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#301 2023-08-05 21:00:55

Void
Member
Registered: 2011-12-29
Posts: 7,202

Re: Geothermal and Geothermal Battery (Changed Title 12/21/23)

Interesting Spacenut.....

kdb512, a Question:

Void,

What does the intermittent energy add to the geothermal heat pump design?

Is this some kind of power buffer?

Why not add a separate geothermal power plant and radiator array, or expand / scale-up the existing power plant?

The use of heat pumps would be optional.

The installation of drilled heat exchangers is a cost.  I presume the deeper you drill, the more difficult.  The larger the installation the greater the cost.

Two worlds seem to me to be very good for some types of installations of this.  Earth and Mars.  Two other worlds at least might work out, Mercury and Luna, maybe also some asteroids.

A possible version of this: lKagQp1.png, could be used with heat pumps with a large building or collections of buildings.

In this case electric power might not be the objective.  In a continental climate with hot summers and cold winters, thermal storage over seasons might be suitable.  In the summer, the buildings would function as solar collectors, and in the winter, as radiators.  This would of course require power for the heat pumps.

In a different case, if you did want to use a Eavor like Geothermal system, you might charge the Geo storage device with electricity resistive heating of excess electricity.  Or if you used a heat pump probably you would be limited to 500 C or less.  You could link a Geo storage with a geothermal, either way. 

Let's say you were on Mars and the geothermal was marginal it might still be useful to have a contribution from it, and it would likely be useful during a cold season or dust storm.  With solar energy, you might use a method to heat a Geo storage device to 1000 C, maybe more.  So, your Geothermal would feed to the Geo storage.  But the nights on Mars may provide cold.  You might have a Geo storage that holds cold.  The permafrost rock of Mars may be as cold as -60 C naturally.  A heat pump might force that colder.  Various working fluids are possible.

So, maybe -100 C vs 200 C??? for the Geothermal.  Then the Geo storage at maybe 1000 C.

Capacity matters any such thermal storage devices will have a capacity.  Even in a Dust Strom or winter, the Geothermal would still exist, and the cold rock reservoir would likely replenish, slowly if near the surface.

For Earth similar things are possible.

Various possibilities might exist.  For instance, in a northern location you might collect ice from a lake to melt with a heat pump, which would possibly allow for a very cold reservoir in rock to be used.

Capacity of reservoirs matters even geothermal may be overtaxed at times when there is no wind or solar or other.  But elsewise it might be allowed to restore from geothermal in the surrounding deeper rock.

Not unlike electrical power like P=I*E.  For Geothermal P=Flow Rates * Temperature differentials.

Some of these may heat buildings or cool them only.  Some might also generate electricity.

Done.

Last edited by Void (2023-08-05 21:39:02)


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#302 2023-08-06 11:57:35

Void
Member
Registered: 2011-12-29
Posts: 7,202

Re: Geothermal and Geothermal Battery (Changed Title 12/21/23)

Returning to a post by Spacenut: http://newmars.com/forums/viewtopic.php … 92#p212192

Another view: https://www.msn.com/en-us/money/other/m … bab8&ei=16

Of course, trust will have to be established for the practicality of this.  But if it turns out to work then it could fit into this topic as yet another component in electrothermal circuits, if I might call "This" "That".

In trying to puzzle a useful device beyond what the articles contain, the process of radiating heat might be interesting.

Mars could be a good place to contemplate, but Earth as well.

To tap into the Mars day/night energy cycles.  Well to do the night part, you have to have electricity at night.  Keep in mind that some of this might be useful for some types of nuclear power systems as well.  I just don't want to kill the other "Children" of thoughts, by applying an idiotic binary contest against the various options.

Radiators for Mars?  Well, we may think that for the passage of heat from a carrier fluid, though a solid wall out to the universe though radiative cooling and convection cooling, 3D printing may be a place to seek to accumulate more ability.

For this we will want electric power at night, to circulate fluids and perhaps even to run heat pumps.  I will be attempting to create a stone cold thermal reservoir, tapping into the cold of night, winter, and perhaps even dust storms.

I am not sure of practicality yet; I am just exploring.

Just now I am considering: https://www.techsciresearch.com/blog/an … th%20light.

Can you put these on radiator fins?

I was thinking of creating a cold reservoir in rock and perhaps using a heat pump to do that, and then recovering electricity though antisolar cells on the radiator fins.  Something like that might be useful, but now I am thinking of a hot side process. 

Considering greenhouses.  What if during the day you collected heat into a hot rock reservoir.  Some kind of solar perhaps, but maybe also allowing some type of nuclear.

To make it simple, lets suppose Nuclear Fission as the hot source.  Our greenhouse as the radiator.  We may or may not involve a turbine.  We may try to use Anti-Solar Cells on radiator fins.  The radiators might be in the greenhouse and may be cooled radiatively and also by circulating air or water.

The Martian day will limit cooling as greater sunlight and higher temperatures are likely.  In cold times however such as night, winter, or dust storms, you might have superior radiative capacity.

Even if using a nuclear reactor for the heat, you would have variable energy creating potential in relatively warm day periods vs. colder situations.  So, actually a hot reservoir in the rock would be of use even with a nuclear-powered setup, as with that you can time delay the radiating of heat to the Martian sky.  Of course, in that situation you may generate more power when the "Sky" is cold than when the sunlight is strong.

But you are also keeping a greenhouse from freezing.

Now you may add solar thermal accumulation in the sunlight times.

So, further advancements in drilling such as those of Eavor may be very desired.  Geothermal may even be incorporated into this setup.  Even if it is a feeble geothermal, having a trickle of energy during a prolonged period of lack of other hot inputs may be of some value. 

Having 1000 units of energy might be your optimal situation, but at times that are lean, having 10 units of energy is way better than 0 units of energy for say 5 months.

Done.

Last edited by Void (2023-08-06 12:41:32)


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#303 2023-08-06 13:49:41

kbd512
Administrator
Registered: 2015-01-02
Posts: 7,469

Re: Geothermal and Geothermal Battery (Changed Title 12/21/23)

Void,

Drilling cost goes up when you drill deep enough to require oil-based mud because the temperature becomes too high for water-based drilling fluid to remain liquid.  Total cost is mostly a function of total time, since it implies specialist labor and materials consumption.  That said, on land you can drill a well 20,000ft deep in a couple of weeks to a month, assuming you have all the people, equipment, and materials on-hand.

