[HN Gopher] A sand battery could transform clean energy
___________________________________________________________________
A sand battery could transform clean energy
Author : mauvehaus
Score : 83 points
Date : 2022-11-04 12:11 UTC (10 hours ago)
(HTM) web link (www.bbc.com)
(TXT) w3m dump (www.bbc.com)
| rob74 wrote:
| Er, this is probably a good heat storage system, but I wouldn't
| call it a "battery". A battery is something that you charge with
| electricity and then provides electricity when you discharge it.
| Or, otherwise said, a pumped-storage plant is closer to the
| definition of a "battery" than this thing...
| mnw21cam wrote:
| It's probably not even that good a heat storage system. And
| that's for two reasons.
|
| 1. Sand has a _lower_ heat capacity than water. Water is _much_
| cheaper than sand. Yes, you can 't heat water to 600C, but
| that's not a problem if you're just wanting to heat houses with
| it. The only reason I can see that they want to use sand is so
| that they can deliver higher temperatures, which are necessary
| for some fairly rare demands, or so they can generate
| electricity, which their system is going to suck at anyway.
|
| 2. There are more efficient ways to get hold of heat. They're
| using electricity to heat it, using a resistive element. A heat
| pump (for example) can give you 3-5 times as much heat as the
| electricity you put in, so why not just heat the houses
| directly with much less electricity used? They are using solar
| electricity to heat the sand, but PV panels are typically only
| 21% efficient, and they're expensive. A concentrating solar
| water heater is _very_ cheap and simple, and will give you your
| heat with a much greater efficiency.
| audunw wrote:
| > 1. Sand has a lower heat capacity than water. Water is much
| cheaper than sand. Yes, you can't heat water to 600C
|
| The price of the storage material is probably almost
| completely irrelevant in the total cost of this solution,
| when comparing sand and water. They even mention using sand
| nobody else wants. But using water will probably increase the
| cost of everything else.
|
| If you can heat sand to a much higher degree, the fact that
| it has lower heat capacity is irrelevant on its own. The fact
| that they explicitly mention that they were setting out to
| find if a solid material was better than water makes me think
| they've considered all these factors and found sand to be
| better in total.
|
| "The fan is the only moving part and it's easy to replace if
| necessary"
|
| Heat pump is a good idea, but it will add quite a lot of up
| front and maintainance cost. I've looked at heat pump water
| heaters myself, and it's hard to get the economics to add up
| in the short term. With a water heater or a system like this,
| the heat pump isn't going to be running constantly, and when
| you're running it you need a lot of power, so you need a
| large unit. Ideally a heat pump should be running almost
| constantly at a low rate to make sure it's operating at high
| efficiency and to pay for itself in a reasonable time.
|
| I don't know if there even are heat pumps that can
| effectively heat things up to several hundred degrees?
|
| I think it makes more sense to put the heat pump between the
| "battery" and the building it's heating, so you draw less
| heat from the battery to supply a large amount of heat to the
| building. Then you can use the same heat pump to extract heat
| from the air when the "battery" is empty. You'll get much
| better utilization of the heat pump.
|
| Btw, I think significantly cheaper and better heat pumps
| would be a hail mary for solving the energy / climate change
| crisis. So many things like this would suddenly become more
| economically viable.
|
| > A concentrating solar water heater is very cheap and simple
|
| Sure, but that's kind of a different solution. This could
| take energy from the grid drawing power from many sources
| spread out over a wider area. A concentrating solar heater
| would require a lot of area at the exact place where you want
| the storage unit. That's not always viable. Using water would
| probably increase the total volume significantly too.
| Xylakant wrote:
| > I think it makes more sense to put the heat pump between
| the "battery" and the building it's heating, so you draw
| less heat from the battery to supply a large amount of heat
| to the building.
|
| That's not how heat pumps work. They move heat from one
| medium to another - so using a heat pump to move one Joule
| from the battery to the house will lower the amount of heat
| in the batter by one Joule, same as if you use any other
| means.
|
| The efficiency gain that heat pumps provide when heating
| houses is that they essentially cool some medium (air,
| ground, water...) outside the building and move the heat
| into the building. Moving the heat uses less electricity
| than turning the electricity into heat via a resistive
| heating element. The outside medium gets warmed up by sun,
| or retains heat from a warmer season.
| amelius wrote:
| > Yes, you can't heat water to 600C, but that's not a problem
| if you're just wanting to heat houses with it.
|
| You can heat a home with 600C and some circuitry that steps
| it down to a comfy 22C. If that's more efficient than heating
| water, then I can see why they do it.
| mnw21cam wrote:
| It's not more efficient, for the reasons stated earlier.
| amelius wrote:
| It can be more efficient in the sense that you need less
| space, for example.
| adamdusty wrote:
| > The battery is charged overnight when the electricity prices
| are lower.
|
| Sounds like the battery is charged via electricity.
| automatic6131 wrote:
| But missing the crucial second half, releases electricity on
| discharge.
| tuatoru wrote:
| It's an accumulator for a district heating system, which
| are apparently common in Nordic countries.
|
| Traditionally district heating systems use waste heat from
| thermal generation of electricity, which heat is free.
| tomrod wrote:
| It's not a chemical battery, which releases energy as
| electricity, but electricity can certainly be generated
| using heat stored in heated/molten sand.
|
| Ultimately its about energy transfer, efficiency, and
| storage.
| Someone wrote:
| "Battery" is most often used with the meaning "Electric
| battery", but it is a broader term.
