Thermal heat storage

SpaceNut · 2019-11-23 10:19:14

Most of us know about the use of stored heat in many forms. From the making of steam to hot water the range of temperatures as a means to do meaningful work. We know that solar heat can be save for later use and that we can concentrate that heat to higher temperature levels as well as to make use of the low temperature savings as well.

When you think about it its just another form of a flow battery only it does not put out a direct voltage as it needs to be comverted back from its saved source to electrical by pellitiers or turbines.

hybrid device captures heat from the sun and stores it as thermal energy

hybrid-molecular-storage-material-and-localized-phase-change-material-hg.jpg

It addresses some of the issues that have stalled wider-scale adoption of solar power, suggesting an avenue for using solar energy around-the-clock, despite limited sunlight hours, cloudy days and other constraints. The researchers report a harvesting efficiency of 73% at small-scale operation and as high as 90% at large-scale operation.
Up to 80% of stored energy was recovered at night, and the researchers said daytime recovery was even higher.
"During the day, the solar thermal energy can be harvested at temperatures as high as 120 degrees centigrade (about 248 Fahrenheit),"

Research papaer

HKU team invents Direct Thermal Charging Cell for converting waste heat to electricity

Low grade heat is abundantly available in industrial processes (80 to 150C), as well as in the environment, living things, solar-thermal (50 to 60C) and geothermal energy. Over 60% of the world's primary energy input, whether it is in the industrial process or domestic energy consumption, is wasted as heat. A majority of this loss as waste heat is regarded as low-grade heat.
The newly designed DTCC is a game-changing electrochemical technology which can open new horizons for applications to convert low-grade heat to electricity efficiently. It is a simple system with the basic unit sized only 1.5 sq.cm and thickness 1 to 1.5 mm. The cell is bendable, stackable and low cost.
The new thermal charging cell uses asymmetric electrodes: a graphene oxide/platinum (GO/Pt) cathode and a polyaniline (PANI) anode in Fe2+/Fe3+ redox electrolyte via isothermal heating operation without building thermal gradient or thermal cycle.
When heated, the cell generates voltage via a thermo-pseudocapacitive effect of GO and then discharges continuously by oxidizing the PANI anode and reducing Fe3+ to Fe2+ under isothermal heating on cathode side till Fe3+ depletion. The energy conversion works continuously under isothermal heating during the entire charge and discharge process. The system can be self-regenerated when cooled down. This synergistic chemical regeneration mechanism allows the device cyclability.

Research paper

GW Johnson · 2019-11-23 11:12:49

Solar heat can be captured in water, and used for space heating. That's all low grade heat, with a low-grade heat end use. No conversion losses to speak of. Not a waste of high-grade energy, either.

But I must say, generating electricity from low grade heat has always been a very low-efficiency process heretofore (thermionic converters). This might well be a breakthrough of sorts. A 200-250 F range of heated fluid temperatures is achievable (see below).

In order to get solar-heated hot water temperatures over about 180-190 F here on Earth requires a modestly-concentrating collector, meaning a simple flat plate collector with modest-sized adjacent mirror surfaces. On Mars, the mirrors need to be larger to overcome the 2:1 intensity deficiency. That's still easily doable.

But you still need to plan on what else to do when the sun doesn't shine, be it night or dust storm.

GW

SpaceNut · 2019-11-23 14:43:12

The quantity since it can be increased with isolated tanks of all sizes allow for a flexible storage of temperature for the input from the collector. The reflective surface can be made from a mylar plastice matial that can be rolled out, then anchored to the frame that holds it in position for making the level of collected energy higher and so will the temperature of the working fluid dependant on the flow rate.

Calliban · 2019-11-25 06:41:42

The huge diurnal temperature fluctuations on Mars make this idea more workable there than it would be on Earth. Assuming a daytime average temperature of zero Celsius and a night-time panel temperature of -50C, say, Carnot efficiency for a vapour cycle would be 18.3%. A practical heat engine can get between half and two-thirds Carnot efficiency. So a flat plate solar thermal power plant would get ~10% efficiency on Mars.

