My cousin's crazy idea
Discussion
My cousin fitted a roof-full of solar panels this year on the Government 25-year eco-wheeze.
Fired up by this, and always on the search for income, he's been investigating the stream at the bottom of his garden and pondering a hydroelectric scheme.
The only problem is that from one side of his (admittedly large) garden to the other the fall is about three feet, and from what I recall the stream is about four feet wide and 3" deep.
So I told him there wouldn't be enough flow to turn anything useful. He replied that he could fix an almost-horizonatal pipe across the garden, thus making a long slow stream into a waterfall. Under this 2'6" waterfall he was going to put some 'microhydro' thing he'd read about, and sell the electricity back to the Grid. When I told him that converting a stream into a waterfall wouldn't give the water any more energy, and there wouldn't be anything like enough power to do that, he said he could use it to power his house instead.
I told him he'd be lucky to make a torch bulb glow.
I suggested (jokingly) that he could use the power from his solar panels to pump the water up to a greater height, thus making a bigger waterfall. I think he took me seriously.
He's not stupid so it's worrying how somebody with no basic science can be so easily suckered by eco-babble and the prospect of saving/making money.
Fired up by this, and always on the search for income, he's been investigating the stream at the bottom of his garden and pondering a hydroelectric scheme.
The only problem is that from one side of his (admittedly large) garden to the other the fall is about three feet, and from what I recall the stream is about four feet wide and 3" deep.
So I told him there wouldn't be enough flow to turn anything useful. He replied that he could fix an almost-horizonatal pipe across the garden, thus making a long slow stream into a waterfall. Under this 2'6" waterfall he was going to put some 'microhydro' thing he'd read about, and sell the electricity back to the Grid. When I told him that converting a stream into a waterfall wouldn't give the water any more energy, and there wouldn't be anything like enough power to do that, he said he could use it to power his house instead.
I told him he'd be lucky to make a torch bulb glow.
I suggested (jokingly) that he could use the power from his solar panels to pump the water up to a greater height, thus making a bigger waterfall. I think he took me seriously.
He's not stupid so it's worrying how somebody with no basic science can be so easily suckered by eco-babble and the prospect of saving/making money.
Edited by Simpo Two on Monday 8th November 18:59
It will take someone a lot better at maths/physics than me, but I imagine a 4ft x 3" body of water focused to flow over an overshot water-wheel would be plenty to continuously turn the wheel to generate electricity.
He'd need to build some sort of raised (almost) horizontal 'race' for the water to flow along the garden then over the wheel mounted at the lowest side of the garden.
He'd need to build some sort of raised (almost) horizontal 'race' for the water to flow along the garden then over the wheel mounted at the lowest side of the garden.
Edited by RSGulp on Monday 8th November 21:38
Spot on, but by the time you add the frictional losses of a generator, and the loss of energy you always get when converting energy, I really don't think you'd light a bulb, let alone sell it to the grid. But if there are any thermodynamicists here who can calculate a wattage output, I'll pass it on!
andy43 said:
With hydro electric, it's the head/height that makes the power from what I've read - under 3 feet of head isn't really going to do much at all. But you knew that...
I'm sure that's true with national grid grade hydro electric where a dam is used to create a huge head which results in massive pressures to the turbines but in a smaller scale operation it's about volume. Many watermills worked on fairly flat but strong flows hence the mill pool phenomenon.
andy43 said:
With hydro electric, it's the head/height that makes the power from what I've read - under 3 feet of head isn't really going to do much at all. But you knew that...
Head IS the critical parameter. Low pressure systems are very inefficient and I agree 3ft of head will produce next to nothing.To test his theory he needs to get hold of an old car alternator and a decent sized car battery, then hook them up to an invertor and take things from there.
If he can start in a basic small scale from there, he may end up being able to light his shed/garage for 'free' and then scale it up to maybe light the house for free.
If I had the space and the stream etc I'd try it!
If he can start in a basic small scale from there, he may end up being able to light his shed/garage for 'free' and then scale it up to maybe light the house for free.
If I had the space and the stream etc I'd try it!
From a pure physics point of view;
PE = m.g.delta h
where PE is potential energy (J), m is mass (kg), g is gravitation constant (9.8ms^-2) and delta h is heigh difference (m).
So if you know the flow rate per second, convert that to a mass (1l of water = 1kg) and multiply by the total fall height and g. That would then be the maximum energy you could extract per second purely from the height difference. I assume you could also take out some kinetic energy as well, and have a slower flowing stream afterwards.
So for every gallon bucket that you can fill per second with a 3foot drop, you get ~50W. So to power a house (couple of kW?) he needs to have about 20 gallons per second flow.
That's with 100% conversion, which of course it won't be. I assume that the head is important to give enough pressure to actually spin the turbine blades?
PE = m.g.delta h
where PE is potential energy (J), m is mass (kg), g is gravitation constant (9.8ms^-2) and delta h is heigh difference (m).
So if you know the flow rate per second, convert that to a mass (1l of water = 1kg) and multiply by the total fall height and g. That would then be the maximum energy you could extract per second purely from the height difference. I assume you could also take out some kinetic energy as well, and have a slower flowing stream afterwards.
So for every gallon bucket that you can fill per second with a 3foot drop, you get ~50W. So to power a house (couple of kW?) he needs to have about 20 gallons per second flow.