|
| https://en.wikipedia.org/wiki/Energy_storage: "A device that
| stores energy is generally called an accumulator or battery"
| Retric wrote:
| <pedantic>No, accumulator is the generic term battery is
| specifically the chemical storage: https://www.merriam-
| webster.com/dictionary/battery
|
| "a group of two or more cells (see CELL sense 5) connected
| together to furnish electric current"
|
| Battery is a generic term for collection of things working
| together, guns/generators/medical tests etc. This why
| batteries where initially called such, they are a collection
| of smaller cells operating together which doesn't apply to
| say pumped storage.
|
| Sometime battery is used descriptively Ex: "A Carnot battery
| is a type of energy storage system that stores electricity in
| thermal energy storage." Note they said it's a type of energy
| storage system rather than type of battery.
| https://en.wikipedia.org/wiki/Carnot_battery
| TheSpiceIsLife wrote:
| Words mean what people who use them intend them to mean.
| Retric wrote:
| If that where true then misspoken words would mean what
| the person intended, unfortunately people aren't
| telepathic.
| mdaEyebot wrote:
| "Mechanical batteries" are a thing, like flywheels or
| hydroelectric reservoirs. Batteries store energy, the
| electricity that flows in and out is just one way to manifest
| that energy. You could measure it in Joules rather than Watt-
| hours.
|
| At the end of the day, a chemical battery is a reusable bomb
| that is designed to go off very, very slowly.
| rz2k wrote:
| I wouldn't want to have tons of 600degC (1112degF) sand
| stored near a wood frame house or a forest either.
|
| > Wood placed in an oven at 700degF. catches fire almost
| immediately. At oven temperatures of 450deg-500degF., the
| wood gradually chars and usually ignites after several hours.
|
| > "Pyrophoric carbon," formed when wood slowly chars, absorbs
| and combines rapidly with oxygen. This produces heat which
| under certain conditions causes the charred wood eventually
| to catch fire at temperatures well below those required to
| ignite the original wood. Cases are recorded where wooden
| flooring in contact with steam pipes at 250deg-300degF. has
| caught fire after years of EXPOSURE.-FACTORY MUTUAL
| RECORD.[1]
|
| I disagree with most of the naysaying in this thread, but
| pretty much all energy storage that is easily accessed can
| also have a failure state that is difficult to handle. It
| would probably be impossible to save a structure with a
| 600degC blob resting against it.
|
| [1] https://www.fireengineering.com/leadership/ignition-
| temperat...
| [deleted]
| datameta wrote:
| Surely the sand battery idea is more for centralized
| designs than for being somewhere in the middle of the
| woods? A chemical battery or a water elevation system would
| suite that locale better. Industrial regions where a sand
| battery would be used aren't traditionally known for their
| wooded nature.
| mdaEyebot wrote:
| I suppose a leak would be serious, but presumably these
| sorts of large-scale batteries would be buried in a
| containment unit.
|
| Flywheel batteries are usually placed in small bunkers,
| because the failure mode of a giant rapidly-spinning
| concrete wheel jumping its bearings is not exactly pretty.
| Dams are usually designed with diversion channels and
| mechanisms to limit the damage if they burst. Etc.
|
| Really, it's strange that we are so cavalier about lithium
| battery failures compared to the other sorts.
| lastofthemojito wrote:
| > The answer nestling in Vatajankoski power plant, 270 km (168
| miles) north-west of Finland's capital, Helsinki, is remarkably
| simple, abundant and cheap: sand.
|
| Wait, I thought there was a sand shortage?
|
| https://www.bbc.com/future/article/20191108-why-the-world-is...
|
| https://www.reuters.com/business/environment/sand-crisis-loo...
|
| I guess there are different types of sand though?
| cjtrowbridge wrote:
| The article goes into detail answering these questions, in case
| you haven't read past the first paragraph before sharing your
| opinions;
|
| "The company uses cheap, low-quality sand that's been rejected
| by builders instead of high quality river-sand which is used in
| vast quantities for construction, leading to a global
| shortage."
| swores wrote:
| From the article:
|
| > _" The company uses cheap, low-quality sand that's been
| rejected by builders instead of high quality river-sand which
| is used in vast quantities for construction, leading to a
| global shortage."_
| mdorazio wrote:
| I'm confused... this is basically the same as molten salt, just
| with sand instead of salt. Molten salt has been around for a very
| long time and is how solar thermal power plants store energy and
| continue to generate power after dark. Is there an innovation
| here that I'm missing?
| marcosdumay wrote:
| I guess not needing an insulated tank (that can crack if the
| power runs out) makes things much cheaper. And the higher the
| operational temperature, the less difference it makes if you
| use a complex phase change design or a simple bunch of cheap
| sand.
|
| But I doubt 600degC is enough to make sand win.
| zdragnar wrote:
| Molten salt is very corrosive, and this only heats to 600C, and
| sodium chloride doesn't melt until 800C.
|
| This is a cheaper, lower maintenance option.
| scythe wrote:
| The molten salt used for energy storage is a sodium nitrate -
| potassium nitrate eutectic with an operating temperature
| range of 200-550 C and a much lower corrosion behavior than
| chloride salts.
| zdragnar wrote:
| ah, fair enough. The design in the photo is much more
| vertical than horizontal- maybe they're designing for space
| constraints? I would imagine 500*C molten salt would be
| significantly more efficient than sand, so the only
| charitable thing I can come up with is they're simply
| putting the cheapest materials they can (discard sand, free
| electricity) to good use.
| michael1999 wrote:
| Non-electic. Direct heat storage for district heating with zero
| high-tech involved. Resistive heaters, air ducts, a silo, sand,
| and some fans -- all established enough for utility use.