The Martian atmosphere is so thin that convective heat losses from panels will be negligible. No cover glass would be needed. Panels could be slabs made from concrete or clay with plastic pipes running through them. A practical heat transfer fluid would be brine, containing concentrated chlorate salts. The heat exchanger could also be made from thermoplastics and would consist of essentially a coiled hosepipe within a large tank of water or brine. During the day, lightly salted ice-water would be melted in one tank by heat flowing from the panels at about zero C. This tank will provide a hot source. At night, a second tank containing concentrated brine would have heat removed through the panels and would freeze at -50C. Insulation for both tanks would be provided by regolith. The tanks could be nothing more complex than excavated holes lined with polyethylene sheeting.

A vapour generation cycle would run between the two tanks continuously, providing base load power. Compressed CO2 would make a workable secondary power-cycle fluid. Alternatively, there is SO2, ammonia, ethane, propane or various fluorocarbon compounds.

To cover outages resulting from dust storms, the tanks would need to be oversized to provide several weeks worth of storage. There will be capital cost implications to this. Overall, the system will be large but relatively low tech. It will need valves and pumps on the primary (brine) side and valves, pumps, turbines, generators and liquid-vapour separators on the secondary CO2 vapour cycle side. Lots of carbon steel on the secondary side; plastics on the primary side.

Power density will be limited by the amount of heat that the panels can dump into the Martian night. Assuming a -50C working temperature for panel radiating as a black body, gives a panel thermal power density of 140watts. The panel can only radiate at night, so time average thermal power density is 70w/m2. Assuming a 10% electrical conversion efficiency gives a panel electrical power density of 7W/m2. This is poor by most standards, but begins to look much better if panels can be made from clay and storage tanks are nothing more elaborate than polythene lined holes in the ground. A 1MWe power plant would cover 143,000m2 or 36 acres.

To store 4 weeks worth of power, would require some 6720MWh (24million MJ) of thermal heat storage in each tank. 1 litre of water has latent heat of freezing of about 400KJ. So each tank would need a volume of 60,000 cubic metres - a cube 39m aside. That is a lot. Especially considering that sourcing water from buried glaciers on Mars, will take about that same amount of energy as concrete manufacture on Earth. Heat could be stored in solid rock by drilling bore holes.

Last edited by Calliban (2019-11-25 07:15:29)

louis · 2019-11-25 07:30:03

Interesting ideas on an established theme.

I think manufacturing methane and oxygen when you have an energy surplus is probably a quicker and better route to energy storage, since we will already be producing methane and oxygen for fuel-propellant. Methane and oxygen can be used directly for heating, for electricity generation or for transport power.

That said, the use of basic materials makes your proposal an attractive one.

Calliban wrote:

The huge diurnal temperature fluctuations on Mars make this idea more workable there than it would be on Earth. Assuming a daytime average temperature of zero Celsius and a night-time panel temperature of -50C, say, Carnot efficiency for a vapour cycle would be 18.3%. A practical heat engine can get between half and two-thirds Carnot efficiency. So a flat plate solar thermal power plant would get ~10% efficiency on Mars.
The Martian atmosphere is so thin that convective heat losses from panels will be negligible. No cover glass would be needed. Panels could be slabs made from concrete or clay with plastic pipes running through them. A practical heat transfer fluid would be brine, containing concentrated chlorate salts. The heat exchanger could also be made from thermoplastics and would consist of essentially a coiled hosepipe within a large tank of water or brine. During the day, lightly salted ice-water would be melted in one tank by heat flowing from the panels at about zero C. This tank will provide a hot source. At night, a second tank containing concentrated brine would have heat removed through the panels and would freeze at -50C. Insulation for both tanks would be provided by regolith. The tanks could be nothing more complex than excavated holes lined with polyethylene sheeting.
A vapour generation cycle would run between the two tanks continuously, providing base load power. Compressed CO2 would make a workable secondary power-cycle fluid. Alternatively, there is SO2, ammonia, ethane, propane or various fluorocarbon compounds.
To cover outages resulting from dust storms, the tanks would need to be oversized to provide several weeks worth of storage. There will be capital cost implications to this. Overall, the system will be large but relatively low tech. It will need valves and pumps on the primary (brine) side and valves, pumps, turbines, generators and liquid-vapour separators on the secondary CO2 vapour cycle side. Lots of carbon steel on the secondary side; plastics on the primary side.
Power density will be limited by the amount of heat that the panels can dump into the Martian night. Assuming a -50C working temperature for panel radiating as a black body, gives a panel thermal power density of 140watts. The panel can only radiate at night, so time average thermal power density is 70w/m2. Assuming a 10% electrical conversion efficiency gives a panel electrical power density of 7W/m2. This is poor by most standards, but begins to look much better if panels can be made from clay and storage tanks are nothing more elaborate than polythene lined holes in the ground. A 1MWe power plant would cover 143,000m2 or 36 acres.
To store 4 weeks worth of power, would require some 6720MWh (24million MJ) of thermal heat storage in each tank. 1 litre of water has latent heat of freezing of about 400KJ. So each tank would need a volume of 60,000 cubic metres - a cube 39m aside. That is a lot. Especially considering that sourcing water from buried glaciers on Mars, will take about that same amount of energy as concrete manufacture on Earth. Heat could be stored in solid rock by drilling bore holes.

