Sample electrical measurement results with varying resistance of potentiometer.
This chapter presents state-of-the-art and major developments in wireless power transfer using solar energy. The brief state-of-the-art is presented for solar photovoltaic technologies which can be combined with wireless power transfer (WPT) to interact with the ambient solar energy. The main purpose of the solar photovoltaic system is to distribute the collected electrical energy in various small-scale power applications wirelessly. These recent developments give technology based on how to transmit electrical power without any wires, with a small-scale by using solar energy. The power can also be transferred wirelessly through an inductive coupling as an antenna. With this wireless electricity we can charge and make wireless electricity as an input source to electronic equipment such as cellphone, MP3 Player etc. In harvesting energy, technologies of ambient solar radiation like solar photovoltaic, kinetic, thermal or electro-magnetic (EM) energy can be used to recharge the batteries. Radio frequency (RF) harvesting technologies are also popular as they are enormously available in the atmosphere. The energy converted to useful DC energy which can be used to charge electrical devices which need low power consumption. The chapter has also presented a parallel plate photovoltaic amplifier connected to a potentiometer as a Resistance-Capacitance (RC) circuit power amplifier. The effect of inductance and resulting power transfer has been theoretically determined in the RC amplifier circuit. The electrical and thermal properties and measurements from a parallel plate photovoltaic amplifier were collected to analyze the unbalanced power transfer and inductance in a nonlinear RC circuit amplifier using equivalent transfer functions. The concept of Wireless Information and Power Transfer using Electromagnetic and Radio Waves of Solar Energy Spectrum is also briefly outlined.
- wireless power transfer
- solar energy
- energy harvesting
Wireless power transfer (WPT) is defined as the transmission of electrical power without wires through various methods and technologies using time-varying electric, magnetic, or electromagnetic fields. The development of various technologies for wireless power transfer is being taken widely across the power electronics domains. There are applications which include microwaves, solar cells, lasers, and electro-magnetic waves’ resonance in wireless power transfer. With wireless power transfer, the electrical devices are continuously charged without the use of power cord. The three types of wireless power transfer systems can be described by microwaves, resonance, and solar cells. From the power source to a receiver in an electrical device or gadget, microwaves can be used to send electro-magnetic radiation. The method of resonance can be applied at certain frequencies to cause an object to oscillate by electro-magnetic radiation. These oscillations can be used to transfer energy between two oscillating sources. The satellite in space with solar cells can be used to capture the solar energy and transmit this energy back to earth. This method would involve the conversion of radio waves frequencies into electrical power and electrical power into radio waves frequencies. The main purpose of the solar photovoltaic system is to distribute the collected electrical energy in various small-scale power applications wirelessly. These recent developments give technology based on how to transmit electrical power without any wires, with a small-scale by using solar energy.
Wireless power transfer (WPT) using solar energy technology is having vast applications. The ability of technology is to transfer power efficiently, safely over distance can improve gadgets and products by making them more reliable, climate and environment benign. Wireless power transfer (WPT) can be used in various applications for example in automatic wireless charging, direct wireless power supply of devices such as cellphones, loudspeakers, digital picture frames, flat screen TV’s, home theater accessories etc. . The power can also be transferred wirelessly through an inductive coupling as an antenna. With this wireless electricity we can charge and make wireless electricity as an input source to electronic equipment such as Handphone, MP3 Player etc. In harvesting energy, technologies of ambient solar radiation like solar photovoltaic, kinetic, thermal or electro-magnetic (EM) energy can be used to recharge the batteries. Radio frequency (RF) harvesting technologies are also popular as they are enormously available in the atmosphere. The energy converted to useful DC energy which can be used to charge electrical devices which need low power consumption.
This chapter outlines the recent developments of wireless power transfer using solar energy. The rest of the chapter contains brief history of the development of wireless power transfer. Various methods and technologies used in wireless power transfer are outlined. The State-of-the-Art of Wireless Power Transfer using Solar Energy is also described along with the literature review. The later part of the chapter contains novel concept of transmitter design of a parallel plate photovoltaic amplifier device integrated in a Building. The design of a receiver using radio waves for wireless information and power transfer is also briefly discussed. Conclusions and equations for design of a transmitter and a receiver are provided in the later part of the chapter.
