Deep Cycle Batteries - which to choose??

[Shack Living]

I have:
* 3 x 80Watt solar panels
* 1 x Jaycar cheap 200Watt 12V wind generator (only $500, and will be a good indicator if we are suited to wind)

I have pretty much worked out the system I want to use, except choosing the batteries?? I would like about 1000AH 12 volt all up, so that I can add more solar panels later and use a charger when I am using generator for power tools

When I research brands and types of deep cycle batteries, I just go in circles. Would like something long lived & reliable!! What to buy??

I hear fork lift batteries are the best? but who makes them? and are they better than batteries for solar systems?

[ho-hum]

Backyardpoultry,

Get in touch with the cleaning contractor at your local supermarket. Supermarkets use big scrubbers powered by up to 800 amps of batteries which are recharged every night. You may be able to get hold of some old batteries to experiment with. Normally when one battery goes the whole set is replaced.

I did clean a supermarket for 4 years and had one change of batteries. The machine ran 6 x 100 amp 12v batteries and was used daily. I was forever amazed at how long they lasted and the use/abuse they took. My auto electrician performed a couple of callouts for me [broken wires etc] and even he commented that he hadnt seen batteries worked so hard and perform so well. I imagine the electric forklifts would be similar.

A local contractor should be able to give you clues on where and what to buy. I didnt ever have a battery 'die' on me like car batteries seem to these days.

floot

[Richard on Maui]

We have the Trojan L-16's, which for stand alone power systems are reputed to be the best for the money. You can get better ones, but they cost a lot more money. Christopher will chime in with lots of wisdom on this subject...
We just replaced our battery bank last Christmas, which we inherited from a series of prior users, and from what I can gather, they lasted, with much abuse, for about 5 or 6 years. So far, the replacement set has worked well. But we are in that golden era now where the batteries are actually increasing in their storage capacity. Or maybe that is just about to end, and we are entering the slow decline. Not sure... I should go check the electrolyte levels actually, and read the hydrometer. Damn!
(Sure would be nice if they came up with a better way to store electricity... :lol: )
Have you set up your wind genny yet?

[Shack Living]

Have you set up your wind genny yet?
Nah, not yet. Its still in its 3 boxes, but seems to come with everythng. Might need to wait for the chrissy holidays, like a lot of my projects. We have been having heaps of wind lately too :lol:

Trojans seem to have a good name, but 5-10 years doesnt seem a long time?

[christopher]

Hi BYP,

Richard is spot on. For the money, L16s are hard to beat! T105s are also good, but smaller capacity, so more paralell strings, more possibilities to have a weak connection, bad cells, etc. 4 L16s will make one 800 amp hour battery at 12vdc, a bit smaller than 1000. Having that extra string, for an additional 400 watts increases your likelihood of battery failure.

If you have the money and can find them, nickel iron batteries are the best, but they COST! Their advantages are that they can be cycled to zero without damage, and nothing, short of mechanical destruction, can be done to damage them that cannot be reversed either elecrtically or chemically.

Good luck!

C

[Jez]

We had a thread around here somewhere on the Ni-Cad batteries and where to get 'em didn't we Chris?

As I recall you could only order them from China, but that may have changed since. Darned if I know why they aren't being promoted more.

[christopher]

Jez,

I think the thread was about nickel iron batteries, not nickel cadmium. Cadmium is toxic, and nickel cadmium batteries have what is called "memory effect", which means that if they are not totally discharged, cycled down to empty, their capacity becomes limited. Nickel iron batteries do not have that limitation.

They are very expensive, and hard to get. Why sell a battery that lasts forever when you can have 'em come back and buy more in a few years?

Wish I could get some nickel iron batteries!

C

[Jez]

Yeah, sorry Chris, it must have been nickel iron batteries and I'm stumbling over terminology again :lol:

I just searched the archive here for the specific thread where it was discussed - through two long ones on solar and DC power - but couldn't find it.

I remember googling it last time we discussed it and finding not a lot for sale (but I did post what I found and I'm 99% sure China was the only one manufacturing them), but just googled it a minute ago and found quite a few...maybe things are changing?

