Almost everything we do that initially seems like a good idea stops being such when we start doing it at scale. Burning fuels wasn't a problem at the eve of the industrial revolution. I wonder what ecological issues will hit us globally as we scale up geothermal energy use. E.g. I've read somewhere that people putting too many ground-exchange heat pumps in a small area can cause problematic cooling of the ground. Right now it's probably only a problem for the energy efficiency of the pumps themselves, but as we scale up, I worry about unintended environmental consequences.
The first sentence of that section says that "geothermal power is considered to be renewable because any projected heat extraction is small compared to the Earth's heat content." I'd like to see some estimates on how much of that heat content is available on the depths we're drilling down to (as opposed to the contents of the whole planet); and again, trees were a renewable resource too, before the industrial revolution.
> The first sentence of that section says that "geothermal power is considered to be renewable because any projected heat extraction is small compared to the Earth's heat content." I'd like to see some estimates on how much of that heat content is available on the depths we're drilling down to (as opposed to the contents of the whole planet);
Wikipedia links to an article with more detail. The crust alone is estimated to hold enough heat to supply all of the Earth's electricity generation at current levels for about 80 million years.
The total heat content of the Earth is of the order of 12.6 x 10^24 MJ, and that of the crust the order of 5.4 x 10^21 MJ (Dickson and Fanelli, 2004). This huge number should be compared to the world electricity generation in 2005, 6.6 x 10^13 MJ.
> and again, trees were a renewable resource too, before the industrial revolution.
Trees are still a renewable resource, more so since we largely stopped using them for fuel as a result of the industrial revolution.
I think it's more compelling, however, to just think about how much bigger the interior of the planet is than our existence at the surface.
We live on maybe ±1km of the surface or so; we don't dig much deeper than that except perhaps when exploring very deep caves or so. The radius of the Earth is approximately 6300 km. One volume is (4 pi/3) R^3 and the other is 4 pi R^2 dR, so the one volume is larger by a factor of 6300/3; we can only hope to visit one two-thousandth of the Earth's total volume with holes 1km deep. Up that to 10km deep and you'll still only get one two-hundredth of the Earth. Oh, and we've only got about a third of that because oceans.
It's worth keeping in mind that when coal reserves were first being estimated in the US, ~1865 - 1875, the total reserves were considered to be over 1 million years' supply at then-current rates of usage.
Oddly enough, constantly growing usage can cut into that time-to-depletion estimate fairly quickly. Present estimates are that US coal reserves are ~200 - 1,000 years, depending on the recoverable yield.
Please refrain from assigning intent to a simple comment.
Given the large amount of statistics and facts that you bring to the question it is clearly evident that you know more about this problem than I do. I merely wish to point out that a simple linear scaling of current consumption levels is not a convincing model for adoption of any new technology / paradigm. You had me on the facts, but lost me on the projection.
When you say something like Keyword there is => "current levels", it comes off as pessimistic and poisonously negative. It's the kind of statement that shuts down conversation rather than encourages it. Rather than inquisitive, this comes off as dismissive. I may have misread your intent, though, and if so I apologize.
I am aware that constant usage is not generally a valid assumption. I made a simplifying assumption that I believe reasonable given the sheer size of the energy store. It doesn't matter much if our usage is constant or increases a thousandfold. There's so much energy in the crust that we essentially could not use it all, and I doubt that we would use enough to cause global issues (vs local issues caused by overuse in certain areas which seems more feasible).
P.S. To be clear, I don't know much about this problem at all. My only data is from Wikipedia and its references.
I made a simplifying assumption that I believe reasonable given the sheer size of the energy store.
One of the points that TeMPOraL made above is "and again, trees were a renewable resource too, before the industrial revolution.". The point being that resources that are seemingly infinite when first used can end up being not so unlimited.
So for example, the person downthread who uses energy trends estimates a lower bound of about 1000 years (if current energy consumption trends continue, we immediately switched to only geothermal, and we used the entire heat of the earth edit: Earth's crust, not the whole earth). So now we have a range of 1,000 to 800,000 years (based on varying assumptions).
800,000 years to take up 0.001% of the total heat would be fine. 1,000 years to take up 100% of the heat would be really bad.
The 1,000 year quote is based on historical data, and 800,000 years is based on flat/zero growth. So there appears to be room for discussion, not all of which is 'fear monger'ing.
> One of the points that TeMPOraL made above is "and again, trees were a renewable resource too, before the industrial revolution.". The point being that resources that are seemingly infinite when first used can end up being not so unlimited.
It's legitimate to ask what our energy usage might grow to. It's not legitimate to dismiss potential energy sources because we cannot predict the future with perfect accuracy. We will never predict the future perfectly, or even close, and if we have a choice between killing the planet in 1000 years or killing it in 100, we'd still be better off taking the first option.
