The interface problem: scope gaps in wind farm construction

If you decide to divide the work on building your wind farm among several companies, you will likely save money. However, the trade-off will be coordination issues.

This is the problem that shows up when two subcontractors are standing next to a half-finished cable trench, each one explaining why the other should complete the work.

An interface gap is something that falls between two scopes of work. It happens when the civil works contractor assumes the electrical contractor will do something, the electrical contractor assumes the opposite, and nobody noticed during the tender phase because the item was not explicitly assigned in either contract.

Some classic examples:

Cable trench backfill. The civil works contractor digs the trench and installs the sand bed. The electrical contractor lays the cables. Who backfills? In some contracts the civil contractor backfills after cable laying. In others, the electrical contractor does everything. The third option is to define very clearly the interface.

Earthing connections at the foundation. The foundation rebar includes an earthing bar (a “connection point”). The MV cable contractor installs the earthing cable. But who makes the connection between the two? Who supplies the clamps? In at least two projects I recall, nobody had priced this item. The cost was trivial (a few hundred euros per turbine) but the delay and the stress to figure out responsibilities was not.

The area between the turbine and the cable route. This is a personal favourite. Who will connect the MV cables that runs from the transformer (usually at the base of the tower or in the nacelle) to the rest of the cable trench network?

How do you prevent this? There is no magic solution, but a few practices help:

Interface matrices. Before tender, create a simple table listing every activity and assigning it to a specific contractor. Column headers are the subcontractors; row headers are activities. Every cell should have exactly one “X”. If a cell is empty, you have a gap. If two cells have an “X”, you have an overlap (which is expensive but at least not a dispute)

“For dummies” language. If you have multiple contracts, the language should match. If the civil works scope says “trench excavation including backfill after cable installation,” the electrical scope should say “cable laying in trenches excavated and backfilled by the civil works contractor.” Any ambiguity between the two documents is a future dispute.

The lesson: the devil is in the details, and the details live at the interfaces.