**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

**13**

pointed at the sun throughout the day.

*Developments in Wireless Power Transfer Using Solar Energy*

improvements with economies at a bigger scale manufacture.

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 [6]. 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

**Working of a Solar Cell:** The working of a solar cell depends upon the phenomenon of photo-electricity, i.e., the liberation of electrons by light falling on a body. The application of this photo-electric phenomenon to semi-conductors such as silicon has proved to be of great use. To displace an electron from a fixed position in the material and make it move freely in the material, a vacant electron position or 'hole' is created in the material by light waves when they strike a semiconductor material with sufficient energy. If a neighboring electron leaves its site to fill the hole site, this hole acts as positive charge and can move this electron. The electron–hole pairs are differentiated by the voltage in the cell material, and this creates a current. By adding small amounts of dopants and impurities to the pure material and by joining two semiconductor materials, an intrinsic voltage may be created. The silicon becomes electron-rich and is referred toas 'n-type' silicon when impurities such as phosphorous are introduced into this silicon. Excess holes are created when impurities such as boron give rise to 'p-type' silicon. A free charge leaks across the common boundary of these n-type sand p-type silicon (one electron rich and the other electron-deficient) and becomes fixed as ions in the region near to the boundary, when these two oppositely charged semiconductors are in contact. At the interface, the fixed (but opposite) ions create an electric field that sends free electrons one way and free holes the other side. No current flows in the solar cell, when no light falls on its surface i.e., in the dark. A current will flow as long as the solar cell is illuminated which can supply electricity to an external load circuit. The current from the solar cell passes directly through the load circuit. The current generated can be changed by the power-conditioning equipment to alternating current at the voltage and current levels different from those provided by the solar cells cell. The sub-systems of the PV module system include energystorage devices such as concentrated lenses, batteries and mirrors that focus the sunlight onto a smaller and hence less costly semiconductor solar cell. If concentration system is utilized, a tracking subsystem may be required to keep the array

**Maximum power point tracking:** Maximum power point tracking (MPPT) is used to maximize the power output from wind turbines and photovoltaic (PV) solar systems. PV solar systems exist in several different configurations with a solar inverter, which is connected directly to the electrical grid. A second adaptation which is called the hybrid inverter. In this hybrid inverter, the most basic version sends power from the solar panels directly to the DC-AC and splits the power at the inverter, where a percentage of the power goes to the grid and the remainder goes to

*DOI: http://dx.doi.org/10.5772/intechopen.97099*

### *Developments in Wireless Power Transfer Using Solar Energy DOI: http://dx.doi.org/10.5772/intechopen.97099*

*Wireless Power Transfer – Recent Development, Applications and New Perspectives*

power into DC power are connected in the rectifying circuit.

ily. Therefore, this is the cause of the health concern [5].

load is connected to the receiving coil to complete the circuit [6].

**2. State-of-the-art: wireless power transfer using solar energy**

trons as opposed to a few klystrons.

microwave ovens, it is one of the main advantages to using many smaller magne-

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

**Use of Microwave Power Transmission in Solar Power Satellites (SPS):** For transmitting power to earth stations, solar power generating satellites can be launched into space. Based on this idea, which was first proposed in 1968 based on experiments carried out in terrestrial laboratories. At high earth orbit in geosynchronous location, the SPS satellites are put in the orbits. This feature enables them to receive light almost whole year by up to 99% of the yearly time. A facility of a large rectenna array built on the Earth is for collecting the incoming microwaves. The satellite is required to be built with a retrodirective transmitter for maintaining a good lock on the rectenna. This helps in locking on to a pilot beam emanated from the ground station. Most of the research is done in the 2.4 GHz to 5.8 GHz range. Therefore, there are some spectrum regulatory issues to deal with their use. Also, the retro directive antenna system is unproven with present technology. The microwave beam could veer off target and can microwave some unsuspecting fam-

**Magnetic Resonance:** In this technology, an oscillator is designed to generate the carrier signal for transmitting the power. Usually, oscillators are not intended to deliver the power, because a power amplifier is required to the oscillator for amplification of the oscillating signal. The output power to the transmission coil is transferred by the power amplifier. For receiving the transmitted power, a receiver coil is built. Since the power received at the receiver side is having an alternating current. Thus, a rectifier is needed for rectification of the AC voltage. An electric