The "1000 years" comment also assumes we'll double our energy usage every 25 years. If we accept that as true then our only viable strategy is to get off this planet because it assumes that in 1000 years we will literally have extracted all energy from the core. We're doomed if this is our future.
Also, please stop mentioning the trees. This has been addressed multiple times now. The industrial revolution didn't result in trees being cut down. Quite the opposite. The large-scale adoption of fossil fuels resulted in forests rebounding worldwide as we stopped relying on timber as a fuel.
> *The 1,000 year quote is based on historical data, and 800,000 years is based on flat/zero growth. So there appears to be room for discussion, not all of which is 'fear monger'ing.
It's rather generous to say it was based on historical data. It was based on taking the log2() of our current energy usage and eyeballing an energy usage chart to produce a guess at a 25-year doubling rate. Our energy growth is no more a constant than our usage, though, so extrapolating this way is as unrealistic as assuming we'll stay at present-day usage forever.
There is certainly room for discussion. Again, though, I'll point out that a discussion should be about options and not just the worst case for geothermal exhaustion. If we found that we could replace all of our fossil fuel use with geothermal but we'd only get to extract energy for 1000 years safely, that would be a great deal, because the obvious alternative is that we literally burn every bit of fossil fuel we can extract from the Earth.
On the trees numbers, the US now actually has more forest or trees than it did at the start of the twentieth century.
The argument sometimes gets confused, since conservationists are concerned about the loss of old-growth forests, and animal habitats vs. the quantity and area of forests.
Fine, let's quadruple consumption – we're good for 20 million years. Ok, okay, let's go to 100x consumption – we're good for 800,000 years. I think we're ok.
Since the magnetic field of the earth, which protects us from the solar winds among other things, is generated by spinning of the molten outer core, do you happen to know how much of that energy would be available before adverse effects happen?
It's obvious that the answer is less than 100%, since a completely solid core would provide no magnetic field. Is there some way to tell whether it's closer to 0.1%, 1% or 10%?
The 80 million years figure is for the heat content of the crust, not the entire earth. The heat content of crust is approx 0.04% of the heat content of earth.
It's not really possible to use enough geothermal for it to have a noticeable effect on the lifespan of the magnetic field. Even completely removing the solid crust of the earth would not really register.
This is a really great point, and probably the key one. It's also probably a good assumption that heat extracted from the Earth's crust after some point would stabilize due to heat differential from the layer's beneath the crust.
So we could take out some percentage of the heat of the crust, thus lowing the total temperature by some amount, but then that loss would be replenished from further down in the core.
It looks like from the calculations elsewhere in the thread that it probably wouldn't even be physically possible to extract that much energy from the crust. We'd just run out since there would be some lag time in replenishing the heat from the core through to the areas of the crust.
Let's assume it's not just 0.1% but 0.001%. That still leaves us a comfortable runway of 19 million years at our current levels.
But also let's hope it's not 0.001% because I'm pretty sure the core will cool more than that on its own over a shorter timespan than 19 million years.
Wikipedia suggests cooling of 100 degrees C every billion years.
19 million years is 1.9% of the billion year rate. So it suggests the core should lose 1.9C in 19 million years. That's about 0.035% of the total temp, using Wikipedia's 5700C as the temp estimate.
That's a great initial guess, given how much uncertainty is (i've recently heard core temp could be 4x the wiki number, and some people estimate the earth's core only has lost a few degrees since it formed, rather than nearly 500 degrees). Neat stuff, thanks for providing the opportunity to look in to this.
I'm honestly not sure. I don't know how much energy is being created inside the Earth and how much is just residual. It's my understanding that the Earth is slowly cooling, though, so radioactivity isn't replenishing heat as rapidly as we're losing it.
No idea how good the source is, however it looks like we have a nice exponential there.
Lets see what the envelope says for an exponent of 2:
Using numbers from parent commentors, log2(6.6 x 10^13) is about 45.9, so we are in our 46th doubling period. A guess on the graph says its 25 years to double.
> The total heat content of the Earth is of the order of 12.6 x 10^24 MJ, and that of the crust the order of 5.4 x 10^21 MJ (Dickson and Fanelli, 2004).
so that's end of crust energy usefulness at the start of the 72nd period and end of Earth energy less than halfway through the 84th period.
So that gives us 500-1000 years of energy from now if we solely use the planets heat. Whether we soley use it or not becomes largely irrelevant due to the exponent, we can stretch it as a major source a few hundred more years or so.
Of course, if in 1000 years we aren't only using this planet we should be good. How many years to the next system again?
You are successfully making the point I was trying to.