| zardo wrote:
| Different application and price point. This doesn't operate at
| a high enough temperature to make generating electricity back
| from it feasible, so it's only good for heating. But, you can
| build big and cheap for seasonal scale storage, and it can be
| underground with a secondary land use on the surface.
| zdragnar wrote:
| This seems rather strange to me, having immersed myself in the
| rocket mass heater community a bit.
|
| Sand is generally the last option to choose for thermal mass,
| because it is so inefficient at storing heat; the very air
| between the grains acts as insulation.
|
| Instead, clay (or clay mixed with straw to form cob) is the
| preferred medium for storing heat, as it is a significantly
| better conductor and stores much more heat energy than the air
| between the grains of sand.
|
| It seems like they are using the air as a medium here- the
| article states that they blow air through the sand, and the
| resistive bands heat up the air, which then sheds some of the
| heat onto the sand (or picks some heat up off the sand, depending
| on if it is storing or discharging).
|
| I guess the cheapness and simplicity of construction makes this a
| better option at the scale they're operating at, but it's pretty
| wild to imagine how much more efficient the system could be if it
| had been designed differently.
| LordHeini wrote:
| Don't confuse heat capacity with conductivity.
|
| And the air is blown through pipes in the sand, which means you
| need something which will easily surround the pipes.
|
| Solid materials would suffer from thermal expansion problems
| (like cracking), while liquids evaporate so sand seem to be a
| reasonable choice.
|
| For their application the conductivity does not really matter
| and the cheap reject sand was chosen because it has the best
| mass to price ratio.
|
| It is heated to 600degC so it would be not the best idea to use
| clay with straw ;)
| zdragnar wrote:
| Ah, I missed the pipes bit. Yes, that is exactly how the mass
| storage heaters I am familiar with work- pipes run through
| clay, which does need to be fully dried before you heat it to
| avoid cracking.
|
| I did overlook the 600*C bit at first- straw would definitely
| be a bad idea, lol. I still would guess that the additional
| cost of clay would be worth it. Clay is both more conductive
| AND has better capacity- the air between the grains of sand
| is an insulator, and has significantly lower storage capacity
| than the grains of sand themselves.
|
| Another option some people use if they don't want a permanent
| installation (or just need occasional portability) is large
| stones with gravel for fill. It's quite a bit less efficient
| than clay, but the larger size of the gravel and rocks inside
| make it a better option than sand.
|
| I imagine they have done the math on the cost of the sand and
| the efficiency they are getting out of it, it just goes
| against everything I have ever learned about thermal mass
| storage from the permie / rocket heater mass storage
| community.
| LordHeini wrote:
| Yep.
|
| I have not seen a picture of the filler but they said its
| the cheapest sand they could get (probably even free).
|
| So i assume it is mostly rocks and gravel anyway.
|
| Not sure about the math here, but it is surely cheaper to
| build a bigger tank with crappy sand than a smaller one
| with more expensive clay.
|
| I would say rocket heaters have more constraints on space
| while for a large industrial tank you would not really care
| about it being large and heavy.
|
| From an efficiency standpoint you will not run into many
| problems, since the efficiency of heat based systems is
| based on the thermal loss.
|
| Thermal loss occurs on the walls and in processing (like
| the rest heat in the air venting out of the system).
|
| The process losses are independent of your storage material
| and often unavoidable.
|
| And since those are large installations, the mass to wall
| ratio is really really good (square-cube law).
|
| If you make them big enough not much insulation is required
| and the overall efficiency is high.
| simplotek wrote:
| > Not sure about the math here, but it is surely cheaper
| to build a bigger tank with crappy sand than a smaller
| one with more expensive clay.
|
| It's also interesting that the sand is heated with energy
| generated from wind turbines and solar panels, which
| means that as long as enough energy is being thrown into
| the thermal capacitor, it will heat up with little cost.
| From this point onward, it's an economics problem. Either
| money is thrown at the efficiency of these heating
| capacitors, which brings at most small gains, or money is
| thrown in building additional storage capacity for cheap
| along with increasing how much energy is fed into the
| system. Would it be more cost effective in replacing sand
| with more efficient materials, or spend the money in,
| say, another cheap thermal energy source?
| zdragnar wrote:
| > Either money is thrown at the efficiency of these
| heating capacitors, which brings at most small gains,
|
| It really depends on whether the air in the system is a
| closed loop or not while they are building up the heat in
| the device. Sand is, at best, going to be about 1/3 as
| efficient as clay in an open system (hot air goes in,
| travels through some pipes, then comes back out as waste
| exhaust). This number is based on experiments with rocket
| mass heaters I've seen. It could actually be worse- I
| honestly can't remember if the 1/3 number was for sand,
| or the large rock (think bowling ball sized) + gravel
| mix, which was more efficient than sand.
|
| In this scenario, since your input energy is basically
| free, more storage capacity = more money, and switching
| to clay could triple your effective capacity.
|
| If, on the other hand, air is blown in a closed loop, you
| really only risk burning out your fan and resistive
| heating elements faster (they don't get cooled down by
| fresh air). In this scenario, 100% of the energy
| eventually transfers into the sand, so you're really only
| losing money if you need to spend more on land for
| setting up additional units.
| 0cf8612b2e1e wrote:
| >... but they said its the cheapest sand they could get
| (probably even free).
|
| For a one time capex on an industrial installation, what
| would it matter? As long as the material is not liquid
| gold, it seems like the material is a drop in the bucket
| for everything else you have to maintain (personal,
| pumps, generators, etc).
| Havoc wrote:
| >the very air between the grains acts as insulation.
|
| That seems like a benefit if you're looking to stretch release
| of energy over many hours?
| sharedfrog wrote:
| Weeks, in their case.