**WiTricity:** The new technology called WiTricity is based on using coupled resonant objects [1]. With the same resonant frequency, two resonant objects manage to exchange energy efficiently, while interacting weakly with extraneous off-resonant objects. The resonant nature of the witricity system guarantees the strong interaction between the sending unit and the receiving unit, while the interaction with the rest of the environment is weak. The design consists of two copper coils, each a selfresonant system. One of the coils, attached to the power source can be a solar power and is termed as the sending unit of the witricity. The irradiation of the environment with electromagnetic waves oscillates the space around it with a non-radiative magnetic field oscillating at MHz frequencies. The non-radiative field intervenes the power exchange with the receiving coil, which is built for the purpose of creat-

Solar cells are semiconductor devices in which incident sunlight releases electric

charges so they can move across the semiconductor freely and thus generate an

**12**

ing resonance with the field.

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 [6]. 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.

**Working of a Solar Cell:** The working of a solar cell depends upon the phenomenon of photo-electricity, i.e., the liberation of electrons by light falling on a body. The application of this photo-electric phenomenon to semi-conductors such as silicon has proved to be of great use. To displace an electron from a fixed position in the material and make it move freely in the material, a vacant electron position or 'hole' is created in the material by light waves when they strike a semiconductor material with sufficient energy. If a neighboring electron leaves its site to fill the hole site, this hole acts as positive charge and can move this electron. The electron–hole pairs are differentiated by the voltage in the cell material, and this creates a current. By adding small amounts of dopants and impurities to the pure material and by joining two semiconductor materials, an intrinsic voltage may be created. The silicon becomes electron-rich and is referred toas 'n-type' silicon when impurities such as phosphorous are introduced into this silicon. Excess holes are created when impurities such as boron give rise to 'p-type' silicon. A free charge leaks across the common boundary of these n-type sand p-type silicon (one electron rich and the other electron-deficient) and becomes fixed as ions in the region near to the boundary, when these two oppositely charged semiconductors are in contact. At the interface, the fixed (but opposite) ions create an electric field that sends free electrons one way and free holes the other side. No current flows in the solar cell, when no light falls on its surface i.e., in the dark. A current will flow as long as the solar cell is illuminated which can supply electricity to an external load circuit. The current from the solar cell passes directly through the load circuit. The current generated can be changed by the power-conditioning equipment to alternating current at the voltage and current levels different from those provided by the solar cells cell. The sub-systems of the PV module system include energystorage devices such as concentrated lenses, batteries and mirrors that focus the sunlight onto a smaller and hence less costly semiconductor solar cell. If concentration system is utilized, a tracking subsystem may be required to keep the array pointed at the sun throughout the day.

**Maximum power point tracking:** Maximum power point tracking (MPPT) is used to maximize the power output from wind turbines and photovoltaic (PV) solar systems. PV solar systems exist in several different configurations with a solar inverter, which is connected directly to the electrical grid. A second adaptation which is called the hybrid inverter. In this hybrid inverter, the most basic version sends power from the solar panels directly to the DC-AC and splits the power at the inverter, where a percentage of the power goes to the grid and the remainder goes to a battery bank. The third type uses a dedicated PV inverter that features the MPPT in which the inverter is not connected at all to the grid. The power flows directly into the battery bank in this configuration. The micro inverters are deployed, one for each PV panel, which are a variation on these configurations. The efficiency of solar PV system by up to 20% by the use of microinverter. The grid-connected power as well as solar PV power and branching off power for battery charging is achieved by incorporating a new MPPT algorithm that is equipped with specialty inverters which serve these three functions,

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.

**Solar Photovoltaic System Technology for Wireless Power Transfer:** The solar photovoltaic panels can be installed on the façade or roofs. These solar photovoltaic panels convert the sunlight into the direct current (DC) power. The electric current is added or drawn from the electric batteries by means of installing the charge controller, which limits the rate of the current. The batteries are one of the most important parts of the solar power system. The charge controller helps in protecting the batteries from overvoltage and overcharging. This helps in increasing the life span of the batteries. From the solar photovoltaic panels, the DC power is transmitted to the inverter. In the inverter, it is converted into alternating current (AC) power.

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 [1]. 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 [6–13].