We are willing to concede that usage patters from 100 years ago are unrealistic current realities.
However we would simultaneously like to use the current reality to project future realities that are much farther away (in some cases 19 million years away).
It doesn't actually matter much if our usage projections are good. What matters is 1) that the energy store is so massive that it's hard to imagine how we could possibly exhaust it, and 2) the current dominant alternative (i.e. fossil fuel) is known to be terrible for us. If we switched to geothermal and set the world up to end humanity in a thousand years, we'd still be better off than continuing our desperate use of fossil fuels and ending humanity even sooner.
The issue is we use up fossil fuels we could still continue for more years, I don't see any reason for it to end much before that. If we make mistake with earth core we would mostly surely setup end of humanity atleast. I would rather focus on getting the world to a place where willno borders and safe religion etc.. which would get lot more runtime for humans than this. If we optimize food production find a better alternative for capatalism we may live better with or with out need for fuel
Our food production is driven by fossil fuels. Everything from the farm equipment to the fertilizers we spread to the trucks we ship it in are powered by fossil fuels. When we run out of fossil fuels, we better have a back up energy source (or sources) ready, because our food production will plummet if not. So will basically every industry, since they all depend on cheap transport and automation at this time. So we'll all starve while the economy collapses around us and our infrastructure falls apart as we have neither the money nor the energy supplies to fix it.
Yeah, our dependence on fossil fuels is a huge problem, and not just because of climate change (which might also kill us).
I agree somewhat, but even though more devices are electrical or electronic and attached to the grid, they are more efficient. My 42" LED TV is using 95W, less than a 100W light bulb, whereas my old 19" tube color TV in 1978 used more.
Mobile phones didn't exist when I was young, and there are certainly a lot of them now even if they are low power devices, so it would be interesting to see electrical usage patterns pre-mobile phones vs. today.
The same goes for cars. Cars were using leaded gasoline in the US and getting 8 to 12 mpg, and now 30 to 35 mpg or greater on the highway, but do people drive more frequently, and with single riders?
Another question is would any cooling of the total Earth's heat energy be offset by global warming? The thermal differential would be less thereby slowing the migration of heat to the surface?
This assumes that nothing mayor is going to change. What if we somehow build a spaceship route from Earth to Mars and we power it through electricity. How much higher would our consumption be if we launch 10,000 spaceships every day?
Or maybe we want to terraform our own planet to counter climate change. These things could use amounts of energy orders of magnitude higher than we use today.
I'm sure 100 years ago didn't expect we would launch 100,000 airplane flights every day [0] :) Nor did they think we would send spaceships to Mars.
What if we also solve fusion and build a Dyson sphere and farm unicorns for automotive fuel?
It seems somewhat unreasonable to assume that our energy usage is going to exponentially increase due to as-yet-unforeseeable future needs and at the same time assume that we'll completely fail to find additional energy sources in the same timeframe.
We can only go through a few more doublings of our current energy production rate before we boil the oceans from a thermodynamic equilibrium standpoint (ignoring greenhouse gases).
Earth has a fixed surface area. And the only way to get rid of waste heat from energy production is to radiate it into space. Finding this equilibrium for given quantities of energy generation into waste heat is a pretty straightforward calculation.
The point of renewables is rarely to do them all "at scale" where we're expecting that one renewable to power the entire planet.
Yes, if we try to use solar for the entire planet, we'll destroy the world trying to mine every last bit of silica. If we try and use wind for the entire planet, we'd need to build something like 6-8 million turbines, possibly causing environmental destruction on the way.
Rather, the point is to say "here's a huge vein of untapped energy, some of which could be tapped without damaging the environment and without releasing carbon."
Green energy is a mix, and extrapolating to "what if everybody did this" is rarely the right question, especially when the current alternative is "keep burning oil."
Just curious - is that much silica needed to power the whole planet? We've got entire deserts full of silica sand and most rocks are composed mostly of silicon. I feel like refining enough silicon to power the world via solar wouldn't be hugely destructive.
Most of the raw Si is used in the steel industry. Only a tiny fraction is used in electronics applications. So, Si would not be the bottleneck (refining it to the high purity needed for electronics applications is very energy-intensive, though).
Industry average for solar PV is currently about 5 grams of silicon consumed per nameplate watt of module capacity. That includes processing losses (wafer sawing, etching, etc.)
I'm going to assume a capacity factor of 20% for solar PV. That's significantly lower than the 28.6% capacity factor recorded for utility scale PV in the US last year, much higher than the ~10% you might expect in Germany. Choosing a high-ish solar capacity factor I'm going to note that most of the world's population lives in countries with better solar resources than Germany and that more solar PV is being installed on the utility scale than on e.g. household rooftops. Utility scale projects are sited for better sun resources and can use mechanical trackers that aren't suited for rooftops; both of those contribute to higher capacity factors than you can get out of opportunistic installations on existing rooftops, whichever country you're building in.