| zdragnar wrote:
| It also actively prevents heat from transferring into the
| sand, and stores far less heat than the sand itself. If you
| really want mass heated to 600C to be stretched as long as
| possible, you need as little air in the mass as possible.
| That's why in residential mass storage, the preference goes
| in order of:
|
| - rock / gravel mix (lowest preference unless portability is
| a requirement)
|
| - clay / cob mix (super fine particles, little to no air)
|
| - water
|
| where water is held separately from the heat source and some
| form of heat exchanger is used. Aside from the mess caused by
| leaks, accidental pressurization turns water thermal mass
| storage into a bit of a bomb (much like a vastly oversized
| pressure cooker) so it's really only used in outdoor wood-
| fired boilers. Also, the temp is usually capped at 180F, so
| nowhere near what these guys are getting.
| sfink wrote:
| > It also actively prevents heat from transferring into the
| sand
|
| So it's slower to charge. And the charge speed is
| presumably adjustable by circulating more air (or moving it
| through faster). It's unclear whether this is a problem for
| its intended application. It may charge fast enough.
|
| > and stores far less heat than the sand itself.
|
| That would only be relevant if you were comparing an equal
| volume. The same mass of clay and sand should store roughly
| the same amount of energy, it's just that the sand one
| would be bigger to accommodate more air. And being bigger
| isn't even a drawback here, since bigger means
| proportionally less surface area to volume that you're
| losing heat through.
|
| > That's why in residential mass storage, ...
|
| "Residential" could imply that you don't want a giant sand
| silo in the middle of some housing units, so I agree there.
| You would need to put this somewhere that size doesn't
| matter much.
| Someone wrote:
| > "Residential" could imply that you don't want a giant
| sand silo in the middle of some housing units, so I agree
| there. You would need to put this somewhere that size
| doesn't matter much.
|
| Can't you build that silo underground? If so, size
| wouldn't matter much. You could have a playground,
| communal garden or, if you must, parking spaces on top of
| it, so it wouldn't really use any area.
| Someone wrote:
| > Also, the temp is usually capped at 180F, so nowhere near
| what these guys are getting.
|
| I think that's a good reason for them to not use water.
| _If_ you're designing for 600degC, I would think using
| water is quite risky.
|
| I would also think sand at 600degC stores more energy per
| volume or mass than water at 180degF.
| sharedfrog wrote:
| They rely on sand to provide some insulation, alongside
| whatever they use in the walls of the containers. They heat the
| centre of the sand higher than the outside.
| isoprophlex wrote:
| No in fact this is a bloody brilliant design: they turn it into
| a huge fluidized bed reactor and extract the heat with air!
|
| See this fun fluidized sand-filled jacuzzi if you're not
| grokking my too brief explanation:
|
| https://m.youtube.com/watch?v=My4RA5I0FKs
| scythe wrote:
| >The battery stores 8 MWh of thermal energy when full. When
| energy demand rises, the battery discharges about 200 kW of power
| through the heat-exchange pipes: that's enough to provide heating
| and hot water for about 100 homes
|
| Cool, so we just need three million of these to take care of
| Europe.
|
| If you look up Kankanpaa on a map, you will find that it is a
| very small town in the middle of nowhere. And I haven't looked
| this up, but I'm suspecting it's got abundant sand
| production/shipping nearby from the Baltic. In those conditions,
| this sand-thermal storage might work well. But for most of the
| world, the space requirement, low energy efficiency, and costs
| associated with building large projects (and digging deep holes)
| in places where people actually, you know, live, will basically
| rule this out.
| naavis wrote:
| Are you implying it shouldn't be developed if it doesn't cover
| 100% of all use cases all over the world?
| saalweachter wrote:
| I wonder what the threshold is for a niche solution.
|
| You don't want to be, like, the only person with a sand-heat-
| battery. Well, _you_ might, as an individual, if you like to
| tinker, but as a municipality it 's a pain. All of your
| problems are unique, you can't just hire a repairman to come
| in and swap out a standard part for another, you don't have a
| standard payscale for your Sand Management Technician, etc
| etc.
|
| How many installations do you need before it becomes a good
| idea? 1% of the total? 50 total in a service area?
| scythe wrote:
| No, I'm implying that the headline claim "transform clean
| energy" is overstated. It mostly applies for far-flung, low-
| density areas. This is still useful, but not transformative
| for most of us.
| ck2 wrote:
| But heat based power always leaks energy?
|
| Why not lift something REALLY heavy and let gravity spin a
| gearbox on the way down?
|
| Like say lift a silo of sand? Up the side of an existing hill on
| a rail/track?
|
| Alternately pump water uphill but in cold/hot climates that would
| be a problem and microbes, etc.
|
| Gravity isn't going to leak or fail. And enough of an angle that
| weight is always coming down regardless of weather.
| burkaman wrote:
| Those methods are good and already in use, and this is one more
| additional energy storage method for places where those are
| expensive or impractical. This method also has the additional
| benefit of directly providing heat, so if you need heat more
| than you need power then this seems like a great choice.
| AtlasBarfed wrote:
| I believe pumping water up a mountain is the only economical
| energy storage battery based on current economics. Lifting
| heavy weights requires such a big facility that it won't beat
| other simpler means. I think pumped hydro is something like
| 70-80% efficient, which is really good.
|
| I believe sodium ion batteries (CATL alleges mass production of
| 160 wh/kg) will be the killer app battery of grid storage that
| doesn't have pumped hydro as a geographic possibility, although
| that's probably 5 years out. A 160 wh/kg sodium ion battery
| (which should have superior cell-to-pack density than
| nickel/cobalt chemistries similar to LFP chemistry) can power a
| standard range model 3.
