Post by DaveWanting to store about 8000kWh of heat from the summer into
the autumn and winter. Previous solutions are usually
thermal, which work but take a lot of mass e.g. sand or
water. Good for an extended growing season in southern
Canada, with the heat store under the glass house.
However in GB, with a small house and garden, there isn't that
much space, so moving from physics to chemistry it seems that
anhydrous calcium chloride is the best, with the exothermic
reaction when hydrated. Should only need about 1500kg which
would fit in the garage, where a 100,000 litre water tank is a
general risk (and losing heat the whole time). Also with a
dehydrated compound there will be indefinite storage with no
loss, if you keep the lid on.
To fully dehydrate again, the temperature of 260 Celsius is a
challenge with passive solar and no electric heating. To
partially dehydrate to some forms of the hydrate 50 Celsius is
enough, so a well designed passive collector would be OK.
There are lots of different forms of the hydrate listed on
https://en.wikipedia.org/wiki/Calcium_chloride
e.g. heat of formation −2608 kJ/mol, which is quite a lot
considering a mole is 110g.
there are some better chemicals, one is a cheap hydrate, one
problem is settling or participating out. most of the research
was done in the 80s after the oil crisis
https://www.energy.gov/sites/default/files/2021-09/bto-peer-2021-stable-thermochemical-salt-hydrates-storage.pdf
https://www.extremetech.com/extreme/130523-zeolite-thermal-storage-retains-heat-indefinitely-absorbs-four-times-more-heat-than-water
Thanks for that. I was thinking of buying 25kG which is under
GBP 40.00. The theory works, just not sure about the end to end
workflow, and I have about 20m^2 of back garden I can spare.
The price is really cheap e.g. if you have minimum order
quantity 100 tons.
Seems like you will have a bucket load of sludge to store until
you dry it out in the summer; might need to powder this in a dry
environment. My conservatory gets to 50 Celsius in the summer,
and it would be nice to store some of this for the winter.
Passive solar is nice, but you need to watch that the
temperature doesn't get too high or radiative losses increase.
IR reflective glass in available, with a little loss of visible
transmission. Interesting to see if it is better.
The electric space storage heaters which are installed in many
UK flats (apartments) are lucky to store heat for 12 hours. If
you could get this up to 72 hours, people would have a lot more
flexibility with time of use pricing. There is a possibility of
free electricity when there is excess wind generation.
Calcium chloride is not that toxic, e.g. ingredient in a tin of
kidney beans. Don't expect the dust is any more dangerous than
cement.
Will do some sums. If I can bring in a day's worth of heating
from the garage in under 20kg, no worse that bringing in
firewood kind of thing. For the thing to work, need to keep
cycling your own calcium chloride,
Practical things to find out how many cycles with tap water
until there is too much contamination to get it to work.
Compared to the 1980s electronic control is cheap and easy, as
is manufacturing prototypes. The nice thing about tech from the
1980s is that it will all be out of patent. In summary, zero
carbon goals may have changed the business case.
Look into Glauber's Salt/Sodium Sulfate. It should be cheap, and
it "melts" at around 30C, but since it really loses water of
hydration it really dissolves in its own water absorbing lots of
heat. Conversely when it reforms into a hydrate it becomes solid
releasing heat. No baking to drive off water, it just absorbs
and releases heat at a certain temperature.
I guess after many cycles it starts to settle out and become less
efficient.
Thanks, you get the idea that I would like to have long term
storage of low grade heat in a low tech construction with common
off the shelf items: e.g. pond liner, air fans, clear
polycarbonate roof sheets, wood, containers, aluminium sheet. This
is storage of energy after evaporation, so should work day and
night in the summer. Things can get tricky once the water is gone.
i.e. in the drying shed need to only open it up when certain
conditions are met, so it doesn't hydrate again. Might need a
biannual cycle like some fruit plants. 1st year - evaporate the
water, 2nd year - make the anhydrous compound (or dihydrate
version). Maybe have a slight pressure in a vessel, and a fancy
membrane, so the water molecules go one way only?
