Does geothermal energy payoff in ther long run?

[Elite Engineer]

Perhaps I'm not understanding the correct concept of geothermal energy, so this suggestion may be a bit ignorant..but:

 

Geothermal energy is essentially using heat from the earth (i.e. hot magma) to heat water, which spins a turbine.. blah blah..you know. Is this strictly done only at

 

existing geysers? Because I was thinking, though it is expensive, wouldn't it still be cost effective in the long run just to dig say 500-1000ft into the earth where it's hot e

 

enough to massive pipes to heat water? Once you dig the hole, and it's paid off, that's basically a never ending heat source, compared to nuclear energy or fossil fuels.

 

We'vemanaged to build a ton of oil rigs and oil pipelines around the world...what's a couple of 1000ft holes going to make different? Am I getting this right or no?

 

~EE

[Sensei]

Have you seen map "geothermal power potential united states" with scale watts per m^2

NY area has 4-5 times smaller potential than the hottest area..

 

[Elite Engineer]

Have you seen map "geothermal power potential united states" with scale watts per m^2

geothermal-power-potential-united-states.jpg

NY area has 4-5 times smaller potential than the hottest area..

I'm sorry, but I dont follow...is this good or bad?

[Ken Fabian]

EE - there are different types but the most readily usable is in volcanically active areas. It can range from using the hot water that wells up for heating, to drilling down to where the water is at higher than surface boiling point - kept liquid by being under pressure. It boils from it's own heat once the pressure is removed, ie raised to the surface. Usually doesn't require pumping. More geographically available is what we would call Hot Rock Geothermal - or Enhanced Geothermal. It makes use of geological hot zones, often deep granites that are heated over eons by their own natural low level radioactivity; fracking allows water to be pumped down and through shattered hot rock, to return from a nearby second well heated at above surface boiling point, like the tapping of natural deep hot water mentioned above. Ultimately the heat is used up.

 

Another kind of geothermal is heat pumps, that are used for small scale heating, using a variant of Refrigeration or Air Conditioner type technology, that absorbs heat from buried pipes at relatively low temperatures - by cooling the fluid first, pumping it down where it's cooler than the ground, where it absorbs heat - then allowing it to be released at higher temperatures. Usually the piping is buried at a depth that allows seasonal reheating, ie over summer, and deep enough that it remains available through winter. It works the same way a fridge pulls heat from food and the heat is released at above room temperature in a radiator at the back. It's advantage is that the process doesn't use as much energy as it picks up from the ground and releases where needed, making it an attactive home heating method.

Edited July 22, 2016 by Ken Fabian

[swansont]

Have you seen map "geothermal power potential united states" with scale watts per m^2

 

 

That's mW/m^2 — thousandths of a watt per square meter

[Sensei]

I'm sorry, but I dont follow...is this good or bad?

 

Bad.

See where are areas were is more sense building such installations: they have small population which could use energy produced this way.

If NY area has 5 times smaller power per area unit, it means 5 times more installations will be needed to have the same result as in "hot areas".

Map of population is nearly inverse of "hot-cold areas map" from 2nd post.

[foxy john]

Check out what they are doing in Iceland, geothermal is quite well established there. Yellowstone would be an ideal location but I suspect your National Parks would object to a power station sucking away all their heat.

[Enthalpy]

The geothermal flux is very small. That's something the proponents of geothermal energy often forget to mention. Integrate it over Earth's surface, you get a flux smaller than Mankind's energy consumption.

 

This isn't damning, because the heat stored in the shallow crust is huge as compared with Mankind's needs. In this sense, geothermal energy is limited, but abundent enough, and by far. Much more abundent than the coal, gas and oil equivalent for instance.

 

Where geysers and hot sources are absent, humans can inject water and harvest hot water or vapour - the Hot Dry Rocks process, yes. It's done in the Rhine valley for instance, several Mm from the next geysers.

