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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

#171

Post by pantalaimon »

dandy23 wrote: post #160
onetimeuse92304 wrote: post #127

100MWh = 3.6 * 10^11 joules sand's heat capacity = 830 J/kg degree C sand battery size is "13m tall and 15m wide". Assuming most voluminous possible shape that's 13m * 15m * 15m = 2925 cubic meters of sand (100% fill, no account for insulation, etc.) Dry sand density is about 1600kg/m3 Total weight of sand would be 2925m3 * 1600kg/m3 = 4.7Mkg (4.7kt) 4.7Mkg of sand has a heat capacity of 830J/kg * 4.7Mkg = 3.9 * 10^9…

I cannot explain the physics, but a big rock that has basked in the sun is really warm for a long time after sunset. A bucket of water loses its temperature faster. The higher density of rock probably plays a big role.

For water evaporative cooling is a big factor

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

#172

Post by aydyn »

onetimeuse92304 wrote: post #127

100MWh = 3.6 * 10^11 joules sand's heat capacity = 830 J/kg degree C sand battery size is "13m tall and 15m wide". Assuming most voluminous possible shape that's 13m * 15m * 15m = 2925 cubic meters of sand (100% fill, no account for insulation, etc.) Dry sand density is about 1600kg/m3 Total weight of sand would be 2925m3 * 1600kg/m3 = 4.7Mkg (4.7kt) 4.7Mkg of sand has a heat capacity of 830J/kg * 4.7Mkg = 3.9 * 10^9…

Other considerations, water grows microorganisms and is a solvent. The upside of sand is (presumably) less maintenance.

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

#173

Post by singleshot_ »

Tade0 wrote: post #163
onetimeuse92304 wrote: post #127

100MWh = 3.6 * 10^11 joules sand's heat capacity = 830 J/kg degree C sand battery size is "13m tall and 15m wide". Assuming most voluminous possible shape that's 13m * 15m * 15m = 2925 cubic meters of sand (100% fill, no account for insulation, etc.) Dry sand density is about 1600kg/m3 Total weight of sand would be 2925m3 * 1600kg/m3 = 4.7Mkg (4.7kt) 4.7Mkg of sand has a heat capacity of 830J/kg * 4.7Mkg = 3.9 * 10^9…

I can think of several reasons I would choose sand: -Order of magnitude smaller coefficient of thermal expansion. -No real risk of phase change - freezing or boiling. -No problems with corrosion/scale in high temperature. On one hand regular water contains minerals which can build up on the heat exchanger element, on the other demineralized water sucks in carbon dioxide and oxygen from the atmosphere, causing corrosi…

Ease of transport.

I’ve got a few trucks in which I could transport tons and tons of and but I’d struggle to move more than a few hundred gallons of water at a time. I’d guess most transportation outfits are similar and costs in accordance. Point: sand.

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

#174

Post by Retric »

slow_typist wrote: post #165
Retric wrote: post #138

Earlier quoted context omitted.

PV’s falling prices have also been associated with falling environmental harm. When you’re talking multiple orders of magnitude you just cannot require as much in production. IE: You can’t burn 500 gallons of gas if the end product costs 500$. That applies not just to transportation but also how much material and thus mining the raw materials you need, including refining them, the amount of chemicals you can use per…

The argument is valid, if energy is not subsidised. However, burning pv for resistance heating is still wasteful and should be avoided. It is only acceptable for peak production that cannot be put to better use.

It’s wasteful of electricity not necessarily resources.

One of the numbers I was looking at compared air sourced heat pump at night when it’s coldest vs this kind of resistive heat battery. Solar panels are far cheaper and better for the environment on a kWh/day basis so even if the COP is 3 (or less it gets colder at night) * 90%(losses from battery) = fewer panels you more than offset it by needing far more batteries.

Obviously solar thermal setups have advantages if you need lots of heat, but they are also wasted most of the year. If 8-10 months a year you’re only using them for hot water then annual efficiency is closer to 25% than 90%.

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

#175

Post by NathanKP »

onlyrealcuzzo wrote: post #151
merelysounds wrote: post #139

Earlier quoted context omitted.

> But sand is quite expensive so my question is, why sand and not water? The article says they will use a byproduct from a local industry, perhaps it's available for cheaper. "The sand itself will also be sustainably sourced – it’ll consist of crushed soapstone, which is a manufacturing byproduct of another local industry. This material can apparently conduct heat even better than regular old sand.".