The biggest problem is finding the right data to check
feasibility. e.g. enthalpy of formation figures for hydrous
versions as I understand it, include the formation of the water
molecule, which isn't helpful, and my initial figures for the
amount of mass needed were far too low.
In the spring in the East of England, can get a few nice warm
sunny days, then the weather gets cloudy, cold and wet and you
need the heating again. Annoying that my conservatory was baking
hot (35+ Celsius on a few days and no way of storing the heat.
Bricks aren't bad, but get 2-3 days at most.
100kWh of heat storage is a good target. Say 80kJ in a mole
(0.11kg). 100kWh is 3600000 x 100 = 360MJ. Mass needed is
(360X10^6 / 80x10^3 ) X0.11 = 495kg. This is still quite a lot,
but e.g. you can get 300l tanks as a heat store in the market. Ask
how warm it will be in 6 months?
Generally the idea is more important than anything I do, (always
someone better at the actual making.) Not sure what people mean by
deterioration. If it gets fully wet, you dry it out, and then it
is either contaminated or not, and you might need to powder it.
With sodium sulphate would want to dry completely to anhydrous for
longer term storage. Is there deterioration from CO2 in the air?
End to end workflow: As mentioned in a previous post, would be
happy enough to move containers around to begin with + top up with
water. Not prepared to handle the actual exposed chemical on a
daily basis, or have exposed crystals in living areas. Full
automation is the only way some people would get this type of
system i.e. no energy at the end of a working day, just get a
ready meal and watch TV. Saw on Wikipedia that Sodium Sulphate was
proposed for thermal storage in 1953. I feel you could build an
evaporator tower, so just need a bucket to capture the result.
Soaked fabric, dry, and brush off the crystals? - could be automated.
As I understand, sodium sulfate is easier than that. As it heats
to 32C, it melts/liquifies and absorbs a substantial amount of
heat. As it cools below that temperature, it releases that heat.
No drying to anhydrous or rehydrating, just keep it where you need
the heat, somewhere where it won't leak.
Yes, it won't store the heat for months, just maybe from the day to
night. It is a good spend of a couple of hundred GBP to get 25kg, a
couple of cool boxes, black paint, batons, aluminium sheeting and
polycarbonate and see how much heat I can collect on a sunny day.
During lockdown watched a lot of videos from Canada with passive air
solar panels, usually with a small fan. If nothing else should
stabilize the temperature, and let me grow plants in a south facing
all glass lean-to.
Trying to melt a bucket load all at once probably isn't best. Just
fill green or brown bottles, and after melting, store them in the
cool box and in the evening bring them out. No dangerous sharp edges,
the only risk is accidental consumption which should be difficult
with something tasting so bad. Noted as well that sodium chloride
can be added, and usually you buy anhydrous sodium sulphate, so the
end result from 25kg is a lot more. Don't want a pressure cap, or
water loss, have a small vent, and top up with mountain spring or
de-ionised water.
For this, also could have three rows of bottles (or equivalent) on the
inside window sill to capture the sun. Then in the evening take them
down into the room and close the curtains. All could be assisted by a
small 12V fan running from a solar panel (no battery or control
circuitry needed.)
There were videos of heatwaves in various countries. Hopefully with
this technology (and others) should keep the maximum inside
temperature below 32 Celsius. Put the bottles outside to refreeze at
night.
Back to the subject: Having 10 tons of salt on the property is a
liability at this moment in time. Biomass is an option - they used to
coppice wood, well managed aerobic digestion is the best option. Can't
really turn them on and off. Lots of things to investigate here. Like
is a heat exchanger running through one the right approach. Likely
need monitoring for methane, and know what to do to take action. If
accepted a yearly clean out may be too dirty for some, but this
wouldn't bother others so is a job for people.
https://www.oxy.com/globalassets/documents/chemicals/products/other-essentials/173-01791.pdf
Di-hydrous has a equivalent energy of solution, but creating it wouldn't
be easy with passive solar + control and venting. e.g. Have air coming
into the evaporation room when the chamber is too cold, then the
moisture will be soaked up and you're back to square one. The given
enthalpy of solution is -72.8 cal/g, or -72.8 x 4.2 J /g or 305kJ/ kg.
