A photovoltaic plant is essentially a system able to convert sunlight into electric power. This ability is made possible thanks to the photovoltaic effect: a physical property of semiconductor materials to absorb energy form the light and to convert it into electric power.
It’s an energy source producible also through small plants able to satisfy the power needs of a family wherever they are and even if not connected to the electric grid.

The most important advantages are:

  • Never-ending source;
  • Absence of pollution and gas emissions;
  • Absence of fossil-fuels consumption.

Moreover, the photovoltaic plants are also:

  • Simple to be installed;
  • Modular because they can be assembled in any dimension and power, depending on the requirements and needs of the specific installation site;
  • Doable both in rural and urban areas;
  • Easy to be integrated with buildings and infrastructures, where they exploit usually unused areas (roof top, façade);
  • With low maintenance costs.

Last, during its entire lifespan a photovoltaic module produces from 4 to 10 times more energy than what has been employed for its production. This is a peculiarity of the renewable energy devices, the only ones able to guarantee an energy return above 1.
The size of a photovoltaic plant can vary from small residential application to large power plants for energy production. Residential applications usually have power ranging from 1 to 5 kWp, depending on the power needs and they are typically installed on the roof top (Figure 6). Moreover, they can be connected to the electric grid (grid-connected) or not (stand-alone).

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Figure Picture of a residential photovoltaic plant.

Large power plants (also called Solar Farms) are ground mounted solar plants with typical power varying from hundreds of kWp to tens of MWp (Figure 7). Their purpose is not to serve local needs but to produce power to be distributed through the electric grid, as a typical energy power plant.

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Figure Picture of a large power plant (Solar Farm).

 

A simple photovoltaic system typically includes an array of solar panels, an inverter, interconnection wiring and sometimes a battery for storage (Figure 8).

 

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Figure Schematic of a photovoltaic system components.

 

 

 

I DON'T HAVE PICTURES

 

 

 

Figure Pictures of photovoltaic modules: monocrystalline (left) and multicrystalline (right).

 

The inverter is a device transforming DC current generated by the modules into AC current (usually 220V) in order to supply energy to all the usual loads or to pump it into the grid.

It also has the function of maximizing the energy produced by the system and the efficiency of energy flows from modules to the loads.

Inverters for grid-connected application usually have an electronic device which allows anytime extracting as much energy as possible from the modules; this is called maximum power point tracker (MPPT) and is thought in order to adapt the characteristics of the PV plant with the loads connected to it. The PV inverter can be a quite small box for small PV plant up to a large service room for large solar farms (10).

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Figure Example of inverter for residential use and large inverter for large solar farms.

 

Some other devices are used to let the PV system works properly; they are essentially wires, switches and electronic devices able to keep constant performance and to optimize the energy output.

Moreover, off-grid PV plants can have a storage system which supplies the loads when the PV plant is not working (typically during night time); it is made by several batteries able to guarantee energy for a certain period of time.