White man’s magic……

8 10 2016

20160418_163158Now that our power station has been commissioned, is actually powering stuff, and because it’s been an evolutionary thing over many months, I’ve decided to chronicle how our rather unique stand alone power system is built in one post, for the benefit of all mankind…. as it were!

The solar power is generated by eight 260W monocrystaline photovoltaic panels, for a 20161008_131339total of 2080 Watts. They are mounted on a custom made steel frame, installed by the first wwoofer I had working for me here… They are connected in two strings of four with each string producing 1000W at 150V DC maximum. The two pairs of wires are fed underground and through the container’s floor in that orange conduit, to the DC circuit box where two 20 Amp circuit breakers protect the system against short circuits or serious malfunctions. Each circuit breaker is dipole, and simultaneously breaks both the positive and negative circuits.


DC Circuits

From this box, the solar power is fed to the MidNite Classic Maximum Power Point Tracker. This magic black box manipulates the incoming electricity so that it is fed into the batteries at the optimum voltage/amperage combination needed to maximise the amount of energy fed into the batteries to keep them charged. I had never used one of these before, but they are well worth the $900 , because it does all sorts of other tricks, like boost charging, battery equalising, floating, and even monitors the amount of energy fed into the batteries, logging all that information where it can be accessed later…… If I decide to later add a wind turbine, I will get a second one to control its output.

The power going into the batteries (and out of them for powering things with the inverter) go through a fuse box with two 160A slow burn fuses. Batteries are capable of producing spectacular amounts of current (think big sparks and fire!) and in the unlikely event of something seriously bad happening to the batteries, these fuses will burn and save the rest of the system. The fuse box is also designed such that it can be used to disconnect the batteries from everything else in an emergency, or for maintenance. There’s one fuse for the positive cable, and one victronfor the negative……

Once charged, the energy contained within the batteries can be extracted back out (through the aforementioned fusebox) by the Victron inverter, which converts the 48V (nominal) DC from the batteries into 230V AC for powering all the things we take for granted in houses, like lights, fridges, TVs and washing machines etc……

This inverter has now had its settings altered to operate at between 64V and 37.5V. It’s because Victrons can be reprogrammed to do this that I opted for this technology, as the Nickel Iron batteries are able to work safely at an even greater voltage range. The blue digital voltmeter is something I added to the inverter to get an instant readout of the battery bank’s voltage.

Just as there is a series of safety devices on the DC side of the system, the AC sector is also wired up to protect the wiring and the people using the electricity! You will also notice the green/yellow striped earth wires to/from the MidNite Classic and the inverter, all connected to the earth in the AC switchboard, all grounded to the container itself.

acsectorBefore going into the AC circuit box, I wired in an old energy meter I have had for years to monitor how much energy we will be consuming in the house (as well as outside to pump water for the gardens etc…). I used to use it for doing energy audits, and they sure don’t make them like this anymore…!

The 230V output is split into three, with another dipole circuit breaker (one for the active and one for the neutral) taking power to where the house will be built, currently permanently switched off. Another 10A circuit breaker takes current to a power point inside the container for running the freezer and charging cordless tool batteries (so far), while a 15A breaker takes power to an external 15A all weather power point outside the container where I currently plug the new pump in (more about this in a later post).

The two power points are protected with safety switches which are now built into the circuit breakers. It’s amazing how fast technology changes/improves these days….

The battery bank consists of forty 1.2V Nickel Iron cells (to make the nominal 48V). You can read about why I selected this battery chemistry here……


Earth/Ground wire to stake


The container is earthed with a copper stake, and everything involved in this system is also earthed through the steel container, one advantage of having a steel building! The safety switches test just fine, the whole system is very safe. To vent the potentially explosive hydrogen gas that bubbles from the batteries, two whirlybird extractors were put into the container’s roof, and six vents at floor level on the western end of the container were also added. It’s where the wind usually comes from, and it will no doubt assist in keeping everything cool, even in summer….


