harnessing river power

Hi, I'm looking for advice on who to talk to about harnessing electric power from a small river that bisects my garden. I don't expect to be able to power anything more than a few lights in the garden. The flow is approximately 0.5m per second, and following some recent revetting, the flow is constricted to about 70cm wide by about the same depth, so there is probably of the order of a quarter of a cubic metre of water flowing per second (I think). So, how do I best get the energy out? Rather than build something from scratch, I'd favour buying a ready made small undershot waterwheel, or submarine screw. Any suggestions?
Cheers, Brian

Alternative Technology centre in Mac would be best place to ask advice but I would used a bike hub dynamo. If you can find one.
What ever you use needs to self excite and permanent magnets seem best way.
When one looks at reverse i.e. size of motor on a garden water fall one starts to realise how much water is required to produce power.
Good look Eric

If you google "diy hydroelectric generation" there is plenty of info.

give up now.

for "A few garden lights" it is going to cost more than the project is worth

as you said you are going to need a wheel, a gearbox and a dynamo how much do you suppose that will cost? Also as already mentioned you are going to need a high flow rate or a very good gearbox to make anything work

Its a shame as it sounds like fun, but as i said the cost for something reasonable in my opinion is not worth it. But do let us know what you do.

Like breezer said, this could be an expensive project but i think it could be interesting if you could maybe salvage second hand parts and keep costs to a minimum. If you have kids the experience of building this would be priceless. On the other hand, if it's just a few garden lights you want there is a vast range of solar powered exterior decorative lights on the market that are easily installed and avoid any Part P issues.

Kab

The cost is not really an issue, not because I've run out of places to stash the cash (far from it!), but rather I just thought it might be fun. A few lights dotted around under the trees for purely aesthetic purposes. As long as it is not silly money, I'd like to give it a go! Thanks for the suggestions. From reading elsewhere I don't think I'll get more than 0.25kw, so I'm unlikely to be contributing to light polition too badly. Cheers, Brian

Another use for a river is use it as a source for a heat pump.

If I remember correctly (going back a few years though) I think you need to pay different water rates if you use a stream to generate electricity.

The power you can get depends on the difference in river height you can get over your garden. With a flow of 0.25 cu m, that is 250kg/s, the maximum power is 25W per cm fall.

Of course, you can't expect anything like 100% efficiency, so the power is likely to be far less than 25W/cm.

but he wants to use an undershot water wheel, so i guess he wants to "bulid a frame with a wheel in it, and plonk it on the stream"

as i said before ( and yes i am going to say it again) dont bother.

its an absolute brilliant idea, i really do love it.

Its all very well getting 2nd hand parts, but who is going to have a small say 3 foot undershot water wheel kicking about? no one, we don't use them as much as we used to. so you will have to make one.

You will need to be a very good carpenter to make an almost balanced wheel that wont instantly rot. assuming you are a good chippy, how much is the wheel going to cost to make in timber?
also as you mentioned undershot, that is not as efficaiant as having the water fall onto the wheeel, which involves you diverting the stream, more expense.

i am sorry but unless you throw a lot of money at it, i really do not see it getting anywhere.

but as i also said, i really do think its a fantastic idea. just some what expensive

how about £2k to buy one*? clicky
*estimated cost in 2006, if it was that good why are ther not more of them?

but note the drop he has (not read it all only looked at pic)

found this

says min 3 foot fall req'd

i feel it is going to cost you "silly money"

But PLEASE keep us informed