The last part of that statement is key to fast drilling.  The key to reducing materials cost is having good solids removal efficiency, because then you need far less drilling fluid / mud.  This is accomplished by using screens and shakers and centrifuges to remove the rock cuttings / rock chips from the drilling fluid so your drill bit isn't grinding up what it's already drilled through.  Keeping your low-gravity solids (LGS) / "rock chips" in check means you can drill really fast using a small quantity of drilling fluid.  The water-based drilling fluid can be dumped onsite, because it only contains a mixture of food-grade products.  The oil-based mud always has to be recovered and recycled, a process we called "reconditioning" (of chemical and weight properties, getting rid of any remaining rock chips using centrifuges), which was done at a liquid mud plant.  The barite remains in suspension in the drilling fluid, despite being very heavy, it has the consistency of flour (even looks like flour), so it doesn't hurt the drill bit despite also being very hard.  The rock chips, on the other hand, especially granite, can very quickly dull or even ruin (overheat) the drilling bit.  As you can imagine, these drill bits are not cheap, so taking care of them is a priority.

The drilling fluid is water or oil-based mud, which mostly contains salt, nut plug to plug porous rock formations that would allow your drilling fluid to escape into the rock formation, viscosifiers and surfactants, and barite to adjust the weight of the drilling fluid.  To clean out the bore hole just prior to casing / cementing, you'll run some kind of brine like bromine, to clean the walls of the bore hole.  We have all kinds of special equipment we put down the hole, also known as "downhole tools", such as giant magnets to remove metal shavings or X-ray cameras and radiation sources to characterize what we just drilled through (what kind of rock or mineral, how hard, how porous, etc).  During casing / cementing operations, you'll insert a steel tube a bit smaller than the bore hole diameter, then pump concrete on the outside of the tube to case that section of the well.  Steel liners / casings could be used, but steel corrodes over time, whereas concrete does not.  You have to keep the bore hole filled with something at all times, or the Earth will fill it up for you- a bore hole collapse or water and oil filling your bore hole.  If the weight of your drilling fluid is to high, it can fracture the rock.  If it's too low, it'll be forced back out of the bore hole.

If you have to do a lot of directional drilling, that takes additional time, so the cost goes up, because all the people and equipment and diesel fuel consuming drilling generators and motors must remain onsite during drilling, cleaning, and cementing.  Even a garden variety onshore well at low to moderate depth would require multiple thousands of tons of equipment and materials, all moved by trucks or railroads.  For example, round-trip time to merely send an inspection tool to a depth of 30,000ft and then back it out of the hole can take 32 hours.  If you have to clean out and case a lot of lateral sections, then that's going to take a significant amount of time unrelated to actual drilling.  The actual drilling tends to be the fastest of all the operations performed.  Faster is generally better because you will always lose some of your drilling fluid during drilling operations.

Every day of operations, reports are submitted to the client with labor charges, total drilling fluid lost / replaced / added, bags or sacks of chemicals added to maintain the chemical and weight properties of the mud (mostly salt and barite).  Most clients require maintaining stocks of chemicals or materials (LCA / Lost Circulation Additives) on the rig to stop the loss of drilling fluid if the rock fractures.  Any time you have a significant loss of drilling fluid we have plugging agents to prevent a well control situation from developing.  Some clients go further and require stocks of backup materials specifically assigned to their project.  The reports also indicate rate-of-penetration (drilling progress), fluid properties, rock formation properties if tools are used to determine this, anomalous conditions noted affecting progress- such as the supply of critical chemicals or drilling fluids / trucker's union labor strikes / etc, plus any equipment damaged or destroyed that the client has to pay for- applies whenever a third party is operating someone else's equipment that was rented or loaned for the project.

There's a mud engineer or two on the drilling rig doing the physical counting and acting as onsite chemist with lab support, he submits reports to the project engineer, and the project engineer is the interface between the drilling company and the client after all the paperwork and lawyer nonsense has been taken care of.  The roughnecks handle the drill rig, shakers, centrifuges, drill pipes, etc.  The truckers or sailors deliver the supplies to the rigs.  The liquid mud plant operators handle the preparation of the drilling fluid unless it's mixed onsite the way water-based mud is.  The warehouse crew handles the barite, chemicals, LCA materials, etc delivered to the rig.

Back at HQ, support staff (what I was) provided visibility and reports for the mountains of generated data to aid the project engineers with forecasting or supply management and post-analysis of the well data, mechanical engineers work on the design / repair / operation of specialized drilling equipment, wireline division (geologists, geochemists, physicists, etc- I only met a few of these people) handles prospecting for more oil deposits, new mud engineers are taught "mud school", new chemicals are developed by chemists in labs to assist in every aspect of drilling and oil production, samples of the product oil and gas are delivered by the client or our own people for further analysis, and on and on.

Does that give you an idea of what's involved?

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#304 2023-08-06 13:53:34

Void
Member
Registered: 2011-12-29
Posts: 7,202

Re: Geothermal and Geothermal Battery (Changed Title 12/21/23)

Yes, thank you for the useful information.  I understand that produced value must justify the effort.

I am not sure how close Eavor Drilling is to that type of drilling.  They seem to indicate that they want to sell their skill so they are representing that customers will exist for it.  Time will tell that story.

And thanks for this kdb512:

Void,

Drilling cost goes up when you drill deep enough to require oil-based mud because the temperature becomes too high for water-based drilling fluid to remain liquid.  Total cost is mostly a function of total time, since it implies specialist labor and materials consumption.  That said, on land you can drill a well 20,000ft deep in a couple of weeks to a month, assuming you have all the people, equipment, and materials on-hand.

That Confirma to me that Geo storage may have a value as let's say you would only drill a few thousand feet for it.  By your information Geothermal of value will have to go much deeper.

Again, thank-you for participating here it is very useful to find the true boundaries of reality.


Done.

Last edited by Void (2023-08-06 13:56:39)


Done.

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#305 2023-08-06 16:33:19

kbd512
Administrator
Registered: 2015-01-02
Posts: 7,469

Re: Geothermal and Geothermal Battery (Changed Title 12/21/23)

Void,

From my own viewpoint, the following energy technologies appear promising:

1. Liquid Fluoride Thorium Molten Salt reactors
* No nuclear fuel sourcing problem
* No long-lived radioactive waste
* Very little total waste generated, about 1/10th to 1/100th that of Uranium-based solid fuel
* No need to shut down the reactor to add or subtract fuel or clean out fission products and neutron poisons- the fuel is liquid so no fuel rod cracking problem to deal with, which is directly related to higher physical volume fission daughter products and radiation damage swelling and then cracking the ceramic fuel pellets and causing the Zircalloy fuel rod cladding to split / burst
* No requirement for fresh water