| hedora wrote:
| There is a company that uses electric trains to drive the
| heavy weights to the top of mountains. They claim 90% round
| trip efficiency:
|
| https://aresnorthamerica.com/gravityline/
|
| which sounds plausible, since rail freight companies have
| spent 200 years micro-optimizing train efficiency.
| Someone wrote:
| > Why not lift something REALLY heavy and let gravity spin a
| gearbox on the way down?
|
| Because lifting something that's heavy doesn't store much
| energy (or, stated alternatively, 1kWh is a lot of energy,
| compared to human muscles)
|
| https://www.quora.com/How-much-mass-in-kg-can-I-lift-
| to-1-m-...:
|
| Q: How much mass in kg can I lift to 1 m height, with 1 kWh of
| energy?
|
| A: Let x kg be the mass to be lifted. The energy required = mgh
| x * 9.8kgm2/s2 or 9.8x Joules 1 KWH = 3.6 million
| Joules. 9.8x = 3.6*106 => x = 3.6*106 /9.8 =
| 3.67*105 kg.
|
| So, that's about 360,000 kg.
|
| The great pyramid of Giza weighs about 6 billion kg
| (https://www.egyptabout.com/2019/02/facts-16-fun-facts-
| about-...), so lifting that by a meter would store less than
| 20,000 kWh.
| elil17 wrote:
| You're balancing the cost of energy leaking vs. the difference
| in capex vs. other inefficiencies of the gravity based system
| (e.g. heat loss due to friction)
| jaclaz wrote:
| Already thought of and also partly tested experimentally,
| cranes:
|
| https://news.ycombinator.com/item?id=17789456
|
| https://news.ycombinator.com/item?id=32240546
|
| https://news.ycombinator.com/item?id=29910248
|
| Rail loop:
|
| https://aresnorthamerica.com/gravityline/
| rjmunro wrote:
| This unit stores 8MWh of energy with 100 tonnes of sand.
| Gravity is about 9.8m/s*2.
|
| If you put the calculation into google "8MWh / 9.8m/s*2 / 100
| tonnes", it tells you that you need lift those 100 tonnes
| 29.39km up, which is over 3 times the height of Everest. And
| the mechanics of the system are much more complicated, more
| expensive to build and maintain.
|
| However, pumping water uphill is done in many places, and is
| more practical because a lake of water can easily weigh
| millions of tonnes. The problem is finding places with suitable
| hill top lakes.
|
| Also, if you are using it for district heating output, storing
| it as heat is convenient.
|
| There might scope to increase efficiency by using some sort of
| heat pump, but getting a heat pump to go up to 600degC is quite
| hard.
| kwhitefoot wrote:
| > The problem is finding places with suitable hill top lakes.
|
| And a similar capacity lake at the bottom of the station to
| hold the water that you are going to pump up to the top.
| Simulacra wrote:
| Is there a central location of these "x could transform y"
| discoveries? Energy storage is vital and it seems every week
| something new is coming out. Most it seems never make it off the
| theoretical paper.
| philipkglass wrote:
| This article is about a pilot scale project that is already
| built. It is significantly further along than a report about a
| _theoretical_ energy storage mechanism or one that has only
| been demonstrated at the laboratory bench scale.
| smt88 wrote:
| This is a stupid idea, and there are some great YouTube videos
| that explain why[1].
|
| tl;dr We already move enormous amounts of drinking water, and
| reservoirs are much better (and cheaper) candidates for batteries
| than sand/cement/etc.
|
| 1. https://www.youtube.com/watch?v=iGGOjD_OtAM
| WalterBright wrote:
| I've proposed on HN multiple times that home HVAC systems could
| have a "battery" that consisted of an insulated box of rocks. It
| could be heated or cooled during periods when renewable energy is
| cheap, and used as a heat source/sink the rest of the time. This
| idea was regularly ridiculed.
|
| I'm glad to see someone thinks it isn't so stupid :-)
| philjohn wrote:
| I mean, that's just a more advanced version of storage heaters
| in the UK that "charge" on Economy 7 tarrif (late evening and
| overnight, cheaper per kwh) then radiate heat the next day.
| simon_000666 wrote:
| Check out these guys : https://sunamp.com/hot-water-thermino-
| overview/
|
| Basically commercial version of a box of rocks.
| bilsbie wrote:
| There's low hanging fruit like that everywhere.
|
| In this case I think new home builders are really conservative
| with trying new things due to the high price of houses and
| strict building codes.
|
| And even though it's a simple idea it's the kind of thing HVAC
| companies would be happy to Charge you 20K for. Just like
| geothermal.
| tuatoru wrote:
| This basic idea (thermal mass energy storage) is perfectly
| sensible, and has a long history.
|
| https://en.wikipedia.org/wiki/Trombe_wall
|
| Coupled with a well designed ventilation system, a Trombe wall
| can also be used for cooling.
| kwhitefoot wrote:
| You can already use a ground source heat pump to do this.
| crazygringo wrote:
| Judging from other comments here, it seems like that's not an
| economic solution for storing electricity -- only for storing
| heat.
|
| And I suppose it's really not so different from simply having a
| hot water heater like so many homes do? That you could program
| to only add more water to when electricity is cheapest? (And
| in-floor heating uses hot water pipes.)
|
| But hot water tanks are very safe, they're only 60degC. I would
| think that 600degC sand (or rocks) is the kind of thing that's
| not particularly safe to have inside your home. That's really,
| really hot.
|
| Have you done the math and figured out how many rocks a home
| would need, how much insulation, and so whether it's even
| viable in theory, setting aside practical engineering/safety
| concerns?
