Function

The onshore substation transforms power to grid voltage, for example up to 400 kV. Where a HVDC export cable is used, the substation converts the power to three-phase AC. It also provides switchgear to protect the grid from the wind farm, and vice versa, for fault conditions.

Who is involved

Onshore substations and its components are manufactured by specialist suppliers contracted by the developer.

Key facts

The onshore substation is often the first part of the wind farm to be built, about a year before offshore construction. In some cases, work may start ahead of FID for the wind farm to mitigate the risk of stranded generation assets.

Typically, they are two parts to the substation: the wind farm side and the grid side. In Ireland, both sides are owned by the national transmission operator, EirGrid.

The wind farm side of the substation is larger, consisting of the majority of the electrical system and a building with a control room, office and storage. The grid side of the substation may be an extension to an existing facility or a new one if this is not practical.

Many of the electrical components will be similar in specification to the offshore substation, but constraints on weight and space are not as critical. The substation will contain metering equipment to measure electricity exported to the grid.

The area of the onshore substation is likely to be about 5 ha for a HVAC system and 7.5 ha for a HVDC system. The onshore substation is ideally located close to the offshore export cable landfall to limit the length of the onshore cable route.

The onshore substation is likely to be contracted to a supplier of transmission systems with a substantial amount of the work contracted to a civil engineering contractor.