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Isidora Herline
Actuators are mainly classifiable into active and passive actuators. The active actuators need an electric energy source for functioning. In contrast, passive actuators do not require a source and function based on natural energy, such as thermal expansion material, and energy stored in the spring [27]. Various required motions are circular, rotational, oscillatory (seismic), and rectilinear. Therefore, electric actuators are classified according to their motion, degree of freedom (DOF), and excitation sources for particular functional motion. As per motion, actuators are rotary actuators, linear actuators, and a new one called a spherical actuator with multiple degrees of freedom [26]. Linear motion actuators are split into two categories: rotary-to-linear (hybrid motion) actuators involving mechanical transmission units (also called electromagnetically linear actuators as shown in Figure 1) and direct linear motion ones not requiring mechanical transmissions units.
This comprehensive literature survey focuses exclusively on renewable applications with electrical actuators. Particular actuators find a place in multiple renewable energy systems, while others have only specific or limited usage. Furthermore, there are certain advantages and disadvantages (provided subsequently in each Section) concerning actuator motion. We also suggest some alternative solutions for conventional actuators. However, the overall advantages of electric actuators against non-electrical actuators (such as hydraulic and pneumatic) are given as follows:
The oil pumped from a storage tank (see at the right in Figure 5) passes (at ambient oil temperature) through the electric valve actuator to the field to be heated by concentrated solar radiation and returns to the tank via injection at the top of the storage tank. Once the heat energy is extracted from hot oil, the cold oil is re-injected at the bottom of the storage tank [64]. Suitably adjusting the oil flow rate helps to regulate the outlet oil flow temperature and track a desired temperature reference value using an electric valve actuator (along with the control system) that plays a vital role in temperature maintenance [61]. Electric valves comprise an electric motor, gear mechanism, hand wheel, limit switch, and butterfly valve working at three positions: two end positions and an intermediate one. One of the extreme positions is perpendicular to the oil flow, i.e., valve closed position, the other is parallel to oil flow, i.e., fully open position, and the third (intermediate) position where continuously and smoothly rotates the valve to regulate the oil flow at any flow rate.
The solution to this issue is that instead of two rotary actuators, one may use only one actuator called a telescopic actuator, as shown in Figure 3b to push and pull at the center of the cleaner for smooth and symmetric motion. This reduction in an actuator also reduces system nonlinearities, making the system less energy-demanding. Furthermore, such a structure is helpful for solar farms due to its autonomous working. Wheeled semi-automatic cleaning robots having two geared motor actuators connected to two ends of the robot also solve the motion interruption problem [24]. Panat et al. [68] shows the electrostatic dust-removal system with a linear guide slide stage actuator motorized by a stepper motor. Williams et al. [15] present an array of nine piezoceramic actuators attached to the backside of the solar panel surface to handle the dust falling on PV panels by mechanical vibrations (acceleration). Nine actuators are excited by three three-channel piezo amplifiers. Sine sweep excitation of different magnitudes and frequencies (especially significantly higher frequency from 400 Hz to 5000 Hz) shows that high acceleration, i.e., the best dust cleaning motion, efficiently improves the dust-removal process. Such cleaning methods are effective in Martian surface missions or lunar surface environments. Dawson et al. [69] state that instead of piezoelectric actuators, inexpensive and low-power piezoelectric buzzers are helpful for panel cleaning. Incorporate piezoelectric vibrational actuators into the structural supports of photovoltaic panels to occasionally induce vibrations to loosen accumulated dust and are mounted at nodes of a grid of spars, as shown in Figure 7a. Despite being compact, low-power consuming, and inexpensive, the commercially available buzzers, which typically have operating frequencies in kHz, need a redesign for lower photovoltaic panels with lower natural vibrational frequencies.
Actuators used in wave energy conversion (WEC) systems are categorized into oscillating water columns (OWCs) and oscillating body systems or wave-activated body systems. Figure 10 shows the second category along with a linear PTO mechanism. This type of motion conversion system (actuator) and PTO device is essential in the perspective of wave power conversion efficiency. Aderinto et al. [85] explained detailed PTO types, scales, and efficiencies, among which were the efficiencies of five different combinations of actuators and PTO devices, and the results of their numerical simulation with computational fluid dynamics (CFD) are shown in Table 5. The direct-drive linear generator system with an oscillating buoy shows 95% efficiency, which is the highest compared to others. Except for linear generators, all other PTOs have losses in their motion conversion process, but in linear generators, no motion conversion is required and, therefore, comes with higher efficiency.
Rahman et al. [86] reported that PTOs, which are also built of piezoelectric actuators, are used to produce a significant quantity of electrical power from the ocean. Therefore, energy converters can be used to power applications that function in the ocean, such as various electrical sensing elements, floating harbors, robotics, etc. Wave energy converters (WECs) can improve their energy conversion efficiency by including several types of piezoelectric materials. Experiments reveal that by straining the material with a pressure of 1.196 kPa at a frequency of 20 Hz, 0.2 W electric power with 2.2 V may be obtained using this technology.
Various mechanical, hydraulic, pneumatic, electrical, and hybrid actuators can alter motion per the requirements of particular applications. However, except for electrical ones, all actuators are restricted due to their size, complex auxiliary equipment, frequent need for maintenance, and sluggish environment in renewable applications. This brief review paper highlights some unique and significant research works on applying electrical actuators to renewable applications. Four renewable energy resources, i.e., solar, wind, bio-energy, and geothermal energy, are considered to review electric actuators applicable to renewable energy systems. This review analyses the types of actuators associated with the mentioned renewable application, their functioning, their motion type, present use, advantages, disadvantages, and operational problems. The information gathered in this paper may open up new ways of optimization opportunities and control challenges in electrical actuators, thereby making more efficient systems. Furthermore, some energy-efficient and cost-effective replacements of convectional actuators with new innovative ones are suggested. This work aims to benefit scientists and new entrants working on actuators in renewable energy systems.
Acrolein is a toxic unsaturated aldehyde and widespread environmental pollutant produced during lipid peroxidation and also by burning of tobacco or liquid fuels. Inhalation or dermal exposure to acrolein could be toxic to organisms. This very reactive aldehyde has a strong affinity for binding to proteins thus forming pathogenic protein-adducts. In the present study we have analyzed formation of bioreactive acrolein-protein adducts in bovine serum albumin solution exposed to exhaust gases of mineral diesel fuel and of mineral diesel fuel supplemented with different amounts of a novel diesel fuel additive denoted Ecodiesel (produced by a genuine procedure of recycling of plant oils used for food preparation). The effects of acrolein-protein adducts were tested on human microvascular endothelial cells and on human osteosarcoma cells that are sensitive to bioactivities of lipid peroxidation products. The results have shown a reduction of the bioreactive acrolein in exhaust gases when mineral diesel was supplemented with 5-20% Ecodiesel. Moreover, acrolein-protein adducts obtained from mineral diesel supplemented with Ecodiesel were less toxic than those obtained from mineral diesel alone. Thus, we assume that supplementing mineral diesel fuel with Ecodiesel would be of benefit for the use of renewable energy, for environment and for human health due to reduced environmental pollution with bioreactive acrolein.
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