Sustainability upgrades in an apartment strata group
Living more sustainably is never attained; it’s an ongoing process. So while initial construction of Christie Walk as a model eco-city development was completed in 2006, upgrades have been an ongoing feature since then. The sense of urgency increases as we realise that climate action in the current decade is critical if we are to have any hope of preserving a liveable planet.
There’s a problem for people living in medium and high density apartments as they try to lift ambition for climate action: Apartment blocks have limited roof space per apartment for PVs and limited options for sharing stored energy for self-consumption and for charging EVs.
Adding 2 more batteries and an EV wall charger
July 11th 2025 marked an important milestone. For our 4-level strata building of 13 apartments, we commissioned two additional batteries – bringing our total to four – plus our first EV wall charger. That sounds relatively straightforward, but it was the culmination of extensive research followed by six months of negotiating permissions and detailed planning.
Time-shifting to avoid peak time-of-use tariffs
In months when solar generation is insufficient to cover total building usage, the system automatically imports enough off-peak (overnight wind) and solar sponge (afternoon) energy from the grid to charge the batteries for subsequent peak morning and evening usage periods. This time-shifting means we avoid buying energy from the grid at peak time-of-use expensive tariffs.
The equity outcome of adding more batteries
Importantly, shaving off the peaks makes the grid cheaper for everyone, not just for those with PVs and batteries. This is because the grid – poles, wires, transformers and substations – has to be built to cope with peak usage. Thousands of households with PVs and batteries – or just with batteries – greatly flatten the peaks in demand, reducing electricity distribution costs for everyone.
Stuffing the duck
Time-shifting also supports the grid by helping to reduce the ‘duck curve’ when peak midday solar production exceeds energy demand on the grid, with the potential for grid instability if not managed effectively.
Future-proofing apartment wiring
Many strata groups wrestle with retrofitting EV charging into their existing electrical system without overloading their switchboards and wiring. We have future-proofed our system so that later we can install additional EV chargers on the same 3-phase 32amp circuit as our first 22kW wall charger. As we described here, to avoid wiring overload Tesla Wall Connectors communicate with each other on Wi-Fi to automatically reduce charge rates if multiple vehicles are charging simultaneously.
A fully integrated system offers many advantages
The Tesla Wall Connector can charge the car from a mix of sources. For example in the video above:
- Total power demand = 11.5kW car + 4.8kW home (13 apartments) + 20kW battery charging = 36.3kW
- Total power supply = 3kW solar (it’s winter!) + 33.3kW grid (cheap solar sponge tariff) = 36.3kW
Charge on Solar
Some EVs – such as Tesla vehicles – have an optional “Charge on Solar at this location” toggle switch. When selected, the car will only charge when sufficient solar is available. Also, if the battery algorithm determines that energy is needed more urgently to charge the home batteries for later use in the building during peak periods, vehicle charging will be automatically throttled back to give priority to charging the home batteries instead.
This EV “Charge on Solar” is another option that helps support the grid by absorbing excess solar exports that would otherwise worsen the grid’s ‘duck curve’.
Negotiating permissions
So why did it take six months of negotiations for our installation approval? According to South Australian Power Networks (SAPN) regulations, our existing 20kW PVs plus 2 batteries with 5kW inverters – total 30kW – was the maximum we could have on a 3-phase connection under the Small Embedded Generation (SEG) provisions. We argued that the 30kVA limit was an antiquated rule that had been created when typical PV arrays were under 5kW, and there were no home batteries; that the regulated limit needed to be lifted. Furthermore, we argued that adding more batteries helps protect the grid rather than endangering it, so the 30kW limit should not be applied when adding batteries.
SAPN listened to our arguments and undertook to review our case when regulations were reviewed. But ultimately, after six months of discussion, SAPN advised that we would have to move up into the Medium Embedded Generation (MEG) category. Now MEG covers inverters with a total capacity of 31kVA to 500kVA, so MEG regulations are designed to cover installations an order of magnitude larger than ours. So the application process was much more detailed and technical than for an SEG application, leading to further delays as we assembled all of the additional data that was required.
End of the road for Tesla Powerwall 2 installations
In the meantime we found that previous information we’d been given – that Tesla Powerwall 2 would continue to be manufactured on demand after the launch of Powerwall 3 – was incorrect. We discovered that the last shipments of Powerwall 2 had arrived in Australia at the end of 2024, and stocks were running out. It was crunch time.
Powerwall 3 incompatible with Powerwall 2
The significance of this is that Powerwall 3 cannot be added to an existing Powerwall 2 installation; the technology is different. Powerwall 2 is AC-coupled only whereas Powerwall 3 has a hybrid on-board inverter that supports up to 20kW of DC solar input. That improves round-trip efficiency, but makes it incompatible with Powerwall 2.
So for us it was a race against time, to track down and reserve two Powerwall 2 units and then to commission them after the Federal Government Cheaper Home Batteries Program rebate commenced on July 1st 2025.
Fortunately our installer – DQ Electrical – did an exceptionally good job for us again and – much to our relief – the system went live with zero problems, with a total of four Powerwall 2 batteries and an EV charger on July 11th 2025.
Outcomes – win, win, win
We’ve only had a few weeks since commissioning, but already we can see it has had the desired effect.
In winter, our 20kW PV system generates only about 27% of the building’s total energy consumption.. So we have to import a significant amount of energy from the grid. That makes it a high priority to ensure that we minimise energy imports during peak hours (6:00 am to 10:00 am and 4:00 pm to 12:00 am) when prices are high and the grid is stressed. Additional battery capacity has enabled much more effective load-shifting. During peak hours:
- June – prior to installation of 2 extra batteries – 52% of usage was from the grid
- August – after installation – only 21%
Next summer – when our PVs produce 25% more than our total building usage – we expect to be mostly self-powered. Our usage is likely to be:
- 39% direct from solar
- 60% from batteries (was 30% last summer)
- 1% from the grid (was 31% last summer)
We’ll also be able to curtail excessive solar exports by charging EVs in the afternoon. That way we’ll minimise negative export tariff, increase the value of our generated energy, and do our bit towards flattening the duck curve.
That’s win, win, win.
Incentives work!
We could not have afforded this project without the support of Federal and Local Government. The battery installation received a rebate thanks to the Federal Government’s $2.3billion Cheaper Home Batteries Program and the overall project received a Climate Smart Buildings Implementation incentive grant under the City of Adelaide Sustainability Incentives Scheme 2025/26. Incentives enable us to lift our ambition on climate action.
Read more of our adventure in low-carbon living
This story is part of our special series:
Aiming beyond NetZero at Christie Walk – Adventures with an environmentally conscious inner-urban community.
Leave a Reply