Wind

Question 1

Why would off shore wind farms run with 35% higher tip ratios?

Answer 1

higher operating tip for similar power implies lower talk and hence lighter nascelle masses and lower cost of manufacture and maintanence

higher rot. speeds and lower torques imply lower swirl angular velocities in the rotor wakes, hence higher efficiency of machine.

Lower solidity rotors can be employed with corresponding weight and cost reductions

higher blade speeds suit the higher wind speeds offshore ie turbines may be operated more often nearer their ideal tipspeed ratios and preserve better blade advance angles

Question 2

Advantages and disadvantages of offshore wind farms

Answer 2

Summaries of four from:
Advantages:
i. Offshore windspeeds are significantly higher
than onshore ones so that energy densities are
much higher and outputs higher.
ii. Smoother fetches reduce earth boundary layer
drag (higher wind speed near surface). This
reduces the need for high towers reducing tower
costs and more significantly foundation size and
cost.
iii. Smoother fetches (sea is in general, smoother
than land) result in lower turbulence levels.
Output torque is more even and fatigue damage
reduced.
iv. Offshore wind resource around the UK is
extensive. There is far more space/ and potential
sites. There is also much less opposition and
difficulty in obtaining planning permission.
Disadvantages:
i. Costs and inconvenience of offshore access -sea
conditions must be good before access is
possible. Foundations are not yet properly
developed for shallow water (20m) and not tried
at all for deeper water (70m).
ii. Risk of marine collision, and of anchor damage to
buried power cables.
iii. Salt spray damage in the machine could pose a
problem.
iv. Few strong grid connecting points are available.