The presence of electro-magnetic waves by devising a mathematical model is predicted by James C. Maxwell in 1864. The Poynting Vector would play an important role in quantifying the electromagnetic energy (John H. Poynting, 1884). Heinrich Hertz first succeeded in showing experimental evidence of radio waves by his spark-gap radio transmitter in 1888, which was bolstered by Maxwell’s theory. The wireless power transfer was started by the prediction and evidence of the radio wave in the end of 19th century. Wireless power transfer of electrical power was pioneered by Nikola Tesla . He conducted experiments on wireless power in 1891 at his “experimental station” at Colorado. A small incandescent lamp by means of a resonant circuit grounded on one end was successfully lighted by Nikola Tesla . The lower end connected to the ground and the upper end free with a coil outside his laboratory. The current was induced in the three turns of wire wound around the lower end of the coil and the lamp was lighted. For trans-Atlantic wireless telephony and demonstration of wireless electrical power transfer by means of Wardenclyffe tower, which was designed by Tesla. The modern development of microwave power transmission which dominates research and development of wireless power transfer today was achieved by William C. Brown. In the early 1960s Brown invented the rectenna which directly converts microwaves to DC current. He demonstrated its ability in 1964 by powering a helicopter from the solely through microwaves.
The generation of microwave power in the microwave power source and its output power is managed by electronic restrain circuits on the transmission side. To match the impedance between the transmitting antenna and the microwave source, a tuner is attached. Based on the direction of signal propagation by Directional Coupler, whose function is to divide the attenuated signals. The transmitting antenna emits the power uniformly through free space to the receiver antenna. An antenna receives the transmitted power and translates the microwave power to DC power on the receiving section. For setting the output impedance of a signal source equal to the rectifying circuit, both impedance matching circuit and the filter is provided. The Schottky barrier diodes which converts the received microwave power into DC power are connected in the rectifying circuit.
2. State-of-the-art: wireless power transfer using solar energy
Solar cells are semiconductor devices in which incident sunlight releases electric charges so they can move across the semiconductor freely and thus generate an electric field to light a bulb or power a motor. The whole phenomenon of producing an electric field of voltages and currents across the solar cell is known as the photovoltaic effect . The incident light for solar cells—sunlight—is freely available and abundant. The intensity of sunlight near the surface of the earth is at the most in the range of one thousand watts per square meter known as 1 sun. The cost must be considered in calculating the cost of the electricity produced by solar cells as the area occupied by the photovoltaic modules power generating system may be relatively large. The cost per unit output is the decisive factor relative to that of alternative power sources, for acquiring, installing, and operating the photovoltaic system. This is dependent on this sole factor that determines whether the solar cells will be used to supply electricity in a given situation. Solar cells are economically competitive with alternative sources in their use in terrestrial applications. The examples of these applications include pumps, communication and refrigerated devices located in remote areas far from existing transmission and distributed power lines. The markets for solar cells are growing rapidly as the cost of power from conventional sources rises, and as the cost of solar cells reduces because of technological improvements with economies at a bigger scale manufacture.
The application related to solar photovoltaic systems contains these MPPT apprehensions. A non-linear output efficiency which can be analyzed based on the I-V curve of the solar cells establishes a complex relationship between temperature and total resistance that produces across solar cells. The output of the PV cells and application of the proper load to obtain maximum power for any given environmental conditions is achieved by the purpose of the MPPT system. MPPT devices are connected into solar photovoltaic system for providing voltage or current conversion, filtering, and regulation for driving various loads, including power grids, batteries, or motors. Solar power inverters are used to convert the DC power to AC power after utilizing MPPT.
