Free(ish) Energy - part III - tides

RiderOnTheStorm

ok, another idea for free energy. The Tide. Its an oldy but a goldie. Its reliable (twice a day, every day, day / night / sunshine or rain or wind since dawn of time) and its measurable and its VERY powerfull. But how do we harness this power? 2 ideas:

1: Swimming pool
Build a big concrete scructure in the sea (near the beach so that it doesnt have to have very tall walls). Let the tide fill the 'pool by means of holes near the top. Hydro-elec generators powered by water coming in. When tide goes out, the pool is now full of water and the water goes out the same holes, spinning the generators again. I can see the pool as being about 1 or 2 or 3 metres deep (depending on rise in the tide in that area) and covering a very large area (in order to hold as much water as possible)

2: Clockwork .....er orange?
The tide is strong enough to lift super tankers! .... and lower them again..... If there was a giant floating platform (think super tanker again!) connected to the floor of the ocean (cables? or girders?) and the tide raises the platform. Then the amount of work = distance X mass. The distance is fairly small (again, 1 2 or 3 metres, depending on the local tide) but the mass is huge! Surely the potential energy is huge! But how to harness all that energy, and release it in a controlled fashon. The best I can think of is girders (with cog-teeth) embedded in the sea, and as the platform rises, then cogs in the platform are turned, which turn generators to make elecricity. The cogs can be huge and heavy, as the tide will easily be able to move them and a good gearing system will get hundreds of revolutions for a small rise. As the tide goes out, the platform lowers, and again the teeth turn the cogs. But would it be enough?

Professor_Fink

You can indeed harness energy from the tide, and from waves. There are already schemes which use these, I'm sure a quick google will for you turn them up.

While these are clean energy sources, it's not 'free' in the sense that you are just moving the energy from one form to another. The moons rotation induces the movement of the tides, and by stopping them moving you are slightly effecting the gravitational force the earth exerts on the moon, as well as countless other things.

By in large such schemes rarely generate enough energy to be worth the cost and enviromental damage caused by building them. That's the main reason a lot of alternative energy sources like these flounder.

Civilian_Target

As the good professor highlights, tidal energy is being harnessed the tidal part of French rivers, but it's generally considered an inferior cousin to wave power (which is still in its infancy).

The problems with tidal power are that:
- It's visually awful
- It's hugely expensive to both build and maintain, you need to dump a lot of concrete into the sea and it's constantly being eroded
- Its uncontrollable - there's two tides a day but you can only achieve maximum efficiency from an outgoing tide, which doesn't necessarily correspond with the peak demand times for electricity.

ressem

This version has a prototype in the UK that's been on TV a few times. http://www.marineturbines.com/home.htm
It's effectively limited to a small number of locations with sufficient currents however.

sciam.com (purchase required) had a magazine dealing with energy sources in September. Some that you mightn't have heard about.

e.g. high altitude wind rotors that use the high altitude and relatively consistent jet stream winds. Models illustrated were of a ladder with blimps used as 'rungs', tethered at each end which spin to generate power, http://www.magenn.com/
Also autogiros for high altitude generation http://www.skywindpower.com/ww/index.htm

RiderOnTheStorm

I agree that this is not free energy, thats why I said free-ish. It is just converting the gravity pull of the moon into a different form of energy. Thus it will be everlasting. Its a bit like solar power, but it works day & night.

I dont like wave power as a source, as I live by the sea, and there are often days with no waves. Same problem as wind generators.

I also dont like the current (no pun intended) tide generators as they do not take advantage of the rise of the sea level, they just turn fans in flowing water. They are glorified water wheels.

My beginning of an idea (and its only the start) is 'how do we take advantage of millions of tons of water rising straight up and down 4 times a day (twice up, twice down)?' That is a collosal amount of energy expended by the moon, how do we convert it to usefull energy? I am not looking for alternative energy sources, I just have an idea about tide, and wanted to know if this sparked any further ideas......

yes, a large swimming pool is an eye sore.
yes, peak production will rarely match need.
weather & erosion are a problem all right.

Civilian_Target

Obviously you don't live by the atlantic - there's always waves there, and certainly there's always roll, which is all you really need.

lostexpectation

well isn't there plans for tidal one in some big estuary in England, but at what point with these sort of devices or even a water wheel do you start to negatively effect the flow of the water?

Professor_Fink

Immediately. There is no 'free energy'.

RiderOnTheStorm

Civilian_Target wrote:

Obviously you don't live by the atlantic - there's always waves there, and certainly there's always roll, which is all you really need.

I think the word 'obvious' should be deleted from the english language. it is used far too often and people dont use it properly....
if you look at my 'location' you will see it says 'Ballybunion' which is, clearly, on the Atlantic coast. AND there are often days when there are no waves.

Professor_Fink wrote:

There is no 'free energy'.

Quite right. You get nothing for nothing, as my dad used to say. But using the tide is converting one form of energy into another. And the pull of the moon, although not free energy in itself, is unlimited and available to be taken, and taking it does not deminish the power it supplies.

I will re-phrase my question:
I have an engine with one piston. It goes up and down 2m per day, twice a day. It is immensly powerfull, almost to the point of being unstoppable. It will lift and lower ANY weight. But it is slow. Can it be used to make commercial energy?

