How a photovoltaic park is built

The production of energy from renewable sources continues to grow worldwide. The International Energy Agency (IEA) estimates that 450 gigawatts (GW) of new green power will be installed worldwide by the end of 2023, two-thirds of which will be photovoltaic (PV) systems. But how do you build a photovoltaic system? How do you install a solar panel? And how does such a system work? The main elements of a photovoltaic park Each solar park is different in size, layout, topography and installed capacity, but the main elements are always the same. Photovoltaic panels: devices consisting of a photovoltaic module or set of modules mounted on a supporting structure; Photovoltaic modules: devices made up of a mosaic of interconnected photovoltaic cells. These cells are the most basic element of a photovoltaic system: they directly convert solar energy into electrical current thanks to a phenomenon called the photovoltaic effect; Tracker: a support structure on which photovoltaic modules are installed that enables automatic adjustment of module orientation – basically, a tracker allows solar panels to follow the sun as it moves across the sky – in order to maximize the production of electricity; Inverter: a device that converts the direct current (DC) produced by modules into alternating current (AC); Transformer: a device capable of raising or lowering the voltage before feeding it into the grid; Access roads and drainage works: useful for inspection and monitoring, and to protect the system in case of rain and flooding; Conduit: protective tubing, usually placed underground, that holds the electrical wires that connect the PV system to the primary substation of the power grid operator. Building a solar park step by step Prior to the opening of the construction site, the authorization process must be completed (for example, according to formal public administration agreements), in which the agencies involved authorize the construction of the solar park and may issue certain requirements for the project. For example, the Archaeological Superintendent’s office may require an archaeological assessment to be conducted or they may require the presence of an archaeologist at the construction site. This phase is followed by preliminary activities prior to the opening of the construction site, such as checking for the possible presence of explosive remnants of war, and conducting tests necessary for planning and design (such as seismic, geological and geotechnical tests to verify soil characteristics). Construction then begins with setting up the construction site, which involves creating access roads, installing temporary offices and toilets, etc., and is followed by the construction of civil works, among which, priority is given to drainage work, such as culverts and lamination tanks, which are essential in order to protect the system from simple rain or flood events. At this stage, so-called "earthmoving" also takes place, in which the ground is reshaped in accordance with construction plans. At this point the mechanical installations start, divided into three phases: The first phase is the placement of the tracker poles, which is generally done by means of a pile driving machine that beats the poles into the ground to a depth determined in the executive design phase. The second phase is to complete the installation of the trackers onto the poles, which is done manually, with the support of forklifts for lifting. There are different types of trackers based on the number of modules they need to move. The third phase is the installation of the photovoltaic panels. Again, this is done manually, and a team of four people can install 250 panels per day. To ensure a good energy yield, it is essential to identify at the design stage the optimal spacing between the trackers so that the PV modules are free to follow the movement of the sun throughout the day while keeping the orientation of the tracker as perpendicular as possible to the sun's rays in order to avoid generating shadows that would reduce the receptive capacity. All the activities described are facilitated by the pre-assembly of many components, which is carried out in a special area by dedicated teams so that only the final assembly remains to be completed in the field. Then it’s time for electrical installation, where wiring, terminals, and electrical connections are arranged. In particular, modules are wired in series to form strings. A high level of precision is needed, not least because string cables can feed into string boxes to optimize the amount of cable installed and increase the reliability of the system. The final, decisive phase is commissioning, which is divided into "cold" and "hot" commissioning. In the first step, all electrical tests are performed before connection to the power grid. Then, the system is energized in reverse: that is, starting from the power grid to the modules, under the supervision of the Commissioning Manager. At that point, the system is ready to begin generating power. How a ground-mounted photovoltaic system works In a photovoltaic system, everything starts with the modules, which convert the energy received from the sun into electrical energy thanks to the so-called photovoltaic effect. Photovoltaic modules are composed mainly of a semiconductor material, silicon, which is one of the most widespread minerals on Earth and therefore easy to find. When we talk about semiconductors, we’re referring to materials that can become conductors of energy when their component atoms receive a sufficient amount of energy for electrons to move, causing the flow of electrons and the production of electrical current. In the case of photovoltaic modules, energy comes from the sun in the form of photons. When this energy is sufficient to allow the electron in silicon to break its bond and move freely, the photovoltaic effect occurs. Semiconductors like silicon have few free electrons and therefore low conductivity. To increase it, silicon crystal doping techniques are used, where "impurities" – such as phosphorus or boron atoms that have a different number of electrons than silicon does – are placed inside the silicon crystal. This results in electrons that don’t bond tightly to the electrons of the other atom and thus are free to move and conduct energy. Solar cells are made by alternating different layers of doped silicon crystals, usually with a p-n junction that connects boron-doped (p, i.e., positive) silicon to phosphorus-doped (n, i.e., negative) silicon, thus creating an electric field that provides a preferred direction for the moving electrons. In this way, when a photon hits one of these junction areas with sufficient energy, it breaks the p-n bond, releasing electrons that will move along a certain path, creating a flow of electricity that can be collected. Each of the cells formed in this way can produce a weak voltage, around 0.5 to 0.6V. Many solar cells connected together form a photovoltaic module. Multiple modules connected together in series make up photovoltaic strings. Multiple strings connected together in parallel form the solar generator or photovoltaic array. The function of the inverter is to transform the direct current produced by the modules into alternating current. There are several types, the most common being central inverters and string inverters. Strings can be connected together via string boxes and converge in the central inverter or connect directly to the string inverter. The distinguishing factor between these two types of inverters is power. A central inverter is very large, collecting power from 1 to 4 MW. String inverters handle much lower power (150/300 kW); they can be placed in the field close to the strings, thereby reducing cable lengths and dispersion. Additional voltage conversion is required; the inverter works on low voltage (up to 1000V AC), but when high power comes into play, it’s necessary to switch to medium voltage (10 to 40 kV) using a transformer. In smaller plants (up to about 10 MW), energy goes directly from the transformer to the delivery substation, where it is fed into the distribution grid; in large plants, it’s necessary to go through an electrical substation that collects the medium-voltage lines and conveys them to a large transformer that takes the power from medium to high voltage, i.e., up to 120/220 kV, before it is fed into the grid. Today, the efficiency of a photovoltaic system is about 24%: that means that the technology allows a quarter of the solar energy received by the modules to be transformed into electricity.

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How a photovoltaic park is built and how it works

How a photovoltaic park is built and how it works