On 20 Oct, 20:25, andrew wrote:
David Hansen wrote:
On Tue, 19 Oct 2010 22:04:51 +0100 someone who may be andrew
wrote this:-

The cost tends to be proportional to the mass of the equipment.

No doubt the case if one is only considering one type of equipment.
However, the Archimedean screw I linked to earlier means a whole new
set of considerations. Vastly easier to make than a turbine and with
no need to ensure dimensional accuracy to the same degree, but I
imagine higher civil costs.

Whether you can make a cheaper, comparably efficient, device doesn't alter
the fact that if has to handle a greater mass of water to get the same
power. So it tends to be more massive.

Pelton wheels are small, convert around 90% of the incoming kinetic energy
to rotary motion and simple but they need a good head.

I fancy playing with a screw device in our weir but cannot see how it would
trap a fraction of the flow let alone work at 90% conversion. *Even if it
were in a tube with minor losses around the periphery why should it get
more out than a simple propeller type turbine in the same tube?

AJH
There is a simple means open to you if you have a weir. That is to
use an ordinary central heating pump (or a larger industrial pump if
you have enough water). The induction motor will run as as
asynchronous generator, the impellor will run as a turbine. It will
need to run in parallel to the mains to generate. It just has to be
turning faster than synchronous speed