Calliban · 2019-11-25 09:19:27

louis wrote:

Interesting ideas on an established theme.
I think manufacturing methane and oxygen when you have an energy surplus is probably a quicker and better route to energy storage, since we will already be producing methane and oxygen for fuel-propellant. Methane and oxygen can be used directly for heating, for electricity generation or for transport power.
That said, the use of basic materials makes your proposal an attractive one.

Methane-oxygen synthesis for power production has extremely low cycle efficiency – about 5%. I examined this in a previous thread.

Assuming that the intention is to provide small amounts of power only very occasionally – say 10% of baseload power, for a dust storm lasting a couple of months occurring once every two years; then it might be an affordable expense, especially if it can be tailed onto the existing propellant production process. But it is wasteful in the extreme. Like everything else, these sorts of decisions will be made on the basis of cost benefit analysis.

Long-term energy storage is always problematic, because it requires large amounts of energy storage that is utilised very poorly. This has a terrible effect on the marginal cost of each kWh. This is why renewable energy is proving so poorly effective at replacing fossil fuels for power generation here on Earth. We can build pumped storage plants that balance supply over a period of hours, but it will never be affordable to store even 1 week of spare power in this way. I suspect that the 'solution' to this problem will have more to do with going without; or maybe just finding an energy source that doesn't fluctuate with the weather. Can anyone think of one?

louis · 2019-11-25 10:55:14

Well I would envisage meth-ox production being tailored to a PV power approach. In those circumstances for things like agricultural and propellant production, probably the two biggest calls on power, you would "make hay while the sun shines" as the old proverb goes which means you don't attempt to maintain production levels when solar radiation dips to very low levels. In such circumstances you would cut back on production of food and propellant. That means two things: (a) you need to have a large food store to see you through major dust storms (not likely to be much of a problem in the early stages of colony development) and (b) you need a larger propellant production facility than you would with nuclear.

You'd probably only be looking to use maybe 10% of your average energy use through meth-ox production. Estimates of how much energy is required to sustain life and basic services vary but 10KwEs per person seems a popular figure (probably an overestimate in my view). For a 10 person colony producing enough propellant to return to Earth in one Starship that would mean 100KwE or 10% of the total energy supply (1MwE).

Even the severest dust storms do not stop solar radiation entirely, so PV will still keep working, albeit at a reduced level. From what I have read, you are maybe getting an average 40% of normal or thereabouts over the life of a dust storm.

The reality is there are unlikely to be any periods when your PV system could not cover the emergency baseload figure. But of course, you need to plan for calamity, so you would need to arrive with a large meth-ox supply and begin building up your reserve. Meth-ox production is a bit like a savings account - you only have to have a slight surplus and the account will build and build until you have a very large surplus available. A reasonable compromise would be to look to build an energy reserve of 245,000 KweHs per ten people comprising meth-ox, chemical batteries and maybe pumped storage - enough to maintain 100 Kwes over 100 sols.