The phase locked loop oscillator with a Power Amplifier is connected to the solar inverter. A step up/down transformer is connected to this end section. The generation of an output signal whose phase is related to the phase of the input signal is achieved by means of the phase locked loop oscillator. There is generation of a periodic signal by means of the phase locked loop oscillator. The comparison of the phase of that signal with the phase of the input periodic signal and corrects the oscillator to keep the phases matched is achieved by means of the phase detector. The power amplifier is used to achieve high amplification of the signal. The stepping up or stepping down the signal, which can be done according to the application is achieved by means of the transformer which is connected to the end section of the amplifier. In the AC line, this alternating current is then transmitted. For powering the connected load or other domestic devices, the power from these AC lines is achieved by means of wireless power transfer.
The principle of witricity can be applied into this scenario . To transfer wireless power between two electromagnetic resonant objects, Witricity can be used which is based on strong coupling. This method is different from other methods like air ionization, microwaves, and induction. The witricity system consists of transmitters and receivers. These contain magnetic loop antennas critically tuned to the same frequency. Due to the operation in the electromagnetic near field, the receiving devices must be no more than the quarter-wavelengths from the transmitter. The witricity uses near field inductive coupling through magnetic fields like those found in transformers. These tuned magnetic fields generated by the primary coil can be arranged to interact actively with matched secondary windings in distant equipment. These magnetic fields are far from more-weakly with any surrounding objects or materials such as radio signals or biological tissue [6, 7, 8, 9, 10, 11, 12, 13].
3. Literature review: wireless power transfer (WPT) using solar energy
Only few relevant papers which highlight solar energy based wireless power transfer are briefly discussed here. Zambari et al., investigated the development of wireless energy transfer module for solar energy harvesting . They studied the module of wireless energy transfer (WET) for interaction with the ambient solar energy. The main objective was to distribute the collected electrical energy from a solar panel module to in house loads appliances wirelessly. The investigations were carried out on the solar panel module with 240 W, 30 V, Poly Crystalline Silicon Photovoltaic solar panel. The design of the WET module was based on magnetic resonance technology. This technology uses two sub-unit modules development; driving circuit and two coils mutually inducted to transfer energy in a suitable resonant frequency. With the advantage of nearly 99% efficiency theoretically, class-D RF power amplifier was used as the driving circuit for transmitted coil switching .
Fareq et al., studied the wireless power transfer by using solar energy . They developed the project based on electrical power without any wires, with a small-scale by using solar energy. The power is transferred wirelessly through an inductive coupling as an antenna. The experiments were conducted and the wireless power transfer can be transfer energy up to 10 cm. with efficiency 0–10 cm; 98.87% -40% . Ojha et al., investigated solar energy based wireless power transfer . They reviewed on wireless power transfer (WPT) using renewable source i.e. solar energy. The principle behind WPT used was inductive coupling wherein an electric field is generated thus transmitting power from transmitter to receiver. The paper has highlighted the important use of components like a solar panel, rechargeable battery, booster circuitry, and load. Wireless transmission of power to work up a load was highlighted in the paper . Lakshmi M. K., et al. investigated wireless power transmission through solar power generation . The phenomenon of transfer power using a renewable source, without using wired medium. This paper mainly focused on combining both wireless and solar technologies together with use of the principle through coupled resonant objects for the transferring electricity. The overall goal of this paper is to design and implement a clean power generation and wireless power transmission system which can be used as a standard means for charging any electronic gadget .
Maqsood et al., investigated wireless power transmission using solar based power satellite technology . The wireless electricity (Power) transmission (WET) was focal point of their research and they presented the concept of transmitting power wirelessly to reduce transmission and distribution losses. The wired distribution losses are 70–75% efficient. The paper also highlighted the benefits of using WET technology specially by using Solar based Power satellites (SBPS) and also focused on how we make electric system cost effective, optimized and well organized . Keerthana et al., investigated Wireless Power Transfer Using Rectenna . The Radio frequency (RF) harvesting technologies were highlighted in the paper. The RF harvesting technologies receive and convert the useful DC energy and can further be used to charge electrical devices which need low power consumption. The paper investigated a microstrip square patch antenna operating at 2.45 GHz. It was fabricated on a low-cost FR4 substrate having a dielectric constant of 4.4 with a thickness of about 1.2 mm. The L-shaped matching network was designed for maximum power transfer between the antenna and the rectifier. The HSMS-2850 zero bias Schottky diode was used as a rectifier. The RF-DC rectification was done with an efficiency of 42.8% at -7 dBm at 2.45 GHz .
