In the latest years more than ever, we are witnessing climate changes and natural catastrophes, largely due to the emissions of CO2. Thus, investing in alternative energy sources, such as solar, wind, geothermal, and hydroelectric energy, rather than fossil fuels, is increasingly needed to reduce greenhouse gas emissions.
Furthermore, in the latter months, the geopolitical and economic situation has highlighted the role of renewable energy in the internal stability of a nation and its capacity of being independent and robust.
Power output from renewable sources depends on variable natural resources, making these plants more difficult to control and presenting challenges for grid operators. For this reason, the grid integration requirements have become at the center of the renewable energy debate.
The connection of a photovoltaic plant to the electrical grid can be at low voltage (230/400V), medium voltage (usually 15kV or 20kV), or high voltage (132kV). The type of connection between the three just illustrated depends on the power of the system. Domestic systems are normally connected in low voltage, as well as all three-phase systems with power below 100 kW, while three-phase systems with power over 200 kW are normally to be connected in medium voltage.
Electrical equipment for the grid connection
C.R. Technology Systems develops all the electrical equipment for the grid connection of conventional and renewable energy plants.
In particular, it includes different types of substations, depending on the plant power and size, and the energy request throughout the year.
These compact-size, turn-key solutions are equipped with MV switchgears, LV switchboards, transformers, inverters, surge arresters, SCADA systems for the control and data collection of the plant, and auxiliary electrical equipment.
The rated voltage can be, depending on the area where the PV is located, from 15kV up to 36kV, and nominal power from 1MVA up to 160/250MVA.
Interconnection to the gird through the interposition of delivery cabin and reception cabin
For systems connected to the MV grid, as Enel distribuzione, C.R. Technology Systems has studied and developed a dedicated solution composed by:
- Reception cabin (according to Enel Distribution, carried out in concrete solution) including the E-Distribuzione homologated MV switchgears.
- Delivery cabin (normally accepted in prefabricated metallic structure) including the interconnecting switchgear comply with the standard CEI-016, collecting the MV lines from filed (e.i. from an STC-Box or STC-Skid)
Interconnection to the grid through elevating substation MV/HV
For larger renewable plants, C.R. Technology Systems proposes E-House substations, STC-Box, including high-voltage elevating transformers. They are plug-in compact substations used to connect green energy to the grid. 36kV grid interconnection design under development.
Temporary interconnection
In situations where the energy demand is fluctuating or seasonal, the best solution is a mobile substation. In this case, the e-House and the electrical equipment are mounted on a trailer and can be moved whenever electricity is needed.
A part from the substation, C.R. Technology Systems, together with its Sister Company, C.R. Project Service, design and carry out power lines and cable ducts in high-voltage (HV) and medium-voltage (MV) for the interconnection.
Types of interconnection to the Italian National Transmission Grid (NTG)
Except for special needs, the plants with power greater than or equal to 10 MW can be directly connected to the NTG.
For input/withdrawal power requirements ≤ 6 MW, the related plants are connected to the grid of the territorially competent Distributor. For higher powers, and in any case for power plants less than 10 MW, the choice will be made taking into account the admissibility of the connection on the MV networks in the area, the passive loads, and the production plants present or expected on the same portion of the grid.
C.R. Technology Systems is able and ready to support the customer for any level of power and voltage that may interconnect its PV plant to the national grid.
It is defined by the National utilities that for power above 10MVA (in one point of connection), the connection will be done in HV (future 36kV), below this power set of 10MVA, the connection is done in the MV system (15-20kV normally).