 

A pipe running in the ground wouldn't receive enough heat power nor harvest heat from enough rocks. HDR injects water and lets it run freely over several hm², preferibly between two watertight layers. After some time, the heat is depleted, and an other location must be exploited (possibly from the same location at the surface), so a set of wells doesn't provide eternal heat.

 

While the turbines, generators, heat network, barracks... can be moved and reused if needed, the wells can't and cost in the low M€ zone, so rentability isn't guaranteed just by waiting. Corrosion and scaling of the surface equipment is a serious concern too, because the hot water was in contact with rocks.

 

Because of that, and because ridiculously little money has been invested so far, the payoff isn't obvious, and current projects concentrate in areas where the returns are as high as possible. But this doesn't imply geysers.

 

Since geothermal energy is available when we need it and takes little ground area, I'm enthusiastic about it - but its rentability isn't easy to predict. Hot sources in Iceland are known to be money bringers, and the country seeks to exploit them beyond its already covered needs; HDR near population centers is less obvious, but I'd like to see more efforts on it.

[EdEarl]

Caves are kept comfortable by geothermal energy, and Earthships use that energy to make homes comfortable, and is viable almost everywhere. It costs a bit more to build an Earthship, but in the long run, with no heating or air conditioning bills, it is money well spent.

[Elite Engineer]

 

Bad.

See where are areas were is more sense building such installations: they have small population which could use energy produced this way.

If NY area has 5 times smaller power per area unit, it means 5 times more installations will be needed to have the same result as in "hot areas".

Map of population is nearly inverse of "hot-cold areas map" from 2nd post.

us-population-map.gif

So is this issue that there is not enough magma under the eastern seaboard than the west and midwest? I assumed that, like the water table, if you dig deep enough eventually you're going to hit the inner crust/magma parts. This sounds like it would work anywhere...just find a plot of land and dig..right or no? Hopefully this picture helps illustrate my message...

[Ken Fabian]

EE - it's not clear from the map Sensei included what sort of geothermal it shows. I suspect it may be or include hot rock geothermal, which is not hot because of heat from magma, but from long term internal low level radioactivity.

[Moreno]

I think geothermal power will be more profitable if methods to transport electric energy over large distances with very little looses wil be perfected. Or you could use geothermal energy to produce aluminum and ship it somewhere.

[Enthalpy]

if you dig deep enough eventually you're going to hit the inner crust/magma parts. This sounds like it would work anywhere.

 

But drilling deeper costs more and the set of wells produces heat for a limited time. Energy is very much a matter of cost, and dirt-cheap coal, gas and oil give renewables a hard time.

I think geothermal power will be more profitable if methods to transport electric energy over large distances with very little looses wil be perfected.

 

Electricity is already transported well over 1000km with little loss. In Brazil, Canada, and soon in southern Africa. This isn't even new technology: over three decades old in Itaipú.

[sethoflagos]

Many, many challenges.

 

From a practical point of view, if steam is the heat transfer medium, it needs to be heated to preferably well in excess of 400 Centigrade to have enough pressure and superheat in it to be processed in a reasonably compact and efficient steam turbine.

 

With an average lithospheric temperature gradient of 25 C per kilometre, that means drilling at least 15 kilometres. Or 3 kilometres beyond the depth of the Kola Superdeep Borehole. (Which took 20 years.)

 

At those sorts of depths the hydrostatic pressure is typically going to be knocking on 5,000 bar. Which means you're going to have to compress your feedwater up to this pressure to get it into the formation. Process piping above 100 bar asks severe questions of design safety. So multiply that by fifty, add in all the aggressive minerals that become fairly soluble in water at that temperature. On the way invent a high performance drill bit that can withstand those sorts of conditions........

 

And that's sort of why geothermal energy is going to be fairly small scale and localised for some time to come.

 

In passing, making a significant disturbance to the hydrostatic and chemical equilibrium around the Yellowstone magma chamber before we know exactly how that beast operates may not be a great move.