Limestone-based Thermal Battery

SpaceNut · 2023-06-20 19:18:51

Seems like a metal tank is required for the heat to approach boiling with no air within it. Out shell is insulated to reduce coupling, from thermal thermos that is IR reflective facing towards the water. As we get higher in temperature, we will need the thickness of a pressure vessel for the water.

The size of the take gives duration of use but it's the temperature the does the power output increase that is need to overcome mass.

The insulation of the hot limestone would need to be a nob-asbestos type board that comes in a variety of thicknesses and would as above fill the outer shell layer of the tank. The tubing used inside of the limestone pushes against any expansion of the tube from the internal pressure and only has an inch of so within the vacuum of the reflective IR next shell. That small section can be over jacked with the next size up and filled to keep pressure integrity through to the connection outside.

The electrical is most likely a non-asbestos cord inside a penetrating fitting using compression to make the seal which is then passed to the charging electrical connection on the outside. Since we are striving for less temperature, we probably can use an oven heating element embedded in the limestone.

Calliban · 2023-06-21 03:53:51

From wiki: https://en.m.wikipedia.org/wiki/Stirlin … Efficiency

'Compared to an internal combustion engine of the same power rating, Stirling engines currently have a higher capital cost and are usually larger and heavier. However, they are more efficient than most internal combustion engines.[84] Their lower maintenance requirements make the overall energy cost comparable. The thermal efficiency is also comparable (for small engines), ranging from 15% to 30%.'

Another point the article makes is that to achieve the sort of power density you will need for a mobile engine, hydrogen or helium is needed as working fluid. That is problematic, because helium is expensive and rare and hot hydrogen diffuses through most metals.

None the less, if we could build a sterling engine that is compact enough to fit into a car and achieves a 25% efficiency, then we have a workable solution. Realistically, energy consumption per mile will be 3x than a comparable battery electric vehicle. That is an unavoidable drawback of using a heat engine for mechanical power. We can partially negate that problem by using hydraulic transmission and including hydraulic braking energy recovery. This is twice as efficient as electrical braking energy recovery. It also allows the engine to operate closer to its optimum efficiency.

Again, if we can also make effective use of the hot water that the vehicle produces, then the energy consumption of electric and stored heat vehicles begin to look more comparable. A 25% efficient engine, will produce 3 units of hot water for every one unit of mechanical power that reaches the wheels. If we assume that a building heat pump has a COP of 3, then those 3 units of hot water will displace another unit of electric power. So real exergy efficiency will be 50%. That compares to about 80% for an EV. But the EV efficiency advantage disappears when the increased embodied energy and less efficient braking energy recovery of the EV are factored in.

A stored heat vehicle becomes an even more attractive proposition if it can be charged with heat instead electricity. In many parts of the US, there is abundant sunshine for much of the year. If dish or trough collectors can be used to collect this and it can be stored in a stationary intermediary heat store, then vehicles could charge up rapidly from this heat store. At the very least, this could provide transport energy in summer months, with electricity only being used in winter. In Europe, SMRs would probably be needed to charge the heat stores. But direct heat is always cheaper than electricity. The concept has strong scale economies. The larger the heat demand and size of the heat store, the more efficient the solution becomes. A ship powered by stored heat, needs less insulation per unit heat than a car or truck. The limestone heat store can double as a ballast weight.

Last edited by Calliban (2023-06-21 04:29:25)

Calliban · 2023-06-21 05:44:38

Regarding the whole public vs private transport thing, we have always had both. Before cars, many people owned horses. That created problems of its own. Cities stunk and streets were full of shite. People walked a lot more, which was admittedly healthier. But it burned a lot of time. There was public transit in the form of boats, stage coaches and later railways. Railways added to air pollution. Ships were often dangerous and were disease vectors. The countryside relied heavily on human and animal labour on much smaller farms to produce and transport food. Country life was poorer because lack of rapid transit prevented participation in industrial production.

The invention and mass production of the car changed everything. It allowed unprecedented freedom of movement. People were able to work in the city but live outside of it in suburbs. New cities in the US were effectively giant, sprawling suburbs. Spacious, but fundamentally soleless places. In Europe, cities developed suburbs, but space was more limited and urban cores had already developed before mass motoring, so the process never went so far. There are just as many cars because people still want the freedom of personal mobility. Cars have definitely degraded the livability of cities. The problem is that sprawled cities just aren't compatible with mass transit, which requires relatively high urban density. European cities have higher urban density, so electric mass transit is more sustainable. Would it be beneficial for American cities to transition to more compact arrangements using electric rail? Probably. And it will probably happen eventually. But it is a decades or centuries long project. And there will still be a need for cars, they just won't be such a significant part of the urban landcscape.

