**Disadvantage of Hydropower Energy**

• Hydropower energy cites depend on rain fall, snow, the weather, and water stream


#### **Table 1.** *Global wind farms database.*

**Figure 3.** *Hydropower energy cite.*

*Introductory Chapter: Green Computing Technologies and Industry in 2021 DOI: http://dx.doi.org/10.5772/intechopen.96847*


#### **4.4 Energy harvesting**

The continuous growth in production of portable RF systems increase the consumption of batteries and electrical energy. Batteries and conventional electrical energy increase the environmental pollution. In last twenty years, the trend of using free space energy such us light, heat, electromagnetic energy, vibration, muscle motion and other energy sources, has become very attractive and useful. Several inventions and methods to produce electricity from green energy sources have been presented, see [1–3]. RF harvesting may be useful and recharge batteries only if we collect as much RF energy as possible. In this case, energy harvesting units can eliminate the need to charge batteries by using electrical cables. It is crucial to harvest RF energy from several RF devices and systems. Wideband or multiband antennas should be used to harvest as much electromagnetic energy as possible. The energy harvesting antenna must meet the system requirements. Due to low electromagnetic energy densities in free space, efficient antennas should be used. The antennas should radiate efficiently at a specific frequency range and polarization. The antenna should receive efficiently electromagnetic waves from a wide angular angle. To meet this requirement the antenna radiation pattern should have a wide beam width. Printed antennas were used to harvest RF energy as presented in the literature, [4–10]. Electromagnetic energy harvesting systems capture waves propagating in the air. This RF energy is stored and used to recharge batteries and other electrical devices. In the last decade there is a huge increase in the amount of RF power in the air. The amount, of electromagnetic waves in the air in 2017 was 11 Exa-bytes per month. The amount, of electromagnetic waves in the air in 2019 was 33 Exa-bytes per month. However, the predicted amount, of electromagnetic waves in the air in 2025 will be around 165 Exa-bytes per month, **Table 2**. **Table 2** presents the expected amount of RF wave in the air for 2G, 3G, 4G, and 5G networks. 5G devices are forecast to account for 45% of the universe mobile data traffic by 2025.

Energy harvesting system is shown in **Figure 4**. The electromagnetic harvesting unit consists of an antenna, a rectifying circuit, and a rechargeable battery. The RF harvesting energy system operates as a Dual Mode harvesting unit. The Low Noise


**Table 2.** *Amount, of electromagnetic waves in the air from 2017 up to 2025.*

**Figure 4.** *Dual mode energy harvesting concept.*

Amplifier, LNA, is part of the RF system. The LNA DC bias voltages are supplied by the DC unit of the RF system. The programmable array consists of 3 to 4 antennas that can harvest RF energy from around 140 MHz up to 18GHz. The total received electromagnetic energy is transformed to DC power. The harvesting system consists of antennas, matching and feed networks, rectifying circuit, and a rechargeable battery. The RF harvesting system function as a dual mode harvesting unit. The harvesting unit can be part of a computing network, server, communication system, medical, IOT, computer, and smartphone. The LNA bias voltages are supplied by the RF system. The energy coupled to the built in test port, -20 dB, may be used to recharge a battery.
