An offshore wind farm's power reaches shore through a submarine export cable, and the physics of that cable — not the turbines — often decides whether the link runs as AC or DC.
Resistive loss (both): P_loss = I² R, R = ρL/A · (skin factor)
HVAC charging current: I_c = ωCV (grows with cable length L)
HVDC converter loss: ~1.5% of power at each end, fixed
HVAC — a long AC cable behaves like a capacitor between conductor and sea return. It draws a reactive "charging current" I_c = ωCV that flows the whole length just to charge that capacitance, whether or not you deliver any real power. Since the cable has a hard thermal current limit, charging current eats into how much real current — and therefore real power — is left over. Push the distance slider far enough and the deliverable capacity collapses toward zero even though the cable is far from overheating on real power alone.
HVDC (via offshore/onshore voltage-source converters) has no charging current — a DC cable is not periodically re-charged — so its loss grows only with I²R, roughly linear-ish in distance. The cost is two AC↔DC converter stations, each burning a fairly fixed ~1.5% of throughput regardless of distance.
The result is a real engineering crossover: for short links HVAC's simplicity wins because there's no converter tax to pay; past roughly 60–100 km (depends on voltage, cable design and farm size) HVDC's freedom from charging current wins instead. This is exactly why real offshore wind farms — Dogger Bank, Hornsea — switch to HVDC only once they sit far enough from shore.
- Wind farm output — total real power fed into the cable at the offshore platform.
- Distance to shore — cable route length; stretches the 3D scene and grows both loss mechanisms.
- Conductor cross-section — bigger copper lowers resistance (R = ρL/A) and raises the thermal current rating, at the real-world cost of a heavier, pricier cable.