In Europe, the velomobile could provide much of the mobility provided by cars without the resource issues.
https://en.m.wikipedia.org/wiki/Velomobile

But no one wants to ride in one of these if they are inndanger of being run over by an SUV. Bit of a problem there.

Last edited by Calliban (2023-06-21 06:06:04)

tahanson43206 · 2023-06-21 07:06:33

For Calliban re #103

Thanks for the nice summary of the history of why automobiles became so popular and successful.

It seems to me that trend is not going to change. Despite the fears and worries of some (on this forum and elsewhere) I think that the energy supply problem we face today is likely to be solved. There is a tremendous amount of human talent working the problem in many nations, and resources are being provided.

The (to me amazing) proliferation of electric scooters in American cities is a signal that low cost electric transportation is likely to be increasing and not decreasing in years ahead. The all-weather equivalent automobile (enclosed cab) to the scooters seems like a possibility. If that were combined with AI delivery of such automobiles when summoned by the customer, it seems to me the need for a personally owned vehicle would decrease in large cities.

Because this ** is ** the Limestone-based Thermal Battery topic, I'd like to offer the suggestion that those all-weather scooter equivalent vehicles might be powered by a thermal store with electric backup.

(th)

Terraformer · 2023-06-21 07:11:01

In Britain at least, there are quite a few byways that could be paved to be suitable for light vehicles such as bicycles and perhaps velomobiles. A 20mph speed limit gives ample time for the few heavy vehicles that use them to notice the other traffic. There are also a lot of quiet estate streets that can be used similarly, they just need to be signposted.

In America, a lot of suburban streets are quite wide as I understand? So there is at least room for segregated infrastructure for human powered vehicles.

Suburbs predate the automobile -- Streetcar Suburb. And the push for paved roads first came from cyclists.

I wonder if we can use a hydraulic accumulator on a velomobile for regenerative breaking, and giving an assist up hills? Probably illegal in the UK, whereas using a battery isn't.

Calliban · 2023-06-21 08:36:38

For discussion on velomobiles.
https://newmars.com/forums/viewtopic.ph … 97#p211097

kbd512 · 2023-06-21 11:38:02

Electric transportation will increase right up to the point where the battery materials and electrical conductor materials cease to be economically extractable, and then the prices will skyrocket (and EVs are already double to triple the price of gasoline powered equivalents), because most of those rare materials, locked up in electronics, will cease to be available. 95% of all smart phones ever created have not been recycled. Now, multiply out the quantity of Lithium-ion batteries and electric motors which never get recycled because it's not economic to do, and now you have a real problem that "more" is definitely not the answer to.

With direct heat energy, you collect about 90% of the Sun's input energy as heat, and start with about 75% of the total input energy from the Sun (pumping losses to get the hot water to where it must go to be used, heat dissipation over short periods of time from imperfect insulation), the machine to collect the energy is very simple (Aluminum coated steel), and easily recyclable (melting it back down into steel and Aluminum is not a problem). The moment you dictate conversion of heat into electricity, or photons into electricity, the amount of total energy converted / delivered per square meter of land area drops to about 25% or less. Beyond that issue, photovoltaics (large scale semi-conductor wafers) / electrical conductors (plastic insulated wiring and plastic electrical connectors) / microelectronic controllers (a slew of very rare and energy-intensive materials) are not easily recyclable and made from very rare and costly to obtain materials.

Sunlight is renewable. Photovoltaic cells are not renewable. Wiring is not renewable. Microelectronics are certainly not renewable. They're all replaceable with new ones, so long as we have the ability to extract more of the raw materials required. We don't recycle microchips. We can remelt the Silicon, now contaminated with all the dopants used to create electronic circuits unless they're chemically removed, but this is in no way "renewable". In practice, we grid up all the electronics, we burn away all the plastic, we collect any Gold / Silver / Copper / Aluminum metals, and we dump everything else into a landfill. All the rare Earth metals and dopants are put back into the Earth, because they cannot be economically recovered, and then we have to mine more of them. That is what actually happens to all the electronic trash we create, and also why I'm so against turning the entire planet into a toxic electronics waste dump.