I'm also going to assume that modules have 25 years of factory-spec-power-equivalent output. Data from real-world solar installations show that the median module lasts about 30 years before it needs replacement (and more rigorous pre-sale testing may be pushing that number up in recent years), but maximum power output also declines over time due to a variety of degradation mechanisms, so I'm fudging these two factors together for 25 years' equivalent of "like new" power output.
Multiplying the capacity factor of 0.2 by the expected 25 years of like-new-power-output, we see that each nameplate watt of solar power installed is expected to provide 5 watt-years of energy output. The steady-state production rate you need for the world to have X watts of solar-generated power over the course of the year is then X/5.
Concrete numbers time: world electricity consumption in 2013 averaged about 2.28 terawatts. The world would need to produce about 457 gigawatts-peak of solar modules per year to produce this much electricity over the course of a year, consuming about 2,285,000 tonnes of silicon. World primary energy consumption in 2015 averaged about 17.3 terawatts. To match that on an annualized basis you'd need to produce 3.46 terawatts-peak of solar modules per year for a silicon consumption of about 17,340,000 tonnes.
Silica is about 46% silicon, so you'd need to mine ~5,000,000 to 38,000,000 tonnes of silica per year in order to produce enough silicon for solar PV to take over world electricity production or all world energy consumption respectively. For comparison, world sand consumption in 2014 was estimated at 15 billion tonnes, roughly 3 orders of magnitude greater. (Silicon producers usually don't start with sand anyway; they use coarsely crushed lumps of silica-rich materials like quartzite, quartz, or chert, which are even more abundant than clean sand.)
Note that I am NOT claiming that you could actually replace all the world's diverse energy sources with electricity from silicon based solar PV. There are of course no oceangoing ships that can be powered by electricity, no electrical passenger aircraft, etc. And even if we were just trying to replace fossils for current electricity generation, storage remains a hard open problem. Without cheap, abundant electricity storage it will be impossible for solar PV to take even a 40% share of world electricity consumption. But I hope that the numbers make it clear that silica availability is not a material constraint on solar PV deployment scale.
> Rather, the point is to say "here's a huge vein of untapped energy, some of which could be tapped without damaging the environment and without releasing carbon."
Did we say that about trees? Fossil fuels? Have we said that about silica, lithium, or rivers (we're having plenty of issues from Georgia to Pennsylvania along the Appalachians because of just that)?
I agree with what you're saying, I just don't think your last sentence is right. Kinda seems like a contradiction if everyone overuses resources (keeps burning oil) and it's causing problems (and we know that is a class of problem that we've experienced with other substances like rubber, trees, fish, dodo birds, lithium - hell, anything we can get our hands on), shouldn't we ensure other problems don't pop up from overusing resources (what if everybody else did this)?
I think the exact point is to not make the same mistake we've made with pretty much every other resource we've ever found...
So... don't overuse resources. And when presented with the question of "how does this scale?" don't ignore how fabulously efficiently we damaged the environment every other time we've scaled production up.
Not sure how you got "keep burning oil" from that...
We're not even near the scaling part. It's silly to argue about how something will have issues if the entire world did it. There are tons of things we do today that wouldn't scale environmentallly if the entire world wanted to do the same thing (e.g. flying).
Silica already covers most of the places were we would like to place panels, we will have much worse problems way before we run out of land, and there is no required rare resource for it.
There are shorter bottlenecks on energy storage. But even then Na-S will get us a long fraction of the way solar can go.
The globe has three primary energy sources leftover heat(1), radioactive decay, and gravitational drag. These adds up to 0.03% of the 173,000 TW of solar power. However, 51.9 TW is greater than the entire energy demand projected to be 27 TW in 2020.
Of note, heat flux increases with both absolute temperature and temperate difference. So, with a deep enough bore you could extract GW's of power for thousands of years. 2-4 mi is rather short unless your tapping heat over a large area.
(1)Leftover heat is currently "100 billion times annual world wide energy demand" so this really can be considered 'renewable.'
PS: ~52 TW / 196.9 million miles = 264w/square mile on average. However, energy is not spread anything close to evenly.
From 'The Solid Earth' by CMR Fowler (the geophysics book closest to my desk), the Earth's surface heat flux is 44 TW. This is not the total heat energy in the earth, it's the amount of internal heat (from the sources you've specified) radiated into space every second. I think that the difference between 44 and 51.9 is not budgetary (in the sense that the 8 TW difference is a different source) but reflects uncertainty in the estimates.