I think on Mars we have an opportunity to explore the possibility of storing methane as clathrates. Could we create those and bury them on Mars in a shadowed area?

https://en.wikipedia.org/wiki/Methane_c … ercial_use

Calliban wrote:

louis wrote:
Interesting ideas on an established theme.
I think manufacturing methane and oxygen when you have an energy surplus is probably a quicker and better route to energy storage, since we will already be producing methane and oxygen for fuel-propellant. Methane and oxygen can be used directly for heating, for electricity generation or for transport power.
That said, the use of basic materials makes your proposal an attractive one.
Methane-oxygen synthesis for power production has extremely low cycle efficiency – about 5%. I examined this in a previous thread.
Assuming that the intention is to provide small amounts of power only very occasionally – say 10% of baseload power, for a dust storm lasting a couple of months occurring once every two years; then it might be an affordable expense, especially if it can be tailed onto the existing propellant production process. But it is wasteful in the extreme. Like everything else, these sorts of decisions will be made on the basis of cost benefit analysis.
Long-term energy storage is always problematic, because it requires large amounts of energy storage that is utilised very poorly. This has a terrible effect on the marginal cost of each kWh. This is why renewable energy is proving so poorly effective at replacing fossil fuels for power generation here on Earth. We can build pumped storage plants that balance supply over a period of hours, but it will never be affordable to store even 1 week of spare power in this way. I suspect that the 'solution' to this problem will have more to do with going without; or maybe just finding an energy source that doesn't fluctuate with the weather. Can anyone think of one?

SpaceNut · 2019-11-25 17:01:29

Argue the methanol solar in the other backup topic, as thats not thermal storage....

louis · 2019-11-25 17:47:12

Fair enough! I know it's annoying when people drag your topic away from the thread focus. That said, I was responding to the idea that
a temperature range engine would be the best approach to energy storage. That I very much doubt. But I can see it would be better on Mars than on Earth.

SpaceNut wrote:

Argue the methanol solar in the other backup topic, as thats not thermal storage....

SpaceNut · 2019-11-25 19:17:19

Trying to work numbers for if its going to work for mars.

https://science.howstuffworks.com/envir … -power.htm

Another method to concentrate the heat to be stored

Something else that we can do with heat
https://www.machinedesign.com/energy/in … nditioning

Here is the Methane backup not nuclear vs solar

This is the topic that void had put forth for Highly Transparent Aerogel/Getting more heat out of sunlight

We have lots of uses for mars heat once we generate it, collect it, store it...
Generation and Use of Thermal Energy in the U.S. Industrial Sector and Opportunities to Reduce its Carbon Emissions

https://www.eia.gov/energyexplained/sol … plants.php

https://energy.gov/eere/energybasics/ar … tem-basics

SpaceNut · 2019-11-26 18:14:25

To give louis an apology and a point back, that no matter what we choose to use for primary power there is always going to be a need for multiple backups for expansion and for a failed supply system.

tahanson43206 · 2021-08-07 07:16:58

In light of the recent (and ongoing) advocacy of thermal energy storage by Calliban, I'd like to bring this topic back into view.

I asked Amazon for a list of books: thermal energy storage for renewable energy

As usual with such a broad request, there are citations that meet only part of the requirements

Amazon came back with a list of 215 titles ...

The first of these looks like a direct hit:

Thermal, Mechanical and Hybrid Chemical Energy Storage Systems
Authors are given as: Klaus Brun, Timothy C. Allison and (et al.) September 28, 2020

That is ** recent ** .... Paperback and Kindle are almost exactly the same price ($80+ and change)

However, the books/titles immediately after this one appear to be worth considering if someone is looking to build an energy storage facility for fun and profit.

Edit: Even if a member of this forum is NOT interested in doing all the work of funding, building, operating and worrying about an energy storage system, everyone in the forum (and many readers not already members) would (presumably) be interested in encouraging development of such energy storage systems in their regions or possibly in their communities. Of all energy storage solutions these would seem least objectionable, although there are human beings would would object to anything.

I heard an estimate in a news discussion recently that 1/4th of any population will object to anything that might be proposed for any reason.

That might be an assessment of human nature. I got the impression it came out of frustration with efforts to try to persuade groups of people to perform simple precautionary medical procedures to protect vulnerable people from illness, but it seems to me (on first hearing) that is is probably close to the mark.

