Jump to content


ebuild is sad to announce its closure - it has become too time and resource intensive to develop, manage and maintain.

However, ebuild will remain on-line in archive mode (ie no posting facilties) for several weeks so that users can use it as an information resource.

Thesis On Storage Heaters (& Other Storage Technologies)


  • Please log in to reply
16 replies to this topic

#1 DavidWright

DavidWright

    Regular Member

  • Members
  • PipPipPip
  • 326 posts
  • LocationSkye

Posted 16 August 2015 - 08:59 PM

Searching for the thermal density of the magnetite bricks used in storage heaters I came aross this recent (well, 2013) Thesis

"ELECTRICAL STORAGE HEATER IN THE CONTEXT OF STORAGE TECHNOLOGIES. Author: Ignacio Becerril Romero"

http://www.esru.stra...13/Becerril.pdf

I found it very interesting. Maybe some others might too?

#2 Triassic

Triassic

    Advanced Member

  • Members
  • PipPipPipPip
  • 1,239 posts
  • LocationCumbria

Posted 16 August 2015 - 09:45 PM

View PostDavidWright, on 16 August 2015 - 08:59 PM, said:

Searching for the thermal density of the magnetite bricks used
Should i be building my house out of them?

#3 DavidWright

DavidWright

    Regular Member

  • Members
  • PipPipPip
  • 326 posts
  • LocationSkye

Posted 17 August 2015 - 01:08 PM

View PostTriassic, on 16 August 2015 - 09:45 PM, said:

Should i be building my house out of them?
Not sure what the BCO would say... :unsure: :)

#4 DavidWright

DavidWright

    Regular Member

  • Members
  • PipPipPip
  • 326 posts
  • LocationSkye

Posted 17 August 2015 - 01:46 PM

Here's a short summary of density, specific heat capacity & thermal capacity properties of some building materials based on data in the thesis. In terms of thermal density magnetite is almost up there with water (but magnetite can of course be heated well over 100C):


Density SHC Thermal Density
kg/m3 J/K.kg J/K.m3
Brick 2000 840 1680000

Concrete 2400 880 2112000

Plaster and plasterboard 2700 1080 2916000

Water 1000 4200 4200000

Structural softwood 550 1700 935000

Typical hardwood 700 1700 1190000

Granite 2700 790 2133000

Brick 1800 840 1512000

Magnetite 5177 752 3893104


The table looks perfect in the editor (Font: Courier New), but as soon as I post the formatting is lost - looks a proportional font?

Is there a better way of posting tables on this Forum than selecting a non-proportional font? I tried "Post from Word" (actually from LibreOffice) which looked encouraging but after posting lost all formatting & I tried BB code, but that wasn't recognised. I tried CODE, but that also seemed to use a proportional font. I didn't try raw html.
Maybe it's just the Firefox in Ubuntu that I'm using & others see it okay?

Attached Files


Edited by DavidWright, 17 August 2015 - 01:51 PM.


#5 SteamyTea

SteamyTea

    Advanced Member

  • Members
  • PipPipPipPip
  • 4,322 posts
  • LocationCornwall

Posted 17 August 2015 - 02:35 PM

Just the density that makes them look so impressive as a storage medium.
Not read the article, do we know what they are made from?

#6 tonyshouse

tonyshouse

    Advanced Member

  • Members
  • PipPipPipPip
  • 1,297 posts
  • LocationThames Valley

Posted 17 August 2015 - 03:53 PM

Likely an ore containing lead or possibly iron

#7 DavidWright

DavidWright

    Regular Member

  • Members
  • PipPipPip
  • 326 posts
  • LocationSkye

Posted 17 August 2015 - 05:11 PM

View PostSteamyTea, on 17 August 2015 - 02:35 PM, said:

Just the density that makes them look so impressive as a storage medium.
Plus the ability to take them to higher temps than water?

View PostSteamyTea, on 17 August 2015 - 02:35 PM, said:

Not read the article, do we know what they are made from?

From the thesis (N.B. I think "TES" is an abbreviation for "Thermal Energy Storage", I haven't noticed it being defined, but that makes sense across a wide range of uses in the Thesis):

Quote

Feolite is just a generic name for iron oxides (FexOy) and, in the case of storage heaters, it is commonly
used to talk about high density ceramic magnetite (Fe3O4).

