We lost our house in summer bushfires. Now we’re going underground and off the grid

The monster approaches. Image: Don Pattison

We lost our house and just about everything in it during the horrific fire season of 2019/20.

Ours had the dubious distinction of being one of the very first houses to be lost on that terrible day that ushered in the Black Summer, and which brought with it scenes that would appall a nation – indeed the world – who had seen fires regularly and thought themselves accustomed to such phenomena.

It was a beautiful house in a spectacular rural location, at the bottom of a valley, beside a creek that had never stopped running in any of the locals’ memory, and in a semi-rainforest habitat that was thought to be immune – or at least resistant – to fire.

The Beautiful House, destroyed. Image: Don Pattison

The creek stopped several months before the fires raged, and the habitat proved to be anything but resistant to the conflagration. Much of it will not grow back in our lifetime, if ever.

It may have been a beautiful house, but it had its shortcomings – especially in light of our growing awareness of, and push towards sustainability. I won’t dwell on the loss and the emotional impact it had on us, as this is not a story of loss and grief.  Rather I use the destruction to set the context for our journey back.

As I write this, we have begun the rebuild of our new home, but it is far from complete, and all I can show in pictures is a concrete slab . . . hardly a very interesting image!

So, what are we building, and why is it of interest to a community interested in “One Step Off the Grid”? It’s because we are taking that step, off the grid.

Long before the Black Summer of 2019/20, we had discussed what we would do if we lost our beautiful home in a bushfire.  We had decided we’d like to stay in the same community, and that we’d build a house that was more suited to our lifestyle and our ambitions, not the least of which was to tread more lightly on the planet.

We made two very important decisions in our deliberations. Decisions that enabled us to move very quickly when nature dealt us its cruel blow.

Firstly, we had decided to be as off-grid as was practical to be.

There is no town water and sewerage where we live, so those aspects were a no-brainer really – other than to consider the strategies of harvesting, storing and supplying water to the house and gardens and then our options for disposing of it when used.

Due to state government regulations we aren’t permitted to use treated wastewater in the way I would like, so we ended up with a worm-bed septic system and have to be content with knowing that the castings are only able to be of benefit to a small ‘forest’ of non-edible natives we will plant in the dispersion zone.

However, on the power side of the off-grid objective, we are able to fully realise our ambitions.

The decision to go off-grid is driven by several observations and analyses. Firstly, the cost of connecting the grid to the new house site is roughly equivalent to installing a fully off-grid power plant.

Secondly, nobody can guarantee me that the daily supply cost (poles and wires) will not continue to climb, and climb, and climb over time as it has done in the past, and that excess (exported) energy tariffs will continue to pay for those charges.

Thirdly, where we live, we are subject to regular outages, brownouts, and surging supply. Some blackouts only last 30 seconds, while others last days or weeks, and all of them are attributable to the stability of the grid itself.

I will come back to the proposed power system and its design shortly, for it is very strongly influenced by the next big decision we made in our lifestyle decision.

You see, we had also decided to build an earth-sheltered home – in common parlance, an ‘underground’ home. The primary motivation for this move was thermal stability, though I have to be honest and say that the significant protection from bushfire is no small amount of icing on the very lovely cake!

Prior to the fire, we had engaged a specialist architect to understand what some of our design and build options and constraints might be.

We had six years of experience in trying (and often failing) to maintain a comfortable living temperature in the beautiful home in the spectacular location, where outside temperatures would regularly range from -5°C (or lower) in winter to +45°C (and higher) in summer . . . on the day that the fires wiped us out it was 44°C before the heat from the fire raised it to inhuman levels.

The Monday after the fires had ravaged our community and were spreading throughout the mid-north coast, I contacted the architect to advise that our theoretical project was no longer theoretical, and began the process of formally retaining him to turn our vision into a reality.

Going ‘underground’ means we will be able to enjoy unenhanced temperature ranges much more suited to human comfort.

