Hydro power

[hotponyshoes]

Watching a Guy Martin thing last night and he was at a hydroelectric plant in Wales.

Some numbers given were
390 cubic meters of water per second flowing through generating enough power for 2.5 million homes.

Big numbers but by my maths that means each home is basically being powered by less than 10 litres per minute.

I get the economics of scale but, ignoring that, you should be able to run a tumble dryer cycle from an ibc full of water easily enough?

Then have a solar powered pump to send the water back up again..
Or, if you used a large amount of water (farms etc) fill the top tanks from mains pressure and use it from the bottom tanks)

Why is there not any small-scale hydro power around?

I suppose the height/head of water in a hydro reservoir will be pretty decent but (if you had the space) you could use multiple ibc's....

 

[pressbrake1]

Lot of energy in 390 tons moving through in one second, we don’t know distance to work out exact energy but it’s a lot
Then take in not all houses are using power at same time luckily

 

[PhillipM]

Head height for a dam is massive, small turbines are far less efficient generally, and as pressbrake says, half of those houses probably have 8w led lightbulb and the TV on.

 

[hotponyshoes]

I was presuming the 2.5million number was the amount of homes using average power.
Looks like the plant can produce 1728mw at max.
Quick Google suggests 1mw is enough to power somewhere between 500-2000 homes for an hour.

 

[Maker]

I suppose the height/head of water in a hydro reservoir will be pretty decent but (if you had the space) you could use multiple ibc's....

Say you stacked up 3 IBCs, (Or rather approximate 3 IBCs as a column of water 1x1.2m square, 3m high), that has a gravitational potential energy of 3600kg * 9.81 [m/s^-2] * 1.5m (Average height) = 53,000 Joules

Assuming a tumble dryer is a constant 2.2kW load, that's 2200J/s, you'll empty your IBCs in less than 30 seconds. Of course that doesn't factor in pipe loses, inefficiencies of small turbines, conversion loses, electrical loses, etc. I don't think there's much point going into all that with such unfeasible numbers...

 

[Bladevane]

I thought it was Cruachan in Scotland he visited. Output is quoted as 440MW. I personally dislike the reference to “can power so many homes” because who knows what an average home consumes.

 

[pressbrake1]

I was presuming the 2.5million number was the amount of homes using average power.
Looks like the plant can produce 1728mw at max.
Quick Google suggests 1mw is enough to power somewhere between 500-2000 homes for an hour.

Time is irreverent
Saying a hour is like a fixed amount like a battery

 

[Gareth J]

Think about it the other way around. Imagine the device you want to run, say 500W. Now find a pump of that rating and see what head/flowrate it'll do.

Obviously there are inefficiencies to factor in, but gives a sense of scale

 

[m_c]

I get the economics of scale but, ignoring that, you should be able to run a tumble dryer cycle from an ibc full of water easily enough?

Only if you stick that IBC a couple hundred metres vertically up a hill.

 

[mtt.tr]

I thought it was Cruachan in Scotland he visited. Output is quoted as 440MW. I personally dislike the reference to “can power so many homes” because who knows what an average home consumes.

I hate,
X amount of double deckers
X amount of football fields.

I'm not a child give me a sodding number

 

[m_c]

I thought it was Cruachan in Scotland he visited. Output is quoted as 440MW. I personally dislike the reference to “can power so many homes” because who knows what an average home consumes.

I've had the privilege of driving up to the Cruachan dam and reservoir.

That's the peak output, but it can only sustain that for around 30minutes IIRC.
It's a pump storage hydro plant with it's main purpose to provide surge power to allow more conventional power plants to increase output/come online during periods where there is a sudden increase in power demand.

It's not really a renewable power source, as very little of it's power output is from natural water flow.

 

[minimutly]

Say you stacked up 3 IBCs, (Or rather approximate 3 IBCs as a column of water 1x1.2m square, 3m high), that has a gravitational potential energy of 3600kg * 9.81 [m/s^-2] * 1.5m (Average height) = 53,000 Joules

Assuming a tumble dryer is a constant 2.2kW load, that's 2200J/s, you'll empty your IBCs in less than 30 seconds. Of course that doesn't factor in pipe loses, inefficiencies of small turbines, conversion loses, electrical loses, etc. I don't think there's much point going into all that with such unfeasible numbers...

