Author Topic: tidal power (Read 3160 times)

allen · « **on:** June 11, 2006, 04:53:17 AM »

I live in Florida and have been pondering the idea of using the height change in tides to power a generator. I have seen this briefly discussed in other topics here and I'm asking for technical feedback. Here are the details I have from my amateur computations:

Generating 1 kw per hour results in saving $0.10 in energy costs, resulting in $876 annual savings.

1 kilowatt requires a motor producing 1.5 hp to 2 hp.

* I have not seen anyway to generate more kilowatts from less horsepower? *

* Let me know if this assumption is incorrect *

1.5 hp requires 7878 in-lbs/min torque/rpm

* assuming computations correct *

A 1000 cubic foot float (25 x 40) generates 50lbs buoyancy per foot or 50,000 lbs

* Let me know if there is anyway to generate more buoyancy in a smaller area *

This travels up or down .14 in/minute with the tide in Florida resulting in 7000 lbs/minutes.

Resulting in about the same force needed by the 1 kw generator.

* Assumption of gearing or use hydraulics to convert from low tidal change speed to high motor rpm speed without power loss. Is this correct? *

Therefore considering a motor, large float, gearing/hydraulics, wiring etc it would take several years for a return on investment. Correct me if I am wrong but unless there are efficiencies I am missing, I may have discovered a more expensive option for power generation?

Thanks much - Allen

willib · « **Reply #1 on:** June 11, 2006, 12:31:40 AM »

Allen i dont want to disswade you from your endeavours , if you lived in Maine i would say there are possibilities to the concept , using tidal flow would be a better idea for you in my opinion .

when the family used to camp in your state, Marathon key,i was allways amazed at the lack of tidal rise and fall compared to nj

the reason i say this is because in your state in particular it rises and drops so slowly , where in Maine if you get stuck out on a sandbar when the tide comes in , you will be swimming back .

willib · « **Reply #2 on:** June 11, 2006, 07:35:18 AM »

how about using wave action to generate power . waves can move a real heavy floating dock up and down fairly quickly, so instead of cursing inconsiderate boaters , they would be welcome !

Nando · « **Reply #3 on:** June 11, 2006, 08:45:51 AM »

The most basic and important point is that there is not good analysis of the tidal site.

To be able to use tidal energy, a common ways is to channel the tidal water to a lower large pond via a channel or pipe with the turbine in it, for bi-directional turbine usage for about a total of 14 hours a day turbine power generation.

In Florida the tidal up/down levels are not proper for such project.

A possible alternate is the use of coastal sea currents if they exist in the local areas to install bottom retained turbines or floats if the sea levels currents have enough energy.

First to find the site, then to calculate the parameters and capabilities based on the site.

Nando

whatsnext · « **Reply #4 on:** June 11, 2006, 09:25:26 AM »

Have you thought about what kind of structure would be needed to control such forces?

kenputer · « **Reply #5 on:** June 11, 2006, 03:11:35 PM »

Here in Nova Scotia we have the Bay of Fundy which has some of the worlds highest tides not to mention the winds that blow up through the bay,they are now doing studies on tidal power avalible there should be interesting to see there progress. We also have one tidal power station in the valley that has been working for the last 20 years or so.

willib · « **Reply #6 on:** June 11, 2006, 04:56:40 PM »

lucky you ,

i got this fact from a Nova Scotia website

"

Highest Ever On Record

The greatest difference between high and low tide ever recorded was at Burncoat Head, Nova Scotia at 16.27 metres (or 53.38 feet) in the Bay of Fundy's Minas Basin."

allen · « **Reply #7 on:** June 11, 2006, 08:08:47 PM »

Thanks to everyone for the responses, let me try to address them here:

cant talk my wife into maine, she loves florida :-)
I live on a small canal lot - no waves, no room for resivour pond, no current.
structure to control - without a lot of engineering thought - a large float (like a floating dock) connected to a stationary sea wall or pole. As the float moves up/down in contrast to the stationary object, gearing etc could be setup to connect to a motor.
53 feet in Nova Scotia - that would bury my house and my neighborhood :-)

Thanks again - for your comments, if you have any others, please respond or email- thanks again - Allen

pepa · « **Reply #8 on:** June 11, 2006, 10:22:31 PM »

hi allen, if norm can make power with legos and a small weight, you can with 7000lbsminute. pepa

pepa · « **Reply #9 on:** June 11, 2006, 10:58:14 PM »

you can get a lot of energy from the rise and fall of a heavy weight with tide movement. A cable looped through a pulley that is anchored to the bottom and making a complete circuit by a few raps on a drum type pulley that is suspended over head (on piling) and attached to floating dock(could be multible systems). As the dock raises or is lowered with the tide the drum pulley, geared up , would turn, giving almost constant torque for a power system. i think that a number of small flywheels(large air compresser pullys) mounted on a single shaft would store and supply a dependable amount of power to a shaft if the gear up system is worked out. just my thoughts, pepa

GaryGary · « **Reply #10 on:** June 12, 2006, 09:45:39 PM »

Hi,

Interesting idea.

