NiFe ... just do it!

Greetings fellow readers,

We are gearing up to move to the "soon to be ours" land at Atamai eco-village. We finally decided which land parcel we were interested in, and it turns out Katie and I preferred Lot 6 the most.
You can see the lot numbers here is Atamai's stage one development.
Katie and Alysha standing in the middle of Lot 6, westerly views to the distant mountain ranges in Kahurangi National Park.
Here is a view looking at a north western view, encompassing Lot 6.
Being the early birds here we could choose between Lots 5, 6 or 8. Lot 8 has amazing views but Lot 6 has a larger platform and more privacy nooks, as well as two stream boundaries - making it the choice for us. Lot 5 was taken off the market so it can be enhanced further. This includes an additional platform and a horse shoe lake. However this meant that we weren't able to afford it because of the increased price tag - dang!

Easements are currently being registered with LINZ, and we hope to get the title in our names in 2-4 weeks.

The cabin on our lot belongs to our soon to be neighbours on Lot 7 - they will live in that while their house is being built. It is kinda cool to know your neighbours even before they become your neighbours, a common story here at Atamai.

We are planning on building an ensuite sleepout unit that will house us while we build our house. We have to be out of our rental accomodation by September when the lovely house owners come to stay. Hence we really have to push for the sleepout to happen, or worst case find somewhere else to rent. This is not desirable as we would like to be on our land during the build (easier to project manage) and the rental payments will not contribute to our final setup. 

The sleepout will be large enough (30m2) to require a building consent. Actually even a 10m2 sleepout will require a building consent because the council specifically wants to know how our waste will be handled. The 30m2 just means it can remain a sleep out even after we build our house (actually the limit is 36m2, which extends to all covered areas under a single roof structure).

Our ideal home will be around 100-120m2 and this will be done in stages as more funding becomes available. We are also looking at a 50-60m2 granny flat adjoining the main house with the potential for a glass house seperating the two dwellings. We are allowed to do this in our area as long as the main house and granny flat span the same roofline.

To increase our resilience and reduce dependence on a high paying salaried position, we are trying hard to achieve what we need without a mortgage. This is easier said than done, but achievable for us by staging our house build. We are fortunate enough to be able to own the land outright without borrowings - thanks to our savings and capital gains over the last 10  years.


We are seriously considering installing a biogas black and grey water treament system. This system uses anaerobic bacteria to break down the waste material, generating methane gas as a by product. Once the hydrogen sulphide and CO2 is scrubbed, it makes for a versatile fuel which can be used for cooking, supplemental heating, and even injection into an electric generator. It is stipulated that a family of our size will be able to generate something like 1-2m3 of Methane per day which is more than enough to power a single large natural gas ring burner for 3 hours daily.

It may be also enough to fire a natural gas califont tied to a radiator (using a thermosiphon or circulation pump) for supplemental heating. The small size of the sleep out together with a high level of insulation means that this might work quite well. Additional material like garden waste can also be added manually to generate more gas to supplement extra use. 

The digestate material (solid and liquids) left over from the digester makes for amazing fertilizer which will come in useful for our plantings. The solids really only need to be emptied once every 10 years or so, but it can be emptied more frequently if the digestate is desirable. Atamai stipulates the closing of the phosphorus loop by recycling our waste - you can think of a biogas system as a different kind of composting toilet.

All this sounds like the latest and greatest in technology, but actually China and India (and most 3rd world nations) have been using these systems for cooking gas for a very long time (>50 years). Us 1st world newbies are only just starting to catch up.

Solar PV setup

Yes, we are going full offgrid electricity with solar. It may seem silly, but we are going for a full offgrid electric PV system despite being in close proximity to the national power grid. The only reason why we might consider otherwise is if we can't quite sort out the system in time before we move to our land, or we might choose to export our excess energy to the grid to earn a small return on it. Getting grid tied for us will incur setup costs which are cheaper than a PV offgrid setup - however the off grid system will be hedged against future price inflations of electricity. In New Zealand this has been fixed to 5% per year (power and line charges) to account for future generation expansion.

I manage to obtain 3.6kw of panels and will be using an experimental inverter system from a local manufacture. This should result is a lower adoption cost, although it is likely to complicate things - ie. more stuff to break down over time. This system will not be so different to the SMA SunnyBoy and SunnyIsland setup that I mentioned in an earlier post. There will be an update to that soon too :)

I'm actually lured by an ancient technology (still in use today 100 years later in electric subways) of using a mechanical rotary converter for coverting the 48VDC battery to 240VAC by running what is basically a DC shunt motor (good for speed regulation, ala 50Hz) coupled to an AC alternator. There are special converters like this where the DC and AC winding are shared so there is no loss in mechanical coupling - just too clever! Some of them have 90% efficiency ratings, which is pretty amazing for a mechanical device. However I will need a step up transformer which will incur more losses (ie. 48V DC => 48V AC => 240V AC). I expect a system like this to be around 60% efficient as my converter will also be smaller (more lossy).