This is just to clarify what the numbers really mean, in case anyone thinks ~50 TW is the total heat energy (i.e. mass * heat capacity * absolute temperature) of the earth. My back of the envelope calculation is the total heat energy (m * Cp * T) = 2.5 E 31 W, using mean temperature of 4500 K (mantle) and 11000 K (core), Cp 1000 (mantle) and 450 (core) (in J / kg), and the fraction of the earth's total mass (6E24 kg) made up by the mantle (0.6) and core (0.3). I'm ignoring temperature dependence of heat capacity because I don't want to look it up. And ignoring latent heat, and other simplifications...
The sun is becoming 10% more luminous every billion years as it approaches its red giant phase. This is very long term, but in effect it will increase the amount of heat on Earth over time.
The Earth will be uninhabitable long before the sun goes red giant though! About a billion years from now [1].
The same thing has occurred to me about wind. I don't know the numbers, of course, but it seems like there is a scale at which the wind no longer has energy it needs to do windy stuff
Good points, but trees were a primary energy source before the industrial revolution. When fossil fuels like coal replaced trees for cooking and heating, trees began to return to the landscape. Some areas of the US are more forested now than they were in the 19th century, also due to more efficient agriculture.
We have a fair bit of geothermal energy/heating in my local area. I've always assumed that it is exchanging heat from underground, heat comes up and cool goes down. The cooling is slowly seeping out through the rock into the magma causing it to solidify. This solid spike of rock now grows as the geothermal exchange continues, the spike grows into a sail, a giant rock sail poking down into the slowly moving magma. Eventually the magma current pushes against the rock sail which is attached to the town above causing the whole lot to flip over like an iceberg.
The heat flux is the important bit, the regions below the extraction zone will be hotter and continue to push heat into the extraction zone. So it only matters if enough heat flows into the extraction zone to make up for the increased heat being taken out (vs the normal rate).
One of the most developed power plants ran out of steam before it ran out of heat.
We came very close to making whales extinct using their blubber for oil lamps. That changed in the mid 1800s when they first kerosene from petroleum. They would dump the gasoline by product into streams in Pennsylvania. The oil business almost went belly up when the light bulb was invented.
I'm curious what environmental consequences you're concerned about? It's not as though this heat is trapped and we're magically releasing it; the alternative is for it to radiate away into space.
Sure, but as it slowly makes its way towards the surface and then space, it keeps the soil warm. I'm worried that various biological processes in soil may be depending on the constant flux of heat from underground, and if we disrupt it, we may end up accidentally degrading or even sterilizing soil over large areas.
I remember when cold fusion came out in the late 1980's. A number of people objected to it on the grounds that using all that cold fusion energy would warm up the planet.
I know when I was in highschool the science textbook we had said "heat pollution" is one of the worst things for the environment and is very hard to track down.
Exactly it may take years and lots of heat energy extraction, but the Earth could end up cold. I don't think it's a renewable.
On the flip side you can do this the other way round: trap solar in a heat store below ground, piping the heat down below. It becomes a giant battery. The earth insulates the heat store (providing there is no water run through / water table to wick out the heat). You reverse the process during cold spells into a building.
Then nothing is renewable. Eventually the sun runs out of fuel.
Renewable cannot be taken to mean truly limitless or nothing is renewable. Renewable means practically limitless. How much heat do we have to pull from the Earth before it causes a problem? I don't know, but I bet it's a lot more than we will in the next 10K years even with heavy investment in geothermal.
The Earth also doesn't have a fixed amount of heat inside. Heat is constantly being produced by, e.g., tidal forces and radioactive decay.
> the Earth could end up cold. I don't think it's a renewable.
The earth's mantle and crust contain decaying radioisotope, and it gives off primordial heat, totalling about 45TW to the surface split roughly half and half (that's just the stuff naturally heating you from the ground).
While that's small potatoes compared to incoming solar radiation (let alone solar energy generation) the current electrical budget of humanity is 20000 TWh per year. That corresponds to about 450h of the "thermal waste" of the planet, or a bit under 3 weeks.
And that's just the waste energy, for the planet to end up cold we'd have to tap into the core, we can't even remotely reach there (humanity's deepest boreholes are ~12km deep, which is about half a thin continental crust and rougly 0.2% through to the earth's center)
While there is plenty of heating going on, it's not actually needed for this to be considered 'renewable'.
Currently stored heat is "approximately 100 billion times current (2010) worldwide annual energy consumption". So at 10x current energy extraction the sun will engulf the earth before the earth cools, thus warming it back up.
Good point, I just went with what the earth gives off as "waste" to the surface anyway, but you're completely right that we could be tapping into the primordial reservoir and not make a dent into it anyway.