At a more fundamental level, can you afford to throw away 2/3rds of all the potential energy you can harvest from the Sun from the word "go", and still have a long-term sustainable system using all these non-renewable electronics / batteries / plastics you're going to toss in the garbage after you're done using them?

Overall, your simple cycle efficiency using hot water is nothing to write home about, perhaps 35% overall, but it's still more than what you get using electricity.

So, why use direct thermal energy from the Sun or a nuclear reactor?:

I. The materials used last 3 times as long as electronics and batteries
There is no such thing as a photovoltaic cell or battery from 75 years ago still in operation today, unlike solar thermal and nuclear thermal power plants, and 75 years from now the same will be true.

II. You start with 3 times as much potential energy to consume, as compared to immediate conversion to electricity
This is the hot water energy which arrives at your gas station or home or place of business, ready-to-use. It's "fuel" by any other name, albeit very low energy density to make transport simple (pumping liquid water at 99C is easy) and spills ignorable events.

III. In terms of money, you can cover 64X more land surface area with solar thermal collectors as compared to photovoltaics
This is key to making low energy density systems affordable and therefore available to the widest possible range of customers.

IV. Most of the materials used are non-toxic and readily recyclable without extraordinary effort or energy input
The energy to recycle is essentially the same as the energy to make from scratch, so the materials "in the system" can largely "stay within the system". The primary materials for the car are 1/4" hot-rolled A36 plate and tubing (basic structural steel). The weight of the hot water box's primary structure is almost exactly 1 metric ton. I expect that the weight of the other chassis components will increase chassis weight to 2 metric tons. The hot water box is sized to contain 1,890kg / 500 US gallons of water, with sufficient void space to allow for thermal expansion if the water freezes. The prototype vehicle will contain in-tank electric heating elements to heat the water to temperature, since electrical power to do that is readily available, whereas the infrastructure to use direct hot water does not presently exist.

Aluminum radiator components are required to transfer thermal power through the heat exchange loop. The refrigerant used will be R290 (Propane), because the critical temperature and pressure are compatible with the intended application, and presently used in the heat exchangers of flash evaporator plants. A Stirling engine driven by the refrigerant gas will pressurize a pneumatic or hydraulic cylinder to accelerate the vehicle and also to directly power hub hydraulic motors. We will attach these motors to each wheel, so no transmission or driveshaft or axles are present to absorb power from the engine. The Stirling engine's piston(s) will have attached Copper radiator fins connected, to transfer heat from compression into an oil or glycol hydraulic fluid for near-isothermal compression.

Near Isothermal Stirling Heat Pump

In the YouTube video shown above, an electric motor is used to drive the Stirling engine compressor because it's intended to function as a more efficient AC compressor. We're using heat energy as input power, and the Stirling engine is producing mechanical output power in our setup. The Stirling engine could just as easily drive electric motors instead of hydro-pneumatics. We could either store the output energy using super-capacitors for rapid acceleration or supply it directly to electric drive motors, because that would also work. It might be "cleaner" that way (simplified power transfer setup), but then the user can no longer service their vehicle without expensive specialty equipment. If it's cheaper to use electric motors, then we should still use electric motors, but I doubt that's the case after all the hybrid power delivery equipment is included. The goal here is a practical and affordable EV with minimal electronics. Drive motor control electronics are okay, but motorized electronic door handles are expensive nonsense. We should remain agnostic on the final drive / propulsion solution, so long as it delivers on the promise of a dramatically lower cost EV.

Is hydraulic efficiency a myth?

Thermal power transfer loop / cycle:
1. hot water tank heated to 99C provides a heat energy storage reservoir
2. in-tank radiator assembly transfers heat into the R290 refrigerant gas, causing it to expand
3. Stirling piston engine re-compresses R290 and generates mechanical power output
4. Power output either compresses a gas in a hydro-pneumatic cylinder for acceleration purposes or is transmitted directly to hub motors using hydraulic fluid
5. External radiator assembly uses air to cool the R290 refrigerant gas before it makes its way back to the hot water tank
6. R290 flows back into the hot water tank where it absorbs more thermal energy, and the power transfer cycle begins again

V. You can feasibly store heat energy in massive quantities, because the "battery" is hot water or hot rock
We have extreme abundance of all the materials required to construct such a system, which we require, because low energy density systems mandate the use of large quantities of materials to collect and store significant amounts of energy. The weight of materials required is an unavoidable consequence of using low energy density systems. Rather than fixating on that aspect of it, we should be more interested in the enormous quantities of hydrocarbon fuels that don't have to be burned, and are thus available for other uses where weight is more critical, such as ships and aircraft.

tahanson43206 · 2023-06-21 12:18:45

For kbd512 re #107

Can you (would you) size a water installation for the test situation SpaceNut and I are offering?