Floor level air vents


batterybankI’m really stoked at how well it’s all working. Even on really rainy days, the solar array was able to feed 4.7kWh of energy into the battery bank, and even on the very worst day when the sky was inky black and it just poured all day long, 1.7kWh was absorbed by the batteries, almost enough to power our old house for a whole day…. The design electricity consumption for the new house is 2kWh/day, though at this stage it’s still unknown how much energy I will need to pump water for the market garden.

I’m finding adjusting to the NiFe batteries a little tricky. Unlike conventional Lead Acid batteries, these prefer to be worked hard. I’m told by people who run them that the harder you cycle them, the more capacity they build up, and the longer they last between electrolyte replacement. Because I’m (so far) only pulling 0.9kWh/day out of them with the freezer, the batteries haven’t been worked enough. So I recently turned the solar power completely off for eight or nine days, just to ‘flatten’ them. They were fully charged again within two days…. Nickel Iron batteries, unlike the other technologies sold everywhere, can be ‘flattened’ as often as you like….. you just need to always make sure there’s enough left to start the freezer again, or else lose the contents!

Now the container sports a 1000 litre IBC for gravity fed water storage….. but you’ll have to wait for the next installment.





14 responses

8 10 2016

>Nickel Iron batteries, unlike the other technologies sold everywhere, can be ‘flattened’ as often as you like

Zinc Bromide Flow batteries can be flattened as well. Redflow (An Aussie company) does them.


10 10 2016

But will they last 100 years……..??

8 10 2016
Lawrence London

What does this mean, i.e. “earthed”? What is a “stake”?
“The container is earthed with a stake, and everything involved in this system is also vents earthed through the steel container.”
staked = metal ground rod, i.e. copper coated steel rod?
earthed = electrical system is grounded?

Do you have a comparison of the different types of batteries available for off the grid electric systems? Are lithium ion not used?

What does “flattening” batteries mean?

Do you have recommendations for wind systems, i.e. Bergey, which makes 1000watt chargers that are very easy to erect.


9 10 2016

Hmmmm…. if you don’t know what an earth/ground or an earth stake is, stay well away from electric work! The container is not earthed via the vents either.. the vents are there to let air into the container so that the hydrogen can quickly escape up through the whirlybirds.

And you don’t know what a flat battery is? LUCKY YOU!!

No, I don’t do comparison charts. This article merely chronicles what I did, and explains why. And I personally wouldn’t touch Lithium ion batteries with a forty foot barge pole.



9 10 2016
Lawrence London

I know what grounding an electrical system or equipment is. I wanted to know if that was what you meant by “earthed”. Seemed logically the same.
Interesting about lithium ion batteries. Is the problem with overheating and fire
in the context of an off the grid system?

10 10 2016

Must be an Australian thing…… I know what grounded means, but here we seem to exclusively use the term ‘earth’.

My issue with Lithium batteries in renewable energy systems is that it’s the wrong technology. Li-ion batteries were developed where lightweight applications are required, like mobile phones, laptops, tablets, power tools, EV’s etc….. they also require very tricky charging regimes, or, as you point out, they are liable to catch on fire as has been seen in the latest Samsung mobiles, and some laptops a couple of years ago. In a household situation, the weight of your battery bank is irrelevant.

But my biggest gripe of all is that they don’t last, and eventually end up in landfill. If millions of tiny mobile phone batteries in landfill is already beginning to be problematic, imagine what happens when very large battery banks start joining the deluge…….

Furthermore, as someone who believes that the future will not be industrialised, replacing dead batteries will become impossible. Whereas if you can keep batteries going by replacing electrolyte you can make yourself….

10 10 2016
Lawrence London

To be more precise I have hear the term “earth ground” used often.

You write:
“Furthermore, as someone who believes that the future will not be industrialised, replacing dead batteries will become impossible. Whereas if you can keep batteries going by replacing electrolyte you can make yourself….”

