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If I recall the median heat flux from the Earth's core is about 0.2 watts per square metre. On a clear sunny day the sun may give 850 W/m^2. Not only that in the case of photovoltaics there are no moving parts or liquids sloshing around. You build it and check on it 10 years later.
Half a gigawatt of HFR geothermal by 2016 will probably be less than 1% of what Olympic Dam uranium will be generating for northern hemisphere customers.
I'm not sure about relative energy densities, but the total amount of geothermal energy is still vast.
By all means build lots of CSP plants in the desert and stick PV on the roofs of all the warehouses in the western suburbs of Sydney - I won't complain.
But I still think its worth building a significant amount of geothermal capacity - both "wet" plants around the ring of fire and HFR where the process can be made to work.
If we have 5 GW of HFR geothermal capacity in 2025 I think we'll be pretty happy with ourselves - that's 5 nuke plants we don't need to build.
Theory (not mine) - Mars had an atmosphere until its core became solid.
Ergo - long term - if the heat of the core is taken away so might the Earths atmosphere.
(Just a reminder of a possible long term outcome - wonder what the direct into the mind movie about the impending loss of atmosphere will be called? Time to join the telephone sanitizers off-planet?)
In the time it takes for humans to measurably lower the earth's interior temperature we will probably have colonized half the galaxy. (assuming we get that far)
Earth's core is hot because of the sustained nuclear reactions that happen there. It is constantly producing and dissipating heat, it is not a reserve, like oil.
Geothermal energy is renewable on the same sense that solar is renewable.
While, today, such a statement is taken as true, similar statements were made about oil and CO2 in the air in the past.
I and any future generations I might know personally will not have to worry about the cooling of the core of the earth. I'd even be willing to bet that moving the heat from the Earth core into the atmosphere would be a bigger issue.
But as soon as you start removing the heat, you start cooling the rock... So you can say that there is a "reserve" of heat in a certain "field". I would say, geothermal energy is renewable on the same sense that abiotic oil is renewable 8O).
Solar, on the other hand, does not have that behaviour. Behind each photon there is another one, and the flow is exactly the same if you take 0% or 100% of them.
BTW, minor nitpicking, Iceland is not in the European Union (nor was in the European Common Market).
Although there have been suggestions to the contrary, the uranium whose fission provides the thermal in geothermal is not in the core but rather distributed in the crust.
Yes, geothermal is renewable (until the U and other unstable isotopes are gone), but the unfortunate timescale (see low heat flux stated above) means that what one is doing is actually mining stored heat. Yes, there is a lot of it (and in certain places it is rather close to the surface), but the very reason that the heat is stored at depth (low thermal conductivity of the rock) also means that harvesting the heat at an economical rate is a challenge. And if you solve that problem (perhaps using e.g. horizontal drilling), then you will nevertheless deplete the heat--you are limited by the thermal conductivity of the rock. Eventually, you will need to drill again elsewhere.
Actually, experience in the Geysers field in California shows you need to drill again rather quickly, owing to low heat conductivity of rock. Over human timescales, geothermal is definitely depletable, but you can compensate by constantly developing adjacent areas. This continual drilling has to be allowed for in your cost estimates, of course.
There's one other thing which has been done that's a bit odd at the Geysers: they're pumping (treated) sewage into the geothermal field to compensate for steam depletion. It regularly causes small earthquakes as the water vaporizes in steam explosions underground.
More at http://arxiv.org/PS_cache/hep-ph/pdf/0501/0501111v2.pdf .
Also, the heat it produces, it produces 99.999+ percent by alpha decay, not fission.
--- G. R. L. Cowan, former hydrogen-energy fan
http://www.eagle.ca/~gcowan/Paper_for_11th_CHC.html :
oxygen expands around boron fire, car goes
It's only, 20 mW, or .02 watts/m^2, or just one tenth what you stated. Solar flux averages out to less than 850 W/m^2 because of night, clouds, and the poles, but it's still well over 100 W/m^2.
If we took the heat coming up from the entire US (9.8M km^2), the sustainable thermal power would about 200GW thermal. Given a 20% conversion efficiency, we would get 40GW electric.
I'm also afraid of what cooling such massive volumes of rock could do to the geosphere. It will cause the rock to become less plastic and to shrink (thermal contraction). If done on a large enough scale, could this cause large scale subsidence (from denser rock sinking) or earthquakes (from thermal stresses and from subsidence)? Could it slow down the movement of the plate in that area by making it less fluid, causing stresses to build up.
My references say geothermal flux if .075 w/m^2, but whatever...