"At some scale" does not imply "at our current scale." Our current energy use is a fraction of the energy we will be using 500 years from now, which really is not that far off in terms of human history.
I would imagine we will be using ~500x in 2516, a doubling every 55 years. All of earths deserts and more would need to be covered, even at 100% solar cell efficiency.
There would be trouble even with magical free energy.
Before the oil shocks in the seventies, oil production and use was more than doubling every decade. [1] If that kind of energy growth resumed unabated, then in about 200 years we'd be producing about as much power as the Earth receives from the sun. We'd cook in our own waste heat, no CO2 required.
In principle heat can be gotten rid of with radiators, like the EATCS[1] on the International Space Station.
To maximize the heat radiated away, you'd need radiators with as much surface area as possible with an unobstructed view of the sky (no cloud cover). They'd also need to be as hot as possible, because thermal radiation power rises with the 4th power of absolute temperature
There have been attempts to detect such thermal radiation from alien civilizations[2].
We already have geothermal cooling in the northeast. The very rich in New England drill holes into the ground and send the house warm air into the ground at one hole and then return air for another hole. Works unbelievably well. I can't tell you why but it feels like cool mountain air and not just A/C.
I really hope this works. It could be a huge answer to LARGE areas that require heat.
An open-loop geothermal is based on a standard drilled well where it pumps water up from the bottom of the well and passed through a water-to-air heat exchanger (heat-pump) and uses it to heat in the winter/cool in the summer. Water is returned to the top of the column ... about 10% is bled off to bring in fresh water.
Wells are typically your standard artesian well drilled down to 400' to 600', the geothermal needs about 12 GPM or more to be effective. If there's not enough water flow, a closed loop system can be used where a "coil" is placed in the well and the well is filled with a bentonite grout. Those are interesting because they can use glycol to run to temps below freezing.
In New England these things are very effective. The issue is the cost. The wells typically cost about $10-15K to drill, I think you get about 1-ton of cooling/heating per 100' on average.
Also, there is a large (and unnecessary) premium on these ... there's just no reason why they should cost more than a regular forced air system (aside from the well drilling, but many people in rural areas in NE have artesian wells anyway). The heat-pump units are comparable in cost to a high efficiency gas boiler ($5-8K).
Most geothermal systems have the air go thru a heat exchanger of some kind and energy transfer with the Earth happens via a much more conductive medium, like anti-freeze liquid. This isn't limited to the very rich either, its as common as installing solar panels.
I actually built the Django app that powers the system "This Old House" installed (http://groundenergysupport.com/) and one of the interesting things that came out of the app is what a dangerous assumption "a suitable sized system" is. I think the client has had trouble getting traction in the industry because some of the installers don't want to see their claims put to the test. Which isn't to say I think these are bad idea or ineffective, just that the sizing seems to be based more on what the installer can sell some times.
Interesting. I'm not surprised to learn that about installers, there's a lot of factors in getting sizing right and pretty difficult for most customers to have confidence until it shows up as lowered efficiency.
The app looks really useful, so I hope you succeed getting adoption.
This will be my first winter with my ground source system, a Climatemaster instead of Waterfurnace. My ground loop is 6' deep, there are 4 trenches 300' long and each one has a pipe down to the end and back for a total of 2,400 feet of pipe.
It is only starting to cool down, but so far so good. I'm very interested to see how it does when the highs are in the 30's and the lows are below freezing.
I did the savings calculator on that site and it said it will cost me more than my current system? I thought there would be cost savings from this? Does it assume I have an AC unit already?
The total length that exchanges the heat at the depth is important. If you got a big yard just got 8 feet deep and a hundred feet long and loop it. If not they go deep. In the Northeast the land of $$$ for an acre and rocks everywhere they usually get a well driller and drill a few hundred feet deep.
Interesting. Is that because of the rate of heat transfer through the rocks to get to the pipe or because you need a longer pipe to exchange heat with the ground?
Apparently the wavelength of the "heat wave" caused by summer/winter heat changes is about 12 feet. So you should bury your pipes 6 feet under, where it will be hottest in winter and coolest in summer.
EGS is a very promising technology. Currently, geothermal energy is better considered hydrothermal energy as hot water in abundance is required to turn the turbines in generators, or by heating fluids w/ lower boiling points to turn the turbines. However, there are a lot more regions with sufficient heat but insufficient groundwater circulation (because they tend to be in relatively impermeable igneous rock, and often in arid regions) that EGS will unlock if it becomes competitively priced (which it should with more technological refinement).
