Читать книгу Step-by-Step Design of Large-Scale Photovoltaic Power Plants - Houshang Karimi - Страница 18

In a PV power plant, the sun's radiant energy is directly converted into electrical energy. There are two categories of PV power plants: conventional and concentrated. Unlike the conventional plants, the concentrated PV plants employ curved lenses or mirrors to focus sunlight on high‐efficiency PV cells. A concentrated plant has a solar tracker and a cooling system, in some cases, to further increase the plant efficiency.

Depending on the application, PV power plants are divided into five categories as briefly explained below.

1 Grid‐connected PV Power PlantPV power plants are usually connected to the local power network. The schematic diagram of a grid‐connected PV plant is shown in Figure 1.4. For the grid‐connected PV plant, the generated electricity is either consumed immediately by local loads or is sold to electricity supply companies. The local loads may include commercial and/or industrial consumers.For the grid‐connected PV plant, the grid acts as an energy storage system and, therefore, there is no need to have battery storage. In the evenings, when the PV plant is unable to produce power, the required electricity can be purchased back from the power network [4].

2 Stand‐alone PV Power PlantThe stand‐alone PV plants are used in the remote areas that have no access to the power grid. A stand‐alone PV plant operates independent of the grid, with part of the produced energy stored in energy storage systems such as batteries. A schematic diagram of a stand‐alone PV plant is shown in Figure 1.5. A stand‐alone PV plant includes PV modules, an inverter, batteries, and a charge controller. The inverter converts the direct current generated by the PV modules to the alternating current for AC applications. The PV plant can supply both the DC and AC loads [4].

3 Direct‐coupled PV Power PlantIn a direct‐coupled PV plant, the PV array is connected directly to the load. The schematic diagram of a direct‐coupled PV plant is shown in Figure 1.6. The load can operate only when there is solar radiation and, therefore, the plant has limited applications. An application of this type of plant is water pumping, where the load operates as long as sunshine is available, and instead of storing the electrical energy, water is usually stored [5].Figure 1.4 Schematic diagram of a grid‐connected PV plant.Source: Modified from Vázquez and Vázquez [4].Figure 1.5 Schematic diagram of a stand‐alone PV plant.Source: Modified from Vázquez and Vázquez [4].Figure 1.6 Schematic diagram of a direct‐coupled PV plant.Source: Modified from Kalogirou [5].

4 Hybrid‐connected PV Power PlantIn the hybrid‐connected PV plant, more than one type of generator is employed. In this type of power plant, one of the generators is a PV plant. The other generators can be wind turbine, diesel engine generator, or the utility grid. The diesel engine generator can also be a renewable source of electricity when the engine is fed with biofuels. The schematic diagram of a hybrid‐connected PV plant is shown in Figure 1.7. The plant can provide electricity for both DC and AC loads [5].

5 Grid Energy StorageFigure 1.8 shows the schematic diagram of a grid energy storage PV power plant. The grid energy storage can be considered as a special model of hybrid‐connected plant. This type of power plant is used for countries where the guaranteed purchase tariff for electricity varies in peak, low, and medium load conditions. In the time periods when the guaranteed electricity purchase tariff is lower, the energy produced by the power plant is stored in batteries. When the tariff rate is higher at peak load conditions, the stored energy is injected into the grid to increase the annual revenue of the power plant.Figure 1.7 Schematic diagram of a hybrid‐connected PV plant.Source: Modified from Kalogirou [5].Figure 1.8 Schematic diagram of a grid energy storage PV plant.

PV power plants can be installed almost anywhere. Based on the location of installation, the PV plants are divided into three main categories: residential, industrial and commercial, and utility‐scale. Figure 1.9 shows the types of PV plants based on their installation location. A residential PV system provides power to a home and/or to the grid. A commercial and industrial PV plant supply power to a corporate organization or an industrial plant. A utility‐scale PV plant provides power to the grid.

Homeowners can benefit from installing a PV system in their property almost everywhere. Depending on the government policies, there are two configurations for operating a residential PV system. In the first configuration, the residential PV system supplies the home energy, and the surplus energy is injected to the grid to offset the electricity bill through net metering. In the second configuration, the produced energy by the residential PV system is totally injected to the grid by a separate meter than the home electricity meter. The price of energy sold to the grid is paid to the home owner. Note that a utility‐scale solar facility generates solar power and feeds it into the grid, i.e. supplying a utility with energy, whereas the commercial and industrial projects supply power to corporate organizations and industrial plants.

Figure 1.9 Different types of PV plants based on their installation location.

Source: Goodrich et al. [6]. Public Domain.

Figure 1.10 Classification of power plants in terms of their mounted places.

The commercial, industrial, and utility‐scale PV plants are classified into five categories as shown in Figure 1.10, namely, ground‐mounted, floating, building‐integrated, rooftop mounted, and agrivoltaics. A ground‐mounted PV plant is installed on a land, whereas a floating PV plant is installed on a water lake. In a building‐integrated PV plant, solar panels are placed in the facade of a building. An agrivoltaics or agrophotovoltaics plant is installed in a greenhouse or agricultural farm and a rooftop mounted PV plant is installed on roof of a house, building, or factory [7].

Figure 1.11 Classification of power plants in terms of size.

Source: Rakhshani et al. [8]. Licensed Under CC BY 4.0.

Figure 1.11 shows that the PV power plants can be categorized into four groups based on their output power: small‐scale, medium‐size, large‐scale, and very LS‐PVPPs [8]. The large‐scale PV plants are known as solar farms and the very large‐scale PV plants are commonly known as solar parks. In addition to a distribution substation, the large‐scale and very‐large‐scale PV plants usually have one or more transmission or sub‐transmission substations.