Off-grid ≠ Sustainable Practice
Lessons from modelling an LBC-aligned home in Victoria
Key takeaway
“Off-grid” can increase cost and embodied carbon at single-home scale by forcing oversized PV and battery systems sized around the worst winter week. Where services exist, a grid-connected, net-positive approach (with islanding and critical-load backup) often delivers better sustainability outcomes.
Background
Off-grid is often equated with sustainability. For a single dwelling in Victoria pursuing Living Building Challenge (LBC) outcomes, we were asked to size PV and battery storage to meet an off-grid brief and approximately one week of energy resilience. We expected the model to refine the system. Instead, it highlighted a structural issue: the off-grid constraint can drive material-intensive solutions that deliver limited additional benefit when a grid connection exists.
What we did
We built a one-year, hourly energy simulation to test performance across seasons and to explicitly stress-test winter. Hourly modelling matters because off-grid systems fail on time mismatch: multi-day runs of low solar generation combined with high heating demand, not on annual energy totals.
As a starting point, we assumed the roof PV was maximised (approximately 78 kW), then iterated battery sizing and operating assumptions against a resilience intent: keep the home habitable and maintain critical services through a one-week low-generation period. Early consultant sizing suggested that 160 kWh of storage would be sufficient, but that estimate relied on simplified, non-hourly assumptions rather than a full-year, hour-by-hour stress test of winter conditions using a representative weather year.
Figures 1 and 2 show the simulated battery state-of-charge during June (a representative winter month) for two storage capacities.
