Photovoltaic Energy

Energy is essential to human activity, regardless of it's nature. Everything requires energy: food, transport, constructions, communication, etc. With the population growth and newly industrialized economies emerging, the energy demand continues to increase rapidly.

Meeting the world's energy needs and reducing environmental impact of energy use requires exploitation of new energy sources, such as Solar Energy.

The sun is an inexhaustible source of energy. Every day it emits enough energy, in the form of sunlight, to satisfact 27 years of global electricity consumption. Sunlight can be converted into electricity with the help of fotosensitive cells. This is known as Photovoltaic Solar Energy.

Photovoltaic parks/plants

The main components of a Photovoltaic (PV) power plant are Photovoltaic modules, mounting (or tracking) systems, inverters, transformers and the grid connection.Solar Photovoltaic modules are made up of Photovoltaic cells, which are most commonly manufactured from silicon but other materials are available. Cells can be based on either wafers (manufactured by cutting wafers from a solid ingot block of material) or “thin film” deposition of material over low cost substrates. In general, silicon-based crystalline wafers provide high efficiency solar cells but are relatively costly to manufacture, whereas thin film cells provide a cheaper alternative but are less efficient.

Since different types of Photovoltaic modules have different characteristics (in terms of efficiency, cost, performance in low irradiation levels, degradation rate), no single type is preferable for all projects. In general, good quality Photovoltaic modules are expected to have a useful life of 25 to 30 years. The PV module market is dominated by a few large manufacturers based predominantly in Europe, North America and China. Selecting the correct module is of fundamental importance to a PV project, keeping in mind the numerous internationally accepted standards.

PV modules must be mounted on a structure. This helps to keep them oriented in the correct direction and provides them with structural support and protection. Mounting structures may be either fixed or tracking. Since fixed tilt mounting systems are simpler, cheaper and have lower maintenance requirements than tracking systems, they are the preferred option for countries with a nascent solar market.

PV modules are generally connected together in series to produce strings of modules of a higher voltage. These strings may then be connected together in parallel to produce a higher current DC input to the inverters. Inverters are solid state electronic devices that convert DC electricity generated by the PV modules into AC electricity, suitable for supply to the grid. In addition, inverters can also perform a range of functions to maximise the output of a Photovoltaic plant.

In general, there are two main classes of inverters: central inverters and string inverters. Central inverters are connected to a number of parallel strings of modules. String inverters are connected to one or more series strings. While numerous string inverters are required for a large plant, individual inverters are smaller and more easily maintained than a central inverter.
While central inverters remain the configuration of choice for most utility-scale PV projects, both configurations have their pros and cons. Central inverters offer high reliability and ease of installation. String inverters, on the other hand, are cheaper to manufacture, simpler to maintain and can give enhanced power plant performance on some sites.

It is important to consider the capacity factor of a PV power plant. This factor (usually expressed as a percentage) is the ratio of the actual output over a period of a year to theoretical output if the plant had operated at nominal power for the entire year.

This apart, the “specific yield” (the total annual energy generated per kWp installed) is often used to help determine the financial value of a plant and compare operating results from different technologies and systems.