## Shallow offshore

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Within British territorial waters, the shallow area is about 40 000 km2, most of it off the coast of England and Wales. This area is about two Waleses.

The average power available from shallow offshore wind farms occupying the whole of this area would be 120 GW, or 48kWh/d per person. But it's hard to imagine this arrangement being satisfactory for shipping. Substantial chunks of this shallow water would, I'm sure, remain off-limits for wind farms. The requirement for shipping corridors and fishing areas must reduce the plausibly-available area; I propose that we assume the available fraction is one third (but please see this chapter's end-notes for a more pessimistic view!). So we estimate the maximum plausible power from shallow offshore wind to be 16 kWh/d per person.

Before moving on, I want to emphasize the large area - two thirds of a Wales - that would be required to deliver this 16kWh/d per person. If

Figure 10.1. Kentish Flats - a shallow offshore wind farm. Each rotor has a diameter of 90 m centred on a hub height of 70 m. Each "3 MW" turbine weighs 500 tons, half of which is its foundation.

Photos © Elsam (elsam.com). Used with permission.

Figure 10.1. Kentish Flats - a shallow offshore wind farm. Each rotor has a diameter of 90 m centred on a hub height of 70 m. Each "3 MW" turbine weighs 500 tons, half of which is its foundation.

Photos © Elsam (elsam.com). Used with permission.

we take the total coastline of Britain (length: 3000 km), and put a strip of turbines 4 km wide all the way round, that strip would have an area of 13 000 km2. That is the area we must fill with turbines to deliver 16 kWh/d per person. To put it another way, consider the number of turbines required. 16 kWh/d per person would be delivered by 44 000 "3MW" turbines, which works out to 15 per kilometre of coastline, if they were evenly spaced around 3000 km of coast.

Offshore wind is tough to pull off because of the corrosive effects of sea water. At the big Danish wind farm, Horns Reef, all 80 turbines had to be dismantled and repaired after only 18 months' exposure to the sea air. The Kentish Flats turbines seem to be having similar problems with their gearboxes, one third needing replacement during the first 18 months.