Lightning occurs when enough charges have been built up in the clouds. This creates a voltage between the clouds and the ground. When this voltage overcomes a certain value, it can overcome the barrier between the clouds and the ground and current will (very briefly) flow from the clouds to the ground. High voltages are also used to transfer energy from one place to another, especially in offshore wind farms. This lecture will explain why high voltage DC transmission cables are needed and what the benefits are. Also, the operating modes of offshore windfarms are discussed.