Is there a sterling engine small enough to be affordable?

We are interested in turning a 12 VDC motor generator to deliver 100 watts into a load.

A function time of one minute would be quite acceptable.

What size water tank would accomplish that?

Is there a vendor you can suggest for the Sterling engine for this test?

(th)

Calliban · 2023-06-21 13:06:04

Hot rock will be a better heat source than hot water if you are charging with electricity. If you use hot water as your heat source at 100°C and outside air as your heat sink at 20°C, then Carnot efficiency is 21.4% and realistic stirling engine efficiency will be about half that. The mass energy density of water heated from 20°C to 100°C, is about the same as the equivelant mass of limestone heated to 325°C. But limestone is over twice as dense and the higher temperature allows higher efficiency of conversion of heat into mechanical power. It doesn't matter as much if the heat comes directly from solar concentrators or a nuclear reactor. But a hot water powered car would be a lousy way of using electricity. This only really works at all if heat can be harvested, stored and used directly, without conversion into electricity.

The reason I suggested that the vehicle carry a tank of water was to provide a heat sink. That way (1) We dont need a radiator on the front of the vehicle; (2) If the engine is only 15-25% efficient, we need to charge the vehicle with 4 and 6.7 units of electrical energy for each unit of mechanical energy that the engine provides. That is a lot more tolerable if we can capture the waste heat in hot water and use it for something else later on. But it adds to weight, increases rolling resistance and reduces effective range.

Let us consider a scenario where solar collectors generate hot water at 100°C, which is then stored in a large, well insulated tank. We then fill our cars with hot water and the heat is converted to motion with 10% efficiency. A 2te car needs 200KJ of work energy to drive 1km on flat asphalt. I am going to assume good braking energy recovery, which is around 80% efficient using hydraulic accumulators. So any energy spent driving up gradients can be recovered going down gradients. If the car refills with 1te of hot water, it will carry some 336MJ of thermal energy, assuming an outside temperature of 20°C. At 10% engine efficiency, that gives 33.6MJ of work energy. I am going to assume that a further 20% will be lost due to braking. That reduces useful work energy to 269MJ.

Effective range = 269,000KJ ÷ 200KJ/km = 1344km.

This assumes no loss of energy to air resistance, which will be minimal if we drive at 20mph everywhere, but will become significant if we drive at motorway speeds. But even if air resistance doubles energy consumption per km, range would still be a respectable 672km, or 418 miles. A hot water powered car begins to look like a workable solution, assuming a low cost source of direct heat.

Last edited by Calliban (2023-06-21 13:30:58)

tahanson43206 · 2023-06-21 13:14:40

For Calliban re system design ....

Use of water as a heat sink makes sense to me ...

For a test configuration, a used over filled with bricks would make a reasonable substitution for limestone, and most ovens can reach 500 F (260 C).

A water tank at room temperature is a reasonable substitute for your water cooling tank.

Can you size these components to deliver 100 watts of electrical load?

Input to the generator is estimated to be 133 watts.

Is there a small Sterling Engine that can produce that amount of power for at least a minute?

(th)

Calliban · 2023-06-21 13:48:52

Looking at UK statistics, cars and taxis drove 221.4bn vehicle-miles in 2021.
https://roadtraffic.dft.gov.uk/summary

If all of this transit were to be provided by hot water vehicles that consume 200KJ of work energy per km (322KJ/mile), that equates to 71.29E12 KJ of work energy, or 7.129E17J of heat. That is 2.1billion m3 of boiling water, or 2.1 cubic kilometres. As the water can be mostly recycled, I don't think this is a resource issue from a water perspective. In terms of energy production, it is 22.59GW of continuous heat. Under UK conditions, each square metre of land gets and average of 500kWh of direct sunlight each year. If solar collectors can harvest 60% of this, that comes to 300kWh/m2. How much collector area would be needed to harvest 7.129E17J/year?

