Worldwide energy situation is becoming even more a serious problem for the whole planet.
Black-out, the always greater energy demand, pollution produced from power stations that causes the climatic troubles nowadays and the consequent environmental impacts, contribute to the remarkably increase of research and use of renewable energy in comparison with traditional energy sources.
In this situation sunlight is the noblest and inexhaustible energy source that comes from the Sun.
Photovoltaic is in fact one of the main and most important technologies that exploits sunlight and convert it into electricity, and is free of negative effects such as noise and fumes.
An ever-growing number of applications can be realized and constructed with photovoltaic: from small and simple consumer needs to large solar electric systems for communities and commercial uses.
In fact photovoltaic systems can be constructed to any size based on energy requirements and can easily be enlarged or moved, thus contributing to the energy needs worldwide.

THE SOLAR CELL

The basic unit in a PV system is the solar cell.
It is made using special semiconductor materials - mostly silicon, which is available with no limit on the earth and is also recycled from the rejects of the electronic industry - and is produced by means of a particular process of purification and processing of silicon.
When photons (particles of solar energy) strike a solar cell, electrons are energyzed and create the electromotive force.
This process of converting light directly into electricity is called PHOTOVOLTAIC.
The performance of a solar cell is measured in terms of efficiency at turning sunlight into electricity.
Various types of silicon solar cells are available in the market in many sizes and shapes :

- Monocrystalline, manufactured with a high-purity single crystal, have the best efficiency and power, and the surface has an uniform and aggregated molecular structure;
- Polycrystalline, this type of cells is obtained from a working process of the silicon with more crystals, which remain more compact and with a different orientation;
- Amorphous, with this technology we produce a non-crystalline silicon which can be put on different surfaces. Cells with amorphous silicon can be mass produced, but have a much lower efficiency than mono and poly and have a significant degradation in power output when exposed to the sun.

COMPOSITION OF A PHOTOVOLTAIC SYSTEM

A photovoltaic system is therefore made of many photovoltaic cells connected together to form modules or panels.
Each single photovoltaic cell is of small dimensions and produces typically a power between 1 and 3 watts and 0,5V, at standard test conditions (STC) of 1000W/m2.
In order to increase the power and have a greater voltage, it’s necessary to connect many cells together to form larger units called modules.
Modules, in turn, can be connected to form arrays, to achieve the power that your application requires.
The sizing of an entire photovoltaic system is called “balance of system”(BOS) through which the best system sizing is studied according to the customer needs. As integrating part of the balance of system there are various components such as : charge controllers, inverters, batteries to store the energy, wiring, etc…

VARIOUS PV SYSTEMS

The typical configurations that can be realized with photovoltaic are :

1) Stand-alone systems (or off-grid)
2) Grid connected systems
3) Hybrid power systems

1) Stand alone systems are completely indipendent systems that rely exclusively on solar energy to meet a need for electricity.
They are especially used in remote places that are not connected to the electrical main utility grid or utility line extensions would be too expensive.
Electricity generated by stand-alone systems can be used in several ways, mainly in direct-current (DC) systems without batteries. In this way energy produced by the modules is directly used by the load: as an example in water pumping systems. The submersible solar pump works during the day and water is stored directly in a tank, and stops working at sunset.
Stand-alone systems may have batteries that store the excess energy generated by the modules in order to have a complete autonomous system which can also provide electricity at night or on cloudy days. With this system you can illuminate streets and homes, run fans and many other appliances available on the market that use DC electricity.
In case of use of conventional AC appliances you will need to add an inverter, and put it between the batteries and the load. This power conditioning device changes the voltage DC to voltage AC, loosing only a small amount of energy during the conversion from DC to AC electricity.
Stand-alone systems with batteries work by connecting the photovoltaic modules to a battery, and then the battery to the load through a charge controller which controls the whole system and keeps the batteries properly charged. Photovoltaic modules charge the battery during the day and then it supplies power to the load as needed.
These systems can be used also as back-up in case of black-out.

Major advantages of using stand-alone systems :
- energy is produced where and when it’s needed, and as back-up during night or on cloudy days
- small systems are easy to transport, operate and install
- all PV modules require only an occasional inspection and cleaning
- they are silent and do not pollute

2) Grid connected systems are photovoltaic systems directly connected to the main utility power through a particular inverter properly studied for these connections.
Their functioning is very easy: during the day the system produces the quantity of energy that the consumer needs (there are no limits of power for the installations but generally home systems can vary from 1Kwp to 3-5Kwp, while for industries from 20-30Kwp to 100Kwp). But this energy is only available during the day. When the consumer requires less electricity than the photovoltaic array is generating, the excess power is fed or sold back to the utility grid.
On the contrary, when the photovoltaic array generates less electricity than needed, the need is automatically met by utility power.
In this way grid connected systems reduce the consumption that consumers have to purchase from the electricity grid, thus being credited for energy returned to the grid, which is deducted from charges for electricity purchased.

3) Hybrid power systems consist on a combination of PV modules with other sources of electrical energy (as example wind generators, hydro, etc…) to charge batteries and provide power to meet the energy demand, considering the local geography and other details of the place of installation.
Hybrid systems, which are not connected to the main utility grid, are used in stand-alone applications and operate indipendently and reliably.
The best applications for these systems are on remote places, like as example, rural villages, telecommunications, etc…

ADVANTAGES AND BENEFITS OF PV ENERGY

Photovoltaic is especially used even more in developing countries where there’s lack or complete absence of conventional energy, but also is rapidly expanding in industrialised countries, especially for grid-connected systems.

Many of the significant environmental benefits obtained by using PV energy and technologies are :

- low impact on the landscape
- no production of air pollution or hazardous waste
- clean and inexhaustible source of energy
- environmental protection
- don’t require liquid or gaseous fuels to be transported or combusted
- can generate power in all weather and climates since PV modules resist under the worse environmental conditions
- can be quickly installed anywhere
- PV systems have clean, safe, reliable and quiet operation
- very low and easy maintenance
- energy security and efficiency
- installed PV systems generate power continuously with minimal operating costs
- PV modules and battery bank are modular so you can double or increase the PV systems anytime
- reduction of dependence on foreign and/or decentralized sources of energy
- PV systems are usually placed close to where the electricity is used, so they require much shorter power distribution lines than those needed to bring power in from the utility grid
- economic growth
- cost-effective
- consumers can produce the energy they need within their own borders
- short payback time (generally two to five years) but with operating time of over 30 years
- reduction of utility energy bills
- operates reliably for long periods of time with virtually no maintenance
- power from the modules is transferred to the utility company. The owner of any grid-conntected PV system can buy and sell electricity to the utility company

TYPICAL PV APPLICATIONS

Ideal to supply power to :

- remote communications stations
- rural villages and remote electric fences on farms, cottages and residences
- remote monitoring
- refrigeration
- power portable devices (i.e. computers)
- navigational sea-buoys, marine navigation aids, off-shore platforms
- home domestic appliances (radios, televisions, lights, refrigerators and other appliances)
- water pumping and irrigation
- recharge or maintain charge of batteries, especially in recreational vehicles, military applications, and sailboats, portable PV systems
- recreational vehicles and boats
- school and hospital warning signals
- repeater stations
- emergency services
- security lighting
- exterior lighting: streetlights, parkings, recreational areas, highways signs, traffic signals, small garden lights
- emergency telephones along highways
- satellites
- telecommunications
- industries
- building integration, either on roofs and in facades
- … and many others more