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Traveling man
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Joined: 15/10/2017
Location: Australia
Posts: 3

Posted: 01:25pm 15 Oct 2017

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Hi guys, first post here. Apolagise for the length, but hoping a clear explanation will help people answer. Cheers.
I am currently traveling aus in a 11 metre bus, full solar on roof that runs all our needs. We have 6 x 260w panels, 1000ah agm storage, 3000w inverter and mppt charger controller.
I have just bought a small block on Russell Island Qld, where I want to build a very small straw bale house, 100% off grid.
I recently have been reading about diy nickel iron batteries and it seems a feasible idea to me.
I need help in understanding the amount of power used daily as I see posts mentioning 7kwh and similar and I dont quite know the maths. In the bus we use 240v appliances, 7kg front load washing machine, 1200w microwave, kettle, toaster, 2 x tv, 2.5kw split system AC, 12v lights and water pump. All this off the solar storage.
So firstly how do I work out average daily kwh's used?
Secondly is Nickel iron a doable project
Thirdly where would I get the raw materials, nickel and iron oxides etc.
Fourthly, has anyone done this type of storage before?
And last, would I be able to feed the solar supply from the bus into the agm batteries as now, and into a house bank of nickel iron? (Usually we are on float by 11am)
Thanks in advance.

Madness

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Joined: 08/10/2011
Location: Australia
Posts: 2498

Posted: 02:07pm 15 Oct 2017

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7 KWH is a reasonable figure for a very modest off-grid home. However air conditioning is going to add a lot to it.

If you google power usage calculators you will find quite a few that will allow you to do a reasonably accurate estimate.

I have not seen anything on a easy doable DIY battery bank. It is something is have looked into and the best option I found was to melt down lead from existing batteries and rebuild them. This is not easy or good for your health. Gumtree is one way to find secondhand batteries, otherwise you are going to have to consider spending $5,000 plus on a new battery bank. Installing a undersized battery bank is not going to be a good outcome.

You need to keep different batteries seperate, even batteries that are the same brand, model of different age should not be connected together. You would be better to use the bis system to power part of the home.

There are only 10 types of people in the world: those who understand binary, and those who don't.

Traveling man
Newbie

Joined: 15/10/2017
Location: Australia
Posts: 3

Posted: 05:02pm 15 Oct 2017

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Thanks Madness, i will google the calculator and continue researching. I was also thinking about how best to use the already working system to power some of the house. Wish the bloody council would let us live in the bus, its fully self contained. Pefect for off grid living.

Warpspeed
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Joined: 09/08/2007
Location: Australia
Posts: 4406

Posted: 07:06pm 15 Oct 2017

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Its not really possible to estimate daily power usage because so very much depends on your mode of living, expectations, and lifestyle.
An elderly couple may have fewer needs and be better organized than a young family with young children or several teenage daughters that never turn things off !!

I looked into NiFe batteries myself a few years ago, including the home made ones.
The technology is over a hundred years old, but by todays standards makes a very low performance battery. The main problem is the very high internal resistance of the cells, which is going to be even worse with home made cells because the construction method might of necessity be fairly crude.

The other major problem is the very wide voltage swing between charging and discharging, which can cause problems for any dc load, especially an inverter.
Both these limitations seriously limit the rate of both charging and discharging.

Its not really possible to run a high powered inverter that can handle high peak loads unless the battery is absolutely ridiculously huge.
Likewise recharging has to be very slow and over a long period. You cannot just pile on more solar panels, because the battery voltage just goes very high without the battery accepting a higher charge current.

In short, NiFe batteries may have been the bees knees a hundred years ago, but the lead acid battery with much higher performance has long ago made them obsolete.
Not even Saft Nife makes them anymore. I used to work for Saft Nife as battery applications engineer in Melbourne about thirty years ago. Back then Nicad batteries were the state of the art secondary battery technology.

The only advantage of NiFe batteries is their extremely long life and tolerance for abuse.
But that is of no real benefit if the battery is simply not up to the job it needs to do.

Sealed Lithium batteries are now rapidly taking over from lead acid batteries for similar reasons. Much more constant terminal voltage, even higher still peak charge and discharge currents, and lower internal resistance.
Edited by Warpspeed 2017-10-17

Cheers, �Tony.

Traveling man
Newbie

Joined: 15/10/2017
Location: Australia
Posts: 3

Posted: 08:23pm 15 Oct 2017

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Well there you go. The guys in Brisbane that did the bus for me, reckon there is no problem in using the existing system to power a small house, using a 240v outlet from the bus, which I already have, an inlet via a small sub board or RCD, keep loads under or at 10A AC, gas water and cooking and low draw led lighting etc.

That certainly sounds like a plan to me. Might possibly need a windmill back up or small gennie. But would like to stay away from gennie if possible.

So I guess I can shelve the Nickel iron idea.

Thanks for the comments. Any others on any of the info above will be welcomed.

Cheers all.

Warpspeed
Guru

Joined: 09/08/2007
Location: Australia
Posts: 4406

Posted: 08:35pm 15 Oct 2017

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A small generator tucked away somewhere, but not for regular use might one day come in very useful. Especially off grid, you need to have a few alternatives available for when things go a bit wrong.

Its the totally unexpected, like storm damage that can throw you.

Cheers, �Tony.

Boppa
Guru

Joined: 08/11/2016
Location: Australia
Posts: 814

Posted: 10:51pm 15 Oct 2017

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One possible solution is to use the bus for some loads, and a smaller system than you would otherwise have bought for others in the house...

as an example, you may have needed a 8kw system for the house standing alone, put say the lighting on the buses system and a 5kw system on the house instead- ie splitting the load

Another option is using the buses system to run a battery charger that helps the houses system, meaning you can downsize the panels a bit on the house (altho panels are getting so cheap its hardly worth it anymore)

lots of options

joebog1
Senior Member

Joined: 07/11/2015
Location: Australia
Posts: 114

Posted: 09:41pm 16 Oct 2017

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Welcome to the forum Ian!!

This is the hay bale electronics store. You will get the information you want, and without the bull sh*t normally associated with the net.

Joe n Nadia

p.s. Chris will know

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