Energy Matters Forums

[AlanJsStuff]

Hi Guys and Gals
New to this forum, I have been researching solar and alternative energy storage for some time.
Recently decided to make a start on getting off grid. Well the storage of hot water is pretty simple, so need power only for those other pesky stuff. Trouble is more stuff more battery storage needed. So instead I have been whittling down the need for those big abtteries.
Recently I realised water as ice has as much energy storage capacity as lithium ion batteries 90wh/kg. Well that was a bolt from out of the blue. Since I also realised back in the bad old days before compressors ice blocks where used succesfully. Also realised refridgeration is the most important device to keep working in the house, on those long hot days.
Result, a simple project for all.
My initial calculation go like this
DOMESTIC EXAMPLE
So want to cool a refridgerator for 2 days with a block of ice.
Typical refrigerators are 600W and run for 50% of the time.
So 600 * 24 * 2 * 0.5 Whr = 14400 Whr
weight of ice = 14400 / 92.995 = 154.847 Kg
or (1cc = 1 gm and 1000cc = 1 liter) 154847 cc = 154.85 liters
154846 cc = 53.7 cm per side
How big a panel
need to freeze 2 days of ice in 6 hours
14400 Whr / 6 Hr = 2400W panel
So I would go for 3 KwHr panel, and a compressor that size to boot.
___________________________
while the size seems big, rememeber insulation is cheap, ice can be bank of blue freezer blocks.
If there is space on top of the fridge, put it there, cut a few holes.
Only problem is some electronics to turn the compressor of the ice block bank on when the sun is shinning enough.
After approaching a couple of autralian companies to give the idea away, non have responded.
Not even Energy Matters.
Oh well now every one has the concept.
cheers
Alanj

[offgridQLD]

"Typical refrigerators are 600W and run for 50% of the time.
So 600 * 24 * 2 * 0.5 Whr = 14400 Whr"

Alanj,
your calculations are much to generous. I run a normal 240v 510lt fridge/freezer offgrid for 1kwh - 1000wh AC / 24hrs. That's roughly 1300wh DC a day or 2600wh dc for two day taking into account 30% loss from PV output to usable AC.


"So I would go for 3 KwHr panel, and a compressor that size to boot."

To produce 1300wh a day to run a normal fridge/ freezer mentioned above I would only need 300 - 400w of solar panels.

Ice might be able to store as much energy pr kg as lithium but isn't much good to you unless you have a way to get back that energy in a usable form that's as efficient as a lithium battery .

If the aim is to avoided battery's or reduce battery bank size. Perhaps a fridge with a large thermal mass of ice that froze during the day from direct pv power with a small battery on float to cover small dips on output. Then the compressor didn't run all night due to this . Though typically a well insulated fridge does this to some extent anyhow.


Kurt

[AlanJsStuff]

Hi Kurt
You are correct, the refrigerator I chose was a 4* type smaller icebox.
I had 14000 w-hrs for the energy stored for the two days, for this unit, a similar number to yours. However using your number 2600w-Hr, I assume only 6 good solar hours a day. So your 2600w-Hr becomes 433 watt you are correct again. I made a mistake; however a good one for this ice system.

Yes correct idea is to use no batteries; ICE is perfect storage for an ice machine.
There would be losses from the compressor, which are likely to be as much as 50%. Compressors are not perfect machines. Still a dedicated 866w (say 1Kw panel) is cheaper than a big bank of batteries, these days.

Indeed a larger refrigerator, with big ice space would come close to doing the job. But loosing half the icebox space might annoy the wife a little. Putting the ice bank on the top of an existing refrigerator, removes the need for fans. However the existing ice box coils need to be installed around the ice bank.

I designed a microprocessor controlled circuitry to direct power to the compressor unit of the ice bank until it was frozen, then directed the remainder to a truck battery to run 12V LED’s. All my lights are converted to 12V led units the total draw is 200W, for 4 hour on time of all lights that’s 800 w-hr, a tiny amount. I use the truck battery so I can run the washing machine once a week and air dry the clothes. Yes I’m scruffy and never iron unless I really have to.

Taking the refrigerator out of the energy storage requirements for a house really reduces battery needs to a minimum.
Thanks for taking an interest, you are the first in Australia to do so.

[Tracker]

..
A bit OT to thread, of protecting against power surges.. but..

