Newhouse Farm

[frenchgardener]

Thanks!
1. River approx 3m wide, half the width is ours, but we would have to see about planning permission!!! We are responsible for clearing the river on our half!!!!
2. River 40/50 cm deep when low - normal. canbe 2m (and up in the garden) a couple of times a year!!
4) Don't know the speed of the current - will have to calculate that!!

I'm not sure how much we would be able to produce!! !Obviously we would want as much power as we could get.
I will try and get more info when back from holidays. Many thanks for all the questions they have given me plenty to think about.

[Mike&Penny]

OK then ........

1) Rule out an "floating" device as this is much too small to bother with that. At such small size you would easliy be able to support a structure hanging from the shore. Similarly the very small size means that you would be able to modify the bottom (to make flat/uniform under the device). I was picturing your initial question in terms of a river, not something on the scale of an irrigation ditch.

2) Assuming able to use 1.5 m width and the depth is 0.5 m then at a flow speed of 1 m/sec the flow power is about 375 watts. A deivce using flow (instead of pressure) is like a windmill which can't extract even 60%* of the energy of the flow. So even an optimal device wouldn't exceed ~180 watts. Call that 100 watts after all system losses are taken into account.

There would be much more at high water times assuming the device could take advantage of that as some designs could.

3) I'd suggest a Darrieus turbine mounted from a cantilevered beam above with the arms/disk supporting the blades above highest water levels. You wouldn't have to worry about starting the device as in this small size range you could probably use parts from a bicycle (pedal to start the device turning and once the stream takes over "freewheels" -- all standard things with bike parts). This sort of turbine would be producing more power as the flow depended as more of the blades would be immersed.

4) Again because of small size, no difficulty making this on a mounting that could remove it from the stream. Big difference between a device weighing at most a couple hundred kilos and one weighing many metric tons! Like I said before, I was picturing a river application. Here the whole unit could be made to lift up and back out of the stream.

5) Nothing terribly difficult to fabricate here. The blades could be wood and the airfoil sections cut (roughed out) with an ordinary table saw plus a number of jigs to hold the wood for different passes (or one adjustable jig). These blades simple unlike a wind turbine prop because no twist to them. You make a bunch of extras to serve as replacements (if using an adjustabe; jig you make the same cut on each before adjusting the jig for the next pass).

6) You would need significant gearing up but it's not as bad as I imagined with a serious size device. Ballpark estimate the Darrieus would be turning at 60 RMP if the stream flow was 1 m/sec (and it operated at ~4 times the flow velocity)

7) Alternatives ---- plain props in flow just like a wind turbine. Could possibly scrounge props from dead outboard motors. This might be less gearing down but you've got bearings/gears below the water surface so need oil, seals and this type device would not increase power as the flow depth increased. So the Darrieus would be easier.
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There is no possibility of social justice on a dead planet except the equality of the grave.

[frenchgardener]

Many thanks for all the wonderful advice - I can really look into it now. Sorry about the river part - in France what we have in the garden is definitely classed as a river - not a stream, maybe in the US it's not the same!!
Anyway - will be looking into it as soon as I know about the planning permission as the French sure are difficult about that!!!!!!!!!

[Mike&Penny]

Well it could be called a river here too if what is meant is a river followed upstream all the way to very near its source. So when you cross a small bridge or large culvert over a small stream the sign might say "thus and so river".

No harm done except I was about to give you design advice related to problems not relevant to your situation and ignoring design ideas particualry well suited.

For example -- in your case it is going to be quite practical to first build a light "track" on the shore with the entire unit mounted on a "truck" with flanged wheels (or skids*) ala a railcar so you can crank the boom up lifting the device up out of the water and then pull the cart back (now you can service** from dry land) and then push back to riverside and lower (for operation). That might also affect your planning permission requirements as the device easily removable from the stream flow on demand.

* Efficiency isn't important unless you are going to be moving it a lot. Unlikely to weight over a metric ton (weighted to counterbalance the boom and keep it on track against lateral forces) so can be skidded with a "come along" (hand crank winch).

** Assembly also made simpler as can be done on dry land.
_________________
There is no possibility of social justice on a dead planet except the equality of the grave.