At 2:47 AM -0400 17/8/04, Lewis Burgess wrote:
>
>So does everyone agree, as Dennis pointed out, that increasing the
>capacity of Aquair-like generator is very costly and that this is the
>main reason why it is not used widely for power generation for rural
>communities? Does this also apply to the Garman and Darrieus turbines?
It is nonsense to say that the cost of permanent magnet alternators
increases exponentially with size. In fact if you double the number
of magnets and double the number of coils then you can get 8 times as
much power at the same rpm, and with the same efficiency.
Larger turbines tend to have lower rpm and this offsets the
advantages, but permanent magnet technology would still be quite
viable if you want DC output. However, larger systems are usually AC
based and would tend to use gearboxes and induction motor or
synchronous alternator generation. the friction in the gearbox and
the cost and maintenance issues are less significant on larger
systems.
>
>Finally, given the information above, is it feasible, given today's
>technology, to design a free-flow or submersible turbine that can
>generate 25kW and still be small enough to fit the site specification
>described above? I still have a glimmer of hope.
I could not follow the site spec. but you have to realise that the
site is what governs the available power and I have a feeling that
the site is too small and the power just is not there. There
certainly are 30 kW stream turbines. For example the underwater
electric kite. I was given this data 3 years ago:
Based on our experience with the kinetic turbines, our
pre-commercial single 10 ft diameter RIVER turbine is producing:
Water velocity, Vo= Maximum Power, kW
Maximum Thrust, lbs
4 knots / ~ 2 m/sec 33.5 kW 7,622.9 lbs.
4.25 knots / ~ 2.125 m/sec 40.1 kW 8,605.6 lbs
4.5 knots / ~ 2.25 m/sec 47.6 kW 9647.8 lbs
4.75 knots / ~ 2.375 m/sec 56.0 kW 10,749.5 lbs
5 knots / ~ 2.5 m/sec 65.4 kW 11,910.8 lbs
Our new Tidal design has an output approximately 8-10 % lower
because of the efficiency of the bi-directional design.
http://uekus.com/
--
Hugh
Scoraig Wind Electric
http://www.scoraigwind.co.uk/
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