2. Solar thermal for making liquid hydrocarbon fuels and hot water for heat pumps instead of ever-increasing electricity generation which thus far has not saved a single Watt-hour of energy- our energy usage keeps going up every year, so there's your "proof", if that's what you require to believe it
* Although costly in terms of total inputs, uses low energy cost materials for trough-based collectors
* Long-lived equipment
* Very simple to build / operate / maintain
* Suitable for a batch process generating enormous amounts of low-grade process heat and high pressure for making liquid fuels, converting sea water or Methane into gasoline or kerosene or diesel

3. Geothermal power using deep well and directional drilling technology
* Low equipment cost
* Mostly uses long-lived equipment, with the exception of buried piping if that piping must be steel
* Though costly to build, the process for doing so is very well understood and no technological problems exist
* Can generate direct heat or electricity or low-grade process heat for making liquid fuels from sea water or Methane
* No toxic waste or radioactive waste
* Can be sited virtually anywhere on land or shallow waters offshore

4. Super-critical CO2 turbines for powering ships
* More efficient than gas turbines, steam turbines, or diesel engines
* Combined-cycle efficiency as high as any combined-cycle aero-derivative or industrial gas turbine
* A bit heavier than an LM2500 for equivalent power, it's actually more compact, and far lighter than a diesel of equivalent power

5. Supersonic inlet velocity gas turbines for powering aircraft and rocket engines
* Lighter / more compact / more fuel efficient than conventional miniature wing / fan blade style axial flow compressors used by all large jet engines (so much smaller when compared to the AGT-1500 that powers our M1 Abrams main battle tank that you could kneel down in the engine compartment to work on the engine)
* Simpler to machine parts- very simple parts geometry, but must be very precisely machined
* Waste heat recovery between stages even higher than the mechanical work input to drive the shaft (not the same thing as being more than 100% efficient, but if it took 1 unit of power to drive the shaft, then 1.1 to 1.45 units of heat output are available for re-injection to reduce the power required to drive said shaft, so you can reduce work input by maybe 10% to 15%)
* Can run efficiently over a wide range of forward velocities, from subsonic to Mach 3 or so, without complex inlet geometry (mostly applicable to fighter jets and high speed recon aircraft)
* Core size is so small relative to fan size that even larger fans become practical for jet airliners
* For a given engine size and power output, it's easier to hide the front of the fan for stealth aircraft

All of these technologies represent big jumps in overall efficiency and power output for a given package size / weight / cost.  We don't need minor improvements, like 5Wh to 10Wh of energy density improvement in batteries per year.  Those improvements, while welcome, don't meaningfully "move the needle" in the right direction fast enough to be a factor.  Only major improvements and drastic changes to the way we generate and use energy are going to help us.

Everything else is merely an energy sink, thus a technological dead-end using existing and projected near-term technology.  Hoping something will come along to change that is not an actual plan.  Fusion may one day be possible, but nobody knows if it's practical.  It may indeed be possible to combine fusion with fission to make fusion practical as Calliban suggested, but we're nowhere near the finish line.

Photovoltaics, wind turbines, and batteries are all net energy sinks.  After you add all the required infrastructure changes to run them on the existing electric grids, which demand perfect sine wave AC power generation at a very specific frequency.  These technologies only exist because of immense hydrocarbon fuel energy input.  There are no photovoltaic-powered photovoltaic manufacturing plants.  If that hydrocarbon fuel energy input becomes scarce, then those photovoltaics cease to have any merit at a global scale.  All the pointless attempts to find exceptions to the rule basically prove what I stated.

I can find an example of a small block V8 engine generating 2,500hp.  Absolutely none of those engines will generate that level of power output for more than a few seconds to minutes before the engine has to be completely rebuilt using new parts.  That is why we never built a Liberty Ship powered by a lone 575 pound small block V8 car engine during WWII.  All of our Liberty Ships were powered by 280,000 pound triple-expansion steam piston engine, which could cope with the stress of generating 2,500hp for years to decades with routine lubrication and maintenance, even though some of them were sunk by the Germans during their first voyage out of the harbor.

Could we have used a single R-2800 engine in our Liberty ships?

Sure.

Would it have been as reliable as an engine weighing more than 100X more?

Not a chance.  A brand new radial engine of that displacement might be capable of making a single transit across the Atlantic before it broke down, but it would never be a reliable engine for a ship at sea for weeks to a few months.  The US Army ditched all of their M4 tanks powered by radial engines the moment mass-produced Ford 1,100 cubic inch liquid-cooled V8 engines became available.  There were clearly a series of reliability trade-offs to be made in engineering.  When the war began, we didn't have a liquid-cooled V8 engine with the power required to move the M4 tanks, which is why the radials were used.  They were clearly not ideal for the task of powering a large heavy vehicle at low-speeds and wildly varying power output levels, though.  Basically, aircraft engines only work well for aircraft.  The more power you cram into a given amount of space, the greater the engineering and material requirements to make it reliable.

The same applies to electronics and software.  Granted, I'll concede that a simple electronic circuit or sensor is liable to be one of the most reliable devices around when we talk about duty cycle, but after that concession we then start to touch upon total complexity.  A modern car computer is orders of magnitude more complex than the Space Shuttle's computer.  The fact that it works at all is the real miracle.  It's funny how people who don't write software or design microchips think all those moving parts they don't see, because they're based upon electrons zipping across short distances at the speed of light, still represent real and immense cost and overall complexity.  I'll probably never figure that one out.

Unless and until we figure out how to make electronics-based energy generating devices as compact and efficient as computers have become, I don't see much of a future for them, as it relates to their use in energy generating systems, because heat engines simply do an overall better job.  I would love to see a photovoltaic device come along that reliably operates for 75 years with no appreciable degradation, is made from common materials, and is infinitely recyclable.  So far as I'm aware, no such device exists.  I think it's highly improbable that such a device will be invented within our lifetimes, though not for lack of trying.  If I'm wrong about this, then I think that's great.  That said, I require real evidence, and thus far none has been produced.

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#306 2023-08-06 17:26:33

Void
Member
Registered: 2011-12-29
Posts: 7,202

Re: Geothermal and Geothermal Battery (Changed Title 12/21/23)

Well, that looks pretty good.  At the point where you mentioned CO2 and Military Matters, I lacked any ability to do a good evaluation as I am not anywhere near your apparent proficiency for that.

I will ask you a question about CO2 turbines.  If a cost-effective way were available to import Carbon to the Moon, do you have any ideas about how to use such CO2 Turbines on the Moon?  Of course, you may know that I am going to be supposing storing hot and cold in rocks, if possible.  The equator of course has the ~50/50 Day/Night.  It is my opinion that Carbon could likely be imported to the Moon economically if you allow for low-speed propulsion methods and robots.

Tesla appears to be into Heat Pumps more now, so that aligns with your vision to some degree.