With 1000kg (40 bags at GBP 30.00 each) costing GBP 1200 for 305 MJ of
storage, or 84kWh, enough for a week or so. An awful lot easier to get
a gas canister; melting/ freezing; direct heat storage in water or
brick. Softwood has energy density of about 22MJ/kg. So instead of a ton
of reusable salt could get 305/22 = 14kg of wood.Continuing the post as a general dump: I feel a drying room for salt
would need a condenser. This isn't easily done in Britain in the
summer, because when the sun is warm, normally is isn't freezing cold.
In places with continental weather this is different. e.g. sunny days
in Feb, when there is snow on the ground. The reason for wanting higher
density storage than water is because in my case I want to carry the
material to where it is needed. Most systems use a pump and water, and a
lot of water for the heat storage.
With reusable dried salt heat energy storage this could be provided as a
utility with a distribution on tracks, going into a building with
something like a cat flap. In the UK, this would never happen, so need
rubber wheels. The box would also have water with the quality needed to
rehydrate. With a sealed box, strontium as per government funded
research, (not the radioactive 90), should be OK, a bit like diesel is a
bad contaminant, but widely available for specific purpose. Drying would
be done as close as possible to the point of use for the cycle economy.
If you remember back, gas wasn't used for heating at first, coal was
used for heating until the 1950s/1960s/early 1970s in Britain. Then
natural gas and central heating came along. Gas was the cooking fuel.
Other countries have a hot water distribution system in towns. There is
a sweet spot for the amount of salt you would want to store, e.g. using
it once a year, likely isn't a good use of resources. Using it seven
times in the heating season should be OK. Also I'm not bothered by hot
water on tap, as you only really need a 50 gallon hot water tank if
you're using a bath. Showers can heat their own water, as do washing
machines now, and dishwashers. Why don't I hang up a few solar water
heater bags in the conservatory to bring the heat in? This would be
cheap and effective. Basically a 20 litre bag bursting in the actual
house upstairs is a disaster. Should decant the water? Moving a lot of
medium heat e.g. 45 degree water isn't so effective. Integrate into the
boiler based heating system. Too many things to go wrong, and the water
isn't hot enough at the right time. Would I drill two 20mm holes for
15mm pipes through the wall for a completely separate heating system?
Yes, all easily removed, and not much damage. In England there can be a
feeling even if you own the property, in effect you're a custodian, so
generally people aren't happy with your building being trashed (building
control has some powers here, usually for safety).
I would like a well installed passive air heater on my wall. Again max
2 20mm holes and I am happy enough with it. This is still at a DIY
working height (e.g. using a platform). Can't do everything at once, but
I would be happy with a black box or two on my wall. Unfortunately for
this tech, which is low tech, isn't on the market. An effective size
would be too heavy to hang on my wall at once safely even at 10 feet. So
need a 600mm square modular system, again with the two 20mm holes. A
passive air heater on the wall would bring in an equivalent amount of
heat to a window of the same size when it is sunny outside. Think sunny
days in Feb/Mar. Can get data here:
https://solcast.com/solar-radiation-map/united-kingdom/
- politics relevance -
The planning regulations in England, in my view, would be better with
more weight on the carbon goals, and less on the aesthetic. Need people
to be able install solar panels in gardens, walls and roofs- passive
air, solar PV, solar panel (water)- without permission, conservation
areas and listed buildings excepted. Also they need to ban shade from
the neighbours' evergreen plants on any part of a domestic dwelling for
the colder 6 months of the year.