> The article says they will use a byproduct from a local industry, perhaps it's available for cheaper. Cheaper than water?!

It's the not the cost of obtaining the water that makes water less viable, it's the cost of storing superheated water. Water has this pesky ability to expand 1600 times larger when it goes over 212 degrees Fahrenheit. That means that if not handled carefully you get deadly steam explosions.

Hot sand / crushed rock doesn't have the same problem. If you read in the linked article it says

> with the sand heated to somewhere around 500-600 degrees Celsius (932-1112 °F).

That would be extraordinarily hard to do with water as you'd need significant containment and safety measures.

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

#176

Post by llm_trw »

pi-e-sigma wrote: post #109
dragontamer wrote: post #42

Earlier quoted context omitted.

1 cubic meters of water chilled 10C below ambient is 40MegaJoules of energy. Or in other words: 11kW-hrs of cooling, comparable to an entire Tesla Powerwall. We aren't talking about entire swimming pools here. Just a few cubic meters of water. Shift the temperature delta as you see fit but... It's actually very space efficient.

Typical residential air conditioning is using 4kW of power. So your 40MJ of energy would be used up in 40MJ/4kW=10000 seconds, or just 3 hours. And its only theoretical, because it assumes 100% efficiency in storage and conversion

It's odd how often battery enthusiasts don't understand the difference between energy and power.

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

#177

Post by mattclarkdotnet »

defrost wrote: post #129
mattclarkdotnet wrote: post #119

Earlier quoted context omitted.

As you allude to, our water in WA is notably soft, maybe that helps? I mean it's full of iron but that mostly just seems to cause staining not clogging. That said, a heat pump running at 4:1 COP coupled to 20% efficient solar panels gets you right back to the same efficiency as solar thermal, with a lot more flexibility.

I'd rather run both in parallel, and I do, as do most of the people here abouts. No single point of failure, sun heats the water directly and provides power, with a breakout box that accepts power in from the grid ( if required), exports excess for points, hopefully that gets better over time, and accepts a local generator input if the PV panels are offline for some reason when there's a local grid power outage. This…

Totally agree. I'm in the city so don't have roof space for both. If I could I would totally do it.

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

#178

Post by ZeroGravitas »

dragontamer wrote: post #4
gorpy7 wrote: post #3

This is great technology, simple and effective. I’ve spent many hours reverse engineering to see how effective and expensive it might be. I’ve found it’s very cost effective but heat can be hard to calculate. i like that they did a prototype. i think i’ll do one at some point. for an individual house it makes more sense to improve my insulation but i think ill still build a small version for fun.

IceBear went out of business with the opposite tech: tanks of water storing the cold generated from excess AC cycles. Cheap electricity can make cold, and then a fan can convert the cold water into cold air during peak hours when electricity was costlier. Fans still took electricity to run, but it'd only be a few hundred watts to run air-conditioning rather than kilowatts of power.

IceBear was competing directly with ever cheaper PV.

It's a tech for time shifting cheap overnight energy to the expensive daytime.

Installing PV gives you cheap power directly and correlates with air-con demand.

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

#179

Post by prometheus76 »

onlyrealcuzzo wrote: post #153
prometheus76 wrote: post #146

Earlier quoted context omitted.

I'm toying with the idea of building one of these to use as a pool heater. Has anyone here tried this?

Why not just do solar heating?

Because I have sunlight for a solar panel year-round, whereas I only have solar heat for a limited time.

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

#180

Post by dragontamer »

Danieru wrote: post #74
dragontamer wrote: post #66

Earlier quoted context omitted.

Energy is (sometimes) free, or even negative priced (!!!!). As it turns out: it's economically infeasible to turn off solar panels, wind, nuclear and sometimes Hydro (depending on water rights, it may be illegal to store water/energy at a water dam). In all of these cases, the energy is 0 cost or even negative cost.

You're confused, negative prices are not driven by techincal limitations. Solar, and especially hydro, and even nuclear can shut down just fine. Solar and Wind instead drive prices negative because they have subsidized contracts. Each country is slightly different in implementation, between Feed-in-Tarif vs Feed-in-Premium. In either method there will exist prices which are negative to the market but positive to the…

> In either method there will exist prices which are negative to the market but positive to the producer.

I'm talking about running air conditioners extra hard during low market prices (which includes free and/or negative priced periods of energy), and then storing that cooling power in single-digit cubic meters of water.

Negative market prices of electricity absolutely applies to this case.

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