Professor_Fink

Actually it does diminish the power you get the next time around, just by a tiny amount.

As regards the piston, sure you can use it to extract as much energy as you want. But something must be driving the piston.

A better analogy is a fly wheel. A massive wheel is spinning, and so contains a lot of energy. If you connect a dynamo to the wheel, you can extract electricity. If the wheel is massive enough, the rate at which you slow it will be very slow. However, it will eventually stop.

Civilian_Target

RiderOnTheStorm wrote:

I think the word 'obvious' should be deleted from the english language. it is used far too often and people dont use it properly....
if you look at my 'location' you will see it says 'Ballybunion' which is, clearly, on the Atlantic coast. AND there are often days when there are no waves.

I live in Donegal. I've never seen the atlantic flat. Sometimes there's no obvious waves, but there's always, always roll. The coastline didn't get that ragged by magic.

Wave power could be a huge, reliable source of energy to our national grid, and we have the scientific strength to become world leaders in this field of research. We should do it.

is_that_so

http://www.boards.ie/vbulletin/showthread.php?t=2054947745&referrerid=&highlight=wavebob
Not sure what the current state of play is on this one but supposedly has lots of potential.

RiderOnTheStorm

Professor_Fink wrote:

As regards the piston, sure you can use it to extract as much energy as you want. But something must be driving the piston.

yes, ultimatly the moon is driving the piston.

A better analogy is a fly wheel. A massive wheel is spinning, and so contains a lot of energy. If you connect a dynamo to the wheel, you can extract electricity. If the wheel is massive enough, the rate at which you slow it will be very slow. However, it will eventually stop.

yes. but I dont see that the tide has reduced in the last few thousand years with the raising and lowering of the billions of tons of ships on it.

all the plans i have seen for tide generated energy have relied on water flowing forward and backwards (like a river in forward then reverse). This is limited to certain areas of coastline where the flow of water can be funneled for max effect. There areas are limited and there are only a couple in England suitable and prob only 1 in Ireland.

So I am wondering if anything can be gained by using the rise & fall of the water (powered by the moon) to generate usable power. One advantage of this rise & fall, is that it is not limited to the coastline and could be placed further out to see.

From my secondary school physics, I remember that Work is raising a mass. and the potential energy is mass x height. Now the height the tide raises the object is small, lets say 2m. But the mass could be a million tons (again think oil-tanker). So the potential energy is huge, but my question is ....... is it only potential energy? or can we use this energy? can it be converted into commercial, usaeable energy? or is it like a volcano or earthquake..... very poerfull energy, but bascially useless as an energy source?

Professor_Fink

The problem is that isn't as much energy ar you think. 1 million tons = 10^9 kg.
So the potential energy is = mgh = 1*10^9 * 9.807 * 2 which is roughly 2*10^10 joules. You can do this only once every 12 hours. So you get 2*10^10/(12*60*60) which is roughly 4.6*10^5 Watts. Or 460kW.

Note, no oil tanker has a mass of a million tonnes, the largest is about 650000 tonnes. So you only get about 300kW for the largest super tanker.

Nuclear power plants generate between 40MW(133 super tankers) and 1GW (3300 super tankers).

Basically your tanker idea is not a very efficient use of space or money and so will never be done. Maybe you could power Westport on it, it would completely destroy most of the coast there.

Also it would be extortionately expensive to maintain due to wear (you've got a million ton lever you keep moving up and down!)

ressem

I also dont like the current (no pun intended) tide generators as they do not take advantage of the rise of the sea level, they just turn fans in flowing water.

where does the water come from to rise the sea level?
The power needed to lift a supertanker 15m twice a day isn't that much by the way.
(edit: oops covered above since half time )

E.g. The proposed Severn barrage, on wikipedia
"The power generated, coming from a lake of 185 square miles and 14 m potential energy depth, would be equivalent to 12 nuclear power stations. Tidal power only runs for some 10 hours a day, but by using the enclosed lake as a reservoir of potential energy more hours of operation could be achieved."

So it's estimated, according to wiki, that the water flowing in and out as a result of tides, which creates the potential difference that you want to exploit, could generate an average of 2 Gigawatts.

RiderOnTheStorm

aah... thats the sort of answer i was looking for. not what i hoped for, you understand. the power from the raising of the water over a large area is not as powerfull as I had hoped. and it seems, not as powerfull as the moving (forward and back) of water on, say, the Severn estuary.

back to the drawing board.

thanks for your patience guys....... :-)

bonkey

Civilian_Target wrote:

The coastline didn't get that ragged by magic.

I know its at best tangentially related, but you seem to be suggesting here that having (say) 99 days in 100 with waves and 1 day in 100 perfectly flat would completely prevent erosion.

The rugged coastline has nothing to do with whether or not there are ever "flat" days. It is arguably proof that the Atlantic isn't always "flat", but thats about it.

Capt'n Midnight

The big problem with tidal dams is that you can't use the full height of the water as the only way would be to let it all out at low tide. Gradual release means you have a much lower head.

Check the tides along the east coast, look at the Irish times weather area inside the back pages and there is a considerable difference in times of high water over even short distances.