Area = 7.129E17/(300 x 3,600,000) = 660,100,000m2, or 660km2 (255 square miles).

That looks quite achievable. Around large cities, SMRs could function in combined heat and power mode producing additional hot water as well as electricity.

How about storing the heat? We need 2 cubic kilometres of hot water per year. I am going to assume we build big insulated tanks that allow it to be stored for months with very little energy loss. If we assume 1 tank for roughly every thousand homes, then we need 22,000 tanks in the UK. Each tank would have volume 95,000m3. That is a cylinder roughly 50m wide and 50m high. A bit like those old gasometer tanks.

Lets say we put 1m thick of rockwool around the outside of steel tank. Roughly how much energy would it lose over a month? The thermal conductivity of rockwool is 0.04W/m.k. Outside temperature averages 10°C. The surface area of the tank is 47,124m2. Running the sums:

Q = KA x dT/dX = 0.04 x 47,124 x 90 = 170kW. Over 30 days, this would add up to 122,400kWh of heat loss. The tank contains some 8.87million kWh. So the tank will lose some 1.4% of its heat per month. This would see to be a low loss rate.

I think hot water powered cars could work. But setting up the required infrastructure would require a lotbof building work. But once completed, the tanks should last for centuries.

Last edited by Calliban (2023-06-21 14:27:14)

kbd512 · 2023-06-21 16:20:38

Calliban,

How is it that a standard HVAC heat pump is around 40% efficient at converting input electrical energy from an electric motor into thermal power transfer capacity?

For example, if 1,000W of electricity are applied to an electric motor driving an AC compressor, then it removes 400W of waste heat from whatever it's cooling. The temperatures involved in my concept are quite similar. Indoors, it's room temperature, meaning 74F. Outside, it's 100F or hotter. The temperature delta is only 26F, yet the average AC compressor is supposedly around 40% efficient, so 600W of input power are lost as waste heat and remaining 400W of power is cooling capacity that removes heat from the inside of a building. This modified Stirling engine claims to be between 60% and 70% efficient, so 1,000W of input electric motor power results in 600W to 700W of heat removal, by virtue of the refrigerant gas recompression cycle being near-isothermal.

Is there some reason we can't run that same process in reverse, going from 212F to 100F, a 112F temperature delta (4X that of a HVAC heat pump), converting at least 40% of the input thermal power from the hot water tank into hydraulic fluid pressure to drive the vehicle?

SpaceNut · 2023-06-23 15:22:29

I have been reading about the compressor versus pump to be a turbine which is using the item is a reverse connected manner, with the compressor needing the guts altered to make it more efficient when operated in this mode. The pump will have a drop of efficiency of 3 to 5% when doing the same. The typical turbo charger is of the wrong air flow ration to make them work in this manner. This boiling down the internal mechanic cavity shape to blade shape for direction of use. Which brings me to doing some research on scroll pumps for this purpose of making the turn a shaft to create power rather than turning the shaft to move media.

SpaceNut · 2023-06-23 15:22:56

Something in this is setting this problem

If Stirling engines could be made better than why is it that the kilowatt reactor unit still only working at 25% of the heat to energy creation still?

Attempts to make this post at 11:35pm my time last night is giving the

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SpaceNut · 2023-06-23 16:55:08

https://en.wikipedia.org/wiki/Centrifugal_compressor
https://en.wikipedia.org/wiki/Turboexpander
https://en.wikipedia.org/wiki/Air_cycle_machine

kbd512 · 2023-06-23 19:55:46

SpaceNut,

I'm not quite following what you're trying to tell me about relative efficiency, but I'll keep pondering over it.

SpaceNut · 2023-06-25 09:35:49

Pumps are designed with torque being applied to the shaft to move the fluid from low to a higher pressure with given internal fins, paddles or other shapes within its chamber. There is some friction of that fluid and heat released as its compresses before it exits the pump orifice that is smaller than the entrance.
A turbine uses the pressure flow of fluids to move a high pressure to low which is the opposite to a pump's direction, the loss is due to the internal wake of fluid flow. This happens with blades of a windmill.