Our architect tells us that his home has never fallen below 18°C, nor risen above 26°C in the extremes of weather in the Adelaide Hills. As a result of those natural conditions, our need to ‘condition’ the temperature inside will be significantly reduced, if not eliminated entirely. An unquestionable benefit when designing the off-grid power plant.

Very briefly, the construction of the earth-sheltered house entails cutting a rather large hole in the hill (we are fortunate to have the perfect hill with a perfect northerly aspect), building the house out of concrete (slab floor, core-filled block external walls and suspended slab roof), then backfilling the hill around three sides of the house.

The roof will be covered in river sand to enable us to harvest rainwater. Yes, I know that concrete has a huge embedded energy footprint, but our energy profile should repay that footprint many, many times over in the lifetime of this building – which should be well beyond our own.

So now, back to the power plant and its sizing and design. In the six-and-a-half years we had lived in the beautiful house in the spectacular location I had been a complete nerd and studiously gathered and analysed our electricity usage such that I am confident of giving sizing instructions to our off-grid system designer.

The following graph shows our average daily usage by season, and these figures are based on an utterly inefficient house.

 

*In the above graph, all values are kW/h. Those represented above the line are imported from the grid, whilst below the line are either self-consumed from the solar system or exported back to the grid as excess to usage.

If we assume that the CL1 usage for hot water can be eliminated by installing a solar-powered hot water system, we are able to get a clear picture of the average daily usage – which included an air-conditioner which often struggled to maintain a liveable temperature in the extremes of summer conditions. The following table shows the average daily usage (excluding hot water) by month in the year leading up to the fires:

 

Nov 18 Dec 18 Jan 19 Feb 19 Mar 19 Apr 19 May 19 Jun 19 Jul 19 Aug 19 Sep 19 Oct 19
Avg Consumption 10.4 11.5 14.74 10.2 10.3 8.7 8.9 8.8 9.2 8.8 8.9 8.9
Max Consumption 23.9 23.2 21.95 21.8 19.4 14.9 11.8 12.4 20.7 10.8 18.4 15.3

 

So, assuming we won’t need an air conditioner to run nearly as hard or as long (if at all) in our underground haven, I have set a daily budget of 10kW/h for the design purposes and hope to significantly beat that budget when we get to actual operational usage.

So, our new power plant involves 20 x 330W Trina solar panels installed on a ground-mount frame. We will split the panels into two arrays facing north-east and north-west respectively in a bid to ‘flatten the curve’ (as it were) and generate energy for longer each day than a single, flat, north-facing array.

The two arrays will be connected via separate MPPTs to a Fimer 5.0kW Inverter which will, in turn, be AC-coupled to a Selectronic SP-Pro 5.0kW system supporting the battery bank, a generator and the main feed to the sub-board.

The battery-bank is comprised of nine PowerPlus Eco Series 4840 batteries giving a nominal storage capacity of 36kW/h.  More battery modules can be added if the initial configuration proves insufficient for our needs.

I am seriously considering other non-solar options to enable us to supplement the solar system. To that end, I would welcome feedback from those who have actual, lived experience installing a small wind generator, so I can gain the benefit of their experience in deciding whether this is a viable consideration moving forward or not.

I have had plenty of ‘opinion’ given to me from those who’ve seen YouTube videos and advised me that it’s not worth it, but none of those self-proclaimed advisers have any actual lived experience to back up their opinion. I thank them for their concern and advice, but would much rather talk with people who have done it.

I have considered some of the options for small-scale stored hydro, but when I factor in the cost of additional water storage, turbine, pumping, piping, etc, I cannot see a viable return on that investment . . . though the concept intrigues me and talks to the inner Heath Robinson who whispers to me “do it . . . do it now!”

Don Pattison is a 65 years-old retired “nerd” who made the Tree-Change after retiring early from a lifetime career in the IT industry – and has never regretted the move. He and his partner live on 8 hectares of Mid-North Coast rural property in the foothills of the Mountains with two dogs that are, at once, utterly naughty and utterly loveable.

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