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biffvernon · Joined: 24 Nov 2005 Posts: 13905 Location: Lincolnshire

Article continues... behind a pay wall.

Of course hot rock geothermal should be a significant part of the mix and it's good to hear that work continues.

But, strictly speaking, it should not be described as renewable. The rate of radioactive heating and up-welling energy from deep down is so slow that what one is actually doing is 'mining' a resource of heat. Extracting the hot water cools the rocks, eventually to the point where you have to give up. Still, in the right locations, that could take a very worthwhile length of time.
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kenneal - lagger · Posted: Wed Dec 08, 2010 6:11 pm Post subject:

The article isn't behind a pay wall, but you might have to register to read it.

It's another from of nuclear in this case, as the radioactive granite decomposes it releases heat. Some geothermal heat comes from fault lines which allow water up from great depths where the heat is of volcanic origin.

Southampton city centre gets some of its heat from geothermal pumping.
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biffvernon · Joined: 24 Nov 2005 Posts: 13905 Location: Lincolnshire

Newcastle borehole: http://www.bbc.co.uk/news/uk-england-tyne-13914718
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kenneal - lagger · Posted: Tue Jun 28, 2011 2:18 am Post subject:

biffvernon · Joined: 24 Nov 2005 Posts: 13905 Location: Lincolnshire

kenneal - lagger · Posted: Tue Jun 28, 2011 2:30 pm Post subject:

There's no reason why it couldn't, apart from, possibly, human greed. If the temperature of the water started dropping just reduce the flow rate until it picks up again.
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biffvernon · Joined: 24 Nov 2005 Posts: 13905 Location: Lincolnshire

I think it's like sucking water out of a swimming pool with a straw - it will run out, but slowly, very slowly because there is a tap dripping into the pool.

With some hot rock geothermal it's actually quick enough to make it not worthwhile. In other places there's no bother. Heat flow rates are critical. I'm just pointing out that, strictly speaking, geothermal is not 'renewable'. One is mining a resource, though in some places the resource is very large.
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kenneal - lagger · Posted: Wed Jun 29, 2011 2:09 am Post subject:

The problem would be if we sucked so much heat out of the core that it solidified causing the earth to lose its magnetic field. That, in turn, would cause the loss of much of our atmosphere. We would have to go at geothermal pretty hard to do that though.
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It is very, very, very serious indeed. This is the big one!" Professor Tim Lang, APPGOPO, 25/03/08. And he was talking about food, not oil or the economy!

biffvernon · Joined: 24 Nov 2005 Posts: 13905 Location: Lincolnshire

The deepest borehole (exploratory not geothermal) has only reached 0.2% of the way to the centre of the Earth so I guess it'll be a while before we achieve the heat death of the planet. Smile

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kenneal - lagger · Posted: Wed Jun 29, 2011 3:02 pm Post subject:

Beware the power of exponential growth!!
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mindscience · Joined: 02 Aug 2011 Posts: 16

That would require some prolonged and very dedicated digging, kenneal Laughing

I agree about the geothermal is not renewable point. My friend has a website that deals with like geothermal energy and he keeps writing renewable energy sources, yet I am inclined to believe that just because something hasn't been proven as non-renewable, there is also a complete lack of evidence to support the former. If that makes any sense.

Consequently, I'd also be inclined to believe that drawing energy from hot rocks with such slow speed of heat generation could prove rather insignificant, if not useless. Yet it is good they are trying to explore more options.
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