We refer to the photovoltaic effect in everything related to obtaining energy through the action of light.
The most used light source for photovoltaic installations is that coming from the Sun, that is, solar energy. Although there are small devices, such as calculators, that can work with artificial light.
Photovoltaic solar energy
Photoelectric cells are the main component of photovoltaic panels. They are semiconductor devices that when ex Definition of photovoltaic (PV) cited by solar radiation, cause electronic jumps and a small difference in diode-like potential at their ends (electric current).
Classification and types of photovoltaic energy
Photovoltaic systems are mainly divided into 2 large families:
- "Island" systems (also called "independent"): they are not connected to any distribution network, so they directly exploit the electricity produced and stored in an on-site energy storage device ( batteries);
- plants "connected to the network" (also calls connected to the network): these are plants connected to an existing electricity distribution network managed by third parties and, often, also to the private electricity system that will be serviced;
A particular case of an island system, called "hybrid", remains connected to the distribution network, but mainly uses its sources, only one, or can have a combination, for example, photovoltaic, wind, generator, even with the help of an accumulator. If none of the sources is available or the accumulator is discharged, a circuit connects the system to the electricity network for continuity of supply.
From the structural point of view, mention must be made of the "architecturally integrated" installation (also known by the acronym BIPV, Building Integrated PhotoVoltaics, or "architecturally integrated photovoltaic systems"). The architectural integration is obtained by placing the photovoltaic modules of the plant within the profile of the building that houses it. The techniques are mainly:
- local replacement of the covering mantle (eg, tiles or tiles) with a suitable covering on which the photovoltaic field is superimposed, so that it is drowned in the covering mantle;
- use of suitable technologies for integration, such as thin films;
- structural use of photovoltaic modules, which also perform the function of a frame, with or without glazing.
The costs to achieve an integrated photovoltaic system are higher than the traditional method, but the aesthetic result is favored by the legislation of the energy account, with the recognition of a significantly higher incentive rate.
Off-grid photovoltaic systems (self-employed)
This family is at the service of those electric companies isolated from other sources of energy, such as the national grid in CA, which are supplied by an electrically isolated and self-sufficient photovoltaic system.
The main components of an island photovoltaic system are in general:
- photovoltaic field, designated to collect energy through photovoltaic modules conveniently arranged in favor of the sun;
- storage battery or accumulator, consisting of one or more appropriately rechargeable batteries (series / parallel) MEP / and retain the electric charge supplied by the modules in the presence of sufficient sunlight to allow deferred use by electrical equipment users With the use of a subsequent control unit, it can triple its useful life.
- management automation: a rear unit type can automatically switch between different renewable energy sources (PV panels, wind, generators, etc., etc.) moving from one to another or for accumulation batteries and finally also to the supplier .
- charge regulator, designed to stabilize the collected energy and manage it within the system according to several possible situations;
- inverter otherwise said DC / AC converter, designed to convert the DC (DC) output voltage from the panel (normally 12 or 24/48 volts) into a higher AC voltage (typically 110 or 230 volts for systems of up to a few kW, 400 volts for systems with a power greater than 5 kW).
The photovoltaic field generally used for island systems is optimized for a specific system voltage, evaluated during the design phase. The most commonly used voltages are 12 or 24 V. Consequently, since most of the photovoltaic modules used in this type of plant have output voltages equal to 12 or 24 V, the so-called electric chains forming the field are made up of a few modules, up to the limit only module per chain . In the latter case, in practice, the PV field is composed of simple electrical parallel between the modules, equipped with chain diode to protect against so-called inverse currents that will be discussed further.
The accumulator is generally composed of monoblocks, or individual elements designed specifically for deep and cyclic loading and unloading. In the systems that must guarantee the continuity of the service even in the most severe conditions, they are not generally used to use automotive accumulators, which in spite of functioning correctly have a low "useful life", that is, to tolerate a smaller number of load and load cycles. discharge compared to accumulators designed and built specifically for this type of use. In the case of pole or height accumulation facilities (eg, street lighting or photovoltaic street lamp), car batteries can not be used because any leakage of electrolyte (which is composed of a highly corrosive solution) could cause harm to people, animals and property. In these installations special accumulators are used in which the liquid electrolyte is replaced by a special gel.
The charge controller is an electronic device that has the following minimum characteristics:
- automatic disconnection of the photovoltaic field (understood as a set of all the modules) of the battery of accumulators in the case in which the voltage supplied by the modules is less than the minimum of the charge accumulators (very cloudy sky, night , failures, interruptions for maintenance, etc.); in this case, in fact, the modules would behave as resistive charges by discharging the accumulators;
- automatic disconnection of the photovoltaic field from the accumulators in case of full recharge and possible derivation of the current produced by the modules to send it directly to the inverter in case there is a request for power from the user's devices;
- automatic disconnection of the photovoltaic field from the accumulators in case of total discharge of the latter (battery now exhausted) and possible derivation of the current produced by the modules to send it directly to the inverter in case there is energy demand of the devices of the user.
Last review: February 26, 2018Back