Generator conneted

I was wondering what would happen if you connected a working generator to the mains whilst power was on.
I am asuming it would not be a good thing?? anybody actually know what happens?
Gary
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wrote:

All the smoke that is trapped in the wires would come out, there may be extreme acoustic events, and photons would strike your eyes.
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On 14/12/2011 09:48, harry wrote:

ITYM a fuel cell using the waste heat to warm water. The Japanese Prime Ministers residence has one such installation - although they have gone very quiet about how well it is working.
Thermopiles are only really cost effective for space flight.
Regards, Martin Brown
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Geothermal all over wales, mendips etc, would be fine in the UK.
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js.b1 wrote:

until that heat source was exhausted..
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On Wed, 14 Dec 2011 14:27:08 +0000, The Natural Philosopher wrote:

But doesn't some geothermal energy come from the expansion/compression of the earth due to solar gravity ?
I was amazed, watching Prof. Cox "Wonders of the Solar System" to learn that one of the moons of Saturn has a molten core due to this effect.
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Jethro wrote:

Isn't there some idea that nuclear reactions are also happening in the earth's core?
--
Tim Watts

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On Thu, 15 Dec 2011 10:44:19 +0000, Tim Watts wrote:

Not heard that one, but it seems entirely plausible. At those temperatures and pressures ...
There's a certain irony in some people running around wittering on about the evils of nuclear power when they're sat atop a massive nuclear reactor.
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On 15/12/2011 10:44, Tim Watts wrote:

And Io around Jupiter has sulphur volcanoes that are tidally powered, but they are in a pretty extreme gravitational environment.

Only if you count radioactive decay. There is no fission.
These days is it predominantly from radioactive decay and some input from flexure of the Earths crust from lunar/solar tides. A very long time ago it was just about possible to have a natural nuclear reactor form in uranium ore bodies when the U235/U238 ratio was higher. eg. Oklo
http://oklo.curtin.edu.au /
Regards, Martin Brown
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On 14/12/2011 11:02, harry wrote:

You have to be kidding. You can have affordable or efficient thermopiles but not both at the same time. It is very niche market.
I tried to put together a candle powered demo for an Xmas lecture using them (fairly high grade units). I was intending to drive one puny LED from the waste heat of a candle flame (about 100W).
I had a high temperature TEC module and a boring one stacked and even operating it between 250C hot side to a large deep frozen heatsink -18C on the cold side I could barely get enough juice out to do anything useful. I decided that at these temperatures it was too hazardous for a childrens' Xmas science lecture and scrapped the idea.
The same TEC units can move 50W or so from the hot plate to the cold plate when suitably powered. But try to generate power with them with a temperature difference applied and it is a lot less efficient. I would be interested to know if anyone has found a setup that works - ideally enough to power a 1W led (but I'd settle for 10mA and 4v).
Previous toys have included candle powered nodding heat engine and a heat engine that on a good day will run off a cup of fresh coffee.
Regards, Martin Brown
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I've used the 50W peltier devices. I found they generated power after you've powered them off and there's still a temperature difference of ~40C across them - enough to continue self-powering their cooling fan and a power-on LED for half a minute. I think these ones were rated up to 250C, but I never ran them over 40-50C differential.
Even as heat pumps, they aren't efficient - it consumes 50W to pump 50W, but as a tiny heat pump, they can be very handy.
--
Andrew Gabriel
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On Wed, 14 Dec 2011 14:18:08 +0000 (UTC), snipped-for-privacy@cucumber.demon.co.uk (Andrew Gabriel) wrote:

A friend had one of those in his narrowboat, powering a fan on the stove top. In such a small space it was very effective.
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On 14/12/2011 16:23, harry wrote:

Yes. They are good individually for 25mV open circuit or 10mV @ 0.2A.
But do you have any idea how many of them I would have needed to generate 1W of electricity at 4v?
A back of the envelope calculation suggests about 400 or so thermocouple junctions to provide the target 1W of output power at 4v and perhaps half that number to get an LED glowing at low current.
The TEC modules at least have a decent number of junctions in series and can source a voltage high enough to use semiconductors.
Regards, Martin Brown
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https://en.wikipedia.org/wiki/Micro_combined_heat_and_power#Engine_types_and_technologies
There's research aimed at changing that: http://www.newscientist.com/article/mg21228406.400-painton-power-the-saviour-of-solar.html But don't hold your breath.
(PV panels that are also solar thermal panels are another matter: https://en.wikipedia.org/wiki/Photovoltaic_thermal_hybrid_solar_collector But no-one's suggesting they'll get hot enough to be worth using the heat for additional electricity generation.)
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They're even less efficient, but on a spacecraft, they are usually driven by a nuclear reactor, which might present a few problems for home generation. You can pick up many abandoned ones from around the northern coasts of the former USSR, where they were used as things like lighthouse power generators. Most of the people who have tried recovering one of these, enticed by the idea of 1-2kW of free power for years, have died very shortly afterwards though.
--
Andrew Gabriel
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I think you are failing to understand CHP. The point of CHP is to raise the overall efficiency of the system by compromising on the efficiency of components in the system. Slightly less efficient electricity generation and comparatively inefficient heat great ion add to total thermal efficiency higher than a good generator or a good boiler working alone.
For this sort of use a Stirling engine generator is good. There's (some) mechanical output to generate electricity and a fair amount of waste heat that can be used for space heating. It has the advantage that it provides electricity when photovoltaic cannot - winter evenings. It's a great idea for a sensibly managed energy economy.
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On 14/12/2011 09:59, Martin Brown wrote:

Especially if you have a nice lump of fissionable material to keep it hot.
--

Graham.

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AFAIK there are no space craft (from Earth) that use fission (as in nuclear reactors). They just use the heat from decay.
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dennis@home wrote:

decay comes from fission
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On 15/12/2011 10:20, The Natural Philosopher wrote:

No it doesn't.
Pu238 is formed by neutron capture from Np237, which is itself a product of either 2x neutron capture by U235 or 1x neutron spallation by U238.
Heat in the Earth today comes from long lived radio isotopes like U235, Th232, K40 that are left over from the Earths formation. Most of the species stil providing heat in the Earths core are left overs from nuclear synthesis in a supernova explosion 4.5By ago.
Decay can be by alpha, beta or gamma or more usually a mixture depending on the isotopic species. Only for alpha decay is a non-trivial other element, Helium produced in the reaction.
Fission reactions are conventionally taken to mean nuclear reactions with particle in (usually a thermal neutron) to disturb the heavy nucleus and two energetic fragments of roughly equal mass out.
Regards, Martin Brown
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