**15**

*Developments in Wireless Power Transfer Using Solar Energy*

*Simplified block diagram for wireless power transfer using solar energy.*

**Working of a Transmitter:** The input from mains is given to the power and frequency controller. The output of this system is given to MOSFET (metal–oxide– semiconductor field-effect transistor)/IGBT (insulated-gate bipolar transistor). The objective of using the MOSFET/IGBT is for conversion of DC power to AC power. It is also used for amplifying square wave at the gate input. The voltage transmitted to the transmitting coil generates magnetic field around it. The capacitor, which is connected to the coil in parallel helps in achieving the resonating circuit. The magnetic field get induced in the receiving coil at the point of the resonant frequency of receiving coil matches with the resonant frequency of the transmitting coil. Different values of "L" and "C" for resonant frequency are used for the matching purpose. To match the resonant frequency of the receiver and the transmitter coil, the switches to vary the time periods of the square wave by controlling the

**Working of a Receiver:** The receiving coil comes in the range of the magnetic field of the transmitting coil. This helps in achieving the voltage across the transmitting coil, which gets induced in the receiving coil because of mutual inductance. This also helps in matching of resonance frequency at the received voltage is in AC power form. Here the AC power is converted into DC for DC load, where rectifier circuit can be used to provide constant DC at the output for driving the load. And if

A simplified block diagram for wireless power transfer using solar energy

**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 [11]. 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;

the load is AC power load then it can be given directly to the output.

*DOI: http://dx.doi.org/10.5772/intechopen.97099*

frequency at output can be used [14].

**Figure 1.**

technology is illustrated in **Figure 1** [14].

*Developments in Wireless Power Transfer Using Solar Energy DOI: http://dx.doi.org/10.5772/intechopen.97099*

**Figure 1.**

*Wireless Power Transfer – Recent Development, Applications and New Perspectives*

inverters which serve these three functions,

to AC power after utilizing MPPT.

(AC) power.

a battery bank. The third type uses a dedicated PV inverter that features the MPPT in which the inverter is not connected at all to the grid. The power flows directly into the battery bank in this configuration. The micro inverters are deployed, one for each PV panel, which are a variation on these configurations. The efficiency of solar PV system by up to 20% by the use of microinverter. The grid-connected power as well as solar PV power and branching off power for battery charging is achieved by incorporating a new MPPT algorithm that is equipped with specialty

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

**Solar Photovoltaic System Technology for Wireless Power Transfer:** The solar photovoltaic panels can be installed on the façade or roofs. These solar photovoltaic panels convert the sunlight into the direct current (DC) power. The electric current is added or drawn from the electric batteries by means of installing the charge controller, which limits the rate of the current. The batteries are one of the most important parts of the solar power system. The charge controller helps in protecting the batteries from overvoltage and overcharging. This helps in increasing the life span of the batteries. From the solar photovoltaic panels, the DC power is transmitted to the inverter. In the inverter, it is converted into alternating current

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

The principle of witricity can be applied into this scenario [1]. 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

lines is achieved by means of wireless power transfer.

objects or materials such as radio signals or biological tissue [6–13].

**14**

*Simplified block diagram for wireless power transfer using solar energy.*

**Working of a Transmitter:** The input from mains is given to the power and frequency controller. The output of this system is given to MOSFET (metal–oxide– semiconductor field-effect transistor)/IGBT (insulated-gate bipolar transistor). The objective of using the MOSFET/IGBT is for conversion of DC power to AC power. It is also used for amplifying square wave at the gate input. The voltage transmitted to the transmitting coil generates magnetic field around it. The capacitor, which is connected to the coil in parallel helps in achieving the resonating circuit. The magnetic field get induced in the receiving coil at the point of the resonant frequency of receiving coil matches with the resonant frequency of the transmitting coil. Different values of "L" and "C" for resonant frequency are used for the matching purpose. To match the resonant frequency of the receiver and the transmitter coil, the switches to vary the time periods of the square wave by controlling the frequency at output can be used [14].

**Working of a Receiver:** The receiving coil comes in the range of the magnetic field of the transmitting coil. This helps in achieving the voltage across the transmitting coil, which gets induced in the receiving coil because of mutual inductance. This also helps in matching of resonance frequency at the received voltage is in AC power form. Here the AC power is converted into DC for DC load, where rectifier circuit can be used to provide constant DC at the output for driving the load. And if the load is AC power load then it can be given directly to the output.

A simplified block diagram for wireless power transfer using solar energy technology is illustrated in **Figure 1** [14].