As for the "Greens" typical agenda, I would keep my eye on Australia.  They have the means if anyone does, more or less.  They have the sunlight and apparently also do some wind.  They have a culture with an industrial tilt possible both from European and Asian roots.

We will see about solar cells.  I think that there are some tricks not yet explored.  One of my ponderings would have solar cells cooled with a heat pump, and with mirror focus to the solar cells.  The main tricks for that would be to not damage the solar cells with too much heat, and also the setup has to be economic.

But I will admit that if China is burning coal to build solar panels that Australia buys, then that if a bit of a cheat.  It is not necessarily foolish for Australia to do it, but it is not so green is it?

But we should be careful, solar panels seem to be claimed to be a net energy production since about 2013, it appears.  Tru or not?  Well? I can't prove it.  I can read it though.

The temperature of solar panels: https://news.energysage.com/solar-panel … erheating/
Quote:

< SOLAR NEWS
solar panels overheating hot weather
How hot do solar panels get? Effect of temperature on solar performance
 
Solar panels are often exposed to high amounts of heat, especially during long, hot summer days. In this article, we will discuss the impact hot weather has on solar panels, and how those effects are mitigated by consumers and manufacturers alike.

Find out what solar panels cost in your area in 2023
Enter your zip code
5-digit zip code
100% free to use, 100% online

Access the lowest solar prices from installers near you

Unbiased energy advisors ready to help


How hot do solar panels actually get?
Home solar panels are tested at 25 °C (77 °F)  and thus solar panel temperature will generally range between 15 °C and 35 °C during which solar cells will produce at maximum efficiency. However, solar panels can get as hot as 65 °C (149 °F) at which point solar cell efficiency will be hindered. Install factors like how close the panels are installed to the roof can impact the typical heat of your solar system.

The majority of solar panels are composed of silicon photovoltaic (PV) cells, which are protected by a sheet of glass and held together with a metal frame. Those materials are comparable to the materials that make up the windows and frame of a car – to understand how hot solar panels get, think about a car that’s been sitting in a hot parking lot on a summer day. The windows and frame will be hot to the touch, but there’s little danger of burns or fire. The actual temperature that your solar panels will be at a given time varies significantly depending on air temperature, how close you are to the equator, level of direct sunlight, and roof material.

So, if we could cool solar panels with a heat pump, we might hope to use a concentrating mirror to increase the output.
And that would be tricky business.  A system would need some complexity for protection in the event of a breakdown.

But a temperature of significance might feed a heat pump.  And I do have concepts for such assemblies, but I am not at all sure that they are worth a struggle to bring into an attempt.  So far, I say no, as I have what I want in life at this time.  But we need to allow that someone will "Pick the Locks" on some of these things eventually.  You do sort of allow for such a possibility, so that is good.

I am rather interested in the CO2 on the Moon thing, if you have time to think it over and post about your thoughts.

Done.

Last edited by Void (2023-08-06 17:41:49)


Done.

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#307 2023-08-07 11:34:07

Void
Member
Registered: 2011-12-29
Posts: 7,202

Re: Geothermal and Geothermal Battery (Changed Title 12/21/23)

Well, for lack of any guidance, I will go ahead about Carbon Dioxide Heat Engines for the Moon.

While I like "Blue Alchemist", CO2 Heat Engines may be worth looking into.

Geothermal may not be very likely on the Moon, at least in most locations.  Geo storage looks interesting to me.

So, I am presuming Solar Concentrating Mirrors and also some type of radiator.

To me, Carbon on the Moon is no sillier than the use of oil in Japan.  It needs importing.

In this case I expect that Carbon could come from Earth if necessary or Asteroids, or Mars.  But the Moon does likely have some CO2 in the cold traps.

https://www.salon.com/2021/11/16/moon-c … n-dioxide/  Quote:

Indeed, recent discoveries of plentiful water ice pockets on the moon tantalized scientists and space agencies. Now, a new finding suggests that there is plentiful carbon dioxide on the moon as well.

So, if you had Eavor well systems on the Moon, you might have to deal with leaks in fractured rock, but I am guessing that some kind of plugging agent may be possible to work with.

Done.


So, if on the equator you would have most of a 2 weekday to add heat.  But in space radiators pointing away from the sunlight could run 24/7.

Nothing about the Moon is likely to be easy, but this sounds to me as it might be in the bounds of possibility.

https://www.eavor.com/#:~:text=Drilling … %20surface.  Quote:

Drilling and construction began in August of 2019. Eavor-Lite™ consists of two vertical wells, joined by two multilateral legs at 2.4km depth, connected by a pipeline at surface.

I like to see the conversion: 1.49129086 miles, so easily 1 cubic mile of Lunar rock could be incorporated into a device similar to this: lKagQp1.png

Of course drilling on the Moon would be a new experience.

I think it likely that the Blue Origin Solar panels could be recycled easily, but using a heat engine may be better.  If cared for the apparatus might be maintained indefinitely.

So, I have already had posts about the possible use of Lithobraking to deliver Carbon to the Moon.

I also believe that eventually dry plant matter could be Lithobraked to the Moon.

If so, then the Moon could become very habitable.  If 1/3rd g is enough, perhaps centrifuges on the Moon would be reasonably assistive.  The vast amount of 1/6th g environment may be useful for manufacturing.

The Moon could indeed transmit power to places in space and the Earth, perhaps.

If rings of power plants were to exist about the circumferences of the Moon, then beamed power to orbit could assist the movements of spacecraft around the Moon and even beyond the Moon.

Last edited by Void (2023-08-07 12:02:08)


Done.

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#308 2023-08-07 13:17:29

kbd512
Administrator
Registered: 2015-01-02
Posts: 7,469

Re: Geothermal and Geothermal Battery (Changed Title 12/21/23)

Void,

My point about the ship engine technology was that the designers of the Liberty class of transport ships selected triple-expansion piston steam engines because that particular engine design was a known reliable 2,500hp engine, that was also approved for use in merchant ships by the American Bureau of Shipping, that could be mass manufactured in the time available.  2,710 Liberty ships were constructed by 18 different shipyards during the roughly 1,460 days of US involvement in WWII.  The first ship was completed on 27 Sept 1941 and the last ship was completed on 30 Oct 1945.  Said giant steam piston engine was not the smallest / most compact / most efficient design available in 1941.  However, the geared steam turbines required lots of precision machining of expensive corrosion resistant steels with special heat treatments.  Carving the gears and turbine blade components from blocks of steel was the capacity bottleneck.  The milling machinery available at the start of the war was insufficient to supply that higher form of engine technology to all the ships streaming out of American shipyards.  To meet production targets, an engineering compromise had to be accepted.  Geared steam turbines were extensively used to power the larger / faster / heavier warships that we constructed in lower total numbers.