(th)

tahanson43206 · 2021-08-07 07:39:21

Follow up with more detail on book:

Thermal, Mechanical and Hybrid Chemical Energy Storage Systems
Authors are given as: Klaus Brun, Timothy C. Allison and (et al.) September 28, 2020
That is ** recent ** .... Paperback and Kindle are almost exactly the same price ($80+ and change)

Chapter 6 is about "Heat engine-based storage systems"

Section 6.2 covers cryogenc systems

Section 6.3 covers Pumped Heat

Section 6.4 covers Hydrogen storage ... I'm dubious about including that in a chapter about thermal storage

Section 6.5 covers compressed air

All in all, this book looks to me like a useful study guide for anyone considering going into business providing energy storage as a service.

Chapter 7 covers: Energy storage servces

Chapter 9 covers "Path to commercialization"

Chapter 10 covers "Advanced" concepts ... flywheels are included.... A rotating flywheel is certainly a source of instantly accessible energy for smoothing power fluctuations. It might well (from my admittedly limited perspective) be superior to other alternatives if the quantity of energy needed on demand is high, and response time must be near instantaneous.

(th)

SpaceNut · 2021-08-07 07:56:17

wow just saw first post content quotes about an iron battery creation with the natural heating and cooling cycles used to charge and discharge..

tahanson43206 · 2021-08-26 12:42:39

The article at the link below is a summary of energy storage today from the perspective of someone working in the field ...

The citation quoted below may be of interest to NewMars, since sand is available in some quantity on Mars ...

https://currently.att.yahoo.com/news/3- … 35519.html

Concentrating solar power is still relatively expensive. To compete with other forms of energy generation and storage, it needs to become more efficient. One way to achieve this is to increase the temperature the salt is heated to, enabling more efficient electricity production. Unfortunately, the salts currently in use aren’t stable at high temperatures. Researchers are working to develop new salts or other materials that can withstand temperatures as high as 1,300 degrees Fahrenheit (705 C).
One leading idea for how to reach higher temperature involves heating up sand instead of salt, which can withstand the higher temperature. The sand would then be moved with conveyor belts from the heating point to storage. The Department of Energy recently announced funding for a pilot concentrated solar power plant based on this concept.

Is there someone in the group who can speculate on what kind of conveyor belt might be used for this?

If such a conveyor belt is possible, I'm wondering how the hot/molten send would be stored.

(th)

louis · 2021-08-26 17:05:49

While it's no doubt useful to keep an eye on all forms of energy storage, is it really going to be an issue on Mars? On Mars you are (assuming a Space X mission) going to have to develop a substantial methane manufacture industry capable of producing perhaps as much as. or at least, 200,000 tons of methane per (earth) annum - assuming Musk's vision of a million person city on Mars were to be seriously pursued. Even if Musk's over-ambitious plans are cut back hugely, you could easily get to a situation where 20,000 tons plus of methane was being produced every year. Using a small proportion of the methane production - perhaps no more than 5% would provide plenty of energy storage.

The one thing you need to do on Mars is use labour efficiently - allocating people to develop expertise in different types of energy production and storage is not very efficient. Best to keep to a simple system of solar plus methane storage.

tahanson43206 wrote:

The article at the link below is a summary of energy storage today from the perspective of someone working in the field ...
The citation quoted below may be of interest to NewMars, since sand is available in some quantity on Mars ...
https://currently.att.yahoo.com/news/3- … 35519.html
Concentrating solar power is still relatively expensive. To compete with other forms of energy generation and storage, it needs to become more efficient. One way to achieve this is to increase the temperature the salt is heated to, enabling more efficient electricity production. Unfortunately, the salts currently in use aren’t stable at high temperatures. Researchers are working to develop new salts or other materials that can withstand temperatures as high as 1,300 degrees Fahrenheit (705 C).
One leading idea for how to reach higher temperature involves heating up sand instead of salt, which can withstand the higher temperature. The sand would then be moved with conveyor belts from the heating point to storage. The Department of Energy recently announced funding for a pilot concentrated solar power plant based on this concept.
Is there someone in the group who can speculate on what kind of conveyor belt might be used for this?
If such a conveyor belt is possible, I'm wondering how the hot/molten send would be stored.
(th)

tahanson43206 · 2021-08-26 17:44:13

For Louis,

This topic is about Thermal heat storage.