Calliban · 2023-06-25 11:07:50

I am no expert on pumps. But I do know that in most situations, centrifugal pumps are the most energy efficient option. But one problem they do have is limited pressure ratio. To increase the ratio of output / input pressure, the impellor rotational velocity can be increased. But this raises two problems. Firstly, fluid friction is proportional to the square of tip speed, so efficiency goes down. Also, if dynamic pressure trailing the impellor tips drops beneath the vapour pressure of the liquid, cavitation will occur. This will destroy the impellor if it continues for very long. To get past this problem, the feed liquid can be pressurised. Rocket propellant tanks are pressurised for exactly this reason. Or, one can use multistage pumps, with each pump having pressure ratio of about 4. Most powerplant condensors have extraction pumps, which remove water at low inlet pressure and increase pressure to a few bars, and then feed pumps which inject water into the boiler. Positive displacement (piston) pumps are another option that do not have cavitation problems. But they tend to be bulky, expensive, less energy efficient because of greater friction and their output is pulsed.

There are lots of other pump designs, some of which are optimised for low pressure or simplicity. But centrifugal and positive displacement piston pumps are the ones that tend to be used most often.

kbd512 wrote:

Calliban,
How is it that a standard HVAC heat pump is around 40% efficient at converting input electrical energy from an electric motor into thermal power transfer capacity?
For example, if 1,000W of electricity are applied to an electric motor driving an AC compressor, then it removes 400W of waste heat from whatever it's cooling. The temperatures involved in my concept are quite similar. Indoors, it's room temperature, meaning 74F. Outside, it's 100F or hotter. The temperature delta is only 26F, yet the average AC compressor is supposedly around 40% efficient, so 600W of input power are lost as waste heat and remaining 400W of power is cooling capacity that removes heat from the inside of a building. This modified Stirling engine claims to be between 60% and 70% efficient, so 1,000W of input electric motor power results in 600W to 700W of heat removal, by virtue of the refrigerant gas recompression cycle being near-isothermal.
Is there some reason we can't run that same process in reverse, going from 212F to 100F, a 112F temperature delta (4X that of a HVAC heat pump), converting at least 40% of the input thermal power from the hot water tank into hydraulic fluid pressure to drive the vehicle?

I don't know why that is. A 40% efficiency is low for a single phase liquid pump.

Last edited by Calliban (2023-06-25 11:21:05)

SpaceNut · 2023-06-25 13:25:21

Here is an example of the power generator that is being added to a wind turbine design for the DYI build.
https://www.resystech.com/uploads/3/4/8 … uxhawt.pdf

Fundamentals of Turboexpanders “Basic Theory and Design”
http://www.simmsusa.com/wp-content/uplo … anders.pdf

Sure, this is small at Build and design OF A 1 KILOWATT ORGANIC RANKINE CYCLE POWER GENERATOR
https://www.geothermal-energy.org/pdf/I … _Final.pdf

But you can only work with what you have....

Update
Th ignore the wind and look at the connection to a shaft to which the rotation turns in this case an "axial flux generator" or aka pancake generator or motor Commonly found in front load washing machines. This is an off the shelf device that can be used to create power. Power generation is caused by shaft rotation coupled to a device that does this.

The turbo expander is just what is going to cause the turning with pressure change from hot co2 through the device that will turn a shaft for the generator.

the last link is what we are trying to create

tahanson43206 · 2023-06-25 14:49:04

For SpaceNut re wind generators .... These look like valuable posts, that might be copied into topics that are more wind focused.

I'd like to see this topic remain fairly close to the original intent, with the caveat that kbd512 can redirect the flow as he might prefer.

I'm looking forward to July, when a new budget will have a small opening for a digital power meter for the test rig I'm hoping to build.

It is not clear to me at this point, that Calliban and kbd512 are going to be able to deliver a solution that uses the Thermal Battery concept to drive a generator, but if it is possible at all, I'm confident they can pull it off.

(th)

Calliban · 2023-06-25 16:27:34

I have been giving some more thought to hot water (90+°C) as a vehicle energy source. It occurs to me that if heat pumps are used to produce the hot water, then the whole process can be scaled up to operate at a high coefficient of performance. Heat engines experience higher efficiency as they scale up, because friction, thermal losses and other irreversibilities decrease with scale. Human beings use a great deal of heat at a range of different temperatures. Cold heat is used for refrigeration. Warm water is used for space heating and clothes washing. Low-medium heat is used for washing. Close to boiling water can be used for cooking. In a sensibly designed system, a town could deploy cascading heat pumps. One set of heat pumps would generate heat at 30°C. Some of this would be directly used. The remainder will form the cold reservoir for the next heat pump which would heat water to 60°C, for washing. Again, some would be used directly, whilst the remainder will form the cold source to a third stage heat pump which would heat the water to 90+°C.