A variety of attempts to use diesel engines or liquid-cooled V12 aero-derivative engines were also experimented with, but none were suitable replacements for steam power.  The diesels actually provided an efficiency advantage over steam turbines, but they were either too heavy for smaller craft or too unreliable at the power levels and duty cycles demanded of them for use aboard ships and trains.  Most people think of diesels as being relatively simple and highly reliable, if a little heavy.  That accurately describes diesel engines made using 1960s metallurgy and production techniques, which is why they replaced all gasoline engines in trucks and almost all steam engines in trains and cargo ships.  A mere 20 years earlier, diesel reliability wasn't nearly as good.  We were still figuring out silly little things like piston ring and piston forging.  Recall that the original Ford engines used Iron pistons.  When Aluminum became reliable enough, it supplanted all Iron pistons.  Modern high duty cycle diesels sometimes use forged steel pistons, but Aluminum remains the preferred material because it's lighter and dissipates heat better.  Back during WWII, everybody but the Russians used gasoline tank engines.  Russian T-34 tanks typically didn't last long enough for their diesel engines to fail, but the time between engine-related breakdowns was measured in single digit operating hours, sort of like the early German jet engines that lasted about 25 hours before major overhaul was required.

This is largely how I view photovoltaic and battery technology.  After a half century of development, these technologies are still not quite ready to be used the way people want to use them.  That's not a knock on the technology, though.  Diesel engines weren't very reliable for more than half a century after they were first invented.  Now diesel engines are an integral part of agriculture, transport, and backup power generation infrastructure.  In time, I suspect batteries will improve to the point that making them fail requires a deliberate abusive act on the part of their user.  Even then, technological limitations will still exist.  Very few fuel cells or batteries will live to see 10 years of continuous service without significant performance degradation.  As with all other machines, they have materials-related service life limitations, which is what plagued early steam and diesel engines.  It took many decades of continuous effort to sort out those mechanical and materials problems.  There's no reason to believe that fuel cells and Lithium-based batteries won't follow the same developmental trajectory.

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#309 2023-08-07 13:19:48

kbd512
Administrator
Registered: 2015-01-02
Posts: 7,469

Re: Geothermal and Geothermal Battery (Changed Title 12/21/23)

Void,

The reason sCO2 turbines are potentially game-changing is what they bring to the table that steam turbines, aero-derivative gas turbines, and diesels, don't.  Apart from steam turbines, those other kinds of engines require Oxygen and fuel.  Steam turbines are quite large and heavy

LM2500s are one of the most thoroughly proven aero-derivative marine and industrial gas turbine engines around.  They top out at about 39% thermal efficiency in simple-cycle operation, which is how most of them are used.  Low-speed diesels can arrive at 40% to 50% simple cycle thermal efficiency without extraordinary effort, but they are very heavy when compared to the LM2500.

GE WWII Cruiser Geared Steam Turbine 18.6MW; total weight unknown, but the boiler and main reduction gear attached to the steam turbine weigh 108t; 21% thermodynamic efficiency at peak output (assuming USS CL-91 Oklahoma City used No5 fuel oil; USN had a special kind of No5 fuel oil back then)
Note: does not include actual turbine weight or condenser weight, just the weight of the boiler supplying the steam and the main reduction gearing; efficiency calc might be off, but not by that much (it's pretty horrendous, regardless)

16,000lbs (7,257.5kg) of No5 fuel oil (at 19,000btu/lb or 12,276Wh/kg) at 18.6MW of output shaft power, means 21% overall thermodynamic efficiency (it was also driving a "supercharger" to blow 22,000ft^3/min of air into the boiler, and those suck at efficiency, even today)

Edit: I literally cannot post any small part of this response.

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#310 2023-08-07 13:26:44

kbd512
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Re: Geothermal and Geothermal Battery (Changed Title 12/21/23)

Void,

GE LM2500 G4 marine gas turbine: 35MW; 20t; 39% thermodynamic efficiency at peak output (less at any lesser output level)

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#311 2023-08-07 13:49:16

Void
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Re: Geothermal and Geothermal Battery (Changed Title 12/21/23)

Thanks,

That is a bit over my head, but I will give it a few reviews over the next few days.  It looks very promising.

My opinion being that it is rather likely that such methods may in fact suit the Moon.

Done.


Done.

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#312 2023-08-07 14:07:29

kbd512
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Re: Geothermal and Geothermal Battery (Changed Title 12/21/23)

Void,

I can't even post the rest.  I did a comparison between marine / industrial geared steam turbines, gas turbines, sCO2 turbines, and diesels.

TLDR; gas turbines are light but thirsty, geared steam turbines are very heavy and very thirsty, modern diesel are lighter than boilers and geared steam turbines but not quite as efficient as sCO2.  sCO2 is the only solution that doesn't require lube oil or water, and it's not much heavier than the LM2500 gas turbine, but has a more compact footprint.

Where does this all lead?

We can have the kind of electric power system you envisioned on the moon or Mars, using solar thermal power to heat up a giant regolith-insulated rock pile, then transfer the heat with steel piping into the turbine to generate electric power after sunset.  There's no wind and very little atmospheric pressure to resist, so solar thermal panels can be Aluminized Mylar mirrors directed at said rock pile.  It negates the otherwise hard requirement for a nuclear reactor.  Mars probably requires so much energy to stay warm, melt ice, grow food, etc, that I don't think the reactor is optional there, but solar thermal may be able to reduce the reactor size to something more manageable.

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#313 2023-08-07 14:43:19

Calliban
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From: Northern England, UK
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Posts: 3,483

Re: Geothermal and Geothermal Battery (Changed Title 12/21/23)

For my dissertation for my nuclear engineering degree, I developed a concept design for a direct cycle, CO2 cooled fast reactor.  The idea behind this reactor was to produce an extremely compact and power-dense plant, which could also achieve the high breeding ratio needed for a rapid nuclear expansion during an energy crisis.  This was achieved by coupling a uranium-plutonium nitride fuelled fast reactor core, to 4x 500MWe S-CO2 power generation loops in a direct cycle.  The overall plant power density was quite insane.  The reactor would have generated twice as much power as an AP1000 pressurised water reactor, on a foot print about one-tenth the size.  In spite of its enormous power, this allowed all of the powerplant components to be factory made and shipped in by rail and rapidly flanged or welded together onsite.  This combined the rapid build advantages of a small modular reactor, with the scale economy advantages of a large nuclear reactor.  S-CO2 gas turbines are the key technology that makes this power density possible.

There were a number of problems with the gas cooled fast reactor that needed solutions.