[Richard on Maui]

Nickel Iron batteries wouldn't be the only thing that China is the only one to manufacture, eh? Probably half the bits in your computer fit that category, eh!?
So, Christopher, are you serious when you say that you can't hurt them? They will last indefinitely? Do you have to add water to them as often?

[christopher]

Richard,

The original nickel iron batteries used in the US pre rural electrification for 36 vdc wind based systems can still be found. They work fine (if not broken). You do need to add water to them, not sure how often. You can eliminate a charge controller. Nickel iron batteries don't need them.

They are the best batteries for RE. They have a wider voltage swing, higher highs and lower lows, so you need to find an inverter that can take the swings. That is the only limiting factor I can think of.

I wish they were made by a battery company not in Chia, because having a warranty would make spending that kind of money less heart palpitation inducing.

C[/i]

[Shack Living]

Jez,
Yeah I read that thread, which sparked my interest on more :D . I wouldn't take the risk of importing Nickel/Iron batteries from china, but wish they would hurry up and improve the technology for batteries. My understanding was that before combustion engines took off, nearly all trucks in the cities were electric (battery) powered. I realise they only went the speed of a horse, but over the past 100 years of research, it seems a poor effort.

[Cornonthecob]

I've tried looking up nickle iron batteries online to no luck.....where should I be looking?

[Jez]

Not spelling 'nickel' right in your search terms would be the problem I reckon Corn. Using Ni-Fe or NiFe can help as well.

Backyard, I can understand your unwillingness to import them...it's a lot of money. I guess with the Ni-Fe batteries it's not a question of improving the technology, more a case of finding that rare company who isn't into profiteering and making products designed for planned obsolescence.

I've found a few 2nd hand Ni-Fe batteries for sale in the US (one 32V with an arc welder and a wind generator included), and industrial size ones made by a company called Rauma Oceanics from Finland (edit: it seems Rauma was shut down by the CIA!!!), and I know for a fact that the thousands of underground EV afficionadoes use Ni-Fe batteries in their cars right up to competing in (and winning) drag races etc, so they must be out there - or thousands of people are getting great use from Chinese ones...just a question of hunting hard enough.

One other lead I have ATM is at this link (Click) (http://www.green-trust.org/offgridtutor.htm) - it discusses Ni-Fe batteries and their benefits, then at the bottom of the page there is an email address for sales:

E-Mail: sales@gri2000.com

I'm going to put some more time into it when I can...it's an important issue...the holy grail is out there somewhere. :D

[ho-hum]

Backyard.. I run a tip [waste facility] and we get a lot of battries. Most batteries these days are nickel plated. Fisherman now moan that they cant make their own sinkers any more as the nickel content makes the sinkers fragile and prone to shattering.

I have read on a few occasions where handy souls have got their battery bank from a tip or some such place. I dont know how to check batteries but I would imagine it would be a skill worth learning if you are getting into 12v systems. It has been a long time since I saw such articles, maybe the technology has moved on.

I did a quick google and didnt locate anything useful, perhaps someone with faster fingers might find a link.

cheers

mike

[Richard on Maui]

One way to check batteries Floot, is to use a hydrometer. You squeeze the electrolyte up into the chamber and the float measures the specific gravitiy. If you recharge them and they still test bad they are bad...
Tell us more about your tip?

[Jez]

Haven't found time to do a good search again on NiFe batteries, but I did notice that Be Utility Free (US site - click to view) (http://www.beutilityfree.com/) have an updated 2006 PDF catalog for NiFe batteries:

NiFe battery specifications and prices (Click to view) (http://www.beutilityfree.com/batterynife/Flyer.pdf)

They're Chinese ones, but it may be worth contacting BUF to see if you can get some sort of guarantee which they will honour on your behalf to the manufacturer.

Contact email:

sales@beutilityfree.com

I'll update this again if and when I find something else to add.

