Photovoltaics Solutions
WHAT’S THE MEANING OF PHOTOVOLTAIC?
Photovoltaics offer consumers the ability to generate electricity in a clean, quiet and reliable way.
Photovoltaic systems are comprised of photovoltaic cells, devices that convert light energy directly into electricity. Because the source of light is usually the sun, they are often called solar cells. The word photovoltaic comes from “photo,” meaning light, and “voltaic,” which refers to producing electricity. Therefore, the photovoltaic process is “producing electricity directly from sunlight.” Photovoltaics are often referred to as PV.

PV cells are normally fabricated using special semiconductor materials that allow electrons, which are energized when the material is exposed to sunlight, to be freed from their atoms. Once freed, they can move through the material and carry an electric current. The current flows in one direction (like a battery), and thus the electricity generated is termed direct current (DC).


HOW DOES IT WORK?
The energy generated by PV modules can be used immediately or stored in batteries for later use. Normally, the excess energy generated in autonomous PV systems during sunny periods is stored in batteries. The batteries then provide electricity at night or when there is not enough solar radiation. For these applications, the number of watts in the array and the capacity of the batteries are carefully sized to give optimum performance.
Some autonomous applications, such as water pumping, often have no need for batteries. Water is pumped when the sun shines and is stored directly in a reservoir or a tank that is installed at a higher level for later use by gravity feed.
Other PV systems convert the electricity into alternating current (AC), feed excess electricity into the grid and draw out electricity at night or when the solar radiation is low. These systems are referred to as grid-connected, grid-tied or net-metered.


THE TYPES OF PV POWER SYSTEMS
The typical configurations that can be realized with photovoltaic are :
  • 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

  • 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.

  • 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