# The Naked Scientists Forum

### Author Topic: renewable energy??? any ideas?  (Read 4587 times)

#### allan marsh

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##### renewable energy??? any ideas?
« on: 14/10/2014 18:42:37 »
wind turbines give power when its windy not always windy and not when the grid needs it
so
solar power is great in the sunny and poor in cloud and zero at night
so
every day every night at different times of day the sea rises, called tides.
no night or day problem and not even reliant on waves.
so.
come on mathmaticians lets see how the tide rises can produce power... numbers numbers numbers plus surface area. lets use 10 acres of surface as a first try then multiacres
lets get Tide power going

#### alancalverd

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##### Re: renewable energy??? any ideas?
« Reply #1 on: 15/10/2014 12:26:24 »
Tidal range varies from day to day and tides run on roughly a 13-hour clock, superimposed on the phase of the moon, so although it is predictable, tidal power isn't constant or continuous.

Anyway, consider a 1 square meter turbine in a tidal flow of 3 m/s (pretty much the limit for a navigable river). That means  3 tonnes of water pass though it at 3 m/s every second, so the available power is 9 kW maximum. If we extract power from both rising and falling tides, we should get the rms power as an average - about 6 kW per square meter. Compare this with a simple vehicle alternator which delivers 1 - 2 kW and you can see that the capital costeffectiveness of tidal power is rather marginal.

#### Bored chemist

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##### Re: renewable energy??? any ideas?
« Reply #2 on: 15/10/2014 19:15:17 »
Why do the calculation, when you can just ask the people who run tidal power stations?
http://en.wikipedia.org/wiki/Rance_Tidal_Power_Station

http://en.wikipedia.org/wiki/List_of_tidal_power_stations

#### allan marsh

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##### Re: renewable energy??? any ideas?
« Reply #3 on: 15/10/2014 21:06:26 »
Tidal turbines like dams have the problem of influx of silt and not on output, so the back area silts up

My question refers say to the QE2 liner rising and falling with the tide .
What vertical power can be acheived if generators are place on the bottom and the mass raised and falls

How much power would the ship produce by its rise and fall?

#### alancalverd

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##### Re: renewable energy??? any ideas?
« Reply #4 on: 15/10/2014 23:48:36 »
Total energy per tide cycle = mgh where m is the mass of the floating body, g is the acceleration due to gravity, and h is the tidal range. Divide by 46800 to get mean power, assuming a 13 hour cycle.

#### David Cooper

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##### Re: renewable energy??? any ideas?
« Reply #5 on: 16/10/2014 18:25:48 »
I'd like to find a way to tap energy straight out of heat. Nanotechnology wind turbines, for example, might be able to use collisions with gas molecules to generate power while cooling down the gas. Put this into a computer and you could use waste heat from the processor to generate more power, as well as taking heat from the environment. Is this physically possible though? Can a collision with a gas molecule move anything enough to generate a small current in a tiny wire?

#### allan marsh

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##### Re: renewable energy??? any ideas?
« Reply #6 on: 16/10/2014 19:50:13 »
Just bought a great peltier effect fan to sit on our wood burning stove... Google fan for wood burning stove, so there is a potential renewable
The Russians used this effect to make a plutonium based 5 KW output unit for space use
Now the UK has 120 tons of plutonium one would think the they should go into the power generation unit field with this monstrous store. It's about time the great cambridge university did not get on with this massive potential
I spent part of my life working with dear plutonium at Dounreay.
About time someone realised they were sitting on a gold mine and not a problem store
Peltier effect can be used, it just need industrialising.

#### syhprum

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##### Re: renewable energy??? any ideas?
« Reply #7 on: 17/10/2014 22:15:58 »
The 120 tons of Plutonium that the USA has is not the highly radio active isotope that can be used in thermoelectric generator but the more mundane variety that needs to be used in specialised fission reactors

#### alancalverd

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##### Re: renewable energy??? any ideas?
« Reply #8 on: 21/10/2014 09:05:51 »
Plutonium/Peltier was used as a reliable heat source in pacemakers, but presented too much of a disposal problem when the wearer died.

Nuclear waste generally represents an untapped resource but it abounds with problems of security and safety: by the time you have ensured that the stuff you are promoting as a local source of heat or gamma radiation is not fissile, and you have established the bona fides of the users, and a proper accounting system......it's cheaper to burn oil.

I use Peltier fans on my woodburner too. The stove generates about 10 kW of heat, from which the Peltier fans derive about 0.5 watts. It's a fun way to circulate warm air around the house rather than up the chimney, but not wildly efficient as a means of generating electricity. However since the main use of electricity in the home is for cooking or heating water, an efficient woodburning stove can provide about 90% of your domestic energy needs from a renewable source that actually looks good, makes no noise, generates oxygen from carbon dioxide, and produces fruit or nuts for  several years before you set fire to it. I guess a full Peltier jacket on an Aga could run the lights too.
« Last Edit: 21/10/2014 12:21:11 by alancalverd »

#### allan marsh

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##### Re: renewable energy??? any ideas?
« Reply #9 on: 22/10/2014 11:19:50 »
to syhprum   no its UK that has 120 tons
secondly which isotope do you refer to 239 or the better neutron giver 241
dont understand your isotope problen after working with the beast in the 60's
which plut isotope is NOT suitable for thermo peltier units
the 5KW space used Russian unit seems robust and effective

#### alancalverd

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##### Re: renewable energy??? any ideas?
« Reply #10 on: 22/10/2014 14:16:50 »
Neither. Pu238 is the preferred source as it is virtually a pure α-emitter with a halflife of 87.7 years. Alphas are almost entirely absorbed in the mass of Pu itself, which can maintain a fairly constant 200 °C in commercial "atomic batteries" and thus power a Peltier system very effectively.

#### syhprum

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##### Re: renewable energy??? any ideas?
« Reply #11 on: 22/10/2014 21:00:10 »
I think you will find the 5kW Russian device was actually a fission reactor not a thermo electric generator, as Alancalverd points out the only PU isotope that provides a useful amount  of heat is U238 which is extremely expensive and difficult to produce to the extent that designers of satellite PSU,s are planning to use the more efficient Stirling engines rather than Peltier junctions

#### syhprum

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##### Re: renewable energy??? any ideas?
« Reply #12 on: 22/10/2014 21:07:08 »
On a recent tourist trip down the Rhine I noticed a small tidal generator similar to those in use in Iraq I do not think it was a very economical source of power only a tourist attraction.

#### alancalverd

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##### Re: renewable energy??? any ideas?
« Reply #13 on: 22/10/2014 23:47:18 »
It seems that Pu238 units run up to 300W (as in the Cassini probe) and indeed to get to kW outputs you need a fission reactor.

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##### Re: renewable energy??? any ideas?
« Reply #13 on: 22/10/2014 23:47:18 »