Letters / Mathematical challenge
Something has been bothering me since your article appeared a week ago: Shetland’s Waves Excite Developers (SN 6/11/12).
As maths and physics were never my strong point, I’d be grateful for other readers’ views about the following: “We were predicting 32 or 33 kilowatts per metre, but this year it’s averaged 40 – that’s right up there with western Ireland and the western isles, though neither of those places have good data on them yet,” enthused [Harvey] Appelbe [of Vattenfall].
Now according to the Pelamis website, their latest P2 wave machine is 180 metres long and has a capacity of 750 kW. Using simple multiplication it can be seen that indeed 14 of them would be required for a 10MW wave farm.
A simple division, however, reveals a ratio of 4kW per metre, rather than the 40kW Mr Appelbe is apparently claiming. Or is he referring to the energy and dimensions of the waves themselves?
It’s perhaps worth reminding folk that if 14 of these machines were laid end to end, the overall length would be just over 2.5 kilometres. A 100MW farm would thus be over 25km long.
Whatever way the machines are positioned, that would cover a fair chunk of the Burra Haaf (as I believe I’ve pointed out before).
Pelamis claim a target capacity factor of 25-40 per cent for their machine, which I understand to mean that actual power generated from a 100MW wave farm would be expected to be in the order of 25-40MW.
James Mackenzie
The Lea
Tresta
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