Photovoltaics

Solar radiation can be converted into electricity through photovoltaic conversion. This process allows the direct conversion of solar energy into electricity by exploiting the physical phenomenon of the photovoltaic effect that occurs when light strikes special materials.

The technological device the process is based on is the photovoltaic cell which consists of a semiconductor material (usually silicon). A packaged interconnectd assembly of photovoltaic cells constitutes the photovoltaic module, commonly called photovoltaic panel.

Crystalline silicon as semiconductor material is certainly the most used: it is one of the most common chemical elements present on Earth's crust in the form of impure silicon dioxide. The most commo ones are monocrystalline silicon, polycrystalline silicon, amorphous silicon (thin film).

A photovoltaic cell efficiency is mainly influenced by temperature and amount of light or radiation. The conversion efficiency varies between 8 and 20% depending on the cell type.

A photovoltaic system consists of:

1. photovoltaic modules or panels;
2. support structure to install modules on the ground, on a building or any building structure;
3. inverters;
4. electrical panels, cables;
5. mechanical rooms to house equipment.

A proper exposure to solar radiation determines the efficiency of photovoltaic modules. The assessment of the annual average eletrical power amount of a photovoltaic system is carried out through a calculation that takes into account: the annual solar radiation of the site (to be correctly determined using appropriate formulas), a correction factor calculated on the basis of orientation, the angle of inclination of the photovoltaic modules, any temporary shadows and technical performances of photovoltaic modules, inverter and other system components

The environmental conditions of the site also affect the energy efficiency of photovoltaic modules: for example, by increasing the operating temperature the energy amount produced by the plant decreases.

The main applications of photovoltaic systems are:

1. plants (with storage system) for off grid supply;
2. plants for low voltage in grid supply;
3. electrical power stations, generally connected to medium voltage grid.

Photovoltaics connection to the grid is ruled by the CEI 11-20 and CEI 82-25 standards. The connection to the grid is low voltage (LV), single stage, for plant nominal power lower than 6 kW; it is low voltage, three-phase, for a nominal power up to 50 kW; for power higher than 75 kW plants are generally connected to medium voltage (MV) through the interposition of a transformer.

Advantages 

1. Absence of polluting emissions during the operating phase
2. Saving of fossil fuels
3. Reliability (a 20-year average lifespan)
4. Modular system
5. Reduced operating and maintenance costs

Disadvantages

1. Randomness of the energy source
2. Expensive cost of the plant
3. Insufficient maturity of the market