A photovoltaic system is a solar power station that allows the conversion of solar energy into electricity using photovoltaic panels.
The basic classification of photovoltaic systems is based on their power. The following types of renewable energy installations are [1]:

• micro-installations,
• small installations,
• medium installations,
• large installations.

A micro-installation is an installation of a renewable energy source with an installed total electric power (defined by the manufacturer as the nominal power of the equipment that produces electricity) of no more than 50 kW, connected to the electricity grid with a nominal voltage of less than 110 kV. The highest growth dynamics of the installed capacity is achieved by way of micro-installations.
A small installation is defined as an installation with a total installed electrical power of more than 50 kW and less than 500 kW, connected to a power grid with a nominal voltage lower than 110 kV.
The largest photovoltaic installations are photovoltaic farms with a capacity greater than 500 kW, which may even reach the order of several hundred MW. In the case of installations between 500 kW and 1 MW, we talk about a medium-sized installation, and above 1 MW - a large installation.
Photovoltaic systems are classified into two groups based on how they interact with the grid:

• island photovoltaic installations (off-grid), i.e. not connected to the electricity grid [2],
• grid-connected photovoltaic installations (on-grid) [3], which include:
• connected to the low voltage grid and are mostly micro and small installations,
• connected to the medium voltage grid, which may include medium and large installations,
• connected to the high-voltage grid, being installations of several MW or tens of MW.

Another criterion for classifying the types of photovoltaic system is the ability of the PV system to track the sun. In this respect, one can distinguish:

• stationary installations that do not follow the movement of the Sun,
• tracking installations that follow the movement of the Sun.

Based on the installation method of photovoltaic systems in a building, PV systems can be classified into two types [4]:

• Building-attached photovoltaic (BAPV) systems, in which PV modules have no direct impact on the building structure and are directly fixed to buildings with a support structure [5],
• Building-integrated photovoltaic (BIPV) systems, in which PV modules are integrated into the building structure [6].

Photovoltaic island systems type off-grid

Photovoltaic island systems type off-grid operate outside the public electricity grid. This type of system consists of photovoltaic panels, an inverter, a charge controller and energy storage. The block diagram of an island photovoltaic system is shown in Fig. 1.

In this type of system, the electricity generated as direct current is converted into alternating current by an inverter. If excess energy is produced, it is stored in so-called energy reservoirs for later use. In domestic installations, batteries are the most commonly used energy storage devices.
Photovoltaic island systems type off-grid are divided into:

• remote from the grid,
• with possible access to the electrical grid.

Off-grid installations are used primarily in places where the costs of connecting to the electricity grid are too high or their connection is impossible for some reason [7]. Examples of these types of sites include: vacation homes, ships, yachts, and automobiles. Off-grid photovoltaic systems are also used to power street lamps, road signs and portable devices. Examples of off-grid photovoltaic installation are presented in Fig. 2, Fig. 3 and Fig. 4.

Figure 3: Lightyear One electric car powered by energy generated by Lightyear ∞ photovoltaic cells. Photo used with permission from Lightyear ∞.

Figure 4: A yacht powered by energy generated by SolTech Service's off-grid island photovoltaic system. Photo used with permission from SolTech Service.