4. Transmitter design: a parallel plate photovoltaic amplifier device integrated in a building
A parallel plate photovoltaic device connected to a potentiometer is analyzed as a star connected 3-Phase Resistance-Capacitance (RC) circuit amplifier. The effect of inductance and resulting power transfer has been determined in the RC circuit amplifier constituting of a parallel plate photovoltaic device. The analysis has also discussed from the electrodynamics point of view, power transfer and effect of induction losses in a 3-Phase RC circuit amplifier constituting of a parallel plate photovoltaic device. The theory of the sinusoidal steady-state response was applied in performing the analysis of the circuit, because of the advantage of representing a periodic function in terms of a sinusoidal exponential function. The full-scale experimental setup for a parallel plate photovoltaic device connected to a potentiometer was installed in an outdoor room facility located at Concordia University, Montréal, Canada [17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34]. The analysis has been performed on the basis of the accepted unified theory for stresses and oscillations, as proposed by the author . The experimental setup is illustrated in Figure 2 . A pair of glass coated photovoltaic (PV) modules forming a parallel plate duct with a plywood board and connected to a potentiometer was used to build an amplifier. A wire-wound variable resistor with resistance up to 50 Ω was a wire-wound circular coil with a sliding knob contact acted as a potentiometer for the circuit . This potentiometer was used to vary electrical resistance across connected PV modules without interrupting the current. A star connected RC circuit amplifier with a parallel plate photovoltaic device connected to a potentiometer was built (Figure 3).
5. Electrical parameters for the RC circuit amplifier
5.1 Discussions on power transfer and effects of inductance
The Figure 5(b) shows that the instantaneous power is negative whenever the voltage and current are of opposite sign. However, as has been illustrated in the Figure 5(b) that positive area of p(t) energy exceeds the negative area. Therefore, the average power is finite. Since the angle, θ, is small between current and voltage, the negative area of p(t) energy become very small. During the first quarter cycle (from 0° to 90°) the applied voltage rises from slightly negative value to a maximum and the capacitor is receiving a charge. The power curve is positive during this period and represents energy stored in the capacitor. From 90° to 180°, the applied voltage is falling from maximum to slightly negative value and the capacitor is discharging. The corresponding power curve is negative and represents energy returned to the circuit during this interval. The third quarter cycle represents a period of charging the capacitor and the fourth quarter represents a discharge period.
6. Development of a receiver using radio waves for wireless information and power transfer
The focus of the current research is to expedite the efforts for development of a receiver using radio waves for wireless information and power transfer using solar energy spectrum. Liang Liu et al. investigated transmit beamforming for simultaneous wireless information and power transfer using radio frequency (RF) transmission . It is essential to have Radio frequency (RF) transmission enabled wireless power transfer (WPT) to power energy-restricted wireless systems (e.g., sensor networks), where dedicated energy transmitters are deployed to broadcast RF signals to charge low-power electric devices (e.g., sensors and RF identification (RFID) tags), as it is a cost-effective solution. Radio Frequency (RF)-based wireless power transfer (WPT) can provide continuous and controllable power supply, and thus is applicable to more energy-demanding applications . Radio frequency (RF) signals have been widely used in wireless communications as the carrier for wireless information transfer (WIT) for several decades.
A query thus arises that whether we can utilize RF signals more efficiently for both WPT and WIT at the same time with a new technique called simultaneous wireless information and power transfer (SWIPT) . The SWIPT is developed by considering a single-antenna point-to-point channel, where the trade-off between the achievable rate for WIT and the received energy for WPT is investigated that the single-antenna receiver can utilize the same received RF signals for both information decoding (ID) and energy harvesting (EH) at the same time without any loss. However, this assumption is difficult to realize in practice since existing information receivers (IRs) and energy receivers (ERs) are separately designed with distinct circuit structures, and as a result, each of them cannot be used to decode information as well as harvest energy at the same time. The two basic receiver structures have been widely adopted in the literature .