| hedora wrote:
| Check out slab on grade foundations. They do what you are
| describing, by moving the air in your house towards the average
| temperature (cooling during the day, warming at night,
| usually). Sadly, they use a lot of concrete, so they have high
| embedded carbon.
| sedivy94 wrote:
| My initial thought is... why bother? There are so many vectors
| for energy loss from source to destination. If the sand is heated
| by coils, why not install on-demand heating on-site?
| avanai wrote:
| They compare its cost effectiveness to lithium electrochemical
| storage batteries, but it seems much more apt to compare it to
| large-scale flow batteries, which also use relatively cheap,
| easily available materials. How does it compare to those?
| marcosdumay wrote:
| It's more apt to compare it to phase change heat storage. What
| somehow doesn't appear anywhere on the article.
|
| (I do believe the article's design fares much worse, even on
| capex alone. I never saw some salt selection that melts at
| 600degC, but I imagine it would have better results even in a
| lower temperature.)
| Havoc wrote:
| Can it use desert sand?
|
| That stuff is useless for construction but might still be good
| for this?
| ben_bai wrote:
| As it is only a heat storage device, yes. The cheapest sand
| will do.
| jandrese wrote:
| This feels like one of those technologies that dead ends because
| the costs of PV solar cells/wind turbines and batteries is
| dropping so fast that by the time it's ready for the mass market
| it is no longer competitive, especially when you add in the
| complexity of engineering the solution to match your problem and
| being a first mover on a new technology.
|
| I note that even the figure provided in the article ($2,000/MWh)
| is out of date, and current prices are closer to $500/MWh and
| still dropping. I'd expect this to be a nice niche solution for
| them but have tepid uptake elsewhere.
| liketochill wrote:
| The capex cost is still above $1500/MWh according to US NREL.
| While PV modules might be dropping in cost and increasing In
| efficiency stuff like labour, transformers, inverters, fire
| suppression systems, transmission lines are not perhaps not
| seeing the same reductions.
|
| https://atb.nrel.gov/electricity/2022/utility-scale_pv
| SamBam wrote:
| I'm confused by your comparison to PV solar cells, although I'm
| probably not just not understanding your comment. This is an
| energy storage device, not an energy generator. Its purpose is
| to smooth out the peaks and troughs of non-steady renewable
| energy flow.
| jandrese wrote:
| That was a more general comment about niche tech like this,
| but the costs I included were for grid scale battery storage.
|
| So this is more cost effective than batteries at the current
| price but also less flexible and requires more engineering up
| front, and the price of batteries keeps dropping. It makes
| sense today but is going to feel the squeeze in the long run.
| mcbishop wrote:
| There's an option of overbuilding PV to fully accommodate
| cloudy days or the winter season (with extra PV going to
| waste on sunnier days). ...Versus making up the difference
| with stored energy.
| netjiro wrote:
| Example of how much you'd have to "overbuild". Look at
| example temperature and incoming solar radiation around
| january - february. Graphs 1 and 3 [1]. And that's for
| Vantaa in the far south of Finland :)
|
| [1] https://research.tuni.fi/uploads/2019/05/0a103135-p0865
| 68.pn...
| ZeroGravitas wrote:
| You actively want to overbuild by what seems like a
| ridiculous amount, because lots and lots of cheap energy
| is a good thing.
|
| See this video which suggests somewhere in the region of
| 5x overbuild of renewables being the least cost option.
|
| https://news.ycombinator.com/item?id=33464463
| tuatoru wrote:
| Same reasoning applies to wind, though, Its price is
| dropping nearly as fast as PV.
|
| But chemical battery prices are _also_ dropping as
| quickly.
|
| At present the BESS (battery energy storage system)
| industry is (to a first approximation) a sideline for
| vehicle battery makers.
|
| Relaxing engineering constraints imposed by vehicle
| use[1] means BESS prices can drop further. This is
| happening as the BESS industry splits off from vehicle
| batteries.
|
| Add vehicle battery swapping like Ample's[2] to an urban
| BESS, you have two businesses in one, that can follow
| supply availability exactly.
|
| 1. Structural strength, vibration resistance, performance
| at extreme high and low temperatures, high mass energy
| density, high power/mass ratio, tolerance for
| overdischarge being the obvious constraints that can be
| relaxed a bit.
|
| 2. https://ample.com/
| rjvs wrote:
| That doesn't help at night, storage is still necessary.
| onceiwasthere wrote:
| Not if you keep overbuilding for star and moonlight!
| tzs wrote:
| You'd still need something to handle the nights around
| new moon, so you'd have to overbuild enough to be
| sufficient when all you have is starlight.
|
| A bit of Googling suggests that the combined energy per
| second that reaches Earth from all the visible stars
| other than the Sun is around 0.0000002% of the amount
| from the Sun.
|
| I recall reading that the area needed with current solar
| panel technology to power the entire US would be 10000
| square miles. With starlight being 0.0000002% of
| sunlight, that suggests we'd need 5 trillion square miles
| of panels to get the same amount of energy at night.
|
| The surface area of the earth is a little under 200
| million square miles.
|
| That suggests that it isn't possible to overbuild enough
| to work off of starlight.
|
| It would be even worse on cloudy nights. On cloudy days
| you still get a significant amount of sunlight coming
| through, because the Sun is giving us so much more than
| we need. Not so with stars.
| jopsen wrote:
| > There's an option of overbuilding PV to fully accommodate
| cloudy days or the winter season
|
| If that is the future -- I hope it is :D
|
| Then there will be hours of the day where electricity is
| practically free, if not actually free. So any mechanism
| for time shifting energy consumption might generate a nice
| buck.
|
| I guess the competition is PV or wind + long distance
| transmission loss.
