An all-electric, off-grid luxury lodge, powered entirely by solar, wind and a battery

In 2019, after being involved in policy for Engineers Australia about the dire state of the planet and how to respond to it, we decided to put our money where our mouth is and bought 107 hectares of natural bush on Kangaroo Island for conservation, and to showcase upmarket off-grid living, and eco-tourism.

We describe our ethos here.

Post Covid was a tricky time to build on an island, so compromises were made, but the 3- bedroom lodge is now complete with solar, battery, wind and a (rarely used) backup genset for power generation.

I’ve always been a strong advocate for a whole systems approach – so we have also gone for good insulation, double glazing, inductive cooktop, time-of-use heat pump and EV charging.

Rain water capture, filtering and bio-cycle reuse for irrigation along with organic recycling is also included – but that’s another discussion as is the extensive native revegetation and local fauna and flora in the 7 Ha of paddock. 

Having led a few 50-100MW off-grid mine projects and done analyses in Homer, I decided to use a similar model (but 10,000x smaller) for the lodge.

Techno-economic modelling a 6- person lodge is more challenging than a mine from a demand perspective because you are dealing with unpredictable human behaviour, particularly as this is a rental property.

Nevertheless, after a few iterations, I sized the system and Colin Lord did the power

configuration with an AC-DC coupled layout (allowing for redundancy and robustness):

– Solar 11kW Canadian solar. We did want Tindo, but that wasn’t possible;

– 2 PV strings to 6 kW AC- Fronius inverter direct to AC bus;

– 1 PV string to 4.8kW DC Victron MPPT controller;

– 28kWh Energy Plus LFP Battery;

– 7.5 kW Selectronic inverter to AC bus;

– 1.5kW Sunnily Horizontal axis wind turbine generator (WTG);

– 5 kVA 2-wire auto start Hyundai diesel generator;

The solar, battery and wiring and integration was done by Colin and his team at Apex, I installed the wind turbine and the genset (with support). 

The model predicted the following generation potential across a typical year:

As expected, there is plenty of power in summer. But we had to cater for the worst case, so July was looked at in more detail as per below graphs, showing the load curve (dark blue), wind (green), solar (yellow), battery (light blue), genset (black) and Inverter (red).

By installing a combustion heater for a few thick overcast days with low wind we were comfortable this further minimised the genset diesel usage.

Fortunately, we decided to split the project, with carport-shed to have a skillion roof facing north for the solar panels and the house a counter skillion for easier rainwater capture – which meant they could be built independently.

The house building only started after the carport-shed, power and water was complete, so just as well we chose to separate them. 

The photos show the wind, solar and genset (inside the shed below turbine), sunrise in winter over the ocean, and a yakka (grass tree / xanthorrhoea) 

We used a Reclaim heat pump with large 400l tank, with separate control system, so we could heat the water off solar during the day and have enough hot water even for a few days, whilst not using any battery power to heat the water – ie making the most of flexible power.

Wind was a bit of a gamble, but the thinking was that a trickle feed of 1.5kW on a cold dark winter would offset the need for larger battery and diesel usage. 

So how did it turn out? 

Some imperfections, but we are very pleasantly surprised.

The genset has only been used twice – once in summer when a very flat Tesla with a 90kWh battery charged at the property (before we had installed a time of use 7kW charger) into the 15A normal socket.

The first I knew about it was Christmas day, when the battery hit the 10% parameter that tripped the system, and we got a call “no power or water”!

This was a bit of a shock waking up to a call like this, and because we live in Adelaide – so a call out was difficult. I immediately suspected extensive EV charging as the culprit as was borne out by the graph below.

I looked at my phone data which showed that on the 24th, the genset actually auto-started just before sunrise (as it should have). The sun came up and genset switched off.

On Christmas day, the genset failed to auto-start (as we all know, fossil fuel generators have a habit of letting you down!). I advised the guest that the system needed a reset and I was able to step him through the startup.

This was made easier, as the sun was up and the DC string could generate the power required – but this could equally have been done with the remaining charge in the battery.

The water pressure is maintained by a pump/accumulator, but with the power down, the water system can’t operate. The alternative is a water tank on a tower – or separate backup system for the water pump. In any event, when power was restored, the water came back on instantly.

We had made provision for an EV charger, so installed an Ohme immediately, such that it would charge an EV at times of solar only, unless override was used, in which case the battery SoC needed to be monitored. The next EV charging was a dream, charging off the abundant solar during the day.

The other surprise is that we still can’t get much performance out of the WTG (less than 10% – even with 15-20 m/s winds). This is a long saga – but it was a risk, which I knew at the time, as the specs were seriously lacking and the print said it only works with lead-acid battery.

The supplier – Solazone insisted it works with LFP, but we suspect the issue is with the controller, which unfortunately does not have adjustable settings.

This doesn’t do much to show the potential benefits of solar/wind/battery combination, and has been a disappointment. But we persist to get it working, though the urgency is not there as the solar/BESS is adequate without genset or wind!

We have found the only other time we needed the genset was on a very thickly clouded day, when we were doing lots of work – and I switched on manually as a precaution. What we have found is that because the house is oriented North and gets plenty of warmth from the sun in winter, has good insulation and temperatures do not go below 5DegC.

The reverse cycle heating copes easily, but if left on all night in mid-winter does risk flattening the battery. The induction cooktop uses instant power draw and the 7kW inverter can cope with 18kW for a short time, so using the induction cooktop, oven, kettle simultaneously with aircon heating is fine – and has not yet been tripped by any guest.

The log fireplace provides ambience and also alleviates electrical heating on long cold dark days, using the abundant wood around the property.

In summer, we do get too much sun coming in, as the eave length is too short. Our design was fine, but the builder could not do this – so we had to compromise. We could put in a window eaves, or just run the aircon flat out when too hot – as there is abundant energy.

This is a bit like the AEMO grid – summer demand on aircons is now not the problem it was because that is when solar is also particularly good. In summer the system is much larger tan needs to be (as its designed for winter), so it’s a case of use energy or lose it. Energy efficiency is in this instance a non-issue.

A final test, was mid-November, when my daughter got married on the property with 100 guests. Admittedly, the caterers were self sufficient (and used gas), but all other power was from the house.

More impressive was brunch the next day, where 80 people were squashed in (foul weather outside), and other than 2 small BBQs, all the power came from the system – 6 waffle irons, oven, hot water urn, hot plates – and hair dryer. The power was regularly over 10kW – which the inverter can handle up to half an hour.

So in summary, off-grid living with appropriate design is now quite feasible and in fact very comfortable at a LCOE better than retail energy pricing in South Australia.

In 2017 I wrote in a RenewEconomy article “Renewable energy is the most cost-effective way to generate secure, reliable, quality electricity in Australia and indeed the world. This claim is based on the assumptions of a whole of life cost analysis – no subsidies and no externalities (“hidden costs”)”.

This claim holds true even more now and off-grid makes total sense if you don’t have a connection.

For those interested – the property cost $210k (what an undervaluation of natural bush!), the solar/BESS/genset $50k (including rebate and gst), wind $15k and total build including everything $650k – and some hard yakka.

Graham Davies is the owner of Ocean Yakka, Director of Resonant Solutions, past President of Engineers Australia SA, and past National chair of Sustainable Engineering Society