Time-Switching receiver (TS) switches between an information decoder and an energy harvester over time. This technique is the simplest way to implement SWIPT by using off-the-shelf commercially available circuits for information decoding (ID) and energy harvesting (EH), respectively. It is crucial to determine their operation modes (ID or EH) over time for TS receiver. This is based on their communication and energy requirements, as well as the channel conditions . Power-Splitting receiver (PS) splits its received signal into two portions with one for information decoding (ID) and the other for energy harvesting (EH). In this technique, it is important to determine the power splitting ratio at each antenna to balance the rate-energy trade-off between the information decoding (ID) and energy harvesting (EH) receivers. Note that time-switching and power-splitting receiver can be regarded as a special and low-complexity realization of power-splitting receiver with only binary (0 or 1) power splitting ratio at each receiving antenna. They are implemented by different hardware circuits (time switcher versus power splitter) in practice .
There are miscellaneous issues investigated by many researchers on wireless power transfer. A. M. Azman et al., investigated superimposition technique in wireless power transfer for enhancing the distance of transmission of the transmission coil . This technique resulted in incrementation of the distance by up to 2 times compared to the system without superimposed technique. Yunfei Chen et al., investigated interference analysis in wireless power transfer . They studied the co-channel interference (CCI) generated by wireless power transfer. They considered the effect on information delivery for three widely used setups of simultaneous wireless information and power transfer (SWIPT), hybrid access point (HAP) and power beacon (PB). In the book on Wireless Power Transfer edited by Johnson I. Agbinya, various innovative techniques for design of Optimal Wireless Power Transfer Systems are discussed . The authors present new methods of delivering flux efficiently using the inductance-based transmitter to an inductance-based receiver by using either flux concentrator or separator. The flux coupling coefficient can be increased by the concentrator. This leads to increased flux delivered to the receiver by a large order of magnitude. Whereas the separator helps in reducing the crosstalk between two identical types of nodes and also leads to significant increase in power delivery. In another paper, Zhen Zhang et al., investigated energy encryption for wireless power transfer . They studied the improved security performance of wirelessly transferred energy as an attempt to switch off other unauthorized energy transmission channels and enhancing security of energy transmission.
This chapter has presented brief outline of the state-of-the-art and developments in wireless power transfer using solar energy. The harvesting technologies of ambient solar radiation like solar photovoltaic, kinetic, thermal or electro-magnetic (EM) energy can be used to recharge the batteries and power various electronic gadgets. Brief on Radio frequency (RF) harvesting technologies is also presented. The energy converted to useful DC energy which can be used to charge electrical devices which need low power consumption. The chapter has also presented analysis of the parallel plate photovoltaic amplifier connected to a potentiometer as a Resistance-Capacitance (RC) circuit power amplifier. The effect of inductance and resulting power transfer was theoretically determined in the RC amplifier circuit. The electrical and thermal properties and measurements from a parallel plate photovoltaic amplifier were collected to analyze the unbalanced power transfer and inductance in a nonlinear RC circuit amplifier using equivalent transfer functions. The concept of Wireless Information and Power Transfer using Electromagnetic and Radio Waves of Solar Energy Spectrum is also briefly outlined. The chapter has also presented miscellaneous issues pertaining to wireless power transfer such as superimposition technique, interference, and security issues. Appendix has presented Equations for transmitter and receiver using mutual inductance of the magnetic resonance between transmitter and receiver.
A transmitting antenna is surrounded by an electromagnetic field. This electromagnetic field is divided into two separate regions-the reactive near field and the radiating field. The energy is stored in the transmitting coil before it propagates as electromagnetic waves to the receiving coil .
The magnetic field experience between transmitter or receiver is called mutual inductance, which can be predicted through:
Where, L1 is inductance of transmitter coil and L2 is inductance of receiver coil.
For circular loop coil the inductance can be calculated by using the following formula :
= 4π × 10−7permeability of vacuum, (H/m)
The coil inductance (
Where, Rac is AC resistivity; Rrad is radiation resistivity. The quality factor