SpaceNut created the topic to discuss "thermal" heat storage.

Your post is about storing energy in the form of a chemical compound.

You didn't mention it, but oxygen must be produced and stored along with methane.

Both liquids must be cooled as well as compressed. Cooling a substance is the opposite of heating it.

Your comments are no doubt interesting when placed in the correct topic.

I think the post about use of sand as a medium for thermal energy storage is a reasonably good fit.

Hopefully someone will come along who can comment upon the suitability of sand as an energy storage medium.

***
For SpaceNut .. please think about how members can respond to ideas they pick up from one topic, that would be best entered into another topic.

In the case immediately at hand, Louis appears to have been inspired by a post about sand to think about how to store energy in liquid form.

Is there a procedure Louis might have followed in this situation.

How might you have handled the situation, if you had been Louis?

(th)

SpaceNut · 2021-08-26 18:20:08

Thermal energy has the issue of isolation to reduce energy heat loss. While mars is a low atmospheric loss rate its a conductive problem back to the mars surface. Sand once heat processed for volatiles and water is heavy and makes it that much harder to not see conductive losses.

The thermal energy of the methane reactor is a bit different than trying to store it as you are using it to convert c. and h to methane with the byproduct being exhaust co and water.
Yes concentrated solar is a means to product the temperatures but the time frame per day is short in comparison the time that we are not producing.

Void · 2021-08-26 19:00:53

By recollection I give a number of loss of 1/2 of heat by radiation should you be around 800 degrees, (I think F). It was just conversation spoken to us by a very high boss where I worked. So, immediately if you are working at those temperatures, you need a scheme to avoid that, or at least you might prefer to do so.

Sand storage is not necessarily wrong. But other options might be considered first.

Here is what I consider to be an effective way to store heat from scraps of electrical power not otherwise utilized:
https://polarnightenergy.fi/news

Else, I do believe that there are people with heliostats that are seeking to store energy in rocks, at very high temperatures, ~1000 C, I think.

It is not wrong for you to seek but perhaps it is necessary to also seek to define the limits. However, if you can sometime come up with a new trick, you might change what the limits are actually. Maybe.

Done.

Last edited by Void (2021-08-26 19:05:57)

Calliban · 2021-08-27 05:16:29

GW Johnson wrote:

Solar heat can be captured in water, and used for space heating. That's all low grade heat, with a low-grade heat end use. No conversion losses to speak of. Not a waste of high-grade energy, either.
But I must say, generating electricity from low grade heat has always been a very low-efficiency process heretofore (thermionic converters). This might well be a breakthrough of sorts. A 200-250 F range of heated fluid temperatures is achievable (see below).
In order to get solar-heated hot water temperatures over about 180-190 F here on Earth requires a modestly-concentrating collector, meaning a simple flat plate collector with modest-sized adjacent mirror surfaces. On Mars, the mirrors need to be larger to overcome the 2:1 intensity deficiency. That's still easily doable.
But you still need to plan on what else to do when the sun doesn't shine, be it night or dust storm.
GW

For thermodynamic machines exploiting a small temperature difference, there is also the issue that high fluid flow rates are needed per unit of harvested power. The thermal energy carried per unit mass of fluid is roughly proportional to temperature difference, though phase change energy flux is much greater than sensible heat under these conditions. When coupled with reduced efficiency over a smaller temperature difference, the fluid flow needed for each unit of power increases dramatically, almost to the inverse square of temperature difference. The result is very bulky heat engines, with big heat transfer surfaces, which are oversized and have high capital cost for the power that they produce. This is why no one bothers building sub-atmospheric steam engines here on Earth.

Mars has much greater diurnal temperature ranges than anywhere on Earth. Maybe this will make a difference. But capital cost of the prime mover is just as important as efficiency. The larger the temperature difference between hot and cold, the smaller the prime mover can be and the greater its whole system power density, collectors included.

