„On Grid“ PV systems (also called “Grid Tie” systems) count among the power generation systems synchronized and connected to the grid.  ey are only able to operate while connected into the grid (some part or all the energy production is injected to the grid) and vice-versa it is not allowed to stay working after grid voltage supply failure (so called “Island Mode” is prohibited). Besides this basic feature standard “On Grid” PV system needs to follow the whole package of the local grid provider requirements generally called “Grid Code”.


Decentralized systems of PVPP means that signi cant part of related power electronics gathering the power from the PV modules is spreading out all over the PVPP area (usually in the  eld) as close as possible to the PV modules.  is architecture is based on so called “string inverters”. String photovoltaic inverters are one or three phase units of smaller power range (one phase inverters typically up to 5 kVA and three phase inverters up to 50 kVA) when the PV strings are connected directly to the inverters.  e string inverters are able to monitor condition of each PV string connected to its DC inlet. All the electrical power is gathered on AC side of the inverter units – in the junction boxes which are also situated within the PV modules area. All the junction boxes bring energy to the transformer station (LV side).  e transformer station is equipped with grid protection (GP) acting via main disconnecting point (MDP) providing PVPP disconnection from the grid in case of the grid malfunction. We recommend considering this topology for rather smaller PV systems (up to 500 kWp).


Centralized “On Grid” PV systems are based on bigger size of so called central inverter units (in power range usually from 20 kVA up to 750 kVA).  e basic feature of these system are that before PV strings entering the inverters they are connected all together in parallel within the string boxes to the one or more so called superstrings. Superstrings are gathered in the junction boxes of the second level of connection called superstring boxes.  e superstring boxes are gathering and delivering the electrical energy to the central inverter units. PV modules are monitored via string monitoring system which is part of the SCADA system.


“O  Grid” hybrid systems (also called “Island hybrid systems”) are power generation systems consist of more kind of power generation units (e.g. PVPP, wind turbine, hydro turbine, etc.) and able to supply electrical energy to the consumption place without local grid connection. Alternatively, even if connected into the grid, this kind of power generation systems is not able to inject any electrical energy into the grid. In this case these systems are only consuming some amount of electrical energy from the grid which is missing on consumption side because of not su cient energy production on its own (for some reason).


Besides the PV modules as a solar generator of the PV system “O  Grid” hybrid system normally includes also another energy sources like a Gen Set (e.g. diesel generator), a Wind Turbine, a Hydro Turbine, Gas Turbine (e.g. utilisation of waste) or a combination of them.  e system is also usually equipped with battery storage bank. Because more kind of energy sources are connected within the system it is also called Hybrid Power Generation System. Again, for decentralized system, more smaller inverter units (up to 50 kVA each) are connected in parallel. Recommended total size of the system is up to 500 kVA.

is hybrid system provides great  exibility in supply and increased autonomy in relation of each energy source. On the other hand this renewable power generation system can be connected to the grid as well. In this case the system will consume only such amount of energy from the grid which is not able to be produced on its own. At the same time it is also important than even connected to the grid this architecture is not able to inject any energy back to the grid (except Gen Set unit) and that is why there is no grid protection (acting via MDP) involved.


Architecture of centralized “O  Grid” hybrid system is similar to centralized “On Grid” system based on bigger size of central inverter units (in power range usually from 100 kVA up to 750 kVA) and it is also considered for the systems in total size above 200 kVA, up to usually 3 MVA.  e PV modules connection is also identical to description for centralized “On Grid” system. Because there are more bigger units involved within this hybrid system, it is suitable to divide them into more containers. One of them is standard Transformer Station.

The next ones are so called “Inverter Stations” and contain all the power electronic units connected to the power DC system. We call it “EMU Valve Controlled DC Combiner” which creates an optimal hardware platform for combining di erent power sources.

Moreover, this “O  Grid” power generation system can be changed to “On Grid”kind of source with marginal investment costs.