(1) In the event of a coolant leak, the gaseous coolant rapidly depressurises, which hardens the neutron spectrum due to loss of moderation.  This adds reactivity to a fast reactor core, because the number of neutrons released by fission increases as neutron energy increases.  This can lead to a power surge (positive void coefficient).  To negate this problem, I added liquid expansion tubes to the core.  In the event of a sudden loss of pressure, liquid lithium would be drawn into the tubes in the core by differential pressure, adding moderation and soaking up neutrons.  The liquid lithium can also function as an actuator for reactor trip, ensuring that tge reactor trips rapidly after a coolant leak.

(2) The heat removal capabilities of the coolant are proportional to its density, which is a function of pressure.  A coolant leak could undermine decay heat removal as the gas depressurised.  To counter this problem, the reactor had four seperate power generation loops.  The pipework diameter of each loop was small enough to ensure that if a leak occured, the rate of depressurisation would be low enough to allow the heat carrying capability of the coolant to remain sufficient to remove decay heat by natural convection.  Whilst coolant density would decline with time, decay heat has its own decay curve.  This allowed natural circulation to be sufficient to remove decay heat for several hours after a an uncontained coolant leak and full reactor power.

(3) Vibration is a severe problem for gas cooled reactors, because flow rate across the fuel elements is very high.  To counter this problem and keep the neutron spectrum as hard as possible, the reactor used tube-in-shell fuel elements.  This allowed hexagonal fuel elements to brace against each other, dampening vibration problems.  The price to pay for this arrangement was high pumping power - as much as 20% of turbine power output.  To reduce the economic penalty of this, the blowers were coupled directly to the turbine shafts.  This provided an added safety benefit.  In the event of loss of all electrics, the coasting turbines and alternators, acted as flywheels, which would continue to power blowers, transfering heat to passive cooling loops.

(4) For long-term decay heat removal after a coolant leak, there are uncertainties around the ability of atmospheric pressure CO2 to remove decay heat by natural circulation.  To provide an additional long term cooling system, four cooling loops with water cooled heat exchangers were added, one to each loop.  One of my proudest innovations was to add thermoelectric generators to the decay heat removal heat exchangers.  The few kW of direct current produced is sufficient to power blowers that will remove decay heat from the core.  In this way, the decay heat removal system is actually powered by the decay heat itself.

If we ever get to Mars, I would like to think I might be able to help build one of these high power-density breeder reactors in my fading years.  I will likely be long dead before we need anything like that.  But you never know.

Last edited by Calliban (2023-08-07 14:51:14)


"Plan and prepare for every possibility, and you will never act. It is nobler to have courage as we stumble into half the things we fear than to analyse every possible obstacle and begin nothing. Great things are achieved by embracing great dangers."

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#314 2023-08-07 15:11:20

Calliban
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From: Northern England, UK
Registered: 2019-08-18
Posts: 3,483

Re: Geothermal and Geothermal Battery (Changed Title 12/21/23)

On the topic of geothermal energy extraction from deep wells.  This is inherently more difficult than oil and gas extraction because of the low energy density of the hot water.  One litre of crude oil contains about 40MJ or energy.  Condensate or NGL would still contain about 20-30MJ/L.  Compare that to water heated from 20°C to 300°C.  Specific enthalpy increases by 1.25MJ/kg.
https://www.engineeringtoolbox.com/wate … _1508.html

We can extract 20-30% of that energy as mechanical or electrical power.  In other words, each litre of crude oil provides 40x as much useful energy as our geothermal hot water and condensates about 30x more.  This means the capital cost of drilling will weigh far more heavily on geothermal power than it will on oil and gas exploration.  Pumping power is an important consideration as well.  Fluid friction through a well several km deep and through a hydraulic fracture system will be high.  This is power that comes directly off of the net power production of the plant.

We do not yet know what geothermal resources we will find on Mars.  But near surface high quality steam appears unlikely, as we would have detected a strong infrared signature from orbit.  Failing that, anywhere that can provide warm ground water within shallow depth would be a tremendous economic advantage to an early Mars base.


"Plan and prepare for every possibility, and you will never act. It is nobler to have courage as we stumble into half the things we fear than to analyse every possible obstacle and begin nothing. Great things are achieved by embracing great dangers."

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#315 2023-08-08 09:11:22

Void
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Re: Geothermal and Geothermal Battery (Changed Title 12/21/23)

I think that anything that can involve Carbon is worth looking into.  Previously the precious material you might want to get would be water or Hydrogen.  Those are still valuable, but I am coming to appreciate Carbon also.

Ships which land on the Moon could have external cargo compartments which could be filled with some type of Carbon.  I know that a lot of people like to joke about Lithobraking, but you could drop that cargo prior to landing.  This then would lighten the load on the ship, so it's landing legs would not be as challenged, and the precision landing will not have to brake as much for the Carbon cargo.  I think that eventually more exotic methods to drop Carbon to the Moon could emerge.  But for now, I like to consider external drop cargo tanks for landing ships.

Carbon can be had from the Moon itself presumably, but extraction of it may be more expensive than bringing Carbon in from the Earth or Mars or Asteroids.

While water is also likely available, it also may have a great value for other purposes on the Moon.

If CO2 is the working fluid on the Moon, then about 2/3rds of that fluid can come from the Moon, the Oxygen.

And a plan like the above would perhaps favor Carbon from Mars/Phobos/Deimos, but from Earth first likely.

I am interested in the possibility that centrifugal gravity on the Moon could supply 1/6th gravity which could be added to the 1/6th true gravity of the Moon.  We are likely to discover something about adult health in space with 1/3rd gravity is available.

We are certainly going to want to know about human and animal reactions to those sorts or g forces being available.  We will want to generate ~.167 g with such devices on the Moon to approximate 1/3 g in the Moons surface gravity field.

http://www.artificial-gravity.com/sw/Sp … inCalc.htm

So, if a suitable sized crater were used, you might put a train tube on its inside perimeter of choice.  Most activities might be in 1/6th g, but periodically the "Train" could be run for purposes of human health, if that is useful.  I suppose you could even build for a greater g force if it turns out to be needed.  Obviously, you could have several trains which run and stop periodically.

And of course, eventually a healthy measure of what is needed would be discovered.

If Mars/PHobos/Deimos are serious exporters of Carbon and biological materials, this can make the Moon very valuable.

And so drilling rock on the Moon will be a skill we would want to see developed.  And for Mars as well of course.

So, the idea of developing nuclear industry for both worlds is not needing to be to the exclusion of the development of drilling on those worlds, for whatever purpose.