One thing in favour of thermal energy storage is that it is a very cheap way of storing energy, especially for direct heat applications. Hot water, sand or crushed rock stored in a tank cost almost nothing. Batteries are expensive by comparison. Vaclav Smil provides a good comparison of cost: A 1 barrel oil storage tank (260 litres) costs $15-18. To store the same amount of energy in Tesla Megapack (1700kWh) would cost around $510,000. Latent heat energy storage has energy density of about 100kWh per cubic metre. So storing heat in a phase change material is 2-3 orders of magnitude cheaper than storage in batteries.

Last edited by Calliban (2021-08-27 06:06:32)

tahanson43206 · 2021-08-27 05:53:41

For SpaceNut, Void and Calliban,

Thank you all for considering the suggestion of melting sand for use as a thermal energy storage device.

Void, it seems to me that your reference to heating rocks comes closest to seeing the point of the exercise.

I am hoping that someone is inspired to investigate the system efficiency of the proposed energy storage method, if the aim is to provide space heating on Mars, where the ambient temperature is below human comfort level.

I am also interesting in suggestions for a method of conveying molten glass from the heating site to underground living quarters.

The model that came to mind overnight, is the Roman Villa designs which included floors through which hot gases from a wood fire flowed to provide very effective "central" heating.

since most Mars dwellers will be in underground habitats well protected from radiation, it is necessary to provide methods of heating the spaces with as little waste as possible, since the available Solar energy supply is so much less than that of Earth.

It seems to me that storing thermal energy in molten sand has a number of distinct advantages:

1) The energy is non-toxic
2) The energy is concentrated
3) The energy can be transported (that was the focus of my original question about conveyor belts)
4) The energy can be harvested without a lot of effort
5) The energy storage medium can be re-used without degradation indefinitely
6) Losses of the energy storage medium through re-use seem unlikely

In considering the proposal to heat the interior of underground space with molten sand, I think the overall simplicity of the method, it's (apparent) efficiency at transfer of thermal energy from the Sun to the habitat, and reliability over extended periods of time make it a strong contender for planning.

I am hoping someone will think about how to most efficiently and safely transport molten sand to the underground heat distribution point.

The medium will have solidified when it is returned to the heating facility. It is the molten state that presents a challenge for operators of a central heating system on Mars.

The method could be used by a single family, in underground quarters some distance from Mars cities or towns.

The quantity of thermal energy needed would be less, but the challenge of safely handling molten sand will be similar.

As the quote (by Calliban) of the comments of GW Johnson remind us, any such system dependent upon Solar energy will be less reliable than nuclear energy. Any habitat heating plan for Mars (or any similar environment) must include a backup component that can sustain the inhabitants when the Solar resource is insufficient.

Update at 8:24 local time:

For SpaceNut .... It's been a while since we updated My Hacienda ....

The recent discussion of molten sand as a thermal energy storage method may yield a useful addition to My Hacienda in the HVAC category.

A related specialization is mirrors for concentration, which I'm pretty sure are ** not ** present in today's My Hacienda collection.

Production of mirrors implies molten sand as a construction medium, so the facility can be used to make itself, once the initial investment yields a combination of mirrors able to create a mirror on it's own.

Production of a suitable reflective backing material on Mars may be a challenge.

For anyone interested in the process of making mirrors on Mars .... please add insight or actual information if you have time.

Update at 8:27 local time ...

Making glass plate using concentrated solar power is a (admittedly long term) way to reduce dust storms on Mars.

A facility to make glass plates using concentrated solar power can be automated, and facilities can be constructed all over Mars as time permits.

(th)

Calliban · 2021-08-27 07:19:01

It was partly concerns over system reliability that led me to explore the diurnal solar heat engine as an alternative to PV on Mars. This would include thermal energy storage in the form of water and brine as phase change materials. Given the high embodied energy and commensurate low EROI of PV, I was interested in investigating thermal systems as an alternative that would provide both inbuilt storage and reduce embodied energy. The high day-night temperature swing allows the use of simpler systems than would ever be possible on Earth. During the day, we could collect heat via flat plate collectors and use it to melt pure water at O°C. At night, temperatures decline to -90°C. The same panels could radiate heat and freeze a brine solution at say -80°C. A heat engine using CO2 working fluid could operate between the two tanks. Given the low cost of water tanks used as heat stores, both hot and cold tank could be oversized to store days or weeks worth of heat, partially mitigating any supply disruption introduced by dust storms.

