## 3 Modern Configuration of Photovoltaic Systems  
Photovoltaic systems consist of different components based on people's needs. They can be classified by their configuration:  
* On-grid system--the main parts are the solar panels, inverter, meter, and consumers. Figure 4 presents a logical scheme of an on-grid system. * Off-grid system--the system stores energy in batteries, and the main parts are the PV panels, charge controller, inverter, batteries, and consumers
* Hybrid system--stores the produced energy in batteries, and when the batteries are fully charged, the produced energy is then inserted into the grid. The main parts of the hybrid system are the solar panels, batteries, inverter, and consumers. Figure 3: Evolution of published articles for AI in photovoltaics. Figure 2: Evolution of published articles for photovoltaic systems’ cybersecurity. An important device for on-grid systems is the inverter. This device has a double role: to convert DC-AC and AC-DC, and to interface the PV system with the grid using one-way or two-way communication. Over the years, researchers have designed and developed more models (multilevel inverters for three-phase AC line voltage, current and voltage inverters, and inverters which have machine learning functions) [9]. Because the behavior of photovoltaic systems is too hard to be predicted (sometimes impossible), modern inverters have intelligent functions, such as voltage regularization and frequency regularization [9]. Stand-alone photovoltaic systems (Figure 5) have the property of charging batteries, and the house's consumers use the energy stored in the batteries. The solar panels should have capability to charge the batteries during the day when there is sunlight. The stored energy will be used during the night or during cloudy or rainy days. In such systems, the battery capacity is very important and the sizing of the battery plays a crucial role. It is necessary that more factors are taken into consideration when a battery is built, such as the energy consumed during the day (W), the energy consumed by the system's devices per day (W), the number of cloudy/rainy days (around 3 days), the battery's coefficient for discharging, and the battery's nominal voltage [4]. The energy consumption for individual load is represented by Wh and calculated using the following equation:  
\[\mathrm{E_{i}=P_{i}*T_{u}} \tag{1}\]  
Figure 4: The logical scheme of an on-grid system. Figure 5: The logical scheme of an off-grid system. where \(\mathrm{E}\) represents the energy demand per day of individual load (Wh), \(\mathrm{P}\)i represents the rating of individual load per day (W), and \(\mathrm{T}\)u is time of use of the load per day (h) [4]. On the market, are more types of batteries: lead-acid, nickel-metal-hydride, li-ion, etc. The batteries can be used for storing electrical energy for a short time (the electrical energy is distributed for 24 h) or for a long period of time (which assures the system's availability for a few days). An important characteristic of a battery is the battery's capacity. It is measured in kilowatt-hour (kWh) or ampere-hour (Ah) at a constant discharge rate [1]. \[\mathrm{Ah}_{\mathrm{bank}}=\mathrm{E}_{\mathrm{t}}/\mathrm{V}_{\mathrm{dc- sys}}\times\mathrm{D}_{\mathrm{aut}}\times 1.25 \tag{2}\]  
where \(\mathrm{Ah}_{\mathrm{bank}}\) is the battery's capacity, \(\mathrm{E}_{\mathrm{t}}\) represents the total energy, \(\mathrm{V}_{\mathrm{dc-sys}}\) is the DC voltage of the system, and \(\mathrm{D}_{\mathrm{aut}}\) represents the number of autonomous days. Then, the obtained value is multiplied by a factor of 1.25, which will increase the capacity by 25% to allow for reasonable system expansion. Batteries present a high risk for explosions and fires. It is recommended to avoid overcharging, low charging, overcurrent, short circuit current, or high temperatures. In one study [6], it was demonstrated that there are many techniques for fire suppression for li-ion batteries, but there could be additional chemical reactions which could cause damage.