This is fantastic. I have never heard for the batteries you or the other commenter mentioned. Glad to know that Li-Ion batteries should not be considered for off grid systems. I had always wondered whether Li-Ion batteries were standard in system these days. Now I know.
I have no idea what alternative batteries are available in the USA. I am in NC, USA. Years ago I considered building may own off grid electrical system on my farm. I looked at a photovoltaic array and a Bergey 1KW windmill charger,
an inverter and a battery bank consisting of a goodly number of Rolls/Surette batteries from Nova Scotia, 400lbs each, deep cycle marine, 10 year guarantee. http://www.rollsbattery.com Also huge cables carrying electricity from source to batteries and inverter,.Expensive. I am really glad I did not go that way. Except for the batteries everything else would have been hugely expensive and boat anchors by now.

10 10 2016
Lawrence London

Iron Edison
Nickel Iron Batteries

10 10 2016
Nathan Surendran

Hi Mike,

Good overview thanks! I assume you’ve got spares for the other parts to ‘last a hundred years’ alongside the batteries..?

Also interested to hear if you have a sense of what wind speeds your PV array is rated up to and if you have attached your container to piles / whatever to deal with increasing wind speeds? http://www.stuff.co.nz/dominion-post/news/84079443/wild-weather-to-continue-into-friday-ease-over-weekend

10 10 2016

It’s already been exposed to 120km/h wind with no ill effects! The ‘feet’ of the steel frame are cast in 600mm deep concrete footings, and are probably superior to those used on the South Australian pylons…… 😉

Re spare electronics, when I can afford it, I will buy back up spares.

10 10 2016
Nathan Surendran

‘already exposed to 120km/h winds with no ill effects’ doesn’t sound very scientific. Your footings could use the uplift calculations from NZS 3604 for verandah roofs to determine if they’re adequate.

And here in Southland NZ, if I’m designing something to last 100 years (like, say, a house) I’m currently recommending to anyone who’ll listen to design to hurricane standards such as those in Queensland.

11 10 2016

Might not sound scientific, but that’s about as bad as the wind ever gets here…. and besides, there’s a triple row of macrocarpa trees upwind from the container that act as an amazing buffer and I’m planning further windbreaks to protect my new polytunnel and the market garden…..

10 10 2016

Hi Mike,
Good work on getting your power station running.

You have picked some quality equipment, it should serve you well.
A couple of quick suggestions to help you get the best out of it.( and bring it closer to meeting AS 4509 / 5033 the Australian standards for such systems )

– Main battery cables look a bit light??? Victron recommend 70mm squared on a 200A fuse for that inverter. (double insulated and secured for safety )

– Solar DC isolators. Your PV array would be deemed to be over 160 VOC in the Tassie climate, thus LV not ELV. While this is still relatively low for modern solar systems (500-1000 VOC) it is still high enough to warrant using DC rated non-polarized MCBs to reduce the risk of burnt contacts and failure.

– Midnite classic. (A great regulator!) It deserves its own protection! this can be achieved by using the third HRC fuse slot with a 63A fuse in the regulator positive line. The output should then go to the battery side of the other pos 160A fuse.
The main advantage of this is to protect the inverter from high voltages if the batteries are disconnected with the solar still generating.

Not sure what nickel iron batteries off-gas but at the moment they are doing it right under the air vents into your power electronics and right next to your DC isolators the definitely do arch when switched under load.

Does the Midnite reg run on cold mornings in Tas? From your description, it would be at over 150 VOC when the panels are cold and if it is a Classic 150 it may not be operating until things warm up?

Love the posts about the farm, keep up the good work,
Cheers G

10 10 2016

Thanks for all the suggestions…… I’ve never seen the PV voltage over 150V, even with no load. They’re normally at ~120V…

Did you REALLY mean to type 70mm2 for the battery cables? It’s so long since I bought them, I can’t even remember what section they are, but 5kW @ 48V is only 100A, and they’re the same size as car battery cables that pull 300A! They are also very short, and yes I know, the batteries are very close to potential arcs, but the volume of the container is huge, and the probability of the hydrogen reaching explosive concentration is miniscule…… I went to a lot of trouble with venting too.

Also, It’s highly unlikely we’ll ever pull 5kW from the inverter… I only bought a fiver, because it was offered to me for the same price as a 3kW one, which is what I was going to buy originally….. we are energy misers!

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