The problem with this concept is that it would suffer from very low effective power density, even worse than PV. A heat engine working between a cold source at 210K and a hot source at 270K, would have a Carnot efficiency of 28%. Typical Rankine cycle achieves about two thirds Carnot efficiency, so realistic efficiency is 19%. However, the power density of the collection panels is limited by the rate at which they can reject heat. If the panels radiate at -80°C, then the stefan-Boltzmann equation tells us that they will be radiating some 79W of heat per square metre. If the panels radiate for 12 hours out of 24, then total radiated heat will be 0.95kWh heat per square metre per day. But for every 1kWh of power generated, the panels must radiate some 4.2kWh of waste heat (19% efficiency). So the effective power density of the panels is 0.22kWh(e) per m2 per day, or on a continuous basis, about 9W/m2. That is only one quarter of the power density of photovoltaic panels. One could argue that thermal panels are much energetically cheaper to produce. But they would require plumbing, which PV panels do not.

Low temperature thermal generation cycles would appear to me to trade one problem for another. Heat is a very efficient energy storage medium, but it works best if heat is intended as the end use. Storing heat in much hotter materials like sand, would also appear to be most efficient as end use storage, because electricity or high quality heat is needed to heat the sand up to begin with. The thermal energy store allows us to displace the load in a way that permits the input electric power to be more variable. Germany has experimented with thermal energy storage in sand and concrete as a means of storing electricity. Variable electrical energy is input to heating elements in the storage material. Steam pipes pass through the store, generating continuous baseload electricity. These concepts work in combined heat and power mode. For each MWh of electricity that goes in, about 30-40% is recovered as electricity and 60-70% as hot water for district heating. On Earth, the downside of this arrangement is that district heating is expensive to install and the heating season is only 3-6 months long. On Mars, the heating season lasts all year and we can design our cities from scratch.

Last edited by Calliban (2021-08-27 08:07:07)

tahanson43206 · 2021-08-27 08:30:01

For Calliban re #22

Thank you for your thoughtful and wide ranging contribution to the topic!

SearchTerm:Calliban on thermal energy -

Your post implies several specializations to support the variations you've described

If an entrepreneur were to decide to compete in this arena, what skills would the staff need?

it would seem necessary to plan to fabricate all the components on Mars, so the support chains need to be identified as well.

That is the purpose of My Hacienda .... Only the surface of specialties that would be needed have been identified so far.

***
It should be possible to quantify the flow of Solar energy through a thermal heating system to delivered comfort in a habitat. Using the Roman villa as a model (as i am misremembering what it was), the molten sand would be transported into a cavity under the floor of the habitat. The floor would be designed so that hot air beneath would propagate throughout the material. Ie, the material would have high heat conductivity as well as strength to support the planned load above. how the heat would be regulated is an interesting question, since the molten sand would arrive at a high temperature which (I presume) would fall off in a logarithmic fashion instead of linear.

The need is to maintain a constant temperature of the habitat floor.

This should be an interesting problem in heat management for someone with a background and experience in that arena.

(th)

SpaceNut · 2021-08-27 09:50:17

Its not so much how you use it as how its created, what's the working media or fluid, what is the rate of creation vs consumption and what is the backup potential of the reserve size of storage.

Calliban · 2021-09-03 06:22:53

This company is developing a regenerative thermal battery that converts electricity into stored heat and then back into electricity again.
https://ease-storage.eu/wp-content/uplo … l_PHES.pdf

The relatively large temperature difference between the hot and cold stores, is probably an attempt to minimise the pumping losses inherent to a system that requires fluid transfer. This maximises efficiency. The main benefits of TES over other means, are the very low cost of the storage medium. This is good if you want to store energy for longer periods than would be affordable with your traditional battery.

Most useful for static energy storage in support of the electric grid. But it could also power large vehicles, like trains, trucks and ships. Generally speaking, thermodynamic systems get more efficient as you scale them up.

Last edited by Calliban (2021-09-03 06:29:41)

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