Your sums are wrong. Energy given, gather than just stored needs flow. You’ve double counted height.
If you have 3.5m times 9.81 times flow (say 20 l/s down your IBC pipe?) gives you 687Watts, until your IBC starts draining lower and lower... I ignored efficiency, usually .75 or thereabouts.
The actual full calculation takes in specific gravity of the fluid of course, but since mostly water is used that neatly cancels out.
I say mostly, because someone who I’ve known for a few years has created a company to use a denser /heavier than water fluid, so you don’t need pipes as big, or as much flow etc.
And to the person who said small turbines are less efficient - no they aren’t really, most turbine efficiency is down to type, and how well they are designed and built. The pipe losses can wipe out a lot of energy, if the velocities are allowed to go above 1.7 m/s or so.

 

[PhillipM]

Tiny turbines are less efficient because if you get down to the size of only a couple of kilowatts your losses to sealing issues and tolerance starts to become a huge chunk if you're trying to make a high-head, low flow water efficient design.

 

[armalites]

I remember a story in the news many years a go where chap had was running a small hydro unit in his bath, left the taps running to power some lights.

 

[Maker]

Your sums are wrong. You’ve double counted height.

I don't think I did.

 

[armalites]

The big issue with renewables has always beenthe fact they they aren't consistant and often the time the power is needed the genration isn't there.

Using solar to power pumps filling a header pond could provide light at night. via hydro

 

[northwest]

I suspect I know why there are no small scale hydro plants, you have to get a license from the local water authority if you intend using, for instance, a water wheel in your own stream, running through your land, You cannot charge the water authority for the use of your land for "their" water to run through though.

 

[minimutly]

Say you stacked up 3 IBCs, (Or rather approximate 3 IBCs as a column of water 1x1.2m square, 3m high), that has a gravitational potential energy of 3600kg * 9.81 [m/s^-2] * 1.5m (Average height) = 53,000 Joules

Assuming a tumble dryer is a constant 2.2kW load, that's 2200J/s, you'll empty your IBCs in less than 30 seconds. Of course that doesn't factor in pipe loses, inefficiencies of small turbines, conversion loses, electrical loses, etc. I don't think there's much point going into all that with such unfeasible numbers...

Your sums are wrong. Energy given, gather than just stored needs flow. You’ve double counted height.
If you have 3.5m times 9.81 times flow (say 20 l/s down your IBC pipe?) gives you 687Watts, until your IBC starts draining lower and lower... I ignored efficiency, usually .75 or thereabouts.
The actual full calculation takes in specific gravity of the fluid of course, but since mostly water is used that neatly cancels out.
I say mostly, because someone who I’ve known for a few years has created a company to use a denser /heavier than water fluid, so you don’t need pipes as big, or as much flow etc.
And to the person who said small turbines are less efficient - no they aren’t really, most turbine efficiency is down to type, and how well they are designed and built. The pipe losses can wipe out a lot of energy, if the velocities are allowed to go above 1.7 m/s or so

I don't think I did.

Ai you did.
Say you stacked up 3 IBCs, (Or rather approximate 3 IBCs as a column of water 1x1.2m square, 3m high), that has a gravitational potential energy of 3600kg * 9.81 [m/s^-2] * 1.5m (Average height) = 53,000 Joules

You have a gravitational energy of 3600kg - this is due to height times the weight of water. Then you multiplied it by 1.5m ...
No flow equals no power.
And to counter @PhillipM , you would need to be down at micro sized bearings before the losses would increase enough to lose you efficiency, and even then it would be tiny and difficult to measure.
I’m not making this up, I do it every day, and have done for some years now.

A couple I built earlier...

 

[armalites]

I suspect I know why there are no small scale hydro plants, you have to get a license from the local water authority if you intend using, for instance, a water wheel in your own stream, running through your land, You cannot charge the water authority for the use of your land for "their" water to run through though.

We even have to pay for drainage into the local river system from our stream

 

[northwest]

They get you coming, they get you going, nothing is "free".