[Shack Living]

I sourced 12 240AH 2V exide flooded batteries for $20 each. They are 4 years old, and from the railway. Seem a good buy so far :? :D

[dgriffith]

I've a source in Australia for Chinese made Nickel-Iron cells. I believe that they're the same ones as the BeUtilityFree cells, although it's a bit hard to tell for certain. I've been quoted $285 + delivery from Victoria for 400Ah cells that I'm looking at using for a place I'm building. A 48V system with 400Ah cells works out at approx 17kWh of usable capacity at about $12K. A similar lead-acid system with 30% discharge for long life would need to be about 60kWh of cells or about $20K if you buy some quality gel-cells.

The big downside is their poor efficiency - whispers on the internet have it at 65-70% compared to lead acid gel cells which can reach 98%. If you've got an excess of power (eg, wind + solar) or are willing to put a few more panels in or run a genset once a week (like I will be), then they're ok. The upside of course is their long, long life and the ability to swap out dud cells if necessary. Also their high tolerance of abuse (over/under charging) makes them handy for places that might be vacant and ticking over for long periods by itself.

There is very little up-to-date info on NiFe cells - there's a battery FAQ that mentions them that seems to be linked all over the internet, but that's about it. I'm planning on putting in a trimetric battery logger/monitor and will be getting some real-world efficiency and capacity figures. And then I plan to post them everywhere all over the internet, so the next poor sod doesn't have to take such a risk.

For inverters - the "Sunny Island 5048" inverter handles NiCd cells (which are *reasonably* close to NiFe) and is about $7500, but it's a 5kW inverter-charger that can sync/boost with a genset or grid so you're getting a fair bit of bang for your buck there. It can also handle the removal of up to three lead-acid or NiFe cells if they fail without drama, so it could be a good bit of gear for those that want max life from a battery pack.

Seeing as my account mysteriously vanished last weekend when I tried to post the contact details for the supplier, I won't bother doing it today. Message me if you want the details.

I will post the operating specs for the 400Ah cells though -

Charge rate: Use charge rate 0.2C5 ; The constant charge current will be 80A for a 400Ah cell.

Recommended charge voltage for 400Ah cells :
1 Boost Charge: 1.72V - 1.74V charging for 8 Hours maximum;
2 Float Charge: 1.5V.

Discharge rate: Recommend discharge the battery under current 200A, max. 200A for 400Ah cell. Max. discharge current of cell will be 2167A. (I presume that's short-circuit current)

You need to factor in a bit of voltage sag under full load. Probably not a good idea to run 12V systems with NiFe cells - the currents tend to get a bit high for the power output.

Cheers
Dave

[Richard on Maui]

Interesting info there dgriffith.

I was just listening to Radio National's Science Show from last weekend, and a fellow was talking about an electricity storage technology called "ultra-capacitors". Anyone know anything about these thingys?

[MonteGoulding]

Would it be more efficient to use any unused power being generated to pump water up into a header tank then have a mini-hydro generator for when it flows down? The same header tank could be usef for other obvious functions.

[dgriffith]

I don't think you'll get any practical benefit with pumping/micro-hydro on stored water. Except for the fact that you've now got a convenient source of water at a height for household use.

Gel lead-acid batteries are currently the most efficient and accessible form of electrical energy storage on the market. If you've excess power, you're probably better off either getting more batteries, using it to heat water in your hot water system or as you've suggested , just to pump it up higher for later household use, to save having to run a pressure pump later when you turn on a tap.

Or just start turning on a few more appliances :D

(Long technical babble follows to explain why. If you just want to trust me on this, stop reading now.)

Joules is a unit of energy, like the amount of water sitting in a tank. Watts is how many Joules you use in one second to do work, like water flowing from a tap. Watts and Joules are very handy to use in situations like this.

For instance, potential (stored) energy of something raised up above the ground is

Energy (Joules) = Mass in kilograms X G (gravity) X height in metres.

So I say I've got a energy surplus equivalent to a 50 watt panel running 6 hours a day. That's 50 watts x 6 hours x 3600 seconds per hour = 1,080,000 joules. Seems like a lot!