Magnetite is frequently used for TES applications due to its high volumetric heat
capacity and good thermal stability at high temperatures (Gronvol and Sveen, 1974;
Otero and Álvarez, 1994). Further materials employed in heat storage applications are
other iron oxides, magnesia (MgO), alumina (Al2O3) and silica (SiO2). However,
because of the lower cost of raw materials and their superior thermal properties, iron
oxides and magnesia are the best candidates for the fabrication of thermal storage bricks


#8 SteamyTea

SteamyTea

    Advanced Member

  • Members
  • PipPipPipPip
  • 4,322 posts
  • LocationCornwall

Posted 18 August 2015 - 08:37 AM

Yes, the higher temperatures are very useful, especially when using electrical resistance heating.
I had a quick look around and it seem that the SHC is 103.9 J/mol·K, and I think that works out at about 3.2kJ/kg (I may have misunderstood the conversion though).
So almost as good as water and don't change phase (melt) until it is 1500°C

#9 DamonHD

DamonHD

    Advanced Member

  • Members
  • PipPipPipPip
  • 1,046 posts
  • LocationLondon, UK

Posted 18 August 2015 - 09:21 AM

OK. So suppose I ignore my normal outrage about electric resistance heating and exergy, which does not apply if I can (say) get my magnetite to ~1400C where it or the nichrome wire I'm heating it with melts, and I want to seasonally store PV output from summer until I need heat in winter. What volume (never mind the weight for now) would I need to cover my space heating? Indeed I'll do my DHW ("flash to steam, baby") also and get rid of gas, for simplicity.

Last year we used 3MWh of gas, ie ~1E10J, for space and water heating.

So at 3893104 J/K.m^3 and (say) at least a 1000C temperature delta (shall I buy shares in Aspen Aerogel now?) that gives me 3.9E9J/m^3 or somewhat under 3m^3 of magnetite to hold the energy for a seasonal store.

Somewhat less of a size issue than a buried water-filled milk tanker or three on my small plot, but ripe with its own health-and-safety issues.

And we don't really have 3MWh of electricity to spare (we generated just under 4MWh last year and used about 1.7MWh as electricity) but not utterly implausible. Nominally with a heat pump the exported electricity would cover our low-grade heat requirements over the year.

Could it be done?

Have I made some horrible order-of-magnitude error?

Rgds

Damon

PS. And at those high temperatures would the store be worth tapping for a little electrical energy, eg for lighting at night, with a Seebeck device?

http://www.earth.org....html#magnetite

Edited by joiner, 18 August 2015 - 11:03 AM.
"mind" for "might"


#10 DavidWright

DavidWright

    Regular Member

  • Members
  • PipPipPip
  • 326 posts
  • LocationSkye

Posted 18 August 2015 - 11:05 AM

View PostDamonHD, on 18 August 2015 - 09:21 AM, said:

Have I made some horrible order-of-magnitude error?
I'm sure the calculation is fine, but perhaps an error of context, i.e. size of store, temperature of store & the matter of time span (Seasonal v Diurnal or thereabouts) compared to the scope of this thesis?

The study looks at using domestic "smart" storage heaters within their design spec. (and quite possibly in places where electric heating might be being used anyway - not all are on the gas grid & not all think that burning stuff is a sensible way of generating heat).

From the abstract of the thesis...

Quote

State-of-the-art storage heaters can provide demand side management (DSM) services
in small isolated grids with significant wind generation. The charging periods of the
heater can be scheduled by the utility provider based on wind output and demand
forecasts.

Big efficient batteries would be great for storing excess electricity, but they aren't here yet...

Edit: Tweak the 1st para.

Edited by DavidWright, 18 August 2015 - 01:18 PM.


#11 SteamyTea

SteamyTea

    Advanced Member

  • Members
  • PipPipPipPip
  • 4,322 posts
  • LocationCornwall

Posted 18 August 2015 - 03:30 PM

The thing about storing electrical energy as thermal energy is to get the generators working at their most efficient, not to store at the most efficient. It costs a lot to slow a generator down and restart it. This makes the use of resistance heating a viable option when you take capital cost into account.

Edited by joiner, 18 August 2015 - 03:50 PM.


