between two fluids, usually fresh and saltwater, e.g. when a river flows into the sea. Collision of fresh and saltwater delivers large amounts of energy, which this technology strives to capture.
Tidal power stations generate tens to hundreds of MW similar to hydropower stations, wave energy converters (WECs) from some kW to MW, salinity gradient power stations from some kW to MW, ocean thermal energy converters (OTECs) from kW to MW and ocean thermo‐electric generators (OTEGs) from some watts to kW.
Ocean energy is still in the process of development, and intensive research is required, progress and demonstration efforts needed for learning and cost reduction before it can contribute to the energy supply. Therefore, the ocean energy market is still in its infancy, and the sector must address many issues to confirm the reliability and affordability of its technologies. A number of barriers are present in ocean energy technologies, which include obtaining site permits, the environmental influence of technology implementation, and grid connectivity for transporting the energy generated.
In 2019, the global installed capacity of ocean energies was 536 MW, a rise of 32 MW relative to 2014. Ocean energies amount to 0.03% of the global renewable energies installed capacity. However, there is huge potential to increase the use of ocean energies. Theoretical ocean energy resources might be enough to meet present and future global electricity demand, with a range of 20 000–80 000 TWh/year, culminating up to 100–400% of the present global demand. Moreover, a global potential of 337 GW could be achieved by 2050, one third of this would be in Europe. For the 2020 milestone, approximations suggest an installed capacity ranging from some hundred MW to 2 GW. Figure 2.12 illustrates the global ocean energy forecast based on device technology and infrastructure available, [38, 39].
2.2.5 Solar Energy
Solar energy production includes the sun's energy to deliver hot water by solar thermal systems (STS) or electricity by solar photovoltaic (PV) and concentrating solar power (CSP) systems. These technologies are technically recognized with many systems employed worldwide over the previous few decades.
2.2.5.1 Photovoltaic
Solar PV systems directly transforms solar energy into electrical energy. The basic foundation of a PV system is the PV cell, which is a semiconductor device that transforms solar energy into DC current. PV cells are then connected to form a PV module, normally in the range of 50–300 W. The PV system consists of modules, inverters, batteries, components, mounting systems, etc. PV systems are usually modular, i.e. modules could be connected together to deliver electrical power in the range of some Watts to hundreds of MW.
There are many different PV cell technologies on the market, utilizing different types of materials, and a greater number will be present in the future. PV cell technologies are divided into three categories, pointed out as first, second, and third generation: (i) wafer‐based crystalline silicon (c‐Si); (ii) thin‐films (TF); and (iii) emerging and novel PV technologies, including concentrating PV, organic/polymer material cells and dye‐sensitized solar cell, advanced thin films and other novel concepts. During the last two decades, PV technologies have substantially enhanced their performance (i.e. efficiency, lifetime, energy pay‐back time) and decreased their costs, and this is projected to continue in the future. Research aims to enhance the efficiency and lifetime, and decrease the investment costs to decrease the electricity production cost. Solar PV has two benefits: first, module manufacturing can be implemented in large plants, which allows for economies of scale; second, PV is a relatively modular technology. In comparison to CSP, PV has the upper hand that it utilizes not only direct sunlight but also the diffuse component of sunlight, i.e. solar PV generates electrical energy even if clouds are present. This ability grants the effective integration in numerous areas around the world relative to CSP [40–42].
Figure 2.12 Global ocean power capacity forecasting.
PV systems are described by two main types: off‐grid and grid‐connected applications. Off‐grid PV systems have a substantial opportunity for economic application in un‐electrified regions of developing countries, and off‐grid centralized PV mini‐grid systems. Centralized PV mini‐grid systems have the potential to be one of the most cost‐efficient for a pre‐defined level of service, and they could have a diesel generator set as an optional balancing system or to function as a hybrid PV‐wind‐diesel system. These types of system are applicable for decreasing and refraining from utilizing the diesel generator in remote regions [43].
Grid‐tied PV systems utilize an inverter to transform electrical current from DC to AC and, after that, supply the electrical power produced to the grid. Relative to an off‐grid installation, system costs are lower due to the fact that energy storage is not needed because the grid is utilized as a buffer. Grid‐connected PV systems are described as two types of applications: distributed and centralized. Grid‐connected distributed PV systems are employed to deliver electric energy to a grid‐connected consumer or to the electric network. These systems have several advantages that include: distribution losses in the electric network are decreased because the system is installed at the point of use; additional land is not needed for the PV system, and prices for mounting the systems can be decreased if the system is mounted on an existing structure; and the PV array itself could be utilized as a cladding or roofing material, as in building‐integrated PV. Usual sizes are 1–10 kW for residential systems, and 10 kW to several MWs for rooftops on public and industrial buildings. Grid‐connected centralized PV systems implement the functions of centralized power stations. The power generated by this system is not related to a particular electricity consumer, and the system is not positioned to perform certain functions on the electricity network other than to produce bulk power. Usually, centralized systems are installed on the ground, and they are greater than 1 MW. The economic benefits of these systems are the optimization of installation and operating costs by bulk buying and the cost‐effectiveness of the PV elements and balance of systems on a large scale. Furthermore, the reliability of centralized PV systems can be better than distributed PV systems as they can implement maintenance systems with monitoring equipment, which could be a smaller section of the total system cost [44].
During 2019, approximately 115 GW of solar PV capacity was installed globally, making the global solar PV capacity arrive at a value of 627 GW. More solar PV capacity was installed in 2019 (up 44% over 2015) than the cumulative world capacity five years earlier [45]. The PV market was multiplied by almost 40 in 10 years, as illustrated in Figure 2.13. The global market expansion is due to the rising competitiveness of solar PV, and to new government programs, higher demand for electrical energy and increasing awareness of solar PV's potential to hinder pollution and carbon dioxide emissions. Figure 2.14 shows the solar PV capacity in the top 10 countries in 2019. Solar PV plays a vital role in electrical energy production in many regions around the world. In 2019, solar PV was responsible for 10.7% of net production in Honduras and met 8.6% of the electricity demand in Italy, 8.3% in Greece and 8.2% in Germany. A minimum of 22 countries had sufficient solar PV capacity at the end of 2019 to meet 3% or more of their electrical energy need [12]. Furthermore, the levelized cost of electricity (LCOE) of solar PV fell 58% between 2010 and 2015, making it extremely competitive at the utility scale. While demand is increasing at a fast pace for off‐grid solar PV, the capacity of grid‐connected systems is increasing much faster. Distributed (residential, commercial and industrial rooftop systems) grid‐connected applications have struggled to ensure a stable global market since 2011, while the centralized largescale projects were associated with the increasing share of yearly installations, as illustrated in