You have 10000 litre tank, 5 metres off the ground, full of water that you want to set up as a micro-hydro system. Water weighs 1 kg per litre, so stored energy in that tank is 10000kg x 9.81 x 5 = 490,000 Joules.

Now, we have a pump that is 50% efficient at getting water up there.
From the amount of stored energy, we can work out that it would take 980,000 Joules of energy to pump all that water up there, to get the 490,000 Joules of energy stored in that tank. The other 50% is wasted as heat and a little bit of noise and vibration from the pump. So pretty much all that 1,080,000 Joules is used up getting the water up into the tank.

Now, for getting power out of the tank with a hydro setup :

We have a hydro setup that is 50% efficient at turning moving water into electricity. The rest isn't captured (the water's still moving when it exits the turbine, some gets lost in the generator, etc). So now we have 245 kilojoules of usable energy up there.

If I could dump that 10,000 litres through that turbine in 1 second, it would put out 245 kilowatts. For 1 second, then the water would run out.

If I did it over 60 minutes (3600 seconds), it would put out 245000/3600 or 68 watts steadily for an hour. That's if the hydro system is 50% efficient, which is a pretty bold claim to make with mechanical systems.

Note that the 68 watts for one hour is a pretty poor amount left at the end of all this, considering I had a surplus equal to a 50 watt panel running for 6 hours at the start of all this.

Now, if I used that surplus energy to heat water in my hot water heater, the results are as follows:

To heat 1 kilo of water 1 degree, you need 4186 joules.
We have 1,080,000 Joules, and for an example, we have a 50 litre tank of water at 20 degrees. It's pretty small for a good reason, which you'll see in a minute.

So when we add 1,080,000 Joules of energy to 50 litres of water, it gets warmer by 1,080,000/ (4186 x 50) or a spectacular 5.1 degrees. So now you've got water at 25 degrees instead of 20. You don't get any losses converting electrical energy into heat in this case - it's pretty much 100% efficient. Of course, your water heater insulation isn't however, so you lose a bit there.

If you've got 250 watts surplus for 6 hours, such as with a wind generator overnight or something, then your water gets an extra 25 degrees warmer, making it 45 degrees , which isn't too bad for a 3 minute shower in the middle of winter.

(end or rather long technical babble)

[Richard on Maui]

That was great dg!

[Cornonthecob]

I need to go and borrow some books.....I can't get my brain around any of this.

[ho-hum]

dg... GREAT STUFF...


[pssssst someone ask him another question quick so we can keep him here!!!!]


cheers,

floot

[jamessteward]

How about a slight change of direction....

Are there any solar water heaters that use a parabolic dish to concentrate the suns heat energy to a point? The dish doesn't have to be circular, a rectangular shape will do provided the curve is parabolic. This is akin to using a magnifying glass to burn paper - something many folk marvelled at as kids.

I believe the available solar energy lies between 125 and 375 W/m²?

This given, and that solar panels are only about 15% efficient, it would seem far better to heat water by direct focus of the suns energy than double conversion of solar to electrical and electrical to heat, wouldn't it? (even though the electrical to heat conversion is 100% efficient...)

Now if the water gets nice and hot, and you could do with some electricity, why not invest in a stirling cycle motor/generator set to make use of the excess heat? See http://en.wikipedia.org/wiki/Stirling_cycle

Cheers.

[Tezza]

This is all above my head but its interesting never the less.....


Just wish someone would hury and invent a hoshold set up that we all can use..

If we wait for money makers to make the hard desicions well be waiting for ever

Tezza

[9anda1f]

http://www.homepower.com/files/solarice.pdf

9anda1f

[jamessteward]

The solar ice maker is a good one. It also shows an example of the parabolic dish I describe. The ammonia absorbtion method for refrigeration is quite old and is the basis of portable camping refrigerators (excepting thermo electric peltier coolers that are horribly inefficient).

This crowd produce a stirling engine device that both heats the home and generates electricity from gas.

http://www.whispergen.com/

In the US and other countries there are already arrays of solar reflectors that drive stirling engines that produce usable electricity.

