoring. For outdoor use, it is undeniable that light energy harvesting is a feasible way to power machine condition monitoring systems with low noise, although solar energy harvesting is restricted by the region, weather, solar panel area, cost and maintainability. A solution is to include rechargeable batteries BIB001 to store the electricity generated by photovoltaic solar cells, which converts the electrical energy into the chemical energy for further storage and recyclable conversion BIB009 . Consequently, photovoltaic cells combined with batteries have the potential to implement online machine condition monitoring. More importantly, solar energy harvesting based condition monitoring system can increase reliability and safety and decrease maintenance costs. But the cost of materials and installation for photovoltaic cells and batteries are significantly expensive  , which is unsuitable for condition monitoring of normal machines.