Stepping up heat in this way allows us the benefits of economies of scale and efficiencies of scale. The first stage 10-30°C pump will be the largest and the yielded heat could be stored underground. The 90°C hot water, could be used as a vehicle energy source and a stationary electricity store. If a heat pump can produce hot water at 75% of carnot efficiency and a heat engine can convert the heat back into mechanical power at 75% carnot efficiency, then overall storage efficiency is 56%. Hot water can be stored in very large volumes in covered reservoirs. Hot water is therefore a way of converting intermittent mechanical wind energy into a storable reservoir of heat that can be converted into mechanical power in vehicles and electrical power plants.

In the UK, sunlight is relatively weak. But there is more wind than we really know what to do with. We would build wind farms, consisting of dozens of wind machines in a line, each connected to the others by a common underground rotating shaft. The shaft would transfer mechanical power to a cascading heat pump. Heat at different temperatures would be yielded by the pump cascade, some of it used directly. The remainder providing heat for the next stage heat pump.

Hot water at 90°C could also be produced by low temperature nuclear reactors that are easy to build. We have discussed aqueous homogenous reactors before. There is also potential to produce non-pressurised heavy water reactors, which generate heat from aluminium clad, natural uranium fuel. This reactor could operate at atmospheric pressure, so shouod be easy to build.

Last edited by Calliban (2023-06-25 16:44:14)

SpaceNut · 2023-06-25 16:59:58

We do not want water as it freezes and then all tubing will split, and the machine is junk....

kbd512 · 2023-06-25 18:46:40

SpaceNut,

I've already accounted for freezing in the volume of the vehicle's hot water tank. As far as the rest of this concept is concerned, if you bury hot water pipes, then they're not going to freeze. We already bury cold water pipes and those don't typically freeze, so hot water pipes with a large volume of hot water constantly moving through them definitely won't freeze. One of the major points of my proposed scheme is to build up a massive reserve of hot water to do what we would otherwise do with electricity and hydrocarbon fuels.

I'm agnostic on solar / nuclear / geothermal power. So long as it's reliable and scalable to the degree required to replace / supplant most of what we use for transport and electrical power generation, it's done its job. I really don't care in the slightest how we get the heat energy into the system, so long as it doesn't require burning massive quantities of additional hydrocarbon fuels. The system is not an object of affection for me, it's merely a means to an end. I don't get "warm fuzzies" because we selected A over B. If someone snapped their fingers and we had the country re-powered with nuclear reactors or geothermal wells, so what? Who cares? I would make the heat source selections based upon total cost and the practicality to build out most it over a reasonably short period of time, of about 10 years or so. Solar thermal ain't gonna work too well in Maine. They need nuclear reactors. Nuclear reactors in the middle of Death Valley is a solution in search of a problem.

I feel the samw way about Mars. We're going to need nuclear reactors on Mars. There's near-zero wind and about as much sunlight as you get in Antarctica on winter day. The conditions on the ground settle the argument about what power source gets selected. The blow-harder solutions are absurdities produced by backwards ideologies that can't come to terms with the limitations of our energy technologies.

Calliban · 2023-06-26 16:26:38

The Chinese have been quite successful in building low temperature heating reactors. These are pool type reactors that operate at atmospheric pressure and produce hot water at 90°C. These powerplants are very simple, because negative reactivity temprrature coefficient is greater at low temperatures and the huge non-pressurised pool provides an enormous decay heat sink. The design can rely on natural circulation for heat transfer and boiloff and make-up for DHR.

Very simple systems like this could provide all of the heat we need for hot water powered vehicles. On Mars, simplified heavy water heating reactors, could provide the heat we need for agriculture, using heavy water moderator and aluminium clad natural uranium as fuel.

Last edited by Calliban (2023-06-26 16:32:32)

Terraformer · 2023-06-27 12:40:31

If we're talking about seasonal storage of large quantities of water, why not go to the other way and create large blocks of ice during the winter? Being able to use a 0c heat sink rather than ambient should boost the energy we can extract from hot water...

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