Stirling cycle engines have for a long time been used on boats to generate electricity as the abundant water makes for a good cold source.

[Jez]

Welcome James.

The evacuated tube (Click) (http://www.made-in-china.com/showroom/jiashensolar/product-detailWboJXeuKHmDx/China-Heat-Collecting-Tube.html) style hot water heaters they're building a lot of in China use direct sun to heat...haven't heard of a different method.

Apparently the evacuated tubes are much cheaper to build than (as you say) the rather inefficient panel style which is common here in Australia.

Yep, if you had a whole roof full of them you'd have plenty of potential energy! 8)

Bit more info on them (Click) (http://www.planetark.org/dailynewsstory.cfm?newsid=36636) - becoming hugely popular in China...and probably would be elsewhere if their distribution became more widespread. One huge advantage (beside the cost) is that they work well on cloudy days and even in freezing temps.

[dgriffith]

I've got a link here somewhere to a mob that makes/assembles evacuated tube systems here in Australia .... they were the only ones out of quite a few solar hot water people that actually replied to my email, so they've got a head start in my book. I'll look it up and post it after I get home from work. Maybe after I have a bit of a nap - night shift kind of slows me down a little :? . They were quite flexible about it , you can buy single evac tubes and the manifold that the tube goes into pretty cheap. ($40 a tube? Can't quite remember) - edit: the company in question is "endless solar" at http://www.endless-solar.com

Looking at getting an evac tube system for my new place - a fair bit of the northern roof area is going to be taken up by panels, so a relatively small, efficient, evac tube system will probably be the go on the westward side of the roof. I'm also getting a lister 6/1 genset, so there'll be a heat exchanger linked to the hot water system for the cloudy days. Seeing as when it's cloudy, I'll probably need to top up the batteries , it's a good idea to use some of that excess heat to top up the hot water system as well.

I should probably post all the info I've got here somewhere - I've been researching a lot of stuff for my new place for a fair while now. Seeing as it's literally a stone's throw from world-heritage-listed rainforest and it's off-grid, it'd probably be useful for people here.

[jamessteward]

Thank you for the welcome.

I have seen these tubes before. They work on the same principle as the vacuum flask for keeping cold drinks cold or hot drinks hot. That is the part that gets heated by the sunlight is insulated via vacuum from the outside world, hence almost completely eliminating the reconvection of absorbed energy. I wonder how they stand up to large hail stones ;-)

What I was barking at was to use a parabolic dish - like the one in the ammonia absobtion ice maker - to concentrate or focus the sunlight energy to a point (or to a long thin strip ;-).

I think the temperatures attained can be much higher at the focal point. Although if these tubes are perfect insulators and cover the same surface area...hmmm maybe they would achieve similar temperatures, that requires some pondering.

Now - a parbolic dish - like the one in the ammonia absobtion ice maker - is pretty easy to manufacture oneself. I made one a while ago from chipboard formers at each end and nicely polished stainless steel for the reflector. It worked very well and heated water to boiling point in a copper tube.

Don't you think one dish and only 1-2 vacuum tubes would be cheaper than a whole array of vacuum tubes?

[dgriffith]

Don't you think one dish and only 1-2 vacuum tubes would be cheaper than a whole array of vacuum tubes?

It would be, but I don't know how well the working fluid inside the tubes would stand up to that kind of heat. Specs for the hot water system state that temps at the tube ends (where they go into the manifold) with no coolant circulation are as high as 220-250 degrees C. If you can keep the operating temp below that (eg, with a pretty good thermosiphon setup) you'd be ok.

[blackandwhite]

Hi,

Im interested in your NIFE setup. Did you get any data together on how well its been performing the last 5 years?

Would be very interesting to see how you went with it

[Benjy136]

There is a site at www.noonco.com/edison where much may be found concerning the making if your NiFe batteries. You can make your own with KOH, nickel and Iron and a container if you'd like to monkey with it..