And for the Moon at least I would not expect to seek true geothermal energy, that would be a surprising development, but drilling to create heat sinks, and using CO2 as the heat exchange fluid makes sense to me.

I am probably going to move to the Terraforming section next.

Done.

Last edited by Void (2023-08-08 09:43:17)


Done.

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#316 2023-08-08 20:51:40

SpaceNut
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Re: Geothermal and Geothermal Battery (Changed Title 12/21/23)

So far, we have a volume of heat and cold sink that have a differential temperature that can be used with several devices to make power. These do have limits as to how much the devices which ever one is chosen can be tolerated.

While we can also create pressures from these with exchangers as seen with many of the earlier posts using a variety of working fluids that as they pressure from heat can cause a turbine to turn and once cooled again can be recycled nearly forever in the system.

Off course we can also put that heat and cold back into the storage system to allow for the cycle to continue to create the power we will require.

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#317 2023-08-09 11:25:34

Void
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Re: Geothermal and Geothermal Battery (Changed Title 12/21/23)

As for the Moon, there could be quite a few ways to store large amounts of thermal energy, and some alternate ways to gather energy.

The Moon likely has enough Carbon and Water for a small number of humans, but to import more, could allow very large populations.  And as some may think it impractical to import such things, I am sure it will depend on how well humans can be healthy on the Moon, and possibly space stations associated with the Moon.

Testing over time will determine the direction of things, I feel.

Done.


Done.

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#318 2023-08-10 16:12:28

kbd512
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Re: Geothermal and Geothermal Battery (Changed Title 12/21/23)

Closed-loop heat engines are the only practical way of supplying long-term power at the 100kW+ output level.  In the case of nuclear thermal, heat from fission drives the working fluid (Helium, Neon, Argon, molten salt, molten metal, water) through the turbo in its turbo-electric generator(s).  In the case of solar thermal, external power from the Sun drives the working fluid through the turbo, but the heat is collected and stored in a large mass of insulated material first.  Mars supplies a near-vacuum (best insulator there is) at Mars Sea Level to prevent the hot sink from rapidly losing stored thermal power to the surrounding environment, but since this power generation system will be ground mounted, the surrounding volcanic regolith or rock must form the walls of the heat storage tank.  One of the stainless steel tanks from an expendable Starship could hold many tons of molten Sulfur.  If it has a double tank wall, to act as a vacuum-insulated stainless thermos, even better.  The LOX and LCH4 header tanks have a combined volume of about 34m^3 and weigh about 630kg to 650kg, each.

As an example of how we could do this, Mars has plenty of places where the ground right below a thin layer of regolith dust covering appears to be pure Sulfur.  Sulfur melts at 112.8C and boils at 444.6C, so the usable temperature range is 331.8C if the hot sink design mandates that the Sulfur remains liquid at all times.  Sulfur has a specific heat capacity of 732 Joules per 1kg of Sulfur per 1°C, so 331°C * 732J/kg°C = 242,292 Joules of heat energy can be stored in 1kg of Sulfur by heating the Sulfur from 113C to 444C.  1 Watt-hour = 3,600 Joules, so 242,292J = 67.3Wh of heat energy.  This would imply 100% efficiency, but no heat engine is 100% efficient at converting heat to electricity.  Perhaps we can realistically obtain about 30Wh of electric energy from 1kg of Sulfur heated to just below its boiling point.  To store 3MWh of energy, we would require 100,000kg / 100t of Sulfur.  Liquid Sulfur is about 1,800kg/m^3, so 56^3 of storage volume should be sufficient.  The Sulfur would be collected from the surface of Mars and does not require much further processing to store energy.

Let's assert that a 18.67m^3 Starship LOX header tanks weighs 633kg, or 900kg with a double-wall and support stand to keep it off the ground.  3 tanks gives us 3MWh of storage using Sulfur collected from the surface.  A complete 10MW geared sCO2 turbine skid weighs about 20t, with no optimization for weight.  A 10MW generator weighs another 20t.  Every 2,700t worth of Starship LOX header tanks is enough equipment to store an additional 3MWh of energy.  A 100kWh / 600kg Tesla Lithium-ion battery with 100% of its capacity drained provides 166.67Wh/kg, so a 3MWh battery weighs 18,000kg.  We have to eat the mass of the 20t 10MW sCO2 turbine and generator, 40t in total, but storing another 3MWh only involves 2,700kg of stainless steel, plus the mass of the mylar to reflect heat into the pipes.  The problem is not how to store a paltry 3MWh of energy, it's how to continue expanding the available storage capacity without adding an enormous amount of additional weight.  If the Sun is blocked for 3 months by dust storms, or that silly little phenomenon known as "seasonality" happens, then you need power storage for 3 months.  The mass of the batteries will rapidly outstrip the mass of additional thermal power generation and storage equipment, and the equipment (photovoltaics or reactors) to charge the batteries will be just as heavy because it's electrical.

To store 18MWh of electricity, you need a bare minimum of 108t of batteries, exclusive of all other required equipment.  To store 18MWh of electricity using stainless tanks and Sulfur, you need 16.2t of stainless LOX header tanks.  108t of steel can store enough heat to provide 120MWh of electricity.

If you brought a single 10kWe KiloPower reactor with you, then you have 30kWt of waste heat that it generates at full output.  That waste heat can be pumped into the Sulfur tanks.  It would take 224 hours and 20 minutes, or about 9.5 days of full power output to store 3MWh of power in the Sulfur tanks.  The current plan is to reject the 30kWt of waste heat into space using giant radiator panels.  I think loading that waste heat into molten Sulfur for future use, is a much better plan.

Eventually, you can collect enough surplus waste heat energy from a single reactor to undertake high power consumption activities such as drilling a geothermal well to tap into the planet's heat reservoir, and then you have permanent heat input without additional reactors or batteries flown in from Earth.  You can use some combination of solar and nuclear thermal power to act as a "spark plug" to light off the industrialization process, but shortly thereafter you must start producing and storing your own thermal power using locally sourced materials and heat sources.  It will take a lot of time and effort to construct GW-class reactors using Martian steel / Uranium / Thorium, but a permanent thermal power source needs to be created as soon as possible.  After you have access to a permanent supply of heat / electricity / thermal energy storage, then you can begin colonization.  Dumping 3/4ths of your reactor's total power output into space is not a very good plan, though.  It needs to be stored, even if you only get half of that input back as electricity or mechanical work output.

Speaking of mechanical work, Mars needs CO2 powered air tools for construction, and those turbines can help fill CO2 tanks to feed the power tools.  Large shops use air powered tools to fix cars and other heavy machinery, not batteries.