I tried to duplicate your calculation of the energy potential for recovering the tidal rise energy in a 25X40 ft patch of water using a different approach, and got a different answer.

If you think in terms of capturing the rising tide in a 25 ft by 40 ft pond (instead of using the 25X40 float), then, when the tide is out, you run the contents of the pond through a 100% efficient turbine to generate power. This makes use of 100% of the tidal rise energy and (I think) should be equivalent to any other scheme that makes use of all the tidal energy (like a float driving a geatrain driving a generator).

If the total tidal rise is (say) 6 ft, then the potential energy you capture in the pond would be:

PE of water in pond = (25ft*40ft*6ft)(62 lb/ft^3)(3 ft) = 1,116,000 ft-lb

Where the 3 ft is the average height of the water in the 25X40 pond.

In Kilowatt-Hours (KWH) this would be (1116000 ft-lb)(1 KWH/2655000 ft-lb) = 0.42 KWH

So, it seems to me, that for your scenario of capturing the energy in a 25X40 ft patch of tidal rise, you would get more like 0.4 KWH per tidal change -- assuming a 6 ft tidal rise, and 100% efficient conversion of the tidal energy to electric energy??

Gary

willib · « **Reply #11 on:** June 12, 2006, 10:05:33 PM »

I like your idea

you could start filling a basin just before high tide , get the power from filling the basin ..

just before low tide let the water out

there are two high tides and two low tides per day , roughly ..

so your .42KWH goes up to 1.68 kwh per day guarenteed.

larger basin more power

willib · « **Reply #12 on:** June 12, 2006, 10:23:48 PM »

by guaranteed , i mean you're guaranteed to get the tide change every day .

your mileage may vary

willib · « **Reply #13 on:** June 13, 2006, 11:27:01 AM »

of course you would need some type of large valve and a turbine in the pipeline connecting the basin to the tidal water.

allen · « **Reply #14 on:** June 13, 2006, 08:44:39 PM »

Gary thanks much - we have an average tidal change height of about 3 feet, this would probably cut your numbers in half - I knew there was something wrong with living closer to the equator :-)

That would still bring me in to .25 aprox kwh - that might be a little low for the cost involved, but any suggestions on finding highly efficient turbines? I also would need a mechanism to activate the two pumps/turbines at high and low. Any suggestions on that setup would be greatly appreciated.

Thanks again - Allen

allen · « **Reply #15 on:** June 13, 2006, 08:45:46 PM »

ok - where is info on Norm's lego power - I have lots of my old legos I just gave to my 5 year old - I would need to sneak them back :-) Thanks again

oztules · « **Reply #16 on:** June 14, 2006, 02:55:19 AM »

Allen, "That would still bring me in to .25 aprox kwh - that might be a little low for the cost involved,"....

I think that it gets worse ....... that .25kwhour is spread over 6 hours..... ie i think it was the total potential energy for the entire tidal event.

...............oztules

willib · « **Reply #17 on:** June 14, 2006, 08:36:24 AM »

with a valve system to hold the water back till just before high tide , then let it in , it should flow pretty fast.

also once the water is in the basin , open the valve again to let it out. also flowing pretty fast.

oztules · « **Reply #18 on:** June 14, 2006, 04:57:15 PM »

he lives quote "on a small canal lot - no waves, no room for resivour pond, no current." unquote

reckon that kills the pond bit

the net amount stays the same, the collection rate is what changes

..............oztules

willib · « **Reply #19 on:** June 14, 2006, 05:45:47 PM »

oh nevermind

ghurd · « **Reply #20 on:** June 14, 2006, 06:27:51 PM »

Norm and Shop4stuff did stuff with weights.

I think Shop4stuff did more with Legos.

From a quick search, at the very bottom of any page.

http://www.fieldlines.com/user/stop4stuff/stories

G-

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Author Topic: tidal power (Read 3160 times)