Now I have a question.
I have a dish receiver with a diameter of 10 ft. with a depth of 2 ft. It's basic construction is fine metal grid. The receiver is positioned approx. 4 ft. out from the center of the dish. I am anticipating converting it to a solar heater for water or elec. My thoughts are to seal the mesh with epoxy and coat it with silver paint, replace the receiver with coiled stainless tubing (Our well water here has a PH of 5.3 ) and face it south, changing the inclination with the seasons and using stainless flexible connections to a steam engine for elec. or an insulated tank for heat. I am open to any input from you wizards out there.

Thank you in advance,

Benjy

[gardenlen]

if we could ever afford a few panels or windy and ancillary equipment we would be buying tested second hand forklift batteries lots cheaper than new.

len

[permasculptor]

I have been thinking of similar idea where you have a evacuated tube with a parabolic trough as a pre heat then a paraboloid (round) dish at the top.I would expect you would get much better eficiency and longevity if you yoused a stainless steel or mirror like finish like the ones found here- http://greenpowerscience.com/SHOPHOME.html

[blackandwhite]

[QUOTE=Benjy136;96885]There is a site at www.noonco.com/edison where much may be found concerning the making if your NiFe batteries. You can make your own with KOH, nickel and Iron and a container if you'd like to monkey with it..

Thanks for the link, much appreciated.

I would still love to hear real world experiences using Nicke Iron (NiFe) batteries for an extended period of time like user 'dgriffith' setup in 2006.

[BananaBender]

if we could ever afford a few panels or windy and ancillary equipment we would be buying tested second hand forklift batteries lots cheaper than new.

len
Buying second hand deep cycle batteries is pointless. All deep cycles have a limited # of cycles and once you start discharging them below 80% of total there life span halves. Making them useless. Second hand batterys == big problems. I dont want to sound like a asshole len but I speak from personal experience and lots of it.

I have lived offgrid for 10 years now and have 32 panels, 24v inverter, automation driving a TR1 lister genset that runs on biodiesel and 5 wind turbines. In the 10 years i have gone through 2 battery banks. The first lot i would discharge completly before recharge and i got 3 years out of them. These where exides and set me back about $18000.
The second lot i have never discharged below 80% and they havnt missed a beat going on 7 years now without any scale build up on plates etc. Both hold charge and discharge like the day i bought them. Water usage is minimal only increasing slightly in 40 degree days of summer. These set me back about the same for 1200aH capacity.

The nickel irons look great on paper, I havnt met anyone who has ever used them nor vouch for them. The only manufacturer seems to be in china and some of the claims seem dubious. I plan on purchasing some next battery bank to see how they perform.

Alot of people think they are experts in solar, especially the idiots who install them but i can tell you now real world usage and performance is nothing like they make it out to be.
The biggest laugh i get is from people thinking they are enviro friendly. A tonne of lead and sulfuric acid isnt friendly to the enviroment at all. Ive got a tonne of "garden gnomes" for any one wanting to argue that with me.

[blackandwhite]

$18,000 sounds expensive.

Under $18,000 can get you 20 x 1.2 NiFe (Nickel Iron) batteries from Victoria: http://www.ironcorebatteries.com.au/page3.php even cheaper (~$13,000) if you import them yourself.

Completely recyclable and environmentally friendly with no sulfuric acid or lead! Higher energy density the lead acid, high rate performance, the one in Edisons car is still running.

I have some friends installing them for off grid solar home in QLD, will be interesting to see how they go in real life test.

[gardenlen]

have you used second hand batteries bananabender?

the people who use them would not agree with you and under the permie' banner of as eco' friendly as can be their charter is re-use/re-cycle, this cuts down on manufacture of new which under the carbon fallacy has a big carbon foot print.

i put my idea you put your idea that is freedom of speech, so if you actually have experience of the personal kind then what you say is pure critical only. those who recycle these batteries set them up in a frame, and deliver them right to where you want them.

so with the price of new batteries there is no way many of us will ever afford this expensive technology it remains with the rich and infamous the plastic benders.

len

[Changellain]

I'm in the middle of the difficult decision about batteries too. I was almost convinced of the NiFe batteries, but I was reading somewhere (http://www.solarpaneltalk.com/showthread.php?3381-Nickel-Iron-vs-Lead-Acid-Off-Grid-battery-debate) that the batteries that are currently made are no-where near as good quality and wont likely last the amount of time suggested. If I could find some good quality second hand ones I might consider it still.. but I don't think I'm willing to gamble the big $$ to bring in the new made in china batteries myself.

I've been looking at good quality Rolls or Raylite batteries. They're expensive as well, but the Rolls come with a 7 +3 year warranty.. Raylites only 3 +2 years. I'm looking for other suggestions as well. I'd rather spend the extra money now than have to replace cheap batteries every 5-6 years.

Any and all suggestions are welcome at this point. They're for an off-grid small home.

[gardenlen]

not sure about where you are changellain?

but research a batteries co' who recycles used batteries, here we need to go to brissy to do that, but as far as i know those using these batteries are more than satisfied. they come with a warranty. and they deliver themselves and put them in place for you.

we would struggle to have any renewable energy but if it relied upon batteries worth $12k to $18k then no way jose, those prices for the rich and famous.

our main ethic is to recycle and not cause new manufacture as much as possible.

the technology seems to be heading in an elitist way. seems to they are softening people up to accommodate power outages, this is likely to become an issue when solar is relied upon as it or wind cannot supply on demand and i can't see them installing big batter banks imagine the cost?

len

[Changellain]

The property is in southern NSW, so a bit too far for QLD batteries. The system is only small, guessing that the panels will charge about 633Ah on a good day - we'll have a more accurate idea when we visit next time with the new multimeter. I'm really only interested in running a 12v DC fridge as the first priority. Other stuff is "nice" but not essential. The fridges I've seen are about 200 litre and use about 70amps per day (except in the USA where I could get the nice 300L Sunfrost ones that use only 30amps per day! I *wish*!!).

If we had the power for a fridge, then all we'd really need is some hot water and we'd be able to move up there at a pinch. While we don't have $10k or more to spend on batteries.. I would be willing to spend upto $4-ish-k if it means they're going to last. (I'm guessing that we won't have any money in 5 years to replace them. :giggle: )

[Grasshopper]

I'm really only interested in running a 12v DC fridge as the first priority. Other stuff is "nice" but not essential. The fridges I've seen are about 200 litre and use about 70amps per day (except in the USA where I could get the nice 300L Sunfrost ones that use only 30amps per day! I *wish*!!).

If we had the power for a fridge, then all we'd really need is some hot water and we'd be able to move up there at a pinch.
You might just need to hack your chest freezer for about $150 and turn it into an efficient fridge.

Energy usage with a chest-freezer-turned-fridge is barely 0.1kWh a day. Modern stand-up refrigerators use around 1kWh a day
http://mtbest.net/chest_fridge.html

[Grasshopper]

You might just need to hack your chest freezer for about $150 and turn it into an efficient fridge.

http://mtbest.net/chest_fridge.html

maybe less if you know a little bit of electrics
http://www.ebay.com.au/itm/TURN-A-CHEST-FREEZER-INTO-A-FRIDGE-THERMOSTAT-KEGERATOR-SOLAR-/290724786878?pt=AU_RefrigeratorsFreezers&hash=item43b08c32be

[Changellain]

Thanks Grasshopper! I've actually done this before. ;)

It did indeed use about .2kW a day in our case. We converted a F&P chest freezer about 3.5 years ago. Sadly it died at about the 3 year mark. We discovered that freezer tubes are designed to be frozen, and if not frozen, they rust quite easily. Ours developed a gas leak and it was a sudden and painful death with no repair possible.

The other downside of the chest freezer is needing a second one for frozen goods. The second one uses about 1kW per day, so it cancels itself out pretty quickly.

It was pretty heartbreaking to throw my beautiful scratch-free fridge away. I'll not do that again until I'm sure that the tubes are made to be rust free under fridge conditions.

Now I have a 200L fridge/freezer upright, and I miss my chest fridge so much. The upright is so much noisier!