150Ltr of ICE is a massive amount, and containing it, and effectively using it, would be hard to implement.
Ice expands on freezing that causes major issues.
I can't see how having (what I think was) a "Tucker Box" type freezer full of ice, is in any way useful.
I can't see how practical it would be , to take a domestic Frost Free refrigerator, and cut holes in the freezer floor.. It would never work normally, when on daylight power, and would FREEZE to goods in the main PC compartment

Firstly, we have to be practical.. I use PET bottles, part filled, with Sodium Nitrate solution.. These are in the top of the freezer.. If something happens whilst away, they will give a small amount of help, but it still won't be automatic..

Were I setting out to devise a "Cold Backup" refrigerator, I would modify a standard domestic (top mount) frost free Fridge/Freezer..
[I am assuming that you have (effectively) an off grid power system for lighting etc., but not good enough to run the fridge overnight..]

SO - changes - The fridge's MECHANICAL thermostat directly operated the freezer-fan and a small 240V relay
The relay operates the compressor via a time clock or a light sensor.. ie.. the compressor would only run when solar power was available.
I would stand, PART filled PET bottles with Salt Solution in the freezer.
The FAN would move air around these bottles, cooling the air, just as the compressor would normally do

These bottles would freeze during the day and then the Thermostat/Fan would demand circulate the cold to the PC compartment..

That would have to work efficiently, with minimal "OBVIOUS" changes to the basic refrigerator..

((If you don't have 240Vac at night and just battery power, then a DC fan would be needed eg. 12V from a Fisher Paykel freezer..))

The real challenge is with the frozen stuff.. There I think the chest freezer has to be the answer.. easily will cope with an overnight sleep.. a special shallow basket tray in the top with those salt-water bottles could help.. but a pain to have to lift them out every time you want to get to the peas..

I think that I would be assuming that there was a daily cycle and just cover that day.
Bad Weather would need to be covered by alternate means - ie generator..

Thanks for taking an interest, you are the first in Australia to do so.

PS - the topic has been covered MANY times, in various ways and in various threads..

My philosophy - KISS - Leave the device as original as possible.. ( Keep the bride happy )

I noted your comments about what seemed to be adding a small freeze on top of the existing fridge..
what, did you seal them together and cut holes between...
Be sure of where the existing condenser coils are, if thinking this way.. MANY modern fridges have the condenser pipes under the outside skin..
Two compressors to run..
..
.

[AlanJsStuff]

Hi Tracker
“A bit OT to thread, of protecting against power surges.. but..”

Well could not find any other place to put it, so since it removed the surges as well put it here.

“150Ltr of ICE is a massive amount, and containing it, and effectively using it, would be hard to implement. Ice expands on freezing that causes major issues.”
Well I suggested using the freezer block available for esky’s


“I can't see how having (what I think was) a "Tucker Box" type freezer full of ice, is in any way useful.”
The point here is to add enough ice with the same energy storage capacity as expensive batteries, so no 240V night time power is needed."

Putting the Ice bank energy store on the top of the refrigerator allows natural convection to cool the refrigerator. An extension would be to allow a flap to open and close to keep the frost free feature. This could be done with a thermo/mechanical device.

Were I setting out to devise a "Cold Backup" refrigerator, I would modify a standard domestic (top mount) frost free Fridge/Freezer..
[I am assuming that you have (effectively) an off grid power system for lighting etc., but not good enough to run the fridge overnight..]

“SO - changes - The fridge's MECHANICAL thermostat directly operated the freezer-fan and a small 240V relay …..


This is a reasonable solution. How many bottles to keep the refrigerator cold for 2 days, my design aim? What is the energy storage W-hr of a bottle?

Thanks for your ideas

[offgridQLD]

Alternatively the extra 500whr (typically overnight battery consumption to run a 500lt fridge) could be purchased for under $500 using lithium battery's . The week spent constructing the ice fridge could be spent earning the $500 in a payed job.

Seriously I understand the fridge/freezer is one of the big consumers and all the more reason to pick a low consumption one . With the price of lithium battery's and the very low consumption of some modern refrigerators I think it could be a lot of work for little gain.

That said I wast about 1kwh a day just pumping water that I could easily pump to a high location during the sun hrs and save running my pressure pump overnight. Perhaps one day when I have nothing better to do.
Kurt

[AlanJsStuff]

Yes indeed Kurt
At 67 I get few job offers these days.

Indeed Lithium batteries are getting cheaper, but Im also am concerned about using materials which are rare Though Lithium is about 1% mark. Solar panels are also consummers of rare earths but they are minimized to decrease costs. The ice has almost infinte life span and abundent. The compressor can be recycled, an a new one installed. Most units use ammonia these days and thus no rare earths.