That's with 100% conversion, which of course it won't be. I assume that the head is important to give enough pressure to actually spin the turbine blades?
AlfaFoxtrot said:
From a pure physics point of view;
PE = m.g.delta h
where PE is potential energy (J), m is mass (kg), g is gravitation constant (9.8ms^-2) and delta h is heigh difference (m).
So if you know the flow rate per second, convert that to a mass (1l of water = 1kg) and multiply by the total fall height and g. That would then be the maximum energy you could extract per second purely from the height difference. I assume you could also take out some kinetic energy as well, and have a slower flowing stream afterwards.
So for every gallon bucket that you can fill per second with a 3foot drop, you get ~50W. So to power a house (couple of kW?) he needs to have about 20 gallons per second flow.
That's with 100% conversion, which of course it won't be. I assume that the head is important to give enough pressure to actually spin the turbine blades?
I'm sorry ,I had to phone a friend. PE = m.g.delta h
where PE is potential energy (J), m is mass (kg), g is gravitation constant (9.8ms^-2) and delta h is heigh difference (m).
So if you know the flow rate per second, convert that to a mass (1l of water = 1kg) and multiply by the total fall height and g. That would then be the maximum energy you could extract per second purely from the height difference. I assume you could also take out some kinetic energy as well, and have a slower flowing stream afterwards.
So for every gallon bucket that you can fill per second with a 3foot drop, you get ~50W. So to power a house (couple of kW?) he needs to have about 20 gallons per second flow.
That's with 100% conversion, which of course it won't be. I assume that the head is important to give enough pressure to actually spin the turbine blades?
Fortunately he has a small hydro scheme.
Some figures:
10 meter head 75mm inlet pipe output 400 watts.
Invertor approx £1000/kilowatt
Batteries approx £1000/1000 amp/hrs
Plus the cost of your turbine and pipe. 200 meters in his case.
I'll let you do your own maths.
Dick Strawbridge used an interesting concept on his 'It's not easy being green' series which used the flow-rate of a stream (which effectively has its 'head' much further upstream and therefore much higher) to raise an amount of water by a couple of metres using its kinetic energy and a clever clicking valve system. He used this to power a water wheel and generate a few watts of power.
You can't simply start digging up banks, damming or diverting a stream or river in the UK. The Environment Agency are strict on this:
"allowing the flow of water to pass without obstruction"
http://www.environment-agency.gov.uk/homeandleisur...
Basically, you're responsible for the river bed half way out (ifthe river is the border) but the water must be left unimpeded to flow over the riverbed. I used to own a riverside property, so have been through all of this stuff.
"allowing the flow of water to pass without obstruction"
http://www.environment-agency.gov.uk/homeandleisur...
Basically, you're responsible for the river bed half way out (ifthe river is the border) but the water must be left unimpeded to flow over the riverbed. I used to own a riverside property, so have been through all of this stuff.
Silver993tt said:
You can't simply start digging up banks, damming or diverting a stream or river in the UK. The Environment Agency are strict on this:
"allowing the flow of water to pass without obstruction"
http://www.environment-agency.gov.uk/homeandleisur...
Basically, you're responsible for the river bed half way out (ifthe river is the border) but the water must be left unimpeded to flow over the riverbed. I used to own a riverside property, so have been through all of this stuff.
^^^^ This"allowing the flow of water to pass without obstruction"
http://www.environment-agency.gov.uk/homeandleisur...
Basically, you're responsible for the river bed half way out (ifthe river is the border) but the water must be left unimpeded to flow over the riverbed. I used to own a riverside property, so have been through all of this stuff.
I think people both up and down'stream' of his house may have some objections.
Nice idea tho'
lambysdad said:
Silver993tt said:
You can't simply start digging up banks, damming or diverting a stream or river in the UK. The Environment Agency are strict on this:
"allowing the flow of water to pass without obstruction"
http://www.environment-agency.gov.uk/homeandleisur...
Basically, you're responsible for the river bed half way out (ifthe river is the border) but the water must be left unimpeded to flow over the riverbed. I used to own a riverside property, so have been through all of this stuff.
^^^^ This"allowing the flow of water to pass without obstruction"
http://www.environment-agency.gov.uk/homeandleisur...
Basically, you're responsible for the river bed half way out (ifthe river is the border) but the water must be left unimpeded to flow over the riverbed. I used to own a riverside property, so have been through all of this stuff.
I think people both up and down'stream' of his house may have some objections.
Nice idea tho'
tenex said:
I'm sorry ,I had to phone a friend.
Fortunately he has a small hydro scheme.
Some figures:
10 meter head 75mm inlet pipe output 400 watts.
Invertor approx £1000/kilowatt
Batteries approx £1000/1000 amp/hrs
Plus the cost of your turbine and pipe. 200 meters in his case.
I'll let you do your own maths.
means although we have a similar stream - about 3' head across our property and pathetic flow unless the weather is like today - it'd be cheaper to get a horse, treadmill and generator. But don't tell him - let him try. Fortunately he has a small hydro scheme.
Some figures:
10 meter head 75mm inlet pipe output 400 watts.
Invertor approx £1000/kilowatt
Batteries approx £1000/1000 amp/hrs
Plus the cost of your turbine and pipe. 200 meters in his case.
I'll let you do your own maths.
£3,000 investment and years of environmental agency paperwork to produce enough power to run a small television.
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