#12 DavidWright

DavidWright

    Regular Member

  • Members
  • PipPipPip
  • 326 posts
  • LocationSkye

Posted 18 August 2015 - 04:25 PM

View PostSteamyTea, on 18 August 2015 - 03:30 PM, said:

The thing about storing electrical energy as thermal energy is to get the generators working at their most efficient, not to store at the most efficient. It costs a lot to slow a generator down and restart it. This makes the use of resistance heating a viable option when you take capital cost into account.
At the risk of being boring & sounding like an old record :D, Scottish Hydro (part of SSE) have been doing this for years, using a side band on national radio to control energising of storage heaters & immersions through the day & night (within contractual max & min limits) right across the Highlands & Islands, with at least part of the reason being to optimise production & use of locally generated energy. Scottish Hydro has been into renewables for a long time...
There's no gas grid up here & optimising use of the energy produced in the area across the day means reduced transmission losses compared to pushing excess hydro (& nowadays, wind) down the country during the day & pulling (mainly) non-renewable E7 back over night.

Edited by DavidWright, 18 August 2015 - 04:26 PM.


#13 DamonHD

DamonHD

    Advanced Member

  • Members
  • PipPipPipPip
  • 1,046 posts
  • LocationLondon, UK

Posted 18 August 2015 - 04:31 PM

Yes, RTS/Teleswitch is a good thing for intraday load matching.

The astonishing thing for me is that the magnetite starts to get into the seasonal storage arena. I'd completely failed to realise that its extended temperature range compared to water means that it may be possibly to store several times more for a given weight and volume.

Rgds

Damon

#14 DavidWright

DavidWright

    Regular Member

  • Members
  • PipPipPip
  • 326 posts
  • LocationSkye

Posted 18 August 2015 - 09:09 PM

View PostDamonHD, on 18 August 2015 - 04:31 PM, said:

The astonishing thing for me is that the magnetite starts to get into the seasonal storage arena. I'd completely failed to realise that its extended temperature range compared to water means that it may be possibly to store several times more for a given weight and volume.
Ah, yes. I see your angle on it now.

#15 notnickclegg

notnickclegg

    Advanced Member

  • Members
  • PipPipPipPip
  • 1,126 posts
  • LocationHampshire/Surrey Borders

Posted 18 August 2015 - 09:20 PM

View PostDamonHD, on 18 August 2015 - 09:21 AM, said:

PS. And at those high temperatures would the store be worth tapping for a little electrical energy, eg for lighting at night, with a Seebeck device?

Seebeck devices are such a wonderful idea. It's just a shame they're so inefficient.

I did see something a while back about a device that looked like giving three or four times the typical efficiency (edited to add: found it: http://www.gizmag.co...material/24210/).

I'd love to see cheap, efficient Seebeck films that could be used anywhere there's waste heat. The back of solar panels is one application: panel cooling that improves PV efficiency while producing its own energy!

Jack

Edit: link + added to final sentence

Edited by notnickclegg, 18 August 2015 - 09:31 PM.


#16 SteamyTea

SteamyTea

    Advanced Member

  • Members
  • PipPipPipPip
  • 4,322 posts
  • LocationCornwall

Posted 18 August 2015 - 09:30 PM

I think the main thing is the heat capacity, rather than the specific heat capacity and the temperature range (was higher than I thought initially).
No sure how hot an electrical element can get (could always strike and arc I guess). But you could use a sterling engine with a large enough high temperature heat store. Or a small steam turbine.

It may be worth looking at the fluctuation in electrical energy demand and seeing how well that count be matched to domestic thermal energy demand (thermal can be times-hifted quite well in my opinion).

I think they could do more with the radio signal, but they want to reinvent the wheel with smart meters (all gone a bit quite on the roll out recently).

#17 DavidWright

DavidWright

    Regular Member

  • Members
  • PipPipPip
  • 326 posts
  • LocationSkye

Posted 19 August 2015 - 03:18 PM

View PostSteamyTea, on 18 August 2015 - 09:30 PM, said:

No sure how hot an electrical element can get (could always strike and arc I guess).
A standard craft pottery kiln (the sort of thing you can plug into a 13A socket) designed for firing porcelain clay goes up to at least 1100C, maybe 1200C?

View PostSteamyTea, on 18 August 2015 - 09:30 PM, said:

I think they could do more with the radio signal, but they want to reinvent the wheel with smart meters.
Indeed. The "Smart" meter roll out seems to be much more about automating reading the meter than about being smart with energy usage...

More about RTS/Teleswitch: https://en.wikipedia...adio_teleswitch

N.B. The bit about "Transmitter Obsolescence"! :unsure: