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Giant 'sand battery' holds a week's heat for a whole town

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Re: Giant 'sand battery' holds a week's heat for a whole town

#81

Post by lstodd »

fbdab103 wrote: post #64
noqc wrote: post #60

Earlier quoted context omitted.

Peak solar is peak A/C usage in the summer, which is typically more expensive than heating. In colder times more energy is used at night, but I think less energy is still used at night in the winter than in the day in summer.

That does not seem right. A hot day in summer might be 35C->20C (95F->68F). Winter is going to be more like -10C->20C (15F->68F) twice the temperature gradient to overcome.

That does not seem right.

-10С to +20C .. I can't even think of a place with such a swing.

Harsh continental climate winter is maybe -30C to -20C or so.

Re: Giant 'sand battery' holds a week's heat for a whole town

#82

Post by noqc »

lstodd wrote: post #81
fbdab103 wrote: post #64

Earlier quoted context omitted.

That does not seem right. A hot day in summer might be 35C->20C (95F->68F). Winter is going to be more like -10C->20C (15F->68F) twice the temperature gradient to overcome.

That does not seem right. -10С to +20C .. I can't even think of a place with such a swing. Harsh continental climate winter is maybe -30C to -20C or so.

he's saying that you need to get the temperature to 20 from -10.

Re: Giant 'sand battery' holds a week's heat for a whole town

#83

Post by progfix »

anonu wrote: post #44

It feels that Europe is so far ahead the US in matters of environmental sustainability. Why is that? Is it more dense than the US, so they need to be more careful with resources?

Civil engineering in general is more advanced in Europe. The oil crisis in the 1970 and the subsequent use of thermal insulation made "Bauphysik" (building physics) an integral part of the planing process. In the US you just rely on more heating/cooling power instead.

Just as an example: >=16cm thermal insulation + heat pump or solar thermal energy + double or triple pane windows have been standard for new single family homes since at least 2005 in Austria.

Re: Giant 'sand battery' holds a week's heat for a whole town

#84

Post by Newlaptop »

noqc wrote: post #60
bicebird wrote: post #25

I was thinking of ways to get around the peak solar generation being when you don't need it for heating and genuinely really heartening to hear about solutions like this. The article doesn't mention the costs or complexity in building each unit but definitely implies it's cheaper than storing it batteries, which makes sense if it's essentially a heating element buried in sand. Wonder what the smallest viable size wou…

Peak solar is peak A/C usage in the summer, which is typically more expensive than heating. In colder times more energy is used at night, but I think less energy is still used at night in the winter than in the day in summer.

Using the term "energy" here is suboptimal because it's mixing grid electricity with gas power.

A/C tends to be powered from electrical grid. Heat is often from propane or fracked gas.

More energy overall is used to heat homes in cold climates, but cooling homes in hot climates creates the challenging grid demand.

Re: Giant 'sand battery' holds a week's heat for a whole town

#85

Post by slow_typist »

Retric wrote: post #75
immibis wrote: post #46

Earlier quoted context omitted.

Any system that involves an electrical solar panel connected to a low-temperature electrical heater is likely to be better served with a solar hot water panel, by about a 10:1 ratio.

More like 4.5:1 solar is 20% or so efficient and solar thermal is only like 90% when including losses. Anyway, the real question here costs both in equipment and labor. Solar hot water panels involve plumbing and need radiators etc they quickly pay for themselves when heating a large home but don’t scale down very well. Running the numbers I was surprised how cost competitive the sand bucket is for something like a c…

The monetary case of PV does not account for the damage that is done to the environment over the entire lifecycle. Solar hot water panels are ecologically superior. Not only are they more efficient in W/sqm. Their production is not as energy intensive (plumbing included), the recycling process is less complex, poisonous materials can mostly be avoided. If heat is the desired product, they probably beat PV by an order of magnitude in the energetic dimension.

Re: Giant 'sand battery' holds a week's heat for a whole town

#86

Post by foofie »

m463 wrote: post #72

I get that sand is inexpensive and simple and I like the idea - especially since it scales to an entire town (!) But I can't help but think of one "technology" that could make a scheme like this MUCH more effective. a phase change. for example, it takes 1 calorie for water to go from 30 to 31 degrees F, but but it take 80 calories to go from solid at 32 to liquid at 32 F. A project I remember reading about that was r…

> But I can't help but think of one "technology" that could make a scheme like this MUCH more effective.

I think this is one of those things that drive home the point that there are fundamental differences between physics and engineering.

The article states that the thermal silos are heated with excess energy from the power grid. This alone tells you right from the start that efficiency is not the primary requirement.

Sand is inert, doesn't decompose or degrade, is readily available, is easy to work with, and has no moving parts. You can make it work in a silo, or digging a well to fill it with sand. In fact, geothermal heat pumps are already used extensively in residential buildings to regulate temperature. You just have to drill a hole in the ground that's deep enough, run a water pipe through it to heat/cool the water, and run that water through your building to heat/cool the environment. The nifty trick of Polar Night Energy is that they introduce the extra step of actively heating the thermal source with cheap energy supplied by the electrical power grid.

This sort of argument is like complaining that a Formula 1 car is far more efficient than a Volkswagen Golf. Yes it is,but that's a mute point.

Re: Giant 'sand battery' holds a week's heat for a whole town

#87

Post by freddie_mercury »

m463 wrote: post #72

I get that sand is inexpensive and simple and I like the idea - especially since it scales to an entire town (!) But I can't help but think of one "technology" that could make a scheme like this MUCH more effective. a phase change. for example, it takes 1 calorie for water to go from 30 to 31 degrees F, but but it take 80 calories to go from solid at 32 to liquid at 32 F. A project I remember reading about that was r…

> I get that sand is inexpensive

It depends where you are. Sand thieves are a thing in many places around the world.

Here's a story from 2015 about how residents in one area have lost 25 hectares of land to sand thieves.

https://tuoitrenews.vn/news/features/20150524/residents-losi...

Or a police captain whose legs were severed while trying to apprehend sand thieves.

https://www.vietnam.vn/en/dien-bien-moi-vu-dai-uy-cong-an-bi...

And here's a longer from article on the phenomenon:

https://www.mekongeye.com/2023/05/01/mekong-delta-sand-minin...

tl;dr sand is used in construction

Re: Giant 'sand battery' holds a week's heat for a whole town

#88

Post by lstodd »

noqc wrote: post #82
lstodd wrote: post #81

Earlier quoted context omitted.

That does not seem right. -10С to +20C .. I can't even think of a place with such a swing. Harsh continental climate winter is maybe -30C to -20C or so.

he's saying that you need to get the temperature to 20 from -10.

Ah. My bad.

Still, if you got this kind of temperature gradients, and I happen to have lived in such a place, you also got at least 100mm mineral wool insulation or eqivalent. Which is poor by the way, and people do invest into 200 or sometimes 300mm. Which makes CO2 and moisture control more of a problem than heating. You basically either heat the outside via ventilation anyway, or invest into heat exchangers. Since complex HVAC systems come with maintenance burden, people just put up 50-100KW-ish heaters, be it natgas or wood and declare the problem fixed.

Re: Giant 'sand battery' holds a week's heat for a whole town

#90

Post by nasmorn »

freddie_mercury wrote: post #87
m463 wrote: post #72

I get that sand is inexpensive and simple and I like the idea - especially since it scales to an entire town (!) But I can't help but think of one "technology" that could make a scheme like this MUCH more effective. a phase change. for example, it takes 1 calorie for water to go from 30 to 31 degrees F, but but it take 80 calories to go from solid at 32 to liquid at 32 F. A project I remember reading about that was r…

> I get that sand is inexpensive It depends where you are. Sand thieves are a thing in many places around the world. Here's a story from 2015 about how residents in one area have lost 25 hectares of land to sand thieves. https://tuoitrenews.vn/news/features/20150524/residents-losi... Or a police captain whose legs were severed while trying to apprehend sand thieves. https://www.vietnam.vn/en/dien-bien-moi-vu-dai-uy-c…

It is still inexpensive, they just steal a lot
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