One of the most advanced test sites is happening now by a joint DOE/University/private collaboration at Newberry Volcano west of Bend, OR http://www.newberrygeothermal.com/
I think there is a lot of room for investment here. Geothermal is, in general, a relatively safe, secure and environmentally friendly method of power generation (the biggest concerns are in dewatering hot springs, which are beloved if not held sacred by locals). EGS may potentially have some similar wastewater issues as fracking, although not to the same scale both due to smaller volume and the lack of a need for nasty surfactants to get organics to desorb from rock. But it's generally not viewed as a viable large-scale technology in the press or more superficial energy analyses.
A hundred miles south of Newberry is OIT, a state tech school. The whole campus has been heated/cooled by Geothermal for decades (including outside sidewalks) and in the last decade, they built a 2MW geothermal power plant, and 2MW solar plant. They sell excess electricity (and hot water for heating) to the hospital next door. http://www.oit.edu/sustainability/clean-energy
Kind of off-topic from the subject of renewables but on-topic for the subject of what to do with waste heat from power generation: a city near me has a power plant on the shore of Lake Michigan. They draw in water from the lake for steam generation and then have to dispose of the hot water somehow. Instead of dumping it straight back into the lake and disrupting the ecosystem with extra hot water, they run it under the sidewalks in the city. 762 gallons of really hot water runs under the sidewalks of the city every minute, keeping the northern-latitude tourist town ice-free, salt-free, snowplow-free no matter how cold it gets.
There are really interesting ways to deal with all kinds of byproduct from industry that are non-obvious. Like heating a hospital with waste heat from a power plant.
NZ does a lot of geothermal so i know a little more about it than most but i'm no geologist. couple points - first, don't confuse depleting the ground water with depleting the heat. a lot of geothermal taps the heated groundwater and yes, you can screw that up by extracting more than is re-plenished. luck/geology is your guide for what the ratio is though. binary systems fare better as you pull the water out, suck off the heat and then inject the liquid back in. secondly, the big problem with geothermal is that the wells cost 10s of millions of dollars. the financial decisions far outway the technical ie, you have to spend $30-40M to get a well that's active upfront but it may take decades to get it paid back. hot dry wells are like throwing money into a pit and then paying someone else to burn it. if you're relatively small then you can eliminate this risk by running your own fluid up and down but remember these wells are only 20-30 cm in diameter. oh - and don't forget that if you mess it up, presurised ground water or mud will use your well to get through an impermeable rock layer and into an aquifer. there's some well head in Indonesia that's been pumping out cubic km's of hot mud for the last 20 years...
This is what enhanced geothermal systems (EGS) are all about: Pumping external water into hot, dry systems. Most of the work is focused on either opening natural fractures or creating new ones between an injection well and an extraction well, so the volume of rock in which heat is extracted is much larger.
Asimov in his novels had Trantor, the planet girding capital city largely extracted it's energy from geo thermal sources. In his novels, they would bury heat exchange rods to tap this power.
Interesting to see this potentially close to fruition. Now if only all roofs, roads and windows could extract solar power...
We literally live on a ball of molten iron and we've barely tapped this potential. If anyone wants free energy it's down there, bubbling away, just waiting to be harnessed.
This sounds great, my biggest concern would be that it's basically the same mechanism as "fracking," but likely minus some of the more esoteric chemicals and the sand.
What are the chances of this having similar seismic impacts with the injection of water at those depths - is there already a significant amount of water down there so the net effect would be replacement of the increased volume of the system's interior? Is the nature of the area involved such that adding water is going to lubricate existing fault lines?
Part of the concern with this is whether we're going to start seeing a significant volume of earthquakes in areas where building codes don't and haven't traditionally required the kind of safety features found in more seismically active areas.
Man I wonder what drill rig they are using for the holes!? 2 to 4 mile is roughly what? 3 to 6.4 km or so. That's a mighty deep hole! I have worked as an offsider on a prototype deep hole surface core rig and our deepest were 1600 metres and they took ages to drill!(I heard stories of the rig drilling 2.5+ holes earlier in its life) The complications you start getting down hole at those depths are pretty weird,the ground can chew bits in 10 metres. Which then take 24 hours to change.
Also wonder what gauge the holes will be, I assume they will leave them cased with the rod string but christ they can't be planning to drill HQ that deep could they? Maybe even 8 inch for the first leg? Anyone seen anymore hardware details?
This might be an incredible way to generate cheap energy. I lived in a remote location called Manikaran in Himalayas in India. It is a small town with limited resources but has an incredibly hot water spring. The locals have built pipelines that connect all major establishment with this boiling hot water which is then used to cook, soak and simply bath or heat up rooms.
The motel like place I stayed in had created an exposed pipe network in the room which emitted heat from this water. Don't want heat ? Just close the tap. Less heat turn the tap a little bit :D
You may have missed the point of this article. The northeastern United States is very geologically stable, so any geothermal energy would have to come by going very, very deep underground. We don't have any hot springs around here. So even if this project works out and eliminates a lot of future carbon emissions, it will hardly be considered cheap.