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#319 2023-08-13 11:41:11

Void
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Registered: 2011-12-29
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Re: Geothermal and Geothermal Battery (Changed Title 12/21/23)

kdb512,

I waited until now to reply as my mind was not working well.  I have been sick.  I have not tested for covid, I hate sticking the q-tip in my nose I sneeze like crazy.  But last weekend I was exposed to a person with a bacterial infection in the airways.  I am guessing that that is the likely thing.  Pretty tough for a while, but it seems to have broke just a couple of hours ago.

Your ideas are interesting, and I don't have any contrary to the but I do have something that might supplement.

Lava Tubes as thermal storage.  I'm supposing that you might push microwaves into them to heat them up, and then have some kind of tubing bonded to the interior surfaces with a fluid for thermal extractions.  Of course, you might heat them with the tubing as well.

It's sort of a starter idea.

Maybe someone has notions?

Done.


Done.

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#320 2023-08-13 15:07:27

SpaceNut
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Re: Geothermal and Geothermal Battery (Changed Title 12/21/23)

good luck with fending off the virus void

Have had a bout with intestinal gut issue but it looks like I am getting better as well after a week.

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#321 2023-08-13 17:27:46

Void
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Registered: 2011-12-29
Posts: 7,202

Re: Geothermal and Geothermal Battery (Changed Title 12/21/23)

Well thanks, the same for you.  I had creaky lungs, which is unpleasant.  I coughed so much that the muscles about my ribs got very sore.
But i'm about 90 to 95% out of it now, I think.  A little scary.

Done.


Done.

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#322 2023-08-13 17:57:35

kbd512
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Re: Geothermal and Geothermal Battery (Changed Title 12/21/23)

Void,

I hope you get to feeling better soon.  Speaking from recent personal experience, being sick or infirm is not much fun.

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#323 2023-08-25 15:43:06

Terraformer
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From: Ceres
Registered: 2007-08-27
Posts: 3,821
Website

Re: Geothermal and Geothermal Battery (Changed Title 12/21/23)

Re. high temperature heat pumps, flat plate collectors in direct sunlight can reach 330K, evacuated tubes 360K. Perhaps these would be used as the heat source, without needing to have reflecting troughs track the sun.

Looking at the cost of drilling, how does it change with depth? An estimate for well drilling is £2500 for 20m, but that's for a single well -- addition boreholes for ground source heat pumps cost 60% of the price of the first one, presumably because the equipment is already at the location, so perhaps three such boreholes would cost ~£6k. Thinking about how a homebrew system (has to be homebrew, I don't think anyone's doing it yet) for solar thermal + seasonal storage might be put together. Insulating the first 5m (don't want to put too much heat into the upper layers of the soil, I still want a garden) leaves 45m of borehole to inject heat through. If they heat the surrounding soil 2m out to 40c, then that's 560 m^3 to store heat in. The heat capacity of soil is given by wiki as 0.8, (I think it's for dry soil?) so each degree it could store perhaps 1.2MJ per cubic metre, 1/3rd of a kWh. Hmm. Taking it down to 30c then would give me 1850kWh of storage. Eek. Using a heat pump I suppose I could bring it down to 20c... also it depends on the soil type. Soil that's 20% water has that much heat capacity just from the water alone. It's probably closer to half to two thirds kWh per m^3. EDIT: yes sandy clay apparently has 1.38 kJ/kg*K, so it's probably more like 0.6kWh/m^3*K. Now we're talking. (I was sure I remembered it being a lot closer to 1kWh/m^3*K...).

For the heat, solar thermal. A roof mounted system that delivers 750kWh a year can cost £4k, but again, I don't know how that changes with increasing size, given that the workers have to get on the roof whether it's a small system or a large system, the piping needs to be installed regardless etc. I'm pretty sure it's sunny enough even in Britain for a house to get enough heat from them. Anyway, trying to figure out how much a system for a single home might be.

The local council is developing it's Local Energy Action Plan, so hopefully I can get in there and encourage district heat source grids. And ensure they're future proofed, so we can stick heat back down the boreholes during the summer and won't lose much of it through the network pipes if we upgrade the system later to deliver 40c fluid rather than 20c.

Ooh. On Luna, the nights let you radiate to a 3K sky. And the days let you collect 100c heat just from the rocks. Probably the cheapest energy generation would be a diurnal engine. Ironically it would be storing energy for the day that would be the issue here. Maybe use the cold night sky to supercool something to use as the heat sink?

Last edited by Terraformer (2023-08-25 15:48:58)


"I'm gonna die surrounded by the biggest idiots in the galaxy." - If this forum was a Mars Colony

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#324 2023-08-25 17:21:43

Calliban
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From: Northern England, UK
Registered: 2019-08-18
Posts: 3,483

Re: Geothermal and Geothermal Battery (Changed Title 12/21/23)

On the moon, the absence of atmosphere makes the regolith a better thermal insulator than rockwool here on Earth.  Unfortunately, the same factor applies to heat transfer tubes putting heat into the ground.  What would work really well would be a bedrock extrusion, surrounded and covered by a thick layer of regolith.  The thermal conductivity within the solid rock would be in single digit W/m.K.  within the regolith, ~E-3 W/m.K.

Radiating to a black sky isn't as good as it sounds. The Stefan-Bootzmann equation still applies.  That is:

Qr = Rho x T^4

Where Rho = 5.67E-8.  At 4K, the effective radiating power of your panels would be about 1 microwatt/m2.  Even radiating at 100K, the radiating power is only going to be 5.67W/m2.

Those low temperatures could allow machines with remarkable thermodynamic efficiency.  But they trash the system power density.  In a practical system, there is a trade off between efficiency and power density.

Last edited by Calliban (2023-08-25 17:26:08)


"Plan and prepare for every possibility, and you will never act. It is nobler to have courage as we stumble into half the things we fear than to analyse every possible obstacle and begin nothing. Great things are achieved by embracing great dangers."

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#325 2023-08-26 03:28:32

Terraformer
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From: Ceres
Registered: 2007-08-27
Posts: 3,821
Website

Re: Geothermal and Geothermal Battery (Changed Title 12/21/23)

Hmm. How hot does a flat plate collector get in direct unfiltered sunlight on Luna?

For recharging a terrestrial ground thermal battery, summer air could be a good source of heat. Effectively uses the land as a vast solar collector. I think a big part of the issue with ground source heat pumps is their reliance on natural recharging. But we don't have to rely on natural recharging of heat into the boreholes.

If we're using a roof source heat pump, we don't need complex collectors. A lot of things can reach 40c in direct sunlight... I wonder what sort of improvements we could get in installation speed and cost for rooftop systems?


"I'm gonna die surrounded by the biggest idiots in the galaxy." - If this forum was a Mars Colony

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