| datameta wrote:
| All true, but there's still the night. Perhaps paired with
| transcontinental energy transmission (like Australia is
| planning for Oceania/SEA, or the Gibraltar idea for
| Sahara->Europe transmission) we can route the excess energy
| away from the local grid and to places where it is night
| time.
|
| Whether this is better than local storage is another
| question.
| alkonaut wrote:
| It still requires wind and/or daylight.
|
| You may be aware that large swaths of Finland, Norway and
| Sweden sees the sun set and not rise again for weeks or
| months. And during this period it's also not uncommon to
| see -20 C or colder. Even worse/ the colder it is, it's
| also typical with very little wind inside large stationary
| high pressures.
|
| Then it's months when the sun barely sets, as well as windy
| periods in spring and fall. Using wind/sun only requires
| storage not just between night and day but between seasons.
| Luckily in these particular regions there is plenty of
| hydro so aren't reliant on wind and sun only to be 100%
| renewable.
| ttkari wrote:
| > There's an option of overbuilding PV to fully accommodate
| cloudy days or the winter season
|
| It would be interesting to see exactly what kind of
| overbuild would be required to "fully accommodate" for the
| winter season with PV in Finland.
| ilyt wrote:
| If you can construct it as central unit for few streets it
| looks as pretty great solution.
|
| "Buy" cheap PV electricity off house owners during the day and
| "sell" them heat in off-peak hours.
|
| You're basically competing with hybrid inverter + battery
| storage + heat pump which is not cheap per house but even if
| heat storage might be cheap, that's plenty of initial cost to
| install all the piping.
| jandrese wrote:
| The caveat is you can't put this energy back on the grid.
| It's been converted to heat and there's no conversion back.
| It's mostly useful for heating homes and water at night.
| napoleongl wrote:
| But thats the problem they are looking to solve... there
| are quite a couple of cold months in Finland and I think a
| large portion of their heating is electric/distict anyway
| so they might as well store heat rather than energy. This
| probably serves as a rather good balancing mechanism to the
| grid actually, and I could definitely see this be a thing I
| northern Sweden for instance , where electricity is
| basically free during the night and when it is windy it's
| actually kind of a problem to get rid of it all.
| Moissanite wrote:
| Resistance heater plus thermal mass as a time-shifting mechanism
| for heat has existed for decades in the UK - they are referred to
| as "storage heaters" and have generally been avoided wherever
| possible because of the high cost of electricity relative to gas.
|
| Operating at large scale like this probably helps, but really the
| main benefit comes from the district heating part.
| stormdennis wrote:
| Indeed. In our prefab classroom in winter, sitting on the class
| storage heater before classes started was the prime real
| estate.
| jonatron wrote:
| Storage heaters might make comeback if gas prices remain high,
| because intermittent wind power and smart meters make it
| possible to use electricity when it's windy and cheap.
| bodyfour wrote:
| Indeed, they are: https://tepeo.com/thezeb
| Moissanite wrote:
| Slightly different, as this seems to hook in to your
| existing water pipes for moving the heat out from a central
| location - but an interesting find. Another I'm watching
| from a distance is microwave-based heating, essentially
| replacing the gas burner in a combi boiler with a flow-
| through microwave heater.
| ZeroGravitas wrote:
| Heat pumps feeding into underfloor heating do a very similar
| thing to this sand battery. They let you feed heat into a
| thermal mass in order to buffer it.
|
| This has the double impact of a) letting you take advantage
| of cheaper electricity by modulating your load slightly, b)
| letting your heat pump run continuously at a lower heat
| output, maximising efficiency as it extracts heat from the
| continually replenished outside air.
| SamBam wrote:
| > district heating
|
| I'm always impressed by how prevalent district heating is in
| parts of Europe, and wonder if anything like that has ever been
| done in the states, or if it seems too much like communism.
|
| Also have people done the math on the transmission losses vs
| the efficiencies of a single heating location?
| DarmokJalad1701 wrote:
| https://en.wikipedia.org/wiki/New_York_City_steam_system
| laurencerowe wrote:
| In my experience the big downside of storage heaters is that
| after heating up overnight they release all their heat while
| you're out at work during the day. Maybe okay if you WFH.
|
| Nowadays heat pumps would be far more efficient, shifting 3-4x
| the heat for the same energy.
| choeger wrote:
| How does it compare to heatpumps, though? If a large-scale
| heatpump was used to power a district, it would only need 1/3 or
| even less of the electricty. From that perspective, does it make
| sense to store thermal energy or does a chemical battery become
| attractive again?
| zhynn wrote:
| Why not use heat pumps to heat the mass? What if the air
| conditioner exhausted the heat into your mass battery? It's not
| either/or.
| moffkalast wrote:
| Well yeah that's what ground source heat pumps basically are.
| They just don't run at 600 degrees.
| Moissanite wrote:
| I think the bigger problem with batteries is capex per kWh,
| rather than efficiency.
| elil17 wrote:
| You have to include the capex cost of the heat pumps. This
| design uses no equipment at the customer's homes, just pipes of
| hot fluid. Those pipes already exist in Finland, where district
| heating is relatively common. The next logical step is pumped
| thermal energy storage, where you pump heat into the sand using
| a heat pump - but there is significant capex associated with
| that.
| hedora wrote:
| Heat pump efficiency drops rapidly with temperature
| differentials. This doesn't matter much when the goal is to
| heat air to room temperature, but it would matter a lot with
| a 600C target temperature. It's likely cheaper to use a
| lithium ion battery to store the electricity, then run a heat
| pump at the house off that. On top of that, it'll use a tiny
| fraction as much electricity.
