**4.2 Wind energy**

Wind energy is a form of renewable energy that has gained significant attention in the last 30 years as a potential solution to the world's increasing energy demands. The natural power of the wind can be used to generate electricity without producing harmful emissions like fuel and other toxic energy sources. Cumulative wind capacity worldwide increased from around 20,000 megawatts to more than 500,000 megawatts in the last 15 years. International green organization efforts to minimize climate changes, such as the 2015 Paris treaty, green renewable energy is continuously growing. Wind energy is a popular renewable source of energy that has a minor impact on the environment compared to producing energy by using coal or fuel. Wind power uses the strong wind flow to provide mechanical power through wind turbines to turn electric generators to produce electrical power. Wind kinetic power is used to operate electric turbines and windmills. Windmills cannot be operated in residential areas. Wind energy farms are usually located offshore or on high mountains. When the wind blows, the turbine's blades spin clockwise, capturing energy. The main shaft of the wind turbine, connected to a gearbox within the nacelle, is triggered to spin when the wind blows. The gearbox sends the wind energy by the gearbox to the generator. Wind power is converted to electricity. Offshore wind turbines provide steady, reliable clean energy in many countries.

(a) (b)

**Figure 2.** *(a) Country wind energy farm (b) offshore wind energy site.*

**Figure 2** presents wind energy turbines. **Figure 2a** presents a country wind energy farm. **Figure 2b** presents an offshore wind energy site. The main advantage of wind energy, in several countries, is that wind is a clean, reliable free source of renewable energy with no air or water pollution. Wind energy turbines are ugly and noisy. A disadvantage of wind energy is that the wind turbines rotating blades kill birds, bats, and other protected birds.

Advantage of Wind Energy


Disadvantage of Wind Energy


*Introductory Chapter: Advances in Green Electronics Technologies in 2023 DOI: http://dx.doi.org/10.5772/intechopen.112615*


#### *4.2.1 Innovation in wind energy – Vertical axis wind turbines*

Vertical axis wind turbines (VAWTs) are a new type of wind turbine. Unlike the traditional horizontal-axis wind turbines used for several decades, vertical-axis wind turbines have a unique design that allows them to capture wind energy from any direction. The blades of VAWTs are positioned vertically and rotate around a central axis, making them ideal for use in urban areas and other locations where wind direction is unpredictable. VAWTs have several advantages. Because of their compact design, VAWTs can be installed in various settings, including residential homes and commercial buildings, making them a viable option for decentralized energy generation. Additionally, VAWTs are generally quieter than their horizontal axis turbines, making them better for noise-sensitive environments. Researchers are investigating new materials and designs that could make VAWTs even more efficient and costeffective. **Table 1** presents the global wind farms database in May 2023.

#### **4.3 Green hydropower, water energy**


In water energy sites, the water flow kinetic energy is converted to electric energy. Waterfalls and fast-running water flow may be used to produce electric energy. In the late 19th century, hydropower became a source for generating electricity. The first

#### **Table 1.**

*2023 global wind offshore farms database in mega Watts.*

commercial hydroelectric power plant was built at Niagara Falls in 1879. In 1881, streetlamps in the city of Niagara Falls were powered by hydropower. Hydroelectricity can be used to store energy in the form of potential energy between two areas with different heights with pumped-storage hydroelectricity. Water is pumped uphill into cities during periods of low demand. This energy can be released to generate energy when demand is high.

In this decade, hydropower has an important role in the transition to green energy through its massive quantities of low-carbon electricity and its unmatched capabilities for providing flexibility and storage. Many hydropower plants can ramp their electricity generation up and down very rapidly compared with other power plants such as nuclear, natural gas, and coal. This makes sustainable hydropower an attractive foundation for integrating greater amounts of wind and solar power, whose output can vary depending on factors like the weather and the time of day or year. Global hydropower capacity is expected to increase by 17% between 2021 and 2030. In 2020, hydropower supplied around 17% of global electricity generation, making it the single largest energy source of low-carbon power. Hydropower output has increased by 70% over the past 20 years, but its share of the global electricity supply has held steady because of the increases in wind, solar PV, natural gas, and coal. Nonetheless, hydropower currently meets most of the electricity demand across 28 different emerging and developing countries, with a total population of 800 million.

#### **4.4 Energy harvesting**

As presented in **Figure 3**, the energy harvesting unit consists of an antenna, rectifying diode and circuit, and a rechargeable battery. **Figure 3a** presents a Circular polarized wearable active receiving sensor with energy harvesting unit. The energy harvesting unit and the radiating element provide a self-powered device. The rectifier diode converts electromagnetic energy, AC energy, to direct current (DC energy). Two types of diode rectifiers are usually used a half wave rectifier or a full wave rectifier, [1–6]. A half-wave rectifier converts only the half cycle of the positive voltage. It allows to harvest only one half of the electromagnetic wave. The efficiency of the half wave rectifier is around 41%. The bridge full wave diode rectifier circuit converts electromagnetic energy to DC energy. The bridge rectifier consists of four diodes D1 through D4. The rectifier output DC voltage, *VODC* ¼ 2*Vm=π*, The full wave rectifier efficiency is around 81%. Electromagnetic power amount in public centers, stadiums, hospitals, and malls may range from 1 to 5 mW/cm<sup>2</sup> . The harvesting system efficiency increases as function of the RF power collected by the harvesting system as listed in **Table 2**. The amplifier amplifies the input power collected by the energy harvesting system and improves the efficiency of the harvesting system. Results listed in **Table 2** are also presented by companies that manufacture RF energy harvesting systems, see [1–7]. If the RF radiating sources are close to the harvesting system, the RF power collected by the harvester will be higher. A wearable medical system with energy harvesting unit is presented in **Figure 3b**.

The continuous growth in the production of portable RF communication systems and cellular phones increases the consumption of electrical energy and batteries. In the last 30 years, the trend to use green free space energy, such as light, electromagnetic energy, heat, vibration, muscle motion, and other energy-green sources, has become very important, attractive, and useful. Several methods, research, and inventions to produce electricity from free green energy sources have been published, see [1–7]. Electromagnetic harvesting may be useful to recharge phones and batteries only