But it does seem to me there are cheap storage solutions for the home.
Pumping water up to a tank anothe example of good old fashioned technology no longer used.
Indeed that is a perfect storage solution instead of a using a high pressure pump.
We used to have a header tank in the roof, which fed the house, showers etc, OK pressure was low, but the shower heads and taps where designed for it.

I am also building a methane digester, for cooking needs. Well digesters produce about 70% methane, 30% carbon dioxide. I'm developing a system to convert that carbon dioxide to methane using solar energy. The system stores the converted methane back into the digester.

Whittling away at the storage solution will I beleive come up trumphs in the end. Unless some smart person develops a cheap, long life battery which uses abundent materials. Something which has not happened after 100 years of looking.

But we live in hope
cheers alanj

[AlanJsStuff]

Hi Tracker
just noticed the PS

PS - the topic has been covered MANY times, in various ways and in various threads..
My philosophy - KISS - Leave the device as original as possible.. ( Keep the bride happy

Agree indeed un happy bride unhappy husband.
Well would like to see a reference to the thread, I am new to this forum, and open to suggestions always.

cheers alanJ

[Tracker]

.... How many bottles to keep the refrigerator cold for 2 days, my design aim? What is the energy storage W-hr of a bottle?....

I think that using a weak salt solution, raises the freezing point and thus increases the effective energy density..
My thinking with the bottles is that air will circulate easily and thus they will "Defrost" more uniformly..
My belief is that having a larger volume will create a situation where you have a "Ice Ball" within the container, and partially "Insulated" from the surroundings, by the melted solution.. ie the solid might be -20, but the liquid, ??? -10c to 0c..

Gordon is far better at all this mathematical stuff.. I'm too old to try and remember enthalpy etc.etc.

...Most units use ammonia these days and thus no rare earths.

Not in the big smoke.. I've NEVER seen one.. and don't be too confident about recycling and repairing fridges..
The Labor Govt. KILLED the service industry with the Carbon Tax, forcing up the cost of ALL refrigerants, and making it more practical for the Chinese to ship new/working stuff here.. ie.. pay $400 to fix an old one of $700 to buy a new one (No CT involved).... So the old one is smashed up and the gas "Accidentally" escapes..
Now that is just great for the environment, isn't it..
(yet to see if the Libs' removal of the CT will reverse the situation.. but I have not fixed (as in compressor change) a fridge for a LONG time..)

It may be a tiny bit better in the country, where it's not as easy to just duck down the road and buy a new fridge..

convert that carbon dioxide to methane using solar energy

That sounds challenging..

PS - Noting the observation about keeping cold for 2 days... again, I would not go that way.. I would concentrate on overnight and then if the sun don't shine -- -- "Plan B"..
ie .. is aiming for 2 days just a bit too ambitious, too intrusive..
..
.

[Gordon-Loomberah]

No domestic fridges have used Ammonia for many years, due to it being a poisonous gas. I think some large commercial units may still be available with it though.

Use a concentrated salt (NaCl) solution if you want the "cool" released, ie the heat absorbed by the ice, at well below 0C. It is possible to have a melting point around -30C with saline solutions. I have some "cold ice" 2l juice bottles which are useful for bringing ice cream home from the supermarket (1/2 hour away), which melt around -30C.
As for making lots of ice and using it to keep the "fridge" cool, I'd only do that in an emergency when you had no power to run the fridge. The COP of most freezers isn't all that high, under 1 for the tests I did with one, so you aren't really getting ahead unless you are able to use excess energy after bringing a battery to float.
You'll also lose your temperature regulation, and will be in real trouble after a week of cloudy weather with no solar energy to freeze ice, unless you want to run a generator. This means burning fossil fuels- I'd suggest that environmentally, you are better using a battery and not having to burn fossil fuels. There isn't much Lithium in LiFePO4 cells, and it is recyclable when they reach the end of their life, hopefully something over 10 years if looked after.

I have a bit of experience with making lots of ice- I had a 450l chest freezer full of 2 and 4kg blocks of ice in late spring/early summer, used at up to 65kg/hot day in order to keep the trout in my aquaponics system cool. You need a lot of compressor running time to make 25kg+ of ice per day- I had 2 chest freezers and the freezer on top of the fridge running to do it. IMO the high cost of buying a large DC fridge unit, able to operate directly from PV panels, since you dont want to use batteries and an inverter, to freeze huge blocks of ice, and the large number of panels required to do that make it an unrealistic goal. Using a good quality low power consumption fridge- have a look at DC fridges, and a LiFePO4 battery would make for a much more useful and efficient system, and it would cost you less to set up.