| elil17 wrote:
| It's true that heat pumps become less efficient at higher
| temperature differences. That's why these systems use lower
| storage temperatures. It's also true that, even then, the
| storage temperature has to by higher than the typical
| evaporator condensor for a heat pump, leading them to be
| less efficient (think 175% efficient vs. 300% efficient).
|
| You're looking at LCOS of $0.23 kWh-1 [1], which is higher
| than Li-ion. However, such a system may offer other
| advantages (better recyclability, no reliance on lithium,
| less risk of fire), or such systems may be cheaper in the
| future, which is why people are researching them.
|
| Additionally, these systems work with existing district
| heating pipes, which is great because it mean's you don't
| have to expand the grid capacity. In places with district
| heating, that could make a lot of sense. (I don't think
| anyone is proposing building new district heating systems,
| just retrofitting old ones).
|
| [1] https://www.sciencedirect.com/science/article/abs/pii/S
| 01968...
|
| Also, Carnot efficiency increases without bound as the
| temperature difference decreases, so lowering the
| temperature of the room or increasing the temperature of
| the outdoors make a huge difference. The same applies vice
| versa for air conditioning which is why people use cooling
| towers.
| ouid wrote:
| the transportation of "heat" is a lot more complicated than the
| transportation of electricity. I'm not opposed to putting
| insulated piping everywhere to transport hot water around. It's
| better than building bridges to nowhere, but i can't help but
| feel that the losses will scale badly. Pipes have a lot of
| surface area.
| jandrese wrote:
| Campuses and some municipalities have steam pipes for
| distribution of heat. However, the economics of moving steam
| around vs. using the steam to turn a turbine to make
| electricity to run heat pumps is dubious. The electric solution
| is much more complicated, but it can also be used to cool the
| buildings in the summer and run lights, so the tradeoffs can be
| worth it.
| kitd wrote:
| This is already widely done in Nordic countries and well
| understood. I went to a geothermal plant about 25km outside
| Reykjavik. It also supplies much of the communal hot water for
| the city. Between the plant and the city, in the depths of
| winter, it loses 1deg C.
| jabl wrote:
| The usual district heating pipes around here have an inner pipe
| where the actual hot water is pumped, then about 10cm of some
| yellowish insulation material (polyurethane?), and then an
| outer pipe to protect the insulation.
|
| AFAIU heat losses through the piping aren't considered a huge
| problem.
| dontlaugh wrote:
| Municipal heating can be extremely efficient, precisely because
| it doesn't take that much insulation to make losses a non-issue
| and heat generation tends to scale up very well.
| yboris wrote:
| An 11-min video on channel _Undecided with Matt Ferrell_ about
| this tech:
|
| https://www.youtube.com/watch?v=G6ZrM-IZlTE
| VBprogrammer wrote:
| I'm really starting to grow tired of this format of video. Lots
| of stock footage and little information, definitely no attempt
| to bring balance into the discussion. Every innovation is a
| breakthrough with no downsides at all.
|
| This is probably a bit harsh to Matt Ferrel it's probably
| copycats I've got more of a problem with.
| giarc wrote:
| Thanks for sharing that. He did a great job simplifying the
| tech and explaining the pro's and cons.
| jandrese wrote:
| _Undecided_ always seems just a bit under-researched and a
| little too credulous of company claims IMHO. They 've got some
| videos of outright investor scams reported with a straight
| face.
| dimenoz wrote:
| From "Just Have a Think" (another excellent channel similar to
| Undecided): https://www.youtube.com/watch?v=sol9FOaKTr0
| sergiomattei wrote:
| Or just use pumped-storage hydroelectricity
| kitd wrote:
| I appreciate the focus on technological simplicity, cost-
| effectiveness and environmental cost. Yes, the battery itself
| isn't as efficient (per m^3) as a chemical one, but the basic
| engineering and well-established supply chains behind setting one
| up will reap gains in themselves and means scaling up will be
| much less challenging. Even the turbine add-on is well understood
| engineering at this stage.
|
| I imagine these could be used to buffer the output from wind
| turbines or solar plants?
| breischl wrote:
| It's a cool idea. The big advantage might be in being cheap,
| simple, and non-toxic, so that it can be easily deployed in less-
| prosperous areas and with less expertise. It seems probably even
| simpler than the "concrete stacking battery" whose name I forget.
| But...
|
| >with currently available technology the process of converting
| heat back into electricity only has an efficiency rate of 30%
|
| Yes they're recovering heat as well, which is great when it
| works. But in general 30% is not great. This probably only makes
| sense to use when you have huge amounts of nearly-free power.
| Like if you massively overbuilt solar/wind (which could be a
| plausible thing to do!) or nuclear.
| unwind wrote:
| I thought heat output was the main effect, thus the talk about
| "district heating pipes" in the list of components.
|
| With nuclear power generation I thought there was no need to
| store energy, since it can generate at all times and ramp
| up/down pretty quickly.
| breischl wrote:
| I'd say the marketing on at least this article is more geared
| at the electric energy. Heat is a form of energy for sure,
| but not a big enough one that it could "transform clean
| energy".
|
| Nuclear can be ramped, but typically is not. I haven't dug
| into why, but I get the impression it's partially economic -
| the plants are very expensive to build and the marginal cost
| of a few hours of fuel is so low that they prefer to just run
| all the damn time. I think there may be some technical
| reasons as well. In general if you look at how utilities
| operate, they will ramp down literally everything else before
| the nuclear plants.
|
| That probably applies less to the Small Modular Reactors
| people keep talking about, but those are still not really a
| factor.
___________________________________________________________________
(page generated 2022-11-04 23:03 UTC)