The beauty of such a system is that it can be maintained by me or local mechanics, hence making it relatively sustainable on the long term reducing cost of ownership. Contrast this to a box of electronics with surface mounted components and micro controllers/processors that go out of date in 10 years. Of course a rotary converter migh end up using heaps of copper or other metals which are getting increasingly rare - but I still like the idea of a 100 year old solution to a 21st century problem :)  Perhaps I'll have one just as a stanby backup alternative if and when the electronics fail and I'm stuck waiting for parts or a replacement.

NiFe battery

Part of any offgrid system is the battery system. In the majority of cases, flooded lead acid batteries (PbA) have been used for decades because of its well known characteristics. However these batteries only have a life of 15-20 years if they are premium quality and maintained well, and undersized to avoid deep discharge cycles. After the rated life, the lead plates start to deteriorate as they have worn away.

So I started on a journey (a long one) in search for a battery technology that was a sustainable alternative. After many hours I decided on nickle iron (NiFe) batteries - here are some links to literature on it.

Although most of you have probably never heard of this battery, it has been around since the early 1900s as it was produced by Thomas Edison. His 80 year old cells were recently retested after sitting around all this time (probably unmaintained and unused) and still was able to charge/discharge near to expected capacities after addition of new electrolyte (with some derating factor for aging over that time frame). Of course that pedigree of battery no longer exist today, they just don't make batteries like they used to.

The NiFe cells are still produce today, mostly in China and Russia. They are used mainly as an alternative to pocket plate NiCd batteries (liquid electrolyte) which serve railway applications. In the end I sourced my cells direct from China (yes I'm nervous) from a company who contract to the chinese military (grit teeth) as well as as a few railway networks amounting to thousands of cells over many years. Both of these seem to indicate a reliable supplier who is capable of making reasonable quality batteries (or they get shot?). I will report more when I get the cells and set them to work. The pricing of these cells were on par with lead acid batteries (when accounting for oversizing to 50% maximum depth of discharge).

NiFe cells are touted to last for 30-50 years, with electrolyte changes every 10-15 years. They use an alkaline potassium hydroxide (KOH) solution which can be used as a soild pH conditioner for acidic soils. You can over charge them and over discharge them without much affect (although don't do it too much or the plates will wear out faster), and don't mind being left in a state of discharge. The KOH solution prevents the iron plates from oxidising (rusting).

This means that I can size a generator purely to meet the house load demand, rather than having to meet the battery charging requirements in addition. This is why I'm sourcing a throttling type diesel generator with pure sinewave inverter so that it can run more efficiently at various household peak load ratings - I'm targetting one at 6KVA as that seems to be the smallest you can get in diesel. The reason I wanted diesel over petrol is so that I could eventually use vegetable oil to power it, in addition to piping surplus biogas to the manifold ... oh so many lovely projects ahead :)

Lead acid batteries don't like to be left in a state of discharge for too long as this leads to sulphation and usually a permanent loss in battery capacity. This is why you have to manage their charge levels appropriately with a backup generator and basically extend their life with a liquid fuel (usually fossil fuel based).

One of the main disadvantages of NiFe cells is their poor charging efficiency (60% worst case). This means the round trip (charge/discharge) efficiency sees a penalty of up to 1/2 of the energy going in not coming out again. This is due mainly to the generation of Hydrogen gas - many of the elements in this battery chemistry can constitute an electrolyser (turns water into H2 and O2). So if the H2 gas can be sequestered, it can be burned in a stirling engine  :) ... one day huh? 

This reduction in efficiency needs to be put into the overall calculations for available power (and sizing of the array). Consideration should be given to minimise the non-solar energy input into the batteries. This is why I'm in favour of running the backup generator only to meet household demand, rather than waste 1/2 of the energy electrolysing water and generating heat.

It it worth noting however that lead acids also generate H2 gas during charging, and their round trip efficiency is about 60% - so not that much better. They generate less H2 because their charging voltage is sufficiently different to where electrolysis occurs.


It would seem I'm not very good at short and frequent updates ... :)   I'll leave you for now but will be back soon on my research on passive solar design ideas.
Oh what fun!

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