Step-by-Step Design of Large-Scale Photovoltaic Power Plants. Houshang Karimi

(35 °C)

Maximum allowable temperature rise that is 70 °CT amb Ambient temperature

Total short‐circuit current of the arrayR(x)ReflectanceA(x)Absorptance at the angle xT(x)TransmittanceC A temperature‐independent constantE g Band gap of the material extrapolated to absolute zero temperatureq Elementary chargeP in(q) Output power of the PV set q, which is the dc input power of each inverterA S, I(q) Shaded area of the PV set q, which is caused due to the shading by the front (southern) PV blockP pv (y, d, t, β )Actual output power of each PV module on year/day and at timeP max, STC Maximum output power at the STC conditionsP max(G, T)Maximum output power at a given irradiance G and temperature TP dc (t)Inverter dc instantaneous powerP ac (t)AC powerP loss (t)Power lossesP dc, pu Per unit value of dc powerP i PV module powerP max, i Module maximum powerr dc Resistance of the dc cableV dc dc voltage at the cable terminalsP PV, peak Installed peak power under STCG(t)Global solar irradiance on the PV plane at time tr ac AC cable resistanceI ac, cable Line current rms valueV LL rms value of the line voltageN it Total number of invertersN i Number of inverters that are connected to an individual AC cableP Fe Core lossesP Cu, N Copper losses under the nominal operating power SN of each identical transformerS t (t)Total apparent power loading of the installation at the moment tN tr Number of identical transformersP MPP MPP powerV MPP MPP voltageI MPP MPP currentV string Total voltage of string∆T Temperature variance between STC and minimum expected temperature.I sc Short‐circuit current at STC∆V Percentage of cable voltage dropL Cable length∆P Percentage of DC cable power losst Short‐circuit duration that is 1 second for MVU n Rated fuse voltageI SN Nominal current of a fuseI testing Testing current of a fuseLpv, 1length of each PV moduleLpv, 2width of each PV moduleη1, DCDC cables power loss coefficientPLDCpower‐length productPm–sh (y, d, t, β)output power of each PV module at the maximum power points (MPP)Pm (y, d, t, β)power that is produced by each PV module at the MPPNttotal number of strings in a PV installationPDC (t)available DC power at the time tGSTCsolar irradiance under STCDPa coefficient that accounts for the power reduction due to the temperature rise in cellsΔθ(°C)rise of the cell temperature above 25 °C

1 Introduction

      1.1 Solar Energy

      The source of solar energy is the sun. Solar energy can be classified as heat which is generated by electromagnetic waves, and light which is produced by photons. Solar energy is the main source of most of the other forms of energy available on the Earth. The solar energy is directly or indirectly converted into other forms of energy, e.g. electrical energy produced through photovoltaic (PV) technologies.

      The most important feature of solar energy is that it is clean and does not harm the environment. In the long run, PV power plants will make a significant contribution to the supply of primary energy in all sectors including domestic, commercial, industrial, and transportation consumers. Moreover, factors such as government support, price of fossil fuels, cost of gas emissions CO₂, and costs of PV plant equipment affect the growth of PV plant installation capacity [1].

Figure 1.1 shows the energy conversion cycle. It shows that fossil fuels and the renewable energy sources such as biomass, wind and solar energy originate from the sun. The solar energy is stored in chemical bonds through photosynthesis of plants and produces fossil fuels millions of years later.

      This book provides an overview of all aspects of designing a large‐scale PV power plant (LS‐PVPP) for the solar energy professionals and the university researchers. The book particularly focuses on the design of all equipment of a large‐scale PV plant from the basic to advanced parts.

1.2 Diverse Solar Energy Applications

Solar energy is used for two groups of applications: non‐power plant and power plant. Figure 1.2 shows various applications of solar energy [2]. Based on Figure 1.2, solar power plants are divided into three categories: solar thermal; PV thermal hybrid; and PV.

Figure 1.1 Energy conversion cycle.

      Source: Modified from Twidell and Weir [1].

      1.2.1 Solar Thermal Power Plant

In a solar thermal power plant, the solar energy is converted into thermal energy which is then converted into electrical energy. Figure 1.3 shows various types of solar thermal power plants as explained below [3].

      1 Parabolic PlantThe parabolic plant has a linear parabolic collector consisting of few rows of parabolic reflectors. The reflectors absorb the reflected rays of solar radiation and warm up the heat transfer fluid.

      2 Central Receiver PlantThe central receiver plant consists of a set of mirrors, where each separately concentrates solar energy and transmits it to a central receiver tower.

      3 Parabolic Dish PlantIn a parabolic dish plant, the sun's rays reflected on a parabolic surface are concentrated at a focal point. The thermal energy is converted into mechanical energy by a Stirling engine. An electric generator converts the mechanical energy into the electrical energy.

      4 Solar Chimney PlantIn a solar chimney plant, a combination of solar air collectors and air conduction towers are used to produce induced air currents. The currents provide mechanical forces in order to rotate a pressure step turbine coupled to a generator to produce electricity.Figure 1.2 Various solar power plant categories.Source: Dincer and Abu‐Rayash [2].Figure 1.3 Various applications of solar thermal energy: (a) Parabolic plant, (b) Central receiver plant, (c) Parabolic dish plant, (d) Solar chimney plant, and (e) Fresnel collector plant.Source: Modified from González‐Roubaud et al. [3].

      5 Fresnel Collector PlantThe Fresnel collector plant includes flat mirror collectors with low width and long length that collect the incoming sunlight on the concentrator and send it to a receiver tube. The receiver tube heats up the fluid inside the tube.

      1.2.2 PV Thermal Hybrid Power Plant

      The PV thermal hybrid power plant consists of a combination of PV panels and a solar thermal collector. The PV panels convert the solar radiation into electrical energy. The solar thermal collector absorbs remaining energy of the solar rays and also removes wasted heat from the panels.

      1.2.3 PV Power Plant

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.