Normally I agree with your assessments but I don't think you're right on this one. Presuming geothermal wells would have a >100 year lifespan with minimal upkeep the upfront costs may be very large but the long-term cost per/MW extracted would go close to zero because of the virtually non-existent marginal costs for operating geothermal wells.
Ignoring externalities created by using fossil fuels for heating (pollution, corruption, etc.), if this technique is sound it could be a more financially sensible decision than any alternative.
Very interesting! I just read about a Finnish geothermal project in which they are drilling two 7km (4.35 miles) deep holes to test feasibility of geothermal energy in areas which do not have naturally occurring geothermal sources close to ground level. It is a serious attempt to produce geothermal energy, and made possible by recent advantages in drilling techniques. They have now reached a depth of roughly 3.5 km.
The ground below about 6 feet remains at a constant 55 degrees year round. If you make use of that as a heat source/sink, you can cut about 30% off of your HVAC bills. I wonder why more people don't do that, especially with new construction, when it can be installed cheaply.
There are similar (research) projects going on in Europe as well. One in Finland is also drilling to get about 4 miles deep[1]. I believe some recent news (that I couldn't find) have said that the project has been progressing ok.
I predict once we have lasers powerful enough to do laser drilling then This will really take off. You'd just be paying the cost of electricity to drill and if the laser is in orbit you could quickly drill power plants all over the earth.
I'd be curious how much power is required to vaporize soil and rock.
Wow that's amazing! It seems like this could revolutionize several industries and create several new ones! I guess there's got to be some kind of catch? Too expensive?
If you're in the US I imagine you'd talk to the EPA. Anything you might do that could potentially harm others or their property has to get approved by one government agency or another. Heck, most things that wouldn't have to be too.
There are living ecosystems underground too. Worms have been found at 1.4 km depth and microbes down to 3 km underground. We are probably destroying ecosystems we don't yet understand.
For a little background on geothermal, keep in mind that while the amount of energy stored in heat within the Earth is indeed vast, it's also extremely hard to make use of generally.
One of the things that I find interesting about physical science is how many similarities there are between things that flow of very different types. In this way, making power from heat is very much like making power from water. We cannot make power from water just sitting around somewhere, no matter how high or low; we can only make power by allowing it to flow from somewhere high to somewhere low and tapping that flow. And for practical purposes, we need flow that has a certain minimum pressure and volume to be able to convert it electrical power in a cost-effective way.
Heat works the same way. There may be a tremendous amount of energy in something very hot, but the only way to use it, convert it into power, is to allow it to flow to somewhere cooler, and tap that flow in a way similar in concept to a water turbine. And just like the water turbine, the heat flow must have a certain temperature difference and rate of flow to be converted into electrical power in a cost-effective way.
Unfortunately, geothermal is terrible at this over most of the Earth's surface. The heat gradient between the hot lower levels of the crust and the surface is so long and gradual that it's effectively impossible to make electrical power from it. It's kind of like trying to extract energy from a flowing stream that's thousands of miles wide, but only a centimeter deep and flowing at barely a trickle. The total amount of energy associated with that flow is enormous, but it's so diffuse that it's difficult to tap.
Note that these guys are planning to use it for heating buildings. That's much easier, as water coming out at 120-150 degrees F is perfectly fine for that. It could potentially save a bunch of energy versus electrical or gas heating, assuming they can pipe it around without losing too much heat. But making electricity effectively requires getting the water hot enough at moderately high pressure to make steam to turn a turbine with. You can play games with exotic working fluids and such to try and get something from lower temperature differences, but it's probably impossible to run a plant at market electricity rates like that.
If we ever want to make really big amounts of energy from geothermal, I haven't really run the numbers on it, but I suspect we'd need to tap into heat below the actual crust, just to get the heat replenishment rate from the mantle high enough. We'd definitely need to be able to drill and maintain holes that deep, and then run some sort of working fluid down to the bottom, let it pick up heat at a multi-gigawatt rate, then pipe it back up to the surface without losing too much of the heat. If we ever figure out how to do that, then we'll have essentially all the power we could ever use in about the safest and least-interfering way I can imagine.
Wikipedia seems to have only basic numbers up:
https://en.wikipedia.org/wiki/Geothermal_energy#Renewability...
The first sentence of that section says that "geothermal power is considered to be renewable because any projected heat extraction is small compared to the Earth's heat content." I'd like to see some estimates on how much of that heat content is available on the depths we're drilling down to (as opposed to the contents of the whole planet); and again, trees were a renewable resource too, before the industrial revolution.