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Old 02-03-2018, 17:58   #1
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Ice as a battery

Make ice while the sun shines. To paraphrase an old farmer's adage. Batteries weigh up rapidly, and have a short life expectancy. LIPOs and other Lithiums have not lived up to their billing in serious voyaging . The technology is not mature enough, nor is the hardware reliable enough as far as I can determine.

The best storage medium is "work done". That is to say do work while you have energy. The most obvious case is ice. Instead of running a refrigerator that mindlessly cycles based on a thermostat, day or night, it only makes sense to make ice while you have energy. An "ice battery" is cheap, and never wears out. Water can be frozen and thawed an infinite number of times. I did the weight calculations on water / ice, as compared to battery storage some time back, and found that it outperforms lead acid batteries in energy stored per pound, unless you run them down more than is recommended. It does it at what amounts to zero cost, and zero maintenance. Lithium batteries will outperform ice on a pound for pound basis, but at a very high cost in comparison. I propose running a freezer when one has surplus energy, freezing ice to use for an ice box. The whole affair could be a single system with a tiny circulating fan, or it could be a simple as transferring frozen containers from freezer to ice box. Higher gravity beer actually works quite well as an "engineered fluid"

Other options of course include things like running a watermaker while you have power, running a slow cooker or electric pressure cooker, or anything else that is periodic.

H.W.
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Old 02-03-2018, 18:13   #2
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Re: Ice as a battery

Absolutely Owly, this has been done for years and is called eutectic refrigeration. Latent heat involved with phase change, sees massive amounts of energy stored if done and controlled properly. Best to use a glycol / water solution that has a lower freeze temperature than straight water.

We have thousands of these marine eutectic systems around the world providing the most power efficient refrigeration possible.
See: our 'Why Eutectic' web page for a detailed explanation.

Cheers OzePete Ozefridge | 12 Volt Refrigeration Systems
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Old 02-03-2018, 18:36   #3
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Re: Ice as a battery

You could use the explanation of ice as well to make energy, no?

As in as it expanded somehow capture that in a pressure to do something ?
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Old 03-03-2018, 04:33   #4
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Re: Ice as a battery

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You could use the explanation of ice as well to make energy, no?

As in as it expanded somehow capture that in a pressure to do something ?
Ice doesn't make energy but is a very efficient medium for storing and making available 'thermal energy' as it phase changes.. Freezes and thaws.

For example, if you wish to lower the temperature of one litre of water by one degree centigrade you only need to remove one watt of heat but to lower the same one litre one degree C as it phase changes from a liquid to a solid (to freeze) requires 80 watts of heat to be removed.
Now having frozen the eutectic mass solid, likewise it will absorb 80 watts of heat to thaw and phase change back to a liquid. (Like a large ice-block in a drink!)

Now imagine the efficiency if the heat removal (freeze) is done when power is abundant and the thaw process maintaining fridge temperature when power is limited! Understand that principle of employing the thermal storage benefit of a phase change material and the benefits are obvious.

BTW just one litre of phase change liquid stores the energy similar to a small 12VDC compressor running non stop for approx 1.5 hrs.
A eutectic refrigeration system is far more power efficient and stores energy at much less weight than the battery(s) needed to power a cyclic system.

Cheers OzePete Ozefridge | 12 Volt Refrigeration Systems
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Old 03-03-2018, 06:13   #5
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Re: Ice as a battery

Google "polar tubes"

Seawater makes a decent eutectic solution, would like to know if adding more salt will usefully raise the phase change temp.

Or is there a source for engineered solutions reasonably priced?
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Old 03-03-2018, 06:55   #6
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Re: Ice as a battery

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Google "polar tubes"

Seawater makes a decent eutectic solution, would like to know if adding more salt will usefully raise the phase change temp.

Or is there a source for engineered solutions reasonably priced?
Water's freezing temp will continue to decrease with addition of salt, but alcohol or glycol are not corrosive, and salt is highly corrosive. Note that I advocated beer ;-) In a pinch you can drink it. Unfortunately lowering the phase change temp does not improve the heat of fusion (energy stored), it just moves the phase change to a more useful temp.

My point really was that doing things with electricity such as making ice, while you have electricity is far better than actually storing electricity.

It's also worth noting the depth of discharge versus battery life curve. If one looks at cost per KWH stored, the penalty for discharging below the recommended top 20% is actually quite small. If there were no penalty, for example, you would have to replace a single battery twice as often as a pair. In reality there is about a 15%-20% penalty if I recollect correctly. That's a pretty small penalty when looking at the huge weight savings, and replacing a large bank all at once is a pretty large hit, replacing fewer batteries a bit more often is easier to swallow if one is on a limited budget.

We are told to use only the top 20% for max life, but that does not give us much more total discharge KWH over the life of the battery. They stress only time, not utilization.

H.W.
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Old 03-03-2018, 07:03   #7
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Re: Ice as a battery

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Originally Posted by OzePete View Post
Absolutely Owly, this has been done for years and is called eutectic refrigeration. Latent heat involved with phase change, sees massive amounts of energy stored if done and controlled properly. Best to use a glycol / water solution that has a lower freeze temperature than straight water.

We have thousands of these marine eutectic systems around the world providing the most power efficient refrigeration possible.
See: our 'Why Eutectic' web page for a detailed explanation.

Cheers OzePete Ozefridge | 12 Volt Refrigeration Systems

Thanks Pete: This is exactly what I was talking about. The challenge then becomes strictly and electrical one of dividing the incoming current between battery charging and refrigeration. Doing this manually, that is to say containers instead of a unified glycol system would allow storage of a lot more "cold" if one has an insulated space to store it.

H.W.
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Old 03-03-2018, 07:29   #8
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Re: Ice as a battery

GREAT and practical discussion guys. Thanks a lot.

We have an Aerogen6 wine generator and two 315 watt solar systems.

It just eats at me to see the wind generator dumping power into resistors to “waste” it. I had thought of heating water but the cooling thing is even better. Good stuff.

Making water is also a useful purpose for excess generation n but the initial cost and complexity is a bit high.
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Old 03-03-2018, 07:39   #9
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Re: Ice as a battery

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Water's freezing temp will continue to decrease with addition of salt, but alcohol or glycol are not corrosive, and salt is highly corrosive.
Polar tubes are usually cheap PVC pipes maybe 2"D, cut to fit the shortest box, with glued endcaps.

Used like the blue freezer packs, cycle between a supercooler and freezer, as you say just before peak power production "excess solar" conditions or before a long dino juice run.

No corrosion issues, and easily replaced if cracked from abuse.

Cheap DIY eutectic holding plates, kinda sorta.

Keeping the solid state longer must be the overall goal right?
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Old 03-03-2018, 10:11   #10
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Re: Ice as a battery

I have to say, this seems like a great idea to me. The biggest power draw--and therefore battery draw--by far in most solar systems is the refrigerator, and you wouldn't have to hear the compressor running at night!

You would obviously need as much insulation as possible, and more volume in freezer area to store all the ice you would need. After that I would think that the problem would be maintaining a reasonably consistent temp in the non-freezer area as the ice started to melt, and sometimes a lot of it would melt if you had a week of cloudy days.

Really it's not so different from when they used to deliver ice blocks. Probably the idea is even better suited to someone with a home system living off the grid.
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Old 03-03-2018, 10:30   #11
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Re: Ice as a battery

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Originally Posted by hpeer View Post
GREAT and practical discussion guys. Thanks a lot.

We have an Aerogen6 wine generator...
wait - I want to hear more about the wine generator!

great discussion. phase change as storage solves the problem for places where the wind and sun shut off at night
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Old 03-03-2018, 10:55   #12
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Re: Ice as a battery

The problem with phase changing beer is that unless it is sealed tight, it is going to go flat.(G)

The problem with "extra" ice storage or eutectic blocks is that they will be bulky, and they will steal cooling from the normal cooling system unless you are pulling them in and out of the ice box (refer) all the time. Unless you're going to have regular excess power to regularly chill them, in which case aren't you just installing two cooling systems?

So it comes back to using eutectic cooling in the refer, and chilling it when you can.
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Old 03-03-2018, 11:39   #13
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Re: Ice as a battery

Up here in Alaska I've been working on a solar beer warmer. I leave the beer out at night and it turns to ice. Using the latent heat of evaporation theory I use a magnifying glass and low solar angle to try to warm to aforementioned beer to coax it back to its liquid form. So far no luck, but by spring I hope to have a break-thru.
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Old 03-03-2018, 11:58   #14
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Re: Ice as a battery

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Unless you're going to have regular excess power to regularly chill them
That is the scenario where eutectics of any sort really make sense.

The polar tubes idea is a poor man's **substitute** for a proper holding plate fridge setup, anyone who can afford the latter should definitely not bother, using both would be silly.
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Old 03-03-2018, 15:02   #15
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Re: Ice as a battery

Yes the holding plates actually replace much battery capacity by using their capability to store energy.

The efficiency of energy conversion from the solid to the liquid state is 100%. No energy iost (love that!). If you only run the compressor when you have excess power available (generator or alternator), and this is enough time to freeze the eutectic solution in the holding plate, you don't much care about the efficiency of the compressor itself and the entire process is taking place outside any battery requirement.

On the other hand if you want to use a lot of solar power, you